Natural tyrosinase inhibitors from Betula platyphylla barks

During the process of searching for tyrosinase inhibitors from natural medicines, one new monoterpene rhamnoside (1) and 13 known compounds (2-14) were isolated from the ethanolic extract of Betula platyphylla barks by repeated column chromatography. These structures were identified by comprehensive spectroscopic data analysis such as high-resolution electrospray ionization mass spectra (HR-ESI-MS), nuclear magnetic resonance (NMR), optical rotatory dispersion (ORD) and acid hydrolysis. In vitro assay revealed that compounds 6, 7 and 14 showed obvious inhibitory activity against tyrosinase.