PHOTOCHEMISTRY OF VITAMIN B_6 : (I) PHOTODECOMPOSITION OF PYRIDOXINE (1) OXIDATION OF SIDE CHAINS AT 4- AND 5-POSITION

Abstract

Pyridoxine in a neutral solution was irradiated with an ultraviolet lamp (characteristic wavelength, 2537Å under aerobic and anaerobic conditions, respectively. Photolysis products, detected on paper chromatograms and paper ionophoregrams, were isolated by Dowex-1 (formate form) column chromatography and identified by their spectroscopic behaviors and other characteristics. The sequence of the photolytic route was determined by successive photolysis of the intermediates. Under aerobic conditions, pyridoxine was oxidized through two different pathways : The one is PIN→PAL→4-PiA (4-PiA lactone)→4,5-di-PiA, and the other is PIN→iso-PAL→5-PiA (4-PiA-lactone)→4,5-di-PiA. 4,5-di-PiA was thought to be further decomposed. On the other hand, pyridoxine was converted to its dimer when exposed to light under anaerobic conditions.