Synthesis of biological precursors of cholic acid.

This paper describes a new and convenient procedure for the synthesis of 5beta-cholestane-3alpha,7alpha,12alpha,24-tetrol (24R and 24 S) and 5beta-cholestane-3alpha,7alpha,12alpha,26-tetrol starting from 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol. Dehydration of the 25-hydroxytetrol with glacial acetic acid and acetic anhydride yielded a mixture of 5beta-cholest-24-ene-3alpha,7alpha,12alpha-triol and the corresponding delta25 compound. Hydroboration and oxidation of the mixture of delta24 and delta25 unsaturated bile alcohols resulted in the formation of 5beta-cholestane-3alpha,7alpha,12alpha,24epsilon-tetrol and 5beta-cholestane-3alpha,7alpha,12alpha,26-tetrol. In addition, smaller amounts of 5beta-cholestane-3alpha,7alpha,12alpha,23epsilon-tetrol and 5beta-cholestane-3alpha,7alpha,12alpha-triol were also obtained. The bile alcohols epimeric at C-24 were resolved by analytical and preparative TLC, characterized by gas-liquid chromatography and mass-spectrometry. Tentatively assignments of the 24R and 24S configuration was made on the basis of molecular rotation differences. These compounds will be useful for biological studies of cholic acid biosynthesis.