7a-OH Epimerization of bile acids via oxido-reduction with Xanthomonas maltophilia.

The microbial 7.-OH epimerisation of cholic, chenodeoxycholic, and 12-ketochenodeoxycholic acids (7.-OH bile acids) with Xanthomonas maltophilia CBS 827.97 to corresponding 7.-OH derivatives with scarcity of oxygen is described. With normal pressure of oxygen the 7-OH oxidation products are obtained. No biotransformations are achieved in anaerobic conditions. The microbial 7.-OH epimerisation is achieved by oxidation of 7-OH function and subsequent reduction. Partial purification, in fact, of the enzymatic fraction revealed the presence of two hydroxysteroid dehydrogenases (HSDH) .- and .-stereospecific together with a glycocholate hydrolase. On the basis of these results a further application is the microbial reduction of 6.-fluoro and 6.-fluoro-3.- hydroxy-7-oxo-5.-cholan-24-oic acid methyl esters to the corresponding 7.-OH and 7.-OH derivatives