Melanogenesis inhibitory and free radical scavenging activities of diarylheptanoids and other phenolic compounds from the bark of Acer nikoense.

Melanogenesis inhibitory and free radical scavenging activities of nine cyclic (1-9) and one acyclic diarylheptanoids (10), and two phenolic compounds, (+)-rhododendrol (11) and (+)-catechin (12), isolated from the ethyl acetate-soluble fraction of the MeOH extract of the bark of Acer nikoense MAXIM. (Aceraceae) were examined. Upon evaluation of compounds 1-12 on the melanogenesis in the B16 melanoma cells, two compounds, 2 and 8, exhibited marked inhibitory activity with 55.6% and 46.8% reduction, respectively, of melanin content at 25 microg/ml without inhibition of cell proliferation. In addition, upon an evaluation of eleven compounds, 1-7 and 9-12 against the scavenging activities of free radicals (against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical), compound 12 (IC(50) 9.0 microgM) followed by compounds 1, 3, 4, and 6 (IC(50) 40.2-44.0 microgM) showed potent scavenging activities.