Studies On Enantioselective Bioactivity,Ecotoxicity,and Environmental Behavior Of Chiral Fungicide Pyrisoxazole And Zoxamide

In recent years,the application proportion of chiral pesticides has become higher and higher.Chiral pesticides enter into the ecological environment system inevitably after the application.The enantiomers often show different bioactivity,toxicity,different environmental behavior including absorption,accumulation,and degradation.Traditional assessment of pesticides often ignore the difference the difference of chiral enantiomers,resulting in the unreliable risk assessment results and potential risks to human health and environmental safety.In this thesis,two kind of novel chiral fungicide pyrisoxazole and zoxamide was selected as the target chiral pesticide.The absolute configuration stability,bioactivity,ecotoxicity and environmental behavior were systemically evaluated in enantiomeric level,in addition,the molecular docking were used to explore the molecular mechanism of the enantioselective bioactivity.The result of this study willprovide more accurate assessment data of chiral pesticide.The specific research contents were shown as follows:.First,the chiral separation and analytical method of pyrisoxazole stereoisomers and zoxamide enantiomer were developed using ultrahigh performance convergence chromatography/tandem mass spectrometry(UPCC-MS/MS)and ultrahigh performance liquid chromatography/tandem mass spectrometry(UPLC-MS/MS).Baseline separation of pyrisoxazole and zoxamide enantiomers was achieved by systemically optimizing the combination of chiral stationary phase(CSP)and organic modifier,proportion of organic modifier,flow rate,system pressure and column temperature.The absolute configuration of pyrisoxazole stereoisomers and zoxamide enantiomers were measured through timedependent density functional theory calculation for circular dichromatographic.Second,in order to evaluate the stability of pyrisoxazole stereoisomer and zoxamide enantiomer,the photolysis test were carried out in 5 kind of organic solvents and water,and hydrolysis test were carried out in 3 kind of pH buffer solution.The results indicated that the absolute configuration of pyrisoxazole stereoisomer and zoxamide enantiomer remained stable in photolysis and hydrolysis test.Third,the enantioselective bioactivity of pyrisoxazole against Alternaria solani,Fulvia fulva(Cooke)Ciferri,Fusarium graminearum Schw.,Botryis cinerea,Dothiorella gregaria Sacc,Fusarium oxysporum Schl.,and zoxamide against Phytophthora capsici Leonian,Alternaria solani,Botryis cinerea,Colletotrichum gloeosporioides Penz,Phytophthora sojae Kaufmann & Gerdemann were evaluated.Significant difference were observed in the bioactivity among pyrisoxazole stereoisomer,the order of the bioactivity of pyrisoxazole stereoisomer was found to be(-)-RS-pyrisoxazole > Rac-pyrisoxazole >(+)-SR-pyrisoxazole >(-)-RR-pyrisoxazole ≈(+)-SS-pyrisoxazole,and(-)-RS-pyrisoxazole was about 98.8-3545.3 times more active than(+)-SS-pyrisoxazole.Zoxamide enantiomers also showed significance difference in bioactivity,the order of bioactivity of zoxamide enantiomer was found to be(-)-R-zoxamide > Rac-zoxamide >(+)-S-zoxamide,and the fungicidal activity of(-)-R-zoxamide was about 9.9-140.0 times higher than that of(+)-S-zoxamide.The VDW(Van der Waals’ force)between(-)-R-zoxamide and phenylalanine(at position 266),alanine(at position 198)was stonger than that of(+)-S-zoxamide,resulting in(-)-R-zoxamide show higher fungicidal activity.Fourth,the acute aquatic toxicity of pyrisoxazole stereoisomer and zoxamide enantiomer to Selenastrum bibraianum and Daphnia magna Straus were evaluated.The result indicated that there were no significant difference in toxicity among pyrisoxazole stereoisomer to Selenastrum bibraianum.However,pyrisoxazole stereoisomer showed significant toxicity difference to Daphnia magna Straus.The order of the toxicity was(-)-RS-pyrisoxazole >(-)-RR-pyrisoxazole > Rac-pyrisoxazole >(+)-SRpyrisoxazole >(+)-SS-pyrisoxazole,and(-)-RS-pyrisoxazole was about 4.0 times more toxic than(+)-SS-pyrisoxazole.In addition,significant difference were observed in the toxicity among zoxamide enantiomer,the order of the bioactivity of zoxamide enantiomer was(-)-R-zoxamide > Rac-zoxamide >(+)-S-zoxamide,and the acute aquatic toxicity of(-)-R-zoxamide was about 4.9-10.8 times higher than that of(+)-S-zoxamide.Fifth,the enantioselective dissipation of pyrisoxazole and zoxamide in greenhouse crops were studied.The result indicated that the enantioselective dissipation depended not only on the plant species but also on the uptake routes.Significant stereoselectivity was observed in tomato and cucumber under foliar spraying and root dripping application modes.(-)-RS-pyrisoxazole and(-)-RR-pyrisoxazole were preferentially degraded in cucumber and tomato under foliar spraying,while under root dripping mode,(+)-SR-pyrisoxazole and(-)-RR-pyrisoxazole were preferentially degraded in cucumber and(-)-RSpyrisoxazole and(-)-RR-pyrisoxazole were preferentially degraded in tomato.In addition,the enantioselective dissipation of zoxamide showed that(-)-R-zoxamide was preferentially degraded in tomato,and(+)-S-zoxamide degraded faster in pepper and grape.No significant enantioselectivity was observed in cucumber.Sixth,the enantioselective dissipation of pyrisoxazole and zoxamide in soil were evaluated.The result indicated that there were no significance dissipation difference among pyrisoxazole stereoisomer in three kind of soils both under aerobic and anaerobic condition.In addition,zoxamide enantiomer showed significant difference on dissipation in three kind of soils under aerobic condition,which manifested(+)-S-zoxamide was preferentially degraded leading to an enrichment of(-)-R-zoxamide.However,no significant enantioselective dissipation of zoxamide enantiomer was observed under anaerobic condition.The absolute configuration of pyrisoxazole stereoisomer and zoxamide enantiomer remained stable in three kind soils both under aerobic and anaerobic condition.Therefore,developing(-)-RS-pyrisoxazole and(-)-R-zoxamide to replace its racemates can reduce the use of pesticides and environmental pollution.