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

Description:
This application is a continuation of application Ser. No. 07/483,729 filed on Feb. 23, 1990, now abandoned. 
    
    
     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 percentages 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-dihydroxycholanic 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-beta-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-beta-dihydroxycholanic acid and up to 1% by weight of 3-alpha-7-beta-dihydroxycholanic acid. 
     Said process is characterised by: 
     a) esterifying the crude product with methanol in the presence of an acid catalyst; 
     b) crystallizing the obtaining 3-alpha-7-beta-dihydroxycholanic methyl ester from an aromatic solvent; 
     c) recrystallizing the methylester 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-beta-dihydroxycholanic acid and about 1% by weight of 3-alpha-7-beta-dihydroxycholanic 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 produce 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-dihydroxycholanic 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 being dissolved under hot conditions in 100 g of methanol and 500 g of benzene. 500 g of water are then added, the mixture is cooled to 0° C. and filtered, and the product is washed with benzene. 
     The pure ester obtained in this manner is treated with 100 g of methanol and 300 g of 30% sodium hydroxide, with 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 is adjusted to 3 with 30% sulphuric acid. 
     The mixture is cooled to 0° C. and filtered, and the product is 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-beta-dihydroxycholanic acid content is less than 0.5%. 
     3-alpha-hydroxycholanic acid is absent. 
     EXAMPLE 2 
     Example 1 repeated using toluene instead of benzene. 76 g of product are obtained having the same characteristics as Example 1.