Resolution Of Optical Isomers Research Articles

Resolution of optical isomers of β-amino ketone compounds with two chiral centres by high performance liquid chromatography

A high performance liquid chromatographic method was developed for the resolution of optical isomers of beta-amino ketone compounds containing two chiral centres. An AE. Lichrom AM 1 chiral chromatographic column (250 mm x 4.6 mm, 5 microm) was used. The influences o the mobile phase polarity, flow rate and elution mode were investigated. The optimum conditions were the use of hexane-isopropyl alcohol as the mobile phase with a flow rate of 1 mL/min and gradient elution. Under the above chromatographic conditions, the optical isomers of four kinds beta-amino ketone compounds containing two chiral centres were baseline separated (Rs > 1.5). It was proved that the method is fast and easy to separate the optical isomers of beta-amino ketone compounds containing two chiral centres.

Effect of Trace Amounts of Water in the Mobile Phase of Normal-Phase Enantioselective High-Performance Liquid Chromatography on Selectivity and Resolution of Optical Isomers

The irreproducibility of normal-phase enantioselective high-performance liquid chromatography (HPLC) could be attributed to the presence or absence of trace amounts of water in one or more components of the mobile phase. The effect of trace amounts of water on chromatographic characteristics in normal-phase enantioselective HPLC was investigated by deliberate addition of controlled, trace amounts of water into the mobile phase for the separation of T-3811ME and its undesired enantiomer. Commercial 2-propanol was pre-mixed with 2% (v/v) water and then used for preparation of the mobile phase in combination with such organic modifiers as ethanol and methanol at different ratios. The results showed up to 30% improvement in the resolution (Rs), 4% in selectivity (alpha), and 39% in efficiency (plate number N) compared to using a mobile phase prepared from neat commercial 2-propanol. Thus, the effect of trace amounts of water in the mobile phase of normal-phase enantioselective HPLC was demonstrated.

Lipase Reactions in Supercritical Fluids

The supercritical fluids (SCF) have several excellent solvent properties such as low viscosity, high diffusivity and high dependence of solubility on pressure and temperature. The critical temperature of carbon dioxide is 304.1 K, low enough to treat thermally labile biomaterials without decomposition, and CO2 is non-toxic to human beings. Supercritical carbon dioxide (SCCO2) have been used in extraction of flavor substance from hop and other flavors and also in removal of undesirable substances such as caffeine in coffee beans and in removal of residual organic solvent in powdery medical raw materials.The interest in the applications of SCF is now enlarged from extraction to the other areas such as chemical and enzymatic reactions, material processings, formation of fine particles etc. Most of the enzymes are stable in anhydrous SCCO2, consequently the lipase reactions in SCF have been studied in the examples of modification of the physical property of triacylglycerols, resolution of optical isomers, syntheses of flavor esters etc. In this review the characteristics of SCF as solvent of enzymatic reactions are summarized with the main results so far obtained for the lipase reactions in SCF.

Chiral high-performance liquid chromatography of some related bicyclic lactams

Chromatographic methods utilising a Chiralcel OC cellulose-based column were developed for the chiral resolution of optical isomers of the cognition-enhancing ISF 4185 and related bicyclic lactams. These methods were scaled up for the preparation of purified samples of enantiomers, one pair of which was submitted to X-ray analysis. The resolution of the enantiomers derived from these compounds appears to be mainly dependent on their ability to hydrogen bond to the chiral stationary phase.

ChemInform Abstract: Application of Chiral Ligand Polymers in Resolution of Optical Isomers

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.

Separation of Ramipril Optical Isomers by High-Performance Liquid Chromatography

Abstract High-performance liquid chromatographic methods for determining the optical purities of ramipril, a novel angiotensin converting enzyme inhibitor, and its synthetic intermediates have been developed. Analytical procedures were established for the resolution of optical isomers of two moieties, precursor I and precursor II, used for the preparation of ramipril. No occurrence of racemization during condensation reaction of the two precursors could be unambiguously confirmed by the proposed methods. On the basis of analytical data ramipril bulk material proved to be optically pure.

Resolution of optical isomers by capillary zone electrophoresis: Study of enantiomeric and diastereoisomeric Co(III) complexes with ethylenediamine and amino acid ligands

AbstractCapillary electrophoresis (CZE), with hydrodynamic injection and UV detection, was applied to the separation of enantiomeric and diastereoisomeric Co (III) complexes.

Resolution of Optical Isomers as the Mixed Chelate Copper(III) Complexes by Reversed Phase Chromatography

Abstract Highly selective separation of D and L amino acids can be effected by reversed phase chromatography of mixed chelate complexes of the analyte acids with equimolar concentrations of Cu(II) and an optically active second amino acid in the mobile phase. The stabilities of the formed diastereomeric ternary complexes will determine the resolution of enantiomers. By this approach, amino acids were resolved as the dansyl and O-phthalaldehyde (OPA) derivatives and imino acids were separated without derivatization. Resolution of D and L dansyl amino acids was accomplished as the mixed complexes of Cu(II) with L-proline, L-arginine, L-histidine and L-histidine methyl ester as the second amino acids. Among the chiral ligands we studied, L-histidine methyl ester is unique in that it possesses both achiral selectivity for the dansyl amino acids and chiral selectivity for the respective D and L enantiomers. With a mobile phase gradient of acetonitrile in a buffer containing Cu(II) L-histidine methyl ester comp...

Resolution of Optical Isomers by Thin‐Layer Chromatography Enantiomeric Purity of D‐Penicillamine

AbstractPenicillamine (1) is condensed with formaldehyde to form the enantiomeric 5,5‐dimethylthiazolidinecarboxylic acids D‐3 and L‐3. These enantiomers are separated by TLC on CHIRALPLATE®.

Resolution of optical isomers by. thin-layer chromatography (TLC). Enantiomeric purity of l-DOPA

Resolution of optical isomers by. thin-layer chromatography (TLC). Enantiomeric purity of l-DOPA

Resolution of optical isomers by thin layer chromatography

A process for the separation of enantiomers by TLC is described. Reversed-phase plates, pre-treated with a copper II complex of N,N-di-n-propyl-L-alanine separate all the dansyl protein amino acids, except proline, each to its D and L enantiomers.

Resolution of optical isomers by chiral high-performance liquid chromatography: Separation of dihydrodiols and tetrahydrodiols of benzo[ a]pyrene and benz[ a]anthracene

Enantiomers of several underivatized dihydrodiols and tetrahydrodiols of benzo[ a]pyrene and benz[ a]anthracene have been resolved with high-performance liquid chromatography using a commercially available column packed with a d-3,5-dinitrobenzoylphenylglycine derivative of aminopropyl silica gel. Separation of optical isomers was confirmed by ultraviolet-visible absorption and circular dichroism spectral analyses. This simple method has been applied to the determination of optical purity of two dihydrodiol metabolites formed from the in vitro incubation of 11-methylbenz[ a]anthracene by rat liver microsomes.

Resolution of optical isomers by high-performance liquid chromatography: A comparison of two selector-selectand systems

Summary The chiral selectivities of two optically active selectors, binaphthyl-2,2′-diyl hydrogen phosphate (binaphthylphosporic acid, BPA) and 2-(2,4,5,7-tetranitro-9-fluorenylideneaminooxy)propionic acid (TAPA), are compared. Whereas all carbo- and heterohelicene selectands can be resolved on TAPA columns, only helicenes containing heteroatoms or electron-donating substituents could be easily separated on BPA. Resolution factors ( r ) for several sulphur-, bromine- and nitrogen-containing helicenes on coated and linked BPA and TAPA columns are given. The highest resolution factor was obtained for 9,10-diaza(7,8;11,12)dibenzo-heptahelicene ( r = 1.60) on a TAPA column silanized with N-2-(aminoethyl)aminopropyl and methyl groups (1:4) before coupling with the selector. Lowering the column temperature to 2° allowed the partial resolution of some carbohelicenes on BPA. Steric and binding requirements for chiral recognition between selectors and selectands and the influence of environmental changes (spacer length, mobile phase, mode of selector application) on the resolution process are discussed.

Resolution of optical isomers by high-pressure liquid chromatography: The separation of benzo[ a]pyrene trans-diol derivatives

The optical isomers of (±) r-7, t-8-dihydroxy-7,8-dihydrobenzo[ a]pyrene and its synthetic precursor (±) r-7, t-8-dihydroxy-7,8,9,10-tetrahydrobenzo[ a]pyrene were resolved as their di-(−)menthoxyacetates using high-pressure liquid chromatography. Saponification of the resolved diesters yielded the corresponding enantiomers. The specific rotation, CD spectra, and ORD curves are reported. The resolution of these optical isomers permits detailed studies on the enzymatic intermediates and the mechanism of benzo[ a]pyrene activation to its carcinogenic form. The method is of general usefulness for the resolution of optical isomers.

Pre-column derivatisation in high-performance liquid chromatography

Pre-colum derivatisation in high-perfomance liquid chromatography is mainly used to increase the detectability of compounds requiring analysis. this normally involves reaction with chromogenic or fluorogenic reagents, and tus the use of the more commonly available HPLC detectors. Derivatisation is more rarely used to alter chromatographic properties of compounds or to allow the resolution of optical isomers. Applications of pre-column derivatisation are discussed by reference to the functional group of the substrate involved in the derivatisation reaction.

Resolution of optical isomers by liquid chromatography

Resolution of optical isomers by liquid chromatography

Resolution of optical isomers by high-performance liquid chromatography, using coated and bonded chiral charge-transfer complexing agents as stationary phases

Ten racemic helicenes ([5] to [14]) and two double helicenes {diphenanthro[4,3- a; 3′,4′- o]picene (I) and 8,20-dibromodiphenanthro[4,3- a; 4′,3′- j]chrysene (II)} were resolved using high-performance liquid chromatography. R(−)- and S(+)-2-(2,4,5,7-tetranito-9-fluorenylideneaminooxy)propionic acid (TAPA) and three R(−)-homologues derived from butyric (TABA), isovaleric (TAIVA) and hexanoic (TAHA) acids were used as chiral charge-transfer (C.T.) complex-forming stationary phases, in situ coated on silica microparticles. The bulkiness of the group at the chiral centre of the C.T. acceptor is critical for the ease of resolution of the C.T. donors. The [6]-[14]-helicenes and the double helicenes I and II were completely resolved on R(−)-TAPA. On the other hand, the optical isomers of [5]-helicene could be separated only on R(−)-TABA and baseline resolution required ten recycling steps. R(−)-TAPA was also incorporated as a bonded solid phase and as a salt. The resolution factors, r, are given, a mechanism of resolution is proposed and the scope of the method and its significance are discussed.

Modern Countercurrent Distribution

Abstract Interest in liquid-liquid extraction continues to grow as evidenced by such divergent applications as industrial waste water treatment1,2 cleanup for pesticide residue analysis3, and resolution of optical isomers.4 This activity results from increased understanding of the chemistry of solvent extraction which is leading to the design of specially selective systems4,5as well as the development of improved extractors emanating from studies of mass transfer phenomena6,7 in continuously flowing systems

Separation of Diastereoisomers by Chromato-graphic Fractionation; the Resolution of Optical Isomers

Abstract Baker and Williams's chromatographic fractionation technique, employing simultaneous temperature and solvent gradients along a column, has been successful in separating three diastereoisomer salt derivatives derived from optical isomers. The d-and l-α-phenylethylamine diastereoisomers of d-mandelic acid and the d-and l-tartrates of l-brucine were separated by approximately 60%. A partial separation was achieved on the d-and l-histidine salts of d-tartaric acid. An aqueous—alcohol—acetonitrile solvent system was used for the separations. Irregular diastereoisomer formation and dissociation of diastereoisomers were problems discussed in the development of the analytical method.

Resolution of Optical Isomers by Gas Liquid Partition Chromatography

Resolution of Optical Isomers by Gas Liquid Partition Chromatography