Michael K. Manthey

Mchanism of reaction of 3-hydroxyanthranilic acid with molecular oxygen

The autoxidation of the tryptophan metabolite, 3-hydroxyanthranilic acid, at pH 7 gives rise to a p-quinone dimer and cinnabarinic acid. A novel dimer formed by radical-radical coupling of 3-hydroxyanthranilic acid is also produced. Labelling studies have shown that the C-2 oxygen in the p-quinone dimer is derived from molecular oxygen. A product versus time study of this reaction has revealed that, in the absence of catalase, cinnabarinic acid is formed but undergoes decomposition by hydrogen peroxide. At pH 7, in the presence of catalase, both the p-quinone dimer and cinnabarinic acid are formed at approximately the same rate and this rate of formation increases with increasing pH. Inclusion of superoxide dismutase was found to increase the rate of formation of cinnabarinic acid, suggesting that superoxide ions may also cause decomposition of cinnabarinic acid. This was confirmed by treating cinnabarinic acid with superoxide. A mechanism involving a common anthranilyl radical intermediate is proposed to account for the formation of the different oxidation products.

The autoxidation of 3-hydroxyanthranilic acid in the presence of amino acids

Abstract The autoxidation of 3-hydroxyanthranilic acid 1 at pH 11.7 in the presence of the amino acids lysine, glycine and alanine gave p-quinone conjugates. The autoxidation of 1 in the presence of proline gave two rearrangement products arising from Strecker degradation of the initially formed proline conjugate. N-α-t-Boc histidine, arginine and cysteine failed to give amino acid conjugates with oxidized 1.