Process for preparing high purity 3-alpha-7-beta-dihydroxycholanic acid

Abstract: A process for preparing 3-alpha-7-beta-dihydroxycholanic acid from a crude product containing up to 15% by weight of 3-alpha-7-alpha-­ dihydroxycholanic acid and up to 1% by weight of 3-alpha-­ hydroxycholanic acid, by esterifying with methanol, crystallizing from an aromatic solvent and recrystallizing from a mixture of methanol, aromatic solvent and water.

Description: Prior art 3-alpha-7-beta-dihydroxycholanic acid is a product of considerable interest in human therapy, in which it is used for many functions such as solubilizing biliary calculi, reducing the percentage of cholesterol in the blood, reducing glycemia, as a diuretic and as a lipid metabolism accelerator. Various processes are known for preparing 3-alpha-7-beta-dihydroxy-cholmic acid. All these processes have the drawback of producing a mixture of 3-alpha-7-beta-dihydroxycholanic acid and by-products such as 3-alpha-7-alpha-dihydroxycholanic acid and 3-alpha-hydroxycholanic acid, which are difficult to separate. All processes for separating the components of said mixture which have been proposed up to the present time have proved industrially costly and of limited efficiency. Summary of the invention We have now discovered a new process which enables high purity 3-alpha-7-beta-dihydroxycholanic acid to be obtained from a crude product containing up to 15% by weight of 3-alpha-7-alpha-dihydroxycholanic acid and up to 1% by weight of 3-alpha-hydroxycholanic acid. Said process is characterised by: a) esterifying the crude product with methanol in the presence of an acid catalyst; b) crystallizing the obtained 3-alpha-7-beta-dihydroxycholanic methyl ester from a mixture of solvents consisting of the same methanol contained in the reaction mixture coming from step (a), an aromatic solvent and water ; c) recrystallizing the ethylester from a mixture of methanol, aromatic solvent and water; d) subjecting the recrystallized methylester to alkaline hydrolysis in a hydroalcoholic environment to obtain pure 3-alpha-7-beta-dihydroxycholanic acid. Detailed description of the invention The characteristics and advantages of the process for obtaining high purity 3-alpha-7-beta-dihydroxycholanic acid according to the present invention will be more apparent from the following detailed description. The starting product used is a 3-alpha-7-beta-dihydroxycholanic crude acid containing 10-15% by weight of 3-alpha-7-alpha-dihydroxycholanic acid and about 1% by weight of 3-alpha-hydroxycholanic acid, as is obtained by known preparation methods. This product is treated with an excess of methanol in the presence of an acid catalyst at boiling point under reflux for 5-10 hours. The weight ratio of methanol to crude acid is between 1:1 and 10:1. The catalyst used can be sulphuric acid, methanesulphonic acid or paratoluenesulphonic acid in a quantity of between 2% and 4% by weight of the crude product. On termination of treatment the methanol is distilled off until the weight ratio of methanol to crude product is 1:1. A quantity of benzene or toluene or xylene varying from 4 to 6 times the initial crude product is then added, after which an equal quantity of water is added. The mixture is boiled under reflux for 20-40 minutes and then cooled to between 0°C and 5°C to crystallize the pure 3-alpha-7-beta-dihydroxycholanic methyl ester (the esters of the other acids contained in the starting product do not crystallize). The crystallized product is filtered off, washed with an aromatic solvent, redissolved under hot conditions in a mixture of methanol and aromatic solvent, e.g. benzene, toluene or xylene, water is added and the product is recrystallized by cooling to 0°C. The recrystallized product is filtered off and washed with solvent, and then subjected to alkaline hydrolysis by means of a mixture of methanol or other water-soluble alcohol, and 30% sodium hydroxide in water by boiling under reflux for 1-3 hours. The methanol is distilled off, the residue taken up in water, the pH adjusted to 7-8, ethyl acetate is added and the mixture acidified to pH 3, after which the product is crystallized by cooling to between 0°C and 5°C, filtered off and washed firstly with water and then with ethyl acetate. The product is dried at 80°C to obtain 3-alpha-7-beta-dihydroxycholanic acid free of 3-alpha-hydroxycholanic acid and containing less than 0.5% of 3-alpha-7-alpha-dihydroxycholanic acid. The following examples of the preparation of high purity 3-alpha-7-beta-dihydroxycholanic acid are given for the purposes of non-limiting illustration. EXAMPLE 1 100 g of crude 3-alpha-7-beta-dihydroxycholanic acid (containing 15% of 3-alpha-7-alpha-dihydroxycholanic acid and 1% of 3-alpha-hydroxycholanic acid) are treated under boiling conditions with 500 g of methanol and 3 g of sulphuric acid for 6 hours. The methanol is then distilled off until the weight ratio of methanol to crude product is 1:1. The residue is taken up in 500 g of benzene and 500 g of water. The mixture is heated for 30 minutes under reflux and is then cooled to 0°C and filtered, the product then being washed with benzene. The wet product is recrystallized by dissolving it under hot conditions in 100 g of methanol and 500 g of benzene. 500 g of water are then added, the mixture cooled to 0°C and filtered, the product being washed with benzene. The pure ester obtained in this manner is treated with 100 g of methanol and 300 g of 30% sodium hydroxide, heating under reflux for 2 hours. The methanol is finally distilled off, the residue taken up in water, and the pH adjusted to 7-8 with 30% sulphuric acid. 200 g of ethyl acetate are added and the pH adjusted to 3 with 30% sulphuric acid. The mixture is cooled to 0°C and filtered, the product being washed well with water and then with ethyl acetate. It is dried at 80°C to obtain 74 g of pure 3-alpha-7-beta-dihydroxycholanic acid. The 3-alpha-7-alpha-dihydroxycholanic acid content is less than 0.5%. 3-alpha-hydroxycholanic acid is absent. EXAMPLE 2 Example 1 is repeated using toluene instead of benzene. 76 g of product are obtained having the same characteristics as Example 1.

Claims: A process for preparing high purity 3-alpha-7-beta-dihydroxycholanic acid from a crude product containing up to 15% by weight of 3-alpha-7-alpha-dihydrcxycholanic acid and up to 1% by weight of 3-alpha-hydroxycholanic acid, characterised by: a) esterifying the crude product with excess methanol in the presence of an acid catalyst; b) crystallizing the obtained 3-alpha-7-beta-dihydroxycholanic methyl ester ; from a mixture of solvents consisting of the same methanol contained in the reaction mixture coming from step (a), an aromatic solvent and water ; c) recryszallizing the methylester of point b) from a mixture of methanol, aromatic solvent and water; d) subjecting the recrystallized methylester to alkaline hydrolysis in a hydroalcoholic environment to obtain pure 3-alpha-7-beta-dihydroxycholanic acid. A process as claimed in claim 1, characterised in that said esterification is conducted by boiling under reflux. A process as claimed in claim 1, characterised in that the weight ratio of methanol to crude product used in step a) is between 1:1 and 10:1. A process as claimed in claim 1, characterised in that said acid catalyst is sulphuric acid or methanesulphonic acid or paratoluenesulphonic acid. A process as claimed in claim 4, characterised in that said acid is used in a quantity of between 2% and 4% by weight of the crude product. A process as claimed in claim 1, characterised in that said crystallization is conducted in benzene or toluene or xylene in a quantity of between 4 and 6 times that of the crude starting product. A process as claimed in claim 1, characterised in that said recrystallization is conducted in a mixture of methanol and benzene or toluene or xylene and water. A process as claimed in claim 1, characterised in that said alkaline hydrolysis is conducted with a mixture of methanol or other water-soluble alcohol, and 30% sodium hydroxide in water. A process as claimed in claim 1, characterised in that said alkaline hydrolysis is conducted by boiling under reflux for 1-3 hours.

Inventors: BONALDI ANTONIO, MOLINARI EGIDIO, BONALDI, ANTONIO, MOLINARI, EGIDIO
Applicants: ERREGIERRE IND CHIM, ERREGIERRE INDUSTRIA CHIMICA SPA
Application year: 1990
Main classification: C07J9
IPC codes: C07J9