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Chirality

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https://www.readbyqxmd.com/read/29024201/enantioseparation-of-racecadotril-using-polysaccharide-type-chiral-stationary-phases-in-polar-organic-mode
#1
Zoltán-István Szabó, Mohammadhassan Foroughbakhshfasaei, Béla Noszál, Gergő Tóth
Enantioseparation of the antidiarrheal drug, racecadotril, was investigated by liquid chromatography using polysaccharide-type chiral stationary phases in polar organic mode. The enantiodiscrimininating properties of 4 different chiral columns (Chiralpak AD, Chiralcel OD, Chiralpak AS, Chiralcel OJ) with 5 different solvents (methanol, ethanol, 1-propanol, 2-propanol, and acetonitrile) at 5 different temperatures (5-40 °C) were investigated. Apart from Chiralpak AS column the other 3 columns showed significant enantioseparation capabilities...
October 11, 2017: Chirality
https://www.readbyqxmd.com/read/29024058/enantiopurity-and-absolute-configuration-determination-of-arene-cis-dihydrodiol-metabolites-and-derivatives-using-chiral-boronic-acids
#2
Derek R Boyd, Narain D Sharma, Peter A Goodrich, John F Malone, Gareth McConville, John S Harrison, Paul J Stevenson, Christopher C R Allen
The relative merits of the methods employed to determine enantiomeric excess (ee) values and absolute configurations of chiral arene and alkene cis-1,2-diol metabolites, including boronate formation, using racemic or enantiopure (+) and (-)-2-(1-methoxyethyl)phenylboronic acid (MEPBA), are discussed. Further applications of: 1) MEPBA derived boronates of chiral mono- and poly-cyclic arene cis-dihydrodiol, cyclohex-2-en-1-one cis-diol, heteroarene cis/trans-2,3-diol, and catechol metabolites in estimating their ee values, and 2) new chiral phenylboronic acids, 2-[1-methoxy-2,2-dimethylpropyl]phenyl boronic acid (MDPBA) and 2-[1-methoxy-1-phenylmethyl]phenyl boronic acid (MPPBA) and their advantages over MEPBA, as reagents for stereochemical analysis of arene and alkene cis-diol metabolites, are presented...
October 11, 2017: Chirality
https://www.readbyqxmd.com/read/28991388/specific-optical-rotation-is-a-versatile-tool-for-the-identification-of-critical-micelle-concentration-and-micellar-growth-of-tartaric-acid-based-diastereomeric-amphiphiles
#3
Vijay Raghavan, Prasad L Polavarapu
Four novel tartaric acid-based diastereomeric chiral amphiphiles, two being enantiomers of the other two, have been synthesized and investigated using chiroptical spectroscopic methods, along with tensiometry and dynamic light scattering experiments. We found that an inflection point in specific optical rotation (SOR) values at ~0.32 mM corresponds to the critical micelle concentration (CMC). The increase in magnitude of SOR values beyond CMC corresponds to the growth of aggregates. For enantiomers, oppositely signed SOR values were observed, ruling out the possibility for the presence of aggregation size mediated artefacts...
October 9, 2017: Chirality
https://www.readbyqxmd.com/read/28981965/absolute-configuration-assignment-of-fluralaner-using-vibrational-circular-dichroism
#4
John Kong, Leo A Joyce, Jinchu Liu, Tiffany M Jarrell, J Chris Culberson, Edward C Sherer
The absolute configurations of the separated enantiomers of fluralaner, a racemic animal health product used to prevent fleas and ticks, have been assigned using vibrational circular dichroism (VCD). The crystallographic structure of the active enantiomer (+)-fluralaner has previously been shown to have the (S) configuration using small molecule crystallography. We sought a faster analytical method to determine the absolute configuration of the separated enantiomers. When comparing the measured IR (infrared) and VCD spectra, it is apparent that the amide carbonyl groups appear in the IR but are nearly absent in the VCD...
October 5, 2017: Chirality
https://www.readbyqxmd.com/read/28981959/chiral-molecular-science-how-were-the-absolute-configurations-of-chiral-molecules-determined-experimental-results-and-theories
#5
Nobuyuki Harada
Molecular chirality is a key concept in chemistry, bioscience, and molecular technology, like the invention of a light-powered chiral molecular motor explained in this review. Thus, the primary research subject is how to determine the absolute configuration (AC) of chiral compounds. This review article focuses on the principle, theory, and practice of the nonempirical methods for determining ACs of chiral compounds, i.e., the Bijvoet method in X-ray crystallography and the circular dichroism (CD) exciton chirality method, together with the historical aspects of AC determination...
October 5, 2017: Chirality
https://www.readbyqxmd.com/read/28976611/sensing-site-specific-structural-characteristics-and-chirality-using-vibrational-circular-dichroism-of-isotope-labeled-peptides
#6
Timothy A Keiderling
Isotope labeling has a long history in chemistry as a tool for probing structure, offering enhanced sensitivity, or enabling site selection with a wide range of spectroscopic tools. Chirality sensitive methods such as electronic circular dichroism are global structural tools and have intrinsically low resolution. Consequently, they are generally insensitive to modifications to enhance site selectivity. The use of isotope labeling to modify vibrational spectra with unique resolvable frequency shifts can provide useful site-specific sensitivity, and these methods have been recently more widely expanded in biopolymer studies...
October 4, 2017: Chirality
https://www.readbyqxmd.com/read/28971527/investigation-of-maltodextrin-based-synergistic-system-with-amino-acid-chiral-ionic-liquid-as-additive-for-enantioseparation-in-capillary-electrophoresis
#7
Jiaquan Chen, Yingxiang Du, Xiaodong Sun
The combined use of chiral ionic liquids (ILs) and chiral selectors in capillary electrophoresis (CE) to establish a synergistic system has proven to be an effective approach for enantioseparation. In this article, tetramethylammonium-L-arginine, a kind of amino acid chiral IL, was applied to investigate its potential synergistic effect with maltodextrin in CE enantioseparation. The established maltodextrin-based synergistic system showed markedly improved enantioseparations compared with the single maltodextrin system...
October 3, 2017: Chirality
https://www.readbyqxmd.com/read/28963758/fast-liquid-chromatography-for-racemic-atenolol-acetate-separation-the-analytical-protocol
#8
Joni Agustian, Azlina Harun Kamaruddin, Hassan Y Aboul-Enein
Kinetic resolution of (R,S)-atenolol is a faster strategy to produce (S)-atenolol. Since this racemate is a less soluble compound, resolution of its ester offers high concentrations in the process. A good analytical method is required to observe the enantiomer concentrations. This paper described application of ultra-fast liquid chromatography on the atenolol ester separation using different resolution media and analytical procedures. Chiralcel OD column resolved the ester. The chromatograms indicated different characteristics of the process...
September 29, 2017: Chirality
https://www.readbyqxmd.com/read/28963733/advances-in-asymmetric-oxidative-kinetic-resolution-of-racemic-secondary-alcohols-catalyzed-by-chiral-mn-iii-salen-complexes
#9
REVIEW
Irshad Ahmad, Shagufta, Abdul Rahman AlMallah
Enantiomerically pure secondary alcohols are essential compounds in organic synthesis and are used as chiral auxiliaries and synthetic intermediates in the pharmaceutical, agrochemical, and fine chemical industries. One of the attractive and practical approaches to achieving optically pure secondary alcohols is oxidative kinetic resolution of racemic secondary alcohols using chiral Mn(III) salen complexes. In the last decade, several chiral Mn(III) salen complexes have been reported with excellent enantioselectivity and activity in the homogeneous and heterogeneous catalysis of the oxidative kinetic resolution of racemic secondary alcohols...
September 29, 2017: Chirality
https://www.readbyqxmd.com/read/28960471/one-pot-synthesis-of-r-1-pyridin-4-yl-ethyl-acetate-using-tandem-catalyst-prepared-by-co-immobilization-of-palladium-and-lipase-on-mesoporous-foam-optimization-and-kinetic-modeling
#10
Deepali B Magadum, Ganapati D Yadav
The synthesis of (R)-1-(pyridin-4-yl)ethyl acetate was achieved over tandem palladium-lipase catalyst with 100% selectivity using 4-acetyl pyridine as a reactant. The 2% w/w palladium and lipase catalyst was successfully co-immobilized in the microenvironment of the mesocellular foam and characterized by various techniques. The palladium metal from catalyst hydrogenated 4-acetyl pyridine to form 1-(pyridin-4-yl)ethanol. The generated intermediate product then underwent kinetic resolution over lipase and selectively gave (R)-1-(pyridin-4- yl)ethyl acetate...
September 29, 2017: Chirality
https://www.readbyqxmd.com/read/28906026/total-synthesis-and-biological-evaluation-of-spirotryprostatin-a-analogs
#11
Yangmin Ma, Chao Fan, Bin Jia, Pei Cheng, Jia Liu, Yuqiang Ma, Ke Qiao
Based on the spirotryprostatin A structure, a series of compounds belonging to spiro-indolyl diketopiperazine structural class were designed and synthesized, which embody an oxindole with an all-carbon quaternary stereocenter. The total synthesis can efficiently be accessed in a seven-step reaction sequence with 18-28% overall yield from commercially available materials, and a highly enantioselective 1,3-dipolar cycloaddition, N-acylation of the resulting stereochemically complex spiro[pyrrolidin-3,3'-oxindole]s core with Fmoc-L-pro-Cl and spontaneous ring closure upon N-deprotection were obtained...
September 14, 2017: Chirality
https://www.readbyqxmd.com/read/28902437/pyriculins-a-and-b-two-monosubstituted-hex-4-ene-2-3-diols-and-other-phytotoxic-metabolites-produced-by-pyricularia-grisea-isolated-from-buffelgrass-cenchrus-ciliaris
#12
Marco Masi, Susan Meyer, Marcin Górecki, Alessandro Mandoli, Lorenzo Di Bari, Gennaro Pescitelli, Alessio Cimmino, Massimo Cristofaro, Suzette Clement, Antonio Evidente
Pyricularia grisea has been identified as a foliar pathogen on buffelgrass (Cenchrus ciliaris) in North America and was studied as a potential source of phytotoxins for buffelgrass control. Two monosubstituted hex-4-ene-2,3-diols, named pyriculins A and B, were isolated from its culture filtrate organic extract together with (10S,11S)-(-)-epipyriculol, trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-napthalenone, and (4S)-(+)-isosclerone. Pyriculins A and B were characterized by spectroscopic (essentially nuclear magnetic resonance [NMR], High-resolution electrospray ionization mass spectrometry [HRESIMS]) and chemical methods such as (4E)-1-(4-hydroxy-1,3-dihydroisobenzofuran-1-yl)hex-4-ene-2,3-diols...
September 13, 2017: Chirality
https://www.readbyqxmd.com/read/28902429/chirality-sensing-with-stereodynamic-copper-i-complexes
#13
Zeus A De Los Santos, Nicholas M Legaux, Christian Wolf
Three Cu(I) complexes derived from stereodynamic diphosphine ligands were synthesized and used for chirality sensing. The coordination of diamines and amino acids to these complexes generates distinct circular dichroism signals. The chiroptical sensor response allows determination of the absolute configuration and the enantiomeric excess of the analyte at low concentrations. This method is operationally simple, fast, and attractive for high-throughput sensing applications.
September 13, 2017: Chirality
https://www.readbyqxmd.com/read/28877407/size-makes-a-difference-chiral-recognition-in-complexes-of-fenchone-with-cyclodextrins-studied-by-means-of-nmr-titration
#14
Karolina Dudzik, Jacek Wojcik, Andrzej Ejchart, Michał Nowakowski
Gibbs energies of complex formation between enantiomers of bicyclic terpenoid, fenchone, and naturally occurring cyclodextrins, βCD and γCD, were determined by means of (13) C and (1) H nuclear magnetic resonance (NMR) titration data. These results were compared with the corresponding data obtained previously for the diastereomeric fenchone/αCD complexes. The size of the inner cavity of host molecules significantly influences stoichiometry, association constants, and enantiomeric differentiation of the studied complexes...
September 6, 2017: Chirality
https://www.readbyqxmd.com/read/28875522/developments-in-the-synthesis-of-the-antiplatelet-and-antithrombotic-drug-s-clopidogrel
#15
REVIEW
Aamer Saeed, Danish Shahzad, Muhammad Faisal, Fayaz Ali Larik, Hesham R El-Seedi, Pervaiz Ali Channar
S-(+)-Methyl 2-(2-chlorophenyl)-2-(6,7-dihydrothieno[3,2-c]pyridin-5(4H)-yl)acetate, also known as (S)-clopidogrel, is marketed under the trade names Plavix and Iscover. It is a potent thienopyridine-class of antithrombotic and antiplatelet drug (antiaggregant). Among the two available stereoisomers of clopidogrel, for pharmaceutical activities only the S-enantiomer is applicable, as no antithrombotic activity is observed in the R-enantiomer and causes political upheavals and social turmoil in animal experiments...
September 6, 2017: Chirality
https://www.readbyqxmd.com/read/28857367/circular-dichroism-spectroscopy-and-dft-calculations-in-determining-absolute-configuration-and-e-z-isomers-of-conjugated-oximes
#16
Joanna E Rode, Jadwiga Frelek
The primary purpose of this work was to demonstrate the suitability of circular dichroism (CD) spectroscopy in stereochemical studies of α,β-unsaturated oximes, with particular emphasis on determination of E and Z geometry of the oxime double bond. As models for this study, O-phenyl and O-triphenylmethyl (trityl) oximes of 4-hydroxy-2-methylcyclopent-2-en-1-one were selected. These model compounds differ in both absolute configuration at C4 carbon atom and E-Z configuration of the oxime double bond. The basic dichroic technique applied was electronic circular dichroism (ECD) assisted by quantum-chemical calculations and vibrational circular dichroism (VCD) for selected cases...
August 31, 2017: Chirality
https://www.readbyqxmd.com/read/28840973/absolute-configuration-of-the-ocimene-monoterpenoids-from-artemisia-absinthium
#17
Luis F Julio, Eleuterio Burgueño-Tapia, Carmen E Díaz, Nury Pérez-Hernández, Azucena González-Coloma, Pedro Joseph-Nathan
The absolute configuration (AC) of the naturally occurring ocimenes (-)-(3S,5Z)-2,6-dimethyl-2,3-epoxyocta-5,7-diene (1) and (-)-(3S,5Z)-2,6-dimethylocta-5,7-dien-2,3-diol (2), isolated from the essential oils of domesticated specimens of Artemisia absinthium, followed by vibrational circular dichroism (VCD) studies of 1, as well as from the acetonide 3 and the monoacetate 4, both derived from 2, since secondary alcohols are not the best functional groups to be present during VCD studies in solution due to intermolecular associations...
August 25, 2017: Chirality
https://www.readbyqxmd.com/read/28833485/enantioselective-resolution-of-4-chloromandelic-acid-by-liquid-liquid-extraction-using-2-chloro-n-carbobenzyloxy-l-amino-acid
#18
Ruichen Lu, Quan He, Cai Feng, Yangfeng Peng
A liquid-liquid extraction resolution of 4-chloro-mandelic acid (4-ClMA) was studied by using 2-chloro-N-carbobenzyloxy-L-amino acid (2-Cl-Z-AA) as a chiral extractant. Important factors affecting the extraction efficiency were investigated, including the type of chiral extractant, pH value of aqueous phase, initial concentration of chiral extractant in organic phase, initial concentration of 4-ClMA in aqueous phase, and resolution temperature. It was observed that the concentration of (R)-4-ClMA was much higher than that of (S)-4-ClMA in organic phase due to a higher stability of the complex formed between (R)-4-ClMA and 2-Cl-Z-AA...
August 23, 2017: Chirality
https://www.readbyqxmd.com/read/28833559/chiroptical-properties-of-dithia-3-3-cyclophanes-composed-of-anthracene-and-pyridine-pyridinium-moieties-a-combined-experimental-and-theoretical-study
#19
Akinori Shimizu, Keisuke Nagasaki, Yoshihisa Inoue, Tadashi Mori
Circular dichroisms (CDs) of neutral and protonated [3.3]anthracenopyridinophane (1 and 1-H(+) ) were investigated experimentally and theoretically. Introducing an anthracene moiety with extended conjugation affected the cyclophane structure with the bent angles being appreciably  reduced from those of parent [3.3]pyridinophane. The Cotton effects (CEs) observed at the (1) Bb band for both 1 and 1-H(+) were fairly strong and apparently bisignate, which, however, turned out not to be a simple exciton couplet but to be composed of multiple transitions...
August 18, 2017: Chirality
https://www.readbyqxmd.com/read/28833487/absolute-configuration-of-an-axially-chiral-sulfonate-determined-from-its-optical-rotatory-dispersion-electronic-circular-dichroism-and-vibrational-circular-dichroism-spectra
#20
Cody L Covington, Vijay Raghavan, Jonathan P Smuts, Daniel W Armstrong, Prasad L Polavarapu
The absolute configuration (AC) of an axially chiral sulfonate (aCSO), 3,5-dimethyl-2-(naphthalen-1-yl)-6-(naphthalen-1-yl)benzenesulfonate (labeled as aCSO5), was investigated using optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectroscopies. All three methods led to the same conclusion and the AC of aCSO5 is reliably determined to be (-)-(aR, aR), or conversely (+)-(aS, aS).
August 18, 2017: Chirality
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