Synthesis of (2R,S)-[2-2H] and [2,3-2H] tryptophan

α-Deuterated tryptophan was prepared either by exchange of the α-hydrogen of tryptophan or by hydrolysis and decarboxylation of ethyl 2-formamido-2-carbethoxy-3-indole propionate, followed by treatment with CH3COO2H. α,β-Dideuterated tryptophan was in turn synthetized from ethyl-α-acetamido-indole-3-acrylate, by catalytic deuteration (2H2/Pd-C) and alkaline hydrolysis (NaO2H/2H2O).