An improved synthesis of 24-13C-labeled bile acids using formyl esters and a modified lead tetraacetate procedure

An improved synthesis of 24-13C-labeled bile acids has been achieved using formyl derivatives of bile acids and a modified lead tetraacetate procedure. The formylated bile acides were degraded by lead tetraacetate and lithium chloride to formylated 23-chloronorcholanes in 72-83% yield. Formylated 23-chloronorcholanes were converted to nitriles in dimethylformamide, which were then hydrolyzed to obtain C-24 labeled bile acids in yield of 80-90% of labeled sodium cyanide used. This method results in a higher yield and a purer product with less manipulation than previously reported procedures for synthesis of labeled bile acids.