GB2140809A - New derivatives of glycyrrhetinic acid - Google Patents

Abstract

The title compounds are of formula: <IMAGE> wherein R is a hydrogen atom or a straight or branched chain, saturated or unsaturated aliphatic radical, which is optionally substituted by an unsubstituted or substituted phenyl radical or R is an unsubstituted or substituted phenyl radical and R' is a residue of maleic or fumaric acid; and the salts thereof with non-toxic, pharmaceutically acceptable inorganic and organic bases. The compounds have antiinflammatory, anti-viral anti-ulcer and analgesic activities.

Description

SPECIFICATION New derivatives of glycyrrhetinic acid The present invention is concerned with new derivatives of glycyrrhetinic acid, with the preparation thereof and with pharmaceutical compositions containing them.

Although many pharmacologically-active derivatives of glycyrrhetinic acid are known and used, several of them suffer from undesirable side effects. or have to be adminstered in comparatively large doses.

Consequently, it is an object of the present invention to provide new, useful and highly active derivatives of glycyrrhetinic acid, which have an outstanding anti-inflammatory activity and also a good anti-viral activity.

The new derivatives of glycyrrhetinic acid according to the present invention are compounds of the general formula: i

wherein R is a hydrogen atom or a straight or branched chained, saturated or unsaturated aliphatic radical, preferably, containing up to 6 carbon atoms, which is optionally substituted by an unsubstituted or substituted phenyl radical or R is an unsubstituted or substituted phenyl radical and R' is a residue of maleic or fumaric acid, i.e. is a radical of the formula:

and the salts thereof with non-toxic, pharmaceutically acceptable inorganic or organic bases.

In principle, the compounds according to general formula (I) can be prepared by reacting a glycyrrhetinic acid derivative of general formula (I), in which R' is a hydrogen atom, with maleic an hydroxide to give the corresponding maleate, whereafter, the maleate is, if desired, isomerised to give the corresponding fumarate.

However, we have found that although this method is satisfactory for preparing the maieates, isomerisation thereof to give the corresponding fumarates is not satisfactory, only impure products being obtained.

Consequently, in order to obtain the fumarates, it is preferable to react a glycyrrhetinic acid derivative of general formula (I), in which R' is a hydrogen atom, with monoethyl fumaryl chloride, the fumarates thereby being obtained in satisfactory yield and with satisfactory purity.

If desired, the maleates and fumarates thus obtained can be salified with an appropriate nontoxic, pharmaceutically-acceptable inorganic or organic base.

When it is desired to obtain a compound of general formula (I), in which R is other than a hydrogen atom, the starting material used in a glycyrrhetinic acid derivative containing the desired substituent R.

The present invention also provides pharmaceutical compositions containing at least one compound of general formula (I), in admixture with an appropriate solid or liquid pharmaceutical diluent or carrier.

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

1) Preparation of mon o- 1 8/3-glycyrrhetyl maleate.

A mixture of 1 70 g. 1 8ss-glycyrrhetinic acid, 1 68 g. maleic anhydride and 730 ml. glacial acetic acid was refluxed gently on a heating mantle for 3 hours. Initially, a solution was obtained but the product then began to precipitate. The mixture was left to cool overnight, filtered and the resultant solid was washed twice with 100 ml. amounts of cold acetic acid and then twice with 100 ml. amounts of cold methanol and finally dried in a vacuum oven at 80"C.

The desired maleate was obtained in a yield of 168.7 g.

Thin layer chromatography (5:1 v/vn-butanol/ammonia) indicated that the product was approximately 98% pure, the only apparent impurity being 18ss-glycyrrhetinic acid.

The infra-red absorption spectrum had major- bands at V max = 3300 - 2500, broad (CO2H), 1727 (ester), 1700-1670 (CO2H), 1655 (enone), 1610 (CH =CH conjugated to carboxyl) cm ~ ' .

The material had a melting point of 245-247"C. and the NMR spectrum (d5-pyridine) supported the expected structure.

2) Preparation of mono- 18P-glycyrrhetyl maleate disodium salt.

To a suspension of 167.7 g. mono-l 8P-glycyrrhetyl maleate in 500 ml. methanol, stirred magnetically, was slowly added a solution of 23.6 g. sodium hydroxide in 560 ml. methanol.

After approximately half of the sodium hydroxide solution had been added, the reaction mixture became very thick and thus difficult to stir, swirling by hand then being used. Towards the end of the addition, a clear solution was obtained, the pH of which was approximately 8.5. The solution was filtered and the filtrate poured slowly, with swirling, into a vessel contaning 5 litres acetone. A white precipitate was formed and the product was allowed to stand for 1 5 minutes.

The precipitated product was filtered off and washed well with acetone, before drying on a water-bath to constant weight. A final drying was carried out in a vacuum oven at 60"C. The desired disodium salt was obtained in a yield of 164.1 g. (91 % of theory).

Thin layer chromatography (5:1 v/v nbutanol/ammonia) indicated that the only impurity which was u.v.-visable was 18P-glycyrrhetinic acid and that this was present in an amount of much less than 0.5%. When the chromatogram was sprayed with concentrated sulphuric acid/ethanol and the plate was heated until the spots turned black, a small amount of an impurity with a slightly higher Rf than the product was seen, which was almost certainly the corresponding 1 1-deoxy derivative. The infra-red absorption spectrum (nujol mull) had major bands at V max = 1710 (ester), 1650 (enone), 1580 (CO2Na) cm~'. The pH of a 10% aqueous solution was 8.0. The product decomposed above 290"C.

A sample of the disodium salt was hydrolysed to the corresponding acid and this material checked for purity. This layer chromatography (5:1 v/v n-butanol/ammonia) indicated that the material was of approximately 99% purity. Both the infra-red and nuclear magnetic resonance spectra were in agreement with the expected structure.

Example 2.

1) Preparation of mono- I 8a-glycyrrhetyl maleate.

A mixture of 1 8.8 g. 1 8a-glycyrrhetinic acid, 18.6 g. maleic anhydride and 80 ml. glacial acetic acid was heated under reflux for 3 hours, with magnetic stirring, a clear solution being obtained. After cooling, a sample was subjected to thin layer chromatographic analysis, using n butanol/0.88 ammonia (5:1 v/v). This showed that the reaction was 80% complete. Distilled water was added to the cooled reaction mixture and the precipitate formed was filtered off, washed with water until the washings were neutral and then dried to constant weight in a vacuum oven at 60"C. to give 16.5 g. of crude mon.o-1 8a-glycyrrhewl maleate. Thin layer chromatography indicated the presence of a small amount of 180c-glycyrrhetinic acid.

2) Preparation of mono-18ez-glycyrrhetyl maleate disodium salt To a stirred suspension of 16.5 g. mono-18ac-glycyrrhetyl maleate in 40.7 ml. methanol was slowly added, at ambient temperature, a solution of 2.31 g. sodium hydroxide in 55 ml.

methanol. After about half of the sodium hydroxide solution had been added, a clear solution had formed. Solid reprecipitated after further solution had been added but this finally dissolved to give a clear solution (pH 8). The solution was filtered and added to 400 ml. acetone. The resultant solid was filtered off, well washed with acetone and dried to constant weight in a vacuum oven at 100"C. to give 14.5 g. of product. This was redissolved in 100 ml. methanol and the solution obtained was added to acetone. The resultant precipitate was filtered off, washed with acetone and dried in a vacuum oven at 100"C. to give 11.36 g. of the desired disodium salt. Thin layer chromatography (rrbutanol/0.88 ammonia; 4:1 v/v) indicated that the product had a purity of more than 99%. The disodium salt has a melting point of > 300 C.

0.5 g. of this disodium salt was dissolved in a minimum amount of water and then acidified with dilute hydrochloric acid. The precipitated solid was filtered off, washed with water until the washings were neutral and then dried to constant weight in a vacuum oven at 100"C. to give 0.31 g. mono-18a-glycyrrhetyl maleate; m.p. 273-275"C. Thin layer chromatography (n butanol/0.88 ammonia; 4:1 v/v) indicated that the product has a purity of more than 99%.

Example 3.

1) Preparation of trans-3-carboethoxypropenoyl chloride (monoethyl fumaryl chloride).

44 g. Monoethyl fumaric acid and 214 ml. thionyl chloride were heated together under reflux for 3 hours. Excess thionyl chloride was then distilled off, toluene was added and subsequently distilled off again and finally the product was distilled under water pump vacuum, the fraction boiling between 74 and 76"C. being collected. (Yield = 58 g.). Nuclear magnetic resonance spectrometry confirmed the expected structure.

2) Preparation of mono- 1 8/3-glycyrrhetyl monoethyl fumarate.

1 5 g. 18ss-Glycyrrhetinic acid, 108 ml. dry toluene and 1 2 ml. anhydrous pyridine were stirred together and cooled in an ice-bath. 7.5 g. trans3-carboethoxypropenoyl chloride in 1 5 ml. toluene was added dropwise to the stirred, cold mixture. Ten minutes after the addition was complete, the mixture was allowed to warm to ambient temperature and stirring was continued overnight. The reaction mixture was diluted with ethyl acetate and washed with dilute hydrochloric acid, water and saturated salt solution. The organic solution was evaporated to dryness. The residue was refluxed with a mixture of 68 ml. pyridine and 1 7 ml. distilled water for 2 hours.When cool, the mixture was poured into ice-water/hydrochloric acid (excess), the precipitated solid was filtered off, washed with dilute hydrochloric acid and then water and dried, the yield being 1 8.1 g. The solid was dissolved in 1 50 ml. boiling acetone, the solution was filtered and then water was added slowly until crystallisation commenced. The solution was cooled to 4"C., the solid was filtered off, washed with 2:1 v/v acetone/water and dried. After recrystallisation from dichloromethane/methanol, the yield of mono-l 8P-glycyrrhetyl monoethyl fumarate was 10.8 g. This material was shown to be more than 99% pure by thin layer chromatography (petroleum spirit b.p. 60-80'C.-dichloromethane-acetone (6:3:2 v/v/v).Nuclear magnetic resonance spectrometry confirmed the expected structure.

3) Preparation of mono-18ssglycyrrhetyl fumarate disodium salt.

1 5 g. mono-l 8P-glycyrrhetyl monoethyl fumarate was slurried with 66 ml. acetone and a solution of 2 g. sodium hydroxide in 45 ml. water was added to the well stirred mixture over the course of 1 hour. The solution was left to stand at ambient temperature for 30 minutes and then poured into 300 ml. acetone. The precipitated solid was filtered off, washed with acetone and dried, the yield being 14.3 g. This solid was dissolved in 75 ml. methanol and the cloudly solution was filtered through a pad of activated charcoal. The filtrate was concentrated to about 50 ml. and poured into 200 ml. acetone. The precipitate was filtered off, washed thoroughly with acetone and dried, the yield being 11 9.Since the product was still slightly coloured, the above purification was repeated, the yield of mono-l 8P-glycryrrhetyl fumarate disodium salt then being 7.9 g.

This layer chromatography (butan-1-ol and 0.880 ammonia, 5:1 v/v) showed less than 1% total impurities. High pressure liquid chromatography (using a Spherisorb lOlL ODS column; solvent system: 70:30 v/v methanol/0.1 M phosphate buffer (pH 7); flow rate 2 ml./minute) shawed less than 1 % total impurities.

The material had a melting point > 300"C. (decomposition above 310"C.) and the infra-red absorption spectrum (nujol mull) had major bands at vmax = 1 710 (ester), 1 640 (enone), 1575 (broad, CO2Na), 980 (trans double bond) cm-1.

A small sample was converted to the corresponding free acid by acidification with dilute hydrochloric acid. The solid was filtered off, washed with water until the washings were neutral and dried to constant weight in a vacuum oven at 70"C. Thin layer chromatography (butan-1-ol and 0.880 ammonia; 5:1 v/v) showed better than 99% purity.

The diacid had a melting point of 317-319"C. and the infra-red absorption spectrum had major bands at v max = 1730, 1710 (ester + carboxylic acids), 1620 (enond), 980 (trans double bond) cm-'. Nuclear magnetic resonance spectrometry confirmed the expected structure.

Example 4.

1) Preparation of mono- 1 8a-glycyrrhetyl monoethyl fumarata A solution of 7.5 g. monoethyl fumaryl chloride in 32 ml. dry toluene was slowly added over the course of 30 minutes to a cold, stirred mixture of 1 5 g. 1 8a- glycyrrhetinic acid, 1 3 ml.

an hydros pyridine and 11 5 ml. dry toluene, a dark red coloured reaction mixture being obtained. The reaction mixture was left to stand at ambient temperature for at least 4 hours, whereafter thin layer chromatography (petroleum ether/dichloromethane/acetone 6:3:2 v/v/v) indicated that the reaction had proceeded to about 80% completion.

The reaction mixture was placed in a separating funnel and treated with an equal volume of ethyl acetate. The organic layer was washed withdilute hydrochloric acid and the aqueous layer was washed with dichloromethane, the organic extracts then being combined. The combined organic extracts were washed twice with distilled water and then dried with anhydrous sodium sulphate. Filtration followed by evaporation to dryness gave 16.28 g. of a dark red oily solid.

This crude product was treated with 64 ml. pyridine and 1 6 ml. distilled water and the mixture then heated under reflux for 2 hours, while stirring. Thereafter, thin layer chromatography (petroleum ether/dichloromethane/acetone 6:3:2 v/v/v) indicated that the reaction was complete. The reaction mixture was then poured into ice water/excess hydrochloric acid and the precipitated solid was filtered off, washed with distilled water until the washings were neutral and dried in a vacuum oven at 60"C to give 13.32 g. of product.

This product was dissolved in 50 ml. acetone and distilled water was added to the hot solution until a cloudiness resulted. After cooling to 4"C,, the resulting crystalline solid was filtered off, washed with acetone/water (2:1 v/v) and dried in a vacuum oven to give 11.48 g.

of purer product.

This product was dissolved in 50 ml. dichloromethane and 200 ml. methanol added thereto.

The solution was filtered, concentrated to about 75 ml. and cooled to 4"C. The resultant crystalline solid was filtered off, washed with a little methanol and dried in a vacuum oven at 60"C. to give 9.05 g. of product. Thin layer chromatography (petroleum ether/dichloromethane/acetone 6:3:2 v/v/v) indicated that the material consisted of only one major spot. Nuclear magnetic resonance spectrometry indicated that the compound had the expected structure.

2) Preparation of mon o- 1 8a-glycyrrhetyl fumarate disodium salt.

41.6 ml. of a 1 M aqueous solution of sodium hydroxide was slowly added over the course of about 45 minutes to a suspension of mono-1 8a-glycyrrhetyl monoethyl fumarate in acetone, whereafter a slight cloudiness remained. The reaction mixture was slowly filtered and the resultant filtrate (pH 8.5) was added to 275 ml. acetone, while stirring. The precipitated solid was then filtered off, washed with acetone and dried at 100"C., the yield being 10.0 g.

This product, which was still coloured, was dissolved in 1 50 ml. methanol and the solution was filtered and decolorising charcoal added thereto. The mixture was boiled for a short time, the charcoal was filtered off and the filtrate was poured into about 500 ml. acetone. The precipitate was filtered off, washed well with acetone and dried at 100"C., the yield being 6.83 g.

The thin layer chromatogram (rebutanol/0.88 ammonia 5:1 v/v) indicated the presence of a small amount of 1 8a-glycyrrhetinic acid; together with a small amount of a slightly more polar product. Concentration of the mother liquors and reprecipitation with acetone gave a second crop of material of 2.5 g.

Recrystallisation of the combined crops from methanol/acetone gave a product with a purity of at least 99%. The product has a melting point of > 300"C.

0.4 g. of the disodium salt was dissolved in water and the solution was acidified with dilute hydrochloric acid. The solid precipitate was filtered off, washed with water until the washings were neutral and then dried in a vacuum oven to constant weight, the yield of the diacid being 0.34 g., m.p. 294-296"C. Thin layer chromatography (rrbutanol/0.88 ammonia 5:1 v/v) indicated that the material was of at least 99% purity. The nuclear magnetic resonance spectrum supported the expected structure.

Various pharmacological tests were carried out on the disodium salts of mono-18ss-glycyrrhe- tyl fumarate and maleate. These showed that both compounds had a significant central nervous system activity as determined by assessing the analgesic effect in the acetic acid-induced writhing test on rats. Both compounds gave a significant inhibition of gastric secretion and, in the charcoal meal test, the disodium maleate gave a significant,stimulation.

Furthermore, in a test for anti-ulcer activity, determined by the ethanol-induced gastric necrosis test, both compounds showed marked and dose-related inhibitory effects.

In addition, we have found that both compounds displayed a surprisingly good anti-viral activity against several viruses, including herpes simplex I, RV9 and murine cytomegalovirus.

Claims (11)

1. Glycyrrhetinic acid derivatives of the general formula:

wherein R is hydrogen atom or a straight or branched chain, saturated or unsaturated aliphatic radical, which is optionally substituted by an unsubstituted or substituted phenyl radical or R is an unsubstituted or substituted phenyl radical and R' is a residue of maleic or fumaric acid; and the salts thereof with non-toxix, pharmaceutically acceptable inorganic and organic bases.

2. Mono-l 8P-glycyrrhetyl and the disodium salt thereof.

3. Mono-1 8a-glycyrrhetyl maleate and the disodium salt thereof.

4. Mono-l 8P-glycyrrhetyl monoethyl fumarate.

5. Mono-l 8P-glycyrrhetyi fumarate disodium salt.

6. Mono-18a-glycyrrhetylmonoethyl fumarate.

7. Mono-18a-glycyrrhetyl fumarate disodium salt.

8. Process for the preparation of glycyrrhetinic acid derivatives according to claim 1, wherein a glycyrrhetinic acid derivative of the general formula given in claim 1 but in which R' is a hydrogen atom is reacted with maleic anhydride to give the corresponding maleate, whereafter, if desired, the maleate is isomerised to give the corresponding fumarate.

9. Process for the preparation of glycyrrhetyl fumarates according to claim 1, wherein a glycyrrhetinic acid derivative of the general formula given in claim 1 but in which R' is a hydrogen atom is reacted with monoethyl fumaryl chloride.

1 0. Process according to claim 8 or 9, wherein the product obtained is salified by reaction with a non-toxic, pharmaceutically -acceptable inorganic or organic base.

11. Process for the preparation of glycyrrhetinic acid derivatives according claim 1, substantially as hereinbefore described and exemplified.

1 2. Glycyrrhetinic acid derivatives according to claim 1, whenever prepared by the process according to any of claims 8 to 11.

1 3. A pharmaceutical composition containing at least one compound according to claim 1, in admixture with an appropriate solid or liquid pharmaceutical diluent or carrier.