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) against Spodoptera 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 the alpha-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 an alpha-hydroxy enone in the B ring correlated well with growth regulatory activity. An acetoxy at C-7 instead of or-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.