New oxidation products of tryptophan

Abstract

Oxidation of L- or DL-tryptophan by one molar equivalent of peroxyacetic acid in water at 0-5° gives principally a mixture of 3a- hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid (A) diastereoisomers, while oxidation by two or three equivalents of oxidant gives mainly N?-formylkynurenine (C₁₁H₁₂N₂O₄) and a diastereoisomeric product (B), C₁₁H₁₂N₂O₅, tentatively assigned the structure 2-amino-3-(4-hydroxy-2-oxo-1,4-dihydro-2H-3,1-benzoxazin-4- yl)propionic acid.     Oxidation of (A) by peroxyacetic acid also gives formylkynurenine and (B). Rearrangement of (A) to oxindolylalanine occurs in 12N HCl at 20° or 2N HCl at 80°. (A) is also obtained by reduction of dioxindolylalanine with sodium borohydride. Compound (B) readily undergoes decarboxylation to kynurenine in 0.1N acetic acid at 80°, while in neutral or alkaline solution rapid autoxidation can occur even at room temperature.