Synthesis and structure-bioactivity relationship of cinnamic acid derivatives as insect control agents

Abstract

Fifty substituted cinnamate esters were synthesized by esterification between substituted cinnamic acid and alcohol. Sixty five compounds were evaluated for the insecticidal activity against common cutworms Spodoptera litura (Fabricius) using ethyl cinnamate as a reference compound. The results revealed that ethyl 2-chlorocinnamate and ethyl 4-methylcinnamate showed the most potent activity and three ethyl cinnamates bearing 4-methoxy, 4-hexyloxy and 4-ferfbutyl groups slightly exhibited more activity than a reference compound. While ethyl 4-fluorocinnamate displayed the activity comparable with a reference compound. In addition, two substituted cinnamamides and three substituted benzyl benzoates were synthesized via acid chloride while ethyl 3-phenylpropionate were synthesized by hydrogenation of ethyl cinnamate. Twenty additional compounds were evaluated for the contact toxicity. All compounds exhibited less activity than a reference compound. Moreover, the potent compounds, ethyl cinnamate, ethyl 2-chlorocinnamate and ethyl 4-methylcinnamate, were chosen to evaluate for the antifeedant activity against S. litura. These compounds revealed the activity comparable to a standard compound, rotenone. Furthermore, the SAR and OSAR of cinnamic acid derivatives were studied. For SAR, it could be concluded that ethyl cinnamates bearing electron-donating group showed higher insecticidal activity than those containing electron-withdrawing group. For OSAR, the HOMO-LUMO gap was important descriptor for the insecticidal activity.