Four limonoids, 1 - 4, five alkaloids, 5 - 9, and four phenolic compounds, 10 - 13, were isolated from a MeOH extract of the bark of Phellodendron amurense (Rutaceae). Among these, compound 13 was new, and its structure was established as rel-(1R,2R,3R)-5-hydroxy-3-(4-hydroxy-3-methoxyphenyl)-6-methoxy-1-(methoxycarbonylmethyl)indane-2-carboxylic acid methyl ester (γ-di(methyl ferulate)) based on the spectrometric analysis. Upon evaluation of compounds 1 - 13 against the melanogenesis in the B16 melanoma cells induced with α-melanocyte-stimulating hormone (α-MSH), four compounds, limonin (1), noroxyhydrastinine (6), haplopine (7), and 4-methoxy-1-methylquinolin-2(1H)-one (8), exhibited potent melanogenesis-inhibitory activities with almost no toxicity to the cells. Western blot analysis revealed that compound 6 inhibited melanogenesis, at least in part, by inhibiting the expression of protein levels of tyrosinase, TRP-1, and TRP-2 in α-MSH-stimulated B16 melanoma cells. In addition, when compounds 1 - 13 were evaluated for their cytotoxic activities against leukemia (HL60), lung (A549), duodenum (AZ521), and breast (SK-BR-3) cancer cell lines, five compounds, berberine (5), 8, canthin-6-one (9), α-di-(methyl ferulate) (12), and 13, exhibited cytotoxicities against one or more cancer cell lines with IC values in the range of 2.6 - 90.0 μm. In particular, compound 5 exhibited strong cytotoxicity against AZ521 (IC 2.6 μm) which was superior to that of the reference cisplatin (IC 9.5 μm).

Nine cyclic diarylheptanoids, 1-9, including two new compounds, i.e., 9-oxoacerogenin A (8) and 9-O-β-D-glucopyranosylacerogenin K (9), along with three acyclic diarylheptanoids, 10-12, and four phenolic compounds, 13-16, were isolated from a MeOH extract of the bark of Acer nikoense (Aceraceae). Acid hydrolysis of 9 yielded acerogenin K (17) and D-glucose. Two of the cyclic diarylheptanoids, acerogenin A (1) and (R)-acerogenin B (5), were converted to their ether and ester derivatives, 18-24 and 27-33, respectively, and to the dehydrated derivatives, 25, 26, 34, and 35. Upon evaluation of compounds 1-16 and 18-35 for their inhibitory activities against melanogenesis in B16 melanoma cells, induced with α-melanocyte-stimulating hormone (α-MSH), eight natural glycosides, i.e., six diarylheptanoid glycosides, 2-4, 6, 9, and 12, and two phenolic glycosides, 15 and 16, exhibited inhibitory activities with 24-61% reduction of melanin content at 100 μM concentration with no or almost no toxicity to the cells (88-106% of cell viability at 100 μM). In addition, when compounds 1-16 and 18-35 were evaluated for cytotoxic activity against human cancer cell lines, two natural acyclic diarylheptanoids, 10 and 11, ten ether and ester derivatives, 18-22 and 27-31, and two dehydrated derivatives, 34 and 35, exhibited potent cytotoxicities against HL60 human leukemia cell line (IC(50) 8.1-19.3 μM), and five compounds, 10, 11, 20, 29, and 30, against CRL1579 human melanoma cell line (IC(50) 10.1-18.4 μM).