Sericosides and Method of Use

This invention relates to novel pharmaceutically active compounds, to processes for their production, to pharmaceutical compositions containing the compounds and to plant extracts from which the compounds may be prepared.

Plants of the genus Terminalia (of the family Combretaceae) are distributed over regions of Africa, Asia, Australia and tropical America. We have now discovered that extracts possessing valuable pharmaceutical properties may be obtained from plants of one particular species of this genus, namely Terminalia sericea.

These extracts have a high content of terpenic compounds and, in addition to the known compounds arjunic acid and arjunetine, they have been found to contain two hitherto unknown compounds which we have named sericic acid and sericoside. These compounds are respectively 2.alpha.,3.beta.,19.alpha.,24-tetrahydroxy-olean-12-en-28-oic acid and its D-glucopyranoside ester, and may be represented by the formula (I) ##STR2## wherein in the case of sericic acid, R= hydrogen and in the case of sericoside, R= glucose.

Sericic acid and sericoside have been found to possess valuable cicatrizing and anti-inflammatory properties which render them particularly useful in treating dermatological disorders, for example by being incorporated into cosmetics and in treating stomach ulcers. Sericic acid and sericoside may also be converted into derivatives which have similar valuable pharmacological properties.

Thus in accordance with one aspect of the present invention, there are provided compounds of the general formula (II) ##STR3## wherein --OR.sub.1, --OR.sub.2, --OR.sub.3 and --OR.sub.4 each represents a free or esterified hydroxyl group and --R.sub.5 represents a glycosyl group, preferably D-glucopyranosyl and pharmaceutically acceptable salts of such compounds which are capable of salt formation.

R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which may be the same or different, may, for example, be substituted or unsubstituted aliphatic or aromatic mono- or poly-carboxylic acid acyl radicals, particularly such radicals containing up to twelve and preferably up to seven carbon atoms.

The aliphatic mono- or poly-carboxylic acid acyl radicals (both substituted and unsubstituted) may be straight or branched, chained or cyclic and furthermore may be saturated or unsaturated. Examples of saturated, unsubstituted aliphatic mono-carboxylic acid acyl radicals include acetyl, propionyl, butyryl, isobutyryl, valeryl, hexanoyl and heptanoyl. Particularly preferred are such radicals containing up to four carbon atoms.

Examples of poly-carboxylic acid acyl radicals include hemi-maleyl, hemi-fumaryl and hemi-succinyl.

Examples of aromatic carboxylic acid acyl radicals include benzoyl and phenylacetyl.

Where such radicals are substituted, the or each substituent may, for example, be selected from halogen (i.e. fluorine, chlorine, bromine or iodine), nitro, hydroxy, ether, keto and amino groups. The aromatic mono- or polycarboxylic acid acyl radicals may additionally or alternatively be substituted by one or more aliphatic radicals (optionally substituted, for example by one or more of the substituents referred to above) and preferably containing up to six carbon atoms as in methyl, ethyl, propyl, isopropyl, butyl, isobutyl, valeryl and hexyl.

Particularly preferred acyl radicals for R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are acetyl, benzoyl and hemi-succinyl.

Where any one of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents an acyl radical derived from a polycarboxylic acid, the remaining carboxyl (--COO--) group or groups may be in the form of the free acid (--COOH) or in the form of a derivative, for example an acid addition salt with a pharmaceutically acceptable cation, or an ester with, for example, an aliphatic alcohol containing up to seven carbon atoms, such as, for example, methanol, ethanol, propanol, isopropanol, n-butanol, pentanol, hexanol and heptanol.

Compounds of general formulae (II) containing carboxyl groups (for example where R.sub.1, R.sub.2, R.sub.3 or R.sub.4 contains a free carboxyl group) may be converted to pharmaceutically acceptable acid addition salts, for example with metals yielding pharmaceutically acceptable cations, such as, for example, sodium, potassium, calcium, magnesium, aluminum or iron. Also, compounds containing substituted or unsubstituted amino groups may be converted to pharmaceutically acceptable acid addition salts with acids yielding pharmaceutically acceptable cations (e.g. hydrochloric or sulphuric acids).

The invention also includes pharmaceutical compositions comprising as active ingredient a compound of the general formula (II) or a pharmaceutically acceptable salt thereof in combination with a pharmaceutically acceptable excipient and processes for producing such compositions which comprise admixing the active ingredient with the excipient. Examples of excipients are starch, lactose, propylene glycol, triethanolamine, water and anti-fermentative agents.

According to a further aspect of the present invention there is provided a process for producing a compound of general formula (II) which comprises extracting tissue of a plant of the species Terminalia sericea, and in particular the roots or the bark of the roots with an organic solvent, isolating sericic acid and/or sericoside from the extract and if desired converting the isolated sericic acid or sericoside to another compound of the general formula (II).

The organic solvent may, for example, be an alcohol (preferably a lower alcohol containing up to six carbon atoms and most preferably up to four carbon atoms, such as methanol, ethanol, n-propanol, isopropanol, or one of the butanols), a ketone (preferably a di-lower alkyl ketone wherein the lower alkyl groups contain up to six and preferably up to four carbon atoms as in acetone, methyl ethyl ketone and di-isopropyl ketone) or an ester (preferably an ester formed with a lower alcohol containing up to six carbon atoms, and most preferably up to four carbon atoms, such as methanol, ethanol, n-propanol, isopropanol, the butanols and amyl alcohol and a lower alkanoic acid containing up to four carbon atoms, such as formic, acetic, propionic or butyric acids).

Particularly useful solvents are ethanol, acetone and ethyl acetate.

Where the organic solvent is miscible with water, mixtures of the solvent and water may be used.

Preferably, prior to isolating sericic acid and/or sericoside from the extract, fatty and resinous substances are removed, for example by evaporating the organic solvent from the extract and contacting the residue so obtained with a liquid hydrocarbon so as to form a partially purified extract. Preferably, the residue is diluted with water or with an alcohol/water mixture before it is contacted with the hydrocarbon. The fatty and resinous substances are preferentially dissolved in the hydrocarbon and may therefore be removed by decanting the resulting hydrocarbon solution.

Sericic acid has been found to be generally more soluble in chlorinated hydrocarbon solvents than in water and sericoside has been found to be generally more soluble in aqueous solvents than chlorinated hydrocarbons. The isolation of sericic acid and sericoside from the partially purified extract obtained as described above therefore preferably includes a fractionation step in which the extract is fractionated into a fraction containing sericic acid and other non-glucosidated terpenes (Fraction A) and a fraction containing sericoside and other terpenic glucosides by contacting a solution of the partially purified extract in water or a mixture of water and an alcohol (for example one of the alcohols specified above) with a chlorinated hydrocarbon solvent such as, for example, chloroform, methylene chloride or dichloroethane, and separating the aqueous and chlorinated hydrocarbon solutions so obtained.

The aqueous solution may then be diluted with alcohol to give an alcohol concentration of not less than 60% and treated to remove proteinaceous material by adding neutral or basic lead acetate solution and filtering to remove any precipitate which is formed. The filtrate may then be evaporated to form an aqueous concentrate by eliminating the alcoholic solvent and the terpenic glucosides extracted repeatedly from the concentrate with a mixture of butanol and benzene (preferably 3:1 to 4:1).

The solution in the butanol/benzene mixture may then be evaporated to small volume and the residue poured into isopropyl ether. The precipitate so obtained contains a major part of the terpenic glucosides (Fraction B).

Sericic acid and sericoside may be obtained from Fractions A and B respectively by recrystallization or chromatographic separation.

It will be appreciated that the sericic acid- and sericoside-containing extracts of Terminalia sericea referred to above and in particular the purified fractions referred to as Fractions A and B constitute further aspects of the present invention.

Sericic acid and sericoside may each be transformed into each of the other compounds of general formulae (II) by known methods of esterification, hydrolysis, oxidation and salt formation and such methods form a further aspect of the present invention.

Thus, for example, sericic acid may be converted to sericoside by esterification with .alpha.-bromo-(tetra-acetyl)-glucose followed by successive elimination of the acetyl radicals and sericoside may be converted to sericic acid by saponification.

A -- separation of Fractions A and B

200 kg. of finely ground roots of plants of the species Terminalia sericea are extracted under weak reflux four times using 600 liters of aqueous alcohol each time. The reunited extracts are evaporated in vacuo to 100 liters and the aqueous residue extracted three times with ligroin using 100 liters of ligroin each time. The ligroin, which contains fatty acids, resins and .beta.-sitosterol removed from the residue is decanted and the residue, in ethanol solution, is diluted with 300 liters of water and extracted three times with dichloroethane using 100 liters each time.

The dichloroethane solution so obtained is evaporated to dryness in vacuo and 2.5 kg. of residue are obtained containing sericic acid and other free triterpenes (Fraction A).

The aqueous residue remaining after the extraction with dichloroethane is diluted with 500 liters of alcohol and 10 kg. of neutral lead acetate dissolved in 30 liters of alcohol are added. An abundant precipitate is formed and is left to stand overnight to sediment. The precipitate is centrifuged and discarded, and the water-alcohol phase is concentrated in vacuo to about 200 liters. The aqueous concentrate is extracted three times with a mixture of t-butanol-benzene in the ratio 3:1 (v/v) using 100 liters each time.

The organic phase is separated and washed with a 10% solution of sodium carbonate and then evaporated in vacuo to 20 liters. The butanolic concentrate so obtained is poured, with vigorous agitation, into 150 liters of diethyl ether. A precipitate comprising triterpenic glucosides is formed and is centrifuged and dried. 5 kg. of product are obtained, containing sericoside and other triterpenic glucosides (Fraction B).

B -- preparation of purified sericic acid by crystallization

1 kg. of Fraction A is dissolved in 5 liters of alcohol. The solution is decolorized with carbon, evaporated to 3 liters and left to stand overnight.

300 g. of crude sericic acid crystallize, which by successive recrystallisation from dilute aqueous alcohol or acetic acid enables 200 g. of pure sericic acid having m.p. 278.degree. -82.degree. C., [.alpha.].sub.D.sup.30 =+ 37.8 (c= 0.32 EtOH 95) to be obtained.

Additional quantities of sericic acid may be obtained by reuniting the mother liquors, which are then evaporated to dryness, to obtain a residue which is acetylated in acetone, using acetic anhydride. 80 g. of sericic acid triacetate are obtained which after recrystallization from glacial acetic acid melts at 183.degree. C. and has [.alpha.].sub.D =+ 4.degree. (c= 2, EtOH 95) IR 3630 cm.sup.-1 1745 cm.sup.-1 and 1705 cm.sup.-1.

By saponification with alcoholic potash the sericic acid triacetate may be converted to sericic acid, in a state of purity such that its properties are entirely identical with that obtained by crystallization, as described above.

C -- preparation of sericic acid by a chromatographic procedure

1 kg. of Fraction A is dissolved in 3 volumes of chloroform and chromatographed on a column containing 15 kg. of silica gel by eluting with a solvent mixture comprising 95:5 chloroform-ethanol. The fractions containing the individual pure components are collected and reunited and after crystallization from methanol, 250 g. of pure sericic acid having a m.p. 278.degree. - 82.degree. C. are obtained along with 20 g. of arjunic acid with m.p. 220.degree. - 22.degree. C.

D -- preparation of sericoside by crystallization

1 kg. of Fraction B is dissolved in 6 liters of alcohol. The solution is decolorized with carbon and evaporated to 3 liters. 1 liter of hot water (at about 50.degree. C.) is added and the liquid is left to stand overnight. 600 g. of crude sericoside crystallize which, after repeated crystallizations from dilute alcohol, furnish 250 g. of pure sericoside having the following characteristics: m.p. 206.degree. -208.degree. C. and [.alpha.].sub.D = + 5.4 (c= 2, pyridine).

E -- preparation of sericoside by chromatography

1 kg. of fraction B is dissolved in 3 liters of an 8:2 (v/v) chloroform-ethanol mixture and chromatographed on 30 kg. of silica gel by eluting with the said solvent mixture. The fractions containing the individual pure products are reunited and concentrated to dryness. After crystallization from methanol there are obtained respectively 320 g. of sericoside having an m.p. of 206.degree. - 208.degree. C. and 210 g. of arjunetine.

Preparation of methyl sericate

10 g. of sericic acid are dissolved in 50 ml. of chloroform and treated with a solution of diazomethane in methylene chloride until complete reaction. The solution is concentrated in vacuo to dryness and the residue is crystallized from acetone.

Preparation of tribenzoyl methyl sericate

10 g. of methyl sericate are dissolved in 50 ml. of anhydrous pyridine and 9.24 g. of benzoyl chloride are added. The reaction mixture is left to stand for one night, then poured into water. Tribenzoyl methyl sericate precipitates, and after crystallization from methanol has a melting point of 199.degree. C.

Preparation of triacetyl 19-keto methyl sericate

10 g. of methyl triacetylsericate (prepared in an analogous manner to methyl tribenzoyl sericate) are dissolved in 500 ml. of anhydrous acetone and Jones's reagent is added until the reaction is complete.

The acetone solution is diluted with 1,500 ml. of water whereupon the product precipitates in amorphous form.

The product is collected by filtration, and recrystallized from aqueous methanol. After drying, there are obtained 9 g. of triacetyl 19-keto methyl sericate having an m.p. of 200 and [.alpha.].sub.D = + 33 (c= 0.5, EtOH).

Preparation of diethylaminoethyl sericate

10 g. of potassium sericate are dissolved in 50 ml. of dimethyl formamide and treated with 3 g. of diethylaminoethyl chloride. The reaction mixture is kept at 50.degree. C. for 5 hours, then poured into 600 ml. of water. An abundant precipitate forms which is filtered, washed with water and recrystallized from aqueous isopropanol. The product melts at 105.degree. - 8.degree. C. and [.alpha.].sub.D = +19.7.degree. (c= 1, EtOH).

Preparation of methyl tetracetyl sericate

20 g. of methyl triacetylsericate are dissolved in 30 ml. of acetic anhydride and 1 ml. of concentrated perchloric acid is added. The reaction mixture is left to stand for 1 hour, then poured into 500 ml. of water.

There is precipitation of the product which, after filtration, is crystallized from ethanol.

The product melts at 223.degree. C.

Preparation of methyl tetracetyl 18.alpha.-sericate

10 g. of methyl triacetyl sericate are dissolved in 50 ml. of 40% hydrobromic acid in acetic acid and left at room temperature for 30 hours. The reaction mixture is poured into water. The product is filtered and precipitates, and after drying it is crystallized from hexane. 6 g. of methyl tetracetyl 18.alpha.-sericate are obtained having an m.p. of 194.degree. C. and [.alpha.].sub.D =+12.6.degree. (c= 0.4 in EtOH).

Preparation of 2,3,24-trihemisuccinyl derivative of sericic acid

10 g. of sericic acid are dissolved in 50 ml. of anhydrous pyridine and 10 g of succinic anhydride are added.

The reaction mixture is reheated to 80.degree. C. for 6 hours, then cooled and diluted with 800 ml. of chloroform.

The solution is counter-washed with 10% aqueous HCl until the pyridine is eliminated and then concentrated to dryness and dehydrated over Na.sub.2 SO.sub.4.

The residue is crystallized from glacial acetic acid and 11 g. of trihemisuccinyl sericic acid with m.p. of 105.degree. - 108.degree. C. and [.alpha.].sub.D =+2.65.degree. (c= 2, EtOH) is obtained.

By following the general procedures of the above Examples 2 to 8, but using appropriate alternative reactants, other compounds of general formulae (II) may be prepared.

The following pharmaceutical data is given to illustrate the anti-inflammatory and cicatrizing properties of the compounds of the invention:

Anti-ulcer activity -- Gastric Ulcer in the rats induced by Shay's method

The anti-ulcer activity of sericic acid and sericoside was determined by administering the compounds to rats in which gastric ulcers were induced by Shay's method. The compounds were administered at the dose of 200 mg./kg. orally five times, at 42, 30, 25 and 6 hours before tying of the pylorus and immediately after the operation and as shown in Table 1 diminished the ulcer index by 48 and 45 percent respectively, compared with the controls.

Ld 50 in Mice

The LD.sub.50 in mice (as determined with intraperitoneal administration) for sericic acid and sericoside was as follows:

Sericic acid > 1,000 mg./kg.

Sericoside > 1,000 mg./kg.

Anti-inflammatory Activity Against Carragenin-induced Oedema in Rats

The anti-inflammatory activities of sericoside and sericic acid were determined by measuring the extent to which the oedema caused by sub-plantar administration of carragenin to rats could be inhibited by prior oral and intraperitoneal administration of the substances.

The following results were obtained:

The cicatrizing activity of sericic acid and sericoside upon experimental wounds was determined on rats in accordance with the method of Morton & Malone (Arch. Int. Pharmacodyn. Ther. 196, 117, 1972).

The treatment of the wounds was effected with a 10% suspension of the active principles in water containing 2% carboxymethyl cellulose (CMC). The suspensions were used in doses of 0.1 ml. for each application, one treatment being effected per day.

From the data shown in the following Table 2 it can be seen that sericic acid and sericoside possess significant healing activity, compared with the controls, especially in the first days of treatment.

Ultra-violet ray erythema in guinea pigs was effected in accordance with the method of Winder et al. (Arch. Int. Pharmacodyn. 106, 261, 1968).

Sericoside and sericic acid were applied to the depilated skin of male albino guinea pigs (average weight 300- 400 g) in the form of a 5% gel (using 200 mg. thereof) one hour prior to irradiation. The animals were depilated 18 hours prior to the irradiation and irradiated for 3 minutes with a 500 W. mercury vapor lamp at a distance of 18 cms.

The controls were treated with a similar gel which did not contain the active ingredients, sericoside or sericic acid.

The compounds under examination were able to reduce the erythema with a most pronounced activity at 8 hours, as shown by the results set forth in the following Table 3.

The following examples of pharmaceutical preparations were prepared by admixing the active ingredients with the excipients referred to and illustrate the manner in which the compounds of the invention may be brought into forms suitable for topical and oral administration.