Oxidation of quinazoline and quinoxaline by xanthine oxidase and aldehyde oxidase

Publisher Website
Google Scholar
Abstract
Quinazoline is oxidized by xanthine oxidase initially (and rapidly) to 4‐hydroxyquinazoline which subsequently is oxidized more slowly to 2,4‐dihydroxyquinazoline. Both oxidative reactions are inhibited strongly by allopurinol. Quinazoline is oxidized by aldehyde oxidase to 4‐hydroxyquinazoline but within a short time (3–5 minutes) the reaction ceases; the proposal that cessation of reaction is due to product inhibition is rendered untenable by our observation that 4‐hydroxyquinazoline is rapidly oxidized by aldehyde oxidase to 2,4‐dihydroxyquinazoline. Preincubation of aldehyde oxidase with quinazoline results in complete inhibition of the ability of the enzyme to oxidize 4‐hydroxyquinazoline and the standard substrateN‐methylnicotinamide. It appears therefore that quinazoline is able to react with aldehyde oxidase and inactivate it. Quinoxaline and 2‐hydroxyquinoxaline are not oxidized by xanthine oxidase but are converted by aldehyde oxidase to 2,3‐dihydroxyquinoxaline; all oxidations mediated by aldehyde oxidase are inhibited completely by menadione.