Preparation, Antifungal Activity Evaluation, and Mechanistic Studies of Unique and Structurally Novel Pyrazole-Heterocyclic-Amide Analogues

Thirty-six novel pyrazole-heterocyclic-amide analogues were designed, synthesized, and characterized. The bioassay results showed that most target compounds exhibited good fungicidal activities against Rhizoctonia solani, Gibberella zeae, Pseudoperonospora cubensis, Helminthosporium maydis, and Coniothyrium diplodiella at 20 μg/mL. Compounds 6d, 6f, 6l, and 6j possessed better fungicidal activities than the commercial fungicide prochloraz against H. maydis . Their half maximal effective concentration (EC 50 ) values were 0.47, 0.26, 0.58, and 0.69 μg/mL, respectively, and the EC 50 value of prochloraz was 0.77 μg/mL. Furthermore, the inhibitory activities for the bioactive compounds were determined against sterol 14α-demethylase (CYP51), the results displayed that they had prominent activities, compounds 6d, 6f, 6l, and 6j also showed better inhibitory activities than prochloraz against CYP51, their half maximal inhibitory concentration (IC 50 ) values were 0.543, 0.29, 0.77, 0.66, and 0.86 μg/mL, respectively. The results of molecular dynamics simulations exhibited that compound 6f displayed stronger affinity to CYP51 than prochloraz, and estimated Δ G bind values of −44.9 and −37.2 kcal/mol were found for 6f and prochloraz, respectively.