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Chirality

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https://www.readbyqxmd.com/read/30103282/supramolecular-chirality-transfer-in-a-stereodynamic-catalysts
#1
Golo Storch, Oliver Trapp
We present rhodium catalysts that contain stereodynamic axially chiral biphenol-derived phosphinite ligands modified with non-stereoselective amides for non-covalent interactions. A chirality transfer was achieved with (R)- or (S)-acetylphenylalanine methyl amide, and the interaction mechanism was investigated by NMR measurements. These interactions at the non-stereoselective interaction sites and the formation of supramolecular complexes result in an enrichment of either the (Rax )- or (Sax ) enantiomer of the tropos catalysts, which in turn provide the (R)- or (S)-acetylphenylalanine methyl ester in the hydrogenation of (Z)-methyl-α-acetamidocinnamate...
August 13, 2018: Chirality
https://www.readbyqxmd.com/read/30096728/chiral-separation-and-determination-of-amino-acid-enantiomers-in-fruit-juice-by-open-tubular-nano-liquid-chromatography
#2
Cemil Aydoğan
A novel chiral porous-layer stationary phase was developed for use in open-tubular nano liquid chromatography. The stationary phase was prepared by an in-situ polymerization of 3-chloro-2-hydroxypropylmethacrylate (HPMA-Cl) and ethylene dimethacrylate (EDMA). The reactive chloro groups at the surface of the porous stationary phase were reacted with β-Cyclodextrin (β-CD). The resulting morphology was characterized by using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR)...
August 10, 2018: Chirality
https://www.readbyqxmd.com/read/30075486/the-determination-of-enantiomer-composition-of-1-3-chlorophenyl-phenyl-methyl-amine-and-1-3-chlorophenyl-phenyl-methyl-urea-galodif-by-nmr-spectroscopy-chiral-hplc-and-polarimetry
#3
Vera Yu Kuksenok, Victoria V Shtrykova, Victor D Filimonov, Alexandr G Druganov, Alexandr A Bondarev, Ksenia S Stankevich
For the first time, a method for enantiomer resolution of the anticonvulsant Galodif (1-((3-chlorophenyl)(phenyl)methyl) urea) by chiral HPLC was developed, whereas the enantiomeric composition of 1-((3-chlorophenyl)(phenyl)methyl) amine-precursor in Galodif synthesis-cannot be resolved by this method. However, starting 1-((3-chlorophenyl)(phenyl)methyl) amine quantitatively forms diastereomeric N-((3-chlorophenyl)(phenyl)methyl)-1-camphorsulfonamides in reaction with chiral (1R)-(+)- or (1S)-(-)-camphor-10-sulfonyl chlorides...
August 3, 2018: Chirality
https://www.readbyqxmd.com/read/30052289/highly-enantioselective-michael-addition-of-pyrazolin-5-ones-to-nitroolefins-catalyzed-by-cinchona-alkaloid-derived-4-methylbenzoylthioureas
#4
Mengchen Yang, Min Zhang, Zhenyu Wang, Li Tang, Wenbin Chen, Shurong Ban, Qingshan Li
Cinchona alkaloid-derived 4-methyl/nitro benzoylthioureas were synthesized, which smoothly catalyzed the asymmetric Michael addition of pyrazolin-5-ones to nitroolefins. The results showed that electronic effects of substituents in the benzene ring of benzoylthioureas have subtle influences on their catalytic abilities and electron donating methyl group is favored than electron withdrawing nitro group. Preliminary Hartree-Fock calculations revealed that in the catalytic cycle, hydrogen bond energies of the complex formed with 4-methylbenzoylthioureas are about 0...
July 27, 2018: Chirality
https://www.readbyqxmd.com/read/29999210/simultaneous-chiral-analysis-of-amphetamine-type-stimulants-and-ephedrine-by-capillary-electrophoresis-coupled-to-time-of-flight-mass-spectrometry
#5
Xuezi Cui, Chen Liang, Feijun Gong, Rong Wang, Chunfang Ni, Yanhong Wu, Guiliang Chen, Yurong Zhang
This study focused on the chiral characteristics of methamphetamine seizures in Shanghai for inferring the synthetic pathways of drugs. Capillary electrophoresis coupled to time-of-flight mass spectrometry was used for simultaneous chiral separation of amphetamine-type stimulants and ephedrine, including S(+)-amphetamine/R(-)-amphetamine, S(+)-methamphetamine/R(-)-methamphetamine, (±)-MDA (3,4-methylenedioxyamphetamine), (±)-MDMA (3,4-methylenedioxymethamphetamine), (±)-MDEA (3,4-methylenedioxy-N-ethylamphetamine), d,l-N-ethylamphetamine, methylephedrine/methylpseudoephedrine, and 1S,2R(+)-ephedrine/(-)-ephedrine...
July 12, 2018: Chirality
https://www.readbyqxmd.com/read/29978905/stereoselective-uptake-and-degradation-of-%C3%A2-o-p-ddd-pesticide-stereomers-in-water-sediment-system
#6
Al Arsh Basheer, Imran Ali
The environmental stereoselective uptake and degradation of (±)-o,p-DDD pesticide stereomers in water-sediment system are described. The results were analyzed by artificial neural network model. The optimized experimental parameters were concentration of o,p-DDD streamers (7.0 μg L-1 ), experimental time (60 min), pH (6), dose (5.0 g L-1 ), and temperature (25°C). The maximum uptake and degradation were 87% and 85% and 33.0% and 30.5% for (-)- and (+)-stereomers of o,p-DDD in 15-day time. Both uptake and degraded phenomenon showed first-order rate reaction...
July 6, 2018: Chirality
https://www.readbyqxmd.com/read/29978505/internal-chirality-descriptors-ir-and-is-and-ire-and-isi-a-proposed-notation-to-extend-the-usefulness-of-the-r-s-system-by-retaining-the-sense-of-stereochemistry-in-cases-of-ligand-ranking-changes
#7
Karel D Klika, Alicja Wzorek, Vadim A Soloshonok
The R/S system, universally applied for indicating the absolute configuration of a structure, is extremely adept for conveying the absolute configuration unequivocally. However, it suffers from one limitation, viz that due to CIP priority rules the rankings of the ligands attached to an asymmetric center can be altered upon a change in a ligand leading to a change in the designated configuration even if bonds to the asymmetric center were not actually formed or broken. This means that the sense of stereochemistry in situations such as within a set of compounds where family relationships are of focus or where the sense of the stereochemical course of a reaction is of interest can be lost or confusion may occur...
July 5, 2018: Chirality
https://www.readbyqxmd.com/read/29969166/evaluation-of-the-edman-degradation-product-of-vancomycin-bonded-to-core-shell-particles-as-a-new-hplc-chiral-stationary-phase
#8
Garrett Hellinghausen, Diego A Lopez, Jauh T Lee, Yadi Wang, Choyce A Weatherly, Abiud E Portillo, Alain Berthod, Daniel W Armstrong
A modified macrocyclic glycopeptide-based chiral stationary phase (CSP), prepared via Edman degradation of vancomycin, was evaluated as a chiral selector for the first time. Its applicability was compared with other macrocyclic glycopeptide-based CSPs: TeicoShell and VancoShell. In addition, another modified macrocyclic glycopeptide-based CSP, NicoShell, was further examined. Initial evaluation was focused on the complementary behavior with these glycopeptides. A screening procedure was used based on previous work for the enantiomeric separation of 50 chiral compounds including amino acids, pesticides, stimulants, and a variety of pharmaceuticals...
July 3, 2018: Chirality
https://www.readbyqxmd.com/read/29969152/solvent-dependent-inversion-of-circular-dichroism-signal-in-naproxen-an-unusual-effect
#9
Valdecir Farias Ximenes, Nelson Henrique Morgon, Aguinaldo Robinson de Souza
The electronic circular dichroism (ECD) spectra of naproxen enantiomers were studied as a function of solvents using experimental (circular dichroism) and theoretical (time-dependent density functional theory) approaches. The (R)- and (S)-naproxen enantiomers presented an unusual inversion in their ECD signals in the presence of ethanol and water when compared with polar aprotic solvents such as acetonitrile. From a practical point of view, these findings deserve great attention because these solvents are widely used for high-performance liquid chromatography analysis in quality control of chiral pharmaceutical drugs...
July 3, 2018: Chirality
https://www.readbyqxmd.com/read/29939430/enantiomeric-separation-of-%C3%AE-blockers-and-tryptophan-using-heparin-as-stationary-and-pseudostationary-phases-in-capillary-electrophoresis
#10
Yi Liu, Lorena L Sombra, Patricia W Stege
The separation methods of the enantiomers of two β-blockers and tryptophan were studied using capillary electrochromatography with heparin covalently as well as non-covalently, bonded onto the capillary inner wall as stationary phase and electrokinetic chromatography with heparin as pseudostationary phase. In the case of heparin, used as a stationary phase, the method was unable to resolve enantiomers in both cases β-blockers and tryptophan. On the other hand, when heparin was used as a pseudostationary phase, the resolution of the enantiomers was obtained only with 3-aminopropyltriethoxysilane which were immobilised onto the inner phase of the capillary...
June 25, 2018: Chirality
https://www.readbyqxmd.com/read/29920777/enantiomeric-separation-of-novel-psychoactive-substances-by-capillary-electrophoresis-using-18-crown-6-tetracarboxylic-acid-as-chiral-selector
#11
Johannes S Hägele, Martin G Schmid
In the recent years, hundreds of Novel Psychoactive Substances (NPS) have entered both the European and the global drug market. These drugs, which are mainly used for recreational matters, have caused serious social problems. Every year, the spectrum of these misused drugs is enlarged by new derivatives, which are produced by modifications of basic structures of already well-known substances. Additionally, a lot of them possess a stereogenic center which leads to 2 enantiomeric forms. The fact that the pharmacological effects and potencies of the enantiomers of these chiral NPS may differ can be assumed from a broad spectrum of active pharmaceutical ingredients...
June 19, 2018: Chirality
https://www.readbyqxmd.com/read/29885046/utilization-of-deep-sea-microbial-esterase-phe21-to-generate-chiral-sec-butyl-acetate-through-kinetic-resolutions
#12
Yilong Wang, Yongkai Xu, Yun Zhang, Aijun Sun, Yunfeng Hu
We previously identified and characterized 1 novel deep-sea microbial esterase PHE21 and used PHE21 as a green biocatalyst to generate chiral ethyl (S)-3-hydroxybutyrate, 1 key chiral chemical, with high enantiomeric excess and yield through kinetic resolution. Herein, we further explored the potential of esterase PHE21 in the enantioselective preparation of secondary butanol, which was hard to be resolved by lipases/esterases. Despite the fact that chiral secondary butanols and their ester derivatives were hard to prepare, esterase PHE21 was used as a green biocatalyst in the generation of (S)-sec-butyl acetate through hydrolytic reactions and the enantiomeric excess, and the conversion of (S)-sec-butyl acetate reached 98% and 52%, respectively, after process optimization...
June 8, 2018: Chirality
https://www.readbyqxmd.com/read/29873852/c-2-symmetric-sulfonamides-as-homogeneous-and-heterogeneous-organocatalysts-that-mimic-enzymes-in-enantioselective-michael-additions
#13
Harold Cruz, Felipe A Servín, Domingo Madrigal, Daniel Chávez, Sergio Perez-Sicairos, Gerardo Aguirre, Andrew L Cooksy, Ratnasamy Somanathan
Herein, we report the synthesis of C2 -symmetric sulfonamides as homogeneous and heterogeneous organocatalysts and their application in the enantioselective conjugate 1,4-Michael addition of carbonylic nucleophiles to β-nitrostyrene. Organocatalysts hydrogen bond to β-nitrostyrene and enamine in the transition state, mimicking an enzyme leading to final products in high yields (up to 98%) and good enantioselectivities (up to 96%). In addition, these results were supported by density functional calculations...
June 6, 2018: Chirality
https://www.readbyqxmd.com/read/29864196/the-development-of-biphasic-chiral-recognition-in-chiral-separation
#14
REVIEW
Xin-Yi Huang, Kai-Jun Quan, Dong Pei, Jian-Fei Liu, Duo-Long Di
In chiral separation, enantioseparation factor is an important parameter which influences the resolution of enantiomers. In this current overview, a biphasic chiral recognition method is introduced to the readers. This method can significantly improve the enantioseparation factor in two-phase solvent through adding lipophilic and hydrophilic chiral selectors which have opposite chiral recognition ability to organic and aqueous phases, respectively. This overview presents the development and applications of biphasic chiral recognition in liquid-liquid extraction and counter current chromatography...
June 4, 2018: Chirality
https://www.readbyqxmd.com/read/29863761/atropisomerism-in-rilpivirine-hydrochloride-spectroscopic-characterization-of-rilpivirine-and-related-impurities
#15
Senthilkumar Natarajan, Hiriyanna Salmara Ganeshbhat, Sujeet Shrivastava, Srimurugan Sankareswaran, Pramod Kumar
Nuclear magnetic resonance (NMR) technique has been used to find the property of atropisomerism in Rilpivirine hydrochloride by variable temperature analysis and various 2D techniques. Both the Rilpivirine hydrochloride (E-isomer) and Impurity-A (Z-isomer) isomers have been differentiated and confirmed by NMR and ultraviolet techniques. Preparative high-performance liquid chromatography isolation for Impurity-A is followed by spectroscopic (NMR, mass spectra, and infrared) investigation that provides a perfect solution for determination of the structure of Rilpivirine and related impurities...
June 4, 2018: Chirality
https://www.readbyqxmd.com/read/29856908/cellulose-type-chiral-stationary-phase-based-on-reduced-graphene-oxide-silica-gel-for-the-enantiomer-separation-of-chiral-compounds
#16
Yuanyuan Li, Qiang Li, Nan Zhu, Zhuxian Gao, Yulong Ma
The graphene oxide (GO) was covalently coupled to the surfaces of silica gel (SiO2 ) microspheres by amide bond to get the graphene oxide@silica gel (GO@SiO2 ). Then, the GO@SiO2 was reduced with hydrazine to the reduced graphene oxide@silica gel (rGO@SiO2 ), and the cellulose derivatives were physically coated on the surfaces of rGO@SiO2 to prepare a chiral stationary phase (CSP) for high performance liquid chromatography. Under the optimum experimental conditions, eight benzene-enriched enantiomers were separated completely, and the resolution of trans-stilbene oxide perfectly reached 4...
June 1, 2018: Chirality
https://www.readbyqxmd.com/read/29856893/urea-derivative-catalyzed-enantioselective-aldol-reaction-of-isatins-with-ketones
#17
Li Ming Wang, Mei Jun Zhao, Zhe Chen, Hong Wen Mu, Ying Jin
Urea derivative has been used to catalyze the asymmetric aldol reaction of isatins with ketones. The resulting 3-alkyl-3-hydroxy-indolin-2-ones products were obtained in good yields (70%-94%) with high enantioselectivities (up to 87%ee).
June 1, 2018: Chirality
https://www.readbyqxmd.com/read/29791052/high-performance-liquid-chromatography-quantification-of-enantiomers-of-a-dihydroxylated-tetrahydrofuran-natural-product
#18
Ke Li, Skye D Fissette, Tyler J Buchinger, Zoe E Middleton, Alistair Boyer, Weiming Li
Both enantiomers of petromyroxol are putative pheromones in sea lamprey (Petromyzon marinus). Here, we describe the separation and quantification of the petromyroxol enantiomers using high-performance liquid chromatography tandem mass spectrometry. The separation was tested on a wide range of chiral columns with normal phases, and effects of the chromatographic parameters such as mobile phase and temperature on the separation were optimized. The AD-H column showed the best separation of enantiomers with n-hexane and ethanol as the mobile phase...
May 23, 2018: Chirality
https://www.readbyqxmd.com/read/29791038/special-issue-proceedings-of-16th-international-conference-on-chiroptical-spectroscopy-rennes-2017
#19
Jeanne Crassous, Narcis Avarvari, Nina Berova, John Caldwell
No abstract text is available yet for this article.
May 23, 2018: Chirality
https://www.readbyqxmd.com/read/29782664/stereoselective-hplc-separation-of-alvimopan-on-cellulose-based-immobilized-polysaccharide-as-a-chiral-stationary-phase
#20
Nitin H Dhekale, Dattatray B Gunjal, Anil H Gore, Yagnakirankumar Komaravolu, K Hima Bindu, Govind B Kolekar
Chiral separation by normal phase high performance liquid chromatography is one of the most powerful technique to quantify the chiral purity of the compounds. In this study, a novel, simple, and specific analytical method was proposed to ascertain the chiral purity of alvimopan (ALV). The normal phase HPLC method was developed based on cellulose tris (3,5-dichlorophenylcarbamate) stationary phase. The separation of ALV isomers achieved by using column CHIRALPAK IC (250 × 4.6 mm, 5 μm), mobile phase n-hexane: isopropyl alcohol: ethanol: diethylamine (650:200:150:5 v/v), column oven temperature 30°C, flow rate 1...
May 21, 2018: Chirality
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