Tyrosinase Inhibitors and Sesquiterpene Diglycosides from Guioa villosa

Through a bioassay-guided phytochemical investigation involving mushroom tyrosinase inhibitory activity, seven farnesyl diglycosides ( 1 - 7), five flavonoids ( 8 - 12), one trimeric proanthocyanidin ( 13), two triterpenes ( 14 and 15), and one cerebroside ( 16), were isolated from the leaves of Caledonian Guioa villosa. Among them, crenulatosides E, F and G ( 1 - 3) were new acyclic sesquiterpene diglycosides. The sesquiterpene diglycosides isolated from the active EtOAc extract showed no inhibitory activity, whereas betulin ( 14), lupeol ( 15) and soyacerebroside I ( 16) demonstrated a potent tyrosinase inhibitory activity.