WO2002062340A1

WO2002062340A1 - Highly lipophilic camptothecin prodrugs, methods of preparation, and formulations thereof

Info

Publication number: WO2002062340A1
Application number: PCT/US2002/003548
Authority: WO
Inventors: David C. Bom; Thomas G. Burke
Original assignee: University Of Kentucky Research Foundation
Priority date: 2001-02-07
Filing date: 2002-02-06
Publication date: 2002-08-15

Abstract

This invention describes novel amino ester prodrug analogs of highly lipophilic silatecans of potential use in the treatment of cancer and AIDS.

Description

HIGHLY LIPOPHILIC CAMPTOTHECIN PRODRUGS, METHODS OF PREPARATION, AND FORMULATIONS THEREOF

Technical Field

The present invention relates to amine-containing prodrugs of highly lipophilic 7- silylalkylcamptothecins (silatecans) and the novel intermediates (containing an unusual six membered morpholine 2,5-dione ring) which the prodrugs form in solution. These silatecan prodrugs, unlike their parent silatecan agents which locate primarily in the bilayer of a liposomal particle, are capable of loading predominantly into the aqueous core of liposomal particles. By providing for core-loaded liposomal particles, the invention of amine-containing prodrugs of highly lipophilic 7-silylalkylcamptothecins (silatecans) allows for liposomal tumor-targeting methods to be implemented in optimizing the utility of this important family of anti-cancer agents. The invention also relates to controlled release formulations of prodrugs of highly lipophilic silatecans achieved through liposomal core-loading of 20-OR ω-aminoalkanoanic ester prodrug, in which R=CO[CH₂]_nNH₂. Through judicious choice of liposomal encapsulation methodologies, lipid ingredients, and the choice of the R=CO[CH₂]_nNH₂HX functionality of the silatecan-20- ester, formulations (where X represents any suitable negatively charged counterion) are developed which release silatecan prodrug from the liposomal particle. Upon reaching the outside of the particle and gaining exposure to the physiological mileau (i.e. pH 6.8 to 7.4), the nucleophilicity of the R=CO[CH₂]_nNH₂HX amine manifests itself and cyclization to the C-21 carbonyl carbon occurs. This cyclization forms novel silatecan intermediates containing an unusual six membered morpholine 2,5-dione ring. These intermediates further decompose triggering a rapid and convenient non-enzymatic decomposition process that releases active silatecans with potent anti- topoisomerase I activities. We describe silatecans with R=CO[CH₂]_nNH₂HX functionalities and formulation conditions which allow this release of active silatecan in a rational and controlled fashion resulting in optimal therapeutic efficacy. The formulations involve entrapment of silatecan-20-ester in the pH-adjusted core of liposomes. The chemistry of the liposomal formulation is optimized in order to retain the silatecan-20-ester in the liposome and prevent it from reacting as it would typically after being placed in aqueous solution, plasma, or blood. The silatecan prodrugs, methods of formulation and formulation ingredients are critical for optimal stability of the silatecan-20-ester within the particle. Upon departing the liposomal particle at the tumor site the silatecan-20-esters undergo spontaneous conversion to the active lactone forms of silatecans, which are potent inhibitors of DNA topoisomerase I and display potent anti-cancer activities. Background of the Invention

Camptothecin and related congeners (Figures la-f) are rapidly emerging as a prominent class of agents useful in the treatment of cancer. (Wall et al., 1966; Wani et al., 1987; Wani et al., 1987; Kaneda et al., 1990; Giovanella et al., 1989; Kingsbury et al, 1991 ; Rowinsky et al., 1992; Houghton et al., 1992; Blaney et al., 1993; Slichenmyer et al, 1993; Hsiang et al., 1985).They display a unique mechanism of action: stabilization of the covalent binding of the enzyme topoisomerase I (topo I), an intranuclear enzyme that is overexpressed in a variety of tumor lines, to DNA (Giovanella et al., 1989; Potmesil et al., 1988). The drug/enzyme/DNA complex leads to reversible, single strand nicks. According to the fork collision model, the nicks are converted to irreversible and lethal double strand DNA breaks during replication. Therefore, due to the mechanism of its cytotoxicity, camptothecin and related analogs can be regarded as S-phase specific. Camptothecins and related agents are only toxic to cells that are undergoing DNA synthesis (Kessel et al., 1972; Li et al., 1972). Rapidly dividing cells (e.g cancerous cells) spend more time in the S-phase relative to healthy tissues. Thus, overexpression of topo I, in combination with the faster rate of mitosis, provide a limited basis for selectivity via which these agents can effect cytotoxicity on cancerous cells rather than healthy host tissues.

The camptothecin class of anticancer agents have exhibited unique dynamics and reactivity in vivo, both with respect to drug hydrolysis and blood protein interactions. These factors have confounded the pharmaceutical development and clinical implementation of camptothecins. In terms of hydrolysis, each of the clinically relevant camptothecins shown in Figure 2 contains an α-hydroxy- δ-lactone pharmacophore. At physiological pH of 7 and above this functionality is reactive, readily converting to the biologically inactive "ring opened" carboxylate form (Jaxel et al., 1989; Hertzberg et al., 1989; Hsiang and Liu, 1988). Thus, as a result of the labile α-hydroxy-δ-lactone pharmacophore, an equilibrium is established between two distinct drug species: 1) the biologically active lactone form where the lactone ring remains closed; and 2) a biologically-inactive carboxylate form generated upon the hydrolysis of the lactone ring of the parent drug (Hsiang et al., 1985; Jaxel et al., 1989).

This hydrolysis problem with camptothecin and many analogs (e.g. 9- aminocamptothecin, 9-nitrocamptothecin) is exacerbated in human blood (Burke and Bom, 2000). In human blood and tissues, the camptothecin equilibrium of active lactone form vs. inactive carboxylate form can be strongly modulated by the presence of human serum albumin (HSA). The lactone form of camptothecin binds to HSA with moderate affinity yet the carboxylate form of camptothecin binds tightly, displaying a 150-fold enhancement in its affinity. Thus, the preferential binding of the carboxylate form to HSA drives the chemical equilibrium to the right in favor of the carboxylate, resulting in the lactone ring hydrolyzing more rapidly and completely (than when camptothecin is in an aqueous solution without HSA). These dynamic processes and protein interactions present a major hurdle to achieving successful chemotherapy for a cancerous disease state. For example, the carboxylate forms of camptothecin, 9-aminocamptothecin and 9-nitrocamptothecin exhibit a very high and species- specific affinity for human serum albumin which can modulate anticancer activity by 3 orders of magnitude (Mi et al, 1995; Zinrmer and Burke, 2000). In human patients it appears that protein binding interactions make it difficult to achieve therapeutically optimal unbound lactone levels of these agents, particularly when one considers that continuous exposures (for tumor cells to cycle through S-phase) of the active lactone form are necessary for the drugs to be efficacious.

Previously it has been noted that the blood stabilities of camptothecins can be strongly modulated through structural changes in the A and B rings of camptothecin (Burke and Mi, 1994). E-ring modifications are also known to impact on blood stability. Cao and Giovanalla (U.S. 5,968,943) describe inactive camptothecin prodrugs with linear alkyl chains at the 20-position (shown in Figure 3b and Table 1) which display altered blood stability, and Wall and Wani (U.S. 5,916,896, U.S. 5,932,588, 5,614,529) and Shapiro et al. (5,496,830) describe water-soluble glycinate esters of camptothecin (shown in Figure 3c) that display reduced toxicities relative to parent drugs. None of the camptothecin glycinate ester inventions described above and whose membrane binding characteristics are summarized in Table 3 are as lipophilic as the silatecans (Bom et al., 2000). In this invention we describe novel, highly lipophilic silatecan amino esters capable of core-loading into liposomal carriers. We also demonstrate how these novel, highly lipophilic silatecan prodrugs decompose in aqueous solution and form novel intermediates whose formation ultimately is responsible for the facile release of active agent.

With respect to the development of the silatecans, the complications of markedly reduced blood lactone levels, together with loss of anticancer activities, indicate that agents with improved activities could be attained through the reduction of the high affinity drug-HSA interactions. Recent rational design efforts (Bom et al., 2000; Burke and Bom, 2000) have resulted in the identification of A,B-ring modified camptothecins (structures summarized in Table 3) displaying improved human blood stabilities combined with potent anti-topoisomerase I activities (Figures 4a and 4b). Bioanalytical measurements have shown that dual 7,10-substitution (where the 10- substituent is a hydroxy group) result in camptothecins displaying vastly improved human blood stabilities (Burke and Mi, 1993). SN-38 contains this dual 7-alkyl-10-hydroxy substitution pattern and in 1994 it was shown that these structural modifications block SN-38 from associating with the high affinity camptothecin carboxylate binding pocket on HSA (Burke and Mi, 1993). More recently the design of another dual 7,10-modified camptothecin has been described, an agent that displays markedly improved human blood stability and potent anti-topoisomerase I anticancer activity (Bom et al., 2000). The new agent, shown in Figure 4b, is 7-t-butyldimethylsilyl-10- hydroxycamptothecin (DB-67). DB-67 was prepared using the radical cascade approach developed by Professor Curran and colleagues at the University of Pittsburgh (Josien et al., 1998; Josien et al., 1997) and its design was based upon the following two considerations: 1) dual 7,10- substitution patterns eliminate the highly specific binding of carboxylate form over lactone form by HSA (Mi and Burke, 1994; Burke et al., 1994; Burke and Mi, 1993); and 2) lactone stabilization is further promoted by enhanced lipophilicity or lipid bilayer partitioning (Mi and Burke, 1994; Burke et al., 1992, 1993). We have shown previously that lipophilicity promotes camptothecin drug stability by favoring lactone partitioning into blood cells, thereby protecting the active lactone forms from hydrolysis. The key α-hydroxy-δ-lactone pharmacophore in DB-67 displays superior stability in human blood when compared with FDA-approved topotecan, CPT-11, and several other clinically relevant camptothecin analogs (Bom et al., 2000; Pollack et al., 1999). DB-67 displayed a tι_/2 of 130 min. and a % lactone at equilibrium value of 30 in human blood; the t-butyldimethylsilyl group enhances lipophilicity (Figure 6) and thereby promotes drug associations with blood cells. DB-67 is 25-times more lipophilic than camptothecin (Figure 7) and readily incorporates as its active lactone form into cellular and liposomal bilayers. Equally important, the dual 7-alkylsilyl and 10-hydroxy substitution in DB-67 blocks the associations of the carboxylate form of DB-67 with the high affinity carboxylate binding pocket on HSA. Together, the enhanced lipophilicity and altered HSA interactions provide DB-67 with the highest human blood stability when compared with clinically relevant camptothecins containing the conventional α-hydroxy-δ-lactone pharmacophore. In vitro cytotoxicity assays have shown that DB-67 is of comparable potency relative to camptothecin and 10-hydroxycamptothecin, as well as the FDA approved analogs topotecan and CPT-11 (Bom et al., 2000). In addition, cell-free cleavage assays reveal that DB-67 forms more stable topoisomerase I cleavage complexes than camptothecin or SN-38. In terms of in vivo potency, DB-67 has been shown to display activity against human glioma in a murine model (Pollack et al., 1999). Overall, these stability and activity profiles of DB-67 indicate how rational drug design can result in new, highly lipophilic agents displaying improved pharmacological properties. As discussed below, the intrinsic highly lipophilic nature of these agents combined with their lack of amino group precludes the use of these agents in tumor-targeted liposomal delivery systems where the agent is core-loaded. Our invention involving derivatization to generate an amine-containing prodrug provides a means to core-load the highly lipophilic silatecans and release the agents in the active form at the tumor site. Core-loading of highly lipophilic silatecans provides for additional blood stability and retention characteristics allowing for tumor-targeting to be achieved.

Liposomes provide an excellent means by which to stabilize the biologically-active lactone form of camptothecins (U.S. Patent 5,552,156; Burke et al., 1992; Burke and Gao, 1994). Water- soluble drugs such as topotecan can be entrapped within the pH-adjusted aqueous compartments of liposomes (Figures 8a-8b) with the acidic microclimate of liposomes stabilizing the active lactone form. Lipophilic drugs can partition into the bilayer where the lactone ring is stabilized and protected from hydrolysis. Liposomes can also serve as controlled release depots. The camptothecins are S- phase specific drugs (Giovanella et al., 1989), and it has been shown that optimal activity is obtained when the tumors of a patient are exposed to the drugs for continuous periods of time (Thompson et al., 1998). Liposomes that target tumors and slowly release drug (such that tumor cells are continuously exposed to drug) appear as attractive drug delivery systems to pursue.

In the United States, liposomal delivery of anticancer drugs has recently entered its most successful period to date. The Food and Drug Administration (FDA) has recently given marketing approval for two liposome-encapsulated, anticancer drugs (Doxil from ALZA and DaunoXome from Gilead) and a liposomal form of a potent antifungal drug. These activities highlight the emergence of liposomes as a practical approach to targeted pharmaceutical delivery. In addition to the U.S. approvals, liposome delivery systems also have been approved in many European countries. Other background information on factors leading to the development of liposomal camptothecins can be found elsewhere (Burke and Bom, 2000) .

Clearly, the past several years have seen rapid advancement and progress in both the camptothecin drug development field as well as the liposomal drug delivery arena. A number of companies have been active in the liposomal formulations of camptothecins in recent years. The lead liposomal camptothecin is GG 211 (Figure Id). Both Gilead and ALZA developed liposomal formulations of this agent. Both companies reported encouraging findings that liposomal formulation resulted in 3 to 5-fold gains in the efficacy of the agents against human cancers carried in murine models. In addition to GG211, Inex has reported favorable results in formulating topotecan in liposomes, showing a significant improvement in efficacy through the liposomal formulation process (Emerson et al., 2000; Tardi et al., 2000). There is also significant interest in liposomal aerosol formulations of 9-AC and 9-NC (Koshkina et al., 2000; Knight et al., 1999), although these drugs only load into the bilayer compartment of liposomes since they lack a basic amino functionality necessary for core-loading. Core-loaded liposomal formulations of CPT-11 have also been prepared and evaluated (Sadzuka et al, 1998, 1999). Liposomal core-loading of camptothecins has been limited to date to agents such as topotecan, CPT-11, and GG-211, which actively load using ion gradients into pre-made liposomes (see Figure 9).

Our research team has been at the forefront of camptothecin drug design and liposomal formulation. We have been involved in the development of DB-67, a highly lipophilic silatecan with most unusual properties. Our selection of DB-67 as a lead silatecan is based upon its high intrinsic potency and its ability to persist in the active lactone form in tissue. The ability of DB-67 to persist as its active species even following dosing of agent in its inactive, ring-opened carboxylate form into whole human blood is depicted. Because of its superior pharmacological properties relative to other camptothecins, DB-67 appears to be an excellent agent to deliver to tumors. The current literature indicates liposome technologies are ideal for tumor targeting, but optimal tumor targeting properties require the agents to be core loaded into the aqueous compartments. The high lipophilicity and lack of amine group for core-loading precludes the use of DB-67 and other highly lipophilic silatecans in these delivery systems. This is because DB-67 and other highly lipophilic silatecans locate predominantly in the bilayer compartment of liposomes which is in direct contact with the suspension medium. Hence, the bilayer-localized drug can readily exchange out of the particle as depicted in Figures 1 la-1 lb. Upon leaving the liposome bilayer the drug hydrolyzed in the pH 7.4 medium mat it has diffused into. Our research on DB-67 led us to seek a prodrug approach which would allow a means for the following: 1) core-loading of the prodrug; 2) the ability to keep the agent sequestered within the particle such that the prodrug bearing particle could circulate in the bloodstream for long, 24- 96 hour periods of time such that tumor-targeting can be achieved; and 3) the prodrug would release DB-67 under the appropriate physiological stimulus decomposed to release active DB-67.

We hypothesize that DB-67 will be a highly efficacious anti-tumor agent and, due to its enhanced blood and tissue stability, display a cytotoxic potency and efficacy index that will surpass the currently FDA approved camptothecin analogs, topotecan and CPT-11. Highly lipophilic camptothecins displaying markedly improved human blood stabilities, greater intrinsic potencies against the topoisomerase I target, greater membrane penetration and diffusion characteristics appear to have significant promise in the treatment of human cancers, particularly in the cases of cancers of the brain and liver. Through the RAID Program

(http://epnwsl ,ncifcrf.gov:2345/dis3d/raidwinl .html) of the National Cancer Institute, we are currently advancing the development of bilayer-loaded liposomal DB-67.

It is important to note, however, that the liposomal formulations of DB-67 being prepared for clinical trials by the NCI RAID program contain drug located in the bilayer of the liposome vesicle. Due to the highly lipophilic nature of DB-67, a liposomal vehicle provides a dispersing medium that prevents drug crystallization at the site of injection. Once in the bloodstream, by virtue of its interfacial location in the liposomal particle, DB-67 can depart the liposome (as depicted in Figure 10) and readily interact with surrounding biological membranes, in particular red blood cells. In this manner DB-67 exits the delivery vehicle relatively rapidly (timescale several minutes to 1 hour). For this reason, passive tumor targeting [i.e. spontaneous drug accumulation in the areas of the tumor with leaky vasculature, or the Enhanced Permeability and Retention (EPR) effect] of liposomal DB-67 cannot be realistically achieved since the EPR process requires days of particle circulation (and drug retention within the particle) in order to effectively target tumors. Thus, we sought to develop a prodrug approach that would permit liposomal core-loading and tumor targeting. We sought to develop prodrug esters of DB-67 that can be effectively and efficiently loaded into the core of the liposome carrier. Clearly, core loading will maintain the DB-67 prodrug ester in the internal aqueous milieu of the liposome and bypass the partitioning of DB-67 into surrounding red blood cell membranes. Such technology in turn supports targeted delivery of the DB-67.prodrug ester to the tumor site.

Summary of the Invention

Our previous rational synthetic efforts described above yielded the camptothecin agent 7-t- butyldimethylsilyl-10-hydroxycamptothecin, which we have termed DB-67. As intended by our drug design strategy, DB-67 is highly lipophilic and displays reduced affinity for human serum albumin in its carboxylate form relative to other members in the camptothecin family. As a result, DB-67 exhibits superior stability in human blood, with a t_m of 130 min. and a % lactone at equilibrium value of 30%. This value should be compared with the % lactone at equilibrium values in whole human blood for camptothecin (1%), topotecan (11.9%), CPT-11 (21.0%), and SN-38 (the active metabolite of CPT-11, 19.5%). The significance of this stability data is underscored by the spectrum of activity for DB-67: in vitro DB-67 has impressive cytotoxic potency and in vivo, using an intracranial human glioma xenograft model, DB-67 has effectively cured mice of the cancerous lesion. Further gains in the activity of DB-67 and related highly lipophilic silatecans are precluded by the inability of these agents to load predominantly in the aqueous core of liposomes which can facilitate tumor targeting of the agent. Methods of more selective delivery of the potent DB-67 and related silatecans are currently being sought.

Accordingly, it is a primary object of the present invention to provide a means of delivering DB-67 and other silatecans more selectively to tumor tissue versus normal tissue. This will further optimize the utility of these agents.

This obstacle is overcome by the invention detailed in this patent. Prodrug esters of the DB-67 agent, in which amine-containing alkyl esters are added at the 20(S) position of the E-ring (Table 4) provide the opportunity to formulated the DB-67 prodrug in the liposome core via active loading methodologies. In brief, in the active core loading process an amine-containing agent is loaded into the particle. For example, a gradient created by ammonia gas diffusing out of the liposome particle can result in diffusion of the drug inward to the core of the particle, otherwise known as active loading. The chemical gradient across the membrane creates a driving force for an amine-containing compound, such as the DB-67 prodrug ester, to replace the lost NH₃ from the interior of the liposome. Once inside the acidic confines of the core, the DB-67 prodrug becomes protonated and remains within the core, as its positive charge impedes retro-diffusion across the liposome bilayer. The protonated amine also prevents the occurrence of nucleophilic attack of the amine on the lactone carbonyl. As liposomes can be actively and/or passively targeted to the tumor, the liposome encapsulated DB-67 prodrug ester can be effectively concentrated at the tumor site, thereby reducing exposure of the healthy host tissues to the cytotoxic agent yet enhancing exposure at the tumor target. Our tumor targeted approach involving liposomal delivery of core loaded DB-67 prodrug esters addresses multiple clinical issues. For example, reduced systemic toxicity can be achieved. Enhanced exposure at the tumor site in terms of relative amounts of drug reaching the tumor can also be achieved. Furthermore, enhanced exposure at the tumor site can be achieved in terms of prolonging the exposure of drug there. The latter effect can be optimized by judicious choice of amine-containing ester chain length (i.e. the choice of n value in the R=C0[CH₂]„NH₂HC1 functionality of the silatecan-20-ester). Mixtures of analogs with different structures or n values can be chosen for optimal controlled release of the active agent. Lipid ingredients and surface decoration materials such as polyethylene glycol coating or antibody coating can also be chosen in order to optimize drug targeting and drug release rates.

When we discovered the reactivity of camptothecin glycinate esters at pH 7.4, we immediately realized that this reactivity was ideal for our liposomal drug delivery systems. At low pH the nontoxic prodrug (inactive against topoisomerase I in this form, albeit it will readily react at pH 7.4 to generate parent lactone with potent anti-topoisomerase I activity) is stable and can readily load into liposomal particles. The pH of liposomal compartments can be lowered to maintain the prodrug structure. Upon departing the tumor-targeted particle and diffusing into the tumor or physiological milieau (with pH values ranging from 6.8 to 7.4), the glycinate esters immediately react to form active agent. We have synthesized a variety of analogs where the length of the amine-containing ester side chain was varied (i.e. the choice of n value in the R=CO[CH₂]_n NH₂HC1 functionality of the silatecan-20-ester). Comparison of the reactivities of the several firing modified silatecan-20-OR esters (where R=C0[CH₂]„NH₂HC1 where n= 1-3) in PBS and in human blood at an initial prodrug concentration of 1 μM was carried out. We realized that the stabilities of the compounds increase with increasing n value. The following order of chemical stability was observed for the agents of interest in both PBS and whole human blood: silatecan- 20(S)-glycinate ester « silatecan-20(S)-3-aminopropanoate ester « silatecan-20(S)-4- aminobutanoate ester. In the case of the propanoate and butanoate ester samples no intermediate peak was observed by HPLC chromatographic analysis. The glycinate ester intermediate is stable enough to be readily separated by HPLC methods. The slower reactivity of the propanoate and butanoate esters provides us with an additional tool to implement as we seek the ideal release rate of active species at the tumor site for optimal tumor regression.

Upon formulation in liposomes, the DB-67-20(S)-4-aminobutanoate ester displays unprecedented stability in human blood, with 80% remaining in the unhydrolyzed form out to 48 hrs. Upon hydrolysis the butanoate ester releases highly potent DB-67, predominantly in its active lactone form (i.e. the active lactone levels exceed those for carboxylate). This is a unique feature of DB-67; the lactone levels are always preferred over carboxylate levels under physiological conditions (i.e. pH 7.0 and above). This is not the case for camptothecin; when dosed in its carboxylate form camptothecin remains in its inactive form in human blood.

The invention includes compounds with the following structures A and B:

wherein R¹ and R² are independently the same or different and are hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an acyloxy group, - OC(0)OR¹², wherein R¹² is an alkyl group, a carbamoyloxy group, a halogen, a hydroxy group, a nitro group, a cyano group, an azido group, a formyl group, a hydrazino group, -C(0)R¹³ wherein R¹³ is an alkyl group, an alkoxy group, an amino group or a hydroxy group, -- SR¹⁴, wherein R¹⁴ is hydrogen, -C(0)R¹³, an alkyl group, or an aryl group; or R¹ and R² together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6; R³ is H, a nitro group, a halogen atom, an amino group, a hydroxy group, or a cyano group, or R² and R³ together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6; R⁴ is H, F, an alkyl group, an alkenyl group, an alkynyl group, a trialkylsilyl group or an alkoxy group; R⁵ is a C ι₅ alkyl group, an allyl group, a benzyl group or a propargyl group; R⁶, R⁷ and R⁸ are independently a Cι_u alkyl group, a C₂.i₅ alkenyl group, a C₂.i₅ alkynyl group, an aryl group or a -(CH₂)_qR¹⁵ group, wherein q is an integer between 1 and 15 and R¹⁵ is a hydroxy group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group; R¹⁰ is an alkylene group, an alkenylene group or an alkynylene group; R^π is -(CH₂)_LNR¹⁶R¹⁷ wherein L may be an integer ranging from 1-30 and R¹⁶ and R¹⁷ are independently the same or different and are hydrogen, a CM_S alkyl group, a C₂.₁₅ alkenyl group, a C₂.ιs alkynyl group, an aryl group, a - (CH₂)_YR¹⁸ group, a -(CH₂)_γC(0)R¹⁸ group or a

-(CH₂)YC0₂R18 wherein Y may be an integer ranging from 1 to 15 and R¹⁸ is a hydroxy group, a thiol group, an alkylthiol, a silyl group, an alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group, a nitro group. The invention also includes the novel intermediate structures containing an unusual six membered morpholine 2,5-dione ring system (formed during the decompsition of the silatecan prodrugs in solution) with the following structures C and D:

wherein R¹ and R² are independently the same or different and are hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an acyloxy group, -OC(0)OR¹², wherein R¹² is an alkyl group, a carbamoyloxy group, a halogen, a hydroxy group, a nitro group, a cyano group, an azido group, a formyl group, a hydrazino group, -C(0)R¹³ wherein R¹³ is an alkyl group, an alkoxy group, an amino group or a hydroxy group, -SR¹⁴, wherein R¹⁴ is hydrogen, -C(0)R¹³, an alkyl group, or an aryl group; or R¹ and R² together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6; R³ is H, a nitro group, a halogen atom, an amino group, a hydroxy group, or a cyano group, or R² and R³ together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6; R⁴ is H, F, an alkyl group, an alkenyl group, an alkynyl group, a trialkylsilyl group or an alkoxy group; R⁵ is a C_rι₅ alkyl group, an allyl group, a benzyl group or a propargyl group; R⁶, R⁷ and R⁸ are independently a Cm alkyl group, a C₂-ι₅ alkenyl group, a C₂.₁₅ alkynyl group, an aryl group or a -(CH₂)_qR¹⁵ group, wherein q is an integer between 1 and 15 and R¹⁵ is a hydroxy group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group; R¹⁰ is an alkylene group, an alkenylene group or an alkynylene group; the nitrogen of the six membered morpholine 2,5-dione ring can be monoalkylated in any of the above cited compounds or contain a monoalkylgroup containing -CN, halogen, -COOH, nitro and amino substituents.

The invention includes the description of novel formulations containing any of the above referenced compounds delivered in a liposomal formulation. More specifically said structures are loaded into the aqueous core of a liposome containing at least one membrane bilayer. The rate of drug delivery or leakage from the liposome is modulated by varying the amine ester side chain, the pH in the core, and the lipid bilayer composition. A method for reducing the toxicity of silatecans is decribed where the silatecan is converted to a nontoxic prodrug and loaded into the core of liposomes in order for tumor targeting to be achieved. A method for extending the in vivo systemic lifetime of the silatecan is described. Pharmaceutical compositions are described that involve a method of formulating a topoisomerase I inhibiting silatecan compound and administering the agent to a mammal in an amount sufficient to inhibit topoisomerase I. A method of treating cancer and human immunodeficiency virus (HIV) by administering from 1 to 500 mg/kg body weight per week of the liposomal silatecan ester. Our invention includes parenteral administration of silatecan ester compounds. A method of treating cancer in a mammal in need thereof, comprising administering to said mammal an effective amount for treating said cancer of the silatecan ester or one of its liposomal forms.

Brief Description of the Drawings

Figures la-f. Clinical candidates and FDA-approved analogs in the camptothecin family of antitumor agents are, respectively, (a) 9-NC Rubitecan, (b) DX-8951f, (c) 9-AC, (d) GI- 147211C/GG-211, (e) Topotecan/TPT and (f) SN-38 and Irinotecan/CPT-11. Figure 2. Camptothecin hydrolysis at physiological pH. Figure 3. Structures of (a) camptothecin and related (b) camptothecin-20-ester analogs

((c) camptothecin glycinate ester hydrochloride) that display modified E-ring lactone stability.

Figure 4. Structural comparison of silatecans (a) DB-174 and (b) DB-67 with the clinically relevant 7,10-modified camptothecin SN-38. 7-Silylalkyl substitution results in markedly enhanced lipophilicity as well as markedly enhanced stability in the presence of membranes. Dual 7,10 modification results in stabilization of the lactone form of DB-67 in the presence of albumin. Because of enhanced lipophilicity and altered interactions with albumin due to dual 7-10 substitution DB-67 displays high human blood stability relative to other camptothecins.

Figures 5a and 5b. Depiction of the poor stability of camptothecin (CPT) and 9- aminocamptothecin (9-AC) in human blood. A drug concentration of 1 M was studied. The poor stability of these compounds in human blood is due to their high affinity for human serum albumin. When human serum albumin is absent, stability is markedly improved (see improved stability of 9-AC in mouse blood relative to human blood). Unlike CPT and 9-AC that bind to human albumin with high affinity in their carboxylate forms, DB-67 does not bind to human albumin in such a highly preferential manner (i.e. for DB-67 K _jjg^ of the carboxylate is not orders of magnitude greater relative to the Kjjg^_. of the lactone form). DB-67 displays improved human blood stability with a t 2 of 130 min. and a % lactone at equilibrium value of 30 in human blood [Bom et al, J. Med. Chem., 43:3970-3980 (2000)]. DB-67 also does not display marked interspecies variations in blood stabilities. Stability profiles were determined using HPLC methods. All experiments were conducted at pH 7.4 and 37 °C. Each data point represents the average of three or more determinations with uncertainty of 10% or less.

Figure 6. The method of fluorescence anisotropy titration was employed to study the equilibrium binding of highly lipophilic DB-67 to small unilamellar vesicles (SUVs) composed of electroneutral dilauroylphosphatidylcholine (DLPC) in PBS. Also shown are data characterizing the binding of camptothecin to DLPC SUVs. The method of fluorescence anisotropy titration was used to construct the adsorption isotherms. Experiments were conducted at drug concentrations of 1 μM in PBS buffer (37 °C). The anisotropy values of DB-67 titrates much more rapidly than the corresponding values for camptothecin. The camptothecins are labile in aqueous solution, so anisotropy values at each lipid concentration were determined immediately (approx. 1 min.) following the addition of the drug. This minimizes the presence of carboxylate species at the lower lipid concentrations where carboxylate formation can occur more readily.

Figure 7. Bar graph summarizing the relative lipophilicities of silatecans and clinically relevant camptothecins for electroneutral DMPC and negatively-charged DMPG.

Figures 8a-8b. Schematic depicting the two compartments for drug loading that are contained within a lipid vesicle. Figure 8a represents the situation where an entrapped drug loads predominantly into the lipid bilayer compartment; Figure 8b represents drug loading into the aqueous cavity contained in the core of the liposomal particle.

Figure 9. Mechanism of active drug loading in a liposomal particle. In the active loading process, an amine-containing agent is loaded into the particle by a gradient caused by ammonia gas diffusing out of the particle, thereby creating a driving force for an amine-containing compound to enter the liposome in order to replace the lost NH₃ from the interior of the particle. Upon being suspended in blood, forces act on the drug and the liposome promoting release of the agent.

Figure 10. Depiction of a very unique property of DB-67 in human blood (1 μM drug concentration) relative to clinically relevant camptothecin. Unlike the latter compound 9- aminocamptothecin and 9-nitrocamptothecin that bind to human albumin with high affinity in their carboxylate forms, DB-67 does not bind to human albumin is such a highly preferential manner (i.e. for DB-67 K_HSA of the carboxylate is not orders of magnitude greater relative to the KH_SA of the lactone form). Because of the attenuated albumin binding and its high degree of lipophilicity, the lactone levels of DB-67 are always preferred over carboxylate levels under physiological conditions (Le. pH 7.0 and above). This is not the case for camptothecin; when dosed in its carboxylate form camptothecin remains in its inactive form in human blood primarily because of its tight binding to HSA in the carboxylate form. Stability profiles were determined using HPLC methods. All experiments were conducted at pH 7.4 and 37 °C.

Figures 11 a- lib. Figure 11a depicts the impact of DMPC/DMPG liposomes on the stability of DB-67 in PBS solution at 37 °C. At the higher lipid concentration of 3 mM, 88.2% of DB-67 is lipid-bound and remains predominantly in its lactone form at these concentrations. At more dilute lipid concentrations of 0.3 mM and 0.03 mM, respectively, a greater fraction of DB-67 hydrolyzes since the lactone pharmacophore is no longer intercalated in the hydrophobic interior of the liposome. These studies indicate that the promotion of drug interactions with lipid bilayers is important for maintaining the drug in its active lactone form. The studies demonstrate the DB- 67, because of its high lipophilicity, locates in the bilayer of the liposomal particle and can readily diffuse from the particle. Our current invention aims to locate a prodrug of the agent in the core of the liposome and thereby promote drug retention within the particle. Figure 1 lb compares the human blood stability of a 1 μM sample of free DB-67 versus a liposomal formulation of the agent. Note that the liposomal formulation does not afford the agent any significant improvement in drug stability, indicating the agent because of its interfacial membrane location can readily ■ diffuse from the particle and hydrolyze into its biologically inactive form.

Figure 12. Proposed reaction mechanism for DB-67-20(S)-glycinate ester hydrochloride in aqueous solution at 37 °C at a prodrug concentration of 1 μM. We are the first to postulate that an intermediate containing a six membered morpholine 2,5-dione ring is formed during DB-67 glycinate ester degradation. Our novel finding concerning the formation of the intermediate correlates with the rapid formation of camptothecin lactone and carboxylate species (versus the much slower formation of lactone and carboxylate forms released following the hydrolysis of an alkyl ester analog of camptothecin such as camptothecin-20(S)-acetate or camptothecin-20(S)- octanoate). We suggest that the generation of these lactam intermediates is central to the rapid decomposition of this class of prodrugs.

Figure 13. Fluorescence excitation and emission spectra of 1 μM solutions of DB-67 (lower panel), DB-67-20-glycinate ester hydrochloride (center panel) and DB-67-20(S)-4- aminobutanoate ester hydrochloride (top panel) in PBS buffer in the presence and absence of 0.1 M dimyristoylphosphatidylcholine (DMPC) small unilamellar liposomes. Experiments were conducted at pH 7.4 and 37 °C. Data is also shown for the agents dissolved in ethanol. Note that there is a strong shifting of the emission spectra to the blue region or shorter wavelengths in the presence of liposomes. This spectral shifting is indicative of drug interaction with the membranes. Emission experiments were conducted using exciting light of 370 nm.

Figure 14. Fluorescence excitation and emission spectra of 1 μM solutions of DB-172 (lower panel), DB-172-20-glycinate ester hydrochloride (center panel) and DB-172-20(S)-3- aminopropanoate ester hydrochloride (top panel) in PBS buffer in the presence and absence of 0.1 M dimyristoylphosphatidylcholine (DMPC) small unilamellar liposomes. Experiments were conducted at pH 7.4 and 37 °C. Data is also shown for the agents dissolved in ethanol. Note the change in the intensity of the agent in the presence of liposomes. This change in intensity is indicative of drug interaction with the membranes. Emission experiments were conducted using exciting light of 370 nm.

Figure 15. The method of fluorescence anisotropy titration was used to study the associations of 1 μM concentrations of DB-67, DB-67-20-glycinate ester, and DB-67-20(S)-4- aminobutanoate ester with small unilamellar vesicles composed of electroneutral DMPC suspended in phosphate buffered saline. Experiments were conducted at prodrug concentrations of 1 μM at 37 °C using exciting light of 370 nm and 400 nm long wave pass filters on the emission channels. Note that in the presence of increasing amounts of liposomes the drug anisotropy values increase until the majority of drug is liposome-bound. Analysis of the data reveal the following association constants or K_DMpc values: 4,000 M^"1 for DB-67, 4,000 M^"1 for DB-67-20-glycinate ester hydrochloride, and 5,600 M^"1 for DB-67-20(S)-4-aminobutanoate ester hydrochloride. In similar studies (data not shown) the method of fluorescence anisotropy titration was used to study the associations of 1 μM concentrations of DB-67, DB-67-20-glycinate ester hydrochloride, and DB-67-20(S)-4-aminobutanoate ester hydrochloride with small unilamellar vesicles composed of negatively charged dimyristoylphosphatidylglycerol (DMPG) suspended in phosphate buffered saline. Experiments were conducted at drug and prodrug concentrations of 1 μM at 37 °C using exciting light of 370 nm and 400 nm long wave pass filters on the emission channels. For increasing amounts of liposomes the drug anisotropy values increase until the majority of drug is liposome-bound. Analysis of the data reveal the following association constants or K_DMPG values: 3,000 M^"1 for DB-67, 8,000 M^"1 for DB-67-20-glycinate ester hydrochloride, and 5,600 M^"1 for DB-67-20(S)-4-aminobutanoate ester hydrochloride. Figure 16. The method of fluorescence anisotropy titration was used to study the associations of 1 μM concentrations of DB- 172, DB-172-20-glycinate ester, and DB-172-20(S)- 4-aminobutanoate ester hydrochloride with small unilamellar vesicles composed of electroneutral DMPC suspended in phosphate buffered saline. Experiments were conducted at prodrug concentrations of 1 μM at 37 °C using exciting light of 370 nm and 400 nm long wave pass filters on the emission channels. Note that in the presence of increasing amounts of liposomes the drug anisotropy values increase until the majority of drug is liposome-bound. Analysis of the data reveal the following association constants or K_DMPC values: 11,000 M^"1 for DB-172, 5,000 M^"1 for DB-172-20-glycinate ester, and 3,100 M^"1 for DB-67-20(S)-3-aminopropanoate ester. In similar studies (data not shown) the method of fluorescence anisotropy titration was used to study the associations of 1 μM concentrations of DB-172, DB-172-20-glycinate ester, and DB-172-20(S)- 3-aminopropanoate ester with small unilamellar vesicles composed of negatively charged dimyristoylphosphatidylglycerol (DMPG) suspended in phosphate buffered saline. Experiments were conducted at drug and prodrug concentrations of 1 μM at 37 °C using exciting light of 370 nm and 400 nm long wave pass filters on the emission channels. For increasing amounts of liposomes the drug anisotropy values increase until the majority of drug is liposome-bound. Analysis of the data reveal the following association constants or K_DMPG values: 11,000 M^"1 for DB-172, 13,000 M^"1 for DB-172-20-glycinate ester, and 12,000 M^_1 for DB-172-20(S)-3- aminopropanoate ester.

Figures 17a-17b. Double-reciprocal plots for the binding of silatecan and silatecan prodrugs (DB-67, DB-67 Gly and DB-67 But shown in Figure 17a and DB-172, DB-172 Gly and DB-172 Prop shown in Figure 17b) to small unilamellar vesicles composed of DMPC in phosphate buffered saline (PBS), pH 7.4. Experiments were conducted as described in legends of Figures 16 and 17. The linearity of the plots indicates that the anisotropy data is well fit by the double-reciprocal method of analysis.

Figures 18a- 18b. HPLC chromatogram depicting the separation of DB-67 (retention time of 6.4 min) from DB-67 carboxylate (retention time of 1.7 min). Samples in PBS buffer were prepared by adding 1 μM DB-67 from a DMSO stock solution. As illustrated in Figure 18a at a very brief incubation time of 1 min. DB-67 in its lactone form predominates. As illustrated in Figure 18b at longer incubation times (t = 3 hours) the drug has hydrolyzed extensively and its inactive, ring-opened carboxylate form predominates. Separation of the lactone and carboxylate forms of DB-67 was achieved using an isocratic mobile phase consisting of a mixture of 41% acetonitrile and 59% of the triethylamine acetate buffer. Both DB-67 lactone and camptothecin forms were detected at an excitation wavelength of 380 nm and an emission wavelength of 560 nm. A flow rate of 1 mL/min was employed.

Figures 19a- 19b. HPLC chromatograms depicting, respectively, how DB-67 glycinate (retention time of 3.6 min) predominates in PBS, pH 3.0, and in DMSO after standing in solution for several hours. Separation of DB-67 glycinate was achieved using an isocratic mobile phase consisting of a mixture of 41% acetonitrile to 59% of the triethylamine acetate buffer. DB-67 glycinate was detected at an excitation wavelength of 560 nm and an emission wavelength of 440 nm. A flow rate of 1 mL/min was employed. Figures 20a-20b. HPLC chromatograms depicting the pronounced and instantaneous reactivity of DB-67-20-glycinate ester hydrochloride upon addition to PBS buffer under near physiological conditions of ionic strength and temperature. The parent DB-67-20-glycinate ester peak appears at a retention time of 3.6 min. Immediately following the addition of DB-67-20- glycinate ester hydrochloride to PBS buffer at a concentration of 1 μM, a new major peak is observed (retention time of 4.2 min). Upon further standing, sampling of the drug solution in PBS shows further conversion to a total of at least three other chemical entities being observed in the solution. Separation of starting material (DB-67-20-glycinate ester) from the hydrolysis products [intermediate (retention time of 4.2 min), DB-67 (retention time of 7.1 min) and DB-67 carboxylate (retention time of 1.9 min) was achieved using an isocratic mobile phase consisting of a mixture of 41% acetonitrile to 59% of the triethylamine acetate buffer. DB-67-20-glycinate ester and its hydrolysis products were detected at an excitation wavelength of 380 nm and an emission wavelength of 560 nm. A flow rate of 1 mL/min was employed. Figure 20a is for an incubation time of one minute. Figure 20b is for an incubation time of three hours.

Figure 21. HPLC chromatogram depicting the high purity and high stability in non-aqueous DMSO solution of a salt preparation of DB-67-20(S)-4-aminobutanoate ester. Upon standing in DMSO for hours the DB-67-20(S)-4-aminobutanoate ester did not show significant evidence of hydrolysis or other forms of chemical reactivity. Separation of DB-67-20(S)-4-aminobutanoate ester was achieved using an isocratic mobile phase consisting of a mixture of 41% acetonitrile to 59%o of the triethylamine acetate buffer. Camptothecin-20-glycinate ester was detected at an excitation wavelength of 380 nm and an emission wavelength of 560 nm. A flow rate of 1 mL/min was employed.

Figures 22a-22b. HPLC chromatograms depicting the diminished reactivity of DB-67- 20(S)-4-aminobutanoate ester (relative to DB-67 glycinate ester) upon addition to PBS buffer under near physiological conditions of ionic strength and temperature. The parent DB-67-20(S)-4- aminobutanoate ester peak appears at a retention time of 3.4 min. Immediately following the addition of DB-67-20(S)-4-aminobutanoate ester hydrochloride to PBS buffer at a concentration of 1 μM, a new peak is observed (retention time of 6.4 min corresponding to the lactone form of DB-67). Upon further standing, sampling of the drug solution in PBS shows further conversion to a total of at least two new chemical entities (DB-67 lactone and carboxylate) being observed in the solution. Separation of starting material (DB-67-20(S)-glycinate ester) from the hydrolysis products [DB-67 (retention time of 6.4 min) and DB-67 carboxylate (retention time of 2.0 min) was achieved using an isocratic mobile phase consisting of a mixture of 41% acetonitrile to 59% of the triethylamine acetate buffer. DB-67-20(S)-4-aminobutanoate ester hydrochloride and its hydrolysis products were detected at an excitation wavelength of 380 nm and an emission wavelength of 569 nm. A flow rate of 1 mL/min was employed. Figure 22a is for an incubation time of one minute. Figure 22b is for an incubation time of 3 hours.

Figures 23a-23b. HPLC chromatogram depicting the separation of DB-172 (retention time of 6.0 min) from DB-172 carboxylate (retention time of 1.7 min). Samples in PBS buffer were prepared by adding 1 μM DB-172 from a DMSO stock solution. As illustrated in Figure 23a at a very brief incubation time of 1 min. DB-172 in its lactone form predominates. As illustrated in Figure 23b at longer incubation times on the order of several hours (i.e. t = 3 hours) the drag has hydrolyzed extensively and its inactive, ring-opened carboxylate form predominates. Separation of the lactone and carboxylate forms of DB-172 was achieved using an isocratic mobile phase consisting of a mixture of 57% acetonitrile and 43% of the triethylamine acetate buffer. Both DB-172 lactone and camptothecin forms were detected at an excitation wavelength of 371 nm and an emission wavelength of 428 nm. A flow rate of 1 mL/min was employed. Figure 24. HPLC chromatogram depicting the high purity and high stability in non-aqueous

DMSO solution of a salt preparation of DB-172-20-glycinate ester. Upon standing in DMSO for hours the DB-172-20-glycinate ester did not show significant evidence of hydrolysis or other forms of chemical reactivity. Separation of DB-172-20-glycinate ester was achieved using an isocratic mobile phase consisting of a mixture of 57% acetonitrile to 43% of the triethylamine acetate buffer. DB-172-20-glycinate ester was detected at an excitation wavelength of 371 nm and an emission wavelength of 428 nm. A flow rate of 1 mL/min was employed.

Figures 25a-25b. HPLC chromatograms depicting the reactivity of DB-172-20-glycinate ester upon addition to PBS buffer under near physiological conditions of ionic strength and temperature. The parent DB-172-20-glycinate ester peak appears at a retention time of 3.1 min. As illustrated in Figure 25a immediately following the addition of DB-172-20-glycinate ester to PBS buffer at a concentration of 1 μM (i.e. t = one minute), a new peak is observed (retention time of 3.6 min corresponding to an intermediate). As illustrated in Figure 25b upon further standing (i.e. t = three hours), sampling of the drug solution in PBS shows further conversion to a total of at least four new chemical entities (DB-172 lactone and carboxylate (2 types), and intermediate) being observed in the solution. Separation of starting material (DB-172-20-glycinate ester) from the hydrolysis products [DB-172 (retention time of 6.2 min), and DB-172 carboxylate (retention time of 1.6 min) was achieved using an isocratic mobile phase consisting of a mixture of 57% acetonitrile to 43% of the triethylamine acetate buffer. DB-172-20-glycinate ester and its hydrolysis products were detected at an excitation wavelength of 371 nm and an emission wavelength of 428 nm. A flow rate of 1 mL/min was employed.

Figure 26. HPLC chromatogram depicting the high purity and high stability in non-aqueous DMSO solution of a salt preparation of DB-172-20(S)-3-aminopropanoate ester. Upon standing in DMSO for hours the DB-172-20(S)-3-aminopropanoate ester did not show significant evidence of hydrolysis or other forms of chemical reactivity. Separation of DB-172-20(S)-3-aminopropanoate ester was achieved using an isocratic mobile phase consisting of a mixture of 57% acetonitrile to 43% of the triethylamine acetate buffer. DB-172-20(S)-3-aminopropanoate ester was detected at an excitation wavelength of 371 nm and an emission wavelength of 428 nm. A flow rate of 1 mL/min was employed.

Figures 27a-27b. HPLC chromatograms depicting the diminished reactivity of DB-172- 20(S)-3-aminopropanoate ester (relative to DB-172 glycinate ester) upon addition to PBS buffer under near physiological conditions of ionic strength and temperature. The parent DB-172-20(S)-3- aminopropanoate ester peak appears at a retention time of 3.1 min. As illustrated in Figure 27a, immediately following the addition of DB-172-20(S)-3-aminopropanoate ester to PBS buffer at a concentration of 1 uM (i.e. t = one minute), a new peak is observed (retention time of 6.6 min corresponding to the lactone form of DB-172). As illustrated in Figure 27b, upon further standing (i.e. t = three hours), sampling of the drug solution in PBS shows further conversion to a total of at least two new chemical entities (DB-172 lactone and carboxylate) being observed in the solution. Separation of starting material (DB-172-20(S)-3 -aminopropanoate ester) from the hydrolysis products [DB-172 (retention time of 6.6 min) and DB-172 carboxylate (retention time of 2.2 min) was achieved using an isocratic mobile phase consisting of a mixture of 57% acetonitrile to 43% of the triethylamine acetate buffer. DB-172-20(S)-3-aminopropanoate ester and its hydrolysis products were detected at an excitation wavelength of 371 nm and an emission wavelength of 428 nm. A flow rate of 1 mL/min was employed.

Figure 28. Stability of DB-67 glycinate ester free drug in PBS (pH 7.4) at 37 °C. The data is plotted as the percentage of area for a given chemical species as a function of total area. Figures 29a-29b. Stability of DB-67-20(S)-4-aminobutanoate ester free drug in PBS, pH

7.4 (Figure 29a) and in whole human blood (Figure 29b) at 37 °C. The data is plotted as the percentage of area for a given chemical species as a function of total area.

Figures 30a-30b. Stability of DB-172 glycinate ester free drug in PBS, pH 7.4 (Figure 30a) and in whole human blood (Figure 30b) at 37 °C. The data is plotted as the percentage of area for a given chemical species as a function of total area.

Figures 31a-31b. Stability of DB-172-20(S)-3-aminopropanoate ester free drug in PBS, pH 7.4 (Figure 31a) and in whole human blood (Figure 31b) at 37 °C. The data is plotted as the percentage of area for a given chemical species as a function of total area.

Figures 32a-32b. Stability of DB-172 glycinate ester in PBS at pH 3.0 (Figure 32a) and pH 5.0 (Figure 32b) at 37 °C. The data is plotted as the percentage of area for a given chemical species as a function of total area.

Figures 33a-33d. Depiction of the pronounced reactivity of DB-67-20-glycinate ester in the presence of varying concentrations of DMPC SUVs in PBS buffer at 37 °C at pH 7.4 at an initial prodrug concentration of 1 μM. Comparison of the stability of DB-67-20-glycinate ester in the presence of high concentrations of DMPC versus low levels of DMPC reveals the presence of membrane initially helps to conserve the parent DB-67-20-glycinate. Stability profiles were determined using HPLC methods.

Figures 34a-34d. Depiction of the pronounced reactivity of DB-172-20-glycinate ester in the presence of varying concentrations of DMPC SUVs in PBS buffer at 37 °C at pH 7.4 at an initial prodrug concentration of 1 μM. Comparison of the stability of DB-172-20-glycinate ester in the presence of high and low concentrations of DMPC reveals the presence of membrane promotes formation of the intermediate. Stability profiles were determined using HPLC methods.

Figure 35. Depiction of the pronounced reactivity of DB-172-20-glycinate ester in the presence of a very high concentration of DMPC SUVs in PBS buffer at 37 °C at pH 7.4 at an initial prodrug concentration of 1 μM. Comparison of the stability of DB-172-20-glycinate ester in the presence of high and low concentrations of DMPC reveals the presence of membrane promotes formation of the intermediate. Stability profiles were determined using HPLC methods.

Figures 36a-36b. Comparison of the stabilities of DB-172-20-glycinate ester in PBS at pH values of 3.0 (Figure 36a) and 5.0 (Figure 36b). Stability profiles were determined using HPLC methods.

Figures 37a-37b. Stability of DB-172 (Figure 37a) and DB-172 glycinate (Figure 37b) in PBS at pH 7.4 and 37 °C. The data are plotted as the percentage of intact drug.

Figure 38. Depiction of the stability of core-loaded liposomal DB-172-20-glycinate ester in whole human blood at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods. All experiments were conducted at an original prodrug concentration of 1 μM.

Figure 39. Depiction of the stability of core-loaded liposomal DB-67-20-glycinate ester in whole human blood at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods. All experiments were conducted at an original prodrug concentration of 1 μM.

Figure 40. Depiction of the stability of core-loaded liposomal DB-67-20(S)-3- aminopropanoate ester in phosphate buffered saline (PBS) at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods and monitored out to 48 hrs. All experiments were conducted at an original prodrug concentration of 1 μM.

Figures 41a-41b. Depiction of the stability of core-loaded liposomal DB-67-20(S)-4- aminobutanoate ester in phosphate buffered saline (PBS) at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods and monitored out to 48 hrs. All experiments were conducted at an original prodrug concentration of 1 μM.

Figures 42a-42b. Depiction of the stability of core-loaded liposomal DB-67-20(S)-4- aminobutanoate in whole human blood at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods and monitored out to 48 hrs. All experiments were conducted at an original prodrug concentration of 1 μM.

Figure 43. Depiction of the stability of bilayer-loaded liposomal DB-67-20(S)-4- aminobutanoate ester in PBS buffer at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods and monitored out to 180 hrs. All experiments were conducted at an original prodrug concentration of 1 μM. Comparison of the data contained in Figure 42 indicates that core-loading is superior to bilayer loading in conserving the DB-67-20(S)-4-aminobutanoate ester prodrug in its native form. Detailed Description of the Invention

The silyl esters claimed herein were prepared following modified procedures from Wall and Wani in US 6,040,313. More specifically, treatment of 1 (DB-172) with DCC, DMAP and the appropriate protected amino acid followed by acidic deprotection of the amino group provided the desired ester salts 2 and 3 in 44% and 29% overall yield, Scheme 1.

1 (DB-172) 2 (DB-UK1-52) n=l X=C1^" 44%

3 (DB-UK1-55) n=2 X=CF₃CO₂ ^" 29%

Synthesis of DB-172 glycinate and lysinate esters —

Following the successful preparation of the DB-172 ester series, we pursued development of the esters of DB-67 5. Addition of DCC, DMAP and N-(tert-butoxycarbonyl)glycine to a solution of the acetoxy protected analog (DB-64) 4 in DMF resulted in the unexpected combined deacetylation and esterification. Subsequent treatment of this product with a solution of HC1 in dioxane provided the desired DB-67 glycinate ester 6 in 7 % overall yield.

The direct deprotection and esterification was convenient, but unfortunately the yield was too low to be of practical value. Therefore we sought to improve this step. Based on control experiments carried out in DMF and CH₂C1₂ we found that DMAP was responsible for cleavage of the acetate ester group. We hypothesized that this process may proceed through a charged intermediate, which would be better stabilized by DMF. Although deacetylation was observed in CH₂C1₂ the reaction was significantly slower and could be completely suppressed by lowering the reaction temperature to 0 ^DC.

With our new observations in hand, we set out to prepare the DB-20(S)-4- aminobutanoate ester of DB-67 7. A solution of DB-64 4 in CH₂C1₂ at 0 ^DC was treated with DCC, DMAP and 4-tert-butoxycarbonylamino-butyric acid providing the desired ester in 39% yield. Treatment of this ester with guanine in CH₂C1₂ and EtOH afforded the selective deprotection of the acetoxy group in 72 % yield. Finally treatment of the hydroxy ester with a solution of TFA in dichloromethane provided the desired DB-67-20(S)-4-aminobutanoate ester hydrochloride salt 7 in 17% overall yield from 4.

6 (DB-UK1-41) 7%

7 (DB-UKl-85) 17%

Preparation of DB-67 Butanate ester The following synthesis and examples are presented to further illustrate the present invention, but is not to be considered as limited thereto. In the examples, NMR spectra were obtained using a Varian VXR 300 MHz instrument and mass spectra were obtained using an Ion Spec Mass Spectrometer.

Example 1:

Experimentals

Example 1:

tert-Butoxycarbonylamino-acetic acid 4-ethyl-3,13-dioxo-l l-(2-trimethylsilanyl-ethyl)-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (1):

DB-172(7-trimethylsilylethylcamptothecin) (30 mg, 0.07 mmol) was placed in an oven dried flask under Nitrogen. Next anhydrous CH₂C1₂ (2.0 ml) was added followed by N-tert- Butoxycarbonylglycine (28 mg, 0.16 mmol), DMAP (5.1 mg, 0.04 mmol) and DCC (33 mg, 0.16 mmol) generating a yellow solution. After 5h at ambient temperature the reaction became cloudy and the methylene chloride was filtered and concentrated at 22 ^DC. The crude material was purified by flash chromatography (95:5 CH₂Cl₂/acetone) followed by preparative TLC (95:5 CH₂Cl₂/acetone x2 elutions) to provide 1 (20.3 mg, 48% yield) as a light yellow solid: *H NMR (CD₂C1₂) 300 MHz D 0.19 (s, 9 H), 0.85-0.9 (m, 2 H), 1.00 (t, J= 7 Hz, 3 H), 1.41 (s, 9 H), 2.08- 2.32 (m, 2 H), 3.06-3.19 (m, 2 H), 4.02-4.22 (m, 2 H), 5.08-5.18 (br s, 1 H), 5.23 (s, 2 H), 5.37 (d, J= 16 Hz, 1 H), 5.66 (d, J= 17 Hz, 1 H), 7.24 (s, 1 H), 7.69 (t, J= 8 Hz, 1 H), 7.81 (t, J= 8 Hz, 1 H), 8.10 (d, J= 8 Hz, 1 H), 8.19 (d, J= 8 Hz, 1 H); ¹³C NMR (CD₂C1₂) 100 MHz D 1.7, 7.9, 18.1, 24.6, 28.5, 32.0, 42.9, 49.7, 67.5, 77.4, 80.4, 96.3, 120.0, 124.1, 126.8, 127.2, 128.0, 130.4, 130.9, 146.1, 147.7, 147.8, 149.9, 152.5, 156.1, 157.8, 167.8, 170.1.

4-Ethyl-3,13-dioxo-ll-(2-trimethylsilanyl-ethyl)-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium chloride (2):

DB-172 ester 1 (20.3 mg, 0.033 mmol) was placed in an oven dried flask under nitrogen and hydrogen chloride in dioxane (4 ml, 4.0 M) was added generating a bright yellow solution.

After 5 h the dioxane was concentrated, the residue was washed with ether 3x2 ml and the bright yellow product was placed under high vacuum overnight providing 16.3 mg of 2 (91% yield) of salt: ¹H NMR (d₆-DMSO) 400 MHz Q0.15 (s, 9 H), 0.82-0.98 (m, 5 H), 2.10-2.24 (m, 2 H), 3.08-

3.18 (m, 2 H), 4.08 (d, J= 18 Hz, 1 H), 4.33 (d, J= 18 Hz, 1 H), 5.32 (d, J= 19 Hz, 1 H), 5.39 (d, J= 19 Hz, 1 H), 5.53 (d, J= 17 Hz, 1 H), 5.57 (d, J= 17 Hz, 1 H), 7.3 (s, 1 H), 7.72-7.82 (m, 1 H),

7.82-7.89 (m, 1 H), 8.15 (d, J= 8 Hz, 1 H), 8.19 (d, J= 8 Hz, 1 H); ¹³C NMR (CD₂C1₂) 100 MHz

□ 1.7, 7.6, 17.1, 23.3, 30.2, 31.7, 49.4, 66.3, 77.5, 93.9, 95.5, 118.7, 123.9, 126.1, 127.3, 127.7,

129.5, 130.1, 144.6, 146.4, 147.1, 148.2, 151.5, 156.4, 166.6; LRMS (MALDI) m/z 544 (M+K),

528 (M+Na), 506 (M+H), 431, 403; HRMS (MALDI) m/z Calcd for C₂₇H₃iN₃0₅SiK (M+K) 544.1673 found 544.1673.

Example 2:

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-3,13-dioxo-l l-(2-trimethylsilanyl-ethyl)- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (3):

DB-172(7-trimethylsilylethylcamptothecin) (106 mg, 0.237 mmol) was placed in an oven dried flask under Nitrogen. Next anhydrous CH₂C1₂ (7.1 ml) was added followed by 3-tert- Butoxycarbonylamino-propionic acid (99 mg, 0.52 mmol), DMAP (18 mg, 0.15 mmol) and DCC (108 mg, 0.52 mmol) generating a yellow solution. After 5h at ambient temperature the reaction became cloudy and the methylene chloride was filtered and concentrated at 22 ^DC. The crude material was purified by flash chromatography (98:2, 95:5 and 9:1 CH₂Cl₂/acetone to provide 3 (60.2 mg, 41% yield) as a light yellow solid: ^XH NMR (CD₂C1₂) 300 MHz □ 0.19 (s, 9 H), 0.90- 0.98 (m, 2 H), 1.00 (t, J= 7 Hz, 3 H), 1.36 (s, 9 H), 2.08-2.32 (m, 2 H), 2.58-2.82 (m, 2 H), 3.08- 3.18 (m, 2 H), 3.32-3.52 (m, 2 H), 5.23 (br s, 3 H), 5.38 (d, J= 17 Hz, 1 H), 5.66 (d, J= 17 Hz, 1 H), 7.17 (s, 1 H), 7.69 (ddd,

1 Hz, 1 H), 8.10 (d, J= 8 Hz, 1 H), 8.17 (d, J= 8 Hz, 1 H); ¹³C NMR (CD₂C1₂) 100 MHz D 1.8, 7.9, 18.0, 24.4, 28.4, 31.9, 35.1, 36.8, 49.6, 67.4, 76.7, 79.3, 95.7, 119.6, 123.8, 126.5, 126.9, 127.7, 130.1, 130.6, 146.1, 147.4, 147.5, 149.6, 152.2, 155.8, 157.5, 168.0, 171.7.

2-[4-Ethyl-3,13-dioxo-ll-(2-trimethylsilanyl-ethyl)-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium trifluoroacetate (4):

DB-172 ester 3 (27.6 mg, 0.04 mmol) was placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (1.0 ml) was added. Next TFA (1.0 ml) was added dropwise at 0 ^DC. After 5 h at 22 ^DC the reaction mixture was concentrated providing a light brown oily residue. The residue was washed with ether (3x1 ml) and placed under high vacuum overnight providing 4 as a bright yellow solid weighing 10.2 mg (36% yield): Η NMR (d₆-DMSO) 400 MHz □ 0.16 (s, 9 H), 0.92 (m, 5 H), 2.10-2.25 (m, 2 H), 2.85-2.98 (m, 2 H), 3.00-3.08 (br m, 2 H), 3.10-3.16 (m, 2 H), 5.32 (d, J= 18 Hz, 1 H), 5.38 (d, J= 18 Hz, 1 H), 5.50 (d, J= 17 Hz, 1 H), 5.55 (d, J= 17 Hz, 1 H), 7.14 (s, 1 H), 7.72-7.90 (m, 4 H), 8.14-8.21 (m, 2 H); HRMS (MALDI) m z Calcd for C_2SH₃₄N₃0₅Si(M+) 520.2262, found 520.2284.

Example 3:

tert-Butoxycarbonylamino-acetic acid ll-(tert-butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13- tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (5):

DB-64(10-Acetoxy-7-TBDMS-camptothecin) (100 mg, 0.19 mmol) was placed in an oven dried flask under Nitrogen. Next anhydrous DMF (2.0 ml) was added followed by N-tert- butoxycarbonylglycine (66.5 mg, 0.38 mmol), DMAP (17 mg, 0.14 mmol) and DCC (78.4 mg, 0.38 mmol) generating a yellow suspension. After 5h at ambient temperature the reaction became cloudy and the DMF was concentrated. The crude material was purified by flash chromatography (98:2, 95:5 and 85:15 CH₂Cl₂/acetone followed by preparative TLC (9:1 CH₂Cl₂/acetone) to provide 5 (23.9 mg, 20% yield) as a light yellow solid: *H NMR (CD₂C1₂) 300 MHz □ 0.56 (s, 3H), 0.59 (s, 3 H), 0.86 (s, 9 H), 0.97 (t, J= 7 Hz, 3 H), 1.40 (s, 9 H), 2.04-2.28 (m, 2 H), 3.98-4.18 (m, 2 H), 5.07-5.14 (m, 1 H), 5.21-5.26 (m, 2 H), 5.40 (d, J= 16 Hz, 1 H), 5.68 (d, J= 16 Hz, 1 H), 7.26 (s, 1 H), 7.45 (dd,

9 Hz, J₂= 2 Hz, 1 H), 7.60 (d, J= 2 Hz, 1 H), 8.04 (d, J= 9 Hz, 1 H); ¹³C NMR (CD₂C1₂) 100 MHz Q-0.8, -0.7, 7.7, 19.3, 27.1, 28.3, 29.3, 31.7, 42.6, 67.1, 77.1, 80.3, 95.8, 111.6, 118.6, 122.5, 131.9, 134.7, 136.5, 140.6, 143.3, 146.3, 146.9, 147.9, 155.9, 156.1, 157.4, 167.3, 169.5.

l l-(tert-Butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium chloride (6):

DB-67 ester 1 (9.9 mg, 0.015 mmol) was placed in an oven dried flask under nitrogen and hydrogen chloride in dioxane (3 ml, 4.0 M) was added, at 0 ^DC, generating a bright yellow solution. After 5 h the dioxane was concentrated, the residue was washed with ether 3x2 ml and the bright yellow product was placed under high vacuum overnight providing 3.0 mg (35% yield) of 6 as a bright yellow salt: 'H NMR (d₆-DMSO) 400 MHz Q0.65 (s, 6 H), 0.90-0.99 (br m, 12 H), 2.09-2.21 (m, 2 H), 3.62-3.74 (m, 3 H), 4.07 (d, J= 18 Hz, 1 H), 4.31 (d, J= 18 Hz, 1 H), 7.17 (s, 1 H), 7.39 (dd, Jj= 9 Hz, J₂= 2 Hz, 1 H), 7.59 (d, J= 2 Hz, 1 H), 8.00 (d, J= 9 Hz, 1 H); HRMS (MALDI) m/z Calcd for C₂₈H₃₃N₃0₆SiNa (M+Na) 558.2038 found 558.2040.

Example 4:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-(tert-butyl-dimethyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (7):

DB-64(10-Acetoxy-7-TBDMS-camptothecin) (47.2 mg, 0.09 mmol) was placed in an oven dried flask under Nitrogen. Next, at 0 ^πC, anhydrous CH₂C1₂ (3.0 ml) was added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol) generating a yellow solution. After 5h at 0 ^DC, the cloudy reaction mixture was poured into sat. brine solution (8 ml) and extracted with CH₂C1₂ (5x15 ml). The organic layer was dried (MgS0₄), concentrated and purified twice by preparative TLC (97:3 CH₂Cl₂/acetone) to provide 25.4 mg (39% yield) of 7 as a light yellow solid: ^JH NMR (CD₂C1₂) 300 MHz D 0.69 (s, 6 H), 0.96-1.01 (m, 12 H), 1.41 (s, 9 H), 1.84 (p, J= 7 Hz, 2 H), 2.06-2.28 (m, 2 H), 2.37 (s, 3 H), 2.54 (t, J= 7 Hz, 2 H), 3.02-3.18 (m, 2 H), 4.86-4.96 (br s, 1 H), 5.20-5.32 (m, 2 H), 5.36 (d, J= 17 Hz, 1 H), 5.62 (d, J= 17 Hz, 1 H), 7.14 (s, 1 H), 7.55 (dd, J_x= 9 Hz, J₂= 2 Hz, 1 H), 8.05 (d, J= 2 Hz, 1 H), 8.21 (d, J= 9 Hz, 1 H); ¹³C NMR (CD₂C1₂) 100 MHz Q0.38, 8.04, 19.6, 21.7, 25.7, 27.5, 28.7, 29.6, 31.6, 32.0, 40.1, 52.9, 67.5, 76.5, 95.6, 119.9, 121.0, 125.2, 132.0, 133.7, 137.2, 143.3, 146.3, 146.4, 146.6, 149.4, 151.1, 156.2, 157.4, 167.9, 169.4, 172.5.

4-tert-Butoxycarbonylamino-butyric acid 1 l-(tert-butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4yl ester (8):

Silatecan ester 7 (25.4 mg, 0.036 mmol) was added to a vial under nitrogen and subsequently dissolved with a mixture of CH₂C1₂ and EtOH (9: 1, 0.9 ml). In a separate oven dried vial was added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) generating a 0.5 mM solution of guanidine. Next, the guanidine free base (72 DI, 0.036 mmol) was added to the solution of 7 at 22 ^DC producing a bright orange reaction mixture. After 2 h, the reaction contents were applied directly to a preparative TLC and eluted with 85:15 CH2C12/acetone providing 16.7 mg (72% yield) of 8 as a light yellow solid: : Η NMR (CD₂C1₂) 400 MHz D 0.561 (s, 6 H), 0.85 (s, 9 H), 0.94 (t, J= 7 Hz, 3 H), 1.40 (s, 9 H), 1.65-1.80 (m, 2 H), 2.00-2.11 (m, 2 H), 2.42-2.52 (m, 2 H), 2.98-3.12 (m, 2 H), 4.98 (br s, 1 H), 5.19-5.30 (m, 2 H), 5.35 (d, J= 17 Hz, 1 H), 5.64 (d, J= 17 Hz, 1 H), 7.15 (s, 1 H), 7.45 (dd, J_!= 9 Hz, J₂= 2 Hz, 1 H), 7.59 (d, J= 2 Hz, 1 H), 8.09 (d, J= 9 Hz, 1 H); ¹³C NMR (CD₂C1₂) 100 MHz D0.5, 7.9, 19.5, 25.5, 27.4, 28.6, 29.5, 31.4, 31.9, 40.0, 53.1, 67.4, 76.6, 79.6, 95.7, 112.0, 119.1, 123.0, 132.3, 135.2, 137.1, 141.2, 143.8, 147.17, 147.19, 148.4, 156.6, 157.9, 168.2, 172.6.

3-[l l-(tert-Butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium trifluoro-acetate (9):

DB-67 ester 8 (15 mg, 0.022 mmol) was placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) was added. Next TFA (0.75 ml) was added dropwise at 0 ^DC. After 5 h at 22 ^DC the reaction mixture was concentrated providing a light brown oily residue. The residue was washed with ether (3x1 ml) and placed under high vacuum overnight providing 9 as a bright yellow solid weighing 9.3 mg (62% yield): ^JH NMR (d₆-DMSO) 400 MHz D 0.65 (s, 6 H), 0.91 (t, J= 7 Hz, 3 H), 0.95 (s, 9 H), 1.80 (p, J= 8 Hz, 2 H), 2.08-2.19 (m, 2 H), 2.68 (t, J= 8 Hz, 2 H); 2.79-2.90 (br m, 2 H), 5.20 (d, J= 18 Hz, 1 H), 5.25 (d, J= 18 Hz, 1 H), 5.45 (d, J= 17 Hz, 1 H), 5.50 (d, J= 17 Hz, 1 H), 6.94 (s, 1 H), 7.39 (dd, = 9 Hz, J₂= 2 Hz, 1 H), 7.57 (d, J= 2 Hz, 1 H), 7.60-7.82 (br s, 2 H), 8.01 (d, J= 9 Hz, 1 H); HRMS (MALDI) m/z Calcd for C₃₀H₃₈N₃O₆Si(M+H) 564.2524, found 564.2556

Glycinates

Example 5:

tert-Butoxycarbonylamino-acetic acid ll-(tert-butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (10):

DB-202 (7-tert-Butyldimethylsilylcamptothecin) (41.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 10.

l l-(tert-Butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (11):

Ester 10 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 11.

Example 6:

tert-Butoxycarbonylamino-acetic acid 1 l-(dimethyl-propyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (12):

DB-279 (7-n-propyldimethylsilylcamptothecin) (40.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 12.

11 -(Dimethyl-propyl-silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyI-ammonium; trifluoro-acetate (13):

Ester 12 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 13.

Example 7: tert-Butoxycarbonylamino-acetic acid 1 l-(butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (14):

DB-212 (7-n-Butyldimethylsilylcamptothecin) (41.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 14.

ll-(Butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (15):

Ester 14 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 15.

Example 8:

tert-Butoxycarbonylamino-acetic acid 1 l-(dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (16):

DB-208 (7-Phenyldimethylsilylcamptothecin) (43.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^πC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 16.

l l-(Dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (17):

Ester 16 (12.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 17.

Example 9:

tert-Butoxycarbonylamino-acetic acid 4-ethyl-3,13-dioxo-l l-trimethylsilanyl-3,4,12,13- tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (18):

CHJ439A (7-Trimethylsilylcamptothecin) (37.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 18.

l l-(Dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (19):

Ester 18 (11.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 19.

Example 10:

tert-Butoxycarbonylamino-acetic acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (20): DB-207 (7-Dimethylethylsilylcamptothecin) (39.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 20.

4-Ethyl-ll-(ethyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (21):

Ester 20 (11.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 21.

Example 11:

tert-Butoxycarbonylamino-acetic acid ll-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo- 3 ,4, 12, 13-tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (22):

DB-148 (7-Chloropropyldimethylsilylcamptothecin) (43.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂CI₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 22.

l l-[(3-Chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (23):

Ester 22 (12.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 23.

Example 12: tert-Butoxycarbonylamino-acetic acid 1 l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo- 3,4, 12, 13-tetrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (24):

DB-41 (7-Cyanopropyldimethylsilylcamptothecin) (42.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 24.

ll-[(3-Cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (25):

Ester 24 (12.6 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 25.

Example 13:

tert-Butoxycarbonylamino-acetic acid 1 l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (26):

DB-209 (7-(3,3-dimethylbutyl)dimethylsilylcamptothecin) (58.2 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 26.

ll-[(3,3-Dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (27):

Ester 26 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 27.

Example 14: tert-Butoxycarbonylamino-acetic acid ll-(dimethyl-vinyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (28):

DB-206 (7-Vinyldimethylsilylcamptothecin) (53 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 28.

11 -(Dimethyl-vinyl-silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13-tetrahydro- 1 H-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (29):

Ester 28 (11.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 29.

Example 15:

tert-Butoxycarbonylamino-acetic acid l l-(allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (30):

DB-210 (7-Allyldimethylsilylcamptothecin) (54.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂CI₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 30.

l l-(Allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (31):

Ester 30 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 31.

Example 16:

tert-Butoxycarbonylamino-acetic acid 4-ethyl-l l-(isobutyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (32):

DB-280 (7-Dimethylisobutylsilylcamptothecin) (55.7 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 32.

4-Ethyl-ll-(isobutyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (33):

Ester 32 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 33.

Example 17: tert-Butoxycarbonylamino-acetic acid 4-ethyl-l l-(isopropyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (34):

DB-276 (7-Dimethylisopropylsilylcamptothecin) (54.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 34.

4-Ethyl- 11 -(isopropyl-dimethyl-silanyl)-3 , 13 -dioxo-3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (35):

Ester 34 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 35.

Example 18:

tert-Butoxycarbonylamino-acetic acid ll-[dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (36):

DB-277 (7-Dimethylthexylsilylcamptothecin) (58.2 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 36.

ll-[Dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (37):

Ester 36 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 37.

Example 19:

tert-Butoxycarbonylamino-acetic acid 1 l-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-3,13- dioxo-3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (38):

DB-278 (7-(l,2-Dimethylpropyl)-dimethylsilylcamptothecin) (57.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 38.

l l-[(l,2-Dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (39):

Ester 38 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 39.

Example 20:

tert-Butoxycarbonylamino-acetic acid ll-[dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (40): DB-213 (7-(3,3,3-Trifluoropropyl)-dimethylsilylcamptothecin) (59.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 40.

l l-[Dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (41):

Ester 40 (13.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 41.

Example 21:

tert-Butoxycarbonylamino-acetic acid 1 l-(benzyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (42):

DB-214 (7-Benzyldimethylsilylcamptothecin) (58.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 42.

ll-(Benzyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (43):

Ester 42 (13.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 43.

Example 22:

tert-Butoxycarbonylamino-acetic acid 1 l-(chloromethyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (44):

DB-215 (7-Chloromethyldimethylsilylcamptothecin) (55.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 44.

11 -(Chloromethyl-dimethyl-silanyl)-4-ethyl-3, 13 -dioxo-3 ,4,12, 13-tetrahydro- 1 H-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; trifluoro-acetate (45):

Ester 44 (12.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 45.

Propanoates

Example 23: 3 -tert-Butoxycarbonylamino-propionic acid 4-ethyl-3 , 13 -dioxo- 11 -trimethylsilanyl-3 ,4,12,13- tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (46):

CHJ439A (7-TrimethylsiIyIcamptothecin) (37.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 46.

2-(4-Ethyl-3,13-dioxo-ll-trimethylsilanyl-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl)-ethyl-ammonium; trifluoro-acetate (47):

Ester 46 (11.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 47.

Example 24:

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (48):

DB-207 (7-Dimethylethylsilylcamptothecin) (39.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 48.

2-[4-Ethyl-ll-(ethyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6₅12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (49):

Ester 48 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 49.

Example 25:

3-tert-Butoxycarbonylamino-propionic acid 1 l-(tert-butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (50):

DB-202 (7-tert-Butyldimethylsilylcamptothecin) (41.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 50.

2-[ll-(tert-Butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (51):

Ester 50 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 51.

Example 26:

3-tert-Butoxycarbonylamino-propionic acid ll-(dimethyl-ρropyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (52): DB-279 (7-n-propyldimethylsilylcamptothecin) (40.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 52.

2-[l l-(Dimethyl-propyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (53):

Ester 52 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 53.

Example 27:

3-tert-Butoxycarbonylamino-propionic acid ll-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (54):

DB-148 (7-Chloropropyldimethylsilylcamptothecin) (43.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 54.

2-{l l-[(3-Chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl} -ethyl-ammonium; trifluoro-acetate (55):

Ester 54 (13.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 55.

Example 28: 3-tert-Butoxycarbonylamino-propionic acid 1 l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (56):

DB-41 (7-Cyanopropyldimethylsilylcamptothecin) (42.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 56.

2-{ll-[(3-Cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; trifluoro-acetate (57):

Ester 56 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 57.

Example 29:

3-tert-Butoxycarbonylamino-propionic acid ll-(allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (58):

DB-210 (7-Allyldimethylsilylcamptothecin) (54.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 58.

2-[ll-(Allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (59):

Ester 58 (12.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 59.

Example 30:

3-tert-Butoxycarbonylamino-propionic acid 1 l-(dimethyl-vinyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (60):

DB-206 (7-Vinyldimethylsilylcamptothecin) (53 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^GC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 60.

2-[ll-(Dimethyl-vinyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (61):

Ester 60 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 61.

Example 31 :

3 -tert-Butoxycarbonylamino-propionic acid 4-ethyl- 11 -(isopropyl-dimethyl-silanyl)-3 , 13 -dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (62): DB-276 (7-Dimethylisopropylsilylcamptothecin) (54.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 62.

2-[4-Ethyl-ll-(isopropyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (63):

Ester 62 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 63.

Example 32

3-tert-Butoxycarbonylamino-propionic acid 1 l-(butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (64):

DB-212 (7-n-Butyldimethylsilylcamptothecin) (41.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂CI₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 64.

2-[ll-(Butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (65):

Ester 64 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 65.

Example 33:

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-l l-(isobutyl-dimethyl-silanyl)-3, 13 -dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (66):

DB-280 (7-Dimethylisobutylsilylcamptothecin) (55.7 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 °C, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 66.

2-[4-Ethyl- 11 -(isobutyl-dimethyl-silanyl)-3, 13-dioxo-3,4, 12, 13 -tetrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (67):

Ester 66 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 67.

Example 34: 3-tert-Butoxycarbonylamino-propionic acid 1 l-[dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4- ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (68):

DB-277 (7-Dimethylthexylsilylcamptothecin) (58.2 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 68.

2- { 11 -[Dimethyl-(1 , 1 ,2-trimethyl-propyl)-silanyl]-4-ethyl-3, 13-dioxo-3,4, 12, 13-tetrahydro- 1H-2- oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; trifluoro-acetate (69):

Ester 68 (13.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 69.

Example 35:

3-tert-Butoxycarbonylamino-propionic acid 1 l-[dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (70):

DB-213 (7-(3,3,3-Trifluoropropyl)-dimethyIsilylcamptothecin) (59.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^πC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 70.

2-{l l-[Dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; trifluoro-acetate (71):

Ester 70 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 71.

Example 36: 3-tert-Butoxycarbonylamino-propionic acid 1 l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl- 3,13 -dioxo-3 ,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (72):

DB-209 (7-(3,3-dimethylbutyl)dimethylsilylcamptothecin) (58.2 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5xi5 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 72.

2- { 11 -[(3 ,3 -Dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3, 13 -dioxo-3 ,4,12,13 -tetrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; trifluoro-acetate (73):

Ester 72 (13.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 73.

Example 37:

3-tert-Butoxycarbonylamino-propionic acid 1 l-(chloromethyl-dimethyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (74):

DB-215 (7-Chloromethyldimethylsilylcamptothecin) (55.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 74.

2-[l l-(Chloromethyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (75):

Ester 74 (12.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 75.

Example 38:

3-tert-Butoxycarbonylamino-propionic acid 1 l-(benzyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (76):

DB-214 (7-Benzyldimethylsilylcamptothecin) (58.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 76.

2-[ 11 -(Benzyl-dimethyl-silanyl)-4-ethyl-3, 13 -dioxo-3 ,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (77):

Ester 76 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 77.

Example 39: 3-tert-Butoxycarbonylamino-propionic acid 1 l-(dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (78):

DB-208 (7-Phenyldimethylsilylcamptothecin) (43.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 78.

2-[ 11 -(Dimethyl-phenyl-silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4, 12,13 -tetrahydro- 1 H-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; trifluoro-acetate (79):

Ester 78 (13.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 79.

Example 40:

3-tert-Butoxycarbonylamino-propionic acid ll-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (80):

DB-278 (7-(l,2-Dimethylpropyl)-dimethylsilylcamptothecin) (57.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^GC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 80.

2-{l l-[(l,2-Dimethyl-propyI)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl} -ethyl-ammonium; trifluoro-acetate (81):

Ester 80 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 81.

20(S)-4-Aminobutanoate Esters.

Example 41:

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-3,13-dioxo-l l-trimethylsilanyl-3,4,12,13- tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (82):

CHJ439A (7-Trimethylsilylcamptothecin) (37.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 82.

3 -(4-Ethyl-3 , 13-dioxo- 11 -frimethylsilanyl-3 ,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl)-propyl-ammonium; trifluoro-acetate (83):

Ester 82 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 83.

Example 42: 4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-3,13-dioxo-l l-(2-trimethylsilanyl-ethyl)- 3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (84):

DB-172 (7-Trimethylsilylethylcamptothecin) (40.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 84.

3-[4-Ethyl-3,13-dioxo-l l-(2-trimethylsilanyl-ethyl)-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (85):

Ester 84 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 85.

Example 43:

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (86):

DB-207 (7-Dimethylethylsilylcamptothecin) (39.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^αC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 86.

3-[4-Ethyl-ll-(ethyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (87):

Ester 86 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 87.

Example 44:

4-tert-Butoxycarbonylamino-butyric acid 1 l-(tert-butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (88):

DB-202 (7-tert-Butyldimethylsilylcamptothecin) (41.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂CI₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 88.

3-[ll-(tert-Butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (89):

Ester 88 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 89.

Example 45: 4-tert-Butoxycarbonylamino-butyric acid 1 l-(dimethyl-propyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (90):

DB-279 (7-n-propyldimethylsilylcamptothecin) (40.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 90.

3-[ll-(Dimethyl-propyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (91):

Ester 90 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 91.

Example 46:

4-tert-Butoxycarbonylamino-butyric acid 11 -(butyl-dimethyl-silanyl)-4-ethyl-3 , 13 -dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (92):

DB-212 (7-n-Butyldimethylsilylcamptothecin) (41.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 92.

3-[ll-(Butyl-dime%l-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-ρropyl-ammonium; trifluoro-acetate (93):

Ester 92 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 93.

Example 47: 4-tert-Butoxycarbonylamino-butyric acid 1 l-(dimethyl-vinyl-silanyl)-4-ethyl-3,13-dioxo- 3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (94):

DB-206 (7-Vinyldimethylsilylcamptothecin) (53 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 94.

3 -[ 11 -(Dimethyl-vinyl-silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4, 12, 13-tetrahydro- 1 H-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (95):

Ester 94 (12.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 95.

Example 48:

4-tert-Butoxycarbonylamino-butyric acid ll-(allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4, 12, 13-tetrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (96):

DB-210 (7-Allyldimethylsilylcamptothecin) (54.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 96.

3-[ll-(Allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (97):

Ester 96 (12.6 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 97.

Example 49:

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-l l-(isopropyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (98):

DB-276 (7-Dimethylisopropylsilylcamptothecin) (54.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 98.

3-[4-Ethyl-ll-(isopropyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6J12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (99):

Ester 98 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 99.

Example 50:

4-tert-Butoxycarbonylamino-butyric acid ll-[dimethyl-(l,l,2-ttimethyl-propyl)-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (100): DB-277 (7-Dimethylthexylsilylcamptothecin) (58.2 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 100.

H θ₃ ³Θ^KZJn°γ V^r _F

O

3 - { 11 -[Dimethyl-( 1 , 1 ,2-trimethyl-propyl)-silanyl]-4-ethyl-3, 13 -dioxo-3 ,4, 12, 13-tetrahydro- 1H-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate

(101):

Ester 100 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 101.

Example 51:

4-tert-Butoxycarbonylamino-butyric acid 11 - [( 1 ,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (102):

DB-278 (7-(l,2-Dimethylpropyl)-dimethylsilylcamptothecin) (57.0 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^πC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 102.

3-{l l-[(l,2-Dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate

(103):

Ester 102 (13.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 103.

Example 52:

4-tert-Butoxycarbonylamino-butyric acid ll-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13- dioxo-3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (104):

DB-148 (7-Chloropropyldimethylsilylcamptothecin) (43.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and

EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 104.

3-{l l-[(3-Chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl} -propyl-ammonium; frifluoro-acetate (105):

Ester 104 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 105.

Example 53: 4-tert-Butoxycarbonylamino-butyric acid 1 l-[(3-cyano-propyl)-dimethyl-silanyI]-4-ethyI-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (106):

DB-41 (7-Cyanopropyldimethylsilylcamptothecin) (42.6 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 106.

3-{l l-[(3-Cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (107):

Ester 106 (13.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 107.

Example 54:

4-tert-Butoxycarbonylamino-butyric acid ll-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (108):

DB-209 (7-(3,3-dimethylbutyl)dimethylsilylcamptothecin) (58.2 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 108.

3-{ll-[(3,3-Dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (109):

Ester 108 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 109.

Example 55: 4-tert-Butoxycarbonylamino-butyric acid 1 l-[dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (110):

DB-213 (7-(3,3,3-Trifluoropropyl)-dimethylsilylcamptothecin) (59.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 110.

3-{l l-[Dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (H I):

Ester 110 (13.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 111.

Example 56:

4-tert-Butoxycarbonylamino-butyric acid l l-(benzyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (112):

DB-214 (7-Benzyldimethylsilylcamptothecin) (58.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 112.

3-[l l-(Benzyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (113):

Ester 112 (13.6 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 113.

Example 57: 4-tert-Butoxycarbonylamino-butyric acid 1 l-(dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (114):

DB-208 (7-Phenyldimethylsilylcamptothecin) (43.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 114.

3-[π-(Dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (115):

Ester 114 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 °C. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 115.

Example 58:

4-tert-Butoxycarbonylamino-butyric acid ll-(chloromethyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3_J4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (116):

DB-215 (7-ChloromethyIdimethylsilylcamptothecin) (55.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^aC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and

EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 116.

3-[ll-(Chloromethyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (117):

Ester 116 (12.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 117.

Example 59:

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-l l-(isobutyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (118):

DB-280 (7-Dimethylisobutylsilylcamptothecin) (55.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 118.

3 -[4-Ethyl- 11 -(isobutyl-dimethyl-silanyl)-3, 13-dioxo-3 ,4, 12, 13 -tetrahydro- 1 H-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (119):

Ester 118 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 119.

10-Hydroxy-7-Silatecan Prodrugs

Glycinates

Example 60:

tert-Butoxycarbonylamino-acetic acid 9-acetoxy-4-ethyl-3,13-dioxo-l 1-ttimethylsilanyl- 3,4, 12, 13-tefrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (120):

10-Acetoxy-7-frimethylsilylcamptothecin (43.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0 ), concentrated and purified > by chromatography providing ester 120.

tert-Butoxycarbonylamino-acetic acid 4-ethyl-9-hydroxy-3,13-dioxo-l 1-frimethylsilanyl- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (121):

Ester 120 (22.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 120 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 121.

4-Ethyl-9-hydroxy-3,13-dioxo-l l-trimethylsilanyl-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (122):

Ester 121 (11.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 122.

Example 61:

tert-Butoxycarbonylamino-acetic acid 9-acetoxy-4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13-dioxo- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (123): DB-161 (lO-Acetoxy-7-dimethylethylsilylcamptothecin) (44.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 123.

tert-Butoxycarbonylamino-acetic acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-9-hydroxy-3, 13 -dioxo- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (124):

Ester 123 (23.4 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 123 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 124.

4-Ethyl-ll-(ethyl-dimethyl-silanyl)-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (125):

Ester 124 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 125.

Example 62: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-(dimethyl-propyl-silanyl)-4-ethyl-3, 13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (126):

DB-269 (10-Acetoxy-7-dimethyl-n-propylsilylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^πC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 126.

tert-Butoxycarbonylamino-acetic acid 1 l-(dimethyl-propyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (127):

Ester 126 (23.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 126 at 22 ^πC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 127.

11 -(Dimethyl-propyl-silanyl)-4-ethyl-9-hydroxy-3 , 13 -dioxo-3 ,4,12,13 -tetrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (128):

Ester 127 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 128.

Example 63: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-ll-(butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (129):

DB-173 (lO-Acetoxy-7-n-butyldimethylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 129.

tert-Butoxycarbonylamino-acetic acid ll-(butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (130):

Ester 129 (24.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 129 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 130.

l l-(Butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (131):

Ester 130 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 131.

Example 64: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (132):

DB-158 (10-Acetoxy-7-Chloropropyldimethylsilylcamptothecin) (48.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 132.

tert-Butoxycarbonylamino-acetic acid 1 l-[(3-chloro-propyI)-dimethyl-silanyl]-4-ethyl-9-hydroxy- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (133):

Ester 132 (25.1 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 miftol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 132 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 133.

l l-[(3-Chloro-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH- 2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (134):

Ester 133 (13.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 134.

Example 65: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (135):

DB-V-172 (10-Acetoxy-7-Cyanopropyldimethylsilylcamptothecin) (47.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^aC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 135.

tert-Butoxycarbonylamino-acetic acid 1 l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (136):

Ester 135 (24.8 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 135 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 136.

l l-[(3-Cyano-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2- oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (137):

Ester 136 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml/is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 137.

Example 66: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-(chloromethyl-dimethyl-silanyl)-4-ethyl- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (138):

lO-Acetoxy-7-Chloromethyldimethylsilylcamptothecin (46.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 °C, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 138.

tert-Butoxycarbonylamino-acetic acid 1 l-(chloromethyl-dimethyl-silanyl)-4-ethyl-9-hydroxy- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (139):

Ester 138 (24.1 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 138 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 139.

ll-(Chloromethyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (140):

Ester 139 (12.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 140.

Example 67:

tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-(dimethyl-vinyl-silanyl)-4-ethyl-3,13-dioxo- 3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (141): DB-160 (lO-Acetoxy-7-Vinyldimethylsilylcamptothecin) (44.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 141.

tert-Butoxycarbonylamino-acetic acid 1 l-(dimethyI-vinyl-silanyI)-4-ethyl-9-hydroxy-3, 13-dioxo- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (142):

Ester 141 (23.3 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 140 at 22 ^αC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 142.

l l-(Dimethyl-vinyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (143):

Ester 142 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^πC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 143.

Example 68:

tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-(allyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo- 3,4, 12, 13-tefrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (144): DB-171 (10-Acetoxy-7-allyldimethylsilylcamptothecin) (45.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert- Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 144.

tert-Butoxycarbonylamino-acetic acid 1 l-(allyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo- 3 ,4, 12, 13-tetrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (145):

Ester 144 (23.8 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 144 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 145.

ll-(Allyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (146):

Ester 145 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 146.

Example 69:

tert-Butoxycarbonylamino-acetic acid 9-acetoxy-4-ethyl-l l-(isopropyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (147): DB-266 (lO-Acetoxy-7-dimethylisopropylsilylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 147.

tert-Butoxycarbonylamino-acetic acid 4-ethyl-9-hydroxy-l l-(isopropyl-dimethyl-silanyl)-3,13- dioxo-3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (148):

Ester 147 (23.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 147 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 148.

4-Ethyl-9-hydroxy-ll-(isopropyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (149):

Ester 148 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 149.

Example 70:

tert-Butoxycarbonylamino-acetic acid 9-acetoxy-4-ethyl-l l-(isobutyI-dimethyI-silanyl)-3,13- dioxo-3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (150): DB-270 (lO-Acetoxy-7-dimethylisobutylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 150.

tert-Butoxycarbonylamino-acetic acid 4-ethyl-9-hydroxy-l l-(isobutyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (151):

Ester 150 (24.4 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 150 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 151.

4-Ethyl-9-hydroxy- 11 -(isobutyl-dimethyl-silanyl)-3 , 13 -dioxo-3 ,4, 12, 13-tetrahydro- lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yIoxycarbonylmethyl-ammonium; frifluoro-acetate (152):

Ester 151 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 152.

Example 71: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-[dimethyl-(l,l,2-trimethyl-propyl)-silanyl]- 4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b i]fluoren-4-yl ester (153):

DB-267 (lO-Acetoxy-7-dimethylthexylsilylcamptothecin) (49.3 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 153.

tert-Butoxycarbonylamino-acetic acid ll-[dimethyl-(l,l,2-frimethyl-propyl)-silanyl]-4-ethyl-9- hydroxy-3 , 13 -dioxo-3 ,4, 12, 13-tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (154):

Ester 153 (25.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 153 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 154.

11 -[Dimethyl-( 1 , 1 ,2-trimethyl-propyl)-silanyl]-4-ethyl-9-hydroxy-3, 13 -dioxo-3 ,4, 12, 13 - tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (155):

Ester 154 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 155.

Example 72: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4- ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (156):

DB-268 (10-Acetoxy-7-[(l,2-dimethylpropyl)dimethylsilyl]camptothecin) (48.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 156.

tert-Butoxycarbonylamino-acetic acid 1 l-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3 , 13 -dioxo-3 ,4,12, 13-tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (157):

Ester 156 (24.9 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 156 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 157.

l l-[(l,2-Dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyhnethyl-ammonium; frifluoro-acetate (158):

Ester 157 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 158.

Example 73: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-4-ethyl-3,13-dioxo-l l-(2-ttimethylsilanyl- ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (159):

DB-179 (lO-Acetoxy-7-frimethylsilylethylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 159.

tert-Butoxycarbonylamino-acetic acid 4-ethyl-9-hydroxy-3,13-dioxo-l l-(2-frimethylsilanyl- ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (160):

Ester 159 (23.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 159 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 160.

4-Ethyl-9-hydroxy-3,13-dioxo-ll-(2-frimethylsilanyl-ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (161):

Ester 160 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 161.

Example 74: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4- ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (162):

DB-163 (10-Acetoxy-[7-(3,3-dimethylbutyl)-dimethylsilyl]camptothecin) (49.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 162.

tert-Butoxycarbonylamino-acetic acid 1 l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (163):

Ester 162 (25.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 162 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 163.

l l-[(3,3-Dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (164):

Ester 163 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 164.

Example 75: tert-Butoxycarbonylamino-acetic acid 9-acetoxy-l l-[dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4- ethyl-3,13-dioxo-3,4,12_;13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (165):

DB-V-174 (10-Acetoxy-[7-(3,3,3-frifluoropropyl)dimethyl-silyI]camptothecin) (50.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^GC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 165.

tert-Butoxycarbonylamino-acetic acid 1 l-[dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4-ethyl-9- hydroxy-3 , 13-dioxo-3 ,4,12,13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (166):

Ester 165 (25.8 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 165 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 166.

1 l-[Dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4-ethyl-9-hydroxy-3, 13-dioxo-3,4,12, 13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyhnethyl-aιnmonium; frifluoro-acetate (167):

Ester 166 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 167.

Propanoates

Example 76:

3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-4-ethyl-ll-(ethyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (168):

lO-Acetoxy-7-frimethylsilylcamptothecin (43.0 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 168.

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-9-hydroxy-3, 13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (169):

Ester 168 (23.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 168 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 169.

2-(4-Ethyl-9-hydroxy-3, 13-dioxo- 11 -frimethylsilanyl-3 ,4, 12, 13 -tefrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl)-ethyl-ammonium; frifluoro-acetate (170):

Ester 169 (12.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 170.

Example 77:

3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (171): DB-161 (10-Acetoxy-7-dimethylethylsilylcamptothecin) (44.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 171.

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-9-hydroxy-3, 13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (172):

Ester 171 (23.9 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 171 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 172.

2-[4-Ethyl- 11 -(ethyl-dimethyl-silanyI)-9-hydroxy-3 , 13 -dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (173):

Ester 172 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 173.

Example 78: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-(dimethyl-propyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (174):

DB-269 (10-Acetoxy-7-dimethyl-n-propylsilylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 174.

3-tert-Butoxycarbonylamino-propionic acid 1 l-(dimethyl-propyl-silanyl)-4-ethyI-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (175):

Ester 174 (24.4 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 174 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 175.

2-[l l-(Dimethyl-propyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (176):

Ester 175 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 176.

Example 79: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-(butyl-dimethyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (177):

DB-V-173 (lO-Acetoxy-7-n-butyldimethylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^αC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 177.

3-tert-Butoxycarbonylamino-propionic acid 1 l-(butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (178):

Ester 177 (24.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 177 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 178.

2-[ll-(Butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (179):

Ester 178 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 179.

Example 80: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-[(3-chloro-propyl)-dimethyl-silanyl]-4- ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (180):

DB-158 (10-Acetoxy-7-Chloropropyldimethylsilylcamptothecin) (48.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 180.

3-tert-Butoxycarbonylamino-propionic acid 1 l-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (181):

Ester 180 (25.6 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 180 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 181.

2- { 11 -[(3-Chloro-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3 , 13 -dioxo-3 ,4, 12, 13 -tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (182):

Ester 181 (13.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 182.

Example 81: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-[(3-cyano-propyl)-dimethyl-silanyl]-4- ethyl-3 , 13-dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (183): DB-V-172 (10-Acetoxy-7-Cyanopropyldimethylsilylcamptothecin) (47.8 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^PC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 183.

3-tert-Butoxycarbonylamino-propionic acid 1 l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (184):

Ester 183 (25.3 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 183 at22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 184.

2- { 1 l-[(3-Cyano-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3, 13-dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl} -ethyl-ammonium; frifluoro-acetate (185):

Ester 184 (13.2 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 185.

Example 82: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-4-ethyl-l l-(isobutyl-dimethyl-silanyl)- 3, 13-dioxo-3,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (186):

DB-270 (lO-Acetoxy-7-dimethylisobutylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 186.

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-9-hydroxy-l l-(isobutyl-dimethyl-silanyl)- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (187):

Ester 186 (13.8 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 186 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 187.

2-[4-Ethyl-9-hydroxy-ll-(isobutyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (188):

Ester 186 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 188.

Example 83:

3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-4-ethyl-l l-(isopropyl-dimethyl-silanyl)- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (189): DB-266 (10-Acetoxy-7-dimethylisopropylsilylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 189.

3-tert-Butoxycarbonylamino-propionic acid 4-ethyl-9-hydroxy-l l-(isopropyl-dimethyl-silanyl)- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (190):

Ester 189 (24.4 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 189 at 22 ^αC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 190.

2-[4-Ethyl-9-hydroxy- 11 -(isopropyl-dimethyl-silanyl)-3 , 13 -dioxo-3 ,4,12,13 -tefrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (191):

Ester 190 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 191.

Example 84: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-[dimethyl-(l, 1,2-frimethyl-propyl)- silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (192):

DB-267 (lO-Acetoxy-7-dimethylthexylsilylcamptothecin) (49.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 192.

3-tert-Butoxycarbonylamino-propionic acid 1 l-[dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4- ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (193):

Ester 192 (25.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 192 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 193.

2-{ll-[Dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (194):

Ester 193 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 194.

Example 85: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-[(l,2-dimethyl-propyl)-dimethyl- silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (195):

DB-268 (10-Acetoxy-7-[(l,2-dimethylpropyl)dimethylsilyl]camptothecin) (48.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 195.

3-tert-Butoxycarbonylamino-propionic acid 1 l-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl- 9-hydroxy-3, 13-dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (196):

Ester 195 (25.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 195 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 196.

2-{ll-[(l,2-Dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b_Jh]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (197):

Ester 196 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 197.

Example 86: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l 1 -(tert-butyl-dimethyl-silanyl)-4-ethy 1- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (198):

DB-64 (lO-Acetoxy-7-tert-butyldimethylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 198.

3-tert-Butoxycarbonylamino-propionic acid 1 l-(tert-butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy- 3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (199):

Ester 198 (24.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 198 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 199.

2-[l l-(tert-Butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (200):

Ester 199 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 200.

Example 87:

3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-(chloromethyl-dimethyl-silanyl)-4- ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (201): 10-Acetoxy-7-Chloromethyldimethylsilylcamptothecin (46.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^GC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 201.

3-tert-Butoxycarbonylamino-propionic acid 1 l-(chloromethyl-dimethyl-silanyl)-4-ethyl-9- hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (202):

Ester 201 (24.6 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 201 at 22 ^πC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 202.

2-[l l-(Chloromethyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (203):

Ester 202 (12.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 203.

Example 88:

3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-(dimethyl-vinyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (204): DB-160 (10-Acetoxy-7-Vinyldimethylsilylcamptothecin) (44.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 204.

3-tert-Butoxycarbonylamino-propionic acid l l-(dimethyl-vinyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (205):

Ester 204 (23.8 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 204 at 22 ^πC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 205.

2- [ 11 -(Dimethyl-vinyl-silanyl)-4-ethyl-9-hydroxy-3, 13 -dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (206):

Ester 205 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 206.

Example 89: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-(allyl-dimethyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (207):

DB-171 (10-Acetoxy-7-allyldimethylsilylcamptothecin) (45.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert- Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 207.

3-tert-Butoxycarbonylamino-propionic acid 1 l-(allyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (208):

Ester 207 (24.3 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 205 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 208.

2-[l l-(Allyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (209):

Ester 208 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 209.

Example 90: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-[dimethyl-(3,3,3-trifluoro-propyl)- silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (210):

DB-V-174 (10-Acetoxy-[7-(3,3,3-trifluoropropyl)dimethylsilyl]camptothecin) (50.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 210.

3-tert-Butoxycarbonylamino-propionic acid 1 l-[dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4-ethyl- 9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (211):

Ester 210 (26.3 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 210 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 211.

2-{ 1 l-[Dimethyl-(3,3,3-ttifluoro-propyl)-silanyl]-4-ethyl-9-hydroxy-3, 13-dioxo-3,4, 12, 13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (212):

Ester 211 (13.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 212.

Example 91: 3-tert-Butoxycarbonylamino-propionic acid 9-acetoxy-l l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (213):

DB-163 (10-Acetoxy-[7-(3,3-dimethylbutyl)-dimethylsilyl]camptothecin) (49.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 213.

3-tert-Butoxycarbonylamino-propionic acid 1 l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (214):

Ester 213 (25.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 213 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 214.

2-{l l-[(3,3-Dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl} -ethyl-ammonium; frifluoro-acetate (215):

Ester 214 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 215.

Example 92: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-4-ethyl-3,13-dioxo-l l-(2-frimethylsilanyl- ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (216):

DB-179 (lO-Acetoxy-7-frimethylsilylethylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^PC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 216.

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-9-hydroxy-3,13-dioxo-l l-(2-frimethylsilanyl- ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6_J12a-diaza-dibenzo[b,h]fluoren-4-yl ester (217):

Ester 216 (24.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. fri a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 216 at 22 ^αC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 217.

2-[4-Ethyl-9-hydroxy-3,13-dioxo-l l-(2-frimethylsilanyl-ethyl)-3,4,12,13-tetrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (218):

Ester 217 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 218.

20(S)-4-Aminobutanoate Esters.

Example 93:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-4-ethyl-3,13-dioxo-l 1-frimethylsilanyl- 3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (219):

lO-Acetoxy-7-frimethylsilylcamptothecin (43.0 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 219.

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-9-hydroxy-3 , 13 -dioxo- 11 -frimethylsilanyl- 3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (220):

Ester 219 (23.9 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 219 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 220.

3-(4-Ethyl-9-hydroxy-3,13-dioxo-ll-trimethylsilanyl-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl)-propyl-ammonium; frifluoro-acetate (221):

Ester 220 (12.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 221.

Example 94:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (222): DB-161 (10-Acetoxy-7-dimethylethylsilylcamptothecin) (44.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 222.

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-l l-(ethyl-dimethyl-silanyl)-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (223):

Ester 222 (24.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 222 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 223.

3-[4-Ethyl-ll-(ethyl-dimethyl-silanyl)-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (224):

Ester 223 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 224.

Example 95:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-ll-(dimethyl-propyl-silanyl)-4-ethyl-3,13- dioxo-3,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (225): DB-269 (10-Acetoxy-7-dimethyl-n-propylsilylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 225.

4-tert-Butoxycarbonylamino-butyric acid 1 l-(dimethyl-propyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (226):

Ester 225 (24.9 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 225 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 226.

3-[ 11 -(Dimethyl-propyl-silanyl)-4-ethyl-9-hydroxy-3 , 13 -dioxo-3 ,4, 12, 13-tefrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (227):

Ester 226 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 227.

Example 96:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-(butyl-dimethyl-silanyl)-4-ethyl-3, 13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (228): DB-V-173 (10-Acetoxy-7-n-butyldimethylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 228.

4-tert-Butoxycarbonylamino-butyric acid 1 l-(butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (229):

Ester 228 (25.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 228 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 229.

3-[l l-(Butyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (230):

Ester 229 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^αC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 230.

Example 97: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]- 4-ethyl-3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (231):

DB-163 (10-Acetoxy-[7-(3,3-dimethylbutyl)-dimethylsilyl]camptothecin) (49.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 231.

4-tert-Butoxycarbonylamino-butyric acid 1 l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3 , 13 -dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (232):

Ester 231 (26.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 231 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 232.

3-{l l-[(3,3-Dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[ ,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (233):

Ester 232 (13.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 233.

Example 98: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-[dimethyl-(3,3,3-frifluoro-propyl)-silanyl]- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (234):

DB-V-174 (10-Acetoxy-[7-(3,3,3-frifluoropropyl)dimethyl-silyl]camptothecin) (50.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 234.

4-tert-Butoxycarbonylamino-butyric acid 1 l-[dimethyl-(3,3,3-frifluoro-propyl)-silanyl]-4-ethyl-9- hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (235):

Ester 234 (26.8 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 232 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 235.

3-{l l-[Dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (236):

Ester 235 (14.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 236.

Example 99:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-(allyl-dimethyl-silanyl)-4-ethyl-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (237):

DB-171 (10-Acetoxy-7-allyldimethylsilylcamptothecin) (45.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 237.

4-tert-Butoxycarbonylamino-butyric acid 1 l-(allyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (238):

Ester 237 (24.8 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 237 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 238.

3 - [ 11 -(Allyl-dimethyl-silanyl)-4-ethyl-9-hy droxy-3 , 13 -dioxo-3 ,4,12,13 -tetrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (239):

Ester 238 (12.9 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 239.

Example 100:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-(dimethyl-vinyl-silanyl)-4-ethyl-3,13- dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (240): DB-160 (lO-Acetoxy-7-Vinyldimethylsilylcamptothecin) (44.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 240.

4-tert-Butoxycarbonylamino-butyric acid 1 l-(dimethyl-vinyl-silanyl)-4-ethyl-9-hydroxy-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (241):

Ester 240 (24.3 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 240 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 241.

3-[l l-(Dimethyl-vinyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (242):

Ester 241 (12.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 242.

Example 101:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-4-ethyl-l l-(isopropyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (243): DB-266 (10-Acetoxy-7-dimethylisopropylsilylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^πC, anhydrous CH₂C1₂ (3.0 ml) is added followed . by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 243.

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-9-hydroxy-l l-(isopropyl-dimethyl-silanyl)-3,13- dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (244):

Ester 243 (24.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 243 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 244.

3- [4-Ethyl-9-hydroxy- 11 -(isopropyl-dimethyl-silanyl)-3, 13 -dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (245):

Ester 244 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 245.

Example 102: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-[dimethyl-(l, 1,2-trimethyl-propyl)- silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (246):

DB-267 (lO-Acetoxy-7-dimethylthexylsilylcamptothecin) (49.3 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 246.

4-tert-Butoxycarbonylamino-butyric acid 1 l-[dimethyl-(l,l,2-frimethyl-propyl)-silanyl]-4-ethyl-9- hydroxy-3, 13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (247):

Ester 246 (26.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 246 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 247.

3-{l l-[Dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (248):

Ester 247 (13.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 248.

Example 103: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-[(l,2-dimethyl-propyl)-dimethyl-silanyl]- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (249):

DB-268 (10-Acetoxy-7-[(l,2-dimethyIpropyI)dimethylsilyl]camptothecin) (48.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 249.

4-tert-Butoxycarbonylamino-butyric acid 1 l-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3, 13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (250):

Ester 249 (25.9 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 249 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 250.

3-{l l-[(l,2-Dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (251):

Ester 250 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 251.

Example 104:

4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-4-ethyl-l l-(isobutyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (252): DB-270 (10-Acetoxy-7-dimethylisobutylsilylcamptothecin) (46.8 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 252.

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-9-hydroxy-l l-(isobutyl-dimethyl-silanyl)-3,13- dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (253):

Ester 252 (25.4 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 DI, 0.036 mmol) is added to the solution of 252 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 253.

3 - [4-Ethyl-9-hydroxy- 11 -(isobutyl-dimethyl-silanyl)-3, 13-dioxo-3,4, 12, 13 -tetrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (254):

Ester 253 (13.3 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 254.

Example 105: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-[(3-chloro-propyl)-dimethyl-silanyl]-4- ethyI-3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (255):

DB-158 (10-Acetoxy-7-Chloropropyldimethylsilylcamptothecin) (48.6 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 255.

4-tert-Butoxycarbonylamino-butyric acid 1 l-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3 , 13 -dioxo-3 ,4,12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (256):

Ester 255 (26.1 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 255 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 256.

3-{l l-[(3-Chloro-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (257):

Ester 256 (13.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 257.

Example 106: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-[(3-cyano-propyl)-dimethyl-silanyl]-4- ethyl-3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (258):

DB-V-172 (10-Acetoxy-7-Cyanopropyldimethylsilylcamptothecin) (47.8 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 258.

4-tert-Butoxycarbonylamino-butyric acid 1 l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-9- hydroxy-3, 13-dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (259):

Ester 258 (25.8 mg, 0.036 mmol) is placed in an oven dried vial under nitrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 258 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 259.

3-{l l-[(3-Cyano-propyl)-dimethyl-silanyl]-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (260):

Ester 259 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 260.

Example 107: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-4-ethyl-3,13-dioxo-l l-(2-frimethylsilanyl- ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (261):

DB-179 (lO-Acetoxy-7-frimethylsilylethylcamptothecin) (45.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 261.

4-tert-Butoxycarbonylamino-butyric acid 4-ethyl-9-hydroxy-3,13-dioxo-l l-(2-frimethylsilanyl- ethyl)-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (262):

Ester 261 (24.9 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 261 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 262.

3-[4-Ethyl-9-hydroxy-3,13-dioxo-l l-(2-trimethylsilanyl-ethyl)-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (263):

Ester 262 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 263.

Example 108: 4-tert-Butoxycarbonylamino-butyric acid 9-acetoxy-l l-(chloromethyl-dimethyl-silanyl)-4-ethyl- 3,13 -dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (264):

10-Acetoxy-7-Chloromethyldimethylsilylcamptothecin (46.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert- Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 264.

4-tert-Butoxycarbonylamino-butyric acid 1 l-(chloromethyl-dimethyl-silanyl)-4-ethyl-9-hydroxy- 3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (265):

Ester 264 (25.1 mg, 0.036 mmol) is placed in an oven dried vial under nifrogen. In a separate oven dried vial is added guanidine hydrochloride (100 mg, 1.05 mmol) followed by EtOH (2 ml) and sodium tert-butoxide (100.9 mg, 1.05 mmol) making a 0.5 mM solution of guanidine. Next the guanidine free base (72 Dl, 0.036 mmol) is added to the solution of 264 at 22 ^DC. After 2 h, the reaction contents are chromatographed providing pure hydroxyester 265.

3-[l l-(Chloromethyl-dimethyl-silanyl)-4-ethyl-9-hydroxy-3,13-dioxo-3,4,12,13-tefrahydro-lH-2- oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (266):

Ester 265 (13.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 266.

10-Amino-7-Silatecan Ester Prodrugs

Glycinates

Example 109: tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-4-ethyl-3, 13-dioxo-l 1- trimethylsilanyl-3 ,4, 12, 13 -tefrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (267):

lO-tert-Butoxycarbonylamino-7-trimethylsilylcamptothecin (48.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^αC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 267.

9-Amino-4-ethyl-3, 13-dioxo-l l-trimethylsilanyl-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (268):

Ester 267 (13.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 268.

Example 110:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-4-ethyl- 11 -(ethyl-dimethyl- silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (269):

DB-232 (lO-tert-Butoxycarbonylamino-7-dimethylethylsilylcamptothecin) (49.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 269.

9-Amino-4-ethyl- 11 -(ethyl-dimethyl-silanyl)-3 , 13 -dioxo-3 ,4,12, 13-tefrahydro- lH-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (270):

Ester 269 (14.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂CI₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 270.

Example 111:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l 1 -(dimethyl-propyl-silanyl)- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (271):

10-tert-Butoxycarbonylamino-7-n-propyldimethylsilylcamptothecin (50.7 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 271.

9- Amino- 11 -(dimethyl-propyl-silanyl)-4-ethyl-3, 13-dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (272):

Ester 270 (14.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 272.

Example 112:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino- 11 -(butyl-dimethyl-silanyl)-4- ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (273): DB-237 (lO-tert-Butoxycarbonylamino-7-n-butyldimethylsilylcamptothecin) (66.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 273.

9-Ammo-ll-(butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (274):

Ester 273 (13.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 274.

Example 113:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-[(3-chloro-propyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl (275):

DB-185 (lO-tert-Butoxycarbonylamino-7-chloropropyldimethyl-silylcamptothecin) (53.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 275.

9- Amino- 11 -[(3 -chloro-propyl)-dimethyl-silanyl]-4-ethyl-3 , 13-dioxo-3 ,4,12,13 -tetrahydro- 1H-2- oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (276):

Ester 275 (15.1 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 276.

Example 114: tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-[(3-cyano-propyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (277):

DB-236 (lO-tert-Butoxycarbonylamino-7-cyanopropyldimethyl-silylcamptothecin) (67.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 277.

9-Amino-l l-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2- oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (278):

Ester 277 (14.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 278.

Example 115:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino- 11 -(dimethyl-vinyl-silanyl)-4- ethyl-3 , 13 -dioxo-3 ,4,12,13 -tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (279):

DB-231 (10-tert-Butoxycarbonylamino-7-vinyldimethylsilylcamptothecin) (49.2 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 279.

9-Amino- 11 -(dimethyl-vinyl-silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4, 12, 13-tetrahydro- lH-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (280): Ester 279 (14.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 280.

Example 116:

tert-Butoxycarbonylamino-acetic acid 1 l-(allyl-dimethyl-silanyl)-9-tert-butoxycarbonylamino-4- ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (281):

DB-235 (lO-tert-Butoxycarbonylamino-7-allyldimethylsilylcamptothecin (50.5 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^aC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 281.

11 -(Allyl-dimethyl-silanyl)-9-amino-4-ethyl-3, 13-dioxo-3 ,4, 12, 13-tefrahydro- 1 H-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyhnethyl-ammonium; frifluoro-acetate (282):

Ester 281 (14.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 282.

Example 117:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino- 11 -(tert-butyl-dimethyl- silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4, 12, 13 -tetrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (283): DB-193 (lO-tert-Butoxycarbonylamino-7-tert-butyldimethylsilyl-camptothecin) (51.9 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 283.

9- Amino- 11 -(tert-butyl-dimethyl-silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4,12,13 -tefrahydro- 1 H-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (284):

Ester 283 (14.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 284.

Example 118:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-4-ethyl- 11 -(isopropyl- dimethyl-silanyl)-3, 13-dioxo-3,4, 12, 13-tefrahydro-lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (285):

10-tert-Butoxycarbonylamino-7-isopropyldimethylsilylcamptothecin (14.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 285.

9-Amino-4-ethyl- 11 -(isopropyl-dimethyl-silanyl)-3 , 13-dioxo-3 ,4, 12, 13 -tetrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (286):

Ester 285 (14.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 286.

Example 119:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-[dimethyl-(l,l,2-ttimethyl- propyl)-silanyl]-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yl ester (287):

10-tert-Butoxycarbonylamino-7-thexyldimethylsilylcamptothecin (54.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 287.

9-Ammo-l l-[dimethyl-(l,l,2-frimethyl-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (288):

Ester 287 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 288.

Example 120: tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-[(l,2-dimethyl-propyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (289):

10-tert-Butoxycarbonylamino-[7-(l,2 dimethylpropyl)-dimethylsilylcamptothecin] (53.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 289.

9-Amino- 11 -[( 1 ,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-3 , 13 -dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (290):

Ester 289 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^πC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 290.

Example 121:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-[(3,3-dimethyl-butyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (291):

DB-234 (10-tert-Butoxycarbonylamino-[7-(3,3-dimethylbutyl)-dimethylsilyl-camρtothecin]) (54.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^αC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 291.

9-Ammo-ll-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12₎13-tetrahydro-lH- 2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (292):

Ester 291 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 292.

Example 122: tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-[dimethyl-(3,3,3-frifluoro- propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (293):

DB-238 (10-tert-Butoxycarbonylamino- [7-(3 ,3 ,3-ttifluoropropyl)-dimethylsilyl-camptothecin]) (55.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^πC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 293.

9- Amino- 11 - [dimethyl-(3 ,3 ,3-frifluoro-propyl)-silanyl]-4-ethyl-3, 13 -dioxo-3 ,4, 12, 13-tefrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (294):

Ester 293 (15.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 °C, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 294.

Example 123:

tert-Butoxycarbonylamino-acetic acid 1 l-(benzyl-dimethyl-silanyl)-9-tert-butoxycarbonylamino- 4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (295):

DB-239 (10-tert-Butoxycarbonylamino-[7-benzyldimethylsilyl-camptothecin]) (55.0 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 295.

9- Amino- 11 -(benzyl-dimethyl-silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13 -tetrahydro- lH-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (296):

Ester 295 (15.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 296.

Example 124: tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-l l-(dimethyl-phenyl-silanyl)- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (297):

DB-233 (10-tert-Butoxycarbonylamino-[7-phenyldimethylsilyl-camptothecin]) (53.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 297.

9-Amino-ll-(dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (298):

Ester 297 (15.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^PC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 298.

Example 125:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-4-ethyl-3,13-dioxo-l l-(2- frimethylsilanyl-ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (299):

DB-180 (10-tert-Butoxycarbonylamino-[7-frimethylsilylethyl-camptothecin]) (50.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 299.

9-Amino-4-ethyl-3,13-dioxo-ll-(2-ttimethylsilanyl-ethyl)-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (300):

Ester 299 (14.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 300.

Example 126:

tert-Butoxycarbonylamino-acetic acid 9-tert-butoxycarbonylamino-4-ethyl-l l-(isobutyl-dimethyl- silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (301):

10-tert-Butoxycarbonylamino-[7-isobutyldimethylsilylcamptothecin] (51.9 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by N-tert-Butoxycarbonylglycine (63 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 301.

9-Amino-4-ethyl- 11 -(isobutyl-dimethyl-silanyl)-3 , 13 -dioxo-3 ,4,12, 13-tefrahydro- lH-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonylmethyl-ammonium; frifluoro-acetate (302):

Ester 301 (14.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 302.

Propanoates

Example 127: 3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-4-ethyl-3,13-dioxo-l 1- (2-frimethylsilanyl-ethyl)-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (303):

DB-180 (10-tert-Butoxycarbonylamino-[7-trimethylsilylethyl-camptothecin]) (50.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 303.

2-[9-Amino-4-ethyl-3,13-dioxo-ll-(2-trimethylsilanyl-ethyl)-3,4,12,13-tefrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (304):

Ester 303 (14.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 304.

Example 128:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-4-ethyl-3,13-dioxo-l 1- frimethylsilanyl-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (305):

lO-tert-Butoxycarbonylamino-7-trimethylsilylcamptothecin (48.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 305.

2-(9-Amino-4-ethyl-3,13-dioxo-ll-trimethylsilanyl-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl)-ethyl-ammonium; frifluoro-acetate (306): Ester 305 (14.1 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 306.

Example 129:

3 -tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-4-ethyl- 11 -(ethyl- dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (307):

DB-232 (10-tert-Butoxycarbonylamino-7-dimethylethylsilylcamptothecin) (49.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 307.

2-[9-Amino-4-ethyl-l l-(ethyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (308):

Ester 307 (14.4 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 308.

Example 130:

3 -tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino- 11 -(dimethyl-propyl- silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (309): lO-tert-Butoxycarbonylamino-7-n-propyldimethylsilylcamptothecin (50.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxy-carbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂Cl₂(5xl5 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 309.

2-[9-Amino- 11 -(dhnethyl-propyl-silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (310):

Ester 309 (14.7 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 310.

Example 131:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-l l-(butyl-dimethy 1- silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (311):

DB-237 (lO-tert-Butoxycarbonylamino-7-n-butyldimethylsilylcamptothecin) (66.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 311.

2-[9-Amino-ll-(butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (312):

Ester 311 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 312.

Example 132:

3 -tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino- 11 -[(3 ,3-dimethyl-butyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (313):

DB-234 (10-tert-Butoxycarbonylamino-[7-(3,3-dimethylbutyl)-dimethylsilyl-camptothecin]) (54.4 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 313.

2-{9-Ammo-l l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (314):

Ester 313 (15.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 314.

Example 133: 3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-l l-[dimethyl-(3,3,3- frifluoro-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (315):

DB-238 (10-tert-Butoxycarbonylamino-[7-(3,3,3-frifluoropropyl)-dimethylsilyl-camptothecin]) (55.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^πC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 315.

2-{9-Amino-ll-[dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (316):

Ester 315 (15.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^αC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 316.

Example 134:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbony l-amino- 1 l-[(3-chloro-propyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (317):

DB-185 (lO-tert-Butoxycarbonylamino-7-chloropropyldimethyl-silylcamptothecin) (53.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 317.

2-{9-Amino-ll-[(3-chloro-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH- 2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (318):

Ester 317 (15.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 318.

Example 135: 3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxy-carbonylamino-l l-[(3-cyano-propyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- diben2_o[b,h]fluoren-4-yl ester (319):

DB-236 (lO-tert-Butoxycarbonylamino-7-cyanopropyldimethyl-silylcamptothecin) (67.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 319.

2-{9-Amino-ll-[(3-cyano-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH- 2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (320):

Ester 319 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 320.

Example 136:

3 -tert-Butoxycarbonylamino-propionic acid 9-tert-butoxy-carbonylamino-4-ethyl- 11 -(isopropyl- dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (321):

10-tert-Butoxycarbonylamino-7-isopropyldimethylsilylcamptothecin (14.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 321.

2- [9-Amino-4-ethyl- 11 -(isopropyl-dimethyl-silanyl)-3 , 13-dioxo-3,4, 12, 13 -tetrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (322):

Ester 321 (14.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 322.

Example 137:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-l l-(tert-buty 1-dimethyl- silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (323):

DB-193 (lO-tert-Butoxycarbonylamino-7-tert-butyldimethylsilylcamptothecin) (51.9 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 323.

2-[9-Amino-ll-(tert-butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (324):

Ester 323 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 324.

Example 138:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-ll-[dimethyl-(l,l,2- frimethyl-proρyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (325): 10-tert-Butoxycarbonylamino-7-thexyldimethylsilylcamptothecin (54.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 325.

2-{9-Amino-ll-[dimethyl-(l,l,2-trimethyl-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13- tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (326):

Ester 325 (15.5 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 326.

Example 139:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-l l-[(l,2-dimethyl- propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (327):

10-tert-Butoxycarbonylamino-[7-(l,2 dimethylpropyl)-dimethylsilylcamptothecin] (53.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 °C, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 327.

2-{9-Amino-ll-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12_J13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ethyl-ammonium; frifluoro-acetate (328):

Ester 327 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 328.

Example 140:

3-tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino-4-ethyl-l l-(isobutyl- dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tettahydro-lH-2-oxa-6,12a-diaza-dibenzo[b_;h]fluoren-4-yl ester (329):

10-tert-Butoxycarbonylamino-[7-isobutyldimethylsilylcamptothecin] (51.9 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 329.

2-[9-Amino-4-ethyl-ll-(isobutyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (330):

Ester 329 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 330.

Example 141: 3-tert-Butoxycarbonylamino-propionic acid 1 l-(benzyl-dimethyl-silanyl)-9-tert- butoxycarbonylamino-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (331):

DB-239 (10-tert-Butoxycarbonylamino-[7-benzyldimethylsilylcamptothecin]) (55.0 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 331.

2- [9- Amino- 11 -(benzyl-dimethy l-silanyl)-4-ethy 1-3 , 13 -dioxo-3 ,4,12,13 -tefrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (332):

Ester 331 (15.6 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 332.

Example 142:

3 -tert-Butoxycarbonylamino-propionic acid 9-tert-butoxycarbonylamino- 11 -(dimethyl-phenyl- silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4,12,13 -tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (333):

DB-233 (10-tert-Butoxycarbonylamino-[7-phenyldimethylsilylcamptothecin]) (53.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-propionic acid (68 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 333.

2-[9-Amino-ll-(dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-ethyl-ammonium; frifluoro-acetate (334):

Ester 333 (15.6 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 334.

20(S)-4-Aminobutanoate Esters.

Example 143:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-4-ethyl-3, 13-dioxo-l 1- frimethylsilanyl-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (335):

lO-tert-Butoxycarbonylamino-7-frimethylsilylcamptothecin (48.1 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^αC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 335.

3-(9-Amino-4-ethyl-3 , 13-dioxo- 11 -frimethylsilanyl-3 ,4, 12, 13 -tetrahydro- 1 H-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yloxycarbonyl)-propyl-ammonium; frifluoro-acetate (336):

Ester 335 (14.4 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 336.

Example 144: 4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-4-ethyl-l l-(ethyl- dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (337):

DB-232 (lO-tert-Butoxycarbonylamino-7-dimethylethylsilylcamptothecin) (49.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^ϋC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 337.

3-[9-Amino-4-ethyl-ll-(ethyl-dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (338):

Ester 337 (14.7 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 338.

Example 145:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino- 11 -(dimethyl-propyl- silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (339):

lO-tert-Butoxycarbonylamino-7-n-propyldimethylsilylcamptothecin (50.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 339.

3 -[9-Amino- 11 -(dimethyl-propyl-silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13-tetrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (340):

Ester 339 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 340.

Example 146:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-l l-(dimethyl-viny 1- silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (341):

DB-231 (lO-tert-Butoxycarbonylamino-7-vinyldimethylsilylcamptothecin) (49.2 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 341.

3 - [9- Amino- 11 -(dimethyl-vinyl-silanyl)-4-ethyl-3 , 13 -dioxo-3 ,4,12,13 -tefrahydro- 1 H-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (342):

Ester 341 (14.6 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 342.

Example 147:

4-tert-Butoxycarbonylamino-butyric acid ll-(allyl-dimethyl-silanyl)-9-tert-butoxycarbonylamino- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (343): DB-235 (10-tert-Butoxycarbonylamino-7-allyldimethylsilylcamptothecin (50.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 343.

3-[ll-(Allyl-dimethyl-silanyl)-9-amino-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (344):

Ester 343 (14.9 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 344.

Example 148:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino- 11 -(butyl-dimethyl- silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13-tetrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (345):

DB-237 (lO-tert-Butoxycarbonylamino-7-n-butyldimethylsilyl-camptothecin) (66.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 345.

3 -[9-Amino- 11 -φutyl-dimethyl-silanyl)-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa-6, 12a- diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (346):

Ester 345 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^πC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 346.

Example 149: 4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonyl-amino-l l-[(3-cyano-propyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (347):

DB-236 (lO-tert-Butoxycarbonylamino-7-cyanopropyldimethyl-silylcamptothecin) (67.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 347.

3- {9-Amino- 11 - [(3 -cyano-propyl)-dimethyl-silanyl]-4-ethyl-3 , 13-dioxo-3 ,4,12,13 -tetrahydro- 1 H- 2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (348):

Ester 347 (15.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 348.

Example 150:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonyl-amino-l l-[(3-chloro-propyl)- dimethyI-silanyI]-4-ethyI-3, 13-dioxo-3,4, 12, 13-tefrahydro-lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yl ester (349):

DB-185 (lO-tert-Butoxycarbonylamino-7-chloropropyldimethyl-silylcamptothecin) (53.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 349.

3 - {9-Amino- 11 - [(3 -chloro-propyl)-dimethyl-silanyl]-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13-tefrahydro- 1 H- 2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (350):

Ester 349 (15.6 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 350.

Example 151: 4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-4-ethyl-l l-(isopropyl- dimethyl-silanyl)-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (351):

10-tert-Butoxycarbonylamino-7-isopropyldimethylsilylcamptothecin (14.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 351.

3 - [9-Amino-4-ethyl- 11 -(isopropyl-dimethyl-silanyl)-3 , 13-dioxo-3 ,4, 12, 13-tefrahydro- 1 H-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (352):

Ester 351 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 352.

Example 152:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-4-ethyl-l l-(isobutyl- dimethyl-silanyl)-3 , 13 -dioxo-3 ,4,12, 13-tefrahydro- 1 H-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (353):

10-tert-Butoxycarbonylamino-[7-isobutyldimethylsilylcamptothecin] (51.9 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 353.

3 -[9-Amino-4-ethyl- 11 -(isobutyl-dimethyl-silanyl)-3 , 13 -dioxo-3 ,4, 12, 13-tefrahydro- 1 H-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (354):

Ester 353 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 354.

Example 153:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino- 11 -(tert-butyl-dimethyl- silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester (355): DB-193 (lO-tert-Butoxycarbonylamino-7-tert-butyldimethylsilyl-camptothecin) (51.9 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 355.

3-[9-Amino-ll-(tert-butyl-dimethyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (356):

Ester 355 (15.2 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 356.

Example 154:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-4-ethyl-3, 13-dioxo-l l-(2- frimethylsilanyl-ethyl)-3,4, 12, 13-tefrahydro- lH-2-oxa-6, 12a-diaza-dibenzo[b,h]fluoren-4-yl ester (357):

DB-180 (10-tert-Butoxycarbonylamino-[7-frimethylsilylethyl-camptothecin]) (50.7 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concentrated and purified by chromatography providing ester 357.

3-[9-Amino-4-ethyl-3, 13-dioxo-l 1 -(2-frimethylsilanyl-ethyl)-3, 4, 12, 13 -tefrahydro- lH-2-oxa- 6, 12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; frifluoro-acetate (358):

Ester 357 (15.0 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^aC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 358.

Example 155:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-l l-[dimethyl-(l, 1,2- frimethyl-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (359):

lO-tert-Butoxycarbonylamino-7-thexyldimethylsilylcamptothecin (54.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 359.

3- {9-Amino- 11 -[dimethyl-(l , 1 ,2-frimethyl-propyl)-silanyl]-4-ethyl-3, 13-dioxo-3,4, 12, 13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (360):

Ester 359 (15.8 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 360.

Example 156: 4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonyl-amino-l l-[(l,2-dimethyl- propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (361):

10-tert-Butoxycarbonylamino-[7-(l,2 dimethylpropyl)-dimethylsilyl-camptothecin] (53.1 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 361.

3-{9-Ammo-ll-[(l,2-dimethyl-propyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (362):

Ester 361 (15.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 362.

Example 157:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-l l-[dimethyl-(3,3,3- frifluoro-propyl)-silanyl]-4-ethyl-3 , 13-dioxo-3 ,4, 12, 13 -tefrahydro- lH-2-oxa-6, 12a-diaza- dibenzo[b,h]fluoren-4-yl ester (363):

DB-238 (10-tert-Butoxycarbonylamino-[7-(3,3,3-frifluoropropyl)-dimethylsilyl-camptothecin]) (55.5 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 363.

3-{9-Amino-ll-[dimethyl-(3,3,3-trifluoro-propyl)-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13- tefrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl}-ρropyl-ammonium; frifluoro-acetate (364):

Ester 363 (16.0 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 364.

Example 158:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-l l-[(3,3-dimethyl-butyl)- dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tefrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yl ester (365):

DB-234 (10-tert-Butoxycarbonylamino-[7-(3,3-dimethylbutyl)-dimethylsilyl-camptothecin]) (54.4 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^DC, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^DC, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 365.

3-{9-Ammo-l l-[(3,3-dimethyl-butyl)-dimethyl-silanyl]-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro- lH-2-oxa-6,12a-diaza-dibenzolD,h]fluoren-4-yloxycarbonyl}-propyl-ammonium; frifluoro-acetate (366):

Ester 365 (15.8 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^DC. After 5 h, at 22 ^DC, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 366.

Example 159:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-l l-(isobutyl- dimethyl-siIanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza- dibenzo[b,h]fluoren-4-yI ester (367):

10-tert-Butoxycarbonylamino-[7-isobutyldimethylsilylcamptothecin] (68.6 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^°C, anhydrous CH₂C1₂ (3.0 ml) is added followed by 3-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^°C, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concenfrated and purified by chromatography providing ester 367.

2-[9-Amino-4-ethyl-ll-(isobutyI-dimethyl-siIanyl)-4-ethyI-3,13-dioxo-3,4,12,13-tetrahydro- lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yIoxycarbonyl]-propyl-ammonium; trifluoro- acetate (368): Ester 367 (13.5 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^°C. After 5 h, at 22 ^°C, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 368.

Example 160:

4-tert-Butoxycarbonylamino-butyric acid 9-tert-butoxycarbonylamino-l l-(dimethyl-phenyl- silanyI)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren- 4-yl ester (369):

DB-233 (10-tert-Butoxycarbonylamino-[7-phenyldimethylsilyl-camptothecin]) (53.7 mg, 0.09 mmol) is added to an oven dried flask under nitrogen. Next, at 0 ^°C, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-tert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^°C, the reaction mixture is poured into sat. brine solution (8 ml) and it is extracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0 ), concenfrated and purified by chromatography providing ester 369.

3-[9-Amino-ll-(dimethyl-phenyl-silanyl)-4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyI]-propyI-ammonium; trifluoro-acetate

(370):

Ester 369 (15.6 mg, 0.02 mmol) is placed in an oven dried flask under nifrogen and anhydrous

CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^°C. After 5 h, at 22 ^°C, the reaction mixture is concenfrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 370.

Example 161:

4-tert-Butoxycarbonylamino-butyric acid ll-(benzyl-dimethyl-silanyl)-9-tert- butoxycarbonylamino- 4-ethyl-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa-6,12a-diaza-dibenzo[b,h]fluoren-4-yl ester

(371):

DB-239 (10-tert-Butoxycarbonylamino-[7-benzyldimethylsilyl-camptothecin]) (55.0 mg, 0.09 mmol) is added to an oven dried flask under nifrogen. Next, at 0 ^°C, anhydrous CH₂C1₂ (3.0 ml) is added followed by 4-fert-Butoxycarbonylamino-butyric acid (74 mg, 0.36 mmol), DMAP (19 mg, 0.15 mmol) and EDCI (72 mg, 0.36 mmol). After 5h, at 0 ^°C, the reaction mixture is poured into sat. brine solution (8 ml) and it is exfracted with CH₂C1₂ (5x15 ml). The organic layer is dried (MgS0₄), concentrated and purified by chromatography providing ester 371.

3-[9-Amino-ll-(benzyl-dimethyl-silanyl)-4-ethyI-3,13-dioxo-3,4,12,13-tetrahydro-lH-2-oxa- 6,12a-diaza-dibenzo[b,h]fluoren-4-yloxycarbonyl]-propyl-ammonium; trifluoro-acetate (372):

Ester 371 (15.9 mg, 0.02 mmol) is placed in an oven dried flask under nitrogen and anhydrous CH₂C1₂ (0.75 ml) is added. Next TFA (0.75 ml) is added dropwise at 0 ^°C. After 5 h, at 22 ^°C, the reaction mixture is concentrated and the residue is washed with ether (3x1 ml). Finally, the product is placed under high vacuum overnight providing the desired ester salt 372.

Example 162:

Characterization of the Membrane Interactions of the Novel, Amino Ester Prodrug Analogs of Silatecans Using Fluorescence Specfroscopic Methodologies.

Chemicals. All camptothecin, silatecan, and silatecan amino ester analogs were in the 20(S) configuration and were of high purity (>98%) as determined by HPLC assays with fluorescence detection. All other agents were reagent grade and were used without further purification. High purity water provided by a Milli-Q UV PLUS purification system (Bedford, MA) was utilized in all experiments. Drug Stock Solution Preparation. Stock solutions of the drugs were prepared in dimethylsulfoxide (A.C.S. specttophotomefric grade, Aldrich, Milwaukee, WI) at a concentration of 2 x IO^"3 M and stored in dark at 4 °C. L- -Dimyristoylphosphatidylcholine (DMPC) and L-α- dimyristoylphosphatidylglycerol (DMPG) were obtained from Avanti Polar Lipids, Alabaster, AL, and were used without further purification. All other chemicals were reagent grade and were used without further purification.

Vesicle Preparation. Small unilamellar vesicle (SUV) suspensions were prepared the day of an experiment by the method of Burke and Tritton (7). Briefly, stock lipid suspensions containing 200 mg/mL lipid in phosphate buffered saline (PBS, pH 7.4) were prepared by Vortex mixing for 5-10 min above the T_M of the lipid. The lipid dispersions were then sonicated using a bath-type sonicator (Laboratory Supplies Co., Hicksville, NY) for 3-4 h until they became optically clear. A decrease in pH from 7.4 to 6.8 was observed for the SUV preparations of DMPG; therefore, the pH of these SUV suspensions was adjusted to 7.4 using small quantities of 2.5 M NaOH in PBS, followed by additional sonication. Each type of vesicle suspension was annealed for 30 min at 37 °C and then used in an experiment.

Fluorescence Instrumentation. Steady-state fluorescence measurements were obtained on a SLM Model 9850 specfrofluorometer with a thermostated cuvette compartment. This instrument was interfaced with an IBM PS/2 model 55 SX computer. Excitation and emission spectra were recorded with an excitation resolution of 8 nm and an emission resolution of 4 nm. In all cases specfra were corrected for background fluorescence and scatter from unlabeled lipids or from solvents by subtraction of the spectrum of a blank. Steady-state fluorescence intensity measurements were made in the absence of polarizers. Steady-state anisofropy (a) measurements were determined with the instrument in the "T-format" for simultaneous measurement of two polarized intensities. The alignment of polarizers was checked routinely using a dilute suspension of 0.25 μm polystyrene microspheres (Polysciences, Inc, Warrington, PA) in water and anisofropy values of >0.99 were obtained. Alternatively, polarizer orientation was checked using a dilute solution of glycogen in water. The anisofropy was calculated from a = (Iyv - GIV_H)/(I_W + GI_VH where G = I_VH/T_HH and the subscripts refer to vertical and horizontal orientations of the excitation and emission polarizers, respectively.

Anisofropy measurements for camptothecins were conducted using exciting light of 370 nm and long pass filters on each emission channel in order to isolate the drug's fluorescence signal from background scatter and/or residual fluorescence. All emission filters were obtained from Oriel Corp (Stamford, CT). The combination of exciting light and emission filters allowed adequate separation of fluorescence from background signal. The contribution of background fluorescence, together with scattered light, was typically less than 1% of the total intensity. Since the lactone rings of camptothecin and related congeners undergo hydrolysis in aqueous medium with half- lives of approximately 20 min., all measurements were completed within the shortest possible time (ca. 0.5 to 1 min) after mixing the drug stock solution with thermally pre-equilibrated solutions such that the experiments were free of hydrolysis product.

Determination of Equilibrium Binding Constants. The method of fluorescence anisofropy titration reported in Burke, T. G., Mishra, A. K., Wani, M. C. and Wall, M. E. "Lipid bilayer partitioning and stability of camptothecin drugs," Biochemistry. 32: 5352-5364 (1993) was employed to determine the concentrations of free and bound species of drug in liposome suspensions containing a total drug concentration of 1 x IO^"6 M and varying lipid concentrations. All experiments were conducted in glass tubes. The overall association constants are defined as K=[A_B]/[A_F][L] where [A_B] represents the concentration of bound drug, [A_F] represents the concentration of free drug, and [L] represents the total lipid concentration of the sample. Double- reciprocal plots of the binding isotherms {l/(bound fraction of drug) vs. l/[lipid]} were linear and K values were determined from their slopes by the method of linear least squares analysis. A computer program based on the K=[A_B]/[A_F][L] relationship was written to predict bound drug levels for specified values of K and total drug.

Characterization of the Lipophilicities of the Amino Ester Prodrugs of Silatecans. Figure 13 summarized the fluorescence excitation and emission specfra of 1 μM solutions of DB-67 (lower panel), DB-67-20-glycinate ester hydrochloride (center panel) and DB-67-20(S)-4-aminobutanoate ester hydrochloride (top panel) in PBS buffer in the presence and absence of 0.1 M dimyristoylphosphatidylcholine (DMPC) small unilamellar liposomes. Experiments were conducted at pH 7.4 and 37 °C. Data is also shown for the agents dissolved in ethanol. Note that there is a strong shifting of the emission specfra to the blue region or shorter wavelengths in the presence of liposomes. This spectral shifting is indicative of drug interaction with the membranes. Emission experiments were conducted using exciting light of 370 nm. Figure 14 summarizes fluorescence excitation and emission specfra of 1 μM solutions of DB-172 (lower panel), DB-172- 20-glycinate ester hydrochloride (center panel) and DB-172-20(S)-3-aminopropanoate ester hydrochloride (top panel) in PBS buffer in the presence and absence of 0.1 M dimyristoylphosphatidylcholine (DMPC) small unilamellar liposomes. Experiment where conducted at pH 7.4 and 37 °C. Data is also shown for the agents dissolved in ethanol. Note the change in the intensity of the agent in the presence of liposomes. This change in intensity is indicative of drug interaction with the membranes.

The method of fluorescence anisofropy titration was used to study the associations of 1 μM concentrations of DB-67, DB-67-20-glycinate ester, and DB-67-20(S)-4-aminobutanoate ester with small unilamellar vesicles composed of electroneutral DMPC suspended in phosphate buffered saline (Figure 15). Note that in the presence of increasing amounts of liposomes the drag anisofropy values increase until the majority of drug is liposome-bound. Analysis of the data reveal the following association constants or K_DMpc values: 4,000 M^"1 for DB-67, 4,000 M^"1 for DB-67-20-glycinate ester hydrochloride, and 5,600 M^"1 for DB-67-20(S)-4-aminobutanoate ester hydrochloride. In similar studies (data not shown) the method of fluorescence anisotropy titration was used to study the associations of 1 μM concentrations of DB-67, DB-67-20-glycinate ester hydrochloride, and DB-67-20(S)-4-aminobutanoate ester hydrochloride with small unilamellar vesicles composed of negatively charged dimyristoylphosphatidylglycerol (DMPG) suspended in phosphate buffered saline. Analysis of the data reveal the following association constants or K_DMPG values: 3,000 M^"1 for DB-67, 8,000 M^"1 for DB-67-20-glycinate ester hydrochloride, and 5,600 M^"1 for DB-67-20(S)-4-aminobutanoate ester hydrochloride. For DB-172 and related analogs the K_DMPC values: 11,000 M^"1 for DB-172, 5,000 M^"1 for DB-172-20-glycinate ester, and 3,100 M^"1 for DB-67-20(S)-3-aminopropanoate ester. For DB-172 and related analogs the K_DMPG values were: 11,000 M^'1 for DB-172, 13,000 M^"1 for DB-172-20-glycinate ester, and 12,000 M^"1 for DB-172-20(S)-3 -aminopropanoate ester. These results are summarized in Table 5. Note the K values are significantly greater than the K values observed for the glycinate esters of previously developed camptothecins (Table 2). Typically the values for silatecan amino esters are 1 to 2 orders of magnitude greater than for the camptothecin glycinate esters, indicating marked differences between our novel silatecan amino esters and the prior art camptothecin glycinate ester compounds.

Example 163:

Characterization of the Membrane Interactions and Liposomal Formulation Characteristics of the Novel, Amino Ester Prodrug Analogs of Silatecans Using High Performance Liquid Chromatographic (HPLC) Methodologies.

HPLC Conditions for the Analysis of Amino Esters of Silatecans. The hydrolysis kinetics of silatecan and silatecan amino esters ( in the presence of liposome suspensions, in core-loaded liposomal preparations, with both types of preparations studied in PBS and whole human blood) were determined by a quantitative Cι₈ reversed-phase high-performance liquid chromatography (HPLC) assay as described previously (Bom et al., 2000). Solution or suspension pH was adjusted to 7.40 ± 0.05. HPLC measurements were conducted on a Waters Alliance 2690 Separations Module which employed a Waters™ 474 Scanning fluorescence detector. Separations were conducted on a Waters Symmetry-Cig 5 μm particle size reversed-phase column. Separation of the lactone, carboxylate forms parent amino esters, intermediates, and other compounds were achieved using an isocratic mobile phase consisting of varying mixtures of acetonitrile and a 2%(v/v) triethylamine acetate buffer (pH 5.5). DB-67 readily eluted at a ratio of 41% acetonitrile to 59% of the triethylamine acetate buffer. DB-67 and related analogs were detected with a Waters Model 474 fluorescence detector at an excitation wavelength of 380 nm and an emission wavelength of 560 nm. Flow rates of 1 mL/min were employed, and the retention times for the lactone species were approximately 7.0 minutes (while the carboxylate species rapidly eluted at approximately 2.0 min). Other silatecans and silatecan amino esters were studied in a similar manner. Fluorescence output signal was monitored and integrated using Waters Millennium³² Chromatography Manager software.

Preparation of Liposomes with Entrapped Silatecan Amino Ester Analogues. The lipid DSPC (142.23mg, MW. 790.17) was hydrated in 6ml (NH₄)₂S0₄ buffer (pH 3.0, 250 mM) at 60°C and vortexed to form blank liposomes (30 mM lipid). The liposomes were size reduced using an extruder from the Avestin Company. The sample was passed through polycarbonate membranes with 100 nm pore size. The liposomes were passed 12 times through a 100 nm pore diameter membrane at 60°C. The extruded liposomes contained ammonium sulfate (pH 3.0) within the interior aqueous compartments of liposomes, as well as in the exterior aqueous bulk phase medium in which they were suspended. Ammonium sulfate was removed from the external bulk aqueous phase immediately prior to remote loading by desalting with Sephadex G-25 column with the mobile phase of 10% sucrose in water, which resulted in liposomes suspended in an exterior aqueous phase comprised of 10% sucrose.

After desalting, the liposomal suspension was adjusted to pH 6.0 with NaOH to form fransmembranes pH gradient with interior aqueous of pH 3.0 and exterior aqueous of pH 6.0. The liposomes were mixed with a selected drug powder to achieve the following drug concentrations: CPT glycinate 2mM, CPT propanoate ImM, CPT butanoate 2mM, DB67 glycinate 2mM and DB67 butanoate ImM, respectively, and rapidly warmed to 60°C. The temperature of the mixture was maintained at 60°C for 1 hour. After remote loading a sample of liposomes was taken to check for the presence of crystal, to determine percent encapsulation and to measure the mean particle size. Unencapsulated drug was removed from the bulk phase medium by a Sephadex G- 25 column with 10% sucrose. The final liposome preparation was stored in a refrigerator (5 °C) and protected from light until use. The percent of encapsulation was determined using size exclusion chromatography to compare the percent drug in the void volume (liposomal encapsulated) to the total drug. The drug concentration in the column fractions was determined by HPLC with fluorescence detector. Mean particle size was determined using quasielecfric laser light scatter (QELS). The results are shown in the Table 6 below. Our results indicate that the silatecan amino esters efficiently load into the liposomes, with 60 to 70 % of the drug loading in.

Parameter CPT CPT CPT DB67 DB67 glycinate propanoate butanoate glycinate butanoate

Lot No. 111600-2 092500-1 100300-2 101700-1 112900-1

Total lipid Cone. 23mM 24mM 20mM 18mM 23mM

Drug Cone. 1.35mM 0.78 2.73mM 0.83mM 0.64mM

Drug: lipid (mol/mol) 17:1 30:1 7.3:1 21.7:1 36:1

Mean particle size 141nm 112nm 131nm 120nm 143nm

Percent encapsulation 67.7 78.5 68.7 41.5 64.4

HPLC chromatograms depicting the separation of DB-67 (retention time of 6.4 min) from DB-67 carboxylate (retention time of 1.7 min) are shown in Figure 18. Unlike the situation with DB- 67, the instantaneous reactivity of DB-67-20-glycinate ester hydrochloride upon addition to PBS buffer under near physiological conditions of ionic strength and temperature is apparent in Figure 20. The parent DB-67-20-glycinate ester peak appears at a retention time of 3.6 min. Immediately following the addition of DB-67-20-glycinate ester hydrochloride to PBS buffer at a concentration of 1 μM, a new major peak is observed (retention time of 4.2 min). Upon further standing, sampling of the drug solution in PBS shows fiirther conversion to a total of at least three other chemical entities being observed in the solution. Separation of starting material (DB-67-20-glycinate ester) from the hydrolysis products [intermediate (retention time of 4.2 min), DB-67 (retention time of 7.1 min) and DB-67 carboxylate (retention time of 1.9 min) was achieved. Figure 22 is a HPLC chromatogram depicting the diminished reactivity of DB-67-20(S)-4-aminobutanoate ester (relative to DB-67 glycinate ester) upon addition to PBS buffer under near physiological conditions of ionic sfrength and temperature. The parent DB-67-20(S)-4-aminobutanoate ester peak appears at a retention time of 3.4 min. Immediately following the addition of DB-67-20(S)-4-aminobutanoate ester to PBS buffer at a concentration of 1 μM, a new peak is observed (retention time of 6.4 min corresponding to the lactone form of DB-67). Upon further standing, sampling of the drug solution in PBS shows further conversion to a total of at least two new chemical entities (DB-67 lactone and carboxylate) being observed in the solution. Separation of starting material (DB-67-20-glycinate ester) from the products [DB-67 (retention time of 6.4 min) and DB-67 carboxylate (retention time of 2.0 min) was achieved. So while aqueous freatment of the glycinate ester yields five peaks in the HPLC chromatogram, only 3 peaks are observed in the case of the butanoate. Similar phenomenon are observed in the cases of DB-172 analogs (i.e. two peaks total in the case of DB- 172 lactone, five peaks total in the case of DB-172 glycinate, and 3 peaks total in the case of the DB-172-20(S)-3-aminopropanoate ester.

Figure 33 through 35 indicate that membrane loading of glycinate esters of silatecans actually destabilize the prodrug, while Figure 38 the markedly improved stability of core-loaded liposomal DB-172-20-glycinate ester in whole human blood at pH 7.4 and 37 °C. Our novel results indicate core-loading of amino esters of highly lipophilic camptothecins can be readily achieved and these formulations are capable of protecting the amino ester prodrugs from spontaneous conversion to the active agents in PBS and whole blood (see Figures 39 through 42). Figure 43. Depiction of the stability of bilayer-loaded liposomal DB-67-20(S)-4-aminobutanoate ester in PBS buffer at pH 7.4 and 37 °C. Stability profiles were determined using HPLC methods and monitored out to 180 hrs. All experiments were conducted at an original prodrag concentration of 1 μM. Comparison of the data contained in Figure 42 versus 43 is another example that core-loading is superior to bilayer loading in conserving the DB-67-20(S)-4- aminobutanoate ester prodrug in its native form.

Lactone Form Carboxylate Form

Compound R Rl R2 R3 R

CPT H H H H H

CPT-20-glycinate COCH2NH2 H H H H

10,11-MDO-CPT H H ^' H -OCH2O-

10,1 l-MDO-CPT-20-glycinate COCH2NH2 H H -OCH2O--

7-Ethyl-10,ll-MDO-CPT H CH3CH2- • H -OCH2O- -Ethyl-10,ll-MDO-CPT-20-glycinate COCH2NH2 CH3CH2- - H -OCH2O-

7-Chloromethyl-l 0,11-MDO-CPT ^• H • CICH2- H -OCH2O- -Chloromethyl-10,ll-MDO-CPT-20- COCH2NΗ2 CICH2- H -OCH2O- glycinate

9-Ammo-CPT H H NH2 H H

^' 9-Amino-CPT-20-glycinate COCH2NH2 H H2 H H

9-Chloro-10,l 1-MDO-CPT H H Cl -OCH2O-

9-Chloro-10₅l l-MDO-CPT-20- COCH2NH2 H Cl -OCH2O- glycinate

9-Amino-10₃l 1-MDO-CPT H H NH2 -OCH2O-

9-Amino-10,l l-MDO-CPT-20- COCH2NH2 H Kϋ2 -OCH2O- glycinate

10-Amino-CPT H _. H H NH2 H

1 O-Amino-CPT-20-glycinate COCH2NH2 H H NH2 H

Table 1 : Structures of Camptothecins and related 20-aminoester prodrug analogs 1 Abbreviations: MDO = methylenedioxy; CPT = camptothecin

Table 1 Overall association constants for camptothecin analogues interacting with unilamellar vesicles of electroneutral DMPC, negatively- charged DMPG in PBS buffer at PH 7.4 and 37°C

Compound K-DMPC K ^•D_. MPG

Camptothecin 100 100

Camptothecin.20-Glycinate.HCl 70 206

10,11-MD-CPT 110 100

10, 11 -MD-CPT-20-Glycinate.HCl 93 345

7-efhyl-10,l 1-MD-CPT. 160 130

7-ethyl-10,l l-MD-CPT-20-Glycinate.HCl 220 ' 1161

7-chloromethyl-10,l 1-MD-CPT 180(3) 160(2) 7-chloromethyl- 10, 11 -MD-CPT-20-Glycinate.HCl 93 310

9-amino-CPT low fluorescence 9-amino-CPT-20-Glycinate.HCl low fluorescence

9-chloro-l 0,11-MD-CPT 310 360 9-cMoro-10,ll-MD-CPT-20-Glycinate.HCl 210 1006

9-amino-10,l 1-MD-CPT low fluorescence 9-amino-10,l l-MD-CPT-20-Glycinate.HCl low fluorescence

10-amino-CPT 37 26

10-amin6-CPT-20-Glycinate.HCl 70 36

Table 2

Lactone Form Carboxylate Form

Compound^ Rl R2

7-Trimeihylsilyl-CPT TMS H

7-tert-Butyldimefhylsilyl-CPT TBDMS H

7-Trimethylsilylethyl-CPT TMSCH₂CH₂- H

7-Cyanopropyldimethylsilyl-CPT ΝC(CH₂)₃(CH₃)₂Si ^' H

7-Chloropropyldimethylsilyl-CPT Cl(CH₂)₃(CH₃)₂Si H

7-Dimethylisobutylsilyl-CPT (CH₃)₂CHCH₂(CH₃)₂Si H

7-Dimethylisopropyl-CPT (CH₃)₂CH(CH₃)₂Si H

7-n-Butyldimethylsilyl-CPT CH₃(CH₂)3(CH₃)₂Si H

7-R-Proρyldimethylsilyl-CPT CH₃(CH₂)₂(CH₃)₂Si H

7-phenyldime%lsilyl-CPT C₆H₅(CH₃)₂Si H

7-Vinyldimethylsilyl-CPT CH₂CH(CH₃)₂Si H

7-Allyldimethylsilyl-CPT CH₂CHCH₂(CH₃)₂Si H

7-tert-Butylethyldimethylsilyl-CPT t-Bu(CH₂)₂(CH₃)₂Si H

10-Hydroxy-7-trimefhylsilyl-CPT TMS OH

10-Hydroxy-7-tert-butyldimethylsilyl-CPT TBDMS OH

10-Hydroxy-7-trimethylsilylethyl-CPT TMSCH₂CH₂- OH 0-Hydroxy-7-cyanoρropyldimethylsilyl-CPT NC(CH₂)₃(CH₃)₂Si OH 0-Hydroxy-7-chloroρropyldimethylsilyl-CPT Cl(CH₂)₃(CH₃)₂Si OH

10-Hydroxy-7-Dimethylisobutylsilyl-CPT (CH₃)₂CHCH₂(CH₃)₂Si OH

10-Hydroxy-7-Dimethylisopropyl-CPT (CH₃)₂CH(CH₃)₂Si OH

10-Hydroxy-7-n-butyldimefhylsilyl-CPT . CH₃(CH₂)₃(CH₃)₂Si OH lO-Hydroxy-7-R-ρropyldimethylsilyl-CPT CH₃(CH₂)₂(CH₃)₂Si OH lO-Hydroxy-7-ρhenyldimethylsilyl-CPT C₆H₅(CH₃)₂Si . OH

10-Hydroxy-7-Niιιyldimethylsilyl-CPT CH₂CH(CH₃)₂Si OH

10-Hydroxy-7-Allyldimethylsilyl-CPT CH₂CHCH₂(CH₃)₂Si OH

10-Ammo-7-trimethylsilyl-CPT TMS NH₂ lO-Amino-7-tert-butyldimethylsilyl-CPT TBDMS NH₂ 10-A_mino-7-trimethylsilylet yl-CPT ^" TMSCH₂CH₂- NH₂ -Amino-7-chloropropyldime hylsilyl-CPT Cl(CH₂)₃(CH₃)₂Si NH₂

Table 2: Structures of Silatecans 1 Abbreviations: CPT = camptothecin

Table 3

Table 4 Overall Association Constants for Camptothecin Analogues Interacting with Unilamellar Vesicles of Electroneutral DMPC and Negatively Charged DMPG in PBS Buffer at pH 7.4 and 37 °C

Compound KϋMPCVN'- ) K_DMPGCM^"1)

DB-67 4,000 2,800

DB-172 10,500 10600

DB-67 glycinate 4,000 8,000

DB-67 butanoate 5,700 7,500

DB-172 glycinate 5,000 13,000

DB-172 propanoate 3,200 12,000

SN-38 260 160

topotecan 10 50

camptothecin 100 100

Table 5 References

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(8) Houghton, P. J.; Cheshire, P. J.; Myers, L.; Stewart, C. F.; Synold, T. W.; Houghton, J. A. 1992. Evaluation of 9-dimethylaminomethyl-lO-hydroxycamptothecin against xenografts derived from adult and childhood solid tumors. Cancer Chemother. Pharmacol. 31: 229-39. (9) Blaney, S. M.; Balis, F. M.; Cole, D. E.; Craig, C; Reid, J. M.; Ames, M. M.;

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(12) Potmesil, M.; Hsiang, Y. H.; Liu, L. F.; Bank, B.; Grossberg, H.; Kirschenbaum, S.; Forlenzar, T. J.; Penziner, A.; Kanganis, D. 1988. Resistance of Human Leukemic and Normal

Lymphocytes to Drug-Induced DNA Cleavage and Low Levels of DNA Topoisomerase II. Cancer Res. 48: 3537-3543.

(13) Kessel, D.; Bosmann, H. B.; Lohr, K. 1972. Camptothecin effects on DNA synthesis in murine leukemia cells. Biochim. Biophys. Acta 269: 210-6. (14) Li, L. H.; Fraser, T. J.; Olin, E. J.; Bhuyan, B. K. 1972. Action of camptothecin on mammalian cells in culture. Cancer Res. 32: 2643-2650.

(15) Jaxel, C; Kohn. K. W.; Wani, M. C; Wall, M. E.; Pommier, Y. 1989. Structure-activity study of the actions of camptothecin derivatives on mammalian topoisomerase I: evidence for a specific receptor site and a relation to antitumor activity. Cancer Res. 49: 1465- 1469.

(16) Hertzberg, R. P.; Caranfa, M. J.; Holden, K. G.; Jakas, D. R.; Gallagher, G.; Mattern, M. R.; Mong, S. M.; Bartus, J. O.; Johnson, R. K.; Kingsbury, W. D. 1989. Modification of the hydroxy lactone ring of camptothecin: inhibition of mammalian topoisomerase I and biological activity. J. Med. Chem. 32: 715-720. (17) Hsiang, Y. H.; Liu, L. F. 1988. Identification of mammalian DNA topoisomerase I as an intracellular target of the anticancer drug camptothecin. Cancer Res. 48: 1722-1726.

(18) Mi, Z.; Burke, T. G. 1994. Differential interactions of camptothecin lactone and carboxylate forms with human blood components. Biochemistry 33: 10325-10336. (19) Hochberg, F.; Grossman, S. A.; Mikkelson, T.; Calabresi, P.; Fisher, J.;

Piantadosi, S. 1998. For the NABTT CNS Consortium, Baltimore, MD. Efficacy of 9- aminocamptothecin (9-AC) in adults with newly diagnosed glioblastoma multiforme (GBM) and recurrent high grade astrocytomas (HGA). Proc. Amer. Soc. Clin. Oncol. 17: 388.

(20) Takimoto, C. H.; Dahut, W.; Harold, N.; Nakashima, H.; Lieberman, R.; Liang, M. D.; Arbuck, S. G.; Chen, A. P.; Hamilton, J. M.; Cantilena, L. R; AUegra, C. J.; Grem, J. L.

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(21) Mi, Z.; Malak, H.; Burke, T. G. 1995. Reduced albumin binding promotes the stability and activity of topotecan in human blood. Biochemistry 34: 13722-13728. (22) Zimmer, S. G.; Burke, T. G. 2000. Human Serum Albumin Markedly Diminishes the Blood Stabilities and Anticancer Activities of Several Clinically Relevant Camptothecins. Proc. Am. Soc. Clin. Oncol. 19: 200A.

(23) Burke, T. G.; Mi, Z. 1994. The structural basis of camptothecin interactions with human serum albumin: impact on drug stability. J. Med. Chem. 37: 40-46.

(24) Burke, T. G.; Mi, Z. 1993. Preferential binding of the carboxylate form of camptothecin by human serum albumin. Anal. Biochem. 212: 285-287.

(25) Burke, T. G.; Mi, Z. 1993. Ethyl substitution at the 7 position extends the half- life of 10-hydroxycamptothecin in the presence of human serum albumin. Journal of Medicinal Chemistry 36: 2580-2.

(26) Bom, D.; Curran, D. P.; Kruszewski, S.; Zimmer, S. G.; Strode, J. T.; Kohlhagen, G.; Du, W.; Chavan, A. J.; Fraley, K. A.; Bingcang, A. L.; Latus, L. J.; Pommier, Y.; Burke, T.G. 2000. The Novel Silatecan 7-tert-Butyldimethylsilyl- 10-hydroxycamptothecin Displays High Lipophilicity, Improved Human Blood Stability, and Potent Anticancer Activity. J. Med. Chem. 43:3970-3980 (2000).

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Claims

In the ClaimsWhat is claimed:

1.) A compound(s) comprising structures A or B,

wherein R¹ and R²are independently the same or different and are hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an acyloxy group, -OC(0)OR¹², wherein R¹² is an alkyl group, a carbamoyloxy group, a halogen, a hydroxy group, a nitro group, a cyano group, an azido group, a formyl group, a hydrazino group, -C(0)R¹³ wherein R¹³ is an alkyl group, an alkoxy group, an amino group or a hydroxy group, -SR¹⁴, wherein R¹⁴ is hydrogen, -C(0)R¹³, an alkyl group, or an aryl group; or R¹ and R² together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6;

R³ is H, a nitro group, a halogen atom, an amino group, a hydroxy group, or a cyano group, or R² and R³ together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6;

R⁴ is H, F, an alkyl group, an alkenyl group, an alkynyl group, a trialkylsilyl group or an alkoxy group;

R⁵ is a Ci-i₅ alkyl group, an allyl group, a benzyl group or a propargyl group;

R⁶, R⁷ and R⁸ are independently a Cm alkyl group, a C₂.ι₅ alkenyl group, a C₂.ιs alkynyl group, an aryl group or a -(CH₂)_qR¹⁵ group, wherein q is an integer between 1 and 15 and R¹⁵ is a hydroxy group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group; R¹⁰ is an alkylene group, an alkenylene group or an alkynylene group;

R¹¹ is -(CH₂)_LNR¹⁶R¹⁷ wherein L may be an integer ranging from 1-30 and R¹⁶ and R¹⁷ are independently the same or different and are hydrogen, a Cj.is alkyl group, a C₂_ι₅ alkenyl group, a C₂.ι₅ alkynyl group, an aryl group, a -(CH₂)γR¹⁸ group, a -(CH₂)_YC(0)R¹⁸ group or a -(CH₂)YC0₂R¹⁸ group wherein Y may be an integer ranging from 1 to 15 and R¹⁸ is a hydroxy group, a thiol group, an alkylthiol, a silyl group, an alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group, a nitro group.

2) The compound of claim 1 loaded into an aqueous core of a liposome.

3.) A compound comprising structures C or D:

wherein R¹ and R² are independently the same or different and are hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an acyloxy group, -OC(0)OR¹², wherein R¹² is an alkyl group, a carbamoyloxy group, a halogen, a hydroxy group, a nitro group, a cyano group, an azido group, a formyl group, a hydrazino group, -C(0)R¹³ wherein R¹³ is an alkyl group, an alkoxy group, an amino group or a hydroxy group, -SR¹⁴, wherein R¹⁴ is hydrogen, -C(0)R¹³, an alkyl group, or an aryl group; or R¹ and R² together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6; R³ is H, a nitro group, a halogen atom, an amino group, a hydroxy group, or a cyano group, or R² and R³ together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6; R⁴ is H, F, an alkyl group, an alkenyl group, an alkynyl group, a trialkylsilyl group or an alkoxy group; R⁵ is a C_ns alkyl group, an allyl group, a benzyl group or a propargyl group; R⁶, R⁷ and R⁸ are independently a Cι.₁₅ alkyl group, a C₂.₁₅ alkenyl group, a C₂.ι₅ alkynyl group, an aryl group or a — (CH₂)_qR¹⁵ group, wherein q is an integer between 1 and 15 and R¹⁵ is a hydroxy group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group; R¹⁰ is an alkylene group, an alkenylene group or an alkynylene group; the nitrogen of the six membered morpholine 2,5-dione ring can be monoalkylated in any of the above cited compounds or contain a monoalkylgroup containing -CN, halogen, -COOH, nitro and amino substituents.

4.) A method of killing mammalian cells undergoing DNA synthesis, comprising: administering to a mammal a pharmaceutically effective amount of a compound having a chemical formula selected from a group consisting of

and

wherein R¹ and R² are independently the same or different and are hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an acyloxy group, -OC(0)OR¹², wherein R¹² is an alkyl group, a carbamoyloxy group, a halogen, a hydroxy group, a nitro group, a cyano group, an azido group, a formyl group, a hydrazino group, -C(0)R¹³ wherein R¹³ is an alkyl group, an alkoxy group, an amino group or a hydroxy group, -SR¹⁴, wherein R¹⁴ is hydrogen, -C(0)R¹³, an alkyl group, or an aryl group; or R¹ and R² together form a group of the formula -0(CH₂)_pO- wherein p represents an integer 1 through 6;

R⁵ is a Cm alkyl group, an allyl group, a benzyl group or a propargyl group;

R⁶, R⁷ and R⁸ are independently a Cns alkyl group, a C₂.ι₅ alkenyl group, a C₂„ι₅ alkynyl group, an aryl group or a -(CH₂)_qR¹⁵ group, wherein q is an integer between 1 and 15 and R¹⁵ is a hydroxy group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group;

R¹⁰ is an alkylene group, an alkenylene group or an alkynylene group;

R¹¹ is -(CH₂)_LNR¹⁶R¹⁷ wherein L may be an integer ranging from 1-30 and R¹⁶ and R¹⁷ are independently the same or different and are hydrogen, a C_MS alkyl group, a C₂_ι₅ alkenyl group, a C₂„ι₅ alkynyl group, an aryl group, a -(CH₂)_YR¹⁸ group, a -(CH₂)_YC(0)R^1S group or a -(CH₂)YC0₂R^1S wherein Y may be an integer ranging from 1 to 15 and R¹⁸ is a hydroxy group, a thiol group, an alkylthiol, a silyl group, an alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group, a nitro group.

5.) The method of claim 4 including loading said pharmaceutically effective amount of said compound into aqueous cores of liposomes each containing at least one membrane bilayer.

6.) The method of claim 5 including controlling rate of delivery of said compound from said cores of said liposomes by varying R^{1 x} .

7.) The method of claim 5 including controlling rate of delivery of said compound from said cores of said liposomes by varying core pH.

8.) The method of claim 5 including controlling rate of delivery of said compound from said cores of said liposomes by varying R^u and core pH.

9.) A method of killing human cells undergoing DNA synthesis, comprising: administering to a human a pharmaceutically effective amount of a compound having a chemical formula selected from a group consisting of

and

R⁴ is H, F, an alkyl group, an alkenyl group, an alkynyl group, a ttialkylsilyl group or an alkoxy group;

R⁵ is a CM_S alkyl group, an allyl group, a benzyl group or a propargyl group;

R⁶, R⁷ and R⁸ are independently a C].₁₅ alkyl group, a C₂.ι₅ alkenyl group, a C₂„ι₅ alkynyl group, an aryl group or a -(CH₂)_qR¹⁵ group, wherein q is an integer between 1 and 15 and R¹⁵ is a hydroxy group, alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group or a nitro group;

R¹⁰ is an alkylene group, an alkenylene group or an alkynylene group;

R¹¹ is -(CH₂)_LNR¹⁶R¹⁷ wherein L may be an integer ranging from 1-30 and R¹⁶ and R¹⁷ are independently the same or different and are hydrogen, a C ₅ alkyl group, a C₂.i₅ alkenyl group, a C₂.₁₅ alkynyl group, an aryl group, a -(CH₂)_YR¹⁸ group, a -(CH₂)_γC(0)R¹⁸ group or a -(CH₂)YC0₂R¹⁸ wherein Y may be an integer ranging from 1 to 15 and R¹⁸ is a hydroxy group, a thiol group, an alkylthiol, a silyl group, an alkoxy group, an amino group, an alkylamino group, a dialkylamino group, a halogen atom, a cyano group, a nitro group.

10.) The method of claim 9 wherein said pharmaceutically effective amount of said compound is loaded into aqueous cores of liposomes each containing at least one membrane bilayer.

11.) The method of claim 10 including controlling rate of delivery of said compound from said cores of said liposomes by varying R¹¹.

12.) The method of claim 10 including controlling rate of delivery of said compound from said cores of said liposomes by varying core pH.

13.) The method of claim 10 including controlling rate of delivery of said compound from said cores of said liposomes by varying R¹¹ and core pH.