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PubMed Journals Articles About "Chiral Technologies, Inc" - Page: 3 RSS

16:57 EST 10th December 2018 | BioPortfolio

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Showing "Chiral Technologies" PubMed Articles 51–75 of 2,400+

Rhodium-Catalyzed Asymmetric Addition of Organoboronic Acids to Aldimines Using Chiral Spiro Monophosphite-Olefin Ligands: Method Development and Mechanistic Studies.

The synthesis of a novel type of chiral spiro monophosphite-olefin (SMPO) ligands based on a hexamethyl-1,1'-spirobiindane scaffold was accomplished starting from Bisphenol C. The optimal ligand could serve as an elegant chiral bidentate ligand in the Rh-catalyzed asymmetric 1,2-addition of organoboronic acids to various acyclic/cyclic aldimines leading to chiral amines with high yields and excellent enantioselectivities. Detailed stereochemical models for enantioselective induction were elucidated through ...


Enantioselective Synthesis of Chiral Cyclopent-2-enones by Nickel-Catalyzed Desymmetrization of Malonate Esters.

The enantioselective synthesis of highly functionalized chiral cyclopent-2-enones by the reaction of alkynyl malonate esters with arylboronic acids is described. These desymmetrizing arylative cyclizations are catalyzed by a chiral phosphinooxazoline-nickel complex, and cyclization is enabled by the reversible E/Z isomerization of alkenylnickel species. The general methodology is also applicable to the synthesis of 1,6-dihydropyridin-3(2H)-ones.

Synthesis of Chiral Nonracemic α-Difluoromethylthio Compounds with Tetrasubstituted Stereogenic Centers via a Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation.

The synthesis of chiral, nonracemic difluoromethylthio (SCFH) compounds that contain a tetrasubstituted stereogenic center is reported. Racemic α-SCFH-β-ketoallylesters 5 were initially prepared by an electrophilic difluoromethylthiolation of β-ketoallylesters 6, followed by a Pd-catalyzed Tsuji decarboxylative asymmetric allylic alkylation (DAAA) to provide a wide variety of chiral, nonracemic α-allyl-α-SCFH-ketones (4) with high enantiopurity. This strategy can be extended to the enantioselective syn...


Role of association in chiral catalysis: from asymmetric synthesis to spin selectivity.

The origin of biomolecules in the pre-biological period is still a matter of debate, as is the unclarified nature of the differences in enantiomer properties, especially the medically important activity of chiral drugs. On the first issue, significant progress has been made in the last decade of the 20th century with the experimental confirmation of Frank's popular theory on chiral catalysis in spontaneous asymmetric synthesis. Prof. Soai examined the chiral catalysis of the alkylation of achiral aldehydes ...

Synthesis of Chiral Acyclic Nucleosides by Sharpless Asymmetric Dihydroxylation: Access to Cidofovir and Buciclovir.

An efficient method to construct chiral acyclic nucleosides via Sharpless asymmetric dihydroxylation of N-allylpyrimidines or N-alkenylpurines is reported. A range of chiral acyclic nucleosides with two adjacent hydroxyl groups present on the side chains could be produced in good yields (up to 97% yield) and excellent enantioselectivities (90-99% ee). The synthetic utility of the reaction was demonstrated by the catalytic asymmetric synthesis of (S)-Cidofovir and (R)-Buciclover.

Catalytic Enantioselective Flow Processes with Solid-Supported Chiral Catalysts.

Sustainability concerns are the wind in the sails for the development of novel, more selective catalytic processes. Hence, chiral catalysts play a crucial role in the green production of enantioenriched compounds. To further increase the green profile of this approach, the use of solid-supported catalytic species is appealing due to the reduced generation of waste, as well as the possibility of reusing the precious catalyst. Even more attractive is the implementation of flow processes based on these immobil...

Chiral Syn-1,3-diol Derivatives via a One-Pot Diastereoselective Carboxylation/ Bromocyclization of Homoallylic Alcohols.

Chiral syn-1,3-diols are fundamental structural motifs in many natural products and drugs. The traditional Narasaka-Prasad diastereoselective reduction from chiral β-hydroxyketones is an important process for the synthesis of these functionalized syn-1,3-diols, but it is of limited applicability for large-scale synthesis because (1) highly diastereoselective control requires extra explosive and flammable EtBOMe as a chelating agent under cryogenic conditions and (2) only a few functional syn-1,3-diol scaff...

Stereoselective HPLC separation of alvimopan on cellulose-based immobilized polysaccharide as a chiral stationary phase.

Chiral separation by normal phase high performance liquid chromatography is one of the most powerful technique to quantify the chiral purity of the compounds. In this study, a novel, simple, and specific analytical method was proposed to ascertain the chiral purity of alvimopan (ALV). The normal phase HPLC method was developed based on cellulose tris (3,5-dichlorophenylcarbamate) stationary phase. The separation of ALV isomers achieved by using column CHIRALPAK IC (250 × 4.6 mm, 5 μm), mobile phase n-...

Chiral Inductions in Excited State Reactions: Photodimerization of Alkyl 2-Naphthoates as a Model.

Enantioselectivity in organic transformations continues to be a topic major interest in organic photochemistry. In the last decade, synergistic combination of photocatalysis and organocatalysis has emerged as a powerful strategy to gain enantioselectivity in photochemical reactions, and remarkable achievements have been obtained. In this strategy the asymmetric induction is provided in ground state. In contrast, in the conventional enantioselective photochemistry the chiral induction is controlled in electr...

Chiral Transmission to Cationic Polycobaltocenes over Multiple Length Scales Using Anionic Surfactants.

Chiral polymers are ubiquitous in nature, and the self-assembly of chiral materials is a field of widespread interest. In this paper, we describe the formation of chiral metallopolymers based on poly(cobaltoceniumethylene) ([PCE] ), which have been prepared through oxidation of poly(cobaltocenylethylene) (PCE) in the presence of enantiopure N-acyl-amino-acid-derived anionic surfactants, such as N-palmitoyl-l-alanine (C-l-Ala) and N-palmitoyl-d-alanine (C-d-Ala). It is postulated that the resulting metallopo...

Nanoimprinted chiral plasmonic substrates with three-dimensional nanostructures.

We report a large-area fabrication method to prepare chiral substrates patterned with arrays of multilayer, three-dimensional nanostructures using a combination of nanoimprint lithography and glancing angle deposition. Several structures are successfully fabricated using this method, including L-shaped, twisted arc and tri-layer twisted Au nanorod structures, demonstrating its generality. As one typical example, arrays of L-shaped nanostructures, consisting of two layers of orthogonally oriented Au nanorods...

Bottom-Up Synthesis of Heteroatom-Doped Chiral Graphene Nanoribbons.

Bottom-up synthesis of graphene nanoribbons (GNRs) has significantly advanced during the past decade, providing various GNR structures with tunable properties. The synthesis of chiral GNRs, however, has been underexplored, and only limited to (3,1)-GNRs. We report herein the surface-assisted synthesis of the first heteroatom-doped chiral (4,1)-GNRs from the rationally designed precursor 6,16-dibromo-9,10,19,20-tetraoxa-9a,19a-diboratetrabenzo[ a,f,j,o]perylene. The structure of the chiral GNRs has been veri...

Development of C-Symmetric Chiral Bifunctional Triamines: Synthesis and Application in Asymmetric Organocatalysis.

The synthesis and application of a newly designed C-symmetric chiral bifunctional triamine family ( C-CBT) is reported. These enantiopure chiral triamine scaffolds can be accessed in multigram amounts from simple amino acids while avoiding chromatographic purification. As a proof of principle, C-CBT has been studied in the aldol reaction of cyclic ketones with isatins, with the target tertiary alcohols being formed in a highly efficient manner. Catalyst recovery by simple extraction techniques and subsequen...

Asymmetric 3 + 2 Cycloaddition Employing N, N'-Cyclic Azomethine Imines Catalyzed by Chiral-at-Metal Rhodium Complex.

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 en...

Kinetic traps to activate stereomutation in supramolecular polymers.

We describe the helical stereomutation in the kinetically controlled coassembly of the reported carbonyl-bridged triarylamines (CBTs). The copolymerization of chiral CBTs (S)-1 or (R)-1 with achiral 2 in sergeants-and-soldiers (SaS) experiments results in a tuneable helicity conditioned by the percentage of the chiral sergeant and by the cooling rate. The dissimilar inherent chirality of the extended monomeric (M) and intramolecularly H-bonded metastable (M*) species as well as the different stability of th...

pseudo1Catenane-Type Pillar5thiacrown Whose Planar Chiral Inversion is Triggered by Metal Cation and Controlled by Anion.

Chiral inversion of single molecules has been a challenging task because chirality information controls structures and func-tions of various molecules, artificial nanostructures, DNA, and proteins. Herein we present a pseudo[1]catenane-type mole-cule whose planar chiral inversion is driven by a metal ion under the control of anions for the first time. Considering an in-out equilibrium of a fused thiacrown and the soft metal binding, pillar[5]thiacrown ( rac-L) was synthesized. Two planar-chiral enantiomers ...

Homochiral Double Helicates Based on Cyclooctatetrathiophene: Chiral Self-sorting with the Intramolecular S···N Interaction.

We have designed and synthesized homochiral double helicates that are constructed via Ag-induced supramolecular self-sorting of saddle-shaped cyclooctatetrathiophene-based pyridine ligands. The intramolecular S···N interaction leads the thiophene and pyridine rings of ligands 1 and 2 to be in coplanar and syn-locked structures. In the presence of Ag+, the racemic ligands 1 and 2 only afforded homochiral double helicates, indicating effective chiral self-sorting process under the influence of the S···N...

Ni(II)-catalyzed asymmetric alkenylations of ketimines.

Chiral allylic amines are not only present in many bioactive compounds, but can also be readily transformed to other chiral amines. Therefore, the asymmetric synthesis of chiral allylic amines is highly desired. Herein, we report two types of Ni(II)-catalyzed asymmetric alkenylation of cyclic ketimines for the preparation of chiral allylic amines. When ketimines bear alkyl or alkoxycarbonyl groups, the alkenylation gives five- and six-membered cyclic α-tertiary allylic amine products with excellent yields ...

Femtosecond Vibrational Sum-Frequency Generation Spectroscopy of Chiral Molecules in Isotropic Liquid.

Vibrationally-resonant optically-active (VOA) sum-frequency generation (SFG) is a second-order nonlinear process sensitive to stereo-specific vibrational structure of chiral molecule. We demonstrate that a femtosecond VOA SFG signal can be measured in the isotropic bulk of a chiral liquid. The chiral, achiral, and VOA SFG spectra of R-, S-limonene and their racemic mixture in the C-H stretching frequency region are characterized. In particular, it is shown that the observed circular intensity difference (CI...

Enantiodivergent Synthesis of Allenes by Point to Axial Chirality Transfer.

An enantiodivergent method for the synthesis of multiply substituted allenes is described. Highly enantioenriched, point chiral boronic esters were synthesized by homologation of lithiated carbamates with α-seleno vinyl boronic esters and eliminated to form axially chiral allene products. By employing either oxidative or alkylative conditions, both syn- and anti-elimination could be achieved with complete stereospecificity. The process enables the synthesis of either (M) or (P) allenes from a single isomer...

Asymmetric Synthesis of Chiral Spiroketal Bisphosphine Ligands and Their Application in Enantioselective Olefin Hydrogenation.

A series of chiral spiroketal bisphosphine ligands containing 1,1'-spirobi(3H,3'H)isobenzofuran backbones was accessed through asymmetric synthesis and subsequently tested in enantioselective Rh-catalyzed hydrogenation of α-dehydroamino acid esters. The ligand providing the highest enantioselectivity (up to 99.5%) was obtained in seven steps in an overall 38% yield. The synthesis could be performed on gram-scale and no kinetic resolution of enantiomers is required. Overall, the developed ligand provides an...

Impact of Optical Purity on Light Harvesting Property in Supramolecular Nanofibers.

Supramolecular ordering and orientation of chromophores are tremendously accomplished in the photosynthetic light harvesting complexes, which are crucial for long-range transfer of collected solar energy. We herein demonstrate the importance of optical purity on the organization of chromophoric chiral molecules for the efficient energy migration. Enantiomeric bichromophoric compounds, which self-assemble into nanofibers capable of chiral recognition, were mixed to form supramolecular co-assemblies with vari...

Adoption of Stroke Rehabilitation Technologies by the User Community: Qualitative Study.

Using technology in stroke rehabilitation is attractive. Devices such as robots or smartphones can help deliver evidence-based levels of practice intensity and automated feedback without additional labor costs. Currently, however, few technologies have been adopted into everyday rehabilitation.

Enantioselective Halo-oxy- and Halo-azacyclizations Induced by Chiral Amidophosphate Catalysts and Halo-Lewis Acids.

Catalytic enantioselective halocyclization of 2-alkenylphenols and enamides have been achieved through the use of chiral amidophosphate catalysts and halo-Lewis acids. DFT calculations suggested that the Lewis basicity of the catalyst played an important role in the reactivity and enantioselectivity. The resulting chiral halogenated chromans can be transformed to α-tocopherol, α-tocotrienol, Daedalin A and Englitazone in short steps. Furthermore, a halogenated product with an unsaturated side chain may pr...

Copper(II)-Catalyzed Asymmetric Photoredox Reactions: Enantioselective Alkylation of Imines Driven by Visible Light.

Asymmetric photoredox catalysis offers exciting opportunities to develop new synthetic approaches to chiral molecules through novel reaction pathways. Employing the first-row transition metal complexes as the chiral photoredox catalysts remains, however, a formidable challenge, although these complexes are economic, environmentally friendly, and often exhibit special reactivities. We report in this Article the development of one class of highly efficient asymmetric/photoredox bifunctional catalysts based on...


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