Abstract
Fraxinellone, a degraded limonoid, has been mainly isolated from some renewable plants in Meliaceae and Rutaceae. In a continuous effort to discover new natural products-based pesticides, two series of fraxinellone derivatives containing N-phenylpyrazole moiety were designed, synthesized and evaluated for their pesticidal activities against Mythimna separata Walker and Plutella xylostella Linnaeus. Two structures of compounds 7g and 8k were unambiguously determined by X-ray diffraction further. The bioassay showed that over half of the target compounds exhibited better insecticidal activity against M. separata than the precursor fraxinellone. Among all the target compounds, the compounds 7g–i and 8g–j exhibited more potent insecticidal activity than toosendanin, a commercial botanical pesticide. Furthermore, the compound 8g displayed more promising larvicidal activity with the LC50 value of 0.31 μmol mL−1 than the toosendanin against P. xylostella. The structure–activity relationship (SAR) revealed that introduction of polyhalogenated phenylpyrazole ring on furyl-ring of fraxinellone could lead more potent compounds both against M. separata and P. xylostella than that of monohalogenated phenylpyrazole ring or electron-donating groups substituted phenylpyrazole ring.
