Synthesis and insect antifeedant activity of plumbagin derivatives

Napthaquinones have received considerable interest in agricultural chemistry because of a novel action mode, extremely high activity against a broad spectrum of insects, low acute toxicity to mammals, and environmentally benign characteristics. A series of plumbagin derivatives (3a–3o) were synthesized under mild esterification conditions in straightforward procedure. The structures of all new compounds were confirmed by NMR, IR, MS, and HREIMS analyses. The plumbagin derivatives were screened for their insecticidal activities against tobacco caterpillar (Spodoptera litura) and castor semilooper (Achaea janata) using a no-choice laboratory bioassay. The results show that some of the title compounds exhibit excellent antifeedant activities against 3rd instar larvae of A. janata and S. litura. The improvement in antifeedant activity requires a reasonable combination of substituents in the parent structure, which provides some hints for further investigation on structure modification.