Lipoxygenase inhibitory constituents of the fruits of noni (Morinda citrifolia) collected in Tahiti.

A phytochemical study of the fruits of noni (Morinda citrifolia) collected in Tahiti led to the isolation of two new lignans, (+)-3,4,3',4'-tetrahydroxy-9,7'alpha-epoxylignano-7 alpha,9'-lactone (1) and (+)-3,3'-bisdemethyltanegool (2), as well as seven known compounds, (-)-pinoresinol (3), (-)-3,3'-bisdemethylpinoresinol (4), quercetin (5), kaempferol (6), scopoletin (7), isoscopoletin (8), and vanillin. The structures of 1 and 2 were determined by spectroscopic techniques. Compounds 3, 6, and 8 were isolated for the first time from noni fruit. Compounds 1-8 were shown to inhibit 5- and/or 15-lipoxygenase, with IC50 values ranging from 0.43 to 16.5 microM. Compound 5 exhibited weak inhibitory activity toward cyclooxygenase-2.