Melanin biosynthesis inhibitors from wood of artocarpus heterophyllus: The effect of isoprenoid substituent of flavone with 4-substituted resorcinol moiety at B Ring

In our efforts to find new whitening agent from natural resources, we focused on wood of Artocarpus heterophyllus which shows anti-melanogenesis activity. By activity-guided fractionation of A. heterophyllus wood extract, norartocarpetin (1) and artocarpesin (2) were isolated. These compounds have 4-substituted resorcinol moiety in B ring, which is an important substructure for revealing the tyrosinase inhibitory activity. Also, the effect of albanin A (3) which has 4-substituted resorcinol moiety at B ring with prenyl substituent at C-3 position, was examined for comparison. The IC₅₀ values of mushroom tyrosinase inhibitory activity of norartocarpetin (1), artocarpesin (2) and albanin A (3) were 1.7, 8.5 and 463 μM, respectively. In melanin formation inhibition on B16 melanoma cells, the IC₅₀ of these compounds (1-3) were 209.1, 45.1 and 40.1 μM, respectively. The roles of each substructure of flavones having 4-substituted resorcinol moiety with or without prenyl substituent on tyrosinase and melanin biosynthesis in B16 melanoma cells were discussed.