Facile oxidative decarboxylation of 3,4-dihydroxyphenylacetic acid catalyzed by copper and manganese ions.
Under physiological conditions, we observed the rapid, pH- and temperature-dependent, oxidative decarboxylation and hydration of 3,4-dihydroxyphenylacetic acid (DOPAC) to form 3,4-dihydroxybenzyl alcohol (DBAlc). This product was oxidized and underwent tautomerization to form 3,4-dihydroxybenzaldehyde (DBAld). This reaction did not occur in the presence of EDTA, was catalyzed by copper (CuI, CuII) and manganese (MnII) and was oxygen dependent. A variety of mono- and dihydroxyphenyl carboxylic acids were tested and the reaction producing DBAlc as an intermediate was observed to be unique to DOPAC. 3.4-Dihydroxymandelic acid (DOMA) was rapidly oxidatively decarboxylated to form DBAld directly. The substrate and catalyst selectivity of this reaction suggest that this may have physiological relevance in the neurotoxic consequences of manganese and copper to the dopaminergic system in man.