Natural tyrosinase inhibitors from Betula platyphylla barks

Abstract 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.