The First 5,6-Dihydroxyindole Tetramer by Oxidation of 5,5',6,6'-Tetrahydroxy- 2,4'-biindolyl and an Unexpected Issue of Positional Reactivity en Route to Eumelanin-Related Polymers

摘要

The first tetramer of the eumetanin precursor 5,6-dihydroxyindole has been obtained, as the acetyl derivative, by peroxidase/H_2O_2-induced oxidative coupling of 5,5',6,6'-tetrahydroxy-2,4'-biindolyl (2) in the presence of Zn(2+) ions. The tetramer, 5,5',5",5''',6,6',6",6'''-octaacetoxy-2,4': 2',3":2",4'''-tetraindolyl (acetylated 7), incorporates an unprecedented 2,3-biindolyl substructure suggestive of a different positional reactivity of the 5,6-dihydroxyindole system when framed into a dimeric scaffold.