beta-Decarboxylation of L-aspartic acid: a metal chelate-catalyzed reaction

beta-decarboxylation of L-aspartic acid was observed in the system, pyridoxal: L-aspartic acid:aluminum(III), 1:100:1 when heated at 80 degrees for three hours. This reaction was followed by electronic spectroscopy and showed quantitative conversion of pyridoxal to pyridoxamine indicating decarboxylation of the ketimine. alpha-Methyl-L-aspartic acid was not decarboxylated indicating the presence of the alpha-proton and prior transamination as requirements for decarboxylation. When pyridoxamine and oxalo-2-propionic acid were reacted at pD 4.60, product analysis by nmr showed the presence of pyridoxamine and alpha-ketobutyric acid, indicating hydrolysis of the decarboxylated ketimine. Decarboxylation was fast compared to spontaneous decarboxylation. A mechanism is proposed for non-enzymatic decarboxylation and the previously suggested mechanism for the inactivation of the enzyme aspartate beta-decarboxylase is discussed.