Kinetics and Mechanism of the Interaction and Transaldimination of Products of Condensation of Pyridoxal Hydrochloride with L-α-, D-α-, and β-Alanines

Abstract

The kinetics and mechanism of the condensation and transaldimination of products of pyridoxal condensation with L-α-, D-α-, and β-alanines are studied via UV spectroscopy and polarimetry. It is found that pyridoxal hydrochloride interacts stereospecifically with L-α- and D-α-alanines, accompanied by the formation of intermediate products with a strictly defined structure that promote the elimination of hydrogen atoms (with L-α-alanine) or CO₂ (with D-α-alanine) and the subsequent formation of a quinoid structure whose hydrolysis yields the final products. The reactions of transaldimination between pyridoxalidene-β-alanine, pyridoxalidene-L-α-, pyridoxalidene-D-α-alanines, and L-α- and D-α-alanines are studied. It is shown that transaldimination proceeds in two stages: the addition of L-α- and D-α-amino acids to Schiff bases with the formation of N-acetals of a strictly defined structure, and the cleavage of one of the amino acids with the formation of new Schiff bases. Schemes are proposed for the mechanisms of the studied reactions.