Tyrosinase Inhibitory Effects and Antioxidant Properties of Paeonol and Its Analogues

With the aim to find out structural features for the tyrosinase inhibitory activity, the inhibitory effects of seven paeonol analogues on the diphenolase of mushroom tyrosinase, the interaction between the inhibitors and the copper ions, and the antioxidant activity by DPPH radical were investigated. These paeonol analogues had suggested remarkable inhibition toward tyrosinase. Among them, paeonol (a) exhibited the strongest inhibition activity (IC50 =0.21 mM) as well as showed potent scavenging activity on the DPPH radical. The inhibition kinetics revealed that paeonol (a) was a mixed-type inhibitor, 2'-hydroxy acetophenone (c), 4'-hydroxy acetophenone (d), and 2,4'-dihydroxy acetophenone (e) were competitive inhibitors, while acetophenone (b), 2'-methoxyacetophenone (f), and 4'-methoxy acetophenone (g) behaved as noncompetitive inhibitors. The maximum absorbing wavelengths of compounds (c), (d), and (e) showed different significant blue shifts, which could explain that they exhibited competitive inhibition by forming a chelate with the copper ions at the catalytic domain of the tyrosinase.