Asymmetric Synthesis of Chiral Clusters Induced by Chiral Phase-Transfer Catalyst

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Chiral Separations by Ligand-Exchange Micellar Electrokinetic

The separation of enantiomers is of great importance in biology, pharmaceutics, agriculture and environment. The different separation modes ( i. e. capillary zone electrophoresis ( CZE ), micellar electrokinetic chromatography ( MEKC ), capillary electrochromatography ( CEC ), etc )     

Enantiomeric Discrimination by Surface-Enhanced Raman Scattering–Chiral Anisotropy of Chiral Nanostructured Gold Films

A surface-enhanced Raman scattering-chiral anisotropy (SERS-ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS-ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs.     

New Chiral Calixarene Derivatives： Syntheses and Their Chiral Recognition Toward Amino Acids by UV-Vis Spectroscopy

Three novel types of chiral calixarene derivatives 5, 8, and 10 were designed and synthesized by introducing chiral units to parent calixarenes. Their chiralities were confirmed by rotational analysis. Chiral recognition properties of these host compounds towards L- and D-threonine were studied by UV-Vis spectroscopy. The results indicated that calixarene derivatives 5 and 8 exhibited good chiral recognition capabilities toward L- or D-threonine. Although calixarene derivative 10 had no evident chiral recognition ability, the supramolecules of calixarene derivative 10 with L- or D-threonine showed a hypochromic effect or hyperchromic effect respectively. Therefore, calixarene derivative 10 might serve as a good chiral UV-indicator.     

Attempt to Resolute Chiral Clusters by Optically Active Hydrazide

Due to the framework chirality optically active clusters can provide the proof that a cluster as a whole, and not one of its fragments, acts as a catalyst, most of the work have been directed to the synthesis of tetrahedron-type chiral clusters1-3. However, there remains another major problem to obtain the pure enantiomers. Although Vahrenkamp had obtained some pioneering results in this area before 19901, only several racemic chiral clusters have been separated into pure enantiomers until now…     

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

Abstract

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 of New MeO-BIPHEP-type Chiral Diphosphines by an Improved Way

In this paper,a series of new optically active MeO-BIPHEP-type ligands,(S)-6,6'-dimethoxy-2,2'-bis(di-p-alkoxyphenyl-phosphine)-1,1'-biphenyl[(S)-5b—(S)-5e]were prepared and characterized.Starting from thecommercially available triethyl phosphorite and m-bromoanisole,an optically active(S)-6,6'-dimethoxybiphenyl-2,2'-diyl-bis(phosphonic acid diester)was prepared by an improved way and converted to the corresponding dichlo-rides,which was used as a key intermediate to react with p-alkoxybenzenemagnesium bromide or p-alkoxyphenyllithium to directly give the enantiomerically pure diphosphines 5.     

Synthesis of Chiral Benzofuran-Derived β-Amino Esters Induced by N-tert-Butanesulfinamide

The benzofuran skeleton is commonly found in a wide variety of natural products that display a wide range of biological activities. For this reason, benzofuran has a high potential for use as a scaffold in both chemical and pharmaceutical syntheses of natural products. This work describes the development of a novel asymmetric synthetic method of benzofuran-derived β-amino esters via K₂CO₃-promoted domino reactions of ortho-hydroxyl aromatic N-tert-butylsulfinyl imines and diethyl bromomalonate. A small library of target compounds was prepared under optimized reaction conditions in moderate to good yields with high distereoselective and enantioselective properties. The newly generated chiral carbon center was of an (S)-configuration as determined by x-ray diffraction.     

Enantioselective Hydrolysis of α-Amino Acid Ester by Chiral Metallomicelles

Metall0ndcellesmadeup0ffunctionalizedsurfactants(orliP0philicligands)caPable0feffectivechelationofmetalionsarecurrentlyreceivingc0nsiderableinterestbecauseoftheircatalyticabilitytomindcmetall0enzymes.OfpatticularinterestarethendcellarmodelsofhydrolghcmetalloenZyInes,whichareabletoprom0tethecleavageofphosphoricandcarboxylicesters0raAndes.'-'M0stofthemaref0cused0ntheligandscontainingidridazole',pyridine'orl,lO-phenanthroline'asthebasicchelatingsubunitandasthem0lecularjunctionfortheparaffmiccha…     

Asymmetric Hydroformylation of Olefins Catalyzed by a Chiral Diphosphite-Rhodium Complex

A C2-symmetrical aryl diphosphite derived from chiral binaphthol was prepared and its rhodium complex was used as catalysts in the asymmetric hydroformylation of olefins. High catalytic activity and good regioselectivity were observed. Up to 31.2% ee and 38.1% ee were achieved for the hydroformylation of 4-fluoro-styrene and vinyl acetate respectively. The influences of ligand-to-metal ratio, reaction temperature and the pressure of syn-gas on the enantioselectivity and regioselectivity were also studied.     

Highly Enantioselective Diels–Alder Reaction Catalyzed by Chiral Imidazolidinone

New chiral imidazolidinone with an indole group was synthesized and used to catalyze the Diels–Alder reaction of α,β-unsaturated aldehyde with diene. High enantiomeric excesses and good yields were obtained. The reaction media were also surveyed. The best result in terms of enantioselectivity was achieved using acrolein and 2,3-dimethylbutdiene (up to 95% ee) in CH₃OH/H₂O.     

Chiral separation of β-adrenergic blockers on CelluCoat column by HPLC

The chiral separation of 10 β-adrenergic blockers (acebutalol, alprenolol, bufuralol, bisoprolol, celiprolol, carazolol, indenolol, metoprolol, oxprenolol and propranolol) was achieved on CelluCoat column (250 mm × 4.6 mm, 5 μm particle size). The mobile phases used were (90:10:0.2, v/v/v) and (95:5:0.2, v/v/v) combinations of n-heptane-ethanol-diethylamine, respectively. The flow rates were 0.5, 1.0 and 2.0 mL min⁻¹ with detection at 225 nm. The capacity (k), selectivity (α) and resolution (R_s) factors were 0.44-12.91, 1.12-2.19 and 1.00-9.50, respectively. The proposed supra-molecular models indicated that the chiral resolution were governed by π-π interactions, hydrogen bondings and steric effect.     

Chiral separation of triazole pesticide enantiomers by high performance liquid chromatography

Four triazole enantiomers of diclobutrazol (erythro form) (1), paclobutrazol (erythro form) (2), diniconazole (3) and uniconazole (4) have been separated by high performance liquid chro-matography (HPLC) on chiral stationary phase (CSP) OA-4700. Chromatographic data and a chiral recongnition model are presented for the separation of these pesticide enantiomers. The influence of column temperature and composition of mobile phase have been described.     

Highly Enantioselective Phenylacetylene Addition to Benzaldehyde Catalyzed by Chiral Tridentate Ligand

Development of new or improved methods for the asymmetric preparation of chiral propargylic alcohols has gained considerable significance during the past years because they are useful building blocks for the synthesis of many biologically active compounds and natural products.[1] A series of chiral tridentate ligands were conveniently synthesized from amino acids with good yields (Scheme 1).[2] A preliminary study of the enantioselective alkynylation of benzaldehyde catalyzed by this chiral tridentate ligand was carried out and up to 83% ee of chiral propargyl alcohols was obtained (Table 1 ). A further investigation of the tridentate ligand is currently underway.     

Chiral Separation of Esmolol and Terazosin by Cyclodextrinmodified Capillary Zone Electrophoresis

IntroductionTheincreasingnecessity0fpharmacologicalresearchforchiraldrugshasrenderedchiralseparationanactiveareaincaPillaryelectroph0resis(CE)today.Variousmodes0fCE,includingcaPillaryzoneelectroph0resis(CZE),micellarelectrokineticchromatography(MEKC),caPillarygelelectrophoresis(CGE)andcapillaryisotachophoresis(CITP),havebeenappliedforthispurp0se',amongwhichCZEisthemostpopularoneforitshighefficiency,lowexpenseandeaseofoperation.Forsuccessfulchiralseparati0ninCZE,theselectortypeisofcr…     

Chiral Separation of N-Benzoyl Phenylalanine Methyl Ester by Nonaqueous Capillary Electrophoresis

Theseparationofopticalisomersisarapidlygrowingareaincapillaryelectrophoresis(CE),andmostchiralseparationbyCEhavebeenperformedinaqueousbackgroundelectrolyte.Organicsolventssuchasmethanolandacetonitrilehavebeenappliedasbuffermodifiersatconcentrationtypicallynothigherthan40%inordertoincreasehydrophobicanalytesolubilityandtoimproveselectivity,resolution,ortoaltertheelectroosmoticflow(EOF)andelectrophoreticmobilityofanalyte.Buttherehavebeenonlyafewreportsonthechiralseparationusingpurenonaqueousme…     

On Chiral Space Groups and Chiral Molecules

Aschemicalnomenclaturewasoriginallydevelopedforcompoundsinthesolutionstate,thereissomeconfusionintheproperuseoftheterm慶hiralfordescribingcertaincrystalstructures.Thishasledtoanumberofcompoundsbeingincorrectlycategorizedasbeingchiralalthoughtheybelongtocentrosymmetricspacegroupsorthosehavingmirrorplanes.Achiralcompoundthatseparatesfromsolutionasacrystallinematerialmustnecessarilypackinamotifsuchthatothermoleculesintheunitcellarenotsuperimposableontheirownmirrorimages.Theconditionforopticalacti…     

Enantioseparation of Novel Chiral Tetrahedral Clusters on a Chiral Stationary Phase (CSP) by High Performance Liquid Chromatography

In recent years, the synthesis of chiral tetrahedral clusters has been studied extensively and various types are accessible , which are a kind of organometallic compounds with greatly growing interest due to their potential application to asymmetric reaction catalysts. As an efficient     

Chiral Separations by Ligand-Exchange Micellar Electrokinetic Chromatography and Microemulsion Electrokinetic Chromatography

heseparationofenantiomersisofgreatim portanceinbiology ,pharmaceutics ,agricultureandenvironment .Thedifferentseparationmodes (i e capillaryzoneelectrophoresis (CZE) ,micellarelec trokineticchromatography (MEKC) ,capillaryelec trochromatography (CEC) ,etc…     

Enantioselective Pinacol Coupling of Aromatic Aldehydes Induced by Chiral Titanium Complexes

The reductive coupling of carbonyl compounds catalyzed by the transition metal is an important group of carbon-carbon bond forming reaction. The pinacol coupling reaction of aldehydes is one of the most efficient methods for synthesis of vicinal diols1. L…