Studies On Stereoselective Bioactivities And Behaviors Of Chiral Triazole Fungicide Of Difenoconazole In Environments

In gerenal, the enantiomers/diastereoisomers of chiral pesticides are different in some biologicalprocesses and thus pose enantioselective environmental behavior and ecotoxicity to nontarget biology.Consequently, the application and environmental safety of chiral pesticides have been becoming a newpoint of scientific researches. In the present study, the enantioselective degradation of chiral triazolefungicide difenoconazole in greenhouse vegetables and agriculture soils based on the high-performanceliquid chromatography (HPLC) with chiral stationary phases (CSPs) technology were investigated. Andthe optical pure diastereoisomers of difenoconazole were also selected to investigate theirenantioselective ecotoxicologies to three aquatic organisms and their enantioselective fungitoxicities to anumber of fungi.The separation of difenoconazole and its major metabolite CGA-205375including theirsimultaneous enantioseparation was studied using four different polysaccharide-type chiral stationaryphases inculding Amylose tris-[(S)–α-methylbenzylcarbamate](AS-H), Amylose tris(3,5-dimethylphenyl carbamate)(AD-H), Cellulose tris-(3,5-dimethylphenyl-carbamate)](OD-H) andcellulose tris-(4-methylbenzoate)(OJ-H) in combination with n-hexane-polar organic alcohols mobilephase. Compared with other three CSPs, cellulose tris-(4-methylbenzoate)(OJ-H) exhibited higherresolving ability for difenoconazole and CGA205375. And after the optimization of otherchromatographic conditions such as the mobile phase composition and column temperature, a baselinechemoseparation and enantioseparation of two enantiomers of CGA205375and four stereoisomers ofdifenoconazole was successfylly afforded.The greenhouse experiment was used to investigate the stereoselective behavior of difenoconazolestereoisomers in cucumber and tomato plants. The results indicated that the degradation of four isomersof difenoconazole followed first-order kinetics and significantly stereoselective behavior was observedin both cucumber and tomato fruits. Preferential dissipation of (-)-difenoconazole-A and(-)-difenoconazole-B were determined in cucumber fruits after foliar treatment, which resulted in plantsenriched with (+)-difenoconazole-A and (+)-difenoconazole-B. Results also showed that(+)-difenoconazole-A and (-)-difenoconazole-B degraded faster than their optical antipode in tomatofruits, which resulted in tomato enriched with stereoisomers of (-)-difenoconazole-A and(-)-difenoconazole-B.Six soils with a wide range of soil properties were selected to investiate the stereoselective behaviorof difenoconazole stereoisomers. Racemic-and enantiopure stereoisomers of difenoconazole wereincubated under aerobic and anaerobic conditions. Results indicated that both aerobic and anaerobicdegradation of stereoisomers of difenconazole in the test soils during incubation period generallycomplied with the first-order kinetics. It could be proved that the dissipation rates of difenoconazoleisomers were greatly influenced by pH value. The results revealed that the dissipation rates of fourstereoisomers of difenoconazole in soils were different, the orders were alkali soil>normal soil>acid soil. Moreover, data showed that the stereoselective degradation of the stereoisomes of difenoconaozle inalkali soil and acid soil was more obivious than that in normal soil. All four stereoisomers ofdifenoconazole in test soils were more slowly degraded under anaerobic conditons as comparison of thatunder aerobic conditions, but anaerobic condition has no more significant enantioselectivity than aerobiccondition. The degradation of difenoconazole stereoisomers in all test soils is enantioselective underboth aerobic and anaerobic conditions, and the (+)-difenoconazole-A and (+)-difenoconazole-B werepreferentially degraded, resulting in relative enrichment of (-)-difenoconazole-A and(-)-difenoconazole-B. The enantiopure stereoisomers of difenoconazole were incubated under bothaerobic and anaerobic conditions, and it revealed that difenoconazole was configurationally stable in soil,showing no interconversion among the stereoisomers.Herein is reported, for the first time, the enantioselectivities of individual stereoisomers of triazolefungicide difenoconazole in acute aquatic toxicity to three aquatic orgnisms including S. obliquus, D.magna and Danio rerio. For the above three aquatic organisms, significant differences were observed inthe acute toxicity among the stereoisomers of difenoconazole. The order of the toxicity to three aquaticorganisms for the stereoisomers of difenoconazole was (-)-difenoconazole-A>(+)-difenoconazole-B>(+)-difenoconazole-A>(-)-difenoconazole-B, rac-difenoconazole had an intermediate potency oftoxicity as compared to its respective individual stereoisomers.It was also the first report about the enantioselectivities of individual stereoisomers of triazolefungicide difenoconazole in the fungitoxicity against a number of fungi including Alternaria solani,Botrytis cinerea, Fulvia fulva (Cooke) Cifferri, Rhizoctonia solani and Colletotrichum lagenarium.Significant differences were observed in the fungicidal activities among the stereoisomers ofdifenoconazole on the test fungi. The fungitoxicity for the stereoisomers of difenoconazole has beenfound to be (-)-difenoconazole-B>(+)-difenoconazole-A>(+)-difenoconazole-B>(-)-difenoconazole-A,rac-difenoconazole had an intermediate potency of fungitoxicity as compared to its respective individualstereoisomers.