Insect antifeedants from tropical plants: structures of dumnin and dumsenin.

Two novel A-seco limonoids, dumnin and dumsenin, were isolated from the methanolic extract of Croton jatrophoides by bioassay-guided fractionation, and the structures were determined by nuclear magnetic resonance, circular dichroism, and mass spectrometry experiments. These compounds showed potent antifeedant activity (PC(50) <or= 2.0 microg/mL) against the larvae of pink bollworm, Pectinophora gossypiella, and/or fall armyworm, Spodoptera frugiperda, providing results comparable to dumsin and zumsin, previously isolated from the same plant.