Probing the Stereochemistry of Successive Sulfoxidation of the Insecticide Fenamiphos in Soils

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• 作者：Xiyun Cai ; Weina Xiong ; Tingting Xia ; Jingwen Chen
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：October 7, 2014
• 年：2014
• 卷：48
• 期：19
• 页码：11277-11285
• 全文大小：452K
• ISSN：1520-5851

文摘

Successive sulfoxidation is widely recognized as a general characteristic of the metabolism of chiral or prochiral thioethers, producing sulfoxides, and sulfones. However, information related to the stereochemistry of this process in soils is rare. In this study, the biotic transformation of the insecticide fenamiphos (a model thioether) was followed over two months in three soils, through separate incubations with fenamiphos parent, the sulfoxide intermediate (FSO), the sulfone intermediate (FSO₂), and their respective stereoisomers. The results showed that the successive sulfoxidation involved oxidation of fenamiphos to FSO and subsequently to FSO₂ as well as diastereomerization/enantiomerization of FSO, all of which were primarily biotic and stereoselective. The concomitant hydrolysis of fenamiphos, FSO, and FSO₂ to phenols that occurred at lower rates was biotically favorable, but not stereoselective. The stereochemistry of this successive sulfoxidation transferred principally through two parallel systems, R(+)-fenamiphos 鈫?SRPR(+)-/SSPR(鈭?-FSO 鈫?R(+)-FSO₂ and S(鈭?-fenamiphos 鈫?SRPS(+)-/SSPS(鈭?-FSO 鈫?S(鈭?-FSO₂, between which unidirectional intersystem crossing occurred at FSO via isomeric conversions and created a system of S(鈭?-fenamiphos 鈫?SRPR(+)-/SSPR(鈭?-FSO 鈫?R(+)-FSO₂. This pattern accounts for the enrichment of the intermediates SSPR(鈭?-/SSPS(鈭?-FSO and R(+)-FSO₂ that are toxicologically close to the highly toxic S(鈭?-fenamiphos, associated with soil application of fenamiphos. Selective formation/depletion of these intermediate stereoisomers leads to dramatic variations in the ecotoxicological effects of the thioether insecticide.