Design, Synthesis and Antifungal/Nematicidal Activity of Novel 1,2,4-Oxadiazole Derivatives Containing Amide Fragments

Plant diseases that are caused by fungi and nematodes have become increasingly serious in recent years. However, there are few pesticide chemicals that can be used for the joint control of fungi and nematodes on the market. To solve this problem, a series of novel 1,2,4-oxadiazole derivatives containing amide fragments were designed and synthesized. Additionally, the bioassays revealed that the compoundF15demonstrated excellent antifungal activity againstSclerotinia sclerotiorum(S. sclerotiorum) in vitro, and the EC50value of that was 2.9 μg/mL, which is comparable with commonly used fungicides thifluzamide and fluopyram. Meanwhile,F15demonstrated excellent curative and protective activity againstS. sclerotiorum-infected cole in vivo. The scanning electron microscopy results showed that the hyphae ofS. sclerotiorumtreated withF15became abnormally collapsed and shriveled, thereby inhibiting the growth of the hyphae. Furthermore,F15exhibited favorable inhibition against the succinate dehydrogenase (SDH) of theS. sclerotiorum(IC50= 12.5 μg/mL), and the combination mode and binding ability between compoundF15and SDH were confirmed by molecular docking. In addition, compoundF11showed excellent nematicidal activity againstMeloidogyne incognitaat 200 μg/mL, the corrected mortality rate was 93.2%, which is higher than that of tioxazafen.Keywords:1,2,4-oxadiazole;antifungal activity;nematicidal activity;succinate dehydrogenase