Syntheses with stable isotopes: Synthesis of deuterium and 13C labeled bile acids

A series of 5β‐cholanic acids labeled with deuterium in the A ring were prepared by exchange labeling of the corresponding ketone by column chromatography on deuterated alumina. Factors affecting yield and labeling efficiency are discussed. 5β‐Cholanic acids labeled with 13C in the carboxyl position were prepared by treatment of the corresponding 23‐chloro‐24‐norcholane with sodium cyanide‐13C followed by alkaline hydrolysis of the nitrile. The intermediates in the synthesis were characterized by high resolution NMR spectroscopy. Mass spectra are also reported for the 13C labeled products.