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Succinate dehydrogenase (SDH) has been demonstrated as a promising target for fungicide discovery. Crystal structure data have indicated that the carboxyl "core" of current SDH inhibitors contributed largely to their binding affinity. Thus, identifying novel carboxyl "core" SDH inhibitors would remarkably improve the biological potency of current SDHI fungicides. Herein, we report the discovery and optimization of novel carboxyl scaffold SDH inhibitor via the integration of in silico library design and a highly specific amide feature-based pharmacophore model. To our delight, a promising SDH inhibitor, A16c (IC = 1.07 μM), with a novel pyrazol-benzoic scaffold was identified, which displayed excellent activity against Rhizoctonia solani (EC = 11.0 μM) and improved potency against Sclerotinia sclerotiorum (EC = 5.5 μM) and Phyricularia grisea (EC = 12.0 μM) in comparison with the positive control thifluzamide, with EC values of 0.09, 33.2, and 33.4 μM, respectively. The results showed that our virtual screening strategy could serve as a powerful tool to accelerate the discovery of novel SDH inhibitors.

The identification of novel succinate dehydrogenase (SDH) inhibitors represents one of the most attractive directions in the field of fungicide research and development. During our continuous efforts to pursue inhibitors belonging to this class, some structurally novel pyrazole-furan carboxamide and pyrazole-pyrrole carboxamide derivatives have been discovered via the introduction of scaffold hopping and bioisosterism to compound 1, a remarkably potent lead obtained by pharmacophore-based virtual screening. As a result of the evaluation against three destructive fungi, including Sclerotinia sclerotiorum, Rhizoctonia solani, and Pyricularia grisea, a majority of them displayed potent fungicidal activities. In particular, compounds 12I-i, 12III-f, and 12III-o exhibited excellent fungicidal activity against S. sclerotiorum and R. solani comparable to that of commercial SDHI thifluzamide and 1.

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