Chemical constituents of the fruits of Morinda citrifolia (Noni) and their antioxidant activity

Purification of a n-BuOH-soluble partition of the MeOH extract of Morinda citrifolia (Noni) fruits led to the isolation of two new iridoid glucosides, 6α-hydroxyadoxoside (1) and 6β,7β-epoxy-8-epi-splendoside (2), as well as 17 known compounds, americanin A (3), narcissoside (4), asperuloside, asperulosidic acid, borreriagenin, citrifolinin B epimer a, citrifolinin B epimer b, cytidine, deacetylasperuloside, dehydromethoxygaertneroside, epi-dihydrocornin, D-glucose, D-mannitol, methyl α-D-fructofuranoside, methyl β-D-fructofuranoside, nicotifloroside, and β-sitosterol 3-O-β-D-glucopyranoside. The structures of the new compounds were determined by spectroscopic data interpretation. Compound 4, borreriagenin, cytidine, deacetylasperuloside, dehydromethoxygaertneroside, epi-dihydrocornin, methyl α-D-fructofuranoside, and methyl β-D-fructofuranoside were isolated for the first time from M. citrifolia. The antioxidant activity was evaluated for all isolates in terms of both DPPH and ONOO^- bioassays. The neolignan, americanin A (3), was found to be a potent antioxidant in these assays.