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Chirality

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https://www.readbyqxmd.com/read/30520127/enantioselective-vinylation-of-aldehydes-with-the-vinyl-grignard-reagent-catalyzed-by-magnesium-complex-of-chiral-binols
#1
Pei Wang, Guo-Rong Ma, Sheng-Li Yu, Chao-Shan Da
Enantioselective vinylation of aldehydes via direct catalytic asymmetric Grignard reaction of aldehdyes and the vinyl Grinard reagent is a long-standing challenge. This work demonstrated that the magnesium (S)-3,3'-dimethyl BINOLate enantioselectively catalyze the direct vinylation of aldehydes with the deactivated vinylmagnesium bromide by bis(2-[N,N'-dimethylamino]ethyl) ether (BDMAEE) in the addition of n-butylmagnesium chloride. The highest ee of 63% was achieved up to date.
December 6, 2018: Chirality
https://www.readbyqxmd.com/read/30515897/computational-chemical-analysis-of-ru-ii-pheox-catalyzed-highly-enantioselective-intramolecular-cyclopropanation-reactions
#2
Yoko Nakagawa, Naofumi Nakayama, Hitoshi Goto, Ikuhide Fujisawa, Soda Chanthamath, Kazutaka Shibatomi, Seiji Iwasa
Computational chemical analysis of Ru(II)-Pheox-catalyzed highly enantioselective intramolecular cyclopropanation reactions was performed using density functional theory (DFT). In this study, cyclopropane ring-fused γ-lactones, which are 5.8 kcal/mol more stable than the corresponding minor enantiomer, are obtained as the major product. The results of the calculations suggest that the enantioselectivity of the Ru(II)-Pheox-catalyzed intramolecular cyclopropanation reaction is affected by the energy differences between the starting structures 5l and 5i...
December 4, 2018: Chirality
https://www.readbyqxmd.com/read/30515892/separation-of-eight-bedaquiline-analogue-diastereomers-by-hplc-on-an-immobilized-polysaccharide-based-chiral-stationary-phase
#3
Shenmeng Jiang, Chengjun Wu, Jia Yu, Tiemin Sun, Xingjie Guo
The high-performance liquid chromatography (HPLC) is a powerful method in the area of stereoisomer separation. In this study, separation of eight bedaquiline analogue diastereomers (compounds 1-8) was first examined on a cellulose tris-(3,5-dichlorophenylcarbamate) chiral stationary phase, ie, Chiralpak IC in the normal phase mode. The influences of organic modifier types, alcohol content, and column temperature on diastereoseparation were evaluated. Under the optimum chromatographic conditions, all the analyte stereoisomers were successfully separated...
December 4, 2018: Chirality
https://www.readbyqxmd.com/read/30468538/improving-the-performance-of-nadolol-stereoisomers-preparative-separation-using-chiralpak-ia-by-smb-chromatography
#4
Rami S Arafah, António E Ribeiro, Alírio E Rodrigues, Luís S Pais
The pseudobinary preparative separation of nadolol stereoisomers is performed by simulated moving bed chromatography (SMB). Using the Chiralpak IA adsorbent, a new 25:75:0.1 (v/v/v) methanol-acetonitrile-diethylamine solvent composition was selected to perform the experimental SMB separation and compare it with the previous results obtained using pure methanol. Using a 2 g L-1 total feed concentration of an equimolar mixture of the four stereoisomers of nadolol, the more retained component was fully recovered (100% purity and 100% recovery), with a system productivity of 0...
November 23, 2018: Chirality
https://www.readbyqxmd.com/read/30468523/absolute-configuration-and-biological-profile-of-pyrazoline-enantiomers-as-mao-inhibitory-activity
#5
Umut Salgin Goksen, Sevgi Sarigul, Patrick Bultinck, Wouter Herrebout, Ilknur Dogan, Kemal Yelekci, Gulberk Ucar, Nesrin Gokhan Kelekci
A new racemic pyrazoline derivative was synthesized and resolved to its enantiomers using analytic and semipreparative high-pressure liquid chromatography. The absolute configuration of both fractions was established using vibrational circular dichroism. The in vitro monoamine oxidase (MAO) inhibitory profiles were evaluated for the racemate and both enantiomers separately for the two isoforms of the enzyme. The racemic compound and both enantiomers were found to inhibit hMAO-A selectively and competitively...
November 23, 2018: Chirality
https://www.readbyqxmd.com/read/30431673/proline-autocatalysis-in-the-origin-of-biological-enantioenriched-chirality
#6
Ananthan Sadagopan
Biological enantioenriched chirality is a phenomenon that in living organisms, amino acids and carbohydrates typically have the same absolute configuration. Perhaps one of the earliest attempts to delineate the origins of this phenomenon was a theory known as asymmetric autocatalysis, a reaction in which the structures of the chiral catalyst and the product are the same, and in which the chiral product acts as a chiral catalyst for its own production. In theory, this would mean that small asymmetries in the product will propagate rapidly...
November 15, 2018: Chirality
https://www.readbyqxmd.com/read/30431670/nmr-chiral-discrimination-of-chalcogen-containing-secondary-alcohols
#7
Naiade B G Marques, Raquel G Jacob, Gelson Perin, Eder J Lenardão, Diego Alves, Márcio S Silva
Here, we report the general strategies by which NMR spectroscopy can be used to determine the enantiopurity and absolute configuration of chalcogen containing secondary alcohols, including the evaluation of the use of chiral solvating and chiral derivatizing agents. The BINOL/DMAP ternary complex demonstrated a simple and fast protocol for determining enantiopurity. The drug Naproxen afforded a stable, nonhygroscopic, and readily available chiral derivatizing agent (CDA) for NMR chiral discrimination of chalcogen containing secondary alcohols...
November 15, 2018: Chirality
https://www.readbyqxmd.com/read/30417573/preparative-separation-of-four-isomers-of-synthetic-anisodamine-by-hplc-and-diastereomer-crystallization
#8
Tong Wu, Jiu-Xin Zhu, Qian Wei, Ping Li, Li-Bo Wang, Jian Huang, Jin-Hui Wang, Li-Ke Tang, Li-Jun Wu, Chang Li, Wei-Na Han
Anisodamine (654-1), a well-known cholinergic antagonist, is marketed as synthetic anisodamine (mixture of four isomers, 654-2) in China. To preparative resolution and comparison of the bioactivities of the four isomers of synthetic anisodamine, current work explores an economic and effective separation method by using preparative high performance liquid chromatography (HPLC) and diastereomer crystallization. Their absolute configurations were established by single-crystal X-ray diffraction and circular dichroism method...
November 11, 2018: Chirality
https://www.readbyqxmd.com/read/30395695/a-simple-quantitative-chiral-analysis-of-amino-acid-esters-by-fluorine-19-nuclear-magnetic-resonance-using-the-modified-james-bull-method
#9
Naoto Hamaguchi, Yuta Okuno, Yohei Oe, Tetsuo Ohta
A simple chiral analysis of amino acid esters by fluorine-19 nuclear magnetic resonance (19 F NMR) through the modified James-Bull method is described. Thus, amino acid ester acid salt was treated with 5-fluoro-2-formylphenylboronic acid and (S)-BINOL in the presence of triethylamine (TEA) and MS4A for 10 minutes. The reaction mixture was analysed by 19 F NMR directly to afford good quantifications.
November 5, 2018: Chirality
https://www.readbyqxmd.com/read/30375664/synthesis-of-magnetic-multiwall-carbon-nanotubes-for-enantioseparation-of-three-pesticide-residues-in-fruits-and-vegetables-by-chiral-liquid-chromatography
#10
Shuo Lei, Xianhui Li, Yang Wang, Lirong Sun, Hao Liu, Longshan Zhao
In this study, magnetic multiwalled carbon nanotubes (MMWCNTs) were synthesized and used as adsorbent for preconcentration of chiral pesticide residues (including epoxiconazole, tebuconazole, and metalaxyl) in lettuce, cabbage, and apple. Several parameters affecting the treatment efficiency were investigated, including extraction solvent and absorption solvent. Under the optimal conditions, all three chiral pesticides showed decent enantiomeric separation (Rs > 1.48). The linearity of each target was good with the correlation coefficient (r2 ) being greater than 0...
October 30, 2018: Chirality
https://www.readbyqxmd.com/read/30321480/stereoselective-pharmacokinetics-of-r-and-s-rabeprazole-in-human-using-chiral-lc-ms-ms-after-administration-of-rabeprazole-sodium-enteric-coated-tablet
#11
Lu-Ning Sun, Yi-Wen Shen, Yu-Wen Ying, Duo Li, Teng-Fei Li, Xue-Hui Zhang, Ping Zhao, Li Ding, Yong-Qing Wang
Rabeprazole is an effective proton pump inhibitor to treat acid-related diseases. To achieve the simultaneous determination of rabeprazole enantiomers in human plasma, a chiral LC-MS/MS method was developed and validated. Acetonitrile including 0.1% ammonium were used as protein precipitating agent. Analytes were separated within 8 minutes on a Chiralpak IC column (4.6 mm × 150 mm, 5 μm). The mobile phase was 10 mM ammonium acetate including 0.2% acetic acid-acetonitrile (35:65, v/v). An API 4000 mass spectrometer was used as detector for the analysis, and the multiple reactions monitoring transitions of m/z 360...
October 15, 2018: Chirality
https://www.readbyqxmd.com/read/30321474/chiral-separation-and-modeling-of-quinolones-on-teicoplanin-macrocyclic-glycopeptide-antibiotics-csp
#12
REVIEW
Imran Ali, Mohd Suhail, Leonid Asnin
New chiral high-performance liquid chromatography (HPLC) method for the enantiomeric resolution of quinolones is developed and described. The column used was Chirobiotic T (150 × 4.6 mm, 5.0 μm). Three mobile phases used were MeOH:ACN:Water:TEA (70:10:20:0.1%), (60:30:10:0.1%), and (50:30:20:0.1%). The flow rate of the mobile phases was 1.0 mL/min with UV detection at different wavelengths. The values of retention, resolution, and separation factors ranged from 1.5 to 6.0, 1.80 to 2.25, and 2.86 to 6...
October 15, 2018: Chirality
https://www.readbyqxmd.com/read/30295968/efficient-access-to-both-enantiomers-of-3-1-hydroxyethyl-phenol-by-regioselective-and-enantioselective-cal-b-catalyzed-hydrolysis-of-diacetate-in-organic-media-by-sodium-carbonate
#13
Nabila Braia, Mounia Merabet-Khelassi, Louisa Aribi-Zouioueche
No abstract text is available yet for this article.
October 8, 2018: Chirality
https://www.readbyqxmd.com/read/30286255/highly-enantioselective-michael-addition-of-%C3%AE-nitroacetate-to-%C3%AE-%C3%AE-unsaturated-pyrazolamide-catalyzed-by-a-bifunctional-squaramide
#14
Yingying Liu, Ling Ye, Zhichuan Shi, Xuejun Yang, Zhigang Zhao, Xuefeng Li
A highly enantioselective (91- > 99% ee) Michael addition of α-nitroacetate to α,β-unsaturated pyrazolamide was developed in the presence of a bifunctional squaramide. Satisfactory isolated yields (42%-99%) have been achieved with a wide range of α,β-unsaturated pyrazolamides, albeit acceptor of this type displayed poor reactivity in the precedent reports. The adducts resulting from this protocol are useful synthetic intermediates for further synthetic modification.
October 4, 2018: Chirality
https://www.readbyqxmd.com/read/30238505/synthesis-of-chiral-salalen-ligands-and-their-in-situ-generated-cu-complexes-for-asymmetric-henry-reaction
#15
Ashish Dixit, Pramod Kumar, Surendra Singh
Chiral salalen ligands derived from (S)-proline and derivatives of salicyaldehydes were synthesized, and their in-situ generated Cu (II) complexes were evaluated in the asymmetric Henry reaction. Salalen ligand of different substituents on the phenyl moiety showed remarkable effect on the enantioselectivity of nitro-aldol product of 4-nitrobenzaldehyde and nitromethane. Cu (II) complex generated in situ with (S)-2-(tert-butyl)-6-((2-(((2-hydroxy-3-methylbenzylidene)amino)methyl)pyrrolidin-1-yl)methyl) phenol (10 mol%) and Cu (OAc)2 ...
September 20, 2018: Chirality
https://www.readbyqxmd.com/read/30238504/enantioselective-toxic-effects-and-digestion-of-furalaxyl-enantiomers-in-scenedesmus-obliquus
#16
Cheng Cheng, Rui Ma, Yuele Lu, Chunxiao Liu, Wenjun Zhang, Shanshan Di, Li Chen, Jinling Diao, Zhiqiang Zhou, Yuxia Hou
Research on the enantioselective environmental behavior of chiral pesticides has been a hot spot of environmental chemistry recently. In this study, the acute toxicity and digestion of furalaxyl enantiomers were determined on the aquatic algae Scendesmus obliquus. After exposure for 96 hours, the EC50 values for (S)-furalaxyl and (R)-furalaxyl were 13.59 and 15.26 mg/L, respectively. In addition, enantioselectivity was observed from the determined chlorophyll contents and antioxidant enzyme (CAT and SOD) activities of algae cells after exposure to furalaxyl enantiomers for 96 hours...
September 20, 2018: Chirality
https://www.readbyqxmd.com/read/30238493/enantioseparation-of-chiral-mandelic-acid-derivatives-by-supercritical-fluid-chromatography
#17
Jiawei Ding, Ming Zhang, Huixue Dai, Chunmian Lin
Mandelic acid and its derivatives are important chiral analogs which are widely used in the pharmaceutical synthetic industry. The present study investigated the enantiomeric separation of six mandelic acids (mandelic acid, 2-chloromandelic acid, 3-chloromandelic acid, 4-chloromandelic acid, 4-bromomandelic acid, 4-methoxymandelic acid) on the Chiralpak AD-3 column by supercritical fluid chromatography. The influences of volume fraction of trifluoroacetic acid, type and percentage of modifier, column temperature, and backpressure on the separation efficiency were investigated...
September 20, 2018: Chirality
https://www.readbyqxmd.com/read/30238626/the-enzymatic-resolution-of-1-4-chlorophenyl-ethylamine-by-novozym-435-to-prepare-a-novel-triazolopyrimidine-herbicide
#18
Yinjun Zhang, Feifei Cheng, Hongde Yan, Jianyong Zheng, Zhao Wang
The kinetic resolution of (R,S)-1-(4-chlorophenyl)ethylamine was accomplished using a commercial lipase from Candida antarctica (Novozym 435). The performance of this lipase was investigated for the enantioselective amidation of (R,S)-1-(4-chlorophenyl)ethylamine, leaving the target product (S)-1-(4-chlorophenyl)ethylamine in its unreacted form. The effects of various types of solvents and an acyl donor, the molar ratio of the substrate to the acyl donor, and the reaction temperature were studied. The optimum reaction conditions were found to result in amidation with methyl 2-tetrahydrofuroate at 40°C in methyl tert-butyl ether, with a substrate/acyl donor molar ratio of 1:2...
November 2018: Chirality
https://www.readbyqxmd.com/read/30230616/chiral-recognition-of-the-carnitine-enantiomers-using-rhodamine-b-as-a-resonance-rayleigh-scattering-probe
#19
Jidong Yang, Xuanping Tan, Yanmei Zhao
A novel and simple method for simultaneous determination of chiral carnitine (CA) enantiomers was proposed. In this work, the rhodamine B (RhB) could react with D-CA and L-CA, and new resonance Rayleigh scattering (RRS) peaks were generated. According to the polarization experiments, it could be testified that scattering peak of this system was composed of resonance fluorescence and scattering light. The RRS intensity of the RhB could be enhanced with the addition of D- or L-CA. However, The RRS signal with L-CA had greater degree increased...
November 2018: Chirality
https://www.readbyqxmd.com/read/30222211/resolution-of-isoborneol-and-its-isomers-by-gc-ms-to-identify-synthetic-and-semi-synthetic-borneol-products
#20
Ming-Yeh Yang, Aye Aye Khine, Jen-Wei Liu, Hui-Chen Cheng, Anren Hu, Hao-Ping Chen, Tzenge-Lien Shih
Borneol is a plant terpene commonly used in traditional Chinese medicine. Optically pure (+)-borneol and (-)-borneol can be obtained by extraction from the plants Dipterocarpaceae and Blumea balsamifera, respectively. "Synthetic borneol" is obtained from the reduction of (±)-camphor to lead to four different stereoisomers: (+)-isoborneol, (-)-isoborneol, (+)-borneol, and (-)-borneol. In contrast, "semi-synthetic borneol" is produced from the reduction of natural camphor, (+)-camphor, to afford two isomers: (-)-isoborneol and (+)-borneol...
November 2018: Chirality
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