Glycosidic Inhibitors of Melanogenesis from Leaves of Passiflora edulis

A new flavonoid glycoside, chrysin 6‐ C ‐ β ‐rutinoside (chrysin α ‐ L ‐rhamnopyranosyl‐(1→6)‐ C ‐ β ‐glucopyranoside; 2 ), and two new triterpene glycosides, (31 R )‐31‐ O ‐methylpassiflorine ( 7 ) and (31 S )‐31‐ O ‐methylpassiflorine ( 8 ), along with 14 known glycosides, including three flavonoid glycosides, 1, 3 , and 4 , six triterpene glycosides, 5, 6 , and 9 – 12 , three cyano glycosides, 13 – 15 , and two other glycosides, 16 and 17 , were isolated from a MeOH extract of the leaves of Passiflora edulis (passion flower; Passifloraceae). The structures of new compounds were elucidated on the basis of extensive spectroscopic analysis and comparison with literature data. Upon evaluation of compounds 1 – 17 against the melanogenesis in the B16 melanoma cells induced with α ‐melanocyte‐stimulating hormone ( α ‐MSH), three compounds, isoorientin ( 1 ), 2 , and (6 S ,9 R )‐roseoside ( 17 ), exhibited inhibitory effects with 37.3–47.2% reduction of melanin content with no, or almost no, toxicity to the cells (90.8–100.2% cell viability) at 100 μ M . Western blot analysis showed that compound 2 reduced the protein levels of MITF, TRP‐1, and tyrosinase, in a concentration‐dependent manner while exerted almost no influence on the level of TRP‐2, suggesting that this compound inhibits melanogenesis on the α ‐MSH‐stimulated B16 melanoma cells by, at least in part, inhibiting the expression of MITF, followed by decreasing the expression of TRP‐1 and tyrosinase. In addition, compounds 1 – 17 were evaluated for their inhibitory effects against the EpsteinBarr virus early antigen (EBV‐EA) activation induced by 12‐ O ‐tetradecanoylphorbol‐13‐acetate (TPA) in Raji cells.