Rapid preparation of tritium-labeled bile acids by enolic exchange on basic alumina containing tritiated water

Abstract

When a 3-keto bile acid methyl ester was chromatographed on basic alumina inactivated with tritiated water, the enolic hydrogen atoms at C-2 and C-4 exchanged with tritium atoms. The 3H-labeled keto ester was reduced with borohydride, and the resultant mixture of 3α- and 3β-hydroxy epimers was resolved by preparative thin-layer chromatography to yield a pure 2,4-3H-labeled bile acid ester. Lithocholic, chenodeoxycholic, deoxycholic, and cholic acids having a specific activity of 1-10 μc/μmole were prepared from their 3-keto derivatives. The tritium label remained intact during alkaline saponification in vitro and enterohepatic cycling in vivo in human subjects

Keywords

• exchange labeling bile acid epimers
• thin-layer chromatography isotope fractionation