Design, Synthesis and Bioactivity of Novel Fluoropyrazole Hydrazides

Laccase is a potential target and has important physiological functions in micro organisms. In order to find compounds with high laccase inhibitory activity, 15 cinnamaldehyde hydrazide derivatives containing difluoromethylpyrazole were designed and synthesized by using the principle of active substructure splicing with 4-chlorocinnamaldehyde thiosemicarbazone (PMDD-5Y) as the lead compound. The structures of the compounds were confirmed by H-1 NMR, C-13 NMR and HRMS. The results of laccase inhibitory activity test showed that all the prepared compounds have good activity, and N'((Z)-3-(3,4-dichlorophenyl)-3-phenylallylidene)-3-(difluoromethyl)-1-methyl-H-1-pyrazole-4-carbohydrazide (5l) and N'-((Z)3-(2-chlorophenyl)-3-(4-chlorophenyl)allylidene)-3-(difluoromethyl)-1-methyl-1H-pyrazole- 4-carbohydrazide (5m) had the half-maximal inhibiting concentration (IC50) values of 0.069 and 0.063 mmol/L, respectively, which were significantly better than that of lead compound PMDD-5Y (IC50=0.553 mmol/L) and positive control cysteine (IC50=0.298 mmol/L). The in vitro bioassay showed that the compounds with good laccase inhibitory activity showed certain fungicidal activity against V. mali, F. graminearum and M. grisea at a concentration of 50 mu g/mL. In vivo trials against M. grisea demonstrated that compound 5l was effective with curative activity of 78.55% at a concentration of 200 mu g/mL, which showed a certain control efficiency in vivo. Further molecular docking study revealed that compound 5l with high laccase inhibitory activity had a good protein binding mode with laccase protein.