Effect of vanillin and its acid and alcohol derivatives on the diphenolase activity of mushroom tyrosinase

For the first time in the present study the effects of vanillin, vanillyl alcohol, vanillic acid, as well as the newly synthesized vanillin derivative, bis-vanillin, were investigated on the oxidation of dopamine hydrochloride by mushroom tyrosinase. Among them, vanillin and bis-vanillin act as activators, while vanillyl alcohol and vanillic acid exhibited inhibitory effects, the IC50 values being estimated 1.5 and 1.0 mM, respectively. These compounds were mixed inhibitors. The presence of aldehyde and metoxy groups at the meta position of aromatic compounds seems to cause them to react as tyrosinase activators, as observed in the case of vanillin and bis-vanillin. The presence of both groups in bis-vanillin results in a stronger activation effect compared to vanillin. The results indicate that the electron-withdrawing capacity of the functional group at the C-1 position is essential for the inhibitory potency of vanillin derivatives. In comparison with other benzoic acid derivatives, the results obtained in this study suggest that the relative positioning of hydroxy and methoxy groups at meta and para positions plays an important role in the inhibition effects of benzoic acids and their inhibition potency.