Design, Synthesis, and Insecticidal Activities of Novel Thioether and Oxide Sulfide-containing Diamide Compounds

Background: With the emerging resistance to mainstream insecticides, it is necessary to develop new insecticides to tackle the problem of pest threat. Diamide insecticides are widely studied because of their broad spectrum of activities, high efficiency, and low toxicity. Most thioether and oxide sulfide-containing compounds have a wide range of biological activities in agricultural chemicals. Objective: The main purpose of the study was to explore novel thioether and oxide sulfide-containing diamide compounds possessing outstanding insecticidal activity. Methods: Based on the “active substructure replacing” method by introducing methylthio groups, 29 sulfide-containing diamide compounds were designed and synthesised. The structures of all synthetic compounds were confirmed by 1H-NMR, 13C-NMR and HRMS. Moreover, the biological activities of all the compounds were tested. Results: The preliminary bioassay indicated that most of the new compounds did not exhibit better activity than the reference insecticide cyproflanilide. However, compounds 18a and 23a showed markedly potent activity against Tetranychus cinnabarinus at 100 mg/L, which was better than cyproflanilide since these compounds possessed 2-methyl-4-cyanophenyl, which might be the reason for their better internal absorption in the plant. Conclusion: The structure-activity relationship showed that some compounds were of potential value to be developed as novel insecticides, but the majority of compounds did not show superior insecticidal activity than cyproflanilide.