Discovery of Succinate Dehydrogenase Inhibitors Containing a Diphenylacetylene Fragment as Antifungal Agents

The scaffold hopping strategy of chain extension is widely used in medicines and pesticides, many of which have introduced alkynes to increase rigidity and activity. Therefore, an alkyne molecule is introduced into the biphenyl structure to form alkyne-containing difluoropyrazole derivatives. Most of the compounds had excellent activity in in vitro activity tests against Rhizoctonia solani. The EC50 values of compounds A1, A13, A15, and A18 were 0.0214, 0.0189, 0.0223, and 0.0173 mg/L, respectively, which were similar to fluxapyroxad (EC50 = 0.0237 mg/L). Activity tests in vivo revealed that compound A12 still had 57.1% control against R. solani at 5 mg/L. The inhibition effects of compounds A12 and A16 against succinate dehydrogenase were 3.58 and 2.22 μM, respectively, better than fluxapyroxad (IC50 = 4.24 μM). The mode of action of these compounds was further explored by molecular docking and scanning electron microscopy analysis, and the results were found to be similar to those of fluxapyroxad. These results demonstrate a new concept of introducing alkyne-based chain extension in succinate dehydrogenase inhibitor fungicides.