o-Quinone formation in the biochemical oxidation of the antitumor drug N2-methyl-9-hydroxyellipticinium acetate

Abstract
The activation of N2-methyl-9-hydroxyellipticinium acetate (4) by a peroxidase-H2O2 system leads to the formation of an o-quinone (7a). This o-quinone is not directly generated from the starting material but through a quinone imine intermediate (6) which is subsequently oxidized. This reaction is highly dependent on pH values. The o-quinone 7a is easily protonated (7b), gives an addition product with methanol (9), and is reduced by cysteine. The o-quinone 7b has a rather low inhibitory effect against L1210 leukemia cell multiplication but acts as an electron carrier and dramatically augments the oxygen consumption in xanthine oxidase-NADH and rat liver microsome-NADPH systems.