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https://www.readbyqxmd.com/read/29775221/reagent-induced-asymmetric-induction-in-addition-reaction-of-reduced-glutathione-onto-bis-mannich-chalcones
#1
Aline Bernardes, Giulio D C D'Oliveira, Aneta Silezin, Mónika Kuzma, Szilárd Molnár, Caridad Noda Pérez, Pál Perjési
The stereochemistry of non-enzyme catalyzed nucleophilic addition of GSH to 4'-hydroxychalcone 1 and its bis-Mannich derivative 2 was investigated at different pH values (pH 3.2, 6.1, 7.4, and 8.0). The stereochemical outcome of the reactions was evaluated by HPLC-UV-Vis method. Under strongly acidic conditions (pH 3.2), an unexpected diastereoselective addition of GSH onto the bis-Mannich derivative 2 was observed. Such a selectivity could not be observed in the similar reaction of 2 with N-acetylcysteine...
May 18, 2018: Archiv der Pharmazie
https://www.readbyqxmd.com/read/29774967/re-optimization-of-the-organocatalyzed-double-aldol-domino-process-to-a-key-enal-intermediate-and-its-application-to-the-total-synthesis-of-%C3%AE-%C3%A2-%C3%A2-prostaglandin-j%C3%A2
#2
Andrejs Pelss, Narasimhulu Gandhamsetty, James Robin Smith, Damien Mailhol, Mattia Silvi, Andrew Watson, Isabel Perez-Powell, Sébastien Prévost, Nina Schützenmeister, Peter Moore, Varinder Kumar Aggarwal
Re-investigation of the L-proline catalyzed double aldol cascade dimerization of succinaldehyde for the synthesis of a key bicyclic enal intermediate, pertinent in the field of stereoselective prostaglandin synthesis, is reported. The yield of this process has been more than doubled, from 14% to a 29% isolated yield on a multi-gram scale (32% NMR yield), through conducting a detailed study of the reaction solvent, temperature and concentration, as well as a catalyst screen. The synthetic utility of this enal intermediate has been further demonstrated through the total synthesis of Δ¹²-prostaglandin J₃, a compound with known anti-leukemic properties...
May 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29774613/divergent-enantioselective-synthesis-of-pyrroles-3h-pyrroles-and-bicyclic-imidazolines-by-ag-or-p-catalyzed-3-2-cycloaddition-of-allenoates-with-activated-isocyanides
#3
Yu Zhao, Germaine Pui Yann Kok, Pan-Lin Shao, Jia-Yu Liao, Siti Nur Fairuz Bte Sheikh Ismail, Weijun Yao, Yixin Lu
We report herein our detailed investigation of divergent, stereoselective formal [3 + 2] cycloadditions of allenoates with activated isocyanides catalyzed by silver or phosphine-based catalysts. Silver catalysis is capable of delivering a range of 3H-pyrroles in high stereoselectivities. These enantioenriched heterocycles can either undergo sequential cyclisation with isocyanoacetates to deliver unprecedented bicyclic imidazolines with excellent yields and stereoselectivity or undergo unusual aromatization pathways leading to poly-substituted pyrroles...
May 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29774487/facile-synthesis-of-%C3%AE-alkoxymethyltriphenylphosphonium-iodides-new-application-of-pph-3-i-2
#4
Humaira Yasmeen Gondal, Zain Maqsood Cheema, Javid Hussain Zaidi, Sammer Yousuf, M Iqbal Choudhary
An efficient one pot method for the synthesis of α-alkoxymethylphosphonium iodides is developed by using PPh3 /I2 combination at room temperature. Reaction conditions are found general to synthesize wide range of structurally variant alkoxymethylphosphonium iodides in high yield (70-91%). These new functionalized phosphonium salts are further used in stereoselective synthesis of vinyl ethers as well as in carbon homologation of aldehydes.
May 17, 2018: Chemistry Central Journal
https://www.readbyqxmd.com/read/29773786/stereodivergent-synthesis-of-vicinal-quaternary-quaternary-stereocenters-and-bioactive-hyperolactones
#5
Haifeng Zheng, Yan Wang, Chaoran Xu, Xi Xu, Lili Lin, Xiaohua Liu, Xiaoming Feng
Although great success has been achieved in asymmetric Claisen rearrangement for the synthesis of chiral γ,δ-unsaturated carbonyl compounds bearing vicinal tertiary-quaternary stereocenters, the development of asymmetric versions for stereodivergent construction of adjacent quaternary-quaternary stereocenters remains a formidable challenge because of the high steric hindrance. Here we report a catalytic enantioselective dearomatization Claisen rearrangement of allyl furyl ethers catalyzed by chiral N,N'-dioxide-NiII complex catalysts...
May 17, 2018: Nature Communications
https://www.readbyqxmd.com/read/29771526/stereoselective-synthesis-of-pyrans-from-epoxyalkenes-dual-catalysis-with-palladium-and-br%C3%A3-nsted-acid
#6
Noah A Setterholm, Frank E McDonald
We describe regio- and stereoselective cycloisomerizations of alcohols tethered to epoxyalkenes, to construct alkene-substituted pyrans. These transformations are best catalyzed by Pd(PPh3)4 in the presence of phosphite ligands, and with diphenylphosphinic acid as an essential Brønsted acid co-catalyst for activation of the epoxyalkene.
May 17, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29771125/palladium-catalyzed-stereoselective-cyclization-of-in-situ-formed-allenyl-hemiacetals-synthesis-of-rosuvastatin-and-pitavastatin
#7
Pierre A Spreider, Bernhard Breit
A diastereoselective palladium-catalyzed cyclization of allenyl hemiacetals is described. It permits the selective synthesis of 1,3-dioxane derivatives, precursors for syn-configured 1,3-diols which make an appearance in all of the statin representatives. The reaction allows the total synthesis of Rosuvastatin and Pitavastatin in a straightforward fashion.
May 17, 2018: Organic Letters
https://www.readbyqxmd.com/read/29770508/asymmetric-sulfur-ylide-mediated-formal-4-1-annulation-reaction-scope-and-mechanism
#8
Sébastien Clergue, Rousseau Olivier, Delaunay Thierry, Dequirez Geoffroy, Tran Trieu-Van, El Aakchioui Soumia, Barozzino-Consiglio Gabriella, Raphael Robiette
A formal (4+1) annulation strategy between sulfur ylides and 1,3-dienes has been developed to afford functionalized cyclopentanoids. The process consists of a stereoselective cyclopropanation reaction followed, in situ, by a stereospecific MgI2-catalyzed vinylcyclopropane-cyclopentene rearrangement. The use of chiral sulfur ylides provides cyclopentanoids with an excellent enantiocontrol. A combined experimental and computational mechanistic study shows that the stereospecificity of the rearrangement can be accounted for by a double SN2 reaction mechanism involving iodide...
May 16, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29768001/crystal-structures-of-the-mango-ii-rna-aptamer-reveal-heterogeneous-fluorophore-binding-and-guide-engineering-of-variants-with-improved-selectivity-and-brightness
#9
Robert Trachman, Amir Abdolahzadeh, Alessio Andreoni, Razvan Cojocaru, Jay R Knutson, Michaël Ryckelynck, Peter John Unrau, Adrian Ferré-D'Amaré
Several RNA aptamers that bind small molecules and enhance their fluorescence have been successfully used to tag and track RNAs in vivo, but these genetically encodable tags have not yet achieved single-fluorophore resolution. Recently, Mango-II, an RNA that binds TO1-Biotin with ~1 nM affinity and enhances its fluorescence by >1,500-fold was isolated by fluorescence selection from the pool that yielded the original RNA Mango. We determined the crystal structures of Mango-II in complex with two fluorophores, TO1-Biotin and TO3-Biotin, and found that despite their high affinity, the ligands adopt multiple distinct conformations, indicative of a binding pocket with modest stereoselectivity...
May 16, 2018: Biochemistry
https://www.readbyqxmd.com/read/29767521/intramolecular-imino-ene-reaction-of-2h-azirines-with-alkenes-rapid-construction-of-spiro-nh-aziridines-from-vinyl-azides
#10
Tai-Shang Liu, Hao Zhou, Peng Chen, Xiu-Rong Huang, Lin-Qing Bao, Chen-Lu Zhuang, Qing-Song Xu, Mei-Hua Shen, Hua-Dong Xu
A range of novel (poly)cyclic alkaloids incorporating an unprecedented 1,5-diazaspiro[2.4]heptane core that carry a spiro NH aziridine moiety and a 7-vinyl group are constructed from the thermal reaction of vinyl azides with tethered alkenes. Vinyl azides are converted to 2H-azirines in situ, which serve as enophiles for intramolecular imino-ene reactions with suitable alkenes. High stereoselectivity and specificity have been achieved for this novel intramolecular imino-ene reaction of azirines.
May 16, 2018: Organic Letters
https://www.readbyqxmd.com/read/29766588/synthesis-of-chlorotrifluoromethylated-pyrrolidines-via-electrocatalytic-radical-ene-yne-cyclization
#11
Ke-Yin Ye, Zhidong Song, Gregory Sauer, Johannes Harenberg, Niankai Fu, Song Lin
The stereoselective synthesis of chlorotrifluoromethylated pyrrolidines was achieved using anodically coupled electrolysis, an electrochemical process that combines two parallel oxidative events in a convergent and productive manner. The bench-stable and commercially available solids CF3SO2Na and MgCl2 were used as the functional group sources to generate CF3· and Cl·, respectively, via electrochemical oxidation, and the subsequent reaction of these radicals with the 1,6-enyne substrate was controlled with an earth-abundant Mn catalyst...
May 15, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29766173/a-manganese-porphyrin-%C3%AE-cyclodextrin-conjugate-as-an-artificial-enzyme-for-the-catalytic-epoxidation-of-polybutadiene
#12
Qi-Wei Zhang, Johannes A A W Elemans, Paul B White, Roeland J M Nolte
We describe a manganese porphyrin-α-cyclodextrin conjugate as a catalyst for the epoxidation of cis-polybutadiene with trans-epoxide preference, which is a reverse stereoselectivity as compared to normal porphyrin catalysts. A clamp-like mechanism is proposed based on a combination of circular dichroism analysis, molecular modeling, and a series of epoxidation experiments.
May 16, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29763332/asymmetric-3-2-cycloaddition-employing-n-n-cyclic-azomethine-imines-catalyzed-by-chiral-at-metal-rhodium-complex
#13
Jun Gong, Qian Wan, Qiang Kang
An efficient asymmetric 1,3-dipolar cycloaddition of α,β-unsaturated 2-acyl imidazoles with N, N'-cyclic azomethine imines catalyzed by a chiral-at-metal rhodium complex is reported. The corresponding N, N'-bicyclic pyrazolidine derivatives with three contiguous tertiary stereocenters were obtained in good yields (up to 99%) with excellent stereoselectivities (>20:1 dr and >99% ee). Remarkably, as little as 0.5 mol % of a chiral Rh(III) complex can promote a gram-scale reaction with excellent yield and enantioselectivity...
May 15, 2018: Organic Letters
https://www.readbyqxmd.com/read/29761878/c-h-activation-enables-a-concise-total-synthesis-of-quinine-and-analogues-with-enhanced-antimalarial-activity
#14
Daniel H O' Donovan, Paul Aillard, Martin Berger, Aurelien de la Torre, Desislava Petkova, Christian Knittl-Frank, Danny Geerdink, Marcel Kaiser, Nuno Maulide
We report a novel approach to the classical natural product Quinine based on two stereoselective key steps, namely a C-H activation and an aldol reaction to unite the two heterocyclic moieties of the target molecule. This straightforward and flexible strategy enables a concise synthesis of natural (-)-Quinine, the first synthesis of unnatural (+)-Quinine and also provides access to unprecedented C3-aryl analogues that can be prepared in only 6 steps. We additionally demonstrate that these structural analogues exhibit improved antimalarial activity compared with (-)-Quinine both in vitro and in mice infected with Plasmodium berghei...
May 15, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29761822/synthesis-of-fused-tricyclic-systems-by-thermal-cope-rearrangement-of-furan-substituted-vinyl-cyclopropanes
#15
Verena Klaus, Stéphane Wittmann, Hans M Senn, J Stephen Clark
A novel method for the stereoselective construction of hexahydroazuleno[4,5-b]furans from simple precursors has been developed. The route involves the use of our recently developed Brønsted acid catalysed cyclisation reaction of acyclic ynenones to prepare fused 1-furanyl-2-alkenylcyclopropanes that undergo highly stereoselective thermal Cope rearrangement to produce fused tricyclic products. Substrates possessing an E-alkene undergo smooth Cope rearrangement at 40 °C, whereas the corresponding Z-isomers do not react at this temperature...
May 15, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29761808/diversion-of-a-thioglycoligase-for-the-synthesis-of-1-o-acyl-arabinofuranoses
#16
Quentin Pavic, Sylvain Tranchimand, Loïc Lemiègre, Laurent Legentil
An arabinofuranosylhydrolase from the GH51 family was transformed into an acyl transferase by mutation of the catalytic acid/base amino acid. The resulting enzyme was able to transfer carboxylic acid onto the anomeric position of arabinose with complete chemo- and stereoselectivity. A wide range of acyl α-l-arabinofuranoses was obtained with yields ranging from 25 to 83%. Using this method, ibuprofen and N-Boc phenylalanine were successfully transformed into their corresponding acyl conjugates, expanding the scope of the reaction to drugs and amino acids...
May 15, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29756780/copper-i-catalyzed-n-o-bond-formation-through-vinyl-nitrene-mediated-pathway-under-mild-conditions
#17
Feifei Wu, Min Zhang, Wei Zhou, Wanzhi Chen, Miaochang Liu, Huayue Wu
Copper(I)-catalyzed N-O bond formation reactions through vinyl nitrene-mediated pathway were described. The reactions of N-alkoxylbenzamides and 2H-azirines afforded α-amino oxime ethers in good to excellent yields at room temperature, which involved the cleavage of C-N and N-O bonds, and the construction of new N-O and C-N bonds. It offers an efficient, regio- and stereoselective synthetic route for α-amino oxime ethers.
May 14, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29756345/common-polymorphisms-of-cyp2b6-influence-stereoselective-bupropion-disposition
#18
Evan D Kharasch, Amanda Crafford
Bupropion hydroxylation is a bioactivation and metabolic pathway, and the standard clinical CYP2B6 probe. This investigation determined the influence of CYP2B6 allelic variants on clinical concentrations and metabolism of bupropion enantiomers. Secondary objectives evaluated the influence of CYP2C19 and P450 oxidoreductase variants. Healthy volunteers in specific cohorts (CYP2B6*1/*1, CYP2B6*1/*6, CYP2B6*6/*6, and also CYP2B6*4 carriers) received single-dose oral bupropion. Plasma and urine bupropion and hydroxybupropion was quantified...
May 14, 2018: Clinical Pharmacology and Therapeutics
https://www.readbyqxmd.com/read/29756294/determination-of-brompheniramine-enantiomers-in-rat-plasma-by-cation-selective-exhaustive-injection-and-sweeping-cyclodextrin-modified-electrokinetic-chromatography-method
#19
Yaqi Yao, Yu Zhao, Xue Zhang, Jia Yu, Xingjie Guo
A method consisting of cation-selective exhaustive injection and sweeping (CSEI-sweeping) as online preconcentration followed by a cyclodextrin modified electrokinetic chromatography (CDEKC) enantioseparation has been developed for the simultaneous determination of two brompheniramine enantiomers in rat plasma. In this method, analytes were electrokinetically injected at a voltage of 8 kV for 80 s in a fused-silica capillary. Prior to the injection, the capillary was rinsed with 50 mM phosphate buffer pH 3...
May 13, 2018: Electrophoresis
https://www.readbyqxmd.com/read/29755827/stereoselective-synthesis-of-isoxazolidines-via-copper-catalyzed-alkene-diamination
#20
Zainab M Khoder, Christina E Wong, Sherry R Chemler
A convenient copper-catalyzed intramolecular/intermolecular alkene diamination reaction to synthesize 3-aminomethyl-functionalized isoxazolidines under mild reaction conditions and with generally high levels of diastereoselectivity was achieved. This reaction demonstrates that previously underutilized unsaturated carbamates are good [Cu]-catalyzed diamination substrates. Sulfonamides, anilines, benzamide, morpholine, and piperidine can serve as the external amine source. This relatively broad amine range is attributed to the mild reaction conditions...
July 7, 2017: ACS Catalysis
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