A Simulative Design And Synthesis Of Herbicidal Analogues Of 3-Acetyl-4-Hydropyrroline-2-Ketone

Tenuazonic acid(TeA),one of the secondary metabolites extracted from Alternaria alternata,can inhibit photosynthetic electron transfer through binding to the electron transfer chain of photosynthetic system II(PS II).Hence,it can directly lead to the burst of reactive oxygen species,and kill weeds rapidly eventually.It has been recognized as a new photosystem II inhibitor and may have a potential to be developed into a novel herbicide.However,the herbicidal activity of synthesized TeA was not stable enough because of the existence of isomers,which may be main cause for synthesized TeA being not so well as the biological source TeA.The previous researches on the modification of TeA pyrrole rings at positions 1 and 3 did not show a significant increase in herbicidal activity.However,the activity may be hypothetically enhanced via prolonging the side chain at position 5,which has not been empirically proved because the analoques abtained through the modification had shorter alkyl chains than TeA,and no other elements were introduced.Therefore,it has not been found that new analogues have higher herbicide activity than TeA.At the present study,the main objective is to synthesize new herbicidal analogues with higher activity by simulating the TeA structure of alkyl side chains at position 5 based on action target model.In this study,the structure model of D1 protein of Eupatorium adenophorum was established by homology modeling based on the amino acid sequence of D1 protein inferred from the cDNA sequence of the cloned psbA gene.The TeA 5 side chain was extended and sulfur was introduced into the side chain,and then the corresponding TeA structure analogues were docked with the D1 protein model.The interaction energy values of those modified analogues were calculated to asses their biological activities.The results showed that the longer the 5-position side chain of the compound,the higher the energy value of its interaction with D1 protein,which may also have higher biological activity.The interaction energy of the analogue with 20 carbon side chain was the highest.However,the interaction energy values between the molecules and D1 protein slightly decreased when the side chain has 7 and 9 carbon atoms.Moreover,the methyl side chain at position 5 played an important role in increasing the energy of interaction between modified molecules and D1 protein.After considering the characteristics,difficulty and cost of synthesis,we selectively synthesized 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1H-pyrrol-2(5H)-one and 3-acetyl-5-((ethylthio)methyl)-4-hydroxy-1H-pyrrol-2(5H)-one via esterification,neutralization and acylation reaction,cyclization and acidification.Furthermore,the bioactivities of the two compounds were detected by rapid chlorophyll fluorescence OJIP analysis technique JIP-test,leaf puncture and Imaging PAM bioassay techniques.The results showed that 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1H-pyrrol-2(5H)-one caused bigger lesions on Eupatorium adenophorum leaves than TeA.JIP-test showed that the photosynthetic electron transfer ability of 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1Hpyrrol-2(5H)-one at 500 μM was significantly higher than that of TeA at the same concentration.At the same time,compared with TeA treatment,the lower PSII photosynthetic efficiency of Eupatorium adenophorum treated with 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1H-pyrrol-2(5H)-one indicated that 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1H-pyrrol-2(5H)-one had better biological activity.The parameters of photosynthetic physiology on target sites of this compound indicated that 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1H-pyrrol-2(5H)-one inhibited the electron transfer activity at the same site as TeA but the inhibition rate was higher.Fuethermore,the microemulsion of 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1Hpyrrol-2(5H)-one and 3-acetyl-5-((ethylthio)methyl)-4-hydroxy-1H-pyrrol-2(5H)-one were formulated.The results showed that the herbicidal activity of 3-acetyl-4-hydroxy-5-(pentan-2-yl)-1H-pyrrol-2(5H)-one was 1.5-2 times higher than that of TeA,while that of 3-acetyl-5-((ethylthio)methyl)-4-hydroxy-1H-pyrrol-2(5H)-one was the same as that of TeA.In addition,TeA aqueous solution was modified into microemulsion formulation with the addition of emulsifying agent 4209-4,methyl oleate and oxalic acid.This formulation showed higher herbicide activity.