Asymmetric tritiation of N‐acetyl α‐β dehydrotryptophanamide

Rhodium‐DiPAMP complex catalyzes the stereoselective addition of two tritium atoms on N‐acetyl −α −β dehydrotryptophanamide. The substrate was prepared by dehydrogenation of N‐acetyltryptophanamide with TSO (Tryptophan‐Side Chain oxidase) from Pseudomonas. Tritiated N‐acetyl‐tryptophanamide was obtained with the theoretical specific radioactivity (58 Ci/mmole). The enantiomeric excess of the L‐diasteroisomer reached 94.4 %. 3NMR spectra indicated the selectivity of 3H‐labelling on the Cα – Cβ double bond. This new approach of tritiation by homogeneous catalysis applied to tryptophanyl‐containing peptides is discussed.