Isolation of tyrosinase and melanogenesis inhibitory flavonoids from Juniperus chinensis fruits

A new biflavonoid, amentoflavone-7-O-ss-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-ss-D-glucoside and quercetin-7-O-alpha-L-rhamnoside, were found to reduce tyrosinase activity at a concentration of 50 mu M. Quercetin-7-O-alpha-L-rhamnoside attenuated cellular tyrosinase activity and melanogenesis in alpha-MSH plus IBMX-stimulated B16F10 melanoma cells. Molecular docking simulation revealed that quercetin-7-O-alpha-L-rhamnoside inhibits tyrosinase activity by hydrogen bonding with residues His85, His244, Thr261, and Gly281 of tyrosinase.