Chemical Constituents from Apios americana and Their Inhibitory Activity on Tyrosinase

The goal of this study was to identify phytochemicals with inhibitory activity against tyrosinase. Nine compounds 1–9 were isolated from the tubers of Apios americana. This is the first report of aromadendrin 5-methyl ether (1) being isolated from the Apios species. Among them, compounds 2 and 8 showed inhibitory activity toward tyrosinase. Based on a Dixon plot, the potential K(i) values of competitive inhibitors 2 and 8 were calculated as 10.3 ± 0.8 µM and 44.2 ± 1.7 µM, respectively. An IC(50) value of 13.2 ± 1.0 µM was calculated for the slow-binding inhibitor 2 after preincubation with tyrosinase. Additionally, the predicted binding sites between the receptor and ligand, as well as secondary structure changes, in the presence of 2 were examined by molecular simulation.