Activity-guided fractionations of leaves and stems from Loranthus acutifolius led to the isolation of 2',4',6-trimethoxyflavone (1), 3',4',5-trihydroxy-6,7,8-trimethoxyflavone (2), 2'4'-dihydroxy-6'-methoxy-chalcone (3) and 4',5-dihydroxy-6,7,8-trimethoxyflavone (4). The potential for inhibition against melanin production and tyrosinase activity of these 4 compounds was tested in B16-F10 cells. 2',4',6-trimethoxyflavone, 3',4',5-trihydroxy-6,7,8-trimethoxyflavone, 2'4'-dihydroxy-6'-methoxy-chalcone and 4',5-dihydroxy-6,7,8-trimethoxyflavone showed an inhibitory activity of melanin production with IC50 of 3.6 ± 0.05 μM, 8.1 ± 0.05 μM, 1.6 ± 0.03 μM and 6.5 ± 0.05 μM, respectively. In addition, 2',4',6-trimethoxyflavone, 3',4',5-trihydroxy-6,7,8-trimethoxyflavone, 2'4'-dihydroxy-6'-methoxy-chalcone and 4',5-dihydroxy-6,7,8-trimethoxyflavone were able to inhibit tyrosinase activity with IC50 of 4.0 ± 0.03 μM, 11.3 ± 0.05 μM, 5.7 ± 0.02 μM and 8.6 ± 0.04 μM, respectively. This is the first time that these compounds are reported in the L. acutifolius species showing anti-melanogenic activities.
Keywords: B16-F10 cells; Loranthus acutifolius; Lorathaceae; flavonoids; melanin; tyrosinase.