The coli-tryptophan-indole reaction

Abstract

The action of tryptophanase on a large number of new tryptophan derivatives in which the alanine side-chain was systematically modified was studied. The following derivatives were tested: (CO2H group modified) Z-tryptophan methyl ester hydrochloride, -[alpha]-amino-[beta]-3-indolylpropion-amide; (NH2 group modified) the phenylurethane, p-nitro-benzoyl-, and N-methylene derivatives of l-tryptophan, methyl l-[alpha]-methylamino-[beta]-3-indolylpropionate hydriodide, r-[alpha]-methylamino-[beta]-3-indolylpropionic acid, methyl-[beta]-dime-thylamino-[beta]-3-indolylpropionate methiodide: (whole side-chain modified but still containing groups of the type NIL. or NHR) [beta]-3-indolylethylamine, 3-indolylacetamide, 3-in-dolealdehyde semicarbazone, 3-indolylglyoxylamide and, finally r-3-indolylglycine, the next lower homologue of tryptophan. With the exception of Z-tryptophan methyl ester hydrochloride and l-tryptophan amide, none of these derivatives gave rise to indole production in the presence of the enzyme system. The indole production from the methyl ester hydrochloride followed a preliminary hydrolysis of the ester to tryptophan, that from the amide and enzymatic deamidisation to tryptophan. The results suggest that the breakdown to indole required, inter alia, the following structural features: a free carboxyl group; an unsubsti-tuted [alpha]-amino group; and a [beta]-carbon atom capable of oxi-dative attack. A tentative mechanism for the breakdown was suggested.