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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

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journal contribution
posted on 29.03.2007, 00:00 by Lucia Panzella, Alessandro Pezzella, Alessandra Napolitano, Marco d'Ischia
The first tetramer of the eumelanin precursor 5,6-dihydroxyindole has been obtained, as the acetyl derivative, by peroxidase/H2O2-induced oxidative coupling of 5,5‘,6,6‘-tetrahydroxy-2,4‘-biindolyl (2) in the presence of Zn2+ 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.