Chiral Crown Ethers Research Articles

Enantioselective Synthesis of α-Alkoxy-Phosphonates by Chiral Phase Transfer Catalysis

Enantioselective PTC phosphorylation of aldehydes performed in a two phase (aq. NaOH/toluene) system mediated by chiral crown ether incorporating one or two sugar units. To avoid the rearrangement of hydroxy phosphonate 3 to nonchiral mixed phosphate ester 4 the hydroxy phosphonate was trapped by alkylation to give 5.

Synthesis and structure of a new type of C2-symmetric chiral crown ether

A new type of chiral crown ether, ( R,R)-2,12-bis(hydroxymethyl)-2,12-dimethyl-18-crown-6 possessing plural reactive functional groups, was isolated from a racemic mixture by lipase-catalyzed acetylation. The absolute configuration of the crown diol was determined based on the X-ray analysis of the complex of the derivative having plural oxyquinoline moieties with KI.

High-Performance liquid chromatographic separation of enantiomers of unusual amino acids possessing cycloalkane or cycloalkene skeletons on a chiral crown ether containing stationary phase

Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation and identification of the enantiomers of mono- and bicyclic racemic β-amino acids:cis- andtrans-2-aminocyclopentane-1-carboxylic acids,cis- andtrans-2-aminocyclohexane-1-carboxylic acids,cis- andtrans-2-amino-4-cyclohexene-1-carboxylic acids,diendo- anddiexo-3-aminobicyclo[2.2.1]heptane-2-carboxylic acids anddiendo- anddiexo-3-amino-5-bicyclo[2.2.1]heptene-2-carboxylic acids. Enantioseparation was carried out by the application of a chiral stationary phase, Crownpak CR(+). The conditions of separation were optimized by changing the temperature, the flow rate and the pH of the mobile phase.

Effect of Temperature on Retention of Cyclic ( -Amino Acid Enantiomers on a Chiral Crown Ether Stationary Phase

The isocratic retention of cyclic β-amino acids is studied on a chiral crown ether column (Crownpak CR [+]) at different temperatures. The natural logarithm of the retention factor (In k) depends linearly on the inverse of temperature (1/7). van't Hoff plots afford thermodynamic parameters, such as the apparent change of enthalpy (AH0) and the apparent change of entropy (AS0) for the transfer of analyte from the mobile phase to the stationary phase. The information obtained from the thermodynamic study is discussed, and the qualitative relationships between the structure and the thermodynamic data are evaluated.

Synthesis and phase-transfer catalytic activity of novel chiral crown ethers immobilized onto polystyrene supports

Polymer-supported novel optically active crown ethers were prepared by the reaction of chiral crown ethers derived from L-(+)-tartaric acid and 4-chloromethylated polystyrene resins crosslinked with 2 mol% of divinylbenzene. The ring substitution which indicates percentages of functionalized unit of the obtained polymers was in the range of 12–33%. The phase-transfer catalytic activity of the polymer-bound crown ethers has been studied on the reaction of 1-halo-octane with NaI or KI under liquid/liquid/solid tri-phase conditions. The catalyst with 18-crown-6 unit exhibited higher activity than the catalyst with 15-crown-5 unit. The activity of the catalyst with 18-crown-6 moiety for the reaction of 1-chloro-octane with KI was independent of catalyst particle size and increased with decreasing the degree of ring substitution, and the reaction rates were considered to be controlled only by the intrinsic reactivity at active site. On the other hand, the activity for the reaction of 1-bromo-octane with KI were dependent on catalyst particle size and exhibited maximum near 15–20% ring substitution, and the reaction rates were concluded to be limited by both the intrinsic reactivity and the intraparticle diffusion of reactants. The recovered catalyst could be reused repeatedly without a decrease in the activity.

Enantiomer separation of amino compounds by a novel chiral stationary phase derived from crown ether

A novel chiral stationary phase (CSP-18C6I) was prepared by immobilizing (+)-18-crown-6 tetracarboxylic acid on 3-aminopropylsilanized silica-gel to separate enantiomers of drugs having a primary amino group. The chiral crown ether was combined with 3-aminopropyl silica gel (0.85 mmol of amine per gram of gel) to provide CSP-18C6I having a chiral selector loading of 0.26 mmol per gram of gel. This CSP-18C6I showed good chiral recognition for thirteen out of eighteen dl-amino acids and seven racemic aminoalcohols using a dilute aqueous solution of perchloric acid as the eluent. Afloqualone (a muscle relaxant), primaquine (an antimalarial), and 1-(1-naphthyl)ethylamine (1-NEA) were resolved on the CSP-18C6I. Furthermore, alanine-β-naphthylamide (Ala-β-NA), which is hydrophobic and did not elute within 60 min by the commercially available CROWNPAK CR(+) with 15% methanol and a column temperature of 40°C, was successfully enantioseparated by the novel CSP-18C6I.

ChemInform Abstract: Asymmetric Michael Addition and Deracemization of Enolate by Chiral Crown Ether.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chirale Kronenether mit integriertem 1,4-verbrückten d-Glucopyranose-Baustein

The chiral crown ethers 7, 8, 9, and 13 containing a 1,4-bridged α-d-glucopyranose moiety were synthesized from methyl 2,3,6-tri-O-benzyl-α-d-glucopyranoside (1) and methyl 2,3-di-O-allyl-6-O-benzyl-α-d-glucopyranoside (2), respectively, by two subsequent etherification reactions followed by an intramolecular transglycosylation. To build up the hexaethylene glycol chain in 4-position of 1 and 2, bis(2-chloroethyl) ether (generating 3 and 4, respectively) and tetraethylene glycol (yielding 5 and 6, respectively) were used. The cyclizations of 5 and 6 in acetonitrile to the crowns 7 and 8 were catalysed by trimethylsilyl trifluoromethanesulfonate assisted by a "template" effect of potassium tetrafluoroborate (yield 45-57%). A high α-stereoselectivity was found for the intramolecular glycosylations even if a benzoylated precursor such as 12 was cyclized (catalyst: BF3 ⋅ Et2O; yield 25-26%). Compound 12 was prepared from 5 by exchange of the benzyl groups for benzoyl functions (10-12). Finally, the crown ether 8 was deallylated to generate the crown 9.

Asymmetric Michael addition and deracemization of enolate by chiral crown ether

Crown ethers anellated to glucose units have been used to catalyse the enantioselective Michael addition of methyl phenylacetate to methyl acrylate in high chemical yields in up to 84% enantiomeric excess. A novel CH-acid deracemization has also been discovered and the mechanistic rationale of the asymmetric induction is discussed. The proposed mechanism of the addition was also substantiated by molecular mechanics calculations.

Chiral Discrimination of Amino Acids by an Optically Active Crown Ether Studied by HPLC, Extraction and a Liquid Membrane Transport Experiments

A chiral crown ether incorporating a methyl α-d-mannopyranoside unit displayed pronounced enantioselection of amino acids in partition liquid chromatography experiments involving solvent systems of limited miscibility: water–ethanol–2,2,4-trimethylpentane. The same system has been used for amino acid transport across a liquid membrane containing the crown ether, and in liquid–liquid extraction experiments. Remarkable enantioselection has been noted for amino acids in all the processes studied.

ChemInform Abstract: Asymmetric Michael Addition of 2‐Nitropropane to a Chalcone Catalyzed by Chiral Crown Ethers Incorporating a D‐Glucose Unit.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of Novel Receptors From 7-Deoxycholic Acid and Studies on Their Cation Binding Properties

The synthesis and cation binding properties of chiral crown ethers derived from 7-deoxycholic acid along with their application in asymmetric Michael reaction are described.

Enantiomer-Selectivity of Ion-selective Electrodes Based on a Chiral Crown-ether Ionophore

A newly synthesized crown ether ionophore can differentiate between R-(+) and S-(-)-1-phenylethylammonium ions when incorporated into a plasticized PVC based electrode membrane, thus providing enantiomer-selectivity. Different membrane compositions were studied. The selectivity coefficient found was 0.71, independent of the membrane composition. This proves the robustness of the ISE method for testing the enantiomeric selectivity of newly synthesized ionophores. Selectivities of the new ionophore towards different hydrophilic cations were also determined.

ChemInform Abstract: Enantioselective Allylation of Nitro Group‐Stabilized Carbanions Catalyzed by Chiral Crown Ether Phosphine‐Palladium Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Lanthanide-Crown Ether Mixtures as Chiral NMR Shift Reagents for Amino Acid Esters, Amines and Amino Alcohols

Two chiral crown ethers, 2,3:4,5-bis[1,2-(3-phenylnaphtho)-1,6,9,12,15,18-hexaoxacycloeicosa-2,4-diene and 1,2:5,6-di-O-isopropylidene-3,4-[(tert-butylbenzenediyl)bis(oxyethoxy)ethyl-D-mannitol, were evaluated as organic-soluble chiral NMR resolving agents. The crown ethers are useful resolving agents for protonated amino acid esters, amines and amino alcohols. Enantiodiscrimination with the crown ethers is better in methanol than in acetonitrile or chloroform. Organic-soluble lanthanide tetrakis(β-diketonate) anions, which are formed in solution by mixing a lanthanide tris(β-diketonate) and silver β-diketonate, can be added to crown–substrate mixtures to enhance the enantiomeric resolution. The lanthanide-induced enhancement occurs because the enantiomers of the substrate have different association constants with the crown ethers. The enantiomer that associates less favorably with the crown ether is more available to complex with the lanthanide. © 1997 by John Wiley & Sons, Ltd.

ChemInform Abstract: Synthesis of Chiral Crown Ethers Having Bromoarylene Moieties on Their Rim. Anomalous Behavior of Racemic Substrates in Cyclization to Crown Ethers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantiomeric separations of primary amino compounds by nonaqueous capillary zone electrophoresis with a chiral crown ether

The enantiomeric separation by capillary electrophoresis (CE) in non-aqueous media was examined. The enantiomeric separations of eight primary amino compounds including aromatic amines, amino acids and amino alcohols were achieved by CE in formamide containing a chiral crown ether, (+)-18-crown-6 tetracarboxylic acid. The addition of tetra- n-butylammonium perchlorate as a supporting electrolyte to the electrophoretic solution improved the separation efficiency and gave the baseline enantiomeric separation of dl-1-phenylethylamine which has not been separated by any other separation mode of CE yet.

Separation of enantiomers and isomers of amino compounds by capillary electrophoresis and high-performance liquid chromatography utilizing crown ethers

Separation of enantiomers and isomers of a wide variety of primary amines by capillary electrophoresis (CE) was investigated employing charged and uncharged crown ethers. Enantiomer separation of primary amines by CE was successful through the addition of a chiral crown ether, 18-crown-6 tetracarboxylic acid (18C6H 4). Thirteen out of 17 enantiomers tested were separated by CE with 18C6H 4. Low pH values (pH 1.9–2.1) and relatively high Tris concentration (20 m M) were effective for the fast enantiomer separation. Enantiomer separation of the same primary amines was also investigated by high-performance liquid chromatography (HPLC) with a chiral Crownpak CR(+) column, although different chiral crown ether moieties were employed in CE and HPLC. Other than enantiomers, separation of positional isomers of aromatic amino compounds such as aminophenols, aminocresols was investigated by both CE with three kinds of 18-membered crown ethers and HPLC with a Crownpak CR(+) column. The use of crown ethers for the separation of amino compounds is discussed in viewpoint of practical applications. The optical purity testing of amino compounds is also demonstrated.

Twenty-five Years of "Crowning" Around: Synthesis of Crown Ethers at Brigham Young University

A review of the synthesis of crown ethers at Brigham Young University ispresented. Topics include: thiacrown ethers, diestercrown ethers,proton-ionizable crown ethers, chiral crown ethers, azacrown ethers,cryptands and other polycyclic ligands, and the Mannich reaction method toprepare azacrown ethers and cryptands.

Intrinsic Contributions to Chiral Recognition: Discrimination Between Enantiomeric Amines by Dimethyldiketopyridino-18-crown-6 in the Gas Phase

We have employed Fourier transform ion cyclotron resonance (FTICR) mass spectrometry to investigate and quantify the recognition of chiral amines in the gas phase by the chiral crown ethers (R,R)- and (S,S)-dimethyldiketopyridino-18-crown-6, using a new procedure wherein the relatively involatile chiral ligand is easily ionized via electrospray to produce a protonated host molecule. A neutral chiral amine and an achiral reference amine, which are generally fairly volatile, were introduced into the ion trapping cell, where they reacted with the protonated host to form crown−ammonium complexes. Equilibrium constants were determined for exchange of the chiral and achiral amine guests. Electrospray of the other enantiomeric host, followed by guest exchange equilibrium constant determination, enabled characterization of the effects of chirality on complexation equilibria. Comparison of the equilibrium constants for the two enantiomeric hosts measures the relative degree of recognition for a given guest. In all...