Tyrosinase inhibitory effects of 1,3-diphenylpropanes from Broussonetia kazinoki

Abstract

Six 1,3-diphenylpropanes exhibiting inhibitory activities against both the monophenolase and diphenolase actions of tyrosinase were isolated from the methanol (95%) extract of Broussonetia kazinoki. These compounds, 1– 6, were identified as kazinol C ( 1), D ( 2), F ( 3), broussonin C ( 4), kazinol S ( 5) and kazinol T ( 6). The latter two species ( 5 and 6) emerged to be new 1,3-diphenylpropanes which we fully spectroscopically characterized. The IC 50 values of compounds ( 1, 3– 5) for monophenolase inhibition were determined to range between 0.43 and 17.9 μM. Compounds 1 and 3– 5 also inhibited diphenolase significantly with IC 50 values of 22.8, 1.7, 0.57, and 26.9 μM, respectively. All four active tyrosinase inhibitors ( 1, 3– 5) were competitive inhibitors. Interestigly they all mainfested simple reversible slow-binding inhibition against diphenolase. The most potent inhibitor, compound 4 diplayed the following kinetic parameters k 3 = 0.0993 μM −1 min −1, k 4 = 0.0048 min -1, and K i app = 0.0485 μM.