Antioxidative properties of nitroxyl radicals and hydroxyamines in reactions with triplet and deaminated kynurenine

The reactions of triplet kynurenine and 4-(2-aminophenyl)-4-oxocrotonic acid, formed upon the thermal decomposition of kynurenine, with nitroxyl radicals and cyclic N-hydroxylamines were studied. Nitroxyl radicals were found to quench efficiently the triplet state of kynurenine (rate constant 3-6 center dot.10(8) L mol(-1) s(-1)). The quenching proceeds via the spin-exchange mechanism and affords no new products. Neither nitroxyl radicals, nor hydroxyl-lamines react with 4-(2-aminophenyl)-4-oxocrotonic acid under conditions similar to physiological.