Synthesis of alpha,beta-unsaturated C24 bile acids

Synthesis of the alpha,beta-unsaturated analogues of cholic acid, deoxycholic acid, chenodeoxycholic acid, and ursodeoxycholic acid is described. Each common bile acid was converted to the corresponding C22 aldehyde which was then converted to the delta 22 bile acid by Wittig reaction with methyl (triphenylphosphoranylidene)acetate. The synthetic unsaturated bile acids were characterized by thin-layer chromatography, gas-liquid chromatography, and mass spectrometry.