Study On The Synthesis And Antifungal Activity Of Novel Benzamides Containing 1-Methyl-1H-Pyrazol-5-ylamine Unit

SDH inhibitors（SDHIs）have been commercialized as an important class of agricultural fungicides with excellent active fragments of pyrazole and benzamide.On the basis of our previous work,a series of novel 1-methyl-pyrazol-5-yl-amino-phenyl-benzamide derivatives featuring benzamide and pyrazole connected by imine bond were designed,synthesized by active fragment splicing strategy to promote the discovery and development of new fungicides.All the synthesized compounds were evaluated for their antifungal activities.The results are as follows:1)A total of 32 novel 1-methyl-pyrazol-5-yl-amino-phenyl-benzamide derivatives were designed and synthesized,and their structures were confirmed by ¹H NMR,¹³C NMR and HRMS（ESI）.2)The antifungal activities of the target compounds were evaluated against 8 plant pathogenetic fungi including Sclerotinia sclerotiorum、Valsa mali、Altenaria alternariae、Curvularialunata boed、Botrytis cinerea、Rhizoctonia solani、Fusarium graminearum、Phytophthora capsica by mycelial growth rate method.The results showed that most of the compounds exhibited good inhibitory activity.Compounds 9,12,13,14,15,20,29,30,32and 36 showed better inhibitory activity against S.s.,but lower than Fluxapyroxad.compounds 13（82.38%）,14（86.72%）,and 20（89.95%）,had an inhibition rate of more than80%on the V.m.,which was better than Fluxapyroxad（86.30%）.The antifungal activity against Altenaria alternariae showed that the inhibition rate of compounds 9,11,12,13,and14 were more than 60%.To further confirm the antifungal activities of the target compounds,the half maximal effective concentration(EC₅₀)values of some compounds were investigated.Compound 14 showed the most excellent antifungal activity against S.s.and V.m.,with EC₅₀value of 11.21 mg/L and 16.70 mg/L.For Valsa mali,compound 14(EC₅₀=11.67 mg/L)were comparable to the positive control Fluxapyroxad(EC₅₀=16.49 mg/L).In general,compounds 14 showed high inhibitory activity against a variety of pathogenic fungi,and could be used as lead compounds for further research.3)The molecular docking experiment was carried out between the compound 14 and SDH protein.The results showed that the pyrazole ring of Fluxapyroxad was deeply embedded in the active pocket.The binding mode is stabilized by different interactions between amino acid residues in the binding site.An conventional hydrogen bonds and a p-πinteraction were formed between the compound 14 and amino acids residue Tyr 58.In addition,Arg 43 amino acid residue forms a p-πinteraction with benzene ring and pyrazole ring,respectively.This is similar to the commercial SDHI Fluxapyroxad,indicating that the target of compound 14 may be SDHI.4)Through the screening of pesticide adjuvant such as solvents and surfactants,the soluble concentrate of compound 14 was successfully developed,and the physical and chemical properties of the preparation conformed to the corresponding standards.The formula is as follows:compound 14,10%;ethanol,30%;dimethyl sulfoxide,15%;emulsifier OP-10,12%;water supplement to 100%.5)The protective and therapeutic effects of compound 14 on S.s.at 50 mg/L were evaluated by in vitro leaf method.It was found that compound 14（71.4%）had the best protection against S.s.at a concentration of 50 mg/L,but lower than the control agent Fluxapyroxad（99.3%）.The protective and therapeutic effects of compounds 14 on S.s.at 100mg/L and 200 mg/L were evaluated by indoor pot experiment.It was found that compound 14had the best protection against S.s.at a concentration of 200 mg/L.In the thesis,a series of novel1-methyl-pyrazol-5-yl-amino-phenyl-benzamide derivatives were designed.Compound 14 was proposed to be a potential SDHI fungicides through biological activity evaluation,which is of great significance for the further development of new succinate dehydrogenase inhibitors.