Agricultural production is seriously threatened by plant
pathogens.
The development of new fungicides with high efficacy and low toxicity
is urgently needed. In this study, a series of pyrazole carboxamide
thiazole derivatives were designed, synthesized, and evaluated for
their antifungal activities against nine plant pathogens in
vitro. Bioassay results showed that most compounds (3i, 5i, 6i, 7i, 9i, 12i, 16i, 19i,
and 23i) exhibited good antifungal activities against Valsa mali. In particular, compounds 6i and 19i exhibited better antifungal activities against Valsa mali with EC50 values of 1.77 and
1.97 mg/L, respectively, than the control drug boscalid (EC50 = 9.19 mg/L). Additionally, compound 23i exhibited excellent inhibitory activity against Rhizoctonia
solani, with an EC50 value of 3.79 mg/L.
Compound 6i at 40 mg/L showed a satisfactory in vivo protective effect against Valsa mali. Scanning electron microscopy analyses revealed that compound 6i could significantly damage the surface morphology to interfere
with the growth of Valsa mali. In molecular
docking, the results showed that compound 6i interacts
with TRP O: 173, SER P: 39, TYR Q: 58, and ARG P: 43 of succinate
dehydrogenase (SDH) through hydrogen bonding and σ–π
interaction, and its binding mode is similar to that of boscalid and SDH. The enzyme activity experiment also further verified its
action mode. Our studies suggested that pyrazole carboxamide thiazole
derivative 6i provided a valuable reference for the further
development of succinate dehydrogenase inhibitors.