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Chiral Analysis (chiral + analysis)

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Chemistry18%

Selected Abstracts

Rhodium(II)-Catalyzed Inter- and Intramolecular Cyclopropanations with Diazo Compounds and Phenyliodonium Ylides: Synthesis and Chiral Analysis

HELVETICA CHIMICA ACTA, Issue 2 2005
Ashraf Ghanem
Different classes of cyclopropanes derived from Meldrum's acid (=2,2-dimethyl-1,3-dioxane-4,6-dione; 4), dimethyl malonate (5), 2-diazo-3-(silyloxy)but-3-enoate 16, 2-diazo-3,3,3-trifluoropropanoate 18, diazo(triethylsilyl)acetate 24a, and diazo(dimethylphenylsilyl)acetate 24b were prepared via dirhodium(II)-catalyzed intermolecular cyclopropanation of a set of olefins 3 (Schemes,1 and 4,6). The reactions proceeded with either diazo-free phenyliodonium ylides or diazo compounds affording the desired cyclopropane derivatives in either racemic or enantiomer-enriched forms. The intramolecular cyclopropanation of allyl diazo(triethylsilyl)acetates 28, 30, and 33 were carried out in the presence of the chiral dirhodium(II) catalyst [Rh2{(S)-nttl)4}] (9) in toluene to afford the corresponding cyclopropane derivatives 29, 31 and 34 with up to 37% ee (Scheme,7). An efficient enantioselective chiral separation method based on enantioselective GC and HPLC was developed. The method provides information about the chemical yields of the cyclopropane derivatives, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the inter- and intramolecular cyclopropanation reactions and avoids time-consuming workup procedures. [source]

Chiral analysis of milnacipran by a nonchiral HPLC , circular dichroism: Improvement of the linearity of dichroic response by temperature control

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 16-17 2008
Marie Lecoeur-Lorin
Abstract The determination of the enantiomeric excess (e.e.) of a basic drug has been investigated in LC using a nonchiral stationary phase and a circular dichroism (CD) detector in order to avoid expensive chiral columns. The CD detector records both dichroic (,,) and UV (,) signals at the same wavelength and calculates the anisotropy factor (g = ,,/,), which is linearly related to the e.e. The enantiomeric and chemical composition of a chiral drug can be simultaneously determined on a nonchiral HPLC support. However, the g factor from the CD signal is temperature dependent. Indeed, the temperature has an influence on the stability of the CD signal and the linear regression between g factor and the e.e. of 1R,2S -enantiomer. So, a decrease in temperature gives rise to an improvement of the above-mentioned linearity correlation. After optimization of chromatographic parameters (porous graphitic carbon-based column, methanol/ phosphate buffer as mobile phase) and selection of CD wavelength, a linear regression of g factor versus e.e. of 1R,2S -enantiomer was obtained at temperature-controlled CD detection and an LOQ of 94% was found. The enantiomeric composition of milnacipran was determined with good accuracy. [source]

Distribution of piperitone oxide stereoisomers in Mentha and Micromeria species and their chemical syntheses

FLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2007
Olga Larkov
Abstract Chiral GC,MS analyses of natural and synthetic trans- and cis- piperitone oxide were performed on an Rt- ,DEX-sm capillary column in order to clarify the stereochemistry of their enantiomeric forms. Only enantiomerically pure laevo-rotatory piperitone oxides, (1S,2S,4S)- trans- piperitone oxide and (1S,2S,4R)- cis- piperitone oxide, were detected by chiral analyses of Micromeria fruticosa (L.) Druce and Mentha longifolia L. The occurrence of the cis - and trans -piperitone oxides was dependent on the population of the species. In all cases (1S,2S,4S)- trans- piperitone oxide was detected together with (4S)-piperitone, while (1S,2S,4R)- cis- piperitone oxide was detected together with (4R)-piperitone in the plants analysed. The four stereoisomers of trans - and cis -piperitone oxide were obtained by alkaline epoxidation of both (4R)- and (4S)-piperitone. The formation of the 1,2-epoxide can take place on either side of the 1,4-substituted six-membered ring. Racemization at C4 was observed under alkaline epoxidation reaction conditions due to keto-enol tautomerism. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Heart-cutting 2D-CE with on-line preconcentration for the chiral analysis of native amino acids

ELECTROPHORESIS, Issue 6 2010
Suzanne Anouti
Abstract The use of transient moving chemical reaction boundary (tMCRB) was investigated for the on-line preconcentration of native amino acids in heart-cutting 2D-CE with multiple detection points using contactless conductivity detection. The tMCRB focusing was obtained by using ammonium formate (pH 8.56) as sample matrix and acetic acid (pH 2.3) as a BGE in the first dimension of the heart-cutting 2D-CE. Different experimental parameters such as the injected volume and the concentration in ammonium formate were optimized for improving the sensitivity of detection. A stacked fraction from the first dimension was selected, isolated in the capillary, and then separated in the second dimension in the presence of a chiral selector ((+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid). This on-line tMCRB preconcentration coupled with heart-cutting 2D-CE was applied with success to the chiral separation of D,L -phenylalanine, and D,L -threonine in a mixture of 22 native amino acids. The sample mixture was diluted in 0.8,M of ammonium formate, and injected at a concentration of 2.5,,M for each enantiomer with a volume corresponding to 10% of the total capillary volume. An LOD (S/N=3) of 2,,M was determined for L -threonine. [source]

Cover Picture: Electrophoresis 16'09

ELECTROPHORESIS, Issue 16 2009
Article first published online: 18 AUG 200
Issue no. 16 is a special on "Enantioseparations". It consists of 19 research papers and 2 review articles distributed over 4 different parts. The two review articles make up Part I and focus on recent developments in microchip enantioseparations and chiral analysis of drugs, metabolites and biomarkers in biological samples. The 19 research papers are distributed over the remaining 3 parts including "Fundamentals and Methodologies", "Chiral Capillary Electrochromatography" and "Biomedical, Pharmaceutical, Food and Environmental Applications of Electromigration Techniques". Issue no. 16 also includes a Fast Track paper on the "Analysis of genetic variation in Globocephaloides populations from macropodid marsupials using a mutation scanning-based approach". [source]

Direct chiral analysis of primary amine drugs in human urine by single drop microextraction in-line coupled to CE

ELECTROPHORESIS, Issue 16 2009
Kihwan Choi
Abstract Three-phase single drop microextraction (SDME) was in-line coupled to chiral CE of weakly basic amine compounds including amphetamine. SDME was used for the matrix isolation and sample preconcentration in order to directly analyze urine samples with the minimal pretreatment of adding NaOH. A small drop of an acidic aqueous acceptor phase covered with a thin layer of octanol was formed at the tip of a capillary by simple manipulation of the liquid handling functions of a commercial CE instrument. While the saline matrix of the urine sample was blocked by the octanol layer, the basic analytes in a basic aqueous donor phase were concentrated into the acidic acceptor drop through the octanol layer by the driving force of the pH difference between the two aqueous phases. The enantiomers of the enriched amines were resolved by using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector for the subsequent CE separation. From 10,min SDME with the agitation of the donor phase by a small stirrer retrofit to the CE instrument, enrichment factors were about a 1000-fold, yielding the LOD of 0.5,ng/mL for amphetamine. This low LOD value as well as the convenience of in-line coupled SDME make the proposed scheme well suited for the demanding chiral analysis of amphetamine-type stimulants. [source]

Cover Picture: Electrophoresis 13'09

ELECTROPHORESIS, Issue 13 2009
Article first published online: 20 JUL 200
Issue 13 is a special issue on "CE and CEC of Amino Acids, Peptides and Proteins" assembling 19 papers on various topics including fast, high efficient and high sensitive "CE and CEC techniques for quality control and purity determination of native and (bio)synthetic amino acids, peptides and proteins, for monitoring of their synthesis, isolation, chemical derivatization and enzymatic digestion and also for investigation of their interactions with other molecules. New methodologies, such as electrodialysis for sample preparation, chiral ligand-exchange CE, immunoaffinity CE, affinity capillary isoelectric focusing, combination of transient isotachophoretic preconcentration with capillary zone electophoresis (CZE) analysis, two-dimensional CE-mass spectrometry (MS) separations and advances in high-sensitive CE-laser induced fluorescence (LIF) and CE-electrochemiluminescence detection schemes, are widely presented here. The applications of CE and CEC methods include chiral analysis of amino acids, determination of low abundant amino acids, peptides and proteins in complex matrices, such as human and animal body fluids and tissue biopsies, and profiling of cell lysates and recombinant proteins, e.g. birch pollen allergen and human interleukin 7. As can be seen from several contributions, preparation of new capillary coatings suppressing the adsorption of peptides and proteins to the fused silica capillary wall in their CZE analyses and/or increasing the selectivity of their open-tubular CEC separations remains a hot topic in the area of CE and CEC developments. In addition, it is shown that through the theoretical modelling of the CZE determined effective electrophoretic mobilities of proteins, the important parameters, such as charge, hydration and shape of their molecules, can be estimated." [source]

Cover Picture: Electrophoresis 1'09

ELECTROPHORESIS, Issue 1 2009
Article first published online: 20 JAN 200
This issue is a paper symposium on "CE and CEC Reviews" with 21 comprehensive reviews describing the latest developments in methodologies, applications, stationary phases in CEC, pseudo stationary phases in EKC, detection and sensitivity enhancement approaches, and proteomics and metabolomics. In addition, issue 1 has a "Fast Track" contribution on two dimensional CE using multiple detection points for chiral analysis of native amino acids. [source]

The role of cyclodextrins in chiral capillary electrophoresis

ELECTROPHORESIS, Issue 8 2008
Zoltán Juvancz Dr.
Abstract The members of the enantiomeric pairs frequently show rather different biological effects, so their chiral selective synthesis, pharmacological studies and analysis are necessary. CE has unique advantages in chiral analysis. The most frequently used chiral selectors are CDs in this field. This paper gives a short view on the advantages on CE in direct chiral separations, emphasizing the role of CDs. The reason for the broad selectivity spectra of CDs is discussed in detail. The physical background of chiral selective separations is briefly shown in CE. Their interaction mechanisms are shortly defined. The general trend of their use is statistically evaluated. Most frequently used CDs and CD derivatives are characterized. Advantages of ionizable CDs and single-isomer derivatives are shown. The general trend of their use is established. [source]

Sensitive chiral analysis by capillary electrophoresis

ELECTROPHORESIS, Issue 1 2006
Carmen García-Ruiz
Abstract In this review, an updated view of the different strategies used up to now to enhance the sensitivity of detection in chiral analysis by CE will be provided to the readers. With this aim, it will include a brief description of the fundamentals and most of the recent applications performed in sensitive chiral analysis by CE using offline and online sample treatment techniques (SPE, liquid,liquid extraction, microdialysis, etc.), on-column preconcentration techniques based on electrophoretic principles (ITP, stacking, and sweeping), and alternative detection systems (spectroscopic, spectrometric, and electrochemical) to the widely used UV-Vis absorption detection. [source]

Comparison of dodecoxycarbonylvaline microemulsion, solvent-modified micellar and micellar pseudostationary phases for the chiral analysis of pharmaceutical compounds

ELECTROPHORESIS, Issue 24 2005
Melissa
No abstracts. [source]

Polymeric alkenoxy amino acid surfactants: II.,Chiral separations of ,-blockers with multiple stereogenic centers

ELECTROPHORESIS, Issue 6 2004
Syed A. A. Rizvi
Abstract Two amino acid-based (leucine and isoleucine) alkenoxy micelle polymers were employed in this study for the separation of multichiral center-bearing ,-blockers, nadolol and labetalol. These polymers include polysodium N -undecenoxy carbonyl- L -leucinate (poly- L -SUCL) and polysodium N -undecenoxy carbonyl- L -isoleucinate (poly- L -SUCIL). Detailed synthesis and characterization were reported in our previous paper [26]. It was found that poly- L -SUCIL gives better chiral separation than poly- L -SUCL for both nadolol and labetalol isomers. The use of 50,100 mM poly- L -SUCIL as a single chiral selector provided separation of four and three isomers of labetalol and nadolol, respectively. Further optimization in separation of both enantiomeric pairs of nadolol and labetalol was achieved by evaluation of type and concentration of organic solvents, capillary temperature as well type and concentration of cyclodextrins. A synergistic approach, using a combination of poly- L -SUCIL and sulfated ,-CD (S-,-CD) was evaluated and it showed dramatic separation for enantiomeric pairs of nadolol. On the other hand for labetalol enantiomers, separation was slightly decreased or remain unaffected using the dual chiral selector system. Finally, simultaneous separation of both nadolol and labetalol enantiomers was achieved in a single run using 25 mM poly- L -SUCIL and 5% w/v of S-,-CD in less then 35 min highlighting the importance of high-throughput chiral analysis. [source]

Enantioseparation of warfarin and its metabolites by capillary zone electrophoresis

ELECTROPHORESIS, Issue 15 2003
Qingyu Zhou
Abstract A capillary zone electrophoresis (CZE) method with direct ultraviolet (UV)-absorbance detection is presented for the simultaneous enantiomeric separation of warfarin and its main metabolites, including warfarin alcohols, 4'-, 6-, and 7-hydroxywarfarin, using highly sulfated ,-cyclodextrin (HS-,-CD) as the chiral selector. This chiral separation method was optimized in terms of the electrophoretic parameters, which included the concentration of HS-,-CD used, the type and composition of organic modifier added to the background electrolyte (BGE) buffer, and the BGE buffer pH. Chiral separation of warfarin and its major metabolites was achieved with high resolution, selectivity, efficiency, repeatability, and reproducibility. This optimized chiral analysis of warfarin along with its metabolites was completed within a satisfactory electrophoresis time of 20 min. [source]