Tyrosinase inhibitors from paper mulberry (Broussonetia papyrifera)

Fractionation of a chloroform-soluble extract from twigs of Broussonetia papyrifera, led to the isolation of one new compound, 3,5,7,4′-tetrahydroxy-3′-(2-hydroxy-3-methylbut-3-enyl)flavone (1), and 10 known compounds, uralenol (2), quercetin (3), isolicoflavonol (4), papyriflavonol A (5), broussoflavonol F (6), 5,7,3′,5′-tetrahydroxyflavanone (7), luteolin (8), isoliquiritigenin (9), broussochalcone A (10) and 5,7,3′,4′-tetrahydroxy-3-methoxyflavone (11). Their structures were identified by interpretation of MS, 1H NMR, 13C NMR, HMQC and HMBC data. Their inhibitory activities on mushroom tyrosinase using l-tyrosine as substrate were investigated and the IC50 values of 3,5,7,4′-tetrahydroxy-3′-(2-hydroxy-3-methylbut-3-enyl)flavone, uralenol, quercetin and broussoflavonol F were found to be 96.6, 49.5, 57.8, and 82.3 μM, respectively, better than arbutin, a well-known tyrosinase inhibitor.