Synthesis and Characterization of Copper(II) Complexes of Cysteinyldopa and Benzothiazine Model Ligands Related to Pheomelanin

A new cysteinyldopa model ligand Cydo {3-[(2-aminoethyl)sulfanyl]-4,6-di-tert-butylbenzene-1,2-diol} was prepared and its reactivity
with CuII explored. Under anaerobic conditions, tetranuclear [Cu4(Cydo)4] is isolated, but in the presence of O2, a benzothiazine
intermediate accumulates that is trapped as the CuII complex [Cu(zine)2]. Under slightly different reaction conditions, the benzothiazine further oxidizes to benzothiazole (zole). All three compounds
were characterized by X-ray crystallography, and the reactions
were monitored spectrophotometrically.