Characterization of a New Flavone and Tyrosinase Inhibition Constituents from the Twigs of Morus alba L.

The twigs of Morus alba L. were found to show strong tyrosinase inhibition activity, and the responsible active components in the extract were further investigated in this study. A flavone, named morusone (1), and sixteen known compounds 2–17 were isolated from M. alba twigs and their structures were identified by interpretation of the corresponding ESI-MS and NMR spectral data. In the tyrosinase inhibitory test, the compounds steppogenin (IC(50) 0.98 ± 0.01 µM), 2,4,2′,4′-tetrahydroxychalcone (IC(50) 0.07 ± 0.02 µM), morachalcone A (IC(50) 0.08 ± 0.02 µM), oxyresveratrol (IC(50) 0.10 ± 0.01 µM), and moracin M (8.00 ± 0.22 µM) exhibited significant tyrosinase inhibition activities, much stronger than that of the positive control kojic acid. These results suggest that M. alba twig extract should served as a good source of natural tyrosinase inhibitors for use in foods as antibrowning agents or in cosmetics as skin-whitening agents.