Preparation and Physicochemical Properties of Natural (23R)-3alpha,7alpha,23- and (23R)-3alpha,12alpha,23-Trihydroxylated Bile Acids and Their (23S)-Epimers

By submitting the ketene silyl acetal (5a) generated from 3alpha,7alpha-dihydroxy-5beta-cholan-24-oic acid [chenodeoxycholic acid (la)], to a variety of oxidants, a new efficient route to (23R)- 3alpha,7alpha, 23-trihydroxy-5beta-cholan-24-oic acid [phocaecholic acid, (3a)l and its (23S) -epimer (4a) has been developed. By this route, the first synthesis of 3alpha,12alpha,23-trihydroxy-5beta-cholan-24-oic acid (bitocholic acid) has been achieved and the stereochemistry at C-23 conclusively assigned as R. Aqueous physical chemical properties of (3a) have been studied and compared with those of (la) and 3alpha,7alpha,12alpha-trihydroxy-5beta-cholan-24-oic acid[cholic acid, (Ib)], in order to gain insight into the influence of the hydroxy group at C-23 on the physical properties of bile acids.