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Antal Peter - One of the best experts on this subject based on the ideXlab platform.
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investigation of the structure selectivity relationships and van t hoff analysis of chromatographic stereoisomer separations of unusual isoxazoline fused 2 aminocyclopentanecarboxylic acids on cinchona alkaloid based chiral stationary Phases
Journal of Chromatography A, 2015Co-Authors: Istvan Ilisz, Ferenc Fülöp, Zsanett Gecse, Gyula Lajko, Melinda Nonn, Wolfgang Lindner, Antal PeterAbstract:Abstract The enantiomers of four unusual, rather rigid isoxazoline-fused 2-aminocyclopentanecarboxylic acids were directly separated on a quinine- or a quinidine-based zwitterionic ion-exchanger as chiral selector. The effects of the Mobile Phase Composition, the structures of the analytes and temperature on the separations were investigated. Experiments were performed at constant Mobile Phase Composition in the temperature range 10–50 °C to study the effects of temperature, and thermodynamic parameters were calculated from plots of ln α versus 1/T. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. It was found that the enantiomer separations were in most cases predominantly enthalpy-driven, but entropically-driven separations were also observed. The sequence of elution of the enantiomers was determined in all cases.
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hplc enantioseparation of β2 homoamino acids using crown ether based chiral stationary Phase
IEEE Journal of Solid-state Circuits, 2009Co-Authors: Robert Berkecz, Myung Ho Hyun, Ferenc Fülöp, Istvan Ilisz, Aleksandra Misicka, Dagmara Tymecka, Hee Jung Choi, Antal PeterAbstract:RP high-performance liquid chromatographic methods were developed for the enantioseparation of eleven unusual beta(2)-homoamino acids. The underivatized analytes were separated on a chiral stationary Phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as chiral selector. The effects of organic (alcoholic) and acidic modifiers, the Mobile Phase Composition and temperature on the separation were investigated. The structures of the substituents in the alpha-position of the analytes substantially influenced the retention and resolution. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers.
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high performance liquid chromatographic enantioseparation of β amino acid stereoisomers on a 18 crown 6 2 3 11 12 tetracarboxylic acid based chiral stationary Phase
Journal of Chromatography A, 2006Co-Authors: Robert Berkecz, Myung Ho Hyun, Enikő Forró, Ferenc Fülöp, Anita Sztojkovivanov, Istvan Ilisz, Antal PeterAbstract:Direct reversed-Phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of 14 unnatural β-amino acids, including several β-3-homo-amino acids on a chiral stationary Phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid bonded to 3-aminopropyl silica gel as chiral selector. The effects of the organic and the acidic modifiers and the Mobile Phase Composition on the separation were investigated. The natures and positions of the substituents on the aromatic ring substantially influenced the retention and enantioseparation. The elution sequence in most cases was determined and the R enantiomers were eluteted before the S enantiomers.
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direct chiral separation of unnatural amino acids by high performance liquid chromatography on a ristocetin a bonded stationary Phase
Chirality, 2001Co-Authors: Gabriella Torok, Antal Peter, Daniel W Armstrong, Geza Toth, Dirk Tourwe, Janos SapiAbstract:Direct high-performance liquid chromatographic chiral separation of numerous underivatized unnatural amino acids on a ristocetin A-bonded chiral stationary Phase used in the reversed-Phase and in the polar organic chromatographic modes is reported. The effects of different parameters such as Mobile Phase Composition, temperature, and the structure of the analytes on the selectivity in both chromatographic modes are discussed. By variation of the parameters, the separation of the stereoisomers was optimized and, as a result, baseline resolution was achieved in most cases. Chirality 13:648–656, 2001. © 2001 Wiley-Liss, Inc.
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high performance liquid chromatographic separation of enantiomers of synthetic amino acids on a ristocetin a chiral stationary Phase
Journal of Chromatography A, 2000Co-Authors: Antal Peter, Daniel W Armstrong, Gabriella Torok, Geza Toth, Dirk TourweAbstract:A macrocyclic glycopeptide, ristocetin A, was used as chiral stationary Phase for the high-performance liquid chromatographic separation of enantiomers of 28 unnatural amino acids, such as analogues of phenylalanine, tyrosine and tryptophan, and analogues containing 1,2,3,4-tetrahydroisoquinoline, tetraline or 1,2,3,4-tetrahydro-2-carboline skeletons. Excellent resolutions were achieved for most of the investigated compounds by using reversed-Phase or a new polar-organic Mobile Phase system. The conditions of separation were optimized by variation of the Mobile Phase Composition, temperature and flow-rate.
Sonia Keunchkarian - One of the best experts on this subject based on the ideXlab platform.
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state of the art and recent developments of immobilized polysaccharide based chiral stationary Phases for enantioseparations by high performance liquid chromatography 2013 2017
Microchemical Journal, 2018Co-Authors: Juan M Padro, Sonia KeunchkarianAbstract:Abstract Polysaccharide-based chiral stationary Phases have been recognized as one of the most powerful ones for high performance liquid chromatography (HPLC) separations of chiral compounds in analytical and also in preparative scale. Immobilized polysaccharide-based chiral stationary Phases constitute a remarkable achievement due to their stable nature on working with standard or common solvents and also with those prohibited for using with coated Phases. This review is mainly focused on the i. applications of these chiral stationary Phases in numerous fields of HPLC separations; ii. comparative aspects between immobilized vs. coated polysaccharide-derived Phases, and iii. revision of several theoretical studies such as enantiorecognition mechanism, Mobile Phase Composition and column temperature effects.
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enantioseparation of α amino acids by means of cinchona alkaloids as selectors in chiral ligand exchange chromatography
Journal of Chromatography A, 2013Co-Authors: Sonia Keunchkarian, Carlos A Franca, Leonardo Gabriel Gagliardi, Cecilia B CastellsAbstract:A conventional nonchiral column was used for the enantioseparation of several racemic α-amino acids (native and derivatized) through the use of Cinchona alkaloids as chiral selectors along with Cu(II) ions in chiral ligand-exchange chromatography. The Mobile Phase Composition (i.e., the organic modifier content and pH) was studied in order to modulate retention and enantioselectivity. Good enantioseparation of many amino acids was obtained using equimolar amounts of Cu(II) and either cinchonidine, quinine or quinidine as chiral selectors in the Mobile Phase. The molecular geometry of the diastereomeric complexes formed was modeled and energetic differences between both compounds were calculated by methods based on semi-empirical force-field. Good correlations were obtained between experimental enantioselectivity factors and calculated energetic differences.
Daniel W Armstrong - One of the best experts on this subject based on the ideXlab platform.
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enantioselective potential of teicoplanin and vancomycin based superficially porous particles packed columns for supercritical fluid chromatography
Journal of Chromatography A, 2020Co-Authors: Denisa Folprechtova, Daniel W Armstrong, Oleksandr Kozlov, Martin G Schmid, Květa Kalikova, Eva TesařovaAbstract:Application of the superficially porous particles (SPPs) grafted with chiral selectors can substantially improve resolution in chromatographic techniques. In this work, we carried out a deeper study on supercritical fluid chromatography systems with 2.7 µm SPPs bonded with teicoplanin and vancomycin. Fast separations of the majority of enantiomers of phytoalexins, substituted tryptophans, and ketamine derivatives, as representatives of important biologically active and structurally diverse chiral compounds have been achieved. The chromatographic behavior of the structurally different analytes served to characterize these separation systems. The influence of separation conditions, namely Mobile Phase Composition, i.e. type of co-solvent and additive on retention, enantioselective resolution and enantioselectivity was examined. The success rate of baseline and partial separations in individual groups of compounds differed with the chiral stationary Phase and also with Mobile Phase Composition. The best, baseline separations for the phytoalexins were achieved on the TeicoShell column using methanol as a co-solvent and trifluoroacetic acid as an additive if used. Mostly partial separations were achieved on the vancomycin-based column for all groups of analytes. Complementary separation behavior of these CSPs was confirmed for the majority of the chiral compounds examined in this work.
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direct chiral separation of unnatural amino acids by high performance liquid chromatography on a ristocetin a bonded stationary Phase
Chirality, 2001Co-Authors: Gabriella Torok, Antal Peter, Daniel W Armstrong, Geza Toth, Dirk Tourwe, Janos SapiAbstract:Direct high-performance liquid chromatographic chiral separation of numerous underivatized unnatural amino acids on a ristocetin A-bonded chiral stationary Phase used in the reversed-Phase and in the polar organic chromatographic modes is reported. The effects of different parameters such as Mobile Phase Composition, temperature, and the structure of the analytes on the selectivity in both chromatographic modes are discussed. By variation of the parameters, the separation of the stereoisomers was optimized and, as a result, baseline resolution was achieved in most cases. Chirality 13:648–656, 2001. © 2001 Wiley-Liss, Inc.
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high performance liquid chromatographic separation of enantiomers of synthetic amino acids on a ristocetin a chiral stationary Phase
Journal of Chromatography A, 2000Co-Authors: Antal Peter, Daniel W Armstrong, Gabriella Torok, Geza Toth, Dirk TourweAbstract:A macrocyclic glycopeptide, ristocetin A, was used as chiral stationary Phase for the high-performance liquid chromatographic separation of enantiomers of 28 unnatural amino acids, such as analogues of phenylalanine, tyrosine and tryptophan, and analogues containing 1,2,3,4-tetrahydroisoquinoline, tetraline or 1,2,3,4-tetrahydro-2-carboline skeletons. Excellent resolutions were achieved for most of the investigated compounds by using reversed-Phase or a new polar-organic Mobile Phase system. The conditions of separation were optimized by variation of the Mobile Phase Composition, temperature and flow-rate.
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effect of selector coverage and Mobile Phase Composition on enantiomeric separations with ristocetin a chiral stationary Phases
Microchemical Journal, 1999Co-Authors: Helen K Ekborgott, Xiande Wang, Daniel W ArmstrongAbstract:Abstract Three different amounts (i.e., selector coverages) of ristocetin A macrocyclic antibiotic have been covalently bonded to silica gel, packed in stainless steel columns, and evaluated as chiral stationary Phases (CSPs) in high-performance liquid chromatography (HPLC). The three columns (i.e., CSPs) were examined and compared in the reversed-Phase, polar-organic, and normal-Phase modes. The retention behavior ( k ′), selectivity (α), resolution ( R S ), and number of theoretical plates ( N ) for all three columns are discussed and compared in each Mobile Phase mode. The coverage of the chiral selector had a profound effect on the chromatographic behavior of the more retained enantiomers. A special Mobile Phase Composition (i.e., methanol plus very small amounts of acid and base modifiers) resulted in improved baseline separations, without greatly affecting the analysis times, for all chiral analytes evaluated. The column stabilities were excellent when switching between different Mobile Phase modes.
Roberto Cirilli - One of the best experts on this subject based on the ideXlab platform.
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high performance liquid chromatography enantioseparation of proton pump inhibitors using the immobilized amylose based chiralpak ia chiral stationary Phase in normal Phase polar organic and reversed Phase conditions
Journal of Chromatography A, 2008Co-Authors: Roberto Cirilli, Rosella Ferretti, Bruno Gallinella, Emiliana De Santis, Leo Zanitti, Francesco La TorreAbstract:The chiral resolving ability of the amylose-based Chiralpak IA chiral stationary Phase towards omeprazole and other proton pump inhibitors under reversed-Phase conditions was investigated. Organic modifier-buffer demonstrated to be a valid alternative elution mode with respect to conventional polar organic and normal-Phases. No evidence of deterioration of performance of the enantioselective column after several multimodal cycles of elution was observed. Mobile Phase Composition was systematically changed in order to modulate the enantiomer elution order of set of compounds studied. A very simple method based on on-line detection of optical rotational sign during enantioselective HPLC was developed to assign the absolute configuration and enantiomeric elution order.
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conformational and temperature effects on separation of stereoisomers of a c3 c4 substituted β lactamic cholesterol absorption inhibitor on amylose based chiral stationary Phases
Journal of Chromatography A, 2001Co-Authors: Roberto Cirilli, Rosella Ferretti, M R Del Giudice, F La TorreAbstract:A direct liquid chromatography method was developed for the diastereo- and enantioselective analysis of a C3,C4-substituted β-lactamic hypolipodemic agent (SCH 48461) and its stereoisomers on two commercially available amylose-based chiral stationary Phases (CSPs), namely, Chiralpak AS and Chiralpak AD. The Mobile Phase Composition (type and content of alcoholic modifier) was considered to achieve baseline resolutions in a single chromatographic run. In order to investigate the influence of molecular flexibility on chiral recognition process, β-lactams were ring-opened and converted into β-amino esters derivatives. Thermodynamic parameters associated with adsorption equilibria between acyclic and cyclic stereoisomers and CSPs were calculated from chromatographic runs at various temperatures.
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stereoselective analysis of benazepril and its stereoisomers by reversed Phase high performance liquid chromatography on a chiral agp column
Journal of Chromatography A, 1998Co-Authors: Roberto Cirilli, F La TorreAbstract:A direct liquid-chromatographic method has been developed for the stereoselective analysis of idrapril and its stereoisomers on a chiral α1 glycoprotein (AGP) column. The influence of flow-rate, temperature, and Mobile Phase Composition on retention and selectivity was evaluated to find the optimum conditions for chiral separation.
Yubing Tang - One of the best experts on this subject based on the ideXlab platform.
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significance of Mobile Phase Composition in enantioseparation of chiral drugs by hplc on a cellulose based chiral stationary Phase
Chirality, 1996Co-Authors: Yubing TangAbstract:Eight randomly selected pharmaceuticals, which included ibuprofen, ketoprofen, albuterol, acebutolol, propafenone, betaxolol, methylphenidate, and homatropine, were directly separated on a cellulose tris(4-methylbenzoate) chiral stationary Phase (CSP) without derivatization via normal Phase mode HPLC. Enantioresolution was achieved by the optimization of the type and the ratio of Mobile Phase modifiers and additives. The modifiers included alcohols; the Mobile Phase additives were trifluoroacetic acid (TFA) and triethylamine (TEA). It was found that methanol and ethanol were superior to isopropanol as Mobile Phase modifiers for enhancing chiral separation of some of the chiral drugs. The results also demonstrated that TFA has a dominant effect on chiral separations for both acidic and basic chiral drugs, although for some basic drug such as homatropine, TEA was more beneficial at improving enantioseparation. The separation of acebutolol enantiomers was achieved for the first time by adding both TFA and TEA to the Mobile Phase. The purpose of this paper is to demonstrate that the applicability of cellulose based CSPs can be expanded by controlling the Mobile Phase Compositions through the addition of trace amounts of achiral additives and the selection of the appropriate alcoholic modifier. © 1996 Wiley-Liss, Inc.
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significance of Mobile Phase Composition in enantioseparation of chiral drugs by hplc on a cellulose based chiral stationary Phase
Chirality, 1996Co-Authors: Yubing TangAbstract:Eight randomly selected pharmaceuticals, which included ibuprofen, ketoprofen, albuterol, acebutolol, propafenone, betaxolol, methylphenidate, and homatropine, were directly separated on a cellulose tris(4-methylbenzoate) chiral stationary Phase (CSP) without derivatization via normal Phase mode HPLC. Enantioresolution was achieved by the optimization of the type and the ratio of Mobile Phase modifiers and additives. The modifiers included alcohols; the Mobile Phase additives were trifluoroacetic acid (TFA) and triethylamine (TEA). It was found that methanol and ethanol were superior to isopropanol as Mobile Phase modifiers for enhancing chiral separation of some of the chiral drugs. The results also demonstrated that TFA has a dominant effect on chiral separations for both acidic and basic chiral drugs, although for some basic drug such as homatropine, TEA was more beneficial at improving enantioseparation. The separation of acebutolol enantiomers was achieved for the first time by adding both TFA and TEA to the Mobile Phase. The purpose of this paper is to demonstrate that the applicability of cellulose based CSPs can be expanded by controlling the Mobile Phase Compositions through the addition of trace amounts of achiral additives and the selection of the appropriate alcoholic modifier.