Studies related to the chemistry of melanins. Part VIII. The pyrrolecarboxylic acids formed by oxidation or hydrolysis of melanins derived from 3,4-dihydroxyphenethylamine or (±)-3,4-dihydroxyphenylalanine

Abstract

Autoxidation or enzymic oxidation of 3,4-dihydroxyphenethylamine yields melanin which, when oxidised by alkaline hydrogen peroxide, gives pyrrole-2,3-dicarboxylic acid and pyrrole-2,3,5-tricarboxylic acid in very low yields. 3,4-Dihydroxy[4-¹⁴C]phenethylamine gives rise, in this way, to the radioactive tricarboxylic acid, suggesting that some units of the polymer may be formed from indole-5,6-quinone units by 2–6 linkage. The above and other pyrrolecarboxylic acids are also formed, not only by oxidation, but also by hydrolysis of both dopamine- and dopa-melanins.