Three New Cyclic Diarylheptanoids and Other Phenolic Compounds from the Bark of Myrica rubra and Their Melanogenesis Inhibitory and Radical Scavenging Activities

Ten cyclic diarylheptanoids (1-10), including three new compounds: myricanone 5-O-alpha-L-arabinofuranosyl-(1 -> 6)-beta-D-glucopyranoside (7), myricanone 17-O-beta-D-(6'-O-galloyl)-glucopyranoside (8), and 16-methoxy acerogenin B 9-O-beta-D-apiofuranosyl-(1 -> 6)-beta-D-glucopyranoside (10), along with two flavonoids (11, 12), were isolated from the extracts of Myrica rubra (Myricaceae) bark. The structures of new compounds were determined on the basis of spectroscopic methods. On evaluation of compounds 1-12 against the melanogenesis in the B16 melanoma cells, six compounds, 3, 5, 7, 8, 10, and 12, exhibited inhibitory effects with 30-56% reduction of melanin content at 25 mu g/mL with no or very weak toxicity to the cells (82-103% of cell viability at 25 mu g/mL). In addition, upon evaluation of compounds 1-12 against the scavenging activities of free radicals [against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical], seven compounds, 1, 3, 5, 6, 8, 11, and 12, showed potent scavenging activity [IC50 2-21 mu M (0.6-7.3 mu g/mL)].