Structure-activity Relationship for the Insect Antifeedant Activity of Benzofuran Derivatives

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  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 μg (5.4×10^-9 mol)/cm² 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.