Synthesis of antifeedants for insects: novel behaviour-modifying chemicals from plants.

The need to protect our food supply from predatory insect attack using more ecologically acceptable methods has led to a rapidly growing interest in behavior-modifying chemicals from natural sources. Compounds which deter insects from feeding (antifeedants) are attracting special attention owing to their potential use in integrated pest control management systems. We have been studying the synthesis of plant-derived compounds that display antifeedant properties. The aim of the work is to understand more precisely the feeding mechanisms of insects at a molecular level so as ultimately to be able to design simpler compounds capable of mimicking the activity of the natural products. Our synthetic studies on the sesquiterpenoid antifeedants, polygodial and warburganal, and on the diterpenoid clerodane, ajurgarin I, have shown the promise of this approach. Current effort is directed towards structure-activity studies and synthesis of the extraordinarily potent antifeedant and growth-disrupting agent azadirachtin, isolated from the Neem tree, Azadirachta indica (A. Juss). This work has led to the correct structure assignment for azadirachtin and afforded many compounds for biological evaluation. It is of special significance that incorporation of the hydroxydihydrofuran portion of azadirachtin in a simple model system formed a compound with antifeedant activity comparable to that of the natural product.