Synthesis of [3H]proadifen for studying binding to liver membranes

Tritium‐labelled proadifen (1, SKF 525A, 2‐(N,N‐diethylamino)‐ethyl‐2,2‐di‐diphenylpentanoate hydrochloride), a potent inhibitor of microsomal drug metabolism in the liver, was synthesized by hydrogenation of the corresponding allylic derivative with tritium gas. The specific activity of the compound obtained was 65 Ci/mmol. [3H]Proadifen was found to bind to washed rat liver membranes with high affinity (KD 1.3 nM) and large capacity Bmax 1300 pmol/g wet weight tissue.