Tocotrienol monomers and dimers from the roots of Litchi chinensis with tyrosinase inhibition activity

Abstract

Four undescribed modified tocotrienols, including two monomers, litchinols A (1) and B (2), and two walsurol dimers, δ,δ-walsurol (3) and γ,δ-bi-O-walsurol (4), as well as seven known compounds (5–11) were isolated from the roots of Litchi chinensis. The structures of the undescribed compounds were elucidated based on analyses of spectroscopic data and ECD spectra. All tocotrienol derivatives (1–6) were evaluated for their tyrosinase inhibition activity. Only monomers 1–2 and 5–6 displayed potent inhibitory activity and greater than kojic acid. Kinetic analysis revealed that the representative compound 2 was uncompetitive inhibitor with the inhibition constant value of 5.70 μM.