Design, Synthesis And Biological Activity Of Sulfonate Compounds Containing 1,3,4-thiadiazole/pyrimidine Structur

Heterocyclic compounds,especially the biological activities of five-membered and six-membered heterocycles containing nitrogen and sulfur have received more and more attention for their wide use in the fields of medicine and pesticides with high efficiency and low toxicity.Also,structures with sulfonate pharmacophore possess excellent activity as antibacterial,antiviral,and insecticidal agents.In this paper,58 sulfonates compounds containing 1,3,4-thiadiazole structure(A₁-A₁₈,B₁-B₂₀,C₁-C₂₀)and 33 sulfonates containing pyrimidine(D₁-D₃₃)were designed and synthesized by splicing the five-membered heterocyclic 1,3,4-thiadiazole and hexacyclic pyrimidine and sulfonate structures,respectively.All 91target compound structures were determined by ¹HNMR,¹³CNMR,¹⁹FNMR and HRMS.They were screened for biological activity targeting four plant pathogens including Xoo,Xoc,Xac,Psa and two crop pests including Plutella xylostella and Myzus persicae.The antibacterial mechanism of highly active compounds was explored by SEM,cytoplasmic content leakage,enzyme activity test and molecular docking.The insecticidal mechanism of highly active compounds was preliminarily explored by means of enzyme activity tests and molecular docking.The main work of this thesis is summarized below.1.The in vitro antibacterial activity test was carried out by the turbidity method,and the results showed that most of the compounds were active.Among them,D₅,showed an excell ent activity against Xoo with the EC₅₀values 4.24 which was significantly lower than that of bismerthiazol（BT）（25.12μg/m L）and thiodiazole copper（TC）（45.81μg/m L）.Compound A_{1 6} had a strong inhibitory effect on Xoc and EC₅₀ value was 18.75μg/m L,which is better than that of TC（70.13μg/m L）and BT（45.7μg/m L）.2.In vivo test of t he highly active compound D ₅ was performed by leaf cutting method on rice plant in pots.The results showed that most of the compounds,especially the pyrimidine sulfonates possesse good inhibitory effects on targeting bacteria.Among them,compound D ₅ performed best.At the concentration of 200μg/m L,the protective and curative activities of compound D₅ against rice bacterial blight were 47.85%and 41.05%,respectively.The protective activity was better than TC（45.65%）,but weaker than BT（57.02%）.Its curative effect is significantly better than that of TC（31.81%）,but weaker than that of BT（52.54%）.3.The outstandingly active compound D ₅ was observed for its action mode on Xoo by SEM and cytoplasmic content leakage test and other biological parameter test.The results showed that compound D ₅ could cause bacterial cells to shrink and the cell content to leak.The antibacterial mechanism suggested that D₅ might cause shrinkage and rupture of pathogens by destroying the cell wall of pathogens Xoo.At the same time,D₅ resulted in the leakage of cytoplasmic contents.In addition,D₅ could increase the activity of related enzymes including CAT,POD,PAL in rice which will enhance plant disease resistance.The Xoo-Cas5d protein was taken for the molecular docking test and binding affinity between them was computationally simulated using scoring functions.The results showed that,comparing to BT,compound D₅ has two more stable binding forces with two more binding sites where two aromatic rings have interactions with other amino acids forming cation-πinteractions and hydrophobic interactions with the carbonyl group of Ser34 and the amine of Arg157,respectiv ely.4.The insecticidal activities of all compounds were carried on Plutella xyl ostell a and Myz us persi ca e by the leaf dipping method.The results indicated that most of compounds especially 1,3,4-thiadiazole containing sulfonates showed good insecticidal activity against Plutella xylostella and moderate insecticidal activity against Myzus persicae.Among them,compound B₁₅ had the best insecticidal activity against Plutella xylostella with an LC₅₀ value 7.61μg/m L and acted better than commercial insecticide diflubenzuron（24.08μg/m L）.5.The insecticidal action mechanism of B₁₅ was evaluated on the interaction with chitinase,juvenile hormone（JH）and ecdysone in Plutella xyl ostell a.The results showed that the chitinase activity of compound B ₁₅to Plutella xylostella increased at first and then decreased with time.At 12h,the chitinase activity was the lowest,which was lower than that of CK group and positive control group.In addition,B₁₅ significantly increased the content of ecdysone.Through the molecular docking experiment of chi-h protein of Plutella xylostella,the results showed that,comparing to diflubenzuron,compound B₁₅ has more stable binding force with two more binding sites.