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

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 (1)H NMR, (13)C 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 EC(50) 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 LC(50) 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.