Tyrosinase inhibitors from crude drugs.

Various crude drugs were examined for their tyrosinase inhibitory activity. Marked activity was observed in Chouji and Yakuchi extracts and the active substances in these extracts were identified as eugenol and yakuchinone A, respectively. Other vanillyl compounds such as ferulic acid, curcumin and yakuchinone B also had higher activities than eugenol or yakuchinone A and inhibited the enzyme competitively. The presence of the hydroxyl group at the 4 position of the aromatic ring of the cinnamoyl moiety and the alpha,beta-unsaturated carbonyl conjugated with an aromatic ring in these substances may play important roles in the competitive inhibition of tyrosinase.