Research On The Stereoselectivity Bioactivity And Environment Behaviors Of Chiral Fungicide Pyrisoxazole

The chiral fungicide pyrisoxazole can inhibit the synthesis of fungal ergosterol and has a high bactericidal activity against plant pathogenic bacteria,especially Botrytis cinerea,and Botrytis cinerea can cause diseases in various plants.Pyrisoxazole has two chiral carbon atoms and consists of four stereoisomers,two pairs enantiomers:?3R,5R?,?3S,5S?,?3R,5S?and?3S,5R?-pyrisoxazole,respectively.However,up to now,the study on the level of enantiomers of pyrisoxazole has not been perfected.Therefore,the biological activity,the stereoselective degradation behavior in cabbage,brassica and pepper,and the stereoselective enrichment behavior in earthworm of pyrisoxazole at the enantiomer level were studied for the first time.In order to clarify the necessity of the behavioral fate of high-efficiency pyrisoxazole in the environment and monomer development and application,establish a more scientific and effective pesticide risk assessment system for pyrisoxazole.The main conclusions of the study are as follows:The biological activities of the race-pyrisoxazole and stereoisomers on Botrytis cinerea were significantly different.The activity order was?-?-A-pyrisoxazole>rac-pyrisoxazole>?+?-B-pyrisoxazole>?-?-B-pyrisoxazole>?+?-A-pyrisoxazole.The activity of?-?-A-pyrisoxazole was highest and?+?-A-pyrisoxazole was lowest,the activity difference of them was significant,EC₅₀ was as much as 73.75 times.However,the activities of?+?-B-dioxazole and?-?-B-dioxazole were slightly different,and the difference in EC₅₀ between them was 3.01 times.Therefore,it was confirmed that the high-efficiency substance in the stereoisomers of the pyrisoxazole was?-?-A-pyrisoxazole.The degradation of the pyrisoxazole stereoisomers in cabbage,pakchoi and pepper all accorded with the first-order kinetics,but the selectivity of degradation behavior was different.In cabbage,there were extremely obvious selective actions for?±?-A-pyrisoxazole and?±?-B-pyrisoxazole enantiomers during the degradation process,with The rate of degradation of higher activity?-?-A-pyrisoxazole and?+?-B-pyrisoxazole is faster than that of their enantiomers.?-?-A-pyrisoxazole and?+?-B-pyrisoxazole is preferentially degraded,resulting lower activity of?+?-A-pyrisoxazole and?-?-B-pyrisoxazole is enriched.At the same time,the pairs of diastereomers of?±?-A-pyrisoxazole and?±?-B-pyrisoxazole also occured selective degradation at the end of the sampling period?14d-21d?,?±?-A-pyrisoxazole is preferentially degraded and?±?-B-pyrisoxazole is enriched in cabbage.The stereoisomer of pyrisoxazole has similar degradation tendency and selective degradation behavior in pakchoi and pepper.?±?-A-pyrisoxazole with high activity has obvious selective degradation behavior.The?-?-A-pyrisoxazole was preferentially degraded,resulting the enrichment of the?+?-A-pyrisoxazole with low activity.However,the degradation of the?±?-B-pyrisoxazole enantiomers didn't have selectivity behavior.In addition,the diastereoisomers?±?-A-pyrisoxazole and?±?-B-pyrisoxazole also happende extremely significant stereoselective behavior during degradation progress,?±?-A-pyrsoxazole is more rapidly degraded than?±?-B-pyrisoxazole.?±?-A-pyrisoxazole is preferentially degraded,resulting the enrichment of?±?-B-pyrisoxazole.There are differences about the enrichment of pyrisoxazole stereoisomers in earthworm.Enrichment of?±?-A-pyrisoxazole enantiomers in significant enantioselectivity and the lowest activity of?+?-A-pyrisoxazole was preferentially enriched than the highest activity of?-?-A-pyrisoxazole.In contrast,?±?-B-pyrisoxazole enantiomers,the diastereoisomers of?±?-A-pyrisoxazole and?±?-B-pyrisoxazole didn't accumulate during the enrichment process.During the whole enrichment process,the bioaccumulation factor?BAF?of?±?-A-pyrisoxazole is different,the BAF value of the high-efficience?-?-A-pyrisoxazole was less than it's enantiomer.The results of the above studies indicate that the high-efficience?-?-A-pyrisoxazole has the highest degradation rate in the test vegetables,The BAF of?-?-A-pyrisoxazole was lowest.The results of this study provide a more comprehensive theoretical basis for the development of a single isomer of?-?-A-pyrisoxazole,and have a positive guiding role for the production of green pesticides.