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■ Cyclic Tautomers of Tryptophans and Tryptamines II. Synthesis of 5-Nitro-, 5-Methoxy-, and 6-Methoxy-tryptophan Derivatives

Tohru Hino,* Mikiko Taniguchi, Akinori Gonsho, and Masako Nakagawa

*Faculty of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Abstract

Nitration of the cyclic tautomer (2b) of N_b-methoxycarbonyl-DL-tryptophan methyl ester with fuming nitric acid followed by treatment with sulfuric acid in methanol gave 5-nitro-N_b-methoxycarbonyl-DL-tryptophan methyl ester (5) in excellent yield. The reaction of 2b with lead tetraacetate in trifluoroacetic acid followed by methylation provided 6-methoxy- (major) and 5-methoxy- (minor) derivatives (7 and 8) which were readily converted to 6- and 5-methoxytryptophan derivatives (10 and 11).