Design, Synthesis And Biological Activity Of 1,2,4-oxadiazole Derivatives Containing 1,3,4-oxa(thi)adiazole Or Pyridine Structure

The security of food crops in the world is very important.Food crops often suffer from bacterial diseases,such as Xanthomonas oryzae pv.oryzae(Xoo),Xanthomonas oryzae pv.oryzicola(Xoc),fungal diseases.Diseases such as Thanatephorus cucumeris(T.cucumeris),and harmful insects such as Meloidogyne incognita(Meloidogyne spp.).These are widespread plant diseases.When the damage is severe,it will affect every growth and development stage of the plant,and in severe cases,it will cause up to 80%of the crop loss and cause huge economic losses.At present,due to the rapid response of pesticides to plant diseases,pesticides are usually used for agricultural pest control.However,long-term abuse of pesticides can cause plant pathogenic organisms to develop resistance to pesticides and may threaten human health.Therefore,the development of high-efficiency,low-toxicity,low-residue and environmentally friendly drugs is the main task of current pesticide research.This study aims to design and synthesize novel 1,2,4-oxadiazole derivatives containing a sthioether/ether moiety and to investigate their antibacterial,antifungal,nematicidal activity.Bioassay results revealed that most of the compounds showed good antibacterial activity.The test results show section of the target compounds had a clearly lower EC₅₀value than control BTM and TDC.compounds 5m,5n,5r,5u,5v,5x and 5y shows stronger antibacterial effect on Xoo,EC₅₀value 36.25,56.75,24.14,28.82,19.44,25.37 and 28.52?g/m L,compared with the control agents BTM(EC₅₀=77.46?g/m L)and TDC(EC₅₀=99.31?g/m L),compounds 5n,5p,5r,5t,5u,5v,and5z Exhibits high Xoc antibacterial ability,EC₅₀value 50.93,31.40,51.11,56.50,19.04,21.78 and 55.32?g/m L,Compared with the control agents BTM(EC₅₀=68.50?g/m L)and TDC(EC₅₀=91.05?g/m L).and test that curative and protection activities of compound 5v against rice bacterial leaf blight under greenhouse conditions at 200?g/m L.Main research findings:1.Designed and synthesized twenty-six new 1,2,4-oxadiazole derivatives containing 1,3,4-ox(thia)diazole/pyridine structure.The structure of the target compound was characterized by hydrogen nuclear magnetic resonance spectroscopy(¹H NMR),carbon nuclear magnetic resonance spectroscopy(¹³C NMR)and high resolution mass spectrometry(HRMS).2.Through the turbidity method of bacterial liquid,it was found some compounds showed significant antibacterial activity against Xoo and Xoc,which was significantly higher than that of the control agent.3.A live pot experiment for testing the target compound 5v against bacterial blight of rice by the leaf-reduction method.