Synthesis and bioactivity evaluation of novel urea derivatives of arylpyrazoles

Objective  To explore new active compounds targeting the central nervous system of insects via structural modification of fipronil, and provide practical experience and theoretical guidance for development of new insecticides.

Method  Using fipronil as the primary material, six new urea derivatives of arylpyrazoles (2a–2f) were synthesized through two step reactions according to intermediate derivatization strategy. The structures were identified by MS,¹H NMR and ¹³C NMR. The bioactivities of the target compounds on third instar larvae of Plutella xylostella were evaluated by the leaf immersion method. The toxic effects of these target compounds on central olfactory neurons in P. xylostella were detected by patch clamp technique.

Result  The preliminary bioassay showed that compound 2a had the most toxicity with 6.17 μg·mL^–1 LC₅₀ after 12 hours. Electrophysiological data showed that compounds 2b, 2d, 2e and 2f acted on the neurons in a different manner compared to the parent compounds. The membrane potential of the neurons displayed a transient depolarization, and gradually hyperpolarized accompanying with the inhibition of self-generation activities.

Conclusion  Introducing urea structure to bioactive molecules is a potential strategy to change the way pesticides act on the central nervous system of insects, and provides a guidance for the development of new pesticides.