10.1016/S0040-4039(00)82888-9
The research investigates the chemical modifications of azadirachtin, a potent insect antifeedant and ecdysis inhibitor derived from the neem tree. The study focuses on the reactions of the C-22,23 enol ether double bond in azadirachtin, aiming to develop high-yielding modifications and understand its structure-activity relationships. The researchers discovered that azadirachtin could be converted to 22,23-dihydro-23-P-methoxyazadirachtin through selective bromomethoxylation and subsequent reduction with tri-n-butyltin hydride. They also found that the acetic acid adduct of azadirachtin, when pyrolyzed, yielded azadirachtin in high yield. The antifeedant effects of the synthesized compounds were evaluated on larvae of two major pest species, Spodoptera littoralis and Heliothis virescens, revealing that compounds with greater steric bulk at C-23 and additional bromine substituents at C-22 exhibited reduced antifeedant activity.