Hydroxy- or methoxy-substituted benzaldoximes and benzaldehyde-O-alkyloximes as tyrosinase inhibitors

Several benzaldoximes, benzaldehyde-O-ethyloximes, and acetophenonoximes were synthesized and evaluated as tyrosinase inhibitors by an assay based on tyrosinase catalyzed L-DOPA oxidation. Whereas benzaldoxime itself is only a weak inhibitor, its derivatives with one or two hydroxy or methoxy moieties in para and meta positions depress tyrosinase activity. Acetophenonoximes and trisubstituted benzaldoximes show no inhibitory activity. The IC50 of 3,4-dihydroxybenzaldehyde-O-ethyloxime (0.3 +/- 0.1 mu mol L-1) is of the same magnitude as tropolone (0.13 +/- 0.08 mu mol L-1), one of the best tyrosinase inhibitors known so far. (C) 2001 Elsevier Science Ltd. All rights reserved.