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

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 <b>Q</b>_<b>18</b> demonstrated superior antifungal efficacy against <i>Colletotrichum camelliae</i> (<i>C. camelliae</i>) with an EC₅₀ value of 6.0 mg/L. The <i>in vivo</i> protective activity of <b>Q</b>_<b>18</b> was 74.7% at 100 mg/L. Scanning electron microscopy and transmission electron microscopy showed that <b>Q</b>_<b>18</b> 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 <b>Q</b>_<b>18</b> with SDH and CYP51, and the IC₅₀ value of <b>Q</b>_<b>18</b> for SDH (9.7 mg/L), it is concluded that <b>Q</b>_<b>18</b> is a potential SDHI and ergosterol biosynthesis inhibitor. Thus, the present study provides fresh insight into the study of derivatives of the amides.