Formation of varanic acid, 3α,7α,12α,24-tetrahydroxy-5β-cholestanoic acid from 3α,7α,12α-trihydroxy-5β-cholestanoic acid in Bombina orientalis

摘要

Varanic acid (3α,7α,12α,24-tetrahydroxy-5β-cholestanoic acid; 24-OH-THCA) is almost the sole component of bile acids in the bile of Bombina orientalis. To examine the mechanism of the formation of 24-OH-THCA, radiolabeled (25R)- and (25S)-3α,7α,12α-trihydroxy-5β-cholestanoic acids [(25R)- and (25S)-THCA] and (24E)-3α,7α,12α-trihydroxy-5β-cholest-24-enoic acid (Δ~(24)-THCA) were administered intraperitoneally to B. orientalis, gallbladder bile was collected after 24 h, and bile acids were subsequently extracted. Then the bile acids were analyzed by means of radio thin-layer chromatography and radio high-performance liquid chroma-tography after conversion to p-bromophenacyl ester derivatives. Although Δ~(24)-THCA was not converted to 24-OH-THCA, (25R)-THCA and (25S)-THCA were transformed to (24R,25R)-24-OH-THCA and (24R,25S)-24-OH-THCA, respectively. These results strongly suggest that 24-OH-THCA was transformed via direct hydrox-ylation of the saturated side chain of THCA, not via hydration to an α,β-unsaturated acid, Δ~(24)-THCA, in B. orientalis.