Process for the preparation of glycine-conjugated bile acids

Abstract: A process for the preparation of glycine-conjugated bile acids as per general formula (I): (I) Y-NH-CH₂-COOH wherein Y is the acyl radical of a bile acid selected from the group consisting of ursodeoxycholic, chenodeoxycholic, lithocholic, 3α-7β-12α-tri-hydroxycholanic, 3α-7β-dihydroxy-12-ketocholanic, deoxycholic, dehydrocholic, iodeoxycholic, iocholic acids and relative compositions for hepatic insufficiency treatment, containing the abovesaid acids as active ingredients, in continuation with suitable excipients and/or diluents.

Description: FIELD OF THE INVENTION The present invention relates to a process for the preparation of glycine-conjugated bile acids and/or pharmaceutically acceptable salts thereof. PRIOR ART DICLOSURE The amides formed by bile acids with the amino function of the amino acids, glycine and taurine, are known as conjugated bile acids and relative bile salts. The bile acids secreted by the liver are almost entirely in the conjugated form. For example, glycoursodeoxycholic acid is the major metabolite that is present in high amounts in bile after ursodeoxycholic acid prolonged administration. The synthesis of bile acids conjugated with taurine and glycine was described by Bergström and Norman (Enciclopedia della Chimica, USES, Firenze, pages 421-426). According to said procedure, a mixed anhydride was obtained by treating a bile acid salt and tributylamine with ethylchlorocarbonate in dioxane at low temperature. The obtained anhydride was reacted with a glycine or taurine sodium salt aqueous solution to produce the sodium salt of the conjugated acid. However, the product yields and, especially, purity obtained by the aforesaid process are not high. The Applicant has surprisingly found a process for the preparation of conjugated bile acids of general formula (I) that is not adversely affected by the disadvantages inherent in the known process. Like the process known from literature, the process of the present invention comprises: a) optionally salifying bile acid of formula (II) (II) Y-OH wherein Y is the acyl radical of a bile acid selected from the group consisting of ursodeoxycholic, chenodeoxycholic, lithocholic, 3α,7β,12α-trihydroxycholanic, 3α,7β-dihydroxy-12-hetocholanic, deoxycholic, dehydrocholic hyodeoxycholic and hyocholic acids, with a tertiary amine of alkyl or heteroaromatic type in an aprotic solvent at a temperature below 20°C; b) reacting either the mixture obtained in (a) containing the aforesaid bile acid salt or previously isolated salt, with a chloroformate of general formula (III): (III) Cl-COOR where R is selected from the group consisting of C 1 -C 5 alkyl, phenyl, benzyl, at a temperature below 20°C in the presence of an aprotic solvent to give the corresponding mixed anhydride of formula (IV): (IV) Y-O-COOR where Y and R are as defined above. But, unlike the process known from literature, the process as per the present invention is characterized by the following stages: c) mixed anhydride (IV) is reacted with a phenol of general formula (V) where R 1 is selected from H and C 1 -C 5 alkyl, C 2 -C 5 acyl and nitro group, at a temperature below 60°C in the presence of an aprotic solvent and of a tertiary amine as per (a) to give the corresponding phenol ester of formula (VI): where Y and R 1 are as defined above; d) the product is separated by water addition, extraction of phenol ester in a solvent, evaporation and crystallization, followed by an optional recrystallization; e) phenol ester is treated with an aqueous solution of glycine as such or in the form of an alkaline metal salt or of a tertiary amine of alkyl or heteroaromatic type, at a temperature ranging from 0°C to 100°C (ammonolysis) optionally in the presence of a protic solvent; f) the product is separated precipitating by acidifying the reaction mixture produced in (e) to a pH between 1 and 4, after optional solvent evaporation and relative filtration; g) the product recovered in (f) is crystallized in a protic or aprotic polar solvent. The process of the present invention - which envisages the essential stages of producing an intermediate, i.e. phenol ester (VI), and removing same from the reaction mixture by crystallization - permits to obtain the desired product in high yields and in high purity degree. DETAILED DESCRIPTION OF THE INVENTION The solvent used in stages (a) and (b) of the process of the present invention may be either an aprotic polar solvent, preferably acetone, ethyl acetate, dioxane, tetrahydrofuran, or an aprotic dipolar solvent, such as dimethylformamide. The intermediates obtained in stages (a) and (b) may be either isolated or not: in the latter case the solvent used in stage (a) of the process under the invention is the same as that used in stage (b). The tertiary amines used in stages (a) and (c) to give the bile acid salt and phenol salt, respectively, are preferably selected from triethylamine, tributylamine, and pyridine. The C 1 -C 5 alkyl chloroformate (III) used in (b) is preferably a methyl or an ethyl. The aprotic solvent used in (c) may be an aprotic polar solvent selected from acetone, ethyl acetate, dioxane, tetrahydrofuran, or an aprotic dipolar solvent, i.e. N,N-dimethylformamide. The solvent used to crystallize the phenol ester (VI), stage (d) of the process of the present invention, is a polar solvent, either protic or aprotic, such as a C 1 to C 4 alcohol, or an aprotic polar solvent, as for example acetone and acetic acid esters with C 1 to C 4 alcohols, preferably acetonitrile either alone or mixed with the aforesaid alcohols. The bases used to obtain the glycine salt in stage (e) of the process of the present invention are selected out of: sodium hydroxide, potassium hydroxide, lithium hydroxide, potassium and sodium carbonate or bicarbonate, as well as the tertiary alkyl amines or pyridine preferably used in stage (a) for bile acid salt production. The solvent used in the aforementioned ammonolysis - stage (e) of the process of the present invention - is a polar solvent, such as water either alone or mixed with C 1 to C 4 alcohol. The acid used in stage (f) for conjugated raw acid (I) precipitation is a mineral acid, such as hydrochloric, sulphuric, and phosphoric acids, or an organic acid such as acetic acid. The solvent used in stage (g) of the process of the present invention for the conjugated bile acid (I) crystallization is a protic polar solvent, such as an alcohol, and preferably ethanol, isopropanol, sec-butanol, or an aprotic polar solvent, such as acetone, or C 1 -C 4 alcohol acetates and preferably ethyl acetate. The following examples are reported by way of indication, not of limitation. EXAMPLE 1 Ursodeoxycholic acid (250 g) was suspended in 1000 ml dioxane and treated with 66 g triethylamine. The mixture was stirred at room temperature for 1 hr. After cooling to 10°C, 70 g ethyl chloroformate was added dropwise at a temperature maintained below 20°C. Once the addition was completed, the mixture was stirred at 15°C-20°C for 1 hr, poured into a solution prepared separately by dissolving 150 ml p-hydroxypropiophenone in 500 ml ethyl acetate and 101 g triethylamine and by heating the obtained solution to 35°C-40°C, which temperature was maintained during the dropwise addition and for one or two more hours. The addition of deionized water (1000 ml) gave two phases. The organic phase was washed with 500 ml deionized water and evaporated to a thick oil, which was crystallized with 1500 ml acetonitrile by heating and subsequent cooling to 15°C. The precipitate was separated by filtration and washed thoroughly with acetonitrile. Drying yielded 300 g ursodeoxycholic acid ester with the following characteristics: crystalline white powder m.p. = 88 - 92°C [α] 20 / D = + 41.5° Ammonolysis: 65 g glycine and 34 g sodium hydroxide were dissolved in deionized water. The solution was added with 280 ml secondary butyl alcohol and 300 g phenol ester obtained as described above. The solution was refluxed for 5 hrs, cooled to 30°C. Then the product was precipitated by acidification with phosphoric acid to a pH ranging from 2.5 to 3. After cooling to 15°C, filtering and washing with water and sec-butanol, the moist product was crystallized by hot dissolution with sec-butanol, followed by cooling, filtering and washing with sec-butanol. 260 g glycoursodeoxycholic acid with the following characteristics were obtained: crystalline white powder m.p. = 230 - 233°C [α] 20 / D = + 54.6° (C: 2% in methanol) Titre = 99.82% EXAMPLE 2 The phenol ester was obtained following the same procedure as per Example 1, but using ethyl acetate instead of dioxane as the reaction solvent for mixed anhydride preparation. 310 g phenol ester with the following characteristics was obtained: m.p. = 89 - 92°C [α] 20 / D = + 42.1° Ammonolysis was carried out according to the same procedure as per Example 1. The product was recrystallized by boiling glycoursodeoxycholic acid with ethyl acetate and water, followed by cooling, filtering, washing with water and ethyl acetate, and drying. 265 g glycoursodeoxycholic acid with the following characteristics was obtained: crystalline white powder m.p. = 231.5 - 232.5°C [α] 20 / D = + 55° (C: 2% in methanol) Titre = 99.9% By using the same basic procedure and using the solvents, bases, and chloroformates indicated above, the following glycine-conjugated bile acids were obtained: glycochenodeoxycholic, glycolithocholic, glyco-3α-7β-12α-trihydroxycholanic, glyco-3α-7β-dihydroxy-12-ketocholanic, glycodeoxycholic, glycodehydrocholic, glycohyodeoxycholic, glycohyocholic.

Claims: A process for the preparation of glycine-conjugated bile acids of general formula (I): (I) Y-NH-CH 2 -COOH wherein Y is the acyl radical of a bile acid selected from the group consisting of: ursodeoxycholic, chenodeoxycholic, lithocholic, 3α-7β-12α-tri-hydroxycholanic, 3α-7β-dihydroxy-12-ketocholanic, deoxycholic, dehydrocholic, hyodeoxycholic, hyocholic acids, comprising: a) optionally salifying bile acid of formula (II) (II) Y-OH wherein Y is as defined above, with a tertiary amine of alkyl or heteroaromatic type in an aprotic solvent at a temperature below 20°C; b) treating the reaction mixture containing the aforesaid bile acid salt, or previously isolated salt, with a chloroformate of general formula (III): (III) Cl-COOR where R is selected from the group consisting of C 1 -C 5 alkyl, phenyl, benzyl, at a temperature below 20°C in the presence of an aprotic solvent to give the corresponding mixed anhydride of formula (IV) (IV) Y-O-COOR where Y and R are as defined above; c) reacting the mixed anhydride (IV) with a phenol of general formula (V): where R 1 is selected from H and C 1 -C 5 alkyl, C 2 -C 5 acyl and nitro group, at a temperature below 60°C in the presence of an aprotic solvent and of a tertiary amine to give the corresponding phenol ester of formula (VI): d) separating the product by water addition, phenol ester extraction in a solvent, evaporation and crystallization, followed by an optional recrystallization; e) treating the phenol ester with an aqueous solution of glycine as is or in the form of an alkaline metal salt or of a tertiary amine of an alkyl or heteroaromatic type, at a temperature ranging from 0°C to 100°C optionally in the presence of a protic solvent; f) separating the product, precipitating by acidifying the reaction mixture produced in (e) to a pH between 1 and 4, after optional solvent evaporation and relative filtration; g) the product recovered in (f) is crystallized in a protic or aprotic polar solvent. The process according to claim 1 wherein the aprotic solvent used in stages (a) and (b) is an aprotic polar solvent selected from acetone, ethyl acetate, dioxane, tetrahydrofuran, or an aprotic dipolar solvent, selected from dimethylformamide. The process according to claim 1 wherein the intermediates obtained in (a) and (b) are not isolated. The process according to claim 1 wherein the tertiary amines used in (a) and (c) to give the bile acid salt and phenol salt, respectively, are selected from triethylamine, tributylamine, and pyridine. The process according to claim 1 wherein C 1 -C 5 alkyl chloroformate (III) used in (b) is methyl or ethyl chloroformate. The process according to claim 1 wherein the aprotic solvent used in (c) is an aprotic polar solvent selected from acetone, ethyl acetate, dioxane, tetrahydrofuran, or an aprotic dipolar solvent, such as N,N-dimethylformamide. The process according to claim 1 wherein the phenol ester crystallization solvent, stage d, is a protic or aprotic polar solvent, preferably acetonitrile either alone or mixed with C 1 -C 4 alcohols. The process according to claim 2 wherein the bases used to obtain the glycine salt employed in stage (e) are selected from: sodium hydroxide, potassium hydroxide, lithium hydroxide, potassium or sodium carbonate or bicarbonate, and the tertiary amines are selected from triethylamine, tributylamine, and pyridine. The process according to claim 1 wherein the acid used in stage (f) for conjugated raw acid (I) precipitation is a mineral acid, selected from hydrochloric, sulphuric, and phosphoric acids, or an organic acid such as acetic acid. The process according to claim 1 wherein the solvent used for conjugated bile acid (I) crystallization, stage g, is a protic polar solvent consisting of an alcohol or an aprotic polar solvent consisting of acetone or C 1 -C 4 alcohol acetates.

Inventors: BONALDI ANTONIO, MOLINARI EGIDIO, RODA ALDO, BONALDI, ANTONIO, MOLINARI, EGIDIO, RODA, ALDO
Applicants: ERREGIERRE IND CHIM, ERREGIERRE INDUSTRIA CHIMICA SPA
Application year: 1993
Main classification: C07J41
IPC codes: A61K31, C07J9, A61P1, C07J41