Synthesis And Antifungal Activity Of Thiophene-Containing Stilbene Derivatives Against Botrytis Cinerea

As one of the major plant pathogens causing deterioration of fruit quality during greenhouse and storage,Botrytis cinerea results in direct economic losses of up to several hundred billion dollars.Therefore,the control of B.cinerea has become an increasingly important part of crop protection.Natural stilbenes play important roles in plant protection by acting as both constitutive and inducible defenses.However,their exogenous applications on crops as fungicidal agents are challenged by their oxidative degradation and limited availability.Although,the structural modification and optimization of stilbene skeletons obtained a series of structurally novel compounds with good biopharmaceutical activity in recent years,little attention has been paid to stilbene derivatives in preventing and controlling B.cinerea and its fungicidal mechanism.Considering the biological profiles of thiophene and1,3,4-oxadiazole motifs,a new class of thiophene-containing 1,3,4-oxadiazole-stilbene derivatives was synthesized based on the concept of active group splicing.On the bases of the activity assay of the target compounds in vitro and in vivo,the mechanism of fungicidal activity of the target compounds was studied through hyphal morphology observation,mycelial respiration rate,succinate dehydrogenase inhibitory test and molecular docking methods.The main conclusions were drawn as follow:?1?A total of 10 new thiophene-containing 1,3,4-oxadiazole-stilbene derivatives were synthesized via oxidative cyclization of acylhydrazones,bromination of NBS,Arbuzov reaction,and Wittig-Hornor reaction.Their chemical structures were identified by ¹H and ¹³C nuclear magnetic resonace?NMR?.?2?On the basis of the above reactions,the amide bond was introduced to the thiophene-containing 1,3,4-oxadiazole-stilbene skeleton through ester hydrolysis and amide reaction.The structures of target compounds were characterized by NMR,melting point,and high resolution mass spectrometry?HRMS?.?3?Fungicidal activity of all compounds against B.cinerea and C.lagenarium in vitro was tested using mycelial growth inhibition method,and all the compounds were tested against B.cinerea in vivo using infected tomato experiments.Among them,the fungicidal activities of compounds were significantly better than those without amide bonds,demonstrating that the introduction of amide bonds is beneficial to increase the fungicidal activity of the target compounds.Notably,compound 8c exhibited potent fungicidal activity with the EC₅₀ value of 106.1?g/m L against B.cinerea,which is comparable to the commercial fungicide carbendazim?108.1?g/mL?.?4?Compound 7f was further tested for their hyphal morphology observation,mycelial respiration rate inhibition activity.The considerably abnormal mycelial morphology was observed in the presence of compound 7f.Bioassay indicated that 7f showed potent respiration inhibitory activity against B.cinerea.In addition,compound 7f also significantly inhibited succinate dehydrogenase activity of B.cinerea.Combined with molecular docking methods,it was found that the introduced amide bond formed a stable hydrogen bond with the receptor,which is beneficial to improve the fungicidal activity of the ligand.The aromatic ring structure in the stilbene group formed?-?conjugated structures,which also plays an important role in enhancing the bioactivity.This study shows that thiophene-containing1,3,4-oxadiazole stilbene derivatives as potential SDH inhibitors providing new ideas for the design and development of highly effective and low-toxic novel fungicides.