Co-reporter:Anping Zhang, Xuemei Xie, and Weiping Liu
Journal of Agricultural and Food Chemistry 2011 Volume 59(Issue 8) pp:4300-4305
Publication Date(Web):March 11, 2011
DOI:10.1021/jf104828q
The environmental significance of enantioselectivity in chiral insecticides and herbicides has been widely studied. However, little information is currently available on the enantioselective behavior of chiral plant growth regulators. In this study, paclobutrazol enantiomers were resolved and prepared by chiral high-performance liquid chromatography with a Sino-chiral OJ column. The relationship among absolute configuration, optical activity and circular dichroism of paclobutrazol enantiomers was established. The enantioselective behavior of paclobutrazol, including enantioselective effect of paclobutrazol on the growth of rice seedlings and cyanobacteria and enantioselective loss of paclobutrazol in rice seedling growth media, in rice culture system was studied. The (2S,3S)-(−)-enantiomer was almost 3.1 times more active than the (2R,3R)-(+)-enantiomer toward shoot growth as measured by 7 day EC50 values. Enantioselectivity could not be determined with respect to root growth of rice seedlings because a typical dosage response was not observed in the range of the concentrations studied. The dissipation of paclobutrazol in rice growth medium is not enantioselective. Enantiomers and diastereoisomer of paclobutrazol all facilitated the growth of cyanobacteria, which increase the effectiveness of rice biofertilizers. The (2S,3S)-(−)-enantiomer showed stronger stimulatory activity on Microcystis aeruginosa cyanobacteria than the (2R,3R)-(+)-enantiomer, whereas the latter was a more potent stimulator of Anabaena sp. growth. These observations indicate that application of the (2S,3S)-(−)-enantiomer of paclobutrazol and Microcystis aeruginosa in rice cultivation is a good strategy for improving rice seedling performance.
Co-reporter:Qingyan Zhou, Na Zhang, Cheng Zhang, Lidong Huang, Yaofang Niu, Yongsong Zhang and Weiping Liu
Journal of Agricultural and Food Chemistry 2010 Volume 58(Issue 7) pp:4202-4206
Publication Date(Web):March 10, 2010
DOI:10.1021/jf9038953
Chiral compounds usually behave enantioselectively in phyto-biochemical processes. Imidazolinones are a class of chiral herbicides that are widely used. They inhibit branched-chain amino acid biosynthesis in plants by targeting acetolactate synthase (ALS). It has been reported that the imidazolinone enantiomers show different inhibiting activities to maize (Zea mays L.) seedlings and ALS. However, to date, the mechanism of enantioselective inhibition of imazethapyr (IM) on ALS activity has not been well studied. In this study, pure enantiomers of IM were used for characterizing their differences in activity to ALS. Computational molecular docking was performed to discover the molecular interaction between IM enantiomers and ALS at the first time. Results showed that the IM enantiomers enantioselectively suppressed the in vitro and in vivo ALS activity of maize leaves. R-(−)-IM was more active than S-(+)-IM. The in vivo ALS activity study showed only a 2-fold difference between R-(−)-IM and S-(+)-IM. Quite different from the in vivo study, the in vitro study showed that the difference in inhibition between the enantiomers fell sharply as concentration increased. At the lowest concentration of 40 μg L−1, R-(−)-IM appeared 25 times more active than S-(+)-IM, but only 7 times at 200 μg L−1. At the highest concentration of 25 mg L−1, in vitro ALS activity was almost completely inhibited by S-(+)-, R-(−)-IM and (±)-IM, there was only 1.1 times differences between S-(+)- and R-(−)-IM. Molecular modeling results provide the rational structural basis to understand the mechanism of enantioselective inhibition of IM on ALS activity.
Co-reporter:Cui Wang;Na Zhang;Ling Li;Quan Zhang;Meirong Zhao
Chirality 2010 Volume 22( Issue 6) pp:612-617
Publication Date(Web):
DOI:10.1002/chir.20800
Abstract
Enantioselectivity in the environmental behavior and ecotoxicity of chiral pesticide is widely observed. However, the investigation of the enantioselective mechanisms remains limited. In this study, we used fenamiphos (FAP), an organophosphorus insecticide, to study enantioselectivity in toxicity to arthropods and the inhibition potential towards acetylcholinesterase (AChE) in the rat pheochromocytoma 12 (PC 12) cell line. Furthermore, we carried out molecular docking to help explain the mechanisms of enantioselective toxicity of FAP. The two enantiomers of FAP were successfully separated and identified as R-(+)-FAP and S-(−)-FAP. Toxicological assays revealed that R-(+)-FAP was 2.4-fold more toxic than S-(−)-FAP to Daphnia magna and approximately threefold more to PC12 cells. Based on molecular docking results, dynamic simulation shows that strong hydrophobic interactions and a key hydrogen bond can only exist between R-(+)-FAP and AChE, which helps explain the preference of R-(+) binding to AChE over that of the S-(−)-enantiomer, and supports our biological results. Our present study considers the impact of stereochemistry on ecotoxicological effects and, ultimately, on development of environmentally safe, insecticidally efficient pesticides. Chirality 2010. © 2009 Wiley-Liss, Inc.
Co-reporter:Cui Wang;Quan Zhang;XiaoFeng Zhang;Jing Liu
Science China Chemistry 2010 Volume 53( Issue 5) pp:1003-1009
Publication Date(Web):2010 May
DOI:10.1007/s11426-010-0143-7
Synthetic pyrethroids (SPs), a family of chiral insecticides consisting of multiple stereoismers, have been regarded as estrogenic endocrine-disrupting chemicals (EDCs). In this study, we applied the yeast two-hybrid and molecular docking (MD) assay to assess the enantioselective estrogenic activities of three commonly used SPs, bifenthrin (cis-BF), permethrin (PM) and fenvalerate (Fen). The β-galactosidase analyses indicated that all of the testing pyrethroids displayed significant (p<0.05) enantioselectivity. The results showed that the estrogenic potential of cis-BF was mainly attributed to 1S-cis-BF. Neither PM nor Fen showed estrogenic effects. However, two stereoisomers of PM possessed estrogenic potential activities. αR-2R-Fen and αS-2S-Fen also induced the β-galactosidase activity. The inability to initiate the reporter gene expression by the racemic chemicals may be due to the low ratios of these isomers or the antagonism among them. The strong hydrophobic interaction and the hydrogen bond between positive estrogenic isomers and ERα support our biological testing results. This research demonstrated that the enantioselective estrogenic activity of chiral SPs was due to selective binding between their isomers and the ERα receptor. The data suggests that enantioselectivity of these chiral pesticides is significant to their estrogenic activities.
Co-reporter:Ling Li, Shanshan Zhou, Lixia Jin, Cheng Zhang, Weiping Liu
Journal of Chromatography B 2010 Volume 878(17–18) pp:1264-1276
Publication Date(Web):15 May 2010
DOI:10.1016/j.jchromb.2009.10.031
In recent years, the continuous evolution of the field of stereochemistry has produced a heightened awareness of the applications of pure enantiomers of agrochemicals. This review describes reports of the enantiomeric separation of commercial organophosphorus pesticides (OPs) and the applications of these methods to research on the enantioselectivity of the toxicity and environmental fate of these compounds. Chiral OPs can be analysed by high-performance liquid chromatography (HPLC), gas chromatography (GC), and capillary electrophoresis (CE). These different separation techniques for OP enantiomers are briefly discussed, and their applications are presented.
Co-reporter:Meirong Zhao, Ying Zhang, Cui Wang, Zhengwei Fu, Weiping Liu and Jay Gan
Chemical Research in Toxicology 2009 Volume 22(Issue 3) pp:504
Publication Date(Web):January 23, 2009
DOI:10.1021/tx800358b
Acetofenate (AF) is a widely used insecticide in China and other regions of southeastern Asia. A previous study showed that AF caused adverse developmental effects in zebrafish. Macrophages, which play a key role in inflammation, host defense, and reactions against a spectrum of autologous and foreign invaders, are crucial for innate immunity. However, cytotoxicity and apoptosis of macrophages caused by organochlorine pesticides (OCPs) have so far received little attention. In this study, we used AF as a model chemical to investigate the cytotoxic effects of OCPs on mouse macrophage cell line RAW264.7. Results from cell viability and apoptosis assays showed that AF induced apparent apoptosis in RAW 264.7 cells. Furthermore, AF induced intracellular reactive oxygen species (ROS) generation and DNA damage and resulted in the alteration of a series of signaling molecules including up-regulation of p53 and cytochrome c protein levels, decline of the Bcl-2/Bax protein ratio, and activation of the caspases cascade through caspase-9 and caspase-3. These results, for the first time, revealed that the increase of endogenous ROS and DNA damage comediating OCP-induced apoptosis in macrophages may be by the mitochondria and p53 signal pathway. Our results suggested that macrophages are involved in AF-induced adverse immune effects. Considering the ubiquitous environmental presence of OCPs, this study provided new information on the potential long-term physiological and immunological effects due to chronic exposures to OCPs.
Co-reporter:Weiping Liu, Jing Ye and Meiqing Jin
Journal of Agricultural and Food Chemistry 2009 Volume 57(Issue 6) pp:2087-2095
Publication Date(Web):March 2, 2009
DOI:10.1021/jf900079y
Chirality exists extensively in nature. Synthetic chiral plant growth regulators and other pesticides usually behave enantioselectively in phyto-biochemical processes. Chiral plant growth regulators regulate the physiological processes of plants enantioselectively, and chiral pesticides cause enantioselective toxicities or ecotoxicities to plants. On the other hand, these chiral agrochemicals can be absorbed and enantioselectively metabolized by plants. This review summarizes the enantioselective effects of chiral plant growth regulators on plants and the phytotoxic and biotransformation effects of chiral herbicides and several persistent organic pollutants (POPs) on plants. Together, this information on the interactions between chiral agrochemicals and plants might shed light on studies on the chemical and biological behaviors of chiral chemicals, and direct research into the selection of plants, which can potentially decontaminate the environment.
Co-reporter:Qingyan Zhou, Chao Xu, Yongsong Zhang and Weiping Liu
Journal of Agricultural and Food Chemistry 2009 Volume 57(Issue 4) pp:1624-1631
Publication Date(Web):January 30, 2009
DOI:10.1021/jf803673e
Chiral compounds usually behave enantioselectively in phyto-biochemical processes. With the increasing application of chiral herbicides, their enantioselective phytotoxicity to plants merits further study, and little information is available in this area. The purpose of this study was to examine the enantioselective phytotoxicity of the herbicide imazethapyr (IM) on the roots of maize (Zea mays L.) seedlings. Enantiomers of IM were separated by HPLC, and their absolute configurations were confirmed as S-(+)-IM and R-(−)-IM by the octant rule. Plant growth measurements and morphological, microscopic, and ultrastructural observations were conducted after treatment with individual IM enantiomers and the racemate. Observations of root morphology showed that the root diameter significantly increased, whereas the root volume, surface area, and number of root tips decreased significantly. IM enantiomers selectively damaged root hair growth and significantly reduced the sloughing of border cells from the tips. IM also had adverse effects on cell organelles, such as statocytes, mitochondria, dictyosomes, and endoplasmic reticulum in maize roots. Moreover, cell membranes and cell walls were thicker than usual after IM treatment. All of the results showed the same trend that the R-(−)-IM affected the root growth of maize seedlings more severely than the S-(+)-IM. The inhibition abilities of (±)-IM was between S-(+)- and R-(−)-IM. The behavior of the active enantiomer, instead of just the racemate, may have more relevance to the herbicidal effects and ecological safety of IM. Therefore, enantiomeric differences should be considered when evaluating the bioavailability of the herbicide IM.
Co-reporter:Shanshan Zhou, Datong Zhang, Huayun Yang, Ying Zhang and Weiping Liu
Journal of Agricultural and Food Chemistry 2009 Volume 57(Issue 3) pp:930-937
Publication Date(Web):January 8, 2009
DOI:10.1021/jf803188f
Storage instability is one of the serious problems that greatly restrict pesticide use. Routine checks on the composition and toxicity of 30% emulsifiable concentrates (EC) of chloramidophos (CP) during storage indicated that 78.6% of the active ingredient had decreased, whereas the anti-acetylcholinesterase (AChE) activity of the formulation was potentiated by 3.5 times. To understand the mechanism for these changes, detailed knowledge of the products present and their effects on anti-AChE potential deserves attention. It was likely that the basis for these changes was methanol, the cosolvent of CP EC, because when the purified CP was stored in methanol at 50 °C for 2 weeks, CP drop and toxic potentiation similar to those observed in CP EC also appeared. The major products of the CP−methanol reaction mixture were isolated and identified by HPLC and GC-MS, respectively, and their inhibitory potentials against AChE and effectiveness as potentiators were assessed. Following redetermination of the main product (O,S-dimethyl-[(2,2,2)-trichloro-1-methoxyethyl]phosphoramidothioate (MCP)) and high anti-AChE material (methamidophos), which were preconfirmed in the reaction mixture in CP EC, it was successfully demonstrated that the majority of CP in the formulation had been transformed to a new stable compound, MCP. Meanwhile, formation of another product, methamidophos, resulted in toxic potentiation.
Co-reporter:Shanshan Zhou, Lumei Wang, Ling Li and Weiping Liu
Journal of Agricultural and Food Chemistry 2009 Volume 57(Issue 15) pp:6920-6926
Publication Date(Web):July 15, 2009
DOI:10.1021/jf901643x
The manufacture and use of single- or enriched-enantiomer pesticides are green-chemistry developments advocated in the 21st century, but predictive work for chiral switch of newly produced chiral active ingredients is limited. In the present study, the stereoselective separation, target activity, and nontarget toxicity of O,S-dimethyl-N-(2,2,2-trichloro-1-methoxyethyl)phosphoramidothioate (MCP), a new organophosphorus compound, were investigated. Because being highly active and safe is a prerequisite for marketing single-isomer products, the above studies were used to offer some implications for the chiral switch of racemic MCP. The results showed that all four stereoisomers of MCP were successfully separated with a Chiralpak AD column on HPLC. The resolved isomers and the pairs of enantiomers were further distinguished using a circular dichroism detector, designating the first and third eluted peaks as one pair of enantiomers and the second and fourth peaks as the other pair. Then, the insecticidal activities and acute and delayed toxicities of the resolved isomers of MCP were evaluated by their acute lethal efficacy against Daphina magna, their inhibitory potentials to acetylcholinesterase (AChE), and axon-like outgrowth of the SH-SY5Y cells, respectively. The inhibition potencies of the isomers against AChE in SH-SY5Y cells were low and slightly stereoselective. On the other hand, a significant difference was observed among the isomers in their activities and delayed neurotoxicities. The 48 h acute toxicities of isomers to D. magna followed the order peak 1 ≈ pair 1 (i.e., equimolar mixture of peaks 1 and 3) > peak 4 ≈ racemate > pair 2 (i.e., equimolar mixture of peaks 2 and 4) > peak 2 > peak 3, with 1.0−6.3-fold differences among them. In comparison, the inhibitory potentials of the isomers toward axon growth of SH-SY5Y cells decreased in the order peak 2 > pair 2 > peak 4 > racemate > peak 3 > pair 1 ≈ peak 1, with at least a 60-fold difference between the strongest and weakest inhibitors. Those results imply that peak 1 has the optimal target selectivity and ecological profile among the four stereoisomers. It was calculated that two-thirds of the usual pesticide usage can be saved concomitantly with a substantial decrease in neuropathic risk if MCP is present only as peak 1 rather than the racemate. When considering the absence of the economically feasible synthetic methods and techniques to produce optically pure isomers of organophosphorus pesticides, pair 1 of MCP shows considerable worth for future applications on the basis of its biological predominance and cost effectiveness.
Co-reporter:Yun Ma;Chao Xu;Yuezhong Wen
Chirality 2009 Volume 21( Issue 4) pp:480-483
Publication Date(Web):
DOI:10.1002/chir.20624
Abstract
Chiral pesticides currently constitute about 50% of all pesticides dosage used in China, and this ratio is increasing as more complex structures are introduced. Dichlorprop methyl (DCPPM) is a chiral herbicide consisting of a pair of enantiomers. In this study, the enantiomeric separation of DCPPM was investigated by gas chromatography (GC) and high-performance liquid chromatography (HPLC) using chiral stationary phases (CSPs), and its enantiomeric degradation was characterized using a DCPPM-degrading bacterial strain isolated from an activated sludge from a textile-printing wastewater treatment plant. Baseline separation by both GC and HPLC was achieved. Incubation with DCPPM-degrading bacteria in different pH solutions showed that the R enantiomer was preferentially degraded over the S enantiomer of DCPPM. The degradation rate constant decreased with increasing pH in the order of kpH5 ≈ kpH7 >kpH9. In comparison, the enantioselectivity as indicated by EF followed the order of pH 7 > pH 9–pH 5. Chirality, 2009. © 2008 Wiley-Liss, Inc.
Co-reporter:Shanshan Zhou;Kunde Lin;Ling Li;Meiqing Jin;Jing Ye
Chirality 2009 Volume 21( Issue 10) pp:922-928
Publication Date(Web):
DOI:10.1002/chir.20690
Abstract
Enantioseletive toxicities of chiral pesticides have become an environmental concern recently. In this study, we evaluated the enantiomeric separation of salithion on a suite of commercial chiral columns and assessed the toxicity of enantiomers toward butyrylcholinesterase and Daphnia magna. Satisfactory separations of salithion enantiomers could be achieved on all tested columns, that is, Chiralcel OD, Chiralcel OJ, and Chiralpak AD column. However, the Chiralpak AD column offered the best separation and was chosen to prepare micro-scale of pure salithion enantiomers for subsequent bioassays. The first and second enantiomers eluted on the Chiralpak AD column were further confirmed to be (−)-S-salithion and (+)-R-salithion, respectively. The half inhibition concentrations to butyrylcholinesterase of racemate, (+)-R-salithion, and (−)-S-salithion were 33.09, 2.92, and 15.60 mg/l, respectively, showing (+)-R-enantiomer being about 5.0 times more potent than its (−)-S-form. However, the median lethal concentrations (96 h) of racemate, (+)-R-salithion, and (−)-S-salithion toward D. magna were 3.54, 1.10, and 0.36 μg/l, respectively, suggesting that (−)-S-salithion was about 3.0 times more toxic than (+)-R-form. Racemic salithion was less toxic than either of the enantiomers in both bioassays, suggesting that antagonistic interactions might occur between the enantiomers during the toxication action. This work reveals that the toxicity of salithion toward butyrylcholinesterase and D. magna is enantioselective, and this factor should be taken into consideration in the environmental risk assessment of salithion. Chirality 2009. © 2009 Wiley-Liss, Inc.
Co-reporter:Zhou Ying;Li Ling;Lin Kunde;Zhu Xinping ;Liu Weiping
Chirality 2009 Volume 21( Issue 4) pp:421-427
Publication Date(Web):
DOI:10.1002/chir.20607
Abstract
Enantiomer separation is one of the most important prerequisites for the investigation of environmental enantioselective behaviors for chiral pesticides. In the present study, the enantiomer separation of 7 triazole fungicides, i.e., hexaconazole (1), triadimefon (2), tebuconazole (3), diniconazole (4), flutriafol (5), propiconazole (6), and difenoconazole (7), were evaluated using normal phase high-performance liquid chromatography. Chrialcel OD column and Chrialcel OJ column were used. The influence of column temperature was studied for the optimization of the resolution as well as the type and percentage of organic modifier in the mobile phase. The retention factors for the enantiomers of all investigated compounds decreased as the temperature increased. The natural logarithms of the selectivity factors (lnα) of hexaconazole (1), tebuconazole (3), flutriafol (5), propiconazole (6) and difenoconazole (7) depended linearly on the inverse of temperature (1/T) while the corresponding values for triadimefon (2) and diniconazole (4) kept unchanged in the studied temperature range 10–35 °C. Van't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy ΔH°, the apparent change in entropy ΔS°and the apparent change in ΔΔH° and ΔΔS°. The thermodynamic parameters (ΔH°, ΔS°, ΔΔH° and ΔΔS°) were calculated in order to provide an understanding of the thermosynamic driving forces for enantioseparation. The established method shows perspective to be used for preparing micro-scale amount of pure enantiomers of the chiral triazoles studied. Chirality, 2009. © 2008 Wiley-Liss, Inc.
Co-reporter:Shengwen Chen
Bulletin of Environmental Contamination and Toxicology 2009 Volume 82( Issue 3) pp:327-331
Publication Date(Web):2009 March
DOI:10.1007/s00128-008-9559-6
Enantioselective degradation occurs frequently for chiral pesticides in field matrices and under laboratory conditions. Metalaxyl is a chiral compound and important fungicide. In this study, the degradation of Rac- and R-metalaxyl under anaerobic conditions was studied. The degradation processes were found to follow first-order kinetics. The degradation of the S-enantiomer (T1/2 = 2.10 days) was much faster than the R-enantiomer (T1/2 = 8.44 days). The half-life of the Rac-metalaxyl mixture was 4.05 days, which was higher than the S-enantiomer, but lower than the R-enantiomer. These results confirm the need for emphasizing the importance of examining the fate of the stereoisomers in an environmental system.
Co-reporter:Jing Ye;Qiong Zhang;Anping Zhang
Bulletin of Environmental Contamination and Toxicology 2009 Volume 83( Issue 1) pp:85-91
Publication Date(Web):2009 July
DOI:10.1007/s00128-009-9773-x
In this study, the acute toxicity (72-h EC50 values) of chiral diclofop acid towards rice Xiushui 63 seedlings and its effects on the Hill reaction activities of chloroplasts were determined. Significant differences were observed between the two enantiomers in 72-h EC50 values and in both in vivo and in vitro relative Hill reaction activities. These observations indicate that the enantiomers of diclofop acid pose different toxicities to rice seedlings: the S-enantiomer is more toxic to leaves and the R-enantiomer is more toxic to roots. These enantioselective toxic effects on rice seedlings should be taken into account in chiral herbicide application.
Co-reporter:Xiyun Cai;Jing Ye;Guangyao Sheng
Environmental Science and Pollution Research 2009 Volume 16( Issue 4) pp:459-465
Publication Date(Web):2009 June
DOI:10.1007/s11356-008-0077-1
As emerging contaminants, transformation products of the pollutants via various environmental processes are rather unknown, and some may predominately contribute to the environmental risks of the parent compounds. Hence, studies on transformation products complement the assessment of the environmental safety of the parent compounds. In this study, degradation experiments and toxicity tests using diclofop-methyl (DM), a widely used herbicide, and selected major transformation products were carried out in algal cultures to assess the time course of DM toxicity and its relevance in the formation of new breakdown products.The alga Chlorella vulgaris was maintained in the algal growth medium HB IV. The inhibition of algal growth was determined by measuring optical density at 680 nm (OD680). Initially, DM and two selected breakdown products were added to the algal cultures, and following degradation experiments analyses were carried out by high performance liquid chromatography. In addition, the possible relationship between DM degradation and toxicity was assessed, based on physico-chemical properties of the compounds and their toxicity.DM was rapidly absorbed onto the surface of the algal cells where it was hydrolyzed to diclofop (DC). Further degradation to 4-(2, 4-dichlorophenoxy) phenol (DP) occurred in the cells. However, only a minor amount of DC was degraded to DP under the same conditions when DC was initially added to the algal culture. When C. vulgaris was exposed to these compounds for 96 h, the determined EC50 showed that DC was about ten times less toxic than DM (EC50 = 0.42 mg/L) and that DP (EC50 = 0.20 mg/L) was the most toxic.Due to strong hydrophobicity and rare dissociation, DM has tendency toward absorption as compared to DC. The higher average degradation rates of DC initially treated by DM revealed the damage of the cell membranes caused by the DM and, thus, enhanced movement of DC into the cells. Following occurrence of phenolic breakdown products, DP suggested that DC should be intracellularly degraded to DP, which had a more potent mode of action and a higher acute toxicity. Moreover, the results for EC50 at various intervals were in accordance with degradation processes of the initial compounds, in which rapid formation of DP was attributed to an increasing toxicity of DM.The toxicity of DM in algal suspensions increased with time due to its degradation to DP, which contributed significantly to the determined toxicity. These results indicate that the toxicity of the pesticide probably depends significantly on degradation. It is thus important to consider the time-dependent environmental processes when evaluating the toxicological effects of pesticides for proper risk assessment.Increasing transformation products of these contaminants are identified in the environment, although they seem to be unknown in terms of the lacking studies on environmental behavior and ecotoxicity concerning them. Certain breakdown products probably greatly contribute to the apparent toxicity of the parent compounds, which is ascribed to the parent compounds in general studies ignoring the dependence of their toxicity on various transformation pathways. These studies that identify new intermediates and assess their toxicity via the environmental processes will be helpful to distinguish the nature of toxicity of the parent contaminants.
Co-reporter:Chao Xu, Meirong Zhao, Weiping Liu, Shengwen Chen, and Jiangying Gan
Chemical Research in Toxicology 2008 Volume 21(Issue 5) pp:1050
Publication Date(Web):April 17, 2008
DOI:10.1021/tx8000016
Enantioselectivity in separation and toxicology of chiral xenobiotics have become one of the frontier topics interfacing chemistry and toxicology. In this study, enantiomers of insecticide acetofenate (AF) were separated on selected chiral columns by HPLC, and enantioselectivity in developmental toxicity was evaluated using the zebrafish embryo-larval assays. The AF enantiomers were baseline separated on Chiralcel OD, Chiralpak AD, and Sumichiral OA-2500I columns under optimized conditions. Pure enantiomers were obtained on Chiralcel OD. Optical rotatory dispersion (ORD) and circular dichroism (CD) detectors were used to determine the elution order and CD spectra of the enantiomers. The absolute configuration of enantiomers was identified as S-(+)-AF and R-(−)-AF by the octant rule from force-field calculations and CD spectra. The individual enantiomers were used in 4-day zebrafish embryo-larval bioassays, and a series of developmental end points were measured and compared. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to investigate the expressions of estrogen receptor alpha (ERα) in zebrafish embryo exposed to varying enantiomers. While the enantiomers showed no difference in acute toxicity, significant enantioselectivity was observed in developmental toxicities such as yolk sac edema and pericardial edema. The data of qRT-PCR showed that there was about 3.2-fold induction in the mRNA levels of ERα between fish exposed to (+)-AF and (−)-AF. The results suggest that enantioselectivity may occur at the developmental level even in the absence of selective acute toxicity and should be considered when evaluating ecotoxicological effects of chiral contaminants.
Co-reporter:Xiyun Cai, Weiping Liu and Guangyao Sheng
Journal of Agricultural and Food Chemistry 2008 Volume 56(Issue 6) pp:2139-2146
Publication Date(Web):March 5, 2008
DOI:10.1021/jf0728855
Aryloxyphenoxypropanoates are a class of chiral herbicides. They have a pair of enantiomers, only the R(+) form of which is herbicidally active. Diclofop, the model compound of these herbicides, is commercialized as the racemate of the ester form, diclofop-methyl, consisting of a 1:1 mixture of the enantiomers. This study evaluated the enantioselectivity in aquatic toxicity and biodegradation of diclofop and diclofop-methyl. The herbicidally inactive S(−) enantiomers of both diclofop-methyl and diclofop were similar to or higher than the corresponding R(+) forms in toxicity to algae, depending on specific species. Although no enantiomeric conversion occurred for diclofop-methyl and diclofop, the difference in the enantioselective degradation of these herbicides observed in algae cultures suggested that their application forms were an important factor determining their enantioselective environmental behavior. The cell permeability and heat treatment of algae revealed that the enantioselective degradation of diclofop in algae cultures was governed primarily by the facilitated uptake by algae, whereas the enantioselective toxicity was primarily governed by the passive uptake. These results suggested that the acute toxicity test such as the 96 h EC50 was insufficient to assess the ecological risk of chiral pesticides because of the differential degradation as well as possibly differential action sites of enantiomers. From this study, it was concluded that the enantioselective degradation and toxicity of chiral herbicides may result in their ecotoxicological effects being difficult to predict and that specific attention should thus be paid to currently used racemic pesticides as less active or inactive enantiomers may pose higher ecological risks.
Co-reporter:Shanshan Zhou, Lumei Wang, Anping Zhang, Kunde Lin and Weiping Liu
Journal of Agricultural and Food Chemistry 2008 Volume 56(Issue 8) pp:2708-2713
Publication Date(Web):March 28, 2008
DOI:10.1021/jf703635p
Cyclodextrins are common compounds capable of forming inclusion complexes with a variety of pesticides to improve their solubility, bioavailability, and stability. In this study, chloramidophos (CP) was inclusion-complexed with β-cyclodextrin (β-CD) by a kneading method in an attempt to gain a more stable but equally effecacious formulation compared with CP alone. A 1:1 CP−β-CD complex with an inclusion constant of 203.0 M−1 was determined to exist by UV spectrophotometry. The structural identification, thermal stability, and biological assays of the CP−β-CD complex were then carried out with a product with the maximum guest loading efficiency. The data mearsured by differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD), where the endothermic peaks of β-CD, the FT-IR bands, and the XRD peaks were generally changed, deduced the formation of complex. Results of the thermal stability assay showed that the degradation rate of CP in 14-day incubation was slowed by a factor of 3.6 when it was complexed with β-CD. Then, activity and toxicity of CP influenced by the encapsulated process of β-CD were evaluated by an in vitro acetylcholinesterase (AChE) inhibition assay and an acute aquatic toxicity assay, respectively. No significant differences were found in both the two biological assays by a t-test. This indicated that the encapsulation process greatly improved the thermal stability of the pesticide with no adverse effects on bioefficacy compared to that of CP. There is a promising outlook for CP−β-CD to be produced as the active ingredient of various formulation additives of CP for its continued application.
Co-reporter:Kunde Lin, Weiping Liu, Ling Li and Jay Gan
Journal of Agricultural and Food Chemistry 2008 Volume 56(Issue 11) pp:4273-4277
Publication Date(Web):May 20, 2008
DOI:10.1021/jf073535l
Although enantioselectivity in the toxicity of chiral pesticides has received considerable attention over recent years, how coexisting enantiomers interact with each other during their toxic action remains unknown. In this study, we attempted to resolve the enantiomers of a chiral organophosphate insecticide, isocarbophos, and investigated the acute toxicity of individual enantiomers and various enantiomer mixtures. Baseline enantiomeric separation of isocarbophos was achieved on a Chiralcel OD column with the mobile phase of n-hexane/isopropanol (90/10, v/v) at a flow rate of 0.8 mL/min. The resolved enantiomers were differentiated by their responses on a circular dichroism detector. The median lethal concentrations (LC50) of racemate, (+)-enantiomer, and (−)-enantiomer of isocarbophos toward Daphnia magna were 13.9, 7.08, and 353 µg/L, respectively, after 48 h of static exposure, displaying a 50-fold difference between the enantiomers. Toxic unit (TU) analysis was employed to evaluate the joint toxicity of isocarbophos enantiomer mixtures. The calculated TUmix for the acute toxicity (48 h test) of various binary mixtures ranged from 0.83 to 1.04, suggesting a mode of additive effect. Further evaluation of available literature data for chiral organophosphorus insecticides showed that the joint toxicity of enantiomers may be additive, synergistic, and antagonistic. Therefore, when significant enantioselectivity exists for a chiral pesticide, it is important to also evaluate the interaction of enantiomers in the joint toxicity effect when enantiomers are present in a mixture.
Co-reporter:Shengwen Chen
Bulletin of Environmental Contamination and Toxicology 2008 Volume 81( Issue 6) pp:531-534
Publication Date(Web):2008 December
DOI:10.1007/s00128-008-9567-6
Chirality in pesticides has become a challenge because of enantiomers’ different toxicities to non-target organisms. Acute and chronic toxicities of Rac-metalaxyl and R-metalaxyl to Daphnia magna were determined and compared. The 48-h LC50 for Rac- and R-metalaxyl to Daphnia magna were 51.5 and 41.9 mg/L. In a 14-day chronic test, the lowest-observed-effective concentration (LOEC) and no-observed-effective concentration (NOEC) of Rac-metalaxyl were 2 and 1 mg/L, respectively, whereas those of R-metalaxyl were 1 and 0.1 mg/L. Body length, days-to-first-brood and number of broods per female were significantly (p < 0.05) affected by R-metalaxyl at >1.0 mg/L, but affected by Rac-metalaxyl at ≥2.0 mg/L.
Co-reporter:Kunde Lin;Chao Xu;Jay Gan;Shanshan Zhou
Chirality 2007 Volume 19(Issue 3) pp:171-178
Publication Date(Web):13 DEC 2006
DOI:10.1002/chir.20359
Chiral high-performance liquid chromatography (HPLC) is one of the most powerful tools to prepare enantiopure standards of chiral compounds. In this study, the enantiomeric separation of imidazolinone herbicides, i.e., imazethapyr, imazapyr, and imazaquin, was investigated using chiral HPLC. The enantioselectivity of Chiralpak AS, Chiralpak AD, Chiralcel OD, and Chiralcel OJ columns for the three analytes was compared under similar chromatographic conditions. Chiralcel OJ column showed the best chiral resolving capacity among the test columns. The resolved enantiomers were distinguished by their signs of circular dichroism detected at 275 nm and their structures confirmed with LC-mass spectrometric analysis. Factors affecting the chiral separation of imidazolinones on Chiralcel OJ column were characterized. Ethanol acted as a better polar modifier than the other alcohols including 2-propanol, 1-butanol, and 1-pentanol. Although the acidic modifier in the mobile phase did not influence chiral recognition, it was necessary for reducing the retention time of enantiomers and suppressing their peak tailing. Thermodynamic evaluation suggests that enantiomeric separation of imidazolinones on Chiralcel OJ column is an enthalpy-driven process from 10 to 40°C. This study also shows that small amounts of pure enantiomers of imidazolinones may be obtained by using the analytical chiral HPLC approach. Chirality 19, 2007. © 2006 Wiley-Liss, Inc.
Co-reporter:Weiping Liu;Jianying Gan;Kunde Lin
Chirality 2006 Volume 18(Issue 9) pp:713-716
Publication Date(Web):14 JUL 2006
DOI:10.1002/chir.20323
Many of the organophosphorus pesticides (OPs) currently used are chiral and therefore consist of mixture of enantiomers. Despite the fact that the biological processes of chiral pesticides are enantioselective, the acute aquatic toxicity of chiral OPs with respect to enantioselectivity has so far received limited research. In this study, the enantiomeric separation and acute aquatic toxicity of trichloronate were investigated. Baseline enantioseparation of trichloronate was successfully achieved using high-performance liquid chromatography on a Chiralcel OJ column, with a mobile phase of n-hexane/n-heptane/ethanol (90/5/5, v/v/v) at the flow rate of 1.0 ml min−1 and room temperature. The resolved enantiomers were characterized for their optical rotation and by gas chromatography coupled with mass spectrometry. Significant differences were found between the enantiomers in acute aquatic toxicity to Ceriodaphnia dubia and Daphnia magna. The (−)-trichloronate was 8–11 times more toxic to the test organisms than its (+)-form, while the racemate showed intermediate toxicity. These results suggest that assessment of the environmental safety of chiral OPs should take stereospecificity into consideration. Chirality, 2006. © 2006 Wiley-Liss, Inc.
Co-reporter:Qingyan Zhou, Weiping Liu, Yongsong Zhang, Kevin K. Liu
Pesticide Biochemistry and Physiology (October 2007) Volume 89(Issue 2) pp:89-96
Publication Date(Web):1 October 2007
DOI:10.1016/j.pestbp.2007.04.004
Herbicides that target the acetolactate synthase (ALS) are among the most widely used weed control chemicals since their introduction into the marketplace in the early 1980s, including five classes (sulfonylureas, imidazolinones, triazolopyrimidines, pyrimidinylthio (or oxy)-benzoates and sulfonylamino-carbonyltriazolinones). The mechanism researches have progressed unprecedentedly in the last two decades. Primary mode of action of the ALS-inhibiting herbicides that interfere with the activity of ALS enzyme seems no longer in doubt. Three lines of investigation from physiology, genetics, molecular and chemical structure aspects came together to prove that ALS is the site of action. Researches on the effects of branched chain amino acids (BCAAs) synthesis or protein metabolism caused by ALS-inhibiting herbicide elicit lots of disputations. Besides these two main works, other secondary effects of ALS inhibition, such as buildup of 2-ketobutyrate (α-ketobutyrate or 2-KB) or 2-aminobutyrate (2-AB, the transamination product of 2-KB), depletion of intermediates of the pathway for some critical processes, disruption of photosynthesis transport and respiration system etc., have also been implicated in the mechanism of plant death. However, there are still some disputations and doubts on the precise mechanisms that need further probing into. Further more, as many ALS-inhibiting herbicides and their derivatives are chiral with one or even more enantiomers, which may behave quite differently in biochemical processes, the effects and the environmental fate of chiral herbicides need to be investigated stereospecifically. By this, we can have a better understanding about the herbicides and avoid unnecessary pollution load.
Co-reporter:Yuanxiang Jin, Rujia Chen, Liwei Sun, Wanyuan Wang, Lin Zhou, Weiping Liu, Zhengwei Fu
Chemosphere (March 2009) Volume 74(Issue 9) pp:1238-1244
Publication Date(Web):1 March 2009
DOI:10.1016/j.chemosphere.2008.11.015
Enantioselectivity in the separation, toxicology, biodegradation and estrogenic activity of chiral pesticides has become a groundbreaking topic recently. In this study, real-time, quantitative polymerase chain reaction was adapted to investigate the induction of estrogen-responsive gene expression in embryo-larval zebrafish after 7 d of exposure to permethrin (PM) enantiomers. The PM enantiomers were completely separated by a chiral HPLC column. The in vivo study found that a 7 d exposure to 250 ng L−1 PM racemate and its enantiomers was sufficient to stimulate vtg1, esrα and cyp19b expression, while 1000 ng L−1 exposure significantly induced gene expression in a pattern similar to that of the control (50 ng L−1 E2), except for vtg2. Significant differences were detected between the enantiomers in the induction of estrogen-responsive gene expression. At the exposure level of 1000 ng L−1, the vtg1, esrα and cyp19b responses to the (−)-trans enantiomer were about 3.2-, 1.8- and 1.5-fold higher, respectively, than those in the group treated with (+)-trans enantiomer (p < 0.05). In the two cis-enantiomer treatment groups, (+)-cis increased the mRNA level of the cyp19b gene about 1.5-fold higher than the (−)-cis-enantiomer did. Of the four enantiomers, the (−)-trans enantiomer showed the greatest estrogenic activity. The results strongly indicate the occurrence of significant enantioselectivity in estrogenic activity of PM enantiomers exposed to embryo-larval zebrafish. These findings add to a growing body of evidence concerning enantioselectivity in the toxicity, endocrine-disrupting activity, and environmental biodegradation of chiral pesticides.
Co-reporter:Chao Xu, Anping Zhang, Weiping Liu
Pesticide Biochemistry and Physiology (June 2007) Volume 88(Issue 2) pp:176-180
Publication Date(Web):1 June 2007
DOI:10.1016/j.pestbp.2006.10.009
Organophosphorus pesticides (OPs) are of environmental significance due to their high toxicity to animals. Binding to plasma proteins may effective influence the toxicological properties of xenobiotics. In an attempt to evaluate the affinity of phenthoate (PTA) to bovine serum albumin (BSA) and inhibitory ability of bound PTA to acetylcholinesterase (AChE), we investigated the interactions between phenthoate (PTA) and bovine serum albumin (BSA) using tryptophan fluorescence quenching and subsequent inhibition on AChE activity by PTA. The results showed that PTA caused the fluorescence quenching of BSA because of the formation of a PTA–BSA complex. Quenching constants (Ksv), determined using the Sterns–Volmer equation to provide a measure of the binding affinity between PTA and BSA at 303, 306, 310 and 313 K were (3.4295 ± 0.0763) × 10−4, (3.2446 ± 0.0635) × 10−4, (3.0434 ± 0.0856) × 10−4 and (2.8262 ± 0.0569) × 10−4 M−1, respectively. The thermodynamic parameters, ΔH and ΔS were −25.04 kJ mol−1 and 168.94 J mol−1 K−1, respectively, which indicated that the electrostatic interactions played a major role in PTA–BSA association. The presence of BSA consistently reduced the inhibitory ability of PTA on AChE, with the relative activity being increased from 46.98 to 61.71% for the concentration range of BSA between 0 and 4.0 g L−1.
Co-reporter:Huayun Yang, Bin Xue, Peng Yu, Shanshan Zhou, Weiping Liu
Chemosphere (July 2010) Volume 80(Issue 6) pp:652-659
Publication Date(Web):1 July 2010
DOI:10.1016/j.chemosphere.2010.04.052
The spatial distributions and chiral signals of organochlorine pesticides (OCPs) in surface sediments from Yueqing Bay and Sanmen Bay, East China Sea were investigated. The total OCPs concentrations ranged from 2.11 to 18.15 ng g−1 dry weight for all the sampling stations. HCHs and DDTs were dominant, although trans-chlorodane/cis-chlorodane were also observed in some sites. The predominant β-HCH and the α-HCH/γ-HCH ratios indicated that the residues of HCHs in these places mainly originated from the historical usage of technical HCH. However, the ratios of (DDE + DDD)/DDT reflected a cocktail input pattern of fresh and weathered DDTs. Based on ERL/ERM guidelines, p,p′-DDT and ΣDDT posed a small risk to the bottom-dwelling consumers, while p,p′-DDD, p,p′-DDE and Σchlorodane were not found at concentrations expected to adversely affect sediment biota. Enantiomeric analysis showed that the degradation of chiral OCPs was enantioselective, resulting in enrichment of (−)-enantiomers for α-HCH, o,p′-DDT and o,p′-DDD in all samples. These results implied that the sediment quality guidelines of chiral OCPs should be reassessed using concentrations of their individual enantiomers.
Co-reporter:Haifeng Qian, Haijia Hu, Yuanyuan Mao, Jian Ma, Anping Zhang, Weiping Liu, Zhengwei Fu
Chemosphere (August 2009) Volume 76(Issue 7) pp:885-892
Publication Date(Web):1 August 2009
DOI:10.1016/j.chemosphere.2009.05.009
Research increasingly suggests that enantiomer selectivity may be a part of the toxicological effects of chiral contaminants. In this study, we selected Japonica rice variety Xiushui 63 seedlings to evaluate the enantioselectivity of imazethapyr (IM). Significant differences in rice seedling morphology, antioxidant enzyme, oxidant marker and gene transcription were observed between the two IM enantiomers. In the seedling morphological assay, IM enantiomers inhibited elongation of primary roots and shoots, and reduced the number of adventitious roots and the density of root hairs. The inhibitory effects were enhanced with increasing concentrations of IM. The maximal root relative inhibition rate reached 80.4%, 67.0%, and 73.5% for R-(−)-IM, S-(+)-IM and racemate at the concentration of 0.5 mg L−1, respectively, and the maximal shoot relative inhibition rate reached 77.7%, 26.9%, and 61.7%, respectively. The activities of SOD, POD and CAT and the content of MDA increased at 0.5 mg L−1 of R-(−)-IM treatment, and were 1.8, 3.3, 1.4, and 2.2 times, respectively, over the activities S-(+)-IM. Real-time PCR showed that R-(−)-IM minimized the transcript abundance of ALS in shoot tissue to 12.2% of the S-(+)-IM, and minimized the transcript abundance of PC in seed to 9.2% of the S-(+)-IM. R-(−)-IM maximized the transcript abundance of β-amylase in shoots to 8.6-time of the S-(+)-IM. Results from this study imply that R-(−)-IM has stronger toxicity on the growth of rice than S-(+)-IM.
Co-reporter:Yuanxiang Jin, Wanyuan Wang, Chao Xu, Zhengwei Fu, Weiping Liu
Aquatic Toxicology (23 June 2008) Volume 88(Issue 2) pp:146-152
Publication Date(Web):23 June 2008
DOI:10.1016/j.aquatox.2008.04.004
Co-reporter:Huigang Liu, Meirong Zhao, Cong Zhang, Yun Ma, Weiping Liu
Toxicology (20 November 2008) Volume 253(Issues 1–3) pp:89-96
Publication Date(Web):20 November 2008
DOI:10.1016/j.tox.2008.08.015
Synthetic pyrethroids (SPs) are used in preference to organochlorines and organophosphates due to their high efficiency, low toxicity to mammals, and ready biodegradability. Previous studies reported that enantioselective toxicity of SPs occurs in aquatic toxicity. Several studies have indicated that SPs could lead to oxidative damage in humans or animals which was associated with their toxic effects. Little is known about the differences in the effects of chronic toxicity induced by individual stereoisomers of chiral SPs. The present study was therefore undertaken to evaluate the enantioselectivity in cytotoxicity, genotoxicity caused by bifenthrin (BF) on human amnion epithelial (FL) cell lines and pesticidal activity on target organism. The cell proliferation and cytoflow analysis indicated that 1S-cis-BF presented more toxic effects than 1R-cis-BF above the concentration of 7.5 mg L−1 (p > 0.05). FL cells incubated with 1S-cis-BF exhibited a dose-dependent accumulation of intracellular reactive oxygen species (ROS). In the comet assay, the number of cells with damaged DNA incubated with 1S-cis-BF was more than that with 1R-cis-BF (p < 0.01). While the LC50 values of enantiomer to the target pest on Pieris rapae L. show that 1R-cis-BF was 300 times more active than 1S-cis-BF. These results indicate that the enantioselective toxicity and activity of BF between non-target organism and target organism was reversal. These implications together suggest that assessment of the environmental safety and new pesticides development with chiral centers should consider enantioselectivity.
Co-reporter:Haifeng Qian, Wei Chen, Jingjing Li, Jie Wang, Zhen Zhou, Weiping Liu, Zhengwei Fu
Aquatic Toxicology (17 May 2009) Volume 92(Issue 4) pp:250-257
Publication Date(Web):17 May 2009
DOI:10.1016/j.aquatox.2009.02.008
Co-reporter:Huigang Liu, Lihong Xu, Meirong Zhao, Weiping Liu, Cong Zhang, Shanshan Zhou
Toxicology (10 July 2009) Volume 261(Issue 3) pp:119-125
Publication Date(Web):10 July 2009
DOI:10.1016/j.tox.2009.05.002
Enantioselectivity in toxicology, and health risk of chiral xenobiotics have become important topics at the forefront of chemistry and toxicology research. Our previous results showed that cis-bifenthrin (cis-BF) induced cytotoxicity and genotoxicity in human amnion epithelial (FL) cells, in an enantioselective manner. However, the exact molecular mechanisms of synthetic pyrethroid-induced, enantioselective apoptosis and cytotoxicity remain unclear. In this study, enantiomers of the synthetic pyrethroid-based insecticide, cis-BF, were separated on selected chiral columns by HPLC. Enantioselectivity in cytotoxicity and apoptosis, mediated by the mitogen-activated protein kinase (MAPK) signalling pathway, were evaluated in the human hepatocellular liver carcinoma (Hep G2) cell line. Exposure to 1S-cis-BF resulted in increased levels of phosphorylated JNK (Jun-N-terminal Kinases)/MAPKs, while exposure to 1R-cis-BF did not affect phosphorylated JNK levels. Pre-treatment with the JNK inhibitor SP600125, blocked 1S-cis-BF-induced cytotoxicity and apoptosis. In addition, 1S-cis-BF enhanced the production of ROS, while pre-treatment with the antioxidant agent MnTBAP resulted in decreased phosphorylation of JNK. To the best of our knowledge, this is the first report demonstrating that cis-BF-induced apoptosis might occur, at least in part, through the enantioselective activation of JNK/MAPK signalling pathway in Hep G2 cells. The results suggest that enantioselectivity should be considered when evaluating eco-toxicological effects and health risks of chiral contaminants, and could also improve the understanding of molecular mechanisms responsible for chiral chemical-induced cytotoxicity and apoptosis.
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