Neolignans, lignans and glycoside from the fruits of Melia toosendan.

Four new neolignans, meliasendanins A-D (1-4), and a new glycoside, toosenoside A (5), together with ten known ones (6-15), were isolated from a n-BuOH partition of the fruits of Melia toosendan. Their structures were elucidated by analyses of extensive spectroscopic data and comparison of the NMR data with those reported previously. Meliasendanin A (1) was a rare neolignan containing isochroman moiety, and its absolute configuration was determined using a CD spectrum. Toosenoside A (5) was an unusual glycoside with a rare naturally occurring aglycone and its structure was confirmed by X-ray single crystal diffraction analysis. The antioxidant activity of the isolated neolignans and lignans was evaluated by ABTS radical-scavenging assay. Compounds 1 and 13 exhibited strong antioxidant activity, with IC₅₀ values of 62.8 and 45.1 μM, respectively.