Synthesis And Biological Activity Screening Of 1,3,4-oxadiazole Derivatives Containing Saturated Nitrogen Heterocycle

Plant viral diseases,especially tobacco mosaic virus,severely lose millions of dollars for agriculture around the world annually.However,commercialized ningnanmycin and ribavirin had unsatisfactory inhibitory effects（30–60%）in field trials.Therefore,there is an urgent need to develop and excavate novel antiviral compounds with novel mechanisms of action,facile preparation,and highly activity.Therefore,in this study,saturated nitrogen-containing heterocyclic fragments were introduced into the 1,3,4-oxadiazole structure,and a series of 1,3,4-oxadiazole derivatives substituted with nitrogen-containing heterocyclic moiety were synthesized,and structurally characterized by NMR(e.g.¹H NMR,¹³C NMR,¹⁹F NMR)and HRMS.The biological activity of the target compounds against tobacco mosaic virus（TMV）was accesseed through using the half leaf method,Meanwhile,ningnanmycin and ribavirin were served as control agents.Compound A₂₂ showed most curative activity with value of 64.2%.Furthermore,compound A₁₄ exhibited most protective activity with the EC₅₀ value of 137.7 mg L^-1,which was superior to the control agents ningnanmycin(248.2 mg L^-1)and ribavirin(590 mg L^-1).Moreover,anti-TMV activity of some compounds were further investigated through supplementation with auxiliaries.Notably,anti-TMV activity of some compounds could be further enhanced（up to 5%to 30%）through supplementation with 0.1%auxiliaries（e.g.,organic silicon,SI;orange peel essential oil,and OPO）.The in vitro antimicrobial activity of target compounds was tested through using turbidimetric method.Meanwhile,Xanthomonas oryzae pv.oryzae（Xoo）and Xanthomonas axonopodis pv.citri（Xac）were served as tested strains,and bismerthiazol（BT）and thiamethoxam copper（TC）were served as as control agents.Among them,compound C₂ showed the best activity against Xoo and Xac with EC₅₀values of 8.68 mg L^-1 and 6.38 mg L^-1,respectively.In addition,compound C₂exhibited excellent protective activity against Xoo in pot experiment.In addition,the target compound A₁₄ with optimal antiviral activity was selected to further investigate its anti-TMV action mechanism.Further,biochemical assays（TMV systemic spread assay,q RT-PCR analysis,western blotting experiment,and defense enzymatic activity assay,etc.）suggested that target compounds could not only suppress biosynthesis of TMV（e.g.,motor protein,MP;coat protein,CP;and green fluorescent protein,GFP）,but also induced plant defense response.