Design,Synthesis And Antifungal Activities Of Novel 3-Acyl Thiotetronic Acid Derivatives

Natural products have the characteristics of diverse biological activity,unique mechanism of action,easy degradation and good compatibility with the environment,and can be used not only for direct development and utilization,but also as lead compounds for further research and development of new pesticide varieties.The five-membered heterocycle-centered natural products,tetramic acid,tetronic acid and thiotetronic acid,have various medical and agricultural biological activities such as antifungal,antiviral and herbicidal activities.In this article,tetramic acid,a metabolite of endophytic fungi with antifungal activity was used as the lead compound.According to the principle of biological isosteric electrons and the strategy of“natural product common pharmacophore oriented”,we designed and synthesized fifty-three structures with novel five-member heterocyclic skeleton thioteronic acid derivatives.The target compounds structure were determined by analytical methods such as ¹H NMR,¹³C NMR,HRMS and X-crystal diffraction,and the antifungal activities of the target compounds against four plant pathogenous fungi such as Valsa mali,Curvularia lunata,Fusarium graminearum and Fusarium oxysporum f.sp.lycopersici.were tested respectively.Biological activity results show that some compounds have good inhibitory activity against four plant pathogens fungi,and there exist structure-activity relationships between structure and activity,The research results laid a foundation for the further development of such research in the future.The details are as follows:1.Design and synthesis of five-membered heterocyclic framework thioteronic acidsUsing natural active product tetramic acid as the lead compound,design and structural modification optimization in position 3,4 and 5 of tetramic acid,and fifty-three novel thiotetronic acid derivatives were synthesized.2.Determination of biological activities of target compounds and structure-activity relationshipThe evaluation of the activity results showed that different plant pathogenic fungi acted at a concentration of 50 ug/mL,and most of the target compounds showed certain inhibitory activities against the Valsa mali,Curvularia lunata,Fusarium graminearum and Fusarium oxysporum f.sp.lycopersici.The EC50 values of compounds 12g,12j and 12o against Valsa mali were 4.482μg/mL,6.108μg/mL and4.125μg/mL,respectively;the EC50 was 5.254μg/mL,1.882μg/mL,and 3.070μg/mL for Curvularia lunata,respectively;the EC₅₀ was 3.058μg/mL,10.661μg/mL,and 3.634μg/mL for Fusarium graminearum,respectively;the EC50 was 7.809μg/mL,4.502μg/mL,and 4.059μg/mL for Fusarium oxysporum f.sp.lycopersici,respectively.It shows good antifungal activity and broad spectrum,and is equivalent to the in vitro activity of azoxystrobin,fluopyram,and carbendazim,and has further research and development value.3.Mechanism of target compounds on plant pathogenic fungiCompounds（12a,12d,12g,12o）had significant inhibitory effects on fatty acid synthase of Valsa mali with IC50 of 6.1,5.3,6.2,and 4.9 g/mL,respectively.The Molecular docking of compound 12o with the fatty acid synthesis pathway enzymeβ-ketoacyl-ACP synthase（C171Q KasA）showed that compound 12o contains a hydrogen bond donor at the active site,which can interact withβ-ketoacyl-ACP synthetase.The active site（catalytic triad Cys112-His244-Asn274）forms a hydrogen bond,the thiophene ring of the compound forms aπ-πstacking action with the benzene ring on Phe404,and the rest extends outward along the elongated active pocket and can interact with residues act nearby to occupy the active channels and prevent the entry of the enzyme substrate acetyl-CoA to a suppressive effect.