Selective Formation of Oxindole- and Formylkynurenine-Type Products from Tryptophan and Its Peptides Treated with a Superoxide-Generating System in the Presence of Iron(III)-EDTA: A Possible Involvement with Iron-Oxygen Complex

Publisher Website
Google Scholar
Abstract
The oxygenation of tryptophan and its peptides by the superoxide-generating system hypoxanthine/xanthine oxidase in the presence of iron(III) and ethylenediaminetetraacetic acid (EDTA) has been investigated. The reaction of a tryptophan derivative, N-(tert-butoxycarbonyl)-L-tryptophan, with hypoxanthine/xanthine oxidase/Fe(III)-EDTA mainly resulted in the oxygenation of the pyrrole ring of the indole nucleus. 2-[(tert-Butoxycarbonyl)-amino]-3-(3-oxindolyl)propionic acid and N-(tert-butoxycarbonyl)-N'-formylkynurenine were identified as the major products. Similar oxindole- and formylkynurenine-type products were also obtained from the N-(tert-butoxycarbonyl) derivative of the tryptophan-containing peptides Ile-Trp, Trp-Leu, Gly-Trp-Leu, and Ala-Trp-Ile. In all cases, however, hydroxylation products of the benzene ring of the indole nucleus were scarcely detected, leading to the assumption that free hydroxyl radical did not play a role in the tryptophan oxidation of this system. Of interest was the fact that the reaction of N-(tert-butoxycarbonyl)-L-tryptophan with H2O2/horseradish peroxidase mainly afforded the same oxindole- and formylkynurenine-type products as those obtained in the hypoxanthine/xanthine oxidase/Fe(III)-EDTA system. Taken together, iron-oxygen complex-type active species may play a role in the tryptophan oxygenation in a superoxide-generating system in the presence of iron-EDTA.

This publication has 0 references indexed in Scilit: