BIOTRANSFORMATIONS ON STEROID NUCLEUS OF BILE-ACIDS

The bile acids in mammals are all derivatives of 5 beta-cholan-26-oic acid. They represent the major quantitative pathway by which cholester ol is metabolized in the body. This article covers the microbial and e nzymatic transformations of free, saturated bile acids, that kept unal tered the C-24 cyclopentane-perhydrophenantrene nucleus. The bile acid s that have been considered include the primary cholic and chenodeoxyc holic acids, the secondary deoxycholic and lithocholic acids as well a s the relevant dehydrocholic, ursocholic and ursodeoxycholic acids. Am ong the bile acid biotransformations, attention is paid to reactions t hat lead to pharmaceutically significant compounds. This is the case o f 7 alpha-hydroxy epimerization of chenodeoxycholic acid to ursodeoxyc holic acid currently used for cholesterol gallstone dissolution therap y and in the treatment of cholestatic liver diseases. Emphasis has pla ced on reporting reactions that may be of general interest and on the practical aspects of work in the field of biotransformations. (C) 1997 by Elsevier Science Inc.