Synthesis of (22R and 22S)-3 alpha, 7 alpha, 22-trihydroxy-5 beta-cholan-24-oic acids and structure of haemulcholic acid, a unique bile acid isolated from fish bile

Abstract

(22R and 22S)-3 alpha, 7 alpha, 22-trihydroxy-5 beta-cholan-24-oic acids were synthesized, starting from chenodeoxycholic acid, in order to establish the chemical structure of haemulcholic acid, which has been found in certain fish as the major bile component. Oxidative decarboxylation of diformoxylated chenodeoxycholic acid with lead tetraacetate yielded 24-nor-5 beta-chol-22-ene-3 alpha, 7 alpha-diol, which was hydroxylated to form a mixture of (22R and 22S)-24-nor-5 beta-cholane-3 alpha, 7 alpha, 22,23-tetrols. Lead tetraacetate oxidation of the mixture yielded 3 alpha, 7 alpha-dihydroxy-23,24-dinor-5 beta-cholan-22-a1. A Reformatsky reaction of the dihydroxydinorcholanal with bromoacetate resulted in the formation of a mixture of (22R and 22S)-3 alpha, 7 alpha, 22-trihydroxy-5 beta-cholan-24-oic acids. The bile acids epimeric at C-22 were resolved by silica gel column chromatography, and their configurations of C-22 were assigned by a modification of Horeau's method and 13C-nuclear magnetic resonance spectroscopy. By direct comparison with synthetic bile acids, the naturally occurring haemulcholic acid was shown to be (22S)-3 alpha, 7 alpha, 22-trihydroxy-5 beta-cholan-24-oic acid.