Prenylated flavonoids from Artocarpus altilis: antioxidant activities and inhibitory effects on melanin production.

Flavonoids, 10-oxoartogomezianone (1), 8-geranyl-3-(hydroxyprenyl)isoetin (2), hydroxyartoflavone A (3), isocycloartobiloxanthone (4), and furanocyclocommunin (5), together with 12 known compounds, were isolated from heartwood and cortex of Artocarpus altilis, and their structures were identified by comparing their spectra with those of similar compounds. To identify natural antioxidants and whitening agents, the ability of these prenylated flavonoids was assessed to scavenge the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(+·)) radical cation, and the superoxide anion (O2(-·)), and their abilities to inhibit tyrosinase and melanin production. It was found that compounds 3, 4, and artoflavone A (15) had moderate DPPH(·)-scavenging activity, whereas compound 4 exhibited significant ABTS(+·)-scavenging activity, and that norartocarpetin (7) and artogomezianone (8) exhibited moderate ABTS(+·)-scavenging activity, with compounds 2, 7, and artocarpin (6) displaying good superoxide anion-scavenging activity. In addition, compounds 7, 8, cudraflavone A (14), and artonin M (17), inhibited melanin production by strongly suppressing tyrosinase activity. Compound 6 reduced the melanin content without inhibiting tyrosinase activity. These results suggest that flavonoids isolated from A. altilis may be candidate antioxidants and/or skin-whitening agents. However, further investigations are required to determine their mechanisms of action.