Studies On Difference In Bioactivity,Ecotoxicity And Enantioselective Behavior Of Fluxametamide And Imazalil Enantiomers

Valifenalate and imazalil are widely applied in agricultural production.Production and application of them do not distinguish the difference between the enantiomers,which may lead to overuse,unpredictable ecological risk and inaccurate risk assessment of pesticides.In this study,a comprehensive research of difference in bioactivity,ecotoxicity and enantioselective behavior of fluxametamide and imazalil enantiomers was conducted at enantiomeric level.These could provide scientific basis for accurate assessment of application risk of chiral pesticides,and development of highly effective and low risk single-enantiomer products.The main conclusions are as follows:First,baseline separation of the enantiomers of fluxametamide,imazalil and its main metabolite R14821(imazalil-M)was performed using ultra performance convergence chromatography and ultrahigh performance liquid chromatography systems.The individual enantiomers with high purity were prepared successfully.The optical rotations and absolute configurations of the enantiomers were confirmed.And the stability of fluxametamide and imazalil enantiomers was revealed in different solvents and soils.Second,significant enantioselective differences of fluxametamide enantiomers against four target pests(Plutella xylostella,Spodoptera exigua,Aphis gossypii and Tetranychus cinnabarinus)and imazalil enantiomers aganist seven kinds of pathogens(Fulvia fulva,Alternaria solani,Phytophthora infestans,Botrytis cinereal,Glomerella cingulate,Valsa mali and Penicillium digitatum)were found.S-(+)-fluxametamide exhibited 52.1-304.4 times and 2.5-3.7 times higher bioactivity than R-(-)-fluxametamide and rac-fluxametamide,respectively.S-(+)-imazalil exhibited 3.0-6.6 times and 1.4-2.2 times higher bioactivity than R-(-)-imazalil and rac-imazalil,respectively.Third,the enantioselective toxicity of fluxametamide enantiomers toward honeybees(Apis mellifera L.)and toxicitiy of imazalil and imazalil-M enantiomers toward aquatic organisms were verified.S-(+)-fluxametamide was found to be over 30 times higher acute toxicity than R-(-)-fluxametamide for honeybees,and rac-fluxametamide exhibited 4.3 times more toxic than S-(+)-fluxametamide to honeybees.The acute toxicity of S-(+)-imazalil was 1.2-fold and 2.2-fold more than R-(-)-imazalil to Pseudokirchneriella subcapitata and Daphnia magna,respectively.However,R-(-)-imazalil was 1.2 times more toxic than S-(+)-imazalil to Danio rerio.And S-(+)-imazalil-M had 2.2-fold and 1.7-fold higher toxicity than R-(-)-imazalil-M to P.subcapitata and D.magna,respectively.Fourth,molecular docking technology in combination with sequence alignment of protein sequence was used for illuminating the mechanism of enantioselective bioactivity between fluxametamide or imazalil enantiomers.The hydrophobic interaction and electrostatic interaction between S-(+)-fluxametamide and ?-aminobutyric acid receptor were found to be stronger than that of R-(-)-fluxametamide.The absolute value of Grid score of S-enantiomer(-60.12 kcal/mol)was greater than Renantiomer(-56.59 kcal/mol).S-(+)-imazalil had lower energy conformation and stronger hydrophobic interaction with binding sites of sterol 14?-demethylase P450 than that of R-(-)-imazalil.The absolute value of Grid score of S-enantiomer(-41.17 kcal/mol)was greater than R-enantiomer(-39.93 kcal/mol).Fifth,the dissipation of fluxametamide enantiomers in cabbage,Chinese cabbage and soil in Hunan was nonenantioselective.The degradation of imazalil in OBIR-2T-47 apple in Henan,grape and field soils in Hebei,Liaoning,Henan and Shandong was nonenantioselective.S-(+)-imazalil preferentially degraded in Gala apple in Shandong and preferentially enriched in Golden Delicious apple in Liaoning,fruit and leaf of tomato and cucumber.Meanwhile,approximately 1.0%-27.3% of imazalil was transformed to imazalil-M in Golden Delicious apple in Liaoning,OBIR-2T-47 apple in Henan,grape,cucumber,tomato leaf and cucumber leaf.Approximately 2.8%-7.3% of imazalil was transformed to imazalil-M in soil from Liaoning,Henan and Shandong.In summary,development of S-(+)-fluxametamide is recommended,which can improve the bioactivity and reduce the risk to honeybees.Development of S-(+)-imazalil can reduce pesticide input and the risk to D.rerio.