The Oxidative Degradation of L-Ascorbic Acid via an α-Ketoaldehyde *

Abstract

Dehydro-L-ascorbic acid, the oxidation product of L-ascorbic acid, is unstable in aqueous solution and decomposed by a hydrolytic disruption of its ring structure to 2,3-diketo-L-gulonic acid. It is shown by means of UV, 1H-, and 13C-NMR spectroscopy that after decarboxylation 3,4,5-trihydroxy-2-keto-L-valeraldehyde, an a-ketoaldehyde, is formed. This substance is oxidized further to L-erythroascorbic acid, coupled with a reduction of 2,3-diketo-L-gulonic acid to L-ascorbic acid. © 1982, Walter de Gruyter. All rights reserved.