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PubMed Journals Articles About "Chiral Technologies, Inc" - Page: 4 RSS

22:32 EDT 20th October 2018 | BioPortfolio

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Showing "Chiral Technologies" PubMed Articles 76–100 of 2,500+

Chiral Atropisomeric Indenocorannulene Bowls: Critique of Cahn-Ingold-Prelog Conception of Molecular Chirality.

Chiral corannulenes abound, but suffer generally from configurational lability associated with bowl-to-bowl inversion, thus obviating questions of stereogenicity and stereo element construction. In contrast, peri-annulated corannulenes show greatly increased barriers for bowl-to-bowl inversion, specifically indenocorannulenes invert on a time scale too slow to observe by normal NMR methods and raise the possibility of creating chiral atropisomeric bowl-shaped aromatics. Monosubstituted indenocorannulenes co...


Remote Central-to-Axial Chirality Conversion: Direct Atroposelective Ester to Biaryl Transformation.

A strategy for the remote central-to-axial chirality conversion by simultaneous planarization of an encoding and a transient stereocenter is presented. Based on a diastereoselective double addition of a chiral 1,5-bifunctional organomagnesium alkoxide reagent to a broad range of aryl ester substrates, axially chiral biaryls are directly obtained upon in situ reduction. Various structurally distinct atropisomeric biaryl silanes that serve as valuable chiral biaryl anion surrogates are accessible in one step ...

Chirality Transfer in Rhodium(I)-Catalyzed 3 + 2-Cycloaddition of Vinyl Aziridines and Oxime Ethers: Atom-Economical Synthesis of Chiral Imidazolidines.

A highly efficient and stereoselective synthesis of enantioenriched imidazolidines by rhodium-catalyzed intermolecular [3 + 2] cycloaddition reaction of chiral vinyl aziridines and oxime ethers has been successfully developed. Notably, both aldoximes and ketoximes are suitable substrates to afford the corresponding chiral imidazolidines in high yields with good stereoselectivity. This transformation represents an unprecedented example that utilizes ketimine derivatives as an aza-[2C]-component in cycloaddit...


Zinc(II)-Catalyzed Asymmetric Diels-Alder Reaction of (E)-1-Phenyldienes with β,γ-Unsaturated α-Ketoesters.

A highly regio-, diastereo- and enantioseletive Diels-Alder reaction of β,γ-unsaturated α-ketoesters with (E)-1-phenyldienes has been accomplished by using a stable and easily available chiral N,N'-dioxide/zinc(II) complex as catalyst. Only one isomer of the corresponding cyclohexenes with three chiral centers were obtained in good to excellent yields with excellent ee values under mild reaction conditions. The configurations of the product and chiral N,N'-dioxide/zinc(II) catalyst were identified by X-r...

Chiral separation of diastereomers of the cyclic nonapeptides vasopressin and desmopressin by uniform field ion mobility mass spectrometry.

In this study ion mobility-mass spectrometry (IM-MS) is used to distinguish chiral diastereomers of the nonapeptides desmopressin and vasopressin. The differences in gas phase cross sectional area (ca. 2%) were sufficient to directly resolve the enantiomers present in a binary mixture. Results from computational modeling indicate that chiral recognition by IM-MS for nonapeptides is possible due to their diastereomer-specific conformations adopted in the gas-phase, namely a compact ring-tail conformer specif...

Post-functionalisation of Tris-pyridyl Aluminate Ligands: Chirality, Coordination and Supramolecular Chemistry.

Post-functionalisation of the aluminate anion [EtAl(6-Me-2-py)3]- (1) (2-py = 2-pyridyl) with alkoxide ligands can be achieved by the selective reactions of the lithium salt 1Li with alcohols in the appropriate stoichiometry. This method can be used to introduce 3-py and 4-py functionality, while maintaining the integrity of the aluminate framework, thereby giving entry to new supramolecular chemistry. Chirality can be introduced either by using a chiral alcohol as a reactant or by the step-wise reaction of...

Comparison of Chiral Recognition of Binaphthyl Derivatives with l-Undecyl-Leucine Surfactants in the Presence of Arginine and Sodium Counterions.

In this study the chiral selectivity of l-undecyl-leucine (und-leu) for binapthyl derivatives was examined with the use of arginine and sodium counterions at pH's ranging from 7 to 11. The objective of this project was to investigate whether a cationic amino acid, such as arginine would achieve enhanced chiral selectivity when utilized as the counterion in the place of sodium in micellar electrokinetic chromatography. The data indicate that und-leu has significantly improved chiral selectivity toward 1,1'-b...

Highly Diastereo- and Enantioselective Synthesis of Cyclo-heptabindoles via Chiral Phosphoric Acid-Catalyzed (4+3)-Cycloaddition.

A highly enantio- and diastereoselective formal (4+3)- cycloaddition of 1,3-diene-1-carbamates with 3-indolylmethanols using a chiral phosphoric acid catalyst is reported. The approach described herein provides efficient access to 6-amino-tetrahydrocyclohepta[b]indoles in good yields with excellent levels of enantioselectivity (>98:2 dr and up to 98% ee) and mostly complete diastereoselectivity. Mild reaction conditions, easy scale-up, and versatile derivatization highlight the practicality of this methodol...

Rhodium-Catalyzed Highly Regio- and Enantioselective Hydrogenation of Tetrasubstituted Allenyl Sulfones: An Efficient Access to Chiral Allylic Sulfones.

A highly regio- and enantioselective hydrogenation of challenging tetrasubstituted allenyl sulfones has been achieved, affording chiral allylic sulfones in good yields with excellent regio- and enantioselectivities (up to 99% yield and 99% ee). This method provides an efficient and concise route to chiral allylic sulfones, thus offering an atom-economic process with a wide range of potential applications in organic synthesis and medicinal chemistry.

Enantioselective Electrophilic Cyanation of Boron Enolates: Scope and Mechanistic Studies.

Chiral β-ketonitriles bearing a stereogenic carbon center at the α-position are an important class of compounds, many of which serve as useful synthetic intermediates for the preparation of chiral 1,3-aminoalcohols, β-hydroxy nitriles and related derivatives. Although the enantioselective electrophilic cyanation of enolate equivalents is one of the most promising approaches for the synthesis of chiral β-ketonitriles, the available methods are largely limited to reactions of 1,3-dicarbonyl compounds. Her...

Selective chiral symmetry breaking and luminescence sensing of a Zn(ii) metal-organic framework.

The chiral Zn(ii) metal-organic framework [(CH3)2NH2]5[Zn1.5(Zn3O)(TATAT)2]·9DMF·17H2O (1) has been prepared from achiral precursors Zn(NO3)2·6H2O and 5,5',5''-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H6TATAT) in a solvent mixture of DMF/MeOH/H2O/HCOOH without any chiral sources. In particular, the non-random handedness excess (1P ≫ 1M) was generated and was verified by single-crystal X-ray diffraction and solid-state circular dichroism spectroscopy. Furthermore, complex 1 displays h...

On-line coupling of achiral Reversed Phase Liquid Chromatography and chiral Supercritical Fluid Chromatography for the analysis of pharmaceutical compounds.

On-line selective comprehensive two-dimensional chromatography combining Reversed Phase Liquid Chromatography and Supercritical Fluid Chromatography (sRPLCxSFC) was investigated for the analysis of chiral pharmaceutical compounds. Preliminary studies were carried out with the aim of overcoming instrumental constraints which are related to such 2D-coupling. The impact of both injection solvent and injection volume on the chiral SFC second separation was assessed with a view to limiting injection effects due ...

A Mismatch-Free Strategy for the Diastereoselective α,α-Bisalkylation of Chiral Nonracemic Methyl Ketones.

A chiral auxiliary-based diastereoselective transformation that entirely avoids the stereochemically mismatched pairing, providing equally high levels of asymmetric induction in the formation of each diastereomer is described. In particular, we show that chiral nonracemic methyl ketones undergo α,α-bisalkylation using phenylalanine-derived N-amino cyclic carbamate (ACC) auxiliaries with essentially perfect diastereoselectivity, as well as excellent yield and regioselectivity. Significantly, with the use o...

Atroposelective Organocatalytic Asymmetric Allylic Alkylation Reaction for Axially Chiral Anilides with Achiral Morita-Baylis-Hillman Carbonates.

A highly efficient method to access axially chiral anilides through asymmetric allylic alkylation reaction with achiral Morita-Baylis-Hillman carbonates by using a biscinchona alkaloid catalyst was reported. Through the atroposelective approach, a broad range of axially chiral anilide products with different acyl groups, such as substituted phenyl, naphthyl, alkyl, enyl, styryl and benzyl, were generated with very good yields, moderate to excellent cis:trans ratios and good to excellent enantioselectivities...

Palladium-Catalyzed Enantioselective Addition of Chiral Metal Enolates to In Situ Generated Ortho-Quinone Methides.

We describe herein a conceptually novel, cooperative Brønsted acid-base catalyzed process for the conjugate addition of cyclic β-keto esters to in situ generated ortho-quinone methides. Upon hemiacetalization densely functionalized chiral chromans with two adjacent quaternary and additionally a tertiary stereogenic center were obtained with very good diastereoselectivity (up to >95:5 d.r.) and typically excellent enantioselectivity (up to >99% ee). The striking feature and key to success is the dual catal...

Searching for Models Exhibiting High Circularly Polarized Luminescence: the Electroactive Inherently Chiral Oligothiophenes.

Two new inherently chiral oligothiophenes characterized by the atropisomeric 3,3'-bithianaphtene scaffold functionalized with fused ring bithiophene derivatives, namely 4H-cyclopenta [2,1-b3:4b']dithiophene (CPDT) and dithieno[3,3-b:2',3'-d]pyrrole (DTP), were synthesized. The racemates were fully characterized and resolved into antipodes by enantioselective HPLC. The enantiomers were analyzed through different chiroptical techniques: electronic circular dichroism (ECD) and vibrational circular dichroism (V...

Asymmetric iodine catalysis-mediated enantioselective oxidative transformations.

The implementation of chiral iodine catalysis has tremendously been developed in the field of asymmetric synthesis over the past decade. It enables the stereoselective creation of C-O as well as C-C, C-N and C-X (X = halogen) bonds through oxidative transformations. Thanks to the low toxicity and ease of handling of iodine compounds, this strategy offers many advantages over classical metal-catalyzed oxidations with chiral ligands. The approaches rely on iodine(i/iii) or (-i/+i) catalysis by using a chiral ...

Twisted bio-nanorods serve as a template for constructing chiroptically active nanoflowers.

Using biomacromolecule-based nanorods as a chiral source is a creative way to fabricate broadband chiroptically active nanoarchitectures. Herein, right-handedly twisted cellulose nanocrystal (CNC) nanorods, serving simultaneously as a chiral template and a building block, were combined with CuO for constructing composite nanoflowers that showed broadband chiroptical activity. Through calcination, the CuO/CNC nanoflowers can transform into chiral CuO with a flower-like architecture. The established preparati...

Inversion of Optical Activity in the Synthesis of Mercury Sulfide Nanoparticles: Role of Ligand Coordination.

Optical activity in inorganic colloidal materials has been readily controlled through interactions of chiral molecules with the nanoparticle (NP) surface. Here, we demonstrate an inversion of optical activity in the synthesis of mercury sulfide (HgS) NPs with an intrinsically chiral crystalline system in the presence of an identical chiral capping ligand. A continuous decrease in the positive first Cotton effect and an eventual reversal of CD profile were observed upon heating the aqueous solution of HgS NP...

Inherently Chiral Au24 Framework with Double-Helical Hexagold Strands.

Chiral gold clusters have attracted attention not only as a unique type of chiral compound but also in relation to the potential applications for chiroptical materials. Herein, we report the use of 2,3-bis(diphenylphosphino)butane enantiomers (chiraphos, L) as chiral auxiliaries results in the preferential formation of an unprecedented Au24 framework with inherent chirality. The crystal structure of [Au24L6Cl4]2+ (1) was revealed to have a square antiprism-like octagold core twinned by two helicene-like hex...

What do we know about technologies for dementia-related wandering? A scoping review: Examen de la portée : Que savons-nous à propos des technologies de gestion de l'errance liée à la démence?

Occupational therapists use technologies to manage wandering-related risks to promote safety and independence among individuals with dementia living in the community.

Chiral Domain Structure in Superfluid ^{3}He-A Studied by Magnetic Resonance Imaging.

The existence of a spatially varying texture in superfluid ^{3}He is a direct manifestation of the complex macroscopic wave function. The real space shape of the texture, namely, a macroscopic wave function, has been studied extensively with the help of theoretical modeling but has never been directly observed experimentally with spatial resolution. We have succeeded in visualizing the texture by a specialized magnetic resonance imaging. With this new technology, we have discovered that the macroscopic chir...

Chiral Phthalocyanines through Axial Coordination.

A novel approach to axially induce chirality on silicon phthalocyanines via a microwave-assisted route is reported. CD analysis provides spectroscopic evidence that chirality is transferred onto both Soret and Q-bands of the phthalocyanine core. A chiral naphthalenediimide ligand was found to induce the largest Cotton effect on the macrocycle absorptions.

General Catalytic Enantioselective Access to Monohalomethyl and Trifluoromethyl Cyclopropanes.

An efficient catalytic enantioselective access to chiral functionalized trifluoromethyl cyclopropanes from two classes of diazo compounds and alpha-trifluoromethyl styrenes using Rh2((S)-BTPCP)4 as a catalyst is described. This method provides an efficient and practical strategy for the synthesis of highly functionalized CF3-cyclopropanes with excellent diastereoselectivities (up to 20:1) and enantioselectivities (up to 99% ee). The depicted methodology represents up to date the most efficient catalytic ena...

Enantioselective synthesis of enantiopure chiral alcohols using carbonyl reductases screened from Yarrowia lipolytica.

We aimed to explore Yarrowia lipolytica carbonyl reductases as effective biocatalysts and to develop efficient asymmetric reduction systems for chiral alcohol synthesis.


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