Structure-related insect antifeedant and growth regulating activities of some limonoids.

Insect antifeedant and growth-regulating activities of 22 limonoids (both natural and their derivatives) againstSpodoptera litura were studied to understand the structure-related bioactivities of the limonoids. The C-seco limonoids (azadirachtins A, B, D, H, and I) were the most effective compounds as a group, while the intact limonoids (cedrelone and its derivatives) were the least effective. The cyclohexenone A ring and theα-hydroxy enone group in the B ring appear to be important for antifeedant activity. The presence of a cyclohexenone or 1,2-epoxide in the A ring coupled with anα-hydroxy enone in the B ring correlated well with growth regulatory activity. An acetoxy at C-7 instead ofα-hydroxy enone and perhaps the carbonyl at C-16 increase growth regulatory activity. Absence of 14–15 epoxide may not drastically reduce antifeedant activity and growth regulatory activity.