Melanogenesis Inhibitory Activities of Iridoid-, Hemiterpene-, and Fatty Acid-glycosides from the Fruits of Morinda citrifolia (Noni)

A new iridoid glycoside, 9-epi-6 alpha-methoxy geniposidic acid (4), three new hemiterpene glycosides, 3-methylbut-3-enyl 2'-O-(beta-D-glucopyranosyl)-beta-D-glucopyranoside (nonioside K) (6), 3-methylbut-3-enyl 6'-O-(beta-D-xylopyranosyl)-beta-D-glucopyranoside (nonioside L) (8), and 3-methylbut-3-enyl 6'-O-(beta-D-xylofuranosyl)-beta-D-glucopyranoside (nonioside M) (9), and two new saccharide fatty acid esters, 6'-O-(beta-D-glucopyranosyl)-1'-O-[(2 xi)-2-methylbutanoyl]-beta-D-glucopyranose (nonioside N) (16) and 6'-O-(beta-D-xylopyranosyl)-1'-O-[(2 xi)-2-methylbutanoyl]-beta-D-glucopyranose (nonioside O) (17), were isolated from a methanol extract. of the fruits of Morinda citrifolia (noni), along with 11 known compounds, namely, three iridoid glycosides (1-3), two hemiterpene glycosides (5 and 7), and live saccharide fatty acid esters (10-15). Upon evaluation of compounds 1-17 on the melanogenesis in the (316 melanoma cells induced with alpha-melanocyte-stimulating hormone (alpha-MSH), 13 compounds (1, 3, 4, 6-14, and 17) exhibited marked inhibitory effects with 34-49% reduction of melanin content at 100 mu M with no or almost no toxicity to the cells (91-116% of cell viability at 100 mu M).