Non-enzymic oxidation of cysteinyldopa catalyzed by metallic ions

Under physiol. conditions, cysteinyldopa (I) behaves similarly to catecholamines, e.g. adrenaline, in forming reversible complexes with various metal cations. As a rule, these complexes are stable under anaerobic conditions, but readily autoxidize in the presence of O to give the 1,4-benzothiazine acid deriv. (II), corresponding to one of the postulated intermediates in the biosynthesis of pheomelanic pigments. Cu2+-catalyzed oxidn. of I proceeds differently to give the red-purple trichochrome F, presumably via decarboxylation and oxidative coupling of the same benzothiazine intermediate. The relevance of these in vitro expts. to the metab. of I is briefly discussed.