GB2167414A - Silibinin derivatives - Google Patents

Abstract

Silibinin derivatives of the general formula:- <IMAGE> wherein n and m, independently of one another, stand for 0 or 1, Alk1 and Alk2, independently of one another, are alkylene radicals containing up to 4 carbon atoms or alkenylene radicals containing 2 to 4 carbon atoms and M1 and M2, independently of each other, stand for hydrogen atoms or alkali metal atoms, are used in pharmaceutical compositions for treating burn damage, liver damage or fungal poisoning.

Description

SPECIFICATION Flavolignan derivatives The present invention is concerned with new flavolignan derivatives, with processes for the preparation thereof and with pharmaceutical compositions containing these new compounds.

Lady's thistle (Silybum marianum (L.) Gaertn. (Carduus marianus L.) is a medicinal plant which has long been known. From the flavolignans occurring in the fruits of this plant, R. Minster isolated a component called silybin (cf. Dissertation R. Minster, Munched, 1966). The chemical structure of this compound was elucidated by A. Pelter and R. Hänsel (cf. Tetrahedron Letters, London, 25, 2911-2916/1968).

It is known that silybin, previously also called silymarin I, is a valuable liver therapeutic substance (cf. Federal Republic of Germany Patent Specification No. 17 67 666). A technical process for the preparation of silybin (silymarin I) is described, for example, in Federal Republic of Germany Patent Specification No. 19 23 082.

As long ago as 1974, H. Wagner, P. Diesel and M. Seitz (Arzneimittelforschung, 24 (4), (466-471) assumed, with regard to silybin, two positional isomers, namely silybin and isosilybin.

This conjecture was investigated and confirmed experimentally by A. Arnone, L. Merlini and A.

Zanarotti (J. Chem. Soc. Chem. Comm., 16, 696-697/1079). According to this, the known silybin consists of two different compounds, namely, the compounds of the following structural formulae A and B:

(A) silibinin

(B) Isosilybin From these structural formulae, it can be seen that these compounds are positional isomers.

The compound of formula A has recently been given the INN designation silibinin. This designation will now be used herein for the compound of formula A.

The therapeutic use of silybin gives rise to the difficulty that silybin is practically insoluble in water.so that silybin-containing injection solutions or preparations, in the case of which a certain water-solubility is necessary, could not be produced. Federal Republic of Germany Patent Specification No. 19 63 318 admittedly describes silybin derivatives which possess a certain watersolubility but these are very complex mixtures of semiesters of succinic acid. This mixture is so complex because there are five esterifiable hydroxyl groups in silybin, the silybin also contains the two above-described positional isomers and the succinic acid used for the esterification is a dicarboxylic acid which can form not only monoesters but also diesters.For pharmaceutical purposes, a product which consists of an unforeseeable number of greatly differing and nonelucidated compounds cannot be used.

It is, therefore, an object of the present invention to provide water-soluble silibinin derivatives which are suitable for pharmaceutical purposes and which are precisely characterised as chemically individual compounds.

We have found that silibinin derivatives of certain alkane and alkylenedicarboxylic acids fulfil these requirements.

Thus, according to the present invention, there are provided silibinin derivatives of the general formula:

wherein n and m, independently of one another, stand for 0 or 1, Alk, and Alk2, independently of one another, are alkylene radicals containing up to 4 carbon atoms or alkenylene radicals containing 2 to 4 carbon atoms and M1 and M2, independently of one another, are hydrogen atoms or alkali metal atoms.

Preferred compounds of general formula (I) are those in which m and n, independently of one another, stand for 0 or 1, Alk1 and Alk2 each stand for an alkylene radical containing 2 carbon atoms and M and M2, independently of one another, stand for alkali metal atoms, m and n, Alk and Alk2 and M1 and M2 preferably have, in each case, the same meanings.

The disodium salt of silibinin-C-2',3-dihydrogen succinate is especially preferred.

In the case of the compounds according to the present invention, the hydroxyl groups which are not attached to a benzene nucleus of the silibinin are partly or completely esterified, for example by oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid or fumaric acid.

Preferably, the two non-aromatically bound hydroxyl groups of the silibinin are simply esterified by one of the mentioned carboxylic acids.

The present invention also provides a process for the preparation of the new compounds of general formula (I), wherein about 1 part by weight of silibinin of the above-given formula (A) is dissolved in 1 to 2 parts by weight of pyridine and reacted, while stirring, with 1 to 3 parts by weight of a dicarboxylic acid anhydride of the general formula::

in which Alk stands for one of the above-defined Alk1 and Alk2 radicals, ethanol is then added until a homogeneous mixture is obtained, subsequently water is admixed therewith, with intensive stirring, esters present of the aromatically bound hydroxyl groups thereby being hydrolysed, as soon as this hydrolysis is complete, the reaction mixture is diluted with ethyl acetate, washed with acidified water which is saturated with ethyl acetate, the ethyl acetate phase is evaporated and the residue is taken up in ethanol and converted with an alcoholic solution of an alkali metal hydroxide into the salt of the free, non-esterified carboxylic acid residue.

The reaction with the dicarboxylic acid anhydride is preferably carried out at 40 to 50"C. The pH of the ethyl acetate-saturated acidified water is advantageously kept at about 1.5 to 2.4.

These compounds, especially the disodium salt of silibinin-C-2',3-dihydrogen succinate, show, surprisingly an outstanding pharmacological action in the case of the treatment of burn injuries.

Furthermore, in spite of the described derivatisation, they retain the complete pharmacological effectiveness of the known silybin as a liver therapeutic. They are especially suitable for the treatment of liver cirrhosis and of toxic-metabolic liver damage.

Surprisingly, the compounds according to the present invention also prove to be extraordinarily effective for the treatment of fungal poisonings, especially the very dangerous poisoning caused by the fungus known as green death cap or deadly ageric (Amanita phalloides). Poisonings by halogenated organic solvents, such as carbon tetrachloride, trichioroethylene, chioroform and the like, can also be surprisingly well treated therewith. In the case of a prophylactic use, the compounds according to the present invention prevent the above-described damage.

Therefore, the present invention also provides pharmaceutical compositions containing at least one of these new compounds, together with pharmaceutically acceptable solid or liquid diluents or carriers. They are usually employed systemically, for example in the form of pills, capsules, solutions and the like, in conventional carriers and possibly together with conventional adjuvants.

The daily dosage for an adult human amounts to about 50 to 500 mg., depending upon the state of the patient and the severity of the symptoms of the disease.

Experiments with the disodium salt of silibinin-C-2:3-dihydrogen succinate (sili-suc-na).

The symptoms which arise in the case of burns are especially brought about by intoxication by products of thermal tissue necrosis. Evidence that autointoxication processes after severe skin burnings are responsible therefor have been carried out in a large variety of ways. Especially convincing are cross-transplantations of burnt and non-burnt skin to healthy and burnt recipient animals, it thereby being demonstrated that unburnt recipients of burnt skin die, whereas burnt recipients of unburnt skin do no show any harmful actions (see K.H. Schmidt, New aspects of autointoxication after severe burnings; The burning disease; F.W. Ahnefeld et al., eds. pub.

Springer Verlag, Berlin, pp. 45-52).

In the case of skin burnings, the liberation or new formation of a number of chemical compounds occurs. In spite of the plurality thereof, it has been possible to elucidate the structure of some of these compounds. It could be shown, inter alia, that the compounds resulting in the case of skin burnings possess a similarity with those compounds which arise in the case of lipid peroxidation. There are also analogies with regard to the toxic actions of these substances. Especially impressive is the formation of toxically-acting saturated and unsaturated aldehydes of varying chain length as a result of lipid peroxidation (Benedetti et al., Identification of 4-hydroxynonenal as a cytotoxic product originating from the peroxidation of liver microsomal lipids, Biochim. Biophys. Acta, 620, 281-296/1980) and the thermal tissue damage (K.H.

Schmidt et al., Studies on the structure and biological effects of pyrotoxins purified from burned skin, World J. Surg., 3, 361-365/1979). It is, therefore, assumed that burnings lead to an oxidative damaging of cell structures.

Therefore, autooxidative changes of membrane lipids were investigated as a result of an autointoxication after severe burnings. In particular, changes in the fatty acid composition of the membrane lipids were investigated. Furthermore, it was tested to what extent the silibinin derivatives according to the present invention influence the changes in the fatty acid composition of the membrane lipids.

Changes in the fatty acid composition of membrane lipids after severe burnings.

Male Wistar rats with an average body weight of 360 g. were kept in groups of three with free access to water and dry feed. Up to the commencement of the experiment, the room temperature was 22"C. and after the commencement of the experiment the animals were kept at 30"C.

The skin burnings were made with a copper stamp with a surface area of 20 cm2 with constant pressure and a temperaure of 250"C. In order to prevent a thermal damage to deeper lying organs, the skin was drawn over an air-cooled hollow spatula. Very exact burning traumata can be made with this animal model which provide constant survival rates.

Before commencement of the experiment, the animals were narcotised with 50 mg./kg. of nembutal. After the burning, 20 ml. Ringer lactate were injected i.p. for shock prophylaxis.

Five experimental groups were used: a) normal group: completely intact animals b) control group I: only silibinin treatment for 6 days with 75.5 mg. sili-suc-na c) control group ll: pseudo-operated animals d) group with burned animals: 25%, 250"C., 20 sec., 0.5 at.

e) test group: animals to which had been administered 75.5 mg. sili-suc-na i.p. for 6 days, starting 1 day before burning.

For the isolation of microsomes, after the end of the experimental period, the animals were bled under narcosis. Subsequently, the liver was removed, weighed and immediately transferred to an ice-coid isolation medium (0.25 M saccharose, 1 mM EDTA, 10 mMol Tris.HCI, pH 7.2).

The liver was cut up and homogenised in the medium. The microsome fraction was pelletised by differential centrifuging. The microsomes were re-suspended and again centrifuged. Subsequently, a suspension was prepared in the case of which 1 ml. of suspension corresponded to 1 g. of liver tissue.

The lipids were determined by the method of J. Folch (A simple method for the isolation and purification of total lipids from animal tissues, J. biol. Chem., 226, 497-508/1957, modification of Bligh and Dyer (A rapid method of total lipid extraction and purification, Can. J. Biochem.

Physiol., 37, 991-917/1959).

The extracted microsome lipids were saponified with an aqueous sodium hydroxide solution.

The free fatty acids were esterified by the addition of BF3-methanoi. After evaporation of the methanol and removal of hydrophilic by-products, the fatty acid esters were determined quantitatively.

In the case of the unburned group of animals, no noteworthy change of the fatty acid pattern could be ascertained. Thus, the narcosis and minor operational intervention did not result in a change of the microsomal lipids. For this reason, for further comparison, the normal group and the control group were combined to one control group.

A comparison of the unburned and of the burned animals with regard to their micrsomal fatty acid pattern showed a serious displacement of unsaturated to saturated fatty acids.

Fig. 1 of the accompanying drawings shows the fatty acid distribution in the microsomal liver lipids and the changes caused by the thermal skin damage. The proportion of palmitic acid (C16) increased after burning from 25.1 to 34.4% of the total fatty acids. In the case of stearic acid (C18), the proportion in the case of the burned animals was, with 46.3%, 13.2% above the value obtained with the control animals. In the case of oleic acid (C18:1), a slight, insignificant decrease is detectable. The proportion of linoleic acid (C18:2) was decreased after burning to about one third of the initial value. Finally, in the case of arachidonic acid (C20:4), after burning there was found only 31% of the initial content.

The following Table shows the influence of sili-suc-na on the proportions of fatty acids in the burned and in the unburned animals: Table I Fattv acid Pattern of the microsomal lipids of the rat liver after sili-suc-na therapy in the case of burned and unburned animals

C16 cis C18:l C18:2 C20:4 unburned 29.891 37.2% 8. gyO 9. 6% 16.2% (control group I) t 6.2 +12.3 +1.1 +3.3 +4.9 25.451 37.5 7.8% 11.4 18. to burned t6.O tS.6 ti.O +5.3 t1 It can be seen that treatment with a silibinin derivative according to the present invention does not give rise to any important changes in the case of the unburned control animals in comparison with the untreated animals.In the case of the burned animals, the therapy resulted in a complete removal of the loss of unsaturated fatty acids.

To summarise, the following can be said: Burnings result in changes of the fatty acid pattern of microsomal lipids. It is to be assumed that this is to be attributed to oxidative damage of the membranes. This is shown especially by the marked decrease of the polyunsaturated fatty acids.

The silibinin derivatives according to the present invention are thus able to inhibit oxidative cell damage. Therefore, they are especially useful for interrupting oxidative damage mechanisms after severe burnings.

As already mentioned, it is assumed that autotoxic reactions after severe burnings lead especially to oxidative cell damage. We have, therefore, investigated what effect a standardised thermal trauma has on the PHA-induced blastogenesis of T-lymphocytes from the spleen and the peripheral blood of rats. Furthermore, we have investigated how the silibinin derivatives according to the present invention influence such Iymphocytaeric functional disturbances after severe burnings.

Action of a standardised thermal trauma on the PHA-induced blastogenesis of T-lymphocytes from the spleen and the peripheral blood of rats.

The back skin of Wistar rats was burned with a copper stamp in the above-described manner.

As control group. there were used pseudo-burned animals on which were carried out all the operative manipulations but without burning. After 2, 4, 7 and 9 days, blood and spleen were removed from the burned and from the control animals under ether narcosis.

For the isolation of the lymphocytes, heparinised blood was coated on to Ficoll-Hypaque solution (density 1.077). Subsequently, it was centrifuged and the lymphocytes obtained tested with tryptane blue for their vitality. For the isolation of the spleen lymphocytes, the organ was comminuted, passed through a sieve and freed from accompanying erythrocytes by means of Gay's lysis solution.

Subsequently, the cell mixture was incubated in a vessel in the presence of 5% heat-inactivated foetal calf serum for 30 minutes in order to reduce the proportion of mono-nuclear cells in the suspension by adhesion to the vessei wall (5%). For culturing, the cells were introduced into flat-bottom microtitre plates. 20% foetal calf serum was then introduced. In this way, the spontaneous blastogenesis was determined by measurement of the incorporation of 3H-thymidine-(2Ci/mM) into the DNA of the cells.

In previous experiments, it was elucidated that an optimum mitogen stimulation takes place in the case of a PHA concentration (mitogen phythaemagglutinin) of 5,amg./ml. In the case of these experiments for the optimisation of the cellular test system, it was also ascertained that the maximum stimulation of the new synthesis of DNA took place after 72 hours. Furthermore, it was ascertained that the optimum concentration of foetal calf serum is 20% in order to achieve the highest stimulation.

As described above, the spontaneous blastogenesis was determined by measurement of the incorporation of 3H-thymidine into the DNA of the cells. The cells were collected 18 hours after the addition of 3H-thymidine, the zero point for the 18 hours thereby coinciding with the time point of maximum stimulation.

For the investigation of the action of the silibinin derivatives according to the present invention, a group of rats were treated with a silibinin derivative. For this purpose, 75.5 mg. of silisuc-na were injected i.p. once per day. This therapy was carried out from the day of burning up to the day one which the organs were removed (maximum up to the 9th day).

For the evaluation of the results obtained with the control animals and with the sili-suc-natreated animals, the stimulation index was calculated. This numerical value represents the quotients of the average value of the stimulated sample and the average value of the control sample.

From the stimulation index thus obtained in the case of each experimental animal, there was calculated an average stimulation index per animal group. The results obtained are expressed by the index SI.

Fig. 2 of the accompanying drawings shows the influence of the sili-suc-na used on the blastogenesis of lymphocytes. In the case of the burned animals, the reduced stimulation ability of the cells was markedly increased by the silibinin derivative.

Already on the second day, in the case of the sili-suc-na-treated animals, there was found an about 10 times higher responsivity of the blood lymphocytes towards PHA. On the fourth posttraumatic day, the value for the stimulation index in the case of blood lymphocytes for treated animals was 8, whereas the corresponding value in the case of the unreated animals was 1.5.

In the case of spleen cells, the stimulation indices of the burned, untreated animals were all markedly under 1. The administration of the silibinin derivative results in a significant improvement on all investigated days, a maximum being found on the 7th post-traumatic day.

Comparative experiments were also carried out which showed that sili-suc-na alone in the case of healthy animals did not result in any significant changes in the stimulation ability of the PHAinduced blastogenesis of T-lymphocytes from the spleen and from the peripheral blood.

Thus, the silibinin derivatives according to the present invention stimulate the blastogenesis of lymphocytes of burned animals in a significant manner.

It was also ascertained that, in the case of animals treated with the silibinin derivatives according to the present invention, the general catabolism was lower since, after the thermal trauma, the animals again rapidly increased in weight.

Fun gal poisonings Poisonings due to deadly ageric (Amanita phalloides) belong to the most serious ones found in medicine. Although only 10 to 30% of all fungal poisonings are caused by the Amanita phalloides, poisonings with this fungus have always attracted great medical interest because of their danger. In older publications, the lethality was said to be 30 to 50%. Thanks to modern intensive medicine, according to a collective study by Floersheim et al. on 205 patients, this value has been reduced, on average, to 22.4%.

The poison from Amanita phalloides, amanitin, can be fatal for adult humans even in an amount of 7 mg., this amount of poison being present in about 50 g. of fresh fungus.

After a series of animal experiments which promised success, the active material sili-suc-na was used in the therapy of poisoning by Amanita phalloides.

28 patients with Amanita phalloides poisoning were treated with sili-suc-na, in addition to conventional therapeutic measures. Of these 28 patients, only one died who had taken comparatively large amounts of the fungus with suicidal intent. This result demonstrated an enormous therapeutic advance in this field.

Preparation of isosilybin-free silibinin A suspension of 500 g. of the product according to Federal Republic of Germany Patent Specification No. 19 23 082 (see column 8, lines 14-19), with a silymarin content of about 70% and an isomer ratio of silybin/silidianin/silicristine of about 3:1:1, the silybin containing about one third of isosilybin, in 2 kg. methanol (about 2.53 litres) is heated to the boil for 15 minutes, while stirring. After this time, some silibinin can already precipitate out of the solution thus obtained. Subsequently, 0.75 to 1.25 kg. (about 0.96-1.58 litres) of methanol are removed in a vacuum and the residue is left to stand for 10 to 28 days at ambient temperature. The precipitated silibinin is filtered off and washed twice with 50 ml. amounts of cold methanol.

After drying in a vacuum at 40"C., the isolated crude silibinin is further purified in the following manner: 60 g. of crude silibinin are dissolved, with heating, in 3 litres of technical grade ethyl acetate.

Subsequently, 20 g. active charcoal are added thereto and the mixture is heated under reflux for a further 2 hours, while stirring. Thereafter, it is clarified by filtration and the solution is evaporated at 50"C. under reduced pressure to about 250 ml. The concentrate is stirred for 15 minutes with the use of an Ultra-Turrax apparatus and, while stirring, mixed with 25 ml. of methanol. Subsequently, the mixture is left to stand overnight at ambient temperature. Before filtering off with suction the thereby precipitated silybin, stirring is again carried out with an Ultra-Turrax apparatus for 5 minutes. The suction-filtered precipitate is washed twice with 50 ml.

amounts of ethyl acetate and dried overnight at 40"C. in a vacuum drying cabinet. The product obtained is subsequently ground and further dried for 48 hours under the same conditions.

The following Examples are given for the purpose of illustrating the present invention: Example 1.

Preparation of silibinin- C-2', 3-dihydrogensuccinate.

50 g. of silibinin are dissolved at 45"C. in 70 ml. pyridine, 50 g. succinic anhydride are added thereto, the mixture is stirred for about 8 hours at 45"C., 30 ml. ethanol are added thereto and the mixture is further stirred until a homogeneous mixture has formed. Subsequently, 60 ml. of water are added thereto, with intensive stirring, for the saponification of the phenyl esters, within the course of about 30 minutes. After stirring for about 1 hour at 30"C., the phenyl esters were quantitatively hydrolysed. The completeness of the hydrolysis is tested by means of HPLC. The hydrolysis is stopped by rapidly adding 1.7 litres of ethyl acetate to the reaction mixture thus obtained.

For the separation of excess succinic acid and of pyridine, the reaction solution diluted with ethyl acetate is extracted twice in countercurrent with 5 litre amounts of water which has been saturated with ethyl acetate and has a pH of 1.85 (adjusted with dilute aqueous hydrochloric acid). The ethyl acetate-saturated, acidified wash water is thereby pumped in a cycle counter to the diluted reaction solution and subsequently the pH is maintained at 1.85 by the addition of dilute hydrochloric acid until this pH value remains constant after the ethyl acetate passage.

Subsequently, for washing out excess hydrochloric acid, the ethyl acetate phase is extracted twice in countercurrent with 3.4 litre amounts of water which has been saturated with ethyl acetate. As soon as the pH value of the wash water is greater than 4.5, the organic phase is separated off quantitatively, evaporated in a vacuum at 40 to 50"C. to one twelfth of the initial volume (about 0.2 litres) and then diluted with 125 ml. ethanol.

The title compound is obtained by reprecipitation from ethanol/water and drying in a vacuum at 50"C. for 15 hours.

For the preparation of an analytical sample, the title compound is reprecipitated three times from ethanol/water and subsequently dried in a vacuum for 15 hours at 50"C.

In the FD mass spectrum a molecule peak appears at the expected molecular weight of 682.

The IR spectrum shows, in the region of the CO valency frequency, two overlapping bands, whereby one, as is also the case for silibinin, is to be associated with the carbonyl function of the pyrone ring at a wavelength of 1635 cm 1. The second band is at 1730 cm 1 and originates from the two ester carbonyl functions.

The 1H-NMR spectrum confirms that a twofold esterification has taken place. Thus, the ratio, determined by integration, of aromatic protons to methylene protons of the succinic acid residue, amounts to 8:8 (ppm range 5.9-7.1). The ratio of these methylene protons (ppm 2.6) to the methyi protons of the methoxy radical (ppm 3.8) amounts to 8.3 and is thus in agreement therewith.

The chemical displacements in the case of the I3C-investigations also show that the esterification of the two alcoholic hydroxyl groups have taken place since the chemical displacements change the most strongly at C" and the adjacent carbon atoms C12-C14, as well as at C2-C4.

Elementary analysis: Ca3H30O16 (M.W. 682.60) calc.: C 58.07%; H 4.4%; 0 37.50% found: 58.05%; 4.57%; 37.31% Example 2.

Preparation of the disodium salt of siiblnine-C-2',3-dihycrogen succinate.

To the ethanolic solution obtained according to Example 1, there is added, while stirring and cooling externally at -5 to 9"C., 6% ethanolic sodium hydroxide solution in an amount based upon the determination of the solids content of this ethanolic solution. The suspension is further stirred for 1 hour at ambient temperature, the beige-coloured precipitated solid is filtered off with suction, suspended twice, in each case for 5 to 10 minutes, with the help of a Turrax, in 150 ml. ethanol and again filtered off with suction.For the removal of residual ethyl acetate, the product is subsequently suspended for 14 hours at ambient temperaure in 280 ml. ethanol, again filtered off with suction, then washed with 70 ml. ethanol and dried for 15 hours in a vacuum drying cabinet at 40 to 45"C. The previously dried product is subsequently ground, sieved to a particle size of less than 0.2 mm. and again dried in a vacuum for 48 hours at 40 to 45"C. There are thus obtained 52 g. (69% of theory) of the title compound.

The title compound does not possess a sharp melting point. At about 80"C., it begins to sinter and melts, with bubble formation, at about 100"C.

The UV spectrum in methanol shows: 2 =288 nm, E=1,73.104.

The molecular weight of the title compound is 726.56. The compound is a light beigecoloured, microcrystalline powder without a specific odour and with a salty taste. It is readily soluble in water, sparingly soluble in ethanol and practically insoluble in acetone, diethyl ether and chloroform.

Example of use.

Preparation of a lyophilisate for intravenous administration.

disdium salt of silibinin-C 2',3-dihydrogen succinate 75.0 mg.

mannitol 10.0 mg.

water for injection purposes ad 1.5 ml.

1.5 ml. of solution is placed in a pointed ampoule of 5 ml. capacity and then freeze-dried in known manner. For storage purposes, the ampoule containing the final lyophilisate is closed in the usual manner.

For use, the lyophilisate is dissolved in 5 ml. of sterile, physiological saline solution to give a clear solution.

Claims (11)

1. Silibinin derivatives of the general formula:

wherein n and m, independently of one another, stand for 0 or 1, Alk1 and Alk2, independently of one another, are alkylene radicals containing up to 4 carbon atoms or alkenylene radicals containing 2 to 4 carbon atoms and M1 and M2, independently of each other, stand for hydrogen atoms or alkali metal atoms.

2. Silibinin derivatives according to claim 1, wherein n and m, independently of each other, stand for 0 or 1, Alk1 and Alk2, each stand for an alkylene radical containing 2 carbon atoms and M1 and M2, independently of each other, stand for alkali metal atoms.

3. Silibinin derivatives according to claim 1, wherein n and m, Alk, and Alk2, as well as M, and M2, have the same meanings.

4. The disodium salt of silibinin-C-2',3-dihydrogen succinate.

5. Process for the preparation of silibinin derivatives according to claim 1, wherein 1 part by weight of silibinine of the formula:

is dissolved in 1 to 2 parts by weight of pyridine and reacted, while stirring, with 1 or 3 parts by weight of a dicarboxylic acid anhydride of the general formula::

in which Alk is an Alk1 and Alk2 radical according to claim 1, ethanol is then added thereto until a homogeneous mixture has formed, subsequently water is ,added thereto, with intensive stirring, esters of the aromatically bound hydroxyl groups present thereby being hydrolysed, as soon as this hydrolysis is complete, the mixture is diluted with ethyl acetate, washed with acidified water which is saturated with ethyl acetate, the ethyl acetate phase is evaporated and the residue is taken up in ethanol and converted with an alcoholic alkali metal hydroxide solution into the salt of the free carboxylic acid residues.

6. Process according to claim 5, wherein the reaction with the dicarboxylic acid anhydride is carried out at a temperature of about 40 to 50"C.

7. Process according to claim 5 or 6, wherein the ethyl acetate saturated, acidified water is maintained at a pH of about 1.5 to 2.4.

8. Process for the preparation of silibinin derivatives according to claim 1, substantially as hereinbefore described and exemplified.

9. Silibinin derivatives according to claim 1, whenever prepared by the process according to any of claims 5 to 8.

10. Pharmaceutical compositions containing at least one silibinin derivative according to claim 1, in admixture with a solid or liquid pharmaceutical diluent or carrier.

11. The use of silibinin derivatives according to claim 1 for the treatment of burn damage, liver cirrhosis, toxic-metabolic liver damage and fungal poisoning.