Insecticidal chromenes from the Asteraceae: structure-activity relations
1987
Isman, Murray B. | Proksch, Peter | Yan, Jwo-Yee
Chromenes (benzopyrans), common to many genera of the Asteraceae, are lethal to the neonate variegated cutworm, Peridroma saucia Hübner, when presented on the inner walls of glass vials at concentrations of 1.0 μmol/vial or less. Closely related benzofurans, including some from the same plants, are relatively inactive at these concentrations. The most potent of seven naturally-occurring and four derived chromenes is the well known allatocidin, precocene II, with an LD₅₀ of 0.134 μmol/vial or 0.67 μg/cm². A more widely distributed chromene, desmethoxyencecalin, is also relatively toxic with an LD₅₀ of 0.98 μg/cm². Structure-activity comparisons of the chromenes tested in this study suggest that the presence of a free hydroxyl group at either C-7 or C-11 significantly diminishes activity. Saturation of the 3,4 double bond, which destroys the allatocidal activity of the precocenes, diminishes, but does not alleviate, contact toxicity of chromenes to cutworm larvae. Brief exposure (24 h) of 2-day-old larvae to chromene residues significantly inhibits subsequent larval growth. The degree of chronic growth inhibition (sublethal toxicity) from five different chromenes is highly correlated to their lethal potencies to neonate larvae.
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