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Patrick J. Guiry - One of the best experts on this subject based on the ideXlab platform.
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application of a one pot friedel crafts alkylation michael addition methodology to the asymmetric synthesis of ergoline derivatives
European Journal of Organic Chemistry, 2017Co-Authors: Christina Despotopoulou, Sean C. Mckeon, Robert Connon, Vincent Coeffard, Helge Mullerbunz, Patrick J. GuiryAbstract:Herein, we report a short and facile stereoselective route to ergoline derivatives. The key steps are a one-pot Friedel–Crafts alkylation/Michael addition sequence which, in the absence of chiral ligands, affords the trans-trans-Stereoisomer in 44 % yield as a racemate. Screening of a range of chiral bisoxazoline ligands allowed this sequence to proceed in 42–55 % yields (six examples), with up to 99 % ee. This approach allows for the first time, substitution at the C4-position and the introduction of 3 chiral centres in one pot. An interesting, base-mediated conversion of the trans-trans-Stereoisomer to the cis-cis-Stereoisomer was discovered and both Stereoisomers were characterized by X-ray crystallography.
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Application of a One-Pot Friedel-Crafts Alkylation/Michael Addition Methodology to the Asymmetric Synthesis of Ergoline Derivatives
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2017Co-Authors: Christina Despotopoulou, Sean C. Mckeon, Robert Connon, Vincent Coeffard, Helge Mueller-bunz, Patrick J. GuiryAbstract:Herein, we report a short and facile stereoselective route to ergoline derivatives. The key steps are a one-pot Friedel-Crafts alkylation/Michael addition sequence which, in the absence of chiral ligands, affords the trans-trans-Stereoisomer in 44% yield as a racemate. Screening of a range of chiral bisoxazoline ligands allowed this sequence to proceed in 42-55% yields (six examples), with up to 99% ee. This approach allows for the first time, substitution at the C-4-position and the introduction of 3 chiral centres in one pot. An interesting, base-mediated conversion of the trans-trans-Stereoisomer to the cis-cis-Stereoisomer was discovered and both Stereoisomers were characterized by X-ray crystallography.
Yongquan Zheng - One of the best experts on this subject based on the ideXlab platform.
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stereoselective bioactivity acute toxicity and dissipation in typical paddy soils of the chiral fungicide propiconazole
Journal of Hazardous Materials, 2018Co-Authors: Xinglu Pan, Youpu Cheng, Fengshou Dong, Xingang Liu, Na Liu, Yongquan ZhengAbstract:Abstract Propiconazole is a widely used systemic agricultural triazole fungicide with two chiral centers. In the present study, systemic assessments of propiconazole Stereoisomers are reported for the first time, including absolute configuration, stereoselective bioactivity toward pathogens (Ustilaginoidea virens, Magnaporthe oryzae, Fusarium moniliforme, Thanatephorus cucumeris, and Rhizoctonia solani), and stereoselective acute toxicity toward aquatic organisms (Scenedesmus obliquus, and Daphnia magna). Moreover, the stereoselective dissipation of propiconazole in three types of paddy soil under laboratory-controlled conditions (aerobic, anaerobic and sterile) was investigated. The degree of bioactivity and acute toxicity of the propiconazole Stereoisomers differed depending on the type of target pathogens and non-target organisms. There were 2.43–23.47 and 1.48–2.13 fold differences between the best and worst Stereoisomer in bioactivity and toxicity, respectively. Under aerobic conditions, (2S,4S)-propiconazole and (2S,4R)-propiconazole were preferentially degraded in the three types of soils. However, no significant stereoselectivity was observed under anaerobic and sterile conditions. Propiconazole was configurationally stable throughout the study. In comprehensive consideration of bioactivity, toxicity and environmental behavior, using Stereoisomer mixture rather than pure Stereoisomer may help to control more species of disease in practical application, and the stereoselectivity should be taken into consideration in risk assessment.
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chiral triazole fungicide difenoconazole absolute stereochemistry stereoselective bioactivity aquatic toxicity and environmental behavior in vegetables and soil
Environmental Science & Technology, 2013Co-Authors: Fengshou Dong, Xiu Chen, Xingang Liu, Bezhan Chankvetadze, Yongpu Cheng, Carlo Bertucci, Daniele Tedesco, Riccardo Zanasi, Yongquan ZhengAbstract:In this study, the systemic assessments of the Stereoisomers of triazole fungicide difenoconazole are reported for the first time, including absolute stereochemistry, stereoselective bioactivity toward pathogens (Alternaria sonali, Fulvia fulva, Botrytis cinerea, and Rhizoctonia solani), and toxicity toward aquatic organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Moreover, the stereoselective degradation of difenoconazole in vegetables (cucumber, Cucumis sativus and tomato, Lycopersicon esculentum) under field conditions and in soil under laboratory-controlled conditions (aerobic and anaerobic) was investigated. There were 1.33-24.2-fold and 1.04-6.78-fold differences in bioactivity and toxicity, respectively. Investigations on the stereoselective degradation of difenoconazole in vegetables showed that the highest-toxic and lowest-bioactive (2S,4S)-Stereoisomer displays a different enrichment behavior in different plant species. Under aerobic or anaerobic conditions, (2R,4R)- and (2R,4S)-difenoconazole were preferentially degraded in the soil. Moreover, difenoconazole was configurationally stable in the test soil matrices. On the basis of biological activity, ecotoxicity, and environmental behavior, it is likely that the use of pure (2R,4S)-difenoconazole instead of the commercial Stereoisomer mix may help to increase the bioactivity and reduce environmental pollution.
Christina Despotopoulou - One of the best experts on this subject based on the ideXlab platform.
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application of a one pot friedel crafts alkylation michael addition methodology to the asymmetric synthesis of ergoline derivatives
European Journal of Organic Chemistry, 2017Co-Authors: Christina Despotopoulou, Sean C. Mckeon, Robert Connon, Vincent Coeffard, Helge Mullerbunz, Patrick J. GuiryAbstract:Herein, we report a short and facile stereoselective route to ergoline derivatives. The key steps are a one-pot Friedel–Crafts alkylation/Michael addition sequence which, in the absence of chiral ligands, affords the trans-trans-Stereoisomer in 44 % yield as a racemate. Screening of a range of chiral bisoxazoline ligands allowed this sequence to proceed in 42–55 % yields (six examples), with up to 99 % ee. This approach allows for the first time, substitution at the C4-position and the introduction of 3 chiral centres in one pot. An interesting, base-mediated conversion of the trans-trans-Stereoisomer to the cis-cis-Stereoisomer was discovered and both Stereoisomers were characterized by X-ray crystallography.
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Application of a One-Pot Friedel-Crafts Alkylation/Michael Addition Methodology to the Asymmetric Synthesis of Ergoline Derivatives
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2017Co-Authors: Christina Despotopoulou, Sean C. Mckeon, Robert Connon, Vincent Coeffard, Helge Mueller-bunz, Patrick J. GuiryAbstract:Herein, we report a short and facile stereoselective route to ergoline derivatives. The key steps are a one-pot Friedel-Crafts alkylation/Michael addition sequence which, in the absence of chiral ligands, affords the trans-trans-Stereoisomer in 44% yield as a racemate. Screening of a range of chiral bisoxazoline ligands allowed this sequence to proceed in 42-55% yields (six examples), with up to 99% ee. This approach allows for the first time, substitution at the C-4-position and the introduction of 3 chiral centres in one pot. An interesting, base-mediated conversion of the trans-trans-Stereoisomer to the cis-cis-Stereoisomer was discovered and both Stereoisomers were characterized by X-ray crystallography.
Thomas Poiger - One of the best experts on this subject based on the ideXlab platform.
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stereoselective metabolism of the sterol biosynthesis inhibitor fungicides fenpropidin fenpropimorph and spiroxamine in grapes sugar beets and wheat
Journal of Agricultural and Food Chemistry, 2016Co-Authors: Ignaz J Buerge, Jurgen Krauss, Rocio Lopezcabeza, Werner Siegfried, Michael Stussi, Felix E Wettstein, Thomas PoigerAbstract:Metabolism of chiral pesticides in crops is typically studied using achiral analytical methods and, consequently, the Stereoisomer composition of residues is unknown. In this study, we developed an enantioselective GC-MS/MS method to quantify residues of the fungicides fenpropidin, fenpropimorph, and spiroxamine in plant matrices. In field trials, the fungicides were applied to grapevines, sugar beets, or wheat. Fenpropidin was metabolized with no or only weak enantioselectivity. For fenpropimorph, slightly enantioselective metabolism was observed in wheat but more pronounced in sugar beets. This enantioselectivity was due to different rates of metabolism and not due to interconversion of enantiomers. The four Stereoisomers of spiroxamine were also metabolized at different rates, but selectivity was only found between diastereomers and not between enantiomers. trans-Spiroxamine was preferentially degraded in grapes and cis-spiroxamine in wheat. These findings may affect the consumer dietary risk assessmen...
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Stereoselective Metabolism of the Sterol Biosynthesis Inhibitor Fungicides Fenpropidin, Fenpropimorph, and Spiroxamine in Grapes, Sugar Beets, and Wheat
2016Co-Authors: Ignaz J Buerge, Werner Siegfried, Felix E Wettstein, Jürgen Krauss, Rocío López-cabeza, Michael Stüssi, Thomas PoigerAbstract:Metabolism of chiral pesticides in crops is typically studied using achiral analytical methods and, consequently, the Stereoisomer composition of residues is unknown. In this study, we developed an enantioselective GC-MS/MS method to quantify residues of the fungicides fenpropidin, fenpropimorph, and spiroxamine in plant matrices. In field trials, the fungicides were applied to grapevines, sugar beets, or wheat. Fenpropidin was metabolized with no or only weak enantioselectivity. For fenpropimorph, slightly enantioselective metabolism was observed in wheat but more pronounced in sugar beets. This enantioselectivity was due to different rates of metabolism and not due to interconversion of enantiomers. The four Stereoisomers of spiroxamine were also metabolized at different rates, but selectivity was only found between diastereomers and not between enantiomers. trans-Spiroxamine was preferentially degraded in grapes and cis-spiroxamine in wheat. These findings may affect the consumer dietary risk assessment because toxicological end points were determined using racemic test substances
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the chiral herbicide beflubutamid i isolation of pure enantiomers by hplc herbicidal activity of enantiomers and analysis by enantioselective gc ms
Environmental Science & Technology, 2013Co-Authors: Ignaz J Buerge, Astrid Bachli, Jeanpierre De Joffrey, Markus D Muller, Simon Spycher, Thomas PoigerAbstract:For many chiral pesticides, little information is available on the properties and fate of individual Stereoisomers. A basic data set would, first of all, include Stereoisomer-specific analytical me...
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Stereoisomer composition of the chiral uv filter 4 methylbenzylidene camphor in environmental samples
Environmental Science & Technology, 2005Co-Authors: Hansrudolf Buser, Thomas Poiger, Markus Muller, Marianne E Balmer, Ignaz J BuergeAbstract:4-Methylbenzylidene camphor (4-MBC) is an important organic UV filter used in many personal care products such as sunscreens and cosmetics. After use, 4-MBC may enter the aquatic environment due to its release from skin during recreational activities (swimming, bathing) and from personal hygiene measures (washing, laundering of cloths) via wastewater treatment plants (WWTPs). In fact, 4-MBC has been detected in wastewater, in surface waters, and even in fish. 4-MBC can exist as distinct cis-(Z)- and trans-(E)-isomers, both of which are chiral. Despite the fact that Stereoisomers often show a different biological behavior, the stereochemistry of 4-MBC has hardly ever been considered in environmental or biological studies. In this study, enantioselective gas chromatography−mass spectrometry (GC−MS) was used to determine the Stereoisomer composition of 4-MBC. For Stereoisomer assignment, the pure enantiomers of (E)-4-MBC were synthesized from (+)- and (−)-camphor. The photochemical isomerization (sunlight) o...
Virginie Lattard - One of the best experts on this subject based on the ideXlab platform.
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enantiomeric fraction evaluation of the four Stereoisomers of difethialone in biological matrices of rat by two enantioselective liquid chromatography tandem mass spectrometry methods chiral stationary phase or derivatization
Journal of Chromatography A, 2020Co-Authors: Isabelle Fourel, Etienne Benoit, Virginie LattardAbstract:Abstract The need for the control of rodent populations with anticoagulant rodenticides remains actual, and enantioselective analytical methods are mandatory to understand ecotoxicity issues of those chiral pesticides. This study presents two enantioselective methods to achieve the residue levels and differentiated persistence of the four Stereoisomers of difethialone (called in this work E1-trans, E2-cis, E3-cis and E4-trans), which is one of the most toxic second generation anticoagulant rodenticide. Their enantiomeric fraction evaluation in biological matrices of rats was determined by two LC-MS/MS methods. The first one (chiral-LC-MS/MS) combined a chiral column employed in reversed-phase mode (with acetonitrile-water mobile phase) to be compatible with mass spectrometry detection. The second one was also a LC-MS/MS method but with a reversed phase column after a derivatization step with (1S)-(−)-camphanic chloride. Extraction process combined Solid-Liquid extraction and sorbent cartridges. The methods were fully validated. The chiral column was chosen as a reference method for our laboratory because it was quicker and cheaper, and enantioresolution and sensitivity were better. This chiral-LC-MS/MS method was used to measure the enantiomeric fraction of the four Stereoisomers of difethialone in rodent biological matrices (liver, plasma, blood and feces) of female rats treated with 3.5 mg/kg of difethialone. The results showed that metabolism is not the same for all the Stereoisomers: cis-E3-difethialone was the most persistent, and E4-trans-difethialone was the most quickly eliminated. This chiral-LC-MS/MS method will be used to study the pharmacokinetics of the four Stereoisomers of difethialone, and for ecotoxicological surveillance to evaluate the specific persistence of each Stereoisomer of difethialone in case of secondary exposure of wildlife non-target species.
