Potential Succinate Dehydrogenase Inhibitors Bearing a Novel Pyrazole-4-sulfonohydrazide Scaffold: Molecular Design, Antifungal Evaluation, and Action Mechanism

Aiming to develop novel antifungalagents with a distinctivemolecularscaffold targeting succinate dehydrogenase (SDH), 24 N '-phenyl-1H-pyrazole-4-sulfonohydrazide derivativeswere first devised, synthesized, and verified by H-1 NMR, C-13 NMR, high-resolution mass spectrometry (HRMS), and single-crystalX-ray diffraction analysis. The bioassays revealed that the targetcompounds possessed highly efficient and broad-spectrum antifungalactivities against four tested plant pathogenic fungi Rhizoctonia solani (R. solani), Botrytis cinerea, Fusarium graminearum, and Alternaria sonali. Strikingly,compound B6 was assessed as the selective inhibitor against R. solani, with an in vitro EC50 value (0.23 mu g/mL) that was similar to that of thifluzamide(0.20 mu g/mL). The in vivo preventative effectof compound B6 (75.76%) at 200 mu g/mL against R. solani was roughly comparable to thifluzamide(84.31%) under the same conditions. The exploration of morphologicalobservations indicated that compound B6 could stronglydamage the mycelium morphology, obviously increase the permeabilityof the cell membrane, and dramatically increase the number of mitochondria.Compound B6 also significantly inhibited SDH enzyme activitywith an IC50 value of 0.28 mu g/mL, and its fluorescencequenching dynamic curves were similar to that of thifluzamide. Moleculardocking and molecular dynamics simulations demonstrated that compound B6 could strongly interact with similar residues around theSDH active pocket as thifluzamide. The present study revealed thatthe novel N '-phenyl-1H-pyrazolepyrazole-4-sulfonohydrazide derivatives are worthy of being furtherinvestigated as the promising replacements of traditional carboxamidederivatives targeting SDH of fungi.