Oxidation of pyruvic acid by flavins in the presence of amines

Abstract

Pyruvic acid or other enolizable α-keto acids in the presence of primary or cyclic secondary amines in aprotic polar solvents efficiently reduce flavins and isoalloxazines to their 1,5-dihydro derivatives. The other product of this reaction is the diamide of citraconic acid ( 1). In the absence of flavin, the diamide of methylsuccinic acid ( 2) is obtained as the major product. The specificity for α-keto acid and amine, stoichiometric requirements, rates and quantities of CO 2 evolution, and the kinetics of the reaction were studied. On the basis of these data a mechanism is proposed that involves an enamine condensation followed by decarboxylation and then either reaction with flavin to give ultimately ( 1) and dihydroflavin, or reaction with an additional amine to give ( 2). The possible import of this kind of mechanism in biochemical systems is briefly discussed.