Inhibitory effects of 5,6,7-trihydroxyflavones on tyrosinase

Baicalein (1), 6-hydroxyapigenin (6), 6-hydroxygalangin (13) and 6-hydroxy-kaempferol (14), which are naturally occurring flavonoids from a set of 14 hydroxy-flavones tested, exhibited high inhibitory effects on tyrosinase with respect to L-DOPA, while each of the 5,6,7-trihydroxyflavones 1, 6, 13 or 14 acted as a cofactor to monophenolase. Moreover, 6-hydroxykaempferol (14) showed the highest activity and was a competitive inhibitor of tyrosinase compared to L-DOPA. 5,6,7-Trihydroxyflavones 1, 6, 13 or 14 showed also high antioxidant activities. Hence, we conclude that the 5,6,7-trihydroxy-flavones are useful as good depigmentation agents with inhibitory effects in addition to their antioxidant properties.