Synthesis and Activity of Novel Pyrazole/Pyrrole Carboxamides Containing a Dinitrogen Six-Membered Heterocyclic as Succinate Dehydrogenase and Ergosterol Biosynthesis Inhibitors against Colletotrichum camelliae

Pyrazole carboxamide derivatives were initially extensively studied as succinate dehydrogenase inhibitors (SDHIs). In the present study, a series of pyrazole/pyrrole carboxamides containing a dinitrogen six-membered heterocyclic were designed based on our reported active skeletons with dual mode of action. Bioactivity results showed that the target compound Q₁₈ demonstrated superior antifungal efficacy against Colletotrichum camelliae (C. camelliae) with an EC₅₀ value of 6.0 mg/L. The in vivo protective activity of Q₁₈ was 74.7% at 100 mg/L. Scanning electron microscopy and transmission electron microscopy showed that Q₁₈ could disrupt the surface morphology of the mycelia and cause lipid peroxidation of cell membrane, which was further verified by the determination of relative conductivity and malondialdehyde contents. Combined with ergosterol content, docking results between Q₁₈ with SDH and CYP51, and the IC₅₀ value of Q₁₈ for SDH (9.7 mg/L), it is concluded that Q₁₈ is a potential SDHI and ergosterol biosynthesis inhibitor. Thus, the present study provides fresh insight into the study of derivatives of the amides.