Design, synthesis, antifungal activity and molecular docking of novel pyrazole‐4‐carboxamides containing tertiary alcohol and difluoromethyl moiety as potential succinate dehydrogenase inhibitors

Abstract BACKGROUND Resistance problems with the long‐term and frequent use of existing fungicides, and the lack of structure diversity of traditional pyrazole‐4‐carboxamide succinate dehydrogenase inhibitors, it is highly required to design and develop new fungicides to address the resistance issue. RESULTS Different from previous pyrazole‐4‐carboxamide succinate dehydrogenase inhibitors by breaking the norm of difluoromethyl at the C‐3 position of pyrazole and introducing a tertiary alcohol group at the C‐3 position, 27 novel pyrazole‐4‐carboxamide derivatives were designed, synthesized and characterized by proton ( 1 H) nuclear magnetic resonance (NMR), carbon‐13 ( 13 C) NMR, fluorine‐19 ( 19 F) NMR and high‐resolution electrospray ionization mass spectrometry (HR‐ESI‐MS). The crystal structures of compounds A14 and C5 were analyzed by single crystal X‐ray diffraction. Their in vitro antifungal activities were evaluated against phytopathogen Fusarium graminearum , Botrytis cinerea , Phytophthora capsica , Sclerotinia sclerotiorum , Thanatephorus cucumeris . The results displayed that most of them exhibited significant antifungal activities against S . sclerotiorum at 50 mg/L, the half maximal effective concentration (EC 50 ) data of A8 and A14 were 3.96 and 2.52 mg/L, respectively. Their in vivo antifungal activities were evaluated against Pseudoperonospora cubensis , Puccinia sorghi Schw, Colletotrichum gloeosporioides , F . graminearum , Erysiphe graminis , Thanatephorus cucumeris , the control efficacies of A6, B3, C3, and C6 against E . graminis reached 100% at a concentration of 400 mg/L. The molecular docking results showed that the binding mode of the target compounds containing tertiary alcohols were similar to that of fluxapyroxad in succinate dehydrogenase. In addition, tertiary alcohols were involved in the formation of hydrogen bonds. CONCLUSION The excellent in vitro and in vivo inhibitory activities of novel pyrazole‐4‐carboxamide derivatives against succinate dehydrogenase were reported for the first time, and they could be used as the potential lead compounds. © 2023 Society of Chemical Industry.