Tyrosinase inhibitors and sesquiterpene diglyclosides 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.