Electrochemical and enzymatic oxidation of tryptophan and 7-methyluric acid ; and, spectroelectrochemical search for a tertiary alcohol intermediate in the electrochemical oxidation of uric acid /

Abstract

Part III describes the spectroelectrochemical evidence for the tertiary-alcohol intermediate formation during the electrochemical oxidation of uric acid. Electrochemical reduction of the tertiary-alcohol intermediate in low and high concentration of phosphate in pH range 3.0-9.5 and the partial regeneration of uric acid have been described in detail.

Linear sweep and cyclic voltammetry, thin-layer spectroelectrochemistry, kinetic data, controlled potential coulometry, electrochemical and enzymatic oxidation of 7-methyluric acid have been described in Part II. 4-methyl-allantoin, 4-methyl-5-hydroxyhydatoin-5-carboxamide, 1-methyl-2,5-diketo-4-imino-imidazole and N'(1)-amido-N(3)-N-methylamido-urea have been identified by U.V., GC and GC-MS and mechanistic pathways have been presented.

Electrochemical and enzymatic oxidation of biologically significant nitrogen heterocyclic compounds such as tryptophan, 7-methyluric acid and uric acid have been reported in Part I, II and III of this dissertation, respectively. In part I detailed electrochemical studies such as linear sweep and cyclic voltammetry, controlled potential coulometry, thin-layer spectroelectrochemistry and electrochemical and enzymatic oxidation results, the separation of the products, product identification by U.V. spectra, HPLC, GC-MS and mechanistic pathway have been presented for tryptophan oxidation. In summary, the electrochemical oxidation of tryptophan at graphite electrodes is an irreversible two electron process which gives an extremely reactive methylene-imine intermediate. This intermediate is attacked by nucleophiles present in the reaction solution to give two more intermediates which can be detected by thin-layer spectroelectrochemistry and cyclic voltammetry. Further chemical and/or electrochemical reactions of these intermediates lead to formation of two stereoisomers of 2-carboxy-3a-hydroxy-1,2,3,3a, 8,8a-hexahydropyrrolo-(2,3b)-indole, oxindolylalanine, dioxindolylalanine and kynurenine.