Intermediate species absorbing in the 500-nm region in Al(III) catalyzed nonenzymatic transamination

Course of the formation of a quinonoid species absorbing in the 500-nm region, which should serve as a model for the key intermediate in reactions catalyzed by pyridoxal phosphate enzymes, was studied in the reaction of pyridoxal, ethyl L-alaninate and Al(III) in methanol by means of UV-visible spectroscopy, chromatography with a multi-UV detector, optical rotation and ¹H-NMR. The species was chromatographically separated in the form of the Al(III) chelate and its quantitative transformation to the aldimine chelate was observed. The formation of the species in the transamination reaction of pyridoxamine, ethyl pyruvate and Al(III) was also studied.