Structure-activity relationship for the insect antifeedant activity of benzofuran derivatives

Coumaran (2,3-dihydrobenzofuran), a secondary metabolite of Cyperus nipponicus, inhibits the feeding of polyphagous insects. This secondary metabolite is regarded as one of the defensive systems of the Cyperaceae. A number of naturally occurring benzofurans that differ in their substitution pattern and oxidation state have been investigated for their ability to inhibit insect feeding by a bioassay with the common cutworm (Spodoptera litura F. Noctuidae) that applies the leaf disk method. The evaluation of the antifeedant activity of each test compound used the ED50 value based on the dose-response curve that was calculated with the probit method. The 2,3-dihydrobenzofuran derivative, 7-acetyl-4,6-dimethoxy-2-isopropenyl-2,3-dihydrobenzofuran, had an ED50 value of 1.3 mu g (5.4 x 10(-9) mol)/cm(2) against the common cutworm. The introduction of methoxy and acetyl groups increased the insect antifeedant activity. Furthermore, the insect antifeedant activity increased with decreasing lipophilicity of the test compounds.