Design, synthesis, and nematicidal activity of novel 1,2,4-oxadiazole derivatives containing amide fragments

Plant-parasitic nematodes are seriously affecting agricultural production worldwide and there are few highly effective and low-risk nematicides to control nematode diseases. In order to discover new nematicides, a series of 1,2,4-oxadiazole derivatives containing amide fragments have been designed and synthesized with the principle of active substructure splicing. The nematicidal activity of the target compounds was evaluated in vitro and it indicated that compound C3 exhibited the most nematicidal activity against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus destructor with the LC₅₀ values of 37.2, 36.6, and 43.4 μg/mL, respectively, which were superior to positive agent tioxazafen. The preliminary mechanism results revealed that compound C3 not only inhibited the reproduction of B. xylophilus populations, but also affected the production of ROS and the accumulation of lipofuscin and lipids. Furthermore, compound C3 showed good inhibition of succinate dehydrogenase (SDH) with the IC₅₀ value of 45.5 µmol/L. Molecular docking indicated that compound C3 had excellent binding to amino acids around the SDH active pocket. This work indicated that 1,2,4-oxadiazole derivative containing amide fragment is a promising template for the discovery of new nematicides and compound C3 can be used as a potential nematicide candidate.