Synthesis, biological activity and toxicity to zebrafish of benzamides substituted with pyrazole-linked 1,2,4-oxadiazole

Abstract

To find pesticidal lead compounds with high activity, a series of novel benzamides substituted with pyrazole-linked 1,2,4-oxadiazole was designed and synthesized by using the splicing principle of active substructures. The chemical structures of the target compounds were confirmed by ¹H NMR, ¹³C NMR and HRMS. The preliminary bioassay showed that most compounds displayed good larvicidal activities against mosquito larvae at 10 mg L⁻¹. In particular, compound 12g exhibited obvious activity; its lethal rate reached up to 100% (at 5 mg L⁻¹) and 55% (at only 2 mg L⁻¹). Furthermore, compound 12f (70.6%) and 12h (100%) showed good fungicidal activities against Pyricularia oryzae, with EC₅₀ values of 8.28 and 5.49 μg mL⁻¹, respectively, which were superior to that of the control drug bixafen (9.15 μg mL⁻¹). Finally, the LC₅₀ of compound 12h to zebrafish embryo was 0.39 mg L⁻¹, so it was classified as a high-toxic compound. Thus, this compound may be used as a potential lead compound for further structural optimisation to develop new compounds with high activity and low toxicity.