ELECTROCHEMICAL REDUCTION OF THE FINAL PRODUCT OF VITAMIN-B-6 CATABOLISM, A SPECTROSCOPIC CHARACTERIZATION OF THE REDUCED PRODUCTS OF 6-PYRIDOXIC ACID

Electroreduction of 4-pyridoxic acid (PA), the final product of vitami n B-6 catabolism, is investigated at neutral pH. The course of the exh austive electrolysis is monitored by cyclic voltammetry and W-visible spectroscopy. The electroreduction corresponds to an exchange of four electrons per reagent molecule. The isolation and identification of th e reduction products are achieved by column chromatography, H-1-NMR an d mass spectrometries. A mixture of two different 2-methyl-3-hydroxy-p yridine derivatives (ratio 2:1) is formed during the electroreduction. The absorption and emission properties of these products match those of other derivatives bearing the basic ring and substituents. The resu lts strongly support an electroreduction involving hemiacetal ring cle avage in place of aldehyde group as an intermediate step in the four e lectron process. This means a significant difference with other activa ted monocarboxylic acids and may involve no formation of pyridoxal ald ehyde and pyridoxine. The formation of pyridoxal hydrate from PA by a two-electron transfer and its further transformation into hemiacetal s eems to play an essential role at the electrode surface.