Synthesis And Fungalcidal Activity Of N-Cyclopropyl Pyrimidine-5-carboxamides

Pyrimidine derivatives and amide derivatives play an important role in the application of fungicides due to their unique mode of action and high biological activity.The fungicides developed in the past usually contain heterocyclic structures.As one of the representatives of nitrogen-containing heterocyclic rings,the pyrimidine ring has always been a hot spot in the creation and development of new drugs.The amide bond is usually used as a bridge connecting the heterocycle and the rest of the drug molecule,and it has excellent activity and occupies a place in the field of fungicides.Among the commercially available succinate dehydrogenase inhibitors（SDHI）,nitrogen-containing heterocycles and amide bonds have become their representative active structures.With the long-term use of traditional fungicides,the accumulation of fungal resistance has become increasingly serious,and a new generation of fungicides with novel structures,high efficiency,low toxicity,and environmental friendliness needs to be developed.1.In this study,using the methods of molecular rational design and substructure active splicing,designed and synthesized 24 substituted pyrimidine formamide compounds containing N-cyclopropyl by replacing the acid part of succinate dehydrogenase fungicides with pyrimidine ring and modifying the amide bond with cyclopropyl group,including N-（substituted benzyl）-N-cyclopropyl-4-methylpyrimidine-5-carboxamides（Ⅰ_a-Ⅰ_g）,N-（substituted benzyl）-N-cyclopropyl-4-methyl-2-（methylthio）pyrimidine-5-carboxamides（Ⅱ_a-Ⅱ_g）and N-（substituted benzyl）-N-cyclopropyl-4-（difluoromethyl）pyrimidine-5-carboxamides（Ⅲ_a-Ⅲ_j）.Substituted ethyl acetoacetate,triethyl orthoformate and formamidine acetate（or S-methylisothiourea sulfate）were used as raw materials to produce substituted pyrimidine-5-carboxylic acid ethyl ester after condensation cyclization reaction,which was hydrolyzed to obtain substituted pyrimidine-5-carboxylic acid;Taking substituted benzaldehyde and Cyclopropylamine as raw materials,cyclopropyl（substituted phenylmethylidene）amine was formed after condensation reaction.After reducing the double bond with sodium borohydride,substituted benzyl Cyclopropylamine was obtained;The prepared substituted pyrimidine-5-carboxylic acid can be condensed with substituted benzyl Cyclopropylamine to prepare the target compound.2.The structure of the target compound was confirmed by IR,~1H NMR,¹³C NMR and HRMS,and the spectra of the target compound were analyzed in detail.3.Using Sclerotinia sclerotiorum,Botrytis cinerea,Fusarium graminearum,Phytophthora sojae as the test strains,and Boscalid as the control,the mycelial growth rate method was used to determine the target compounds at 50μg/mL and 100μg/mL separately in vitro fungalcidal activity.4.The results of fungalcidal activity test showed that the 24 target compounds synthesized had certain activities.Among them,the compound Ⅰ_e（R₁=CH₃,R₂=SCH₃,R=3,4-di Cl）has higher antifungal activity.The inhibition rates of Sclerotinia sclerotiorum,Botrytis cinerea,Fusarium graminearum,Phytophthora sojae at 100μg/mL are 57.99%,48.50%,51.07%and 40.44%respectively.Through the structure-activity relationship analysis,it was found that the fungalcidal effect of the target compound with electron withdrawing group substitution on the benzene ring was better than that without electron donating group substitution on the benzene ring,while the change of substituent on the pyrimidine ring had no obvious effect on the fungalcidal activity.5.Molecular docking was carried out between compound Ⅰ_ewith good antifungal activity and compound Ⅲ_awith poor activity.The results show that the carbonyl oxygen atom on the amide bond and the nitrogen atom on the pyrimidine ring of compound Ⅰ_ecan form hydrogen bonds with the amino acid residues TRP-173 and SER-39 of the target enzyme,with bond lengths of 2.9（?）and 2.8（?）,respectively;There is only a weak hydrogen bond between the N atom on the pyrimidine ring of compound Ⅲ_aand the amino acid residue SER-39 of the target enzyme,and the bond length is 3.3（?）.The results are consistent with the bioactive experimental data.