Discovery of highly efficient novel antifungal leads targeting succinate dehydrogenase: pyrazole-4-carboxamide derivatives with an N-phenyl substituted amide fragment

Authors: SUN, XIN-PENG - Zhejiang University Of Technology; YU, CHENG-SHENG - Zhejiang University Of Technology; LI-JING, MIN - Huzhou University; Cantrell, Charles; HUA, XUE-WEN - Liaocheng University; SUN, NA-BO - Zhejiang University; LIU, XING-HAI - Zhejiang University Of Technology

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2023
Publication Date: 11/29/2023
Citation: Sun, X., Yu, C., Li-Jing, M., Cantrell, C.L., Hua, X., Sun, N., Liu, X. 2023. Discovery of highly efficient novel antifungal leads targeting succinate dehydrogenase: pyrazole-4-carboxamide derivatives with an N-phenyl substituted amide fragment. Journal of Agricultural and Food Chemistry. 71:19312-19323. https://doi.org/10.1021/acs.jafc.3c04842.
DOI: https://doi.org/10.1021/acs.jafc.3c04842

Interpretive Summary: Phytopathogenic fungi are causing substantial harm to grain crops, resulting in diminished yield, compromised quality, and ultimately posing a threat to human health. Currently, the use of fungicides is the most common method of plant protection. Succinate dehydrogenase (SDH), also known as succinate ubiquinone oxidoreductase (SQR) or mitochondrial complex II, is an ideal target for studying new fungicides. In this study, in order to discover new compounds as succinate dehydrogenase inhibitor (SDHI) fungicides, pydiflumetofen was selected as the lead compound. A series of novel pyrazole-4-carboxamide derivatives containing N-phenyl substituted amide fragments were designed and synthesized. The antifungal activity of these target compounds was detected and is reported here for the first time.

Technical Abstract: Developing environmentally-friendly fungicides are crucial to tackle the issue of rising pesticide resistance. In this study, a series of novel pyrazole-4-carboxamide derivatives containing N-phenyl substituted amide fragments were designed and synthesized. The structures of target compounds were confirmed by 1H NMR, 13C NMR and HRMS, and the crystal structure of most active compound N-(1-(4-(4-(tert-butyl)benzamido)phenyl)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide (U22) was further determined by X-ray single-crystal diffraction. The bioassay results indicated that the twenty six target compounds possessed good in vitro antifungal activity against Sclerotinia sclerotiorum with EC50 values for compounds U12, U13, U15, U16, U18, U22 and U23 were 4.17±0.46, 8.04±0.71, 7.01±0.71, 12.77±1.00, 8.11±0.70, 0.94±0.11 and 9.48±0.83 µg·mL-1, respectively. Furthermore, in vivo antifungal activity results against S. sclerotiorum indicated that compounds U12 (80.6%) and U22 (89.9%) possessed excellent preventative efficacy at 200 µg·mL-1. Scanning electron microscopy and transmission electron microscopy studies found that compound U22 could destroy hyphal morphology and damage mitochondria, cell membranes and vacuoles. The results of molecular docking of compound U22 and pydiflumetofen with succinate dehydrogenase (SDH) indicated they interact well with the active site of SDH. Structure–activity relationships are also discussed. This study validated our approach and design strategy to produce compounds with enhanced biological activity as compared to parent structure.