Probing the stereochemistry of successive sulfoxidation of the insecticide fenamiphos in soils.
Probing the stereochemistry of successive sulfoxidation of the insecticide fenamiphos in soils.
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DOI：
10.1021/es502834v
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发表时间：
2014-09
影响因子：
11.4
通讯作者：
Xiyun Cai;Weina Xiong;Tingting Xia;Jingwen Chen
中科院分区：
文献类型：
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作者：
Xiyun Cai;Weina Xiong;Tingting Xia;Jingwen Chen
连续的亚磺氧化被广泛认为是手性或前手性硫醚代谢的一般特征，产生亚硫醚和砜。然而，与土壤中这一过程的立体化学有关的信息很少。在这项研究中，通过分别与杀虫磷母体、亚砜中间体(FSO)、砜中间体(FSO2)及其各自的立体异构体进行培养，跟踪了杀虫剂杀虫胺磷(一种模型硫醚)在三种土壤中的生物转化情况。结果表明，连续的亚磺化反应包括杀灭磷氧化成FSO和FSO的非对映异构化/对映异构化，这些反应主要是生物的和立体选择性的。杀灭磷、FSO和FSO2以较低的速率同时水解为酚在生物上是有利的，但不是立体选择性的。这一连续的亚硫氧化反应的立体化学主要通过两个平行体系转移：R(+)-杀灭磷→srpr(+)-/sspr(-)-fso→R(+)-fso R(+)-fso和S(-)-杀灭磷→srps(+)-/sps(-)-fso→S(-)-fso，它们之间通过异构体转化发生了单向的系间交叉，形成了S(-)-杀灭磷→srpr(+)-/sspr(-)-fso→R(+)-fso2体系。这一模式解释了土壤施药与剧毒的S(-)-敌畏磷毒性相近的中间体SSPR(-)/SSPS(-)-FSO和R(+)-FSO_2的富集性。这些中间立体异构体的选择性形成/消耗导致硫醚杀虫剂的生态毒理效应发生显著变化。
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 → SRPR(+)-/SSPR(-)-FSO → R(+)-FSO2 and S(-)-fenamiphos → SRPS(+)-/SSPS(-)-FSO → S(-)-FSO2, between which unidirectional intersystem crossing occurred at FSO via isomeric conversions and created a system of S(-)-fenamiphos → SRPR(+)-/SSPR(-)-FSO → R(+)-FSO2. This pattern accounts for the enrichment of the intermediates SSPR(-)-/SSPS(-)-FSO and R(+)-FSO2 that are toxicologically close to the highly toxic S(-)-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.