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https://www.readbyqxmd.com/read/29150682/enantioselective-transformation-of-fluoxetine-in-water-and-its-ecotoxicological-relevance
#1
María Jesús Andrés-Costa, Kathryn Proctor, Marco T Sabatini, Anthony P Gee, Simon E Lewis, Yolanda Pico, Barbara Kasprzyk-Hordern
European legislation focusing on water quality is expected to broaden to encompass several pharmaceuticals as priority hazardous substances. This manuscript aims to challenge current regulatory approaches that do not recognize stereochemistry of chiral pharmaceuticals by testing the hypothesis that environmental transformation and effects of chiral pharmaceuticals are stereoselective. Our experiments revealed that, while degradation of chiral fluoxetine (FL) in river water occurs via non-enantioselective photochemical and mildly-enantioselective microbial processes favoring the (R)-enantiomer, a pronounced enantioselectivity favoring (S)-FL (leading to the formation of (S)-NFL (norfluoxetine)) is observed during activated sludge treatment...
November 17, 2017: Scientific Reports
https://www.readbyqxmd.com/read/29149518/control-of-n-heterocyclic-carbene-catalyzed-switchable-linear-and-cycloaddition-reactions-of-enals-asymmetric-synthesis-of-oxindole-%C3%AE-amino-acid-derivatives
#2
Dieter Enders, Xiang-Yu Chen, Jia-Wen Xiong, Qiang Liu, Sun Li, He Sheng, Carolina von Essen, Kari Rissanen
A strategy to control the switchable linear and cycloaddition reactions of enals through NHC catalyisis has been developed. The new scalable protocol leads to γ-amino acid esters bearing a tetrasubstituted stereocenter in good yields and high stereoselectivities via homo-Mannich reactions of enals and isatin-derived ketimines. By simply changing the N-ketimine substituent to an ortho-hydroxy phenyl group, the corresponding spirocyclic oxindolo-γ-lactams are obtained.
November 17, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/29148759/exploring-the-mechanism-and-stereoselectivity-in-chiral-cinchona-catalyzed-hetero-dimerization-of-ketenes
#3
Bangaru Bhaskararao, Garima Jindal, Raghavan B Sunoj
Catalytic hetero-dimerization of ketenes can lead to important four membered β-lactones. A recent asymmetric organocatalytic [2+2] cycloaddition between methylketene (MK) and methylphenylketene (MPK) in the presence of pseudo-enantiomeric cinchona catalysts (trimethylsilyl quinine (TMSQ) or methyl quinidine (MeQd)) provided β-lactones with high enantio- and diastereo-selectivities. We employ DFT(M06-2X) computations to understand the mechanism and the origin of stereoselectivity in this ketene hetero-dimerization...
November 17, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29148749/glycosyl-cross-coupling-of-anomeric-nucleophiles-scope-mechanism-and-applications-in-the-synthesis-of-aryl-c-glycosides
#4
Feng Zhu, Jacob Rodriguez, Tianyi Yang, Ilia Kevlishvili, Eric Miller, Duk Yi, Sloane O'Neill, Michael Rourke, Peng Liu, Maciej A Walczak
Stereoselective manipulations at the C1 anomeric position of saccharides are one of the central goals of preparative carbohydrate chemistry. Historically, the majority of reactions forming a bond with anomeric carbon has focused on reactions of nucleophiles with saccharide donors equipped with a leaving group. Here, we describe a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles. First, methods for the preparation of anomeric stannanes have been developed and optimized to afford both anomers of common saccharides in high anomeric selectivities...
November 17, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29148735/stereoselective-stabilization-of-polymeric-vitamin-e-conjugate-micelles
#5
Min Gao, Jian Deng, Huiying Chu, Yu Tang, Zheng Wang, Yanjun Zhao, Guohui Li
Vitamin E (α-tocopherol) (TPGS) micelle is a robust nanocarrier in delivering hydrophobic active pharmaceutical ingredients, but is suffering from poor stability that is essential in terms of pharmaceutical and biomedical applications. Taking advantage of the chirality of vitamin E, this work reports the stereoselective stabilization of polymer-vitamin E conjugate micelles. Vitamin E was covalently linked to multivalent methoxy poly(ethylene glycol)-co-poly(glutamic acid), generating amphiphilic conjugates that could self-assemble into micelles...
November 17, 2017: Biomacromolecules
https://www.readbyqxmd.com/read/29143478/regio-and-stereoselective-iron-catalyzed-oxyazidation-of-enamides-using-hypervalent-iodine-reagent
#6
Isabelle Gillaizeau, Sylvain Bertho, Romain Rey-Rodriguez, Pascal Retailleau, Cyril Colas
A novel regio- and diastereoselective iron-catalyzed intermolecular oxyazidation of enamides using various azidobenziodoxolone (ABX) derivatives is presented. A variety of alpha-N3 amino derivatives and of alpha-N3 piperidines is nicely synthesized in good yields and under mild reaction conditions. The reaction involves a radical process using cheap FeCl2 as the initiator.
November 16, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29140703/synthesis-of-2s-2-chloro-2-fluoro-ribolactone-via-stereoselective-electrophilic-fluorination
#7
Coralie De Schutter, Ozkan Sari, Steven J Coats, Franck Amblard, Raymond Felix Schinazi
A novel and efficient route for the preparation of (2S)-2-chloro-2-fluoro lactone 29 is described. This approach takes advantage of a highly efficient diastereoselective electrophilic fluorination reaction (94% yield; >50:1 dr).
November 15, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29140277/enantioselective-biosynthesis-of-l-phenyllactic-acid-by-whole-cells-of-recombinant-escherichia-coli
#8
Yibo Zhu, Ying Wang, Jiayuzi Xu, Jiahao Chen, Limei Wang, Bin Qi
BACKGROUND: l-Phenyllactic acid (l-PLA)-a valuable building block in the pharmaceutical and chemical industry-has recently emerged as an important monomer in the composition of the novel degradable biocompatible material of polyphenyllactic acid. However, both normally chemically synthesized and naturally occurring phenyllactic acid are racemic, and the product yields of reported l-PLA synthesis processes remain unsatisfactory. METHODS: We developed a novel recombinant Escherichia coli strain, co-expressing l-lactate dehydrogenase (l-LDH) from Lactobacillus plantarum subsp...
November 15, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/29136927/enantioselective-determination-of-metconazole-in-multi-matrices-by-high-performance-liquid-chromatography
#9
Rujian He, Jun Fan, Qi Tan, Yecai Lai, Xiaodong Chen, Tai Wang, Ying Jiang, Yaomou Zhang, Weiguang Zhang
A reliable and effective HPLC analytical method has been developed to stereoselectively quantify metconazole in soil and flour matrices. Effects of polysaccharide chiral stationary phase, type and content of alcoholic modifier on separation of racemic metconazole have been discussed in detail. Resolution and quantitative determination of metconazole stereoisomers were performed by using an Enantiopak OD column, with the n-hexane-ethanol mixture (97:3, v/v) at the flow rate of 1.0mL/min. Then, extraction and cleanup procedures followed by the modified QuEChERS (quick, easy, cheap, effective, rugged and safe) method were used for metconazole racemate in soil and flour matrices...
February 1, 2018: Talanta
https://www.readbyqxmd.com/read/29135242/computational-study-on-%C3%AE-c-h-functionalization-of-%C3%AE-%C3%AE-unsaturated-ester-catalyzed-by-n-heterocyclic-carbene-mechanisms-origin-of-stereoselectivity-and-role-of-catalyst
#10
Yang Wang, Donghui Wei, Mingsheng Tang
The N-heterocyclic carbene (NHC)-catalyzed γ-C-H deprotonation/functionalization of α,β-unsaturated esters with hydrazones leading to the δ-lactams has been theoretically investigated by using the density functional theory. Three possible reaction mechanisms including Mechanism A, for which the NHC catalyst serves as a nucleophilic catalyst to attack on the carbonyl carbon atom to initiate the reaction, for Mechanism B, in which NHC triggers the reaction through the hydrogen bond, and Mechanism C is the direct deprotonation/functionalization process without the presence of NHC have been suggested and studied in detail...
November 14, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29131945/enantioselectivity-of-2-2-3-5-6-pentachlorobiphenyl-pcb-95-atropisomers-toward-ryanodine-receptors-ryrs-and-their-influences-on-hippocampal-neuronal-networks
#11
Wei Feng, Jing Zheng, Gaelle Robin, Yao Dong, Makoto Ichikawa, Yoshihisa Inoue, Tadashi Mori, Takeshi Nakano, Isaac N Pessah
Nineteen ortho-substituted PCBs are chiral and found enantioselectively enriched in ecosystems. Their differential actions on biological targets are not understood. PCB 95 (2,2',3,5',6-pentachlorobiphenyl), a chiral PCB of current environmental relevance, is among the most potent towards modifying ryanodine receptors (RyR) function and Ca2+ signaling. PCB 95 atropisomers are separated and assigned aR- and aS-PCB 95 using 3 chiral-columns HPLC and circular dichroism spectroscopy. Studies of RyR1-enriched microsomes show aR-PCB 95 with >4X greater potency (EC50=0...
November 13, 2017: Environmental Science & Technology
https://www.readbyqxmd.com/read/29131934/methyl-dna-phosphate-adduct-formation-in-rats-treated-chronically-with-4-methylnitrosamino-1-3-pyridyl-1-butanone-and-enantiomers-of-its-metabolite-4-methylnitrosamino-1-3-pyridyl-1-butanol
#12
Bin Ma, Adam T Zarth, Erik S Carlson, Peter W Villalta, Pramod Upadhyaya, Irina Stepanov, Stephen S Hecht
The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a powerful lung carcinogen in animal models and is considered a causative factor for lung cancer in tobacco users. NNK is stereoselectively and reversibly metabolized to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is also a lung carcinogen. Both NNK and NNAL undergo metabolic activation by α-hydroxylation on their methyl groups to form pyridyloxobutyl and pyridylhydroxybutyl DNA base and phosphate adducts, respectively...
November 13, 2017: Chemical Research in Toxicology
https://www.readbyqxmd.com/read/29131622/computational-study-of-engineered-cytochrome-p450-catalyzed-c-h-amination-the-origin-of-the-regio-and-stereoselectivity
#13
Zhe Li, D Jean Burnell, Russell Jaye Boyd
Cytochrome P450 enzymes were recently engineered to catalyze the C-H amination reaction of aryl sulfonyl azides with excellent regio- and stereoselectivity (Arnold and coworkers JACS, 2014, 136, 15505). The mechanism of this reaction was studied by quantum mechanical (QM)/molecular mechanical (MM) calculations in this work. The C-H activation is found to be a stepwise process consisting of hydrogen abstraction (H-abstraction) of the reactive C-H bond by an iron nitrenoid cofactor to produce the biradical intermediate and the subsequent radical rebinding to form the final product...
November 13, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/29131418/stereoselective-nanozyme-based-on-ceria-nanoparticles-engineered-with-amino-acids
#14
Xiaogang Qu, Yuhuan Sun, Chuanqi Zhao, Nan Gao, Jinsong Ren
Stereoselectivity towards substrate is one of the most important characteristics of enzymes. Amino acids, as cofactors of many enzymes, play important roles in stereochemistry. Herein, chiral nanozymes were constructed by grafting a series of D- or L-amino acids on surfaces of ceria (cerium oxide) nanoparticles. We selected the most commonly used drug for combating Parkinson's disease 3, 4-dihydroxyphenylalanine (DOPA) enantiomers as examples for chiral catalysis. Through detailed kinetic studies of eight amino acids modified cerium oxide nanoparticles (CeNP), we found that phenylalanine-modified CeNP was optimal for the DOPA oxidation reaction and showed excellent stereoselectivity towards its enantiomers...
November 12, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29130687/short-enantioselective-total-syntheses-of-cheloviolenes-a-and-b-and-dendrillolide-c-via-convergent-fragment-coupling-using-a-tertiary-carbon-radical
#15
Michelle R Garnsey, Yuriy Slutskyy, Christopher R Jamison, Peng Zhao, Juyeol Lee, Young Ho Rhee, Larry E Overman
The development of a convergent fragment coupling strategy for the enantioselective total syntheses of a group of rearranged spongian diterpenoids that harbor the cis-2,8-dioxabicyclo[3.3.0]octan-3-one unit is described. The key bond disconnection relies on a late-stage fragment coupling between a tertiary carbon radical and an electron-deficient alkene to unite two ring systems and form two new stereocenters, one of which is quaternary, in a stereoselective and efficient manner. This strategy is applied toward scalable 14-15 step syntheses of three rearranged spongian diterpenoids, cheloviolenes A and B, and dendrillolide C...
November 13, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29130465/manipulating-the-stereoselectivity-of-the-thermostable-baeyer-villiger-monooxygenase-tmchmo-by-directed-evolution
#16
Guangyue Li, Maximilian J L J Fürst, Hamid Reza Mansouri, Anna K Ressmann, Adriana Ilie, Florian Rudroff, Marko D Mihovilovic, Marco W Fraaije, Manfred T Reetz
Baeyer-Villiger monooxygenases (BVMOs) and evolved mutants have been shown to be excellent biocatalysts in many stereoselective Baeyer-Villiger transformations, but industrial applications are rare which is partly due to the insufficient thermostability of BVMOs under operating conditions. In the present study, the substrate scope of the recently discovered thermally stable BVMO, TmCHMO from Thermocrispum municipale, was studied. This revealed that the wild-type (WT) enzyme catalyzes the oxidation of a variety of structurally different ketones with notable activity and enantioselectivity, including the desymmetrization of 4-methylcyclohexanone (99% ee, S)...
November 13, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29130307/unveiling-mechanism-of-a-quinine-squaramide-catalyzed-enantioselective-aza-friedel-crafts-reaction-between-cyclic-trifluoromethyl-ketimine-and-naphthol-a-dft-study
#17
Ping Wang, Yun Gao, Yang Zhao, Wei Liu, Yong Wang
A mechanism study of quinine-squaramide catalyzed enantioselective aza-Friedel-Crafts (aza-F-C) reaction is described using density functional theory (DFT). The most favorable pathway is obtained through the discussions of four possible modes of hydrogen bond interactions, in which the nucleophile is activated by the squaramide N-H groups (N-Ha and N-Hb) and the electrophile binds to the protonated amine by hydrogen bonding. Meanwhile, we have also studied the energy barrier of the stereocontrolling transition states that might play a role of stereoselectivity...
November 11, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29126742/ionic-liquid-mediated-stereoselective-synthesis-of-alanine-linked-hybrid-quinazoline-4-3h-one-derivatives-perturbing-the-malarial-reductase-activity-in-folate-pathway
#18
Tarosh S Patel, Jaimin D Bhatt, Satish F Vanparia, Urmila H Patel, Ritu B Dixit, Chaitanya J Chudasama, Bhavesh D Patel, Bharat C Dixit
Grimmel's method was optimized as well as modified leading to the cyclization and incorporation of alanine linked sulphonamide in 4-quinazolin-(3H)-ones. Further, the generation of heterocyclic motif at position-3 of 4-quinazolinones was explored by synthesis of imines, which unfortunately led to an isomeric mixture of stereoisomers. The hurdle of diastereomers encountered on the path was eminently rectified by development of new rapid and reproducible methodology involving the use of imidazolium based ionic liquid as solvents as well as catalyst for cyclization as well as synthesis of imines in situ at position-3 leading to procurement of single E-isomer as the target hybrid heterocyclic molecules...
October 31, 2017: Bioorganic & Medicinal Chemistry
https://www.readbyqxmd.com/read/29126076/a-rapid-and-sensitive-chiral-lc-ms-ms-method-for-the-determination-of-ketamine-and-norketamine-in-mouse-plasma-brain-and-cerebrospinal-fluid-applicable-to-the-stereoselective-pharmacokinetic-study-of-ketamine
#19
Hidetoh Toki, Takuya Ichikawa, Akiko Mizuno-Yasuhira, Jun-Ichi Yamaguchi
A novel method for the rapid and sensitive chiral determination of ketamine and norketamine in mouse plasma, brain and cerebrospinal fluid (CSF) was developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method reduces the required matrix volume, compared with a previously reported chiral assay method for ketamine and norketamine. The method involves the deproteinization of a small amount of biological matrix (corresponding to 5μL of plasma, 10mg of brain, or 2.5μL of CSF) using a water-miscible organic solvent containing (2)H4-norketamine as an internal standard, the direct injection of the organic supernatant into an LC-MS/MS system, chiral separation on a CHIRALPAK AS-3R column (4...
October 7, 2017: Journal of Pharmaceutical and Biomedical Analysis
https://www.readbyqxmd.com/read/29125741/achieving-molecular-complexity-via-stereoselective-multiple-domino-reactions-promoted-by-a-secondary-amine-organocatalyst
#20
Pankaj Chauhan, Suruchi Mahajan, Dieter Enders
In the last two decades, organocatalysis has emerged as an intensively investigated and rapidly growing area of research facilitating many known and many new transformations to provide efficient novel entries to complex molecules of high stereochemical purity. The organocatalysts have not only shown their efficiency for catalyzing the reactions in which one bond is formed, but they have also been effectively exploited in various versions of one-pot reactions. Domino reactions are one of the most important classes of one-pot reactions, where the target structure can be obtained in one pot without changing any reaction conditions while each reaction occurs as a consequence of the intermediates generated in previous steps...
November 10, 2017: Accounts of Chemical Research
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