Design, Synthesis And Insecticidal Activity Of Pyrido[1,2-a]pyrimidinone Mesoionic Compounds Containing Isoxazole/isoxazoline Unit

In view of the resistance of common insecticides to aphids,planthoppers and other pests,toxicity to beneficial organisms,and environmental unfriendly issues,this paper focuses on current insecticide research hotspots-mesoionic insecticides.Isoxazole and isoxazoline with insecticidal activity were introduced into pyrido[1,2-a]pyrimidinone through scaffold hopping strategy,and a series of novel mesoionic derivatives were designed and synthesized.Compounds E1-E39 were tested for their insecticidal activity against A.craccivora,Planthopper white-backed,and Plutella xylostella by spray and leaf dip methods,respectively.The series of compounds showed different insecticidal activity against A.craccivora.Besides,the mechanism of action of the compound E1 was investigated by means of proteomics,enzyme activity testing and molecular docking.The specific work is summarized as follows.（1）Thirty-nine pyrido[1,2-a]pyrimidinone compounds containing isoxazole/isoxazoline were designed and synthesized,and their insecticidal activities were evaluated against A.craccivora,Planthopper white-backed,and Plutella xylostel la.The biological activity test results showed that most of the compounds had excellent insecticidal activities against A.craccivora.Among them,the LC₅₀ of compounds E1,E2,E23,E35 and E36 were 0.73 mg/L,0.88 mg/L,1.25 mg/L,1.97 mg/L and 1.28 mg/L,respectively,which are better than TFM(LC₅₀=2.43 mg/L).The structures of the compounds were identified by ¹H NMR,¹³C NMR,¹⁹F NMR and HMRS.（2）The mode of action of compound E1 was tested for contact killing,gastric poisoning and endotoxic mode of action using the liquid film method,dip method and root uptake method,respectively.The LC₅₀ values were 1.97 mg/L and 33.72 mg/L for the gastric and thixotropic effects,respectively,indicating that compound E1 has both gastric and contact killing effects,and the gastric toxicity was dominant and the endosorption was poor.（3）The results of enzyme activity test showed that compound E1 had a certain effect on Ach E in the nervous system of the A.craccivora,especially on nicotinic acetylcholinesterase,but had no effect on glutathione-S-transferase and carboxylesterase,which further proved that the target compound E1 might act on the nervous system of the A.craccivora.（4）Molecular docking and molecular dynamics simulations showed that compound E1 and TFM have similar binding sites,indicating that E1 and TFM have the same target site and can effectively bind to acetylcholine receptors with binding energies of-46.9 kcal mol^-1 and-26.7 kcal mol^-1,respectively.Meanwhile,it was found that the introduction of aromatic groups increased the binding ability of the compound and protein to a certain extent,and thus improved the insecticidal activity of the compound,but too much introduction would probably reduce the water solubility of the compound and thus lead to the reduction of its insecticidal activity.（5）According to the preliminary analysis of proteomics technology,the differentially expressed protein of compound E1 was mainly concentrated in the pathways related to the nervous system.These pathways are related to mitochondrial dysfunction,oxidative stress,abnormal protein aggregation and damage of autophage.It is further suggested that compound E1 may exert its insecticidal activity by acting on the nervous system of aphids.