A new biflavonoid, amentoflavone-7-O-β-D-glucoside, and thirteen known flavonoids were isolated from the fruits of Juniperus chinensis using a bioactivity-guided method and their tyrosinase inhibitory effects were tested using a mushroom tyrosinase bioassay. Two isolates, hypolaetin-7-O-β-D-glucoside and quercetin-7-O-α-L-rhamnoside, were found to reduce tyrosinase activity at a concentration of 50 μM. Quercetin-7-O-α-L-rhamnoside attenuated cellular tyrosinase activity and melanogenesis in α-MSH plus IBMX-stimulated B16F10 melanoma cells. Molecular docking simulation revealed that quercetin-7-O-α-L-rhamnoside inhibits tyrosinase activity by hydrogen bonding with residues His85, His244, Thr261, and Gly281 of tyrosinase. Abbreviations: EtOH, ethanol; CH2Cl2, dichloromethane; EtOAc, ethylacetate; n-BuOH, n-butanol; MeOH, metanol; CHCl3,chloroform; DMSO, dimethylsulfoxide; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; α-MSH, α-melanocyte stimulating hormone; L-DOPA, L-3, 4-dihydroxyphenylalanine.
Keywords: Juniperus chinensis fruit; amentoflavone-7-O-β-D-glucoside; melanogenesis; quercetin-7-O-α-L-rhamnoside; tyrosinase.