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20 pages, 2528 KiB

Open AccessFeature PaperArticle

Chiral Thioxanthones as Modulators of P-glycoprotein: Synthesis and Enantioselectivity Studies

by Ana Lopes, Eva Martins, Renata Silva, Madalena M. M. Pinto, Fernando Remião, Emília Sousa and Carla Fernandes

Molecules 2018, 23(3), 626; https://doi.org/10.3390/molecules23030626 - 10 Mar 2018

Cited by 19 | Viewed by 4652

Abstract

Recently, thioxanthone derivatives were found to protect cells against toxic P-glycoprotein (P-gp) substrates, acting as potent inducers/activators of this efflux pump. The study of new P-gp chiral modulators produced from thioxanthone derivatives could clarify the enantioselectivity of this ABC transporter towards this new [...] Read more.

Recently, thioxanthone derivatives were found to protect cells against toxic P-glycoprotein (P-gp) substrates, acting as potent inducers/activators of this efflux pump. The study of new P-gp chiral modulators produced from thioxanthone derivatives could clarify the enantioselectivity of this ABC transporter towards this new class of modulators. The aim of this study was to evaluate the P-gp modulatory ability of four enantiomeric pairs of new synthesized chiral aminated thioxanthones (ATxs) 1–8, studying the influence of the stereochemistry on P-gp induction/ activation in cultured Caco-2 cells. The data displayed that all the tested compounds (at 20 μM) significantly decreased the intracellular accumulation of a P-gp fluorescent substrate (rhodamine 123) when incubated simultaneously for 60 min, demonstrating an increased activity of the efflux, when compared to control cells. Additionally, all of them except ATx 3 (+), caused similar results when the accumulation of the P-gp fluorescent substrate was evaluated after pre-incubating cells with the test compounds for 24 h, significantly reducing the rhodamine 123 intracellular accumulation as a result of a significant increase in P-gp activity. However, ATx 2 (−) was the only derivative that, after 24 h of incubation, significantly increased P-gp expression. These results demonstrated a significantly increased P-gp activity, even without an increase in P-gp expression. Therefore, ATxs 1–8 were shown to behave as P-gp activators. Furthermore, no significant differences were detected in the activity of the protein when comparing the enantiomeric pairs. Nevertheless, ATx 2 (−) modulates P-gp expression differently from its enantiomer, ATx 1 (+). These results disclosed new activators and inducers of P-gp and highlight the existence of enantioselectivity in the induction mechanism. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
Structures of the studied chiral aminated thioxanthones, ATxs 1–8. Full article ">Figure 2
Chromatograms of the investigated compounds (A) (R)-1-((1-hydroxypropan-2-yl)amino)-4-propoxy-9H-thioxanthen-9-one (ATx 2 (−)), (B) (S)-1-((1-hydroxypropan-2-yl)amino)-4-propoxy-9H-thioxanthen-9-one (ATx 1 (+)), (C) (S,R)-1-((1-hydroxypropan-2-yl)amino)-4-propoxy-9H-thioxanthen-9-one (mixture of ATx 1 (+) and ATx 2 (−)) on Lux® 5 µm amylose-1 at 0.5 mL/min−1; n-hexane:ethanol (70:30 v/v), 0.5 mL/min, λmax 254 nm. Full article ">Figure 3
Chiral thioxanthones ATxs 1–8 (0–50 μM) cytotoxicity in Caco-2 cells evaluated by the Neutral Red uptake assay, 24 h after exposure. Results are presented as mean ± standard error mean (SEM) from at least 5 independent experiments (performed in triplicate). Statistical comparisons were estimated using the nonparametric method of Kruskal–Wallis (one-way ANOVA on ranks), followed by the Dunn’s multiple comparisons post hoc test (* p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001 vs. control (0 μM)). Full article ">Figure 4
Flow cytometry analysis of P-gp expression levels in Caco-2 cells exposed to ATxs 1–8 (20 µM) for 24 h. Results are presented as mean ± standard error mean (SEM) from 5 independent experiments (performed in duplicate). Statistical comparisons were made using One-way ANOVA, followed by Tukey’s multiple comparisons test (*** p < 0.001 vs. control (0 µM); # p < 0.05 for ATx 1 (+) vs. ATx 2 (−)). Full article ">Figure 5
P-gp activity evaluated through the RHO 123 accumulation in the presence of chiral ATxs 1–8 (20 µM) during the RHO 123 accumulation phase. Results are presented as mean ± SEM from five independent experiments (performed in triplicate). Statistical comparisons were estimated using One-way ANOVA, followed by Tukey’s multiple comparisons test (* p < 0.05; *** p < 0.001; **** p < 0.0001 vs. control (0 μM)). Full article ">Figure 6
P-gp activity evaluated through the RHO 123 accumulation in Caco-2 cells exposed to chiral thioxanthones (20 µM) for 24 h. Results are presented as mean ± SEM from four independent experiments (performed in duplicate). Statistical comparisons were estimated using One-way ANOVA, followed by Tukey’s multiple comparisons test (*** p < 0.001; **** p < 0.0001 vs. control (0 μM)). Full article ">Figure 7
P-gp ATPase activity in the presence of chiral ATxs 1–8. Results are expressed as mean ± SEM from three independent experiments (performed in triplicate). Statistical comparisons were estimated using One-way ANOVA, followed by Tukey’s multiple comparisons test (** p < 0.01 vs. basal P-gp ATPase activity). Full article ">Scheme 1
Reaction conditions for the synthesis of chiral thioxanthones 1–8 (ATxs 1–8). Full article ">

22 pages, 3440 KiB

Open AccessArticle

Enantiomeric Resolution and Docking Studies of Chiral Xanthonic Derivatives on Chirobiotic Columns

by Ye‛ Zaw Phyo, Sara Cravo, Andreia Palmeira, Maria Elizabeth Tiritan, Anake Kijjoa, Madalena M. M. Pinto and Carla Fernandes

Molecules 2018, 23(1), 142; https://doi.org/10.3390/molecules23010142 - 11 Jan 2018

Cited by 36 | Viewed by 4547

Abstract

A systematic study of enantioresolution of a library of xanthonic derivatives, prepared “in-house”, was successfully carried out with four commercially available macrocyclic glycopeptide-based columns, namely Chirobiotic^TM T, Chirobiotic^TM R, Chirobiotic^TM V and Chirobiotic^TM TAG. Evaluation was conducted in multimodal [...] Read more.

A systematic study of enantioresolution of a library of xanthonic derivatives, prepared “in-house”, was successfully carried out with four commercially available macrocyclic glycopeptide-based columns, namely Chirobiotic^TM T, Chirobiotic^TM R, Chirobiotic^TM V and Chirobiotic^TM TAG. Evaluation was conducted in multimodal elution conditions: normal-phase, polar organic, polar ionic and reversed-phase. The effects of the mobile phase composition, the percentage of organic modifier, the pH of the mobile phase, the nature and concentration of different mobile phase additives on the chromatographic parameters are discussed. Chirobiotic^TM T and Chirobiotic^TM V, under normal-phase and reversed-phase modes, respectively, presented the best chromatographic parameters. Considering the importance of understanding the chiral recognition mechanisms associated with the chromatographic enantioresolution, and the scarce data available for macrocyclic glycopeptide-based columns, computational studies by molecular docking were also carried out. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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4155 KiB

Open AccessArticle

Discrimination of Stereoisomers by Their Enantioselective Interactions with Chiral Cholesterol-Containing Membranes

by Hironori Tsuchiya and Maki Mizogami

Molecules 2018, 23(1), 49; https://doi.org/10.3390/molecules23010049 - 25 Dec 2017

Cited by 15 | Viewed by 8186

Abstract

Discrimination between enantiomers is an important subject in medicinal and biological chemistry because they exhibit markedly different bioactivity and toxicity. Although stereoisomers should vary in the mechanistic interactions with chiral targets, their discrimination associated with the mode of action on membrane lipids is [...] Read more.

Discrimination between enantiomers is an important subject in medicinal and biological chemistry because they exhibit markedly different bioactivity and toxicity. Although stereoisomers should vary in the mechanistic interactions with chiral targets, their discrimination associated with the mode of action on membrane lipids is scarce. The aim of this study is to reveal whether enantiomers selectively act on chiral lipid membranes. Different classes of stereoisomers were subjected at 5–200 μM to reactions with biomimetic phospholipid membranes containing ~40 mol % cholesterol to endow the lipid bilayers with chirality and their membrane interactions were comparatively evaluated by measuring fluorescence polarization. All of the tested compounds interacted with cholesterol-containing membranes to modify their physicochemical property with different potencies between enantiomers, correlating to those of their experimental and clinical effects. The rank order of membrane interactivity was reversed by changing cholesterol to C3-epimeric α-cholesterol. The same selectivity was also obtained from membranes prepared with 5α-cholestan-3β-ol and 5β-cholestan-3α-ol diastereomers. The opposite configuration allows molecules to interact with chiral sterol-containing membranes enantioselectively, and the specific β configuration of cholesterol’s 3-hydroxyl group is responsible for such selectivity. The enantioselective membrane interaction has medicinal implications for the characterization of the stereostructures with higher bioactivity and lower toxicity. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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Figure 1

Figure 1
Stereoisomers with stereospecific bioactivity and toxicity. NMDA: N-methyl-d-aspartate. Full article ">Figure 2
Membrane-constituting chiral phospholipids and sterols. Full article ">Figure 3
Interactions of bupivacaine stereoisomers (50 μM for each) with neuro-mimetic membranes in the absence (a) or presence (b) of 10 mol % cholesterol. ** p <0.01 compared with rac-bupivacaine. Full article ">Figure 4
Effects of 0–40 mol % cholesterol (a); 0–40 mol % epicholesterol (b); 20 mol % cholesterol and 20 mol % epicholesterol (c); 0–40 mol % 5α-cholestan-3β-ol (d); 0–40 mol % 5β-cholestan-3α-ol (e); and 20 mol % 5α-cholestan-3β-ol and 20 mol % 5β-cholestan-3α-ol (f) on interactions of bupivacaine stereoisomers (50 μM for each) with cardiomyocyte-mimetic membranes. ** p <0.01 compared with rac-bupivacaine. Full article ">Figure 5
Comparisons of cardiomyocyte-mimetic membranes prepared with epimeric (a) and diastereomeric (b) sterols. ** p <0.01 compared with epicholesterol or 5β-cholestan-3α-ol. Full article ">Figure 6
Membrane interactions of stereoisomers of 25 μM bupivacaine (a); 50 μM ropivacaine (b); 50 μM medetomidine (c); 50 μM propranolol (d); 50 μM ketamine (e); 50 μM menthol (f); 200 μM ibuprofen (g); and 100 μM catechin (h). ** p <0.01 compared with enantiomeric antipode, racemate, or epimer. Full article ">Figure 7
n-AS(P) polarization changes of cardiomyocyte-mimetic membranes induced by 50 μM bupivacaine enantiomers (a) and relative changes of R(+)-bupivacaine to S(−)-bupivacaine (b). ** p <0.01 compared with S(−)-bupivacaine. Full article ">Figure 8
Possible interactions of bupivacaine enantiomers with cholesterol-containing membranes. Full article ">

2178 KiB

Open AccessCommunication

Chiral Symmetry Breaking in Magnetoelectrochemical Etching with Chloride Additives

by Iwao Mogi, Ryoichi Aogaki and Kohki Takahashi

Molecules 2018, 23(1), 19; https://doi.org/10.3390/molecules23010019 - 22 Dec 2017

Cited by 10 | Viewed by 3755

Abstract

Magnetoelectrolysis (electrolysis under magnetic fields) produces chiral surfaces on metal thin films, which can recognize the enantiomers of amino acids. Here, the chiral surface formation on copper films is reported in magnetoelectrochemical etching (MEE) at 5T with chloride additives. In the absence of [...] Read more.

Magnetoelectrolysis (electrolysis under magnetic fields) produces chiral surfaces on metal thin films, which can recognize the enantiomers of amino acids. Here, the chiral surface formation on copper films is reported in magnetoelectrochemical etching (MEE) at 5T with chloride additives. In the absence of additives, the surface chirality signs of MEE films depended on the magnetic field polarity. On the contrary, the MEE films prepared with the additives exhibited only d-activity in both magnetic field polarities. This result implies that the specific adsorption of chloride additives induces the chiral symmetry breaking for the magnetic field polarity. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
MHD effects in magnetoelectrochemical etching with vertical magnetic fields B. The Lorentz force acting on the ionic current i causes two types MHD flows; macroscopic vertical MHD flow around the electrode edge and micro-MHD vortices around the non-equilibrium fluctuations (pits) on the deposit surface. Full article ">Figure 2
Microphotographs of MEE film surfaces prepared at a deposition current of 23 mA·cm−2. (a) +5T-film around a pit; (b) zoom-in photograph at the edge of pit (the rectangle part in (a)); (c) schematic of multi-scale micro-MHD vortices around a pit; (d) 0T-film. Full article ">Figure 3
Chiral behaviors of the MEE film electrodes for the oxidation of alanine enantiomers. (a) +5T-film prepared at a deposition current of 23 mA·cm−2 without KCl; (b) −5T-film at 23 mA·cm−2 without KCl; (c) +5T-film at 20 mA·cm−2 with 0.1 mM KCl; and (d) −5T-film at 20 mA·cm−2 with 0.1 mM KCl. Full article ">Figure 4
The ee ratio profiles of the MEE films versus the deposition currents. (a) +5T-film prepared without KCL; (b) −5T-film without KCl; (c) +5T-film with 0.10 mM KCl; (d) −5T-film with 0.10 mM KCl; (e) +5T-film with 0.20 mM KCl; and (f) −5T-film with 0.20 mM KCl. The error bars reflect the values of multiple experiments for each condition. Full article ">

2958 KiB

Open AccessArticle

Enantiomeric-Enriched Ferrocenes: Synthesis, Chiral Resolution, and Mathematic Evaluation of CD-chiral Selector Energies with Ferrocene-Conjugates

by Lubov V. Snegur, Yurii A. Borisov, Yuliya V. Kuzmenko, Vadim A. Davankov, Mikhail M. Ilyin, Mikhail M. Ilyin, Jr., Dmitry E. Arhipov, Alexander A. Korlyukov, Sergey S. Kiselev and Alexander A. Simenel

Molecules 2017, 22(9), 1410; https://doi.org/10.3390/molecules22091410 - 25 Aug 2017

Cited by 7 | Viewed by 5523

Abstract

Enantiomeric-enriched ferrocene-modified pyrazoles were synthesized via the reaction of the ferrocene alcohol, (S)-FcCH(OH)CH₃ (Fc = ferrocenyl), with various pyrazoles in acidic conditions at room temperature within several minutes. X-ray structural data for racemic (R,S)-1N-(3,5-dimethyl [...] Read more.

Enantiomeric-enriched ferrocene-modified pyrazoles were synthesized via the reaction of the ferrocene alcohol, (S)-FcCH(OH)CH₃ (Fc = ferrocenyl), with various pyrazoles in acidic conditions at room temperature within several minutes. X-ray structural data for racemic (R,S)-1N-(3,5-dimethyl pyrazolyl)ethyl ferrocene (1) and its (S)-enantiomer (S)-1 were determined. A series of racemic pyrazolylalkyl ferrocenes was separated into enantiomers by analytical HPLC on β- and γ-cyclodextrins (CD) chiral stationary phases. The quantum chemical calculations of interaction energies of β-CD were carried out for both (R)- and (S)-enantiomers. A high correlation between experimental HPLC data and calculated interaction energies values was obtained. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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Figure 1
Complex (R)-(3,5-dimethylpyrazolyl)-α-ethyl ferrrocene CD-cyclodextrin (calculated data). Full article ">Figure 2
Complex (S)-(3,5-dimethylpyrazolyl)-α-ethyl ferrocene-CD-cyclodextrin (calculated data). Full article ">Figure 3
Correlation between experimental HPLC data (alpha) and ΔE calculated interaction energies values. α = 0.69862 + 0.09203 ΔE. The multiplier at ΔE is a tangent of the angle inclination of a line. Full article ">Figure 4
Molecular structure of 1 presented in thermal ellipsoids at 50% probability. Selected lengths, Å, and angles (°), C6-C11 1.509(4); N1-C11 1.470(3); C11-C12 1.527(4); Fe1-C6 2.040(2); N1-N2 1.366(3); N1-C11-C6 110.5(2); N1-C11-C12 109.5(2); C7-C6-C11 126.4(2); C6-C11-C12 113.1(2). Full article ">Scheme 1
Enantiospecific synthesis of (S)-ferrocenylethylpyrazoles. (i) Methylene dichloride, HBF4 45% water solution, 3,5-dimethylpyrazole (R1 = R2 = CH3), or pyrazoles (R1 = R2 = H), 3-trifluoromethyl-5-methylpyrazole (R1 = CF3, R2 = CH3), 3,5-di(trifluoromethyl)pyrazoles (R1 = R2 = CF3), 22–25 °C, 5 min; ascorbic acid (5–10 mg) was added during the work-up of the product. Full article ">

Review

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18 pages, 3775 KiB

Open AccessFeature PaperReview

Enantiomeric Mixtures in Natural Product Chemistry: Separation and Absolute Configuration Assignment

by Andrea N. L. Batista, Fernando M. dos Santos, João M. Batista and Quezia B. Cass

Molecules 2018, 23(2), 492; https://doi.org/10.3390/molecules23020492 - 23 Feb 2018

Cited by 52 | Viewed by 10014

Abstract

Chiral natural product molecules are generally assumed to be biosynthesized in an enantiomerically pure or enriched fashion. Nevertheless, a significant amount of racemates or enantiomerically enriched mixtures has been reported from natural sources. This number is estimated to be even larger since the [...] Read more.

Chiral natural product molecules are generally assumed to be biosynthesized in an enantiomerically pure or enriched fashion. Nevertheless, a significant amount of racemates or enantiomerically enriched mixtures has been reported from natural sources. This number is estimated to be even larger since the enantiomeric purity of secondary metabolites is rarely checked in the natural product isolation pipeline. This latter fact may have drastic effects on the evaluation of the biological activity of chiral natural products. A second bottleneck is the determination of their absolute configurations. Despite the widespread use of optical rotation and electronic circular dichroism, most of the stereochemical assignments are based on empirical correlations with similar compounds reported in the literature. As an alternative, the combination of vibrational circular dichroism and quantum chemical calculations has emerged as a powerful and reliable tool for both conformational and configurational analysis of natural products, even for those lacking UV-Vis chromophores. In this review, we aim to provide the reader with a critical overview of the occurrence of enantiomeric mixtures of secondary metabolites in nature as well the best practices for their detection, enantioselective separation using liquid chromatography, and determination of absolute configuration by means of vibrational circular dichroism and density functional theory calculations. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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51 pages, 6620 KiB

Open AccessFeature PaperReview

Marine Natural Peptides: Determination of Absolute Configuration Using Liquid Chromatography Methods and Evaluation of Bioactivities

by Ye’ Zaw Phyo, João Ribeiro, Carla Fernandes, Anake Kijjoa and Madalena M. M. Pinto

Molecules 2018, 23(2), 306; https://doi.org/10.3390/molecules23020306 - 31 Jan 2018

Cited by 28 | Viewed by 6705

Abstract

Over the last decades, many naturally occurring peptides have attracted the attention of medicinal chemists due to their promising applicability as pharmaceuticals or as models for drugs used in therapeutics. Marine peptides are chiral molecules comprising different amino acid residues. Therefore, it is [...] Read more.

Over the last decades, many naturally occurring peptides have attracted the attention of medicinal chemists due to their promising applicability as pharmaceuticals or as models for drugs used in therapeutics. Marine peptides are chiral molecules comprising different amino acid residues. Therefore, it is essential to establish the configuration of the stereogenic carbon of their amino acid constituents for a total characterization and further synthesis to obtain higher amount of the bioactive marine peptides or as a basis for structural modifications for more potent derivatives. Moreover, it is also a crucial issue taking into account the mechanisms of molecular recognition and the influence of molecular three-dimensionality in this process. In this review, a literature survey covering the report on the determination of absolute configuration of the amino acid residues of diverse marine peptides by chromatographic methodologies is presented. A brief summary of their biological activities was also included emphasizing to the most promising marine peptides. A case study describing an experience of our group was also included. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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47 pages, 13174 KiB

Open AccessFeature PaperReview

Chiral Drug Analysis in Forensic Chemistry: An Overview

by Cláudia Ribeiro, Cristiana Santos, Valter Gonçalves, Ana Ramos, Carlos Afonso and Maria Elizabeth Tiritan

Molecules 2018, 23(2), 262; https://doi.org/10.3390/molecules23020262 - 28 Jan 2018

Cited by 68 | Viewed by 12457

Abstract

Many substances of forensic interest are chiral and available either as racemates or pure enantiomers. Application of chiral analysis in biological samples can be useful for the determination of legal or illicit drugs consumption or interpretation of unexpected toxicological effects. Chiral substances can [...] Read more.

Many substances of forensic interest are chiral and available either as racemates or pure enantiomers. Application of chiral analysis in biological samples can be useful for the determination of legal or illicit drugs consumption or interpretation of unexpected toxicological effects. Chiral substances can also be found in environmental samples and revealed to be useful for determination of community drug usage (sewage epidemiology), identification of illicit drug manufacturing locations, illegal discharge of sewage and in environmental risk assessment. Thus, the purpose of this paper is to provide an overview of the application of chiral analysis in biological and environmental samples and their relevance in the forensic field. Most frequently analytical methods used to quantify the enantiomers are liquid and gas chromatography using both indirect, with enantiomerically pure derivatizing reagents, and direct methods recurring to chiral stationary phases. Full article

(This article belongs to the Special Issue Chirality in Health and Environment: Recent developments)

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Figure 1

Figure 1
Application of chiral drug analysis in forensic chemistry. Full article ">Figure 2
Relative number of each class of chiral drug referred in the reviewed enantioselective published studies and the analytical methods used for separation of the chiral drugs in biological fluids. Full article ">Figure 3
Chromatogram representing the enantioseparation of R/S-AM, R/S-MA, R/S-MDA, R/S-MDMA and R/S-MDEA as R-MTPCl derivatives in whole blood concentrations at (A) 2 µg/g and (B) at 0.002 µg/g, respectively. Reproduction with permission of Elsevier (Figure 1 from Rasmussen et al. [<a href="#B67-molecules-23-00262" class="html-bibr">67</a>]). Full article ">Figure 4
Relative number of each class of chiral drug referred in the reviewed enantioselective published studies and the analytical methods for separation of the chiral drugs in environmental samples. Full article ">Figure 5
Chromatogram and mass spectra of WWTP effluent sample showing the enantiomers of FLX, VNF, BSP, MET and PHO. Reproduction with permission of Elsevier (Figure 2 from Ribeiro et al. [<a href="#B39-molecules-23-00262" class="html-bibr">39</a>]). Full article ">

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