SYNTHESES OF HIGH SPECIFIC ACTIVITY 2,3-[H-3](2)-9-CIS-RETINOIC-ACID AND 3,4-[H-3](2)-9-CIS-RETINOIC-ACID

B-cis-Retinoic acid (9-cis-RA) is an endogenous hormone which binds and activates the retinoic acid receptors (RARs) and the retinoic X receptors (RXRs). In order to investigate the function of 9-cis-RA in vitro and in vivo high specific activity labeled 9-cis-RA was prepared. Two tritium labels were efficiently introduced at the 2,3- or 3,4-positions, respectively, in the cyclohexene ring moiety resulting in labeled 9-cis-RA with specific activity of 58-60 Ci/mmol. The critical ring-labeling step relies on a highly regioselective tritiation of either a terminal or an isolated double bond in the presence of the conjugated retinoate side chain. Moreover, the labeling is performed at the penultimate synthetic step resulting in optimization of radiochemical yields and ease of synthesis. This is the first reported synthesis of ring-labeled [H-3](2)-9-cis-RA, and the methodology described herein is applicable to the synthesis of other retinoic acid isomers.