Syntheses of substituted L- and D-tryptophans.

Several 5-substituted Nb-methoxycarbonyl-L- and -D-tryptophan derivatives were synthesized from proline by a new route involving electrochemical oxidation, as well as by the known procedures. Removal of the Nb-methoxycarbonyl group was accomplished by treatment with Me3SiI in refluxing chloroform, then alkaline hydrolysis of the methyl esters afforded 5-substituted L- and D-tryptophans with high optical purities.