Cyclic Voltammetry and Chronoamperometry of 1-Methylxanthine: Evidence for an Unstable para-Quinonoid Diimine Intermediate

Abstract

The electrooxidation of the adenosine antagonist 1-methylxanthine has been studied in the pH range 2·5–10·7 at the pyrolytic graphite electrode. The initial 4e, 4H⁺ oxidation step leads to the formation of an unstable diimine, for which the half-life was found to be 1·8 s by chronoamperometry. The diimine is readily attacked by water to give a carbinolamine which decomposes in a pseudo first-order reaction to give, as the major products, 1-methylalloxan at pH 3·0 and 5-hydroxy-5-(methylcarbamoyl)hydantoin at pH 7·0. The oxidation products were identified. The diimine can also be reversibly reduced to the 2,6,8-trioxopurine anion derivative which is also formed by the 2e, 2H⁺ reduction of the carbinolamine. A tentative mechanism for the formation of the products has also been suggested.