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  • Electronic Resource  (539)
  • 1995-1999  (539)
  • 1920-1924
  • 1996  (539)
  • Organic Chemistry  (539)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 6-10 
    ISSN: 0899-0042
    Keywords: enantiopure levodropropizine ; synthesis ; (R)-glycidol ; enantiomeric separation ; chiral HPLC ; enantiomeric enrichment ; binary melting point phase diagram ; crystal structure determination ; intermolecular hydrogen-bonding interactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure levodropropizine can be synthesized in high yield by the direct nucleophilic addition of 1-phenylpiperazine to (R)-glycidol followed by recrystallization in absolute ethanol. A chiral HPLC method has been developed for the determination of its optical purity. The enantiomeric enrichment behavior of this compound in the recrystallization process is discussed according to its binary melting point phase diagram. Single crystal x-ray structural analysis shows the intermolecular hydrogen-bonding interactions between the hydroxyl and piperazinyl groups within the crystal lattice of levodropropizine. © 1996 Wiley-Liss, Inc.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 24-29 
    ISSN: 0899-0042
    Keywords: CHO cells ; HeLa cells ; lipid peroxidation ; catalase ; D-amino acids ; L-amino acids ; toxicity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While the L-configuration of amino acids predominates in all known living systems, D-enantiomers of amino acids have been detected with highly sensitive chromatographic techniques in human physiological fluids. In the present study, the survival of Chinese hamster ovary cells (CHO) and HeLa cells was inhibited by exposure to high concentrations of some D- or L-amino acids. Inhibition of colony formation, though, was not necessarily observed to be chiral-dependent. Some L-amino acids (LAAS) were found to be toxic while other D-amino acids (DAAS) were innocuous in both cultures. This is contradictory to the previous observations that DAAS were generally considered to be harmful. Frequently it was implied, although not experimentally proven, that the LAAS were not toxic. One of the metabolites produced by oxidative deamination of D- or LAAS is hydrogen peroxide (H2O2), a reactive oxygen species (ROS) that is decomposed by catalase. Increased intracellular H2O2 can result in peroxidation of lipids. We measured catalase activity and the lipid peroxide levels (LPO) after incubating cells in either D- or LAAS. The amino acids (AAS) that were found to inhibit colony formation were found to be associated with higher levels of catalase activity and LPO. Therefore, we hypothesize that enhanced ROS generation may be, in part, responsible for the observed toxicity of some amino acids. © 1996 Wiley-Liss, Inc.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 35-38 
    ISSN: 0899-0042
    Keywords: ion channels ; receptors ; state-dependent interactions ; stereoselectivity ; local anesthetics ; 1,4-dihydropyridines ; Ca2+ channels ; Na+ channels ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion channels are pharmocologic receptors and as such exhibit stereoselective interactions with drugs. Ion channels are conformationally mobile transmembrane proteins existing in a number of open and closed states. Drug interactions with these different states may differ quantitatively and qualitatively. Stereoselectivity may not be a constant factor and may change according to channel state as determined by stimulus mode or experimental conditions. Selected examples are cited for Na+ and Ca2+ channels. © 1996 Wiley-Liss, Inc.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 39-48 
    ISSN: 0899-0042
    Keywords: α-pinene ; β-pinene ; camphene ; limonene ; borneol ; isoborneol ; succinite ; geochemistry ; stereochemistry ; pine resins ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among the more prevalent chiral monoterpenoid compounds in conifers are α-pinene, β-pinene, and smaller amounts of camphene and limonene. The most prevalent chiral monoterpenoid compounds in fossilized resin (referred to as amber in this paper) appear to be borneol, isoborneol, and camphene. Most of these compounds have easily measured enantiomeric excesses. The borneol and isoborneol in some amber samples have pronounced enantiomeric excesses despite the fact that they are tens of millions of years old. The enantiomeric ratios of the monoterpenoids in different ambers vary tremendously and often are distinct. However, in any single amber sample, the stereochemistry (absolute configuration) of the excess monoterpenoid enantiomers appears to be identical. The camphene in amber may be a secondary reaction product formed over time, possibly from the dehydration of borneol. Although a compound's original stereochemistry can be preserved, it also may diminish with the number and type of chemical transformations over geological time. The monoterpene enantiomeric ratios in modern conifer resins vary tremendously. Future stereochemical studies are outlined that could provide the data necessary for more exact geochemical interpretations and possibly for obtaining pertinent paleobiological information. © 1996 Wiley-Liss, Inc.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 77-83 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Excellent separations were achieved using a coated column to suppress electroosmotic flow and employing a countercurrent process between chiral selector and racemic solute. Using the macrocyclic antibiotic vancomycin as a chiral selector in capillary electrophoresis the resolution of nonsteroidal antiinflammatories and dansyl amino acids was achieved. Improvement in sensitivity due to the elimination of background absorbance and increased efficiency due to the removal of wall adsorption effects are both achieved using this technique. © 1996 Wiley-Liss. Inc.
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  • 6
    ISSN: 0899-0042
    Keywords: chiral purity ; pharmaceutical ; achiral ; cyclodextrin ; SBE cyclodextrin ; purity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the past several years, capillary electrophoresis (CE) has generated considerable interest from pharmaceutical companies for control of both the chiral and achiral purity of bulk drugs and drug products. This paper evaluates the use of CE as: (1) a technique complementary to HPLC for the determination of peak homogeneity of a drug, (2) for determination of chiral purity, and (3) for determination of achiral purity. It would be greatly advantageous if CE could be used to determine both the chiral and achiral purity in a single assay. This investigation compares the results obtained for the separation of the enantiomers of duloxetine using several neutral cyclodextrins to those obtained using anionic cyclodextrins (sulfobutyl ether derivatives) as chiral selectors added to the separation buffer. In addition, it reports chiral separations obtained by using neutral cyclodextrins in a sulfonic acid-coated capillary column, which give a negatively charged capillary surface and electro-osmotic flow even in low pH buffers. The possible mechanism of separation is discussed. © 1996 Wiley-Liss, Inc.
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  • 7
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Investigations into the parameters affecting the enantiomeric separation of an intermediate in the synthesis of a drug targeted for cardiac arrhythmia is presented. The separation was achieved under subcritical fluid chromatography using CO2 modified with methanol and co-modifiers isopropyl amine and methylene chloride. The stationary phase was a cellulose based stationary phase manufactured under the trade name Chiracel OB. The results showed the addition of methylene chloride had a noticeable effect on resolution while the separation factor, α, remained constant. The co-modifier, isopropyl amine, did not considerably influence the resolution, or separation factor. Temperature studies were performed in order to establish the thermodynamic parameters of the interaction between the enantiomers and the stationary phase. Plots of In k′ vs. 1/T proved to be curved, while plots of In α vs. 1/T were linear. © 1996 Wiley-Liss, Inc.
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  • 8
    ISSN: 0899-0042
    Keywords: chiral ligand exchange chromatography ; chiral coating ; chiral discrimination ; chiral copper(II) complexes ; amino acids ; amino acid esters ; amino acid amides ; hydroxy acids ; dipeptides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) complexes of N2-octyl-(S)-phenylalaninamide (Noc-Phe-NH2), N2-dodecyl-(S)-phenylalaninamide (Ndo-Phe-NH2), and N2-octyl-(S)-norleucinamide (Noc-NLeu-NH2), dynamically adsorbed on a reversed-phase C18 column, were able to perform the direct enantiomeric separation of unmodified amino acids, amino acid amides and esters, hydroxy acids, and dipeptides by elution with aqueous or mixed aqueous-organic solutions containing copper(II) sulphate or acetate. The role played by several parameters in the separation procedure was examined with the copper(II) complex of Noc-Phe-NH2 [concentration of the copper(II) ion in the eluent, pH and eluent polarity, amount of adsorbed selector]. The separation was shown to occur entirely on the stationary phase. The mechanism of chiral discrimination is discussed in terms of the chromatographic parameters and of the structure of the copper(II) complexes in solution and in the solid state. The chiral stationary phase maintained its separation ability for about 3 months. However, the column could be easily restored by recovering the selector with methanol and repeating the loading procedure. © 1996 Wiley-Liss, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 234-243 
    ISSN: 0899-0042
    Keywords: enantiomeric ; non-racemic mixtures ; binaphtol ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that chromatography with achiral phases of non-racemic mixture of binaphthol can furnish fractions which differ in enantiomeric excess. The first fraction contains one pure enantiomer i.e., has an enantiomeric excess (ee %) close to 100% and the following fractions have an ee % close to 0% (racemic mixture). As a consequence, such chromatography may be used to enrich a non-racemic mixture of binaphthol in one enantiomer. In this paper a model is proposed allowing us to calculate with good accuracy the experimental elution curves. This simple model is capable of using only a few chromatographic experiments to predict the enantiomeric enrichment of a non-racemic mixture and to calculate precisely the retention time of each fraction. © 1996 Wiley-Liss, Inc.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 249-257 
    ISSN: 0899-0042
    Keywords: chiral SubFC resolution ; analysis time ; column efficiency ; library of chiral columns ; selectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model is presented that predicts a defined relationship between chiral SubFC resolution and analysis time. This model is based upon ideal chromatographic behavior and requires column efficiency and selectivity to be independent of mobile phase modifier level and flow rate. The validity of these assumptions was found to be imperfect but acceptable for two model compounds on two commonly used chiral columns.A major implication of the model is that the maximum resolution obtainable with a particular column and mobile phase modifier may be predicted from one injection. The retention time required to obtain a desired resolution is also calculable. This information enables the practitioner to discern quickly the futility of method development efforts. Insufficient maximum resolution predicted from the first injection would require an increase in selectivity to achieve a useful separation. Selectivity may then be altered by temperature, modifier, or stationary phase. The increased column efficiency of SubFC at typical flow rates rescues separations that fail by HPLC, thus shrinking the practitioner's required library of chiral columns. This work demonstrates that SubFC also allows the practitioner to skim through that library very quickly. © 1996 Wiley-Liss, Inc.
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 11-17 
    ISSN: 0899-0042
    Keywords: thalidomide enantiomers ; mobile phase additive ; stereoselective analysis ; high-performance liquid chromatography ; chiral separation ; β-cyclodextrin ; inclusion complex ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: R- and S-Thalidomide were resolved by reversed-phase HPLC on a C-18 column with β-cyclodextrin in the mobile phase. As the concentration of β-cyclodextrin was increased stepwise from 0 to 20 mM, enantiomeric resolution increased and retention times decreased significantly. The influence of different organic modifiers in the mobile phase were evaluated, and ethanol, among others, proved to be effective. Equilibrium constants for the formation of β-cyclodextrin inclusion complexes of R- and S-thalidomide in EtOH-buffer (5:95) were calculated to be 64 and 76 M-1, respectively. © 1996 Wiley-Liss, Inc.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 58-66 
    ISSN: 0899-0042
    Keywords: molecular mechanics ; HPLC ; chiral separation ; methylphenobarbitone ; hexobarbitone ; ibuprofen ; mandelic acid ; ephedrine ; pseudoephedrine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Cyclodextrin and its derivatives have been utilised to effect chiral separation in HPLC and CZE, both as stationary phases and mobile phase additives. The basis of the method is assumed to depend upon the formation of inclusion complexes of differing stabilities between enantiomeric analytes and the cyclodextrin, resulting in a differential dynamic distribution between chromatographic phases. In this study, force field calculations have been employed to model the inclusion complexes of enantiomeric brompheniramine, ephedrine, pseudoephedrine, ibuprofen, mandelic acid, methylphenobarbitone, and hexobarbitone with β-cyclodextrin. The resulting values for Δ(ΔH), the difference in enthalpy of complex formation between enantiomeric pairs has been compared with literature chromatographic data to explain the ability of the systems to achieve enantiomeric separations. © 1996 Wiley-Liss, Inc.
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  • 15
    ISSN: 0899-0042
    Keywords: optical resolution ; conglomerate ; preferential crystallization ; optically active 2-amino-3-chloropropanoic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The racemic structures of (RS)-2-amino-3-chloropropanoic acid [(RS)-ACP] and (RS)-2-amino-3-chloropropanoic acid hydrochloride [(RS-ACP·HCl] were examined to obtain (R)- and (S)-ACP via optical resolution by preferential crystallization. The melting point, infrared spectrum, solubility, and ternary solubility diagram suggested that (RS)-ACP·HCl exists as a conglomerate and that (RS)-ACP forms a racemic compound. Optical resolution by preferential crystallization of (RS)-ACP·HCl was successfully achieved to yield (R)- and (S)-ACP·HCl. Optically pure (R)- and (S)-ACP were obtained from the purified (R)-and (S)-ACP·HCl, respectively. © 1996 Wiley-Liss, Inc.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 207-213 
    ISSN: 0899-0042
    Keywords: CS-670 ; anti-inflammatory drug ; stereoselective metabolism GC-MS ; diastereomer HPLC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CS-670, a novel nonsteroidal anti-inflammatory drug, is a racemic prodrug. Plasma concentrations and urinary excretion of CS-670 and its metabolites were determined in experimental subjects after oral administration at a single 120 mg dose. CS-670 and four metabolites, the saturated ketone (M-A), unsaturated-alcohol (M-B), cis-alcohol (M-C), and trans-alcohol (M-D), were quantitated by GC-MS. The major metabolites in human plasma were M-B, M-C, and M-D and their terminal half-lives (t½) were 0.9, 2.6, and 1.2 h, respectively. The total recovery in the urine was 26% of the dose, but unchanged CS-670 accounted for less than 2% over a 48 h period. In addition, the absolute configurations of the metabolites were examined by HPLC after derivatization with chiral reagents. It was found that the configuration of the propionic acid moiety of the metabolites, M-B, M-C, and M-D, in human plasma, was rapidly inverted from (-)-(R) to the (+)-(S) configuration in stereoselective biotransformation. Furthermore, the configurations of the 1′- and 2′-carbons of M-C and M-D, were found to be (1′R,2′S) and (1′R,2′S), respectively. These results show that CS-670 is readily biotransformed by chiral inversion of the 2-arylpropionic acid moiety and stereoselective reduction of the α, β-unsaturated ketone moiety in humans. © 1996 Wiley-Liss, Inc.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 356-356 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
    ISSN: 0899-0042
    Keywords: NSAIDs ; esterification ; resolution ; Candida antarctica lipase ; Mucor miehei lipase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The resolution of rac-suprofen (1) catalysed by lipase in organic solvents was investigated. Direct esterification of rac-1 with methanol in dichorometane catalysed by Novozym® 435 furnished the pharmacologically active (+)-(S)-suprofen as unreacted product with excellent enantiomeric excess. The same procedure in toluene using Mucor miehei lipase adsorbed in Celite as catalyst afforded (-)-(R)-suprofen with good optical purity. © 1996 Wiley-Liss, Inc.
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  • 19
    ISSN: 0899-0042
    Keywords: enantioseparation ; HPLC ; cyclodextrin ; phenylcarbamate ; chiral stationary phase ; optical resolution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New dichloro-, dimethyl-, and chloromethylphenylcarbamate derivatives of cyclodextrins (CDs) were prepared and their enantiomeric recognition abilities were evaluated as chiral stationary phases (CSPs) in normal phase high-performance liquid chromatography (HPLC). The effects of the type of cyclodextrins, the nature and position of the substituents on the phenyl ring, binding mode and spacer on the chiral recognition were studied in detail. No marked change of chiral recognition abilities was established by reversing the binding side of CDs (i.e., by the narrower [primary] opening of the cone-shaped CD to silica gel with the wider [secondary] opening sides). This result indirectly proves the previously drawn conclusion about the minor role of inclusion phenomena in chiral recognition in this case. Nevertheless, chiral recognition of these CSPs toward some compounds critically depends on the type of CDs used. All CD derivatives described in this study show rather low enantiomeric resolving abilities compared with corresponding polysaccharide (cellulose and amylose) derivatives, although very high enantioselectivity of separation was observed for a few compounds, such as racemic flavanone and cyclopropanedicarboxilic acid dianilide. © 1996 Wiley-Liss, Inc.
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  • 20
    ISSN: 0899-0042
    Keywords: rac-propranolol ; enantiomers ; drug intoxication ; cardiovascular function ; respiratory function ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The contribution of the individual enantiomers ([+]-[R]- and [-]-[S]-propranolol) to rac-propranolol intoxication was studied in anaesthetized, spontaneously breathing (SB) rats and artificially ventilated (AV) rats and rabbits. In the SB rat, propranolol (30 mg.kg-1.h-1 i.v.) decreased heart rate and mean arterial blood pressure and caused hypoventilation, serious hypoxaemia, respiratory acidosis, and death by respiratory arrest. Survival time (ST) in the (+)-(R)-propranolol group (ST 91 ± 5 min) was significantly longer than in the rac-propranolol group (ST 68 ± 6 min). In AV rats and rabbits toxic doses of rac-, (-)-(S)- and (+)-(R)-propranolol, 30 mg.kg-1.h-1 and 15 mg.kg-1.h-1 i.v., respectively, induced comparable effects on haemodynamic variables as in the SB rat. Artificial ventilation lengthened ST by a factor of three to four in rats. In the AV rat, ST's were not significantly different between the rac-, (-)-(S)- and (+)-(R)-propranolol groups. In the rabbit, as in the SB rat, ST in the (+)-(R)-propranolol group was significantly longer than ST's in the rac- and (-)-(S)-propranolol groups. The acute respiratory acidosis in SB rats and the prolonged ST in AV rats suggest that respiratory failure is the primary and cardiovascular failure the secondary cause of death in propranolol intoxication. The potentiation of the toxic effect of the enantiomers observed after dosing the racemate instead of the pure enantiomers could not be explained by a stereoselective difference in plasma propanolol concentration. © 1996 Wiley-Liss, Inc.
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 22
    ISSN: 0899-0042
    Keywords: enantiomers ; HPLC ; DNS-animo acids ; fluorescence quenching ; ligand-exchange mechanism ; adsorption ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copper(II) complexes of two new diastereomeric ligands, N2-(R)- and N2-(S)-2′-hydroxypropyl-(S)-phenylalaninamide [(R, S)-1 and (S, S)-1], have been used as additives to the eluent in high-performance liquid chromatography (HPLC) reversed phase for the chiral separation of DNS-amino acids. The aim was that of comparing the separation process obtained by the chiral eluent with that obtained by an analogous bonded stationary phase containing (S)-phenylalaninamide, previously studied [CSP-(S)-Phe-NH2]. The affinity of the ternary complexes for the C18 column was determined by adsorption experiments in HPLC. It was shown that the two systems (chiral eluent, chiral stationary phase) work according to different mechanisms. Ternary complex formation in solution was studied by fluorescence spectroscopy. It was shown that chiral separation with the Cu(II) complexes added to the eluent was determined by the relative affinities of the ternary complexes for the column-stationary phase rather than by their stabilities in solution. With CSP-(S)-Phe-NH2 the separation is accounted for by the relative stabilities of the ternary complexes, which depends mainly on the “allowed” geometry of the complex and on the steric repulsion of the amino acid side chain with the spacer. © 1996 Wiley-Liss, Inc.
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  • 23
    ISSN: 0899-0042
    Keywords: rac-amlodipine ; amlodipine ; liquid chromatography ; chiral ; charged cyclodextrin ; optimisation ; central composite design ; mobile phase additive ; experimental design ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A negatively charged derivative of β-cyclodextrin, sulphobutyl ether-β-cyclodextrin (SBE-β-CD), was examined as a chiral mobile phase additive in reversed-phase high-performance liquid chromatography for the enantiomeric resolution of the calcium channel blocker rac-amlodipine. Theoretical and practical aspects are discussed for setting up a central composite design applicable to any analytical method. These include the correct location of factor points for maintaining orthogonality within the design and the augmentation of centrepoint experiments to allow a larger factor space by increasing the distance of axial star points. Optimised separation was achieved using a reverse-phase column with eluent comprising: acetonitrile (ACN) - potassium dihydrogen phosphate (pH 3.93) containing 2.66 mM SBE-bgr;-CD (26.5:73.5% v/v) at a flow rate of 1.0 ml/min. This yielded a Kaiser peak separation index, Pi = 0.96, at tR2 = 52 min with satisfactory reproducibility, relative standard deviation values: tR1, 0.39%; tR2, 0.47% (n = 5). These experimental results were in excellent agreement with those predicted by the SAS software package for a chromatographic response function model. Multiple regression analysis in four dimensions, with three response models based on Rs, Pi, and a function of Pi, produced response surfaces which revealed zones of optimum robustness and illustrated the interactions involved between the key chromatographic factors. Putative proposals for a mechanism involving the interaction of each of the positively charged enantiomers with the negatively charged cyclodextrin are also discussed. These examine the possibility of ion-pairing and inclusion phenomena to account for the excellent resolution observed. © 1996 Wiley-Liss, Inc.
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  • 24
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 503-510 
    ISSN: 0899-0042
    Keywords: enantioseparations ; carrageenans ; sulfated polysaccharides ; beta blockers ; tryptophan and derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lambda-carrageenan, a linear high molecular weight sulfated polysaccharide, has been employed as a chiral selector in capillary electrophoresis for the separation of enantiomers of weakly basic pharmaceutical compounds. The racemic compounds that were enantioresolved included propranolol, pindolol, tryptophanol, laudanosine and laudanosoline. In addition, the diastereomeric pair of cinchonine and cinchonidine were also resolved. Method conditions such as buffer pH, electrolyte concentration, column temperature, and chiral selector concentration were found to be important for improvement of enantioselectivity. © 1996 Wiley-Liss, Inc.
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  • 25
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 122-125 
    ISSN: 0899-0042
    Keywords: aminophosphonic acids ; asymmetric synthesis ; chiral HPLC ; ligand-exchange chromatography ; enantiomeric analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An aqueous solution of the (+)-monoethyl ester of N-(l′-hydroxymethyl-)propyl-α-aminobenzylphosphonic acid has been proposed as a suitable chiral eluent for enantiomeric analysis of amino acids by ligand-exchange chromatography. Asymmetric synthesis of the chiral selector using (-)-(R)-2-aminobutan-1-ol as a starting reactant is described. The dependence of the parameters of separation of valine enantiomers on concentration of the complexing ion, pH, and temperature has been investigated. It is shown that the order in which enantiomers are eluted from a column depends on the concentration of the complexing ion and pH. © 1996 Wiley-Liss, Inc.
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  • 26
    ISSN: 0899-0042
    Keywords: Cellulose tris-(3,5-dimethylphenyl carbamate) ; resolution ; tetramisole ; propanolol ; microporous APS-silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity of a series of chiral analytes was examined on tris-(3,5-dimethylphenyl carbamate) coated onto microporous APS-silica. The effects of the nature of the carbohydrate, the weight ratio of carbamate/support and the type of alcohol present in the mobile phase were investigated. Among the chiral analytes examined, propanolol showed an extremely good resolution. The resolution of tetramisole was optimized and the method developed was shown to be suitable for analysis of the drug in commercial tablets and in a suspension. © 1996 Wiley-Liss, Inc.
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  • 27
    Electronic Resource
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    Chirality 8 (1996), S. 352-352 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 28
    ISSN: 0899-0042
    Keywords: 13C NMR ; chiral recognition difference ; elution order ; cellulose tris(4-methylbenzoate) ; 1-phenylethanol ; 1-indanol ; 1,2,3,4-tetrahydro-1-naphthol ; glutethimide ; Tröger's base ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To elucidate chiral recognition difference between pairs of enantiomers which interacted with a cellulosic stationary phase of chiral discrimination high performance liquid chromatography (HPLC), 13C NMR spectroscopy was applied for enantiomers of 1-phenylethanol, 1-indanol, 1,2,3,4,-tetrahydro-1-naphthol, glutethimide, and Tröger's base. Their 13C nuclear spin-spin relaxation times (T2Cs) and spectra were obtained in deuterated HPLC solvents in the presence of column packing material made of cellulose tris(4-methylbenzoate) coated on silica gel. The first-eluted enantiomers on the HPLC showed longer T2Cs and stronger signal intensities of 13C NMR spectra than the second-eluted enantiomers. These results indicated that the chiral recognition difference of enantiomers was observed by their T2Cs and intensities of 13C NMR spectra. The T2C difference was found to reflect the retention order of enantiomers on the chiral HPLC column. © 1996 Wiley-Liss, Inc.
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  • 29
    Electronic Resource
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    Chirality 8 (1996), S. 1-1 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 30
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 3-5 
    ISSN: 0899-0042
    Keywords: stereospecific decarboxylation ; asymmetric synthesis ; inhalational anesthetic ; halothane ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new synthesis of non-racemic halothane (1-bromo-1-chloro-2,2,2-trifluoroethane) is reported. The stereospecificity of the key reaction, decarboxylation of a salt of optically enriched 1-bromo-1-chloro-2,2,2-trifluoropropionic acid to give halothane, is shown to be highly dependent on the nature of the cation. When the cation is trialkylammonium, a high level of stereospecificity is observed. © 1996 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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  • 31
    Electronic Resource
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    Chirality 8 (1996), S. 18-23 
    ISSN: 0899-0042
    Keywords: racemate ; enantiomer ; bioavailability ; pharmacokinetic ; ibutilide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ibutilide fumarate, a new drug for the treatment of cardiac arrhythmias, contains a stereogenic center bearing a secondary alcohol group. Several single dose and multiple dose studies of racemic ibutilide or its enantiomers were performed by the oral and intravenous routes in dogs. A chiral assay was used to examine racemization and the individual enantiomer pharmacokinetics. Following low oral or intravenous doses (approximately 0.3 mg/kg), the pharmacokinetics of the enantiomers were nearly identical, with no substantial chiral conversion. Both enantiomers exhibited high clearance rates, large volumes of distribution, and low oral bioavailability. As the dose increased, pharmacokinetic differences between the enantiomers were observed. The greatest differences (3-fold) were seen after oral administration at 4 mg/kg, indicating that first-pass metabolism of ibutilide was highly enantioselective at high doses. The clearances of the enantiomers differed by up to 34% at 5 mg/kg followed intravenous administration of the racemate. At high doses, other non-linear pharmacokinetic behavior was also apparent. The intravenous clearance of ibutilide declined from 5.3 L/h/kg at 0.3 mg/kg to 3.7 L/h/kg at a dose of 5 mg/kg. The absolute oral bioavailability of the racemate increased from 2% at 0.3 mg/kg to as much as 84% at 5 mg/kg. © 1996 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 32
    ISSN: 0899-0042
    Keywords: gas chromatography ; modified β-cyclodextrin column ; chiral separation ; assay ; mexiletine ; hydroxylated metabolites ; urine ; conjugation/deconjugation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of mexiletine and four of its hydroxylated metabolites were directly separated by capillary gas chromatography using a heptakis(6-O-tert-butyl-dimethylsilyl-2,3-di-O-methyl)-β-cyclodextrin column. The method was applied to the analysis of urine samples from cancer patients who were treated with racemic mexiletine as part of a study of the use of mexiletine in the relief of neuropathic pain. Samples analyzed before and after deconjugation of the urine with β-glucuronidase/arylsulfatase showed a high stereoselectivity in the formation and conjugation of these compounds. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 33
    Electronic Resource
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    Chirality 8 (1996), S. 49-57 
    ISSN: 0899-0042
    Keywords: racemization ; fermented beverages ; beer ; D-amino acids ; D-leucine ; D-phenylalanine ; D-proline ; cyclodextrin columns ; column switching ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Even though amino acids are important trace components in the brewing of beers, they have not been extensively evaluated in these beverages. Studies involving the enantiomeric composition of these amino acids are even less prevalent. A brief summary of the brewing process for malt beverages is given. The total concentration and enantiomeric composition of three amino acids (leucine, phenylalanine, and proline) were determined in 25 different beers. Proline tended to have the highest average absolute concentration and the lowest percentage of the D-enantiomer in most samples. In some cases the relative amounts of D-phenylalanine and D-leucine exceeded 10% of the individual amino acids. The enantiomeric composition of the amino acids in different beer samples did not vary as extensively as the absolute concentrations. The reason for the concentration differences between proline and the other amino acids is discussed. A knowledge of amino acid concentrations and enantiomeric compositions appears to be useful in characterizing specific beers and brewing processes. © 1996 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 34
    ISSN: 0899-0042
    Keywords: spectral analysis ; spectral contrast ; HPLC ; MECC ; peak homogeneity ; peak tracking ; method development ; photodiode array detection ; isomers ; enantiomers ; diastereomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of mathematically enhanced ultraviolet/visible (UV/VIS) absorbance spectral analysis and spectral contrast software techniques in high performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (MECC) as an aid for the determination of peak homogeneity, identification, and tracking during method development was investigated. Various structurally similar pharmaceutical compounds, and compounds present as either cis/trans isomers, diastereomers, or enantiomers were used as test compounds to probe the limits of this technique. Two tricyclic antidepressants, nortriptyline and imipramine, were employed to study the effects of HPLC mobile phase composition and pH on the ability to identify and track peaks during method development. It was found that method changes altered the spectral matches used for identification, but not enough to cause incorrect peak identification. It was also shown using HPLC that the cis/trans isomers of doxepin and the diastereomers ephedrine and pseudoephedrine could be distinguished.The mathematically enhanced spectral analysis and spectral contrast software techniques were also employed with MECC. Peaks tracking during method development as pH and the concentration of surfactant changes is shown for a separation of various penicillin type antibiotics. It was shown that during chiral MECC (CMECC) analyses ephedrine/pseudoephedrine diastereomers as well as ephedrine enantiomers could be distinguished. The determination of enantiomers is possible in CMECC since enantiomers are eluted as diastereomeric complexes, as opposed to HPLC where they are eluted in their native state. © 1996 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
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  • 35
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    Chirality 8 (1996), S. 126-130 
    ISSN: 0899-0042
    Keywords: cyclodextrin ; chiral ; propranolol ; chromatography ; stationary phase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A β-cyclodextrin bonded stationary phase was employed for the enantioresolution of propranolol and several analogues in conjunction with various polar organic mobile phases. The effects of structural alterations in the non-polar regions of the analytes were found to exert profound changes upon chiral resolution and capacity values, indicating that features which cannot hydrogen-bond with the cyclodextrin molecule still play an important role in this chiral recognition process. This was linked to a repulsive steric effect facilitating the necessary conditions for chiral resolution. The degree of ionization of the analytes and the type and concentration of organic modifier used were also seen to influence the analytes1 enantio-selectivity and capacity values. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 36
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    Chirality 8 (1996), S. 147-152 
    ISSN: 0899-0042
    Keywords: amylose ; (S)-α-methylbenzyl carbamate ; chiral sulfoxides ; microporous silica ; polysaccharide phases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric resolution of chiral sulfoxides was investigated on amylose (S)-α-methylbenzyl carbamate phase coated on aminopropylated 7 μm silica with 500Å diameter pores. This was shown to be very successful in the separation of alkyl/aryl, aryl/aryl, and non-aromatic sulfoxides. The effect of pore size using naked silica was also investigated, demonstrating that the pore size does not affect the resolution. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 37
    ISSN: 0899-0042
    Keywords: propranolol enantiomers ; fluorinated analogs ; chiralcel OD and chiralcel OD-R columns ; chiral recognition mechanism(s) ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric separation of several racemic aryloxyaminopropan-2-ol derivatives related to propranolol on normal and reversed phase of cellulose tris (3,5-dimethylphenylcarbamate) chiral stationary phases known as Chiralcel OD and Chiralcel OD-R were studied. It was observed that the chiral separation depends on the substitution pattern of the aryl group, i.e., 1-naphthyl, 2-naphthyl, and phenyl group and polarity on the basic nitrogen in the side chain. In both normal and reversed phase modes the (+)-R-enantiomer eluted first in all of the analogs resolved. It can be concluded that: (1) substituents on the side chain did affect the interaction of the enantiomers with the polar carbamate moiety in the CSP; and (2) the dipole-dipole stacking between the π-donor 3,5-dimethylphenyl carbamate group pending from the glucose rings of the CSP and π-acceptor aryl group of the analyte is crucial for the efficient chiral discrimination. The chiral recognition mechanism(s) between these analogs and the chiral stationary phases are proposed. © 1996 Wiley-Liss, Inc.
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  • 38
    ISSN: 0899-0042
    Keywords: arylpropionic acid ; ketoprofen ; enantiomer ; stereoselectivity ; Coenzyme A thioester ; hybrid triacylglycerols ; inversion ; adipose tissue ; hepatocytes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric bioinversion of ketoprofen (KP) enantiomers and their incorporation into triacylglycerols were investigated in the rat (1) in vitro, using liver homogenates, subcellular fractions, and hepatocytes, and (2) in vivo, in different tissue samples after oral administration of the radiolabelled compounds. In liver homogenates or subcellular fractions, the enantiomer (S)-ketoprofen (S-KP) was recovered unchanged, whereas (R)-ketoprofen (R-KP) was partially converted into its Coenzyme A (CoA) thioester and inverted to S-KP. Both processes occurred mainly in the mitochondrial fraction. This supports the mechanism of inversion via stereoselective formation of CoA thioesters of R-KP, already described for other non-steroidal anti-inflammatory drugs. Incorporation into triacylglycerols was detected after incubation with intact hepatocytes in the presence of added glycerol. The process was stereoselective for R-KP vs. S-KP (covalently bound radioactivity 26,742 ± 4,665 dpm/106 cells vs. 6,644 ± 3,179 dpm/106 cells, respectively). However, no incorporation was found in liver samples after oral administration of either R-KP or S-KP. On the contrary, in adipose tissue samples a significant and stereoselective formation of hybrid triacylglycerols was observed: 11,076 ± 2,790 dpm.g-1 for R-KP vs. 660 ± 268 dpm.g-1 for S-KP. The incorporated R/S ratio, higher in adipose tissue (R/S = 17) than in hepatocytes (R/S = 4), indicates that fat may be the main tissue store for the xenobiotic R-KP in rats. © 1996 Wiley-Liss, Inc.
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  • 39
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    Chirality 8 (1996), S. 84-87 
    ISSN: 0899-0042
    Keywords: capillary electrophoresis ; aminophosphonic acid ; enantiomers ; osteoporosis ; cyclodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic aminophosphonic acids were completely resolved into their enantiomers by capillary electrophoresis using β-cyclodextrin as a chiral selector in a borate electrolyte. The reproducibility of sample injection, solute migration time, and detection limits of the solute were studied. The calibration curve obtained from peak areas was linear over the concentration range of 10 to 300 μg/mL. © 1996 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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  • 40
    ISSN: 0899-0042
    Keywords: teicoplanin ; glycopeptide antibiotics ; capillary electrophoresis ; enantioselectivity ; separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Teicoplanin is the third in a series of macrocyclic glycopeptide antibiotics that has been evaluated as a chiral selector in capillary electrophoresis (CE). It was used to resolve over 100 anionic racemates at low selector concentrations. Like the other related glycopeptide antibiotics, its enantioselectivity tends to be opposite to that of the ansa-type antibiotics which prefers cationic compounds, particularly amines. Factors that affect teicoplanin-based enantioseparations include the selector concentration, pH, and the concentration of the organic modifier. The temperature and the nature and strength of the buffer are also known-to affect the stability of the chiral selector as well as the enantioseparation. Teicoplanin exhibited some features that were not noted with the other glycopeptide antibiotics. For example, it aggregates (forms micelles) in aqueous solutions and this influences its enantioselectivity. Unlike the other studied glycopeptides, teicoplanin precipitates in alcohol-water mixtures. It also binds less to the capillary wall than vancomycin as evidenced by the faster electroosmotic flow velocity. The micellization of teicoplanin is pH dependent so that the effect of pH on enantiorecognition is more complex for teicoplanin than for other chiral selectors. Also it is shown that the simple model proposed to explain the role of organic modifiers in cyclodextrin-based CE enantioseparations may not apply to these and other systems. © 1996 Wiley-Liss, Inc.
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  • 41
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    Chirality 8 (1996), S. 131-135 
    ISSN: 0899-0042
    Keywords: polysaccharides ; optical resolution ; phase loading ; racemic compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution of a range of racemic compounds was investigated using bis(aryl carbamate) derivatives of chitin coated onto microporous organosilane-modified silica. The influence on chiral discrimination of factors such as the carbamate/support weight ratio, the nature of polysaccharide, and the influence of the aryl group substituents was investigated. The bis(3,5-dimethylphenyl carbamate) derivative of a noncommerical chitin gave the best results. © 1996 Wiley-Liss, Inc.
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  • 42
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    Chirality 8 (1996), S. 136-142 
    ISSN: 0899-0042
    Keywords: enantioseparations ; high-performance liquid chromatography ; mobile phase modifier and additive ; cellulose-based CSP ; chiral acidic and basic drugs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 3 Ill.
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  • 43
    ISSN: 0899-0042
    Keywords: amino acids ; chiral rhodium complexes ; aminophosphine-phosphinite ; D- and L-enantiomers ; NMR spectra ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted N-Cbz and N-Boc protected arylamino acrylic acids and esters have been prepared and used in asymmetric hydrogenations catalyzed by PROPRAPHOSRh. Stereoselectivities 〉 90% ee could be achieved, the rate of which is dependent on the position of the substituent in the aromatic ring. The N-Boc derivatives provide advantages compared with the N-Cbz analogues. The amino acid derivatives were fully characterized by 19F, 13C, and 1H NMR spectroscopy. © 1996 Wiley-Liss, Inc.
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  • 44
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    Chirality 8 (1996), S. 397-401 
    ISSN: 0899-0042
    Keywords: chiral derivatization ; capillary GC ; capillary SFC ; diastereoisomeric esters ; optical resolution ; (S)-Trolox methyl ether ; primary alcohols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (S)-Trolox methyl ether is known as a powerful chiral reagent for the e.e. determination of chiral alcohols by separation of the corresponding diastereoisomeric esters on achiral GC and SFC columns. In order to further improve his methodology, five possible candidates resultings from variation of structural elements of parent reagent have been tested for derivatization with selected alcohols and subsequent analysis of the diastereoisomeric pairs of esters. The results of this optimization procedure showing the ways to new potent reagents are discussed. © 1996 Wiley-Liss, Inc.
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  • 45
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    Chirality 8 (1996), S. 258-263 
    ISSN: 0899-0042
    Keywords: stereoselectivity ; radioactivity ; distribution ; hepatocytes ; metabolism ; protein binding ; analbuminemic rats ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselective pharmacokinetics of two enantiomers of [14C]-labeled KE-298 [2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanonic acid] were investigated in rats. The blood levels of radioactivity after the oral administration of (+)-(S)-[14C]KE-298 were higher than that for (-)-(R)-[14C]KE-298; the AUC of the former was approximately twice that of the latter. No significant stereoselectivity was observed in absorption rate. The tissue/plasma level ratios at 30 min after oral administration of (-)-(R)-[14C]KE-298 in the liver and kidney, the major metabolic and/or excretory organs, were 2 to 3 times higher than those for (+)-(S)-[14C]KE-298. Neither was evidence of stereoselectivity found in the excretion of radioactivity. During incubation with isolated rat hepatocytes in vitro, the metabolic rates of KE-298 enantiomers were not significantly different. Plasma protein binding 30 min after the oral administration of (+)-(S)-[14C]KE-298 and (-)-(R)-[14C]KE-298 was 99.3% and 97.0%, respectively. Comparing the unbound fraction, (-)-(R)-[14C]KE-298 was approximately 4 times higher than (+)-(S)-[14C]KE-298. In order to make clear the relationship between stereoselective pharmacokinetics and protein binding for [14C]KE-298, the comparative pharmacokinetics of (+)-(S)-[14C]KE-298 and (-)-(R)-[14CC]KE-298 were investigated in analbuminemic rats. In these animals, no evidence of stereoselectivity was found for either blood level-time profiles or plasma protein binding. These results revealed that the stereoselective pharmacokinetics of KE-298 in rats might be due to enantiomeric differences in binding to plasma albumin. © 1996 Wiley-Liss, Inc.
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  • 46
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    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 47
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    Chirality 8 (1996), S. 316-324 
    ISSN: 0899-0042
    Keywords: sulfated cyclodextrin ; catecholamine ; chiral ; CZE ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The utility of negatively charged sulfated cyclodextrins (SCD) as chiral additives (CA) in capillary electrophoresis (CE) was studied in the chiral resolution of several compounds of pharmaceutical interest, including catecholamines such as norepinephrine, epinephrine, DOPA and their precursors, phenylalanine, and tyrosine. Experiments were conducted using 10 mM sodium phosphate monobasic solution and 2% SCD adjusted to pH 3.2 with phosphoric acid. Chiral recognition mechanisms were explored using structurally related analytes including basic, acidic, and neutral compounds as well as 3,5-dinitrobenzoyl phenylglycine, phenylalanine, and homophenylalanine. The advantage of the reversed electrophoretic polarity mode for the enantioresolution of these compounds is also discussed. © 1996 Wiley-Liss, Inc.
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  • 48
    ISSN: 0899-0042
    Keywords: chiral discrimination ; β-Cyclodextrin ; complexation ; enantiodiscrimination ; computational chemistry ; molecular modeling ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiodifferentiation of methyl mandelate by β-Cyclodextrin in the liquid phase is explored in detail. Temperature dependent studies using a β-cyclodextrin chiral stationary phase provided differential binding enthalpies and entropies. NMR studies revealed where around the host molecule the guest tends to reside. Molecular dynamics simulations correctly predict the retention order and provide an atomistic account of how chiral discrimination takes place. It is found that short range dispersion forces rather than long range coulombic forces are responsible for both complexation and for enantiodiscrimination. The intermolecular hydrogen bonds are not discriminating and the idea that a tight fit of included species within a cyclodextrin cavity be a requirement for chiral discrimination is questioned. © 1996 Wiley-Liss, Inc.
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  • 49
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    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 50
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    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 51
    ISSN: 0899-0042
    Keywords: aminotetralin ; catechol group ; homochiral derivatization ; (+)-(R)-1-phenylethyl isocyanate ; enantiomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new chiral derivatization procedure for the HPLC resolution of chiral catecholamines and structurally related compounds is described. The homochiral reagent, (+)-(R)-1-phenylethyl isocyanate (RPEIC), was added to separate and quantitate the enantiomers of rac-5,6-dihydroxy-2-methyl-aminotetralin, the main metabolite of rac-5,6-diisobutyryl-2-methyl-aminotetralin, a potent dopamine agonist, by reversed-phase HLPC analysis. To avoid catecholamine degradation in the basic reaction medium and to obtain the selective and quantitative derivatization of the amino group of the compound, the reversible complex formation between diphenylborinic acid (DPBA) and the catechol group, in alkaline medium, was performed before homochiral isocyanate addition. The RPEIC derivatization was completed in 30 min and then the DPBA complex was dissociated by adding dilute acid. The structure of intermediates and urea derivatives was confirmed by mass spectrometry. The use of an electrochemical detector, operating in redox mode, allowed HPLC quantitation of enantiomers at the nanogram level in plasma and urine. The derivatization procedure is also suitable for other catecholamine-related compounds. © 1996 Wiley-Liss, Inc.
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  • 52
    ISSN: 0899-0042
    Keywords: diarylcarbinol ; arylarylmethanol ; chiral stationary phase ; enantioseparation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fast and efficient baseline separation of asymmetrically substituted diarylmethanols and 1,1-diarylethanols was achieved on an endcapped, amide-linked N-3,5-dinitrobenzoylated, (R, R)-1,2-diphenyl-1,2-ethanediamine-derived chiral stationary phase (CSP). Optimal enantioselectivities on this CSP were obtained using 1% 2-propanol in n-heptane as the mobile phase. Enantiorecognition was found to be governed by π-basicity and the substitution pattern of the aromatic substituents. © 1996 Wiley-Liss, Inc.
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  • 53
    ISSN: 0899-0042
    Keywords: hydrolysis ; carboxylesterase ; bioconversion ; plasma concentration ; pharmacokinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The in vitro and in vivo stereoselective hydrolysis characteristics of the mutual prodrug FP-PPA, which is a conjugate of flurbiprofen (FP) with the histamine H2-antagonist PPA, to reduce gastrointestinal lesions induced by FP were investigated and compared with those of FP methyl ester (rac-FP-Me) and FP ethyleneglycol ester (rac-FP-EG). The rac-FP derivatives were hydrolyzed preferentially to the (+)-S-isomer in plasma and to the (-)-R-isomer in liver and small intestinal mucosa. Interestingly, in the gastric mucosa, the stereoselectivity of hydrolysis of (-)-R-FP-PPA was opposite from that of rac-FP-Me and rac-FP-EG, which suggested that the stereoselective hydrolysis of FP-PPA was helpful in reducing gastric damage induced by (+)-S-FP. However, hydrolysis of all rac-FP derivatives was found to be catalyzed by carboxylesterases in the gastric mucosa. The stereoselective disposition of FP enantiomers early after intravenous administration of rac-FP-PPA could be explained by the stereoselective formation of (-)-R-FP from rac-FP-PPA in the liver. (-)-R-FP-PPA was completely hydrolyzed to form (-)-R-FP in vivo, while 78% of (+)-S-FP-PPA was hydrolyzed to (+)-S-FP, with a corresponding decrease in the area under the curve. Twenty-five percent of (+)-S-FP-PPA might be eliminated as the intact prodrug or its metabolites other than FP. The most important bioconversion of FP-PPA occurred in plasma, and additional hydrolysis of the R-enantiomer in liver resulted in the stereoselectivity observed following both i.v. and p.o. administration. © 1996 Wiley-Liss, Inc.
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  • 54
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    Chirality 8 (1996), S. 525-530 
    ISSN: 0899-0042
    Keywords: temazepam ; 3-O-methyltemazepam ; 3-O-ethyltemazepam ; stereoselectivity ; nucleophilic substitution ; racemization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric 3-O-methyltemazepam and 3-Oethyltemazepam were highly stereoselectively substituted by the 3-methoxy group of methanol in acidic anhydrous methanol and by the 3-ethoxy group of ethanol in acidic anhydrous ethanol, respectively. The stereoselectivity of the homonucleophilic substitution reactions was determined by circular dichroism spectropolarimetry and gas chromatography-mass spectrometry. In anhydrous solutions containing 0.5 M D2SO4 at 50°C, for example, the stereoselectivity was ∼63:1 for enantiomeric 3-O-methyltemazepam in CD3OD and ∼94:1 for enantiomeric 3-O-ethyltemazepam in C2D5OD. The high stereoselectivity at C3 position was primarily due to the presence of a methyl group at N1 position. © 1996 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
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  • 55
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    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 56
    ISSN: 0899-0042
    Keywords: chiral stationary phases ; Chiralpak AD ; CD spectra ; entropy ; enthalpy ; 1H NMR spectra ; synperiplanar conformer of dihydropyridines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct HPLC enantiomeric separation of five fluorenone-1,4-dihydropyridine-3,5-dicarboxylic diesters has been achieved using a Chiralpak AD stationary phase obtaining simultaneously good enantioselectivities, resolution factors, and elution times. CD spectra of the individual enantiomers for two compounds were measured. Thermodynamic parameters associated with the adsorption equilibria of the enantiomers with the chiral stationary phase were obtained from HPLC runs at various temperatures. The conformational preferences of the synperiplanar fluorenone group and of the cis/cis ester groups were obtained by 1H NMR spectra, including NOE experiments. © 1996 Wiley-Liss, Inc.
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  • 57
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    Chirality 8 (1996), S. 271-280 
    ISSN: 0899-0042
    Keywords: non-steroidal anti-inflammatory drugs ; human serum albumin ; chirality ; chloride ; fatty acids ; equilibrium dialysis ; dansylamide ; dansylsarcosine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Non-steroidal anti-inflammatory drugs (NSAIDs) are strongly bound to human serum albumin (HSA), mainly to sites I and II. The aim of this study was to characterize the binding site(s) of etodolac enantiomers under physiological conditions (580 μM HSA) using equilibrium dialysis. The protein binding of etodolac enantiomers, alone or in various ratios, was studied in order to evaluate the potential competition between them. Our results showed that (S)-etodolac was more strongly bound to HSA than (R)-etodolac. The displacement of one enantiomer by its antipode was observed only at high concentrations of the competitor, and was more pronounced for the (S)-form. Displacement studies of the enantiomers by specific probes of sites I and II of albumin, dansylamide, and dansylsarcosine, respectively, showed that (R)-etodolac was slightly displaced by both these probes whereas the free concentration of (S)-etodolac increased markedly in the presence of dansylsarcosine. Moreover, the binding of ligands to sites I and II is usually affected by alkaline pH, by chloride ions, and by fatty acids. For etodolac, the presence of 0.1 and 1 M chloride ions and increasing pH (5.5-9) decreased the binding of both enantiomers. The same result was obtained with addition of octanoic acid. Conversely, the addition of oleic, palmitic, or stearic acid to the protein solution increased the binding of (R)-etodolac, but decreased that of its antipode. All these findings suggest that (R)- and (S)-etodolac interact mainly with site II of HSA, and that the (R)-isomer is also bound to site I under physiological conditions. © 1996 Wiley-Liss, Inc.
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  • 58
    ISSN: 0899-0042
    Keywords: chiral complexing agent ; nuclear magnetic resonance spectroscopy ; tobacco alkaloids ; nicotine-like compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric purity of several tobacco alkaloids and nicotine-like compounds was determined using 1H NMR (300 MHz) spectroscopy in the presence of (-)-(R)-1,1′binaphthyl-2,2′-diylphosphoric acid (BNPPA) as a chiral complexing agent. The most significant signal splitting resulting from diastereoisomeric complexation are seen for chemical shifts in the proximity of the pyridinyl nitrogen. Chemical shift data exclude any contribution of the pyrrolidinyl protons to chiral recognition, but when the pyrrolidine ring is replaced by a piperidine ring, i.e., for compounds such as rac-anabasine and rac-anatabine, non-equivalence between enantiomers was observed for protons close to the piperidine ring. A new approach for the preparation of the pure (-)-(S)-and (+)-(R)-enantiomers of nornicotine, a tobacco alkaloid and metabolite of nicotine, was developed. The optically pure enantiomers thus obtained were used to establish the minimum sensitivity of the NMR spectroscopic method of chiral analysis. These findings provide a new, general, and facile method for the determination of enantiomeric purity of tobacco alkaloids and nicotine-like compounds. © 1996 Wiley-Liss, Inc.
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  • 59
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    Chirality 8 (1996), S. 311-315 
    ISSN: 0899-0042
    Keywords: virtual triligand chiral center ; chirality of saturated heterocycles with six-membered ring ; rules for the specification of the configuration ; desymmetrization of adamantane ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chirality of the title heterocycles is discussed considering their genesis by desymmetrization of the corresponding adamantanes. Some rules for the specification of the absolute configurations of the enantiomers (R or S) for this type of compounds are proposed. © 1996 Wiley-Liss, Inc.
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  • 60
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    Chirality 8 (1996), S. 332-340 
    ISSN: 0899-0042
    Keywords: 1-[4-[[1-(2-amino-7-methyl-4-hydroxo-6-pteridinyl)ethyl]amino]phenyl]-1-deoxy-D-ribitol ; (S)-6-[1-(4-carboxymethyllanilino)ethyl]pterin ; D(+)-neopterin ; L-biopterin ; (S)-6-(1-hydroxyethyl)pterin ; (S)-6-(1-hydroxyethyl)-7-methylpterin ; (R)-6-(1-phenoxyethyl)pterin ; stereospecific synthesis ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configuration at the C-9 of methanopterin (MPT) has been determined by comparing the circular dichroism (CD) spectra of MPT and its hydrolytic fragment, 1-[4-[[1-(2-amino-7-methyl-4-hydroxy-6-pteridinyl)-ethyl]amino]phenyl]-1-deoxy-D-ribitol (HP-1), with the CD spectra of a series of model compounds of known stereochemistry. These compounds included (S)-6-[1-(4-carboxymethylanilino)ethyl]pterin, (S-6(1-hydroxyethyl)-7-methylpterin, (S-6-(1-hydroxyethyl)pterin, (R)-6-(1-phenoxyethyl)pterin, D(+)-neopterin, and L-biopterin. From this comparison it was concluded that MPT has the R configuration at C-9 and is thus configurationally related to D(+)-neopterin, which has the S configuration at C-1. From previous work establishing the relative stereochemistry at C-6, C-7, and C-9 of N5-N10-methenyl-5,6,7,8-tetrahydromethanopterin (N5-N10-methenyl-H4MPT) as R, S, and R, respectively, it is clear that the remaining asymmetric carbons at C-6 and C-7 of H4MPT have the S and S configuration, respectively. Comparison of these latter two positions to the equivalent carbons in 5,6,7,8-tetrahydrofolate (H4folate) show that the steps involved in the biological reduction of MPT to H4MPT occur with the same stereochemical outcome as those involved in the biological reduction of folate to H4folate. © 1996 Wiley-Liss, Inc.
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  • 61
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    Chirality 8 (1996), S. 354-354 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 62
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    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 63
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    Chirality 8 (1996), S. 408-408 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 64
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    Chirality 8 (1996), S. 418-422 
    ISSN: 0899-0042
    Keywords: lipase ; resolution ; amino acids ; unnatural amino acids ; enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic amino acids were resolved by lipase via hydrolysis of their esters. Lipases (Pseudomonas lipase from Amano PS, Rhizopus lipase from Serva, and porcine pancrease lipase from Sigma) could selectively hydrolyze the L-amino acid esters in aqueous solution with high reactivities and selectivities. The effect of the structural changes in the ester moiety on the stereoselectivity of the lipases was also investigated using D,L-homophenylalanine as a model. Procedures were developed for the resolution of natural and unnatural amino acids. © 1996 Wiley-Liss, Inc.
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  • 65
    ISSN: 0899-0042
    Keywords: N-ethyl-N-methylaniline N-oxide ; chiral nitrogen centre ; flavin-containing monooxygenase ; stereoselective metabolic N-oxidation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The prochiral tertiary amine N-ethyl-N-methylaniline (EMA) is known to be stereoselectively N-oxygenated in the presence of hepatic microsomal preparations. This biotransformation is thought to be mediated predominantly by the flavin-containing monooxygenase (FMO) enzyme system. In order to characterise this reaction further, the in vitro metabolism of EMA in the presence of hepatic microsomal preparations derived from a number of laboratory species has been examined. EMA N-oxide formation was stereoselective with respect to the (-)-S-enantiomer in the presence of microsomal preparations from all species examined, with the degree of selectivity decreasing in the order of rabbit 〉 rat ∼ LACA mouse ∼ DBA/2Ha mouse 〉 guinea-pig 〉 dog. The enantiomeric composition of the metabolically derived EMA N-oxide appeared to be determined solely by the differential rate of formation of the two enantiomers as opposed to any differences in affinities for the substrate in its pro-R and pro-S conformations. The use of enzyme inhibitors, activators and inducers indicated that EMA N-oxide formation was predominantly mediated by FMO in the presence of rabbit hepatic microsomes and that these agents did not generally affect the stereochemical outcome of the biotransformation. © 1996 Wiley-Liss, Inc.
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  • 66
    ISSN: 0899-0042
    Keywords: chiral stationary phase ; enantioseparation ; resolution ; chiral recognition ; high-performance liquid chromatography ; cellulose tris(3,5-dimethylphenylcarbamate) ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) was coated on large-pore silica gels and used as a chiral stationary phase (CSP) for high-performance liquid chromatographic separation of enantiomers. The influences of pore size of silica gel, coating amount of CDMPC, coating solvent, and column temperature on chiral discrimination were investigated. CSPs prepared with a large-pore silica gel having a small surface area showed higher chiral recognition. The amount of CDMPC adsorbed on the silica gel influenced the chiral recognition of some racemates. Loading capacity of racemates increased with an increase of the amount of CDMPC supported on the silica gel, and a CSP coated with 45% CDMPC by weight can be used for both analytical and semi-preparative scale separations. The CDMPC, coated using acetone as the coating solvent, exhibited, in many cases, higher enantioselectivity than that obtained with tetrahydrofuran F as the coating solvent. © 1996 Wiley-Liss, Inc.
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  • 67
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    Chirality 8 (1996), S. 477-480 
    ISSN: 0899-0042
    Keywords: myocardial drug accumulation ; stereoselectivity ; enantiomers ; thiopental ; volume of distribution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Myocardial uptake of thiopental enantiomers by an isolated perfused rat heart preparation was examined after perfusion with protein-free perfusate. Outflow perfusate samples were collected at frequent intervals for 20 min during single-pass perfusion with 10 μg/ml racemic thiopental (washin phase) and for another 45 min during perfusion with drug-free perfusate (washout phase). (+)- and (-)-thiopental concentrations were assayed by chiral high-performance liquid chromatography. Heart rate, perfusion pressure, and electrocardiogram were also monitored. During the washin phase, there was no significant difference between the mean values of the equilibration rate constants of (+)- and (-)-thiopental enantiomers (0.44 ± 0.07 min-1 and 0.43 ± 0.09 min-1, respectively, P 〉 0.05). Mean volumes of distribution of (+)- and (-)-thiopental enantiomers were similar (6.34 ± 1.20 and 6.45 ± 1.29 ml/g for the washin phase and 7.22 ± 0.71 and 7.47 ± 0.81 ml/g for the washout phase, respectively, P 〉 0.05). This indicates that tissue accumulation of thiopental enantiomers in the isolated perfused rat heart was not stereoselective. Uptake of thiopental by the heart was perfusion flow rate-limited and independent of capillary permeability. These findings suggest that myocardial tissue concentration of racemic thiopental should be an accurate predictor of myocardial drug effect. © 1996 Wiley-Liss, Inc.
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  • 68
    ISSN: 0899-0042
    Keywords: fluorogenic alkyldiacylglycerols ; albumin glycerolipid interaction ; microbial lipases ; lipoprotein lipase ; cutinase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new type of fluorogenic alkyldiacyl glycerols was synthesized and used as fluorogenic substrates for the analysis of lipase activities and stereoselectivities. These compounds contain perylene as a fluorophore and the trinitrophenylamino (TNP) residue as a quencher. Both substituents are covalently bound to the ω-ends of the sn-2 and sn-1(3) acyl chains, respectively. Upon glycerolipid hydrolysis, the residues are separated from each other thus allowing determination of lipase activity by the continuous increase in fluorescence intensity which is caused by dequenching. Using enantiomeric pairs of these compounds, we were able to analyze lipase stereoselectivity depending on the reaction medium. Mixtures of enantiomeric fluorogenic alkyldiacyl glycerols, selectively labelled with pyrene or perylene as fluorophores, can be used for a dual-wavelength “stereoassay” of lipases. Since absorption and emission maxima of both labels are clearly separated, hydrolysis of the respective enantiomeric substrates can be determined simultaneously, and the difference in the rates of hydrolysis can be taken as a parameter for the stereopreference of a lipase. Hydrolysis rates measured with perylene-substituted lipids are generally lower than those obtained with the pyrene analogs. Thus, with a mixture of perylene and pyrene-substituted lipids, we observe a higher apparent stereoselectivity of lipases since we measure a combination of stereo- and substrate selectivity. In the presence of albumin, all microbial lipases tested so far exhibit stereopreference for the sn-1 glycerol position. In our assay, the apparent stereoselectivities are highest if in the presence of albumin, the sn-1 position carries pyrene and the sn-3 position is substituted with perylene. The lipase stereoselectivity assay described here requires the simultaneous measurement of the fluorescence intensities at two different wavelengths in a single cuvette and can thus be carried out using existing and cheap instrumentation that was developed for the fluorimetric analysis of Ca++ concentrations. © 1996 Wiley-Liss, Inc.
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  • 69
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    Chirality 8 (1996), S. 511-517 
    ISSN: 0899-0042
    Keywords: enantiospecific bioanalysis ; enantiomers ; β-cyclodextrin ; plasma ; protein binding ; isomerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: rac-Simendan, (±)-(R, S)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)-phenyl]hydrazono]propanedinitrile, and the levorotatory enantiomer levosimendan, are drug candidates intended for the treatment of congestive heart failure. An enantiospecific high-performance liquid chromatographic (HPLC) method suitable for determination of the ratio of the enantiomer concentrations in blood plasma samples was developed. Direct resolution of the enantiomers was achieved by using a chiral β-cyclodextrin stationary phase in reversed phase mode. With an eluent containing 24-33% of methanol in a 0.5% (v/v) triethylammonium acetate buffer, pH 6.0, and a flow rate of 1 ml/min, a resolution (1.2-1.6) adequate for the determinations was achieved. By using UV detection, the relative concentration of the enantiomers in plasma was assessed down to 10 ng/ml. For the racemate, the results indicated a slightly enantioselective disposition and plasma protein binding in rat, dog, and man. The pure enantiomer, levosimendan, was found not to isomerize in vivo. © 1996 Wiley-Liss, Inc.
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  • 70
    ISSN: 0899-0042
    Keywords: chiral capillary electrophoresis ; chiral micelle ; phenoxy acid herbicides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral alkylglucoside surfactant, namely n-octyl-β-D-maltopyranoside (OM), was evaluated in the enantiomeric separation of phenoxy acid herbicides. The enantiomeric resolution of the phenoxy acid herbicides could be manipulated readily by adjusting the surfactant concentration, ionic strength, pH, the percent organic modifier and separation temperature. The optimum surfactant concentration needed for maximum enantiomeric resolution varied among the different analytes, and was an inverse function of the hydrophobicity of the phenoxy acid herbicides with the most hydrophobic solute requiring less surfactant concentration for attaining a baseline enantiomeric resolution. Due to the ionic nature of the phenoxy acid herbicides, increasing the pH of the running electrolyte increased the degree of ionization of the acidic herbicides thus decreasing their association with the chiral micelles and in turn their enantiomeric resolution. Increasing the ionic strength of the running electrolyte seems to enhance both the solubilization of the solute in the micelle and the chiral interaction of the solute with the micelle with a net increase in enantiomeric resolution. The percent of added methanol had a varying effect on the resolution of the various enantiomers in the sense that it enhanced the enantiomeric resolution for the most hydrophobic solutes while it decreased the enantiomeric resolution for the weakly hydrophobic ones. Thermostating the capillary column at subambient temperature improved enantiomeric resolution. © 1996 Wiley-Liss, Inc.
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  • 71
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    Chirality 8 (1996), S. 201-206 
    ISSN: 0899-0042
    Keywords: carbenicillin ; stereoselective ; binding ; HSA ; interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of carbenicillin (CBPC) epimers to human serum albumin (HSA) was found to be stereoselective. Epimer-epimer interaction was also observed in the binding to HSA. There were at least three binding sites on HSA for CBPC epimers, one of which (stereoselective site) was more in favor of S-CBPC than R-CBPC. At the stereoselective site, the binding constant of S-CBPC was approximately 4-fold greater than that of R-CBPC. The affinities to other binding sites (non-stereoselective sites) were similar between the epimers, and the affinity of S-CBPC of the non-stereoselective sites was much smaller than that for the stereoselective site.R-CBPC and S-CBPC appeared to displace each other at all the binding sites, i.e., the binding of the epimers was competitive at the non-stereoselective sites as well as at the stereoselective site. By using site marker ligands, it was revealed that CBPC epimers may bind to Site I (warfarin binding site), but not to Site II (diazepam binding site). A binding model with an assumption of competitive interactions at all the binding sites simulated the binding characteristics of CBPC epimers fairly well. © 1996 Wiley-Liss, Inc.
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  • 72
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    Chirality 8 (1996), S. 214-223 
    ISSN: 0899-0042
    Keywords: oxazepam ; racemization ; reversed-phase and chiral stationary phase high-performance liquid chromatography ; circular dichroism spectropolarimetry ; mass spectrometry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric and racemic oxazepam (OX), 3-O-methyloxazepam (MeOX), and 3-O-ethyloxazepam (EtOX) were used to study racemization, heteronucleophilic, and homonucleophilic substitution reactions in anhydrous acidic methanol and ethanol. Kinetics of racemization and nucleophilic substitution reactions in nondeuterated and deuterated solvents were determined by circular dichroism spectropolarimetry, chiral stationary phase high-performance liquid chromatography (HPLC), reversed-phase HPLC, and mass spectrometry. Several reactions occurred when (S)-OX, for example, was dissolved in acidic methanol: (1) (S)-OX itself underwent spontaneous racemization, (2) the 3-hydroxyl group of (S)-OX was stereoselectively substituted by the methoxy group of methanol to form MeOX enriched in (S)-MeOX, (3) the 3-methoxy group of (S)-MeOX was stereoselectively substituted by the methoxy group of methanol to form MeOX enriched in (S)-MeOX, and (4) the 3-methoxy group of (R)-MeOX was stereoselectively substituted by the methoxy group of methanol to form MeOX enriched in (R)-MeOX. Repetitive reactions 3 and 4 eventually resulted in a racemic MeOX. Similar reactions occurred for an enantiomeric OX in acidic ethanol. © 1996 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
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  • 73
    ISSN: 0899-0042
    Keywords: drug development ; enantiomers ; HPLC ; in vitro metabolism ; mass spectrometry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In vitro metabolism models have been used to determine the relative metabolic stability of novel 2-aminotetralin analogues for the treatment of CNS diseases. Few of these new compounds had been produced as stereochemically pure materials and the achiral analytical techniques, used initially, measured the average metabolic clearance of the two enantiomers of the racemic mixtures.A chiral HPLC assay, using a Chiral AGP column, was developed for two of these racemic analogues and was used to measure the clearance of the enantiomers from suspensions of freshly isolated rat hepatocytes.Robust separations were obtained for both compounds and a number of metabolic products. The enantiomers of only one analogue were subject to different rates of metabolism. The extent of the difference was dependent upon the initial starting concentration of the incubation. The identity of certain metabolites was investigated using LC/MS. The enantioselectivity appears to have arisen from the restricted hydroxylation of one analogue compared to that of the other. © 1996 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
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  • 74
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 291-293 
    ISSN: 0899-0042
    Keywords: coenzymes ; 1H NMR 13C NMR ; diastereomers ; gas chromatograpy-mass spectrometry ; methanofuran ; Methanobacterium thermoautotrophicum strain ΔH ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3,4,6-Hexanetetracarboxylic acid was first identified as a natural product during the structural characterization of methanofuran, one of several coenzymes involved in methanogenesis. A combination of high resolution 1H NMR, 13C NMR, and gas chromatography-mass spectrometry has been used to establish that the naturally occurring diastereomer of 1,3,4,6-hexanetetracarboxylic acid in methanogenic Archaea is meso. © 1996 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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  • 75
    ISSN: 0899-0042
    Keywords: β-methylaspartase ; alkylfumarates ; (2S,3S)-3-methylaspartic acid ; (2S,3S)-3-isopropylaspartic acid ; bioconversion ; (3S,4R)-benzyl 3-alkylmalolactonates ; poly[benzyl-β-(2S,3S)-3-alkylmalates] ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (2S,3S)-3-methyl- and 3-isopropylaspartic acids were synthesized by bioconversion of the corresponding alkylfumarates (mesaconate and 3-isopropylfumarate) using β-methylaspartase from cell-free extracts of Clostridium tetanomorphum. Optically pure (2S,3S)-3-alkylaspartic acids were transformed in several steps to benzyl (3S,4R)-3-alkylmalolactonates without any racemization of the two chiral centers. These optically active α,β-substituted-β-lactones were polymerized by anionic ring opening polymerization yielding optically active semi-crystalline polyesters. 13C NMR analysis of poly[benzyl β-3-isopropylmalate] in CDCl3 has shown that only the iso-type stereosequence is present in the polymer, indicating that the macromolecular chain is constituted by the only units of benzyl β-(2S,3S)-3-isopropylmalate monomer. The polymerization reaction was done without any racemization of the two stereogenic centers as in the case of benzyl (3S,4R)-3-methylmalolactonate. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 76
    ISSN: 0899-0042
    Keywords: enantiomeric separation ; chiral recognition ; derivatized cyclodextrin ; supercritical fluid chromatography ; drug analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric separation of a variety of drugs and related compounds was achieved on an (S)-naphthylethylcarbamoylated-β-cyclodextrin (S-NEC-CD) chiral stationary phase (CSP) using sub- and supercritical fluid chromatography (SFC). Compounds previously resolved on native or derivatized cyclodextrin CSPs in liquid chromatography (LC) using reversed phase or polar organic mobile phase modes could be resolved in SFC using a simple carbon dioxide/methanol eluent. Resolution of cromakalim, which is not possible on the S-NEC-CD column in LC, was readily accomplished in SFC. The importance of modifier, temperature, and pressure was assessed in relation to retention, selectivity, and resolution. The nature of the modifier and the modifier concentration were found to be crucial parameters. © 1996 Wiley-Liss, Inc. Contribution of the National Institute of Standards and Technology. Not subject to copyright.
    Additional Material: 5 Ill.
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  • 77
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    Chirality 8 (1996), S. 351-351 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 78
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 353-353 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 79
    ISSN: 0899-0042
    Keywords: analgesic ; cognition enhancer ; ACh releaser ; enantioselectivity ; stereospecific synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of two α-tropanyl esters, SM21 (1) and PG9 (2), derived from (+)-R-hyoscyamine, that act by increasing the central cholinergic tone, were obtained by esterification after resolution of the corresponding racemic acids [(-)-S-1, (-)-R-2 and (+)-S-2] and by stereospecific synthesis [(+)-R-1]. Their analgesic and cognition-enhancing activities were tested in mice and their ACh-releasing properties determined on rat parietal cortex. These compounds show enantioselectivity in analgesic and cognition-enhancing tests on mice, the eutomers being the isomers which possess the same spatial arrangement of the groups on the chiral atom as (+)-R hyoscyamine [(+)-R-SM21, (+)-S-PG9]. The ACh-releasing effect of the enantiomers of SM21 in rats is in agreement with the results in mice, while PG9 enantiomers do not show any appreciable enantioselectivity in this test. On the basis of the different effects of the 5-HT4 antagonist SDZ 205557 on analgesia induced by the enantiomers of 1 and 2 and by (+)-R-hyoscyamine and the α-tropanyl ester of 2-phenylpropionic acid 3, a mechanism of action is proposed for this class of compounds. © 1996 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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  • 80
    ISSN: 0899-0042
    Keywords: circular dishroism (CD) study ; exciton coupling ; azastilbene chromophore ; absolute conformation of coupled chromophores ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CD study of the chiral enamines 4-9 revealed the presence of the azastil-bene-like chromophore, and exciton coupling between this chromophore (A) and aromatic chromophore B. Coupled excitons in 5 and 8 suggest M (-) absolute conformation between chromophores A and B. © 1996 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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  • 81
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 305-310 
    ISSN: 0899-0042
    Keywords: Saccharomyces cerevisiae ; oxidoreductase enzymes ; asymmetric β-keto-ester reduction ; enzymatic kinetic resolution ; chiral 2-allyl-2-carboethoxy-cyclopentanol ; 2-oxabicyclo-[3.3.0]-octane ; 2-oxabicyclo-[4.3.0]-nonane derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective reduction of 2-allyl-2-carboethoxy-cyclopentanone (2) was accomplished in high enantiomeric excess ( 〉 99%), using baker's yeast in the presence of CuO, to obtain the (+)-2-allyl-2-carboethoxy-cyclopentanol derivative (6). This methodology also provides an entry to corresponding β-keto ester (-)-(2), representing an important strategy to prepare chiral functionalized 2-oxabicyclic[3.3.0]octane and 2-oxabicyclic[4.4.0]nonane derivatives, useful synthons to access new bioactive compounds. © 1996 Wiley-Liss, Inc.
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  • 82
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 83
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 356-356 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 84
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 357-363 
    ISSN: 0899-0042
    Keywords: excited state ; CPL spectroscopy ; CD spectroscopy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 85
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 364-371 
    ISSN: 0899-0042
    Keywords: antipsoriatic agent ; 10-(3-chlorophenyl)-6,8,9,10-tetrahydrobenzo[b][1,8]naphthyridin-5(7H)-one ; stereogenic axis ; interconversion half-lives ; dynamic HPLCs ; SIMUL ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The antipsoriatic 10-(3-chlorophenyl)-6,8,9,10-tetrahydrobenzo[b][1,8] naphthyridin-5(7H)-one, Sch 40120, is chiral only because it lacks planarity and possesses a stereogenic axis. It comprises short-lived, interconverting atropisomeric enantiomers distinguished by the chlorine substitutent. The atropisomers form diastereomeric complexes with the shift reagent (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol, which were detected by 1H NMR spectroscopy. Liquid chromatography on an ovomucoid chiral column isolated each enantiomer from the racemic mixture. Re-injections of the separated enantiomers onto the same column held constant at 10°C established that each enantiomer formed the other. Under identical chromatographic conditions, both stereoisomers independently recreated the racemic mixture. The calculated enantiomer half-life lasted 1.6 min at the physiological temperature of 37°C. Simulations of dynamic liquid chromatograms acquired with a chiral stationary phase indirectly yielded values of the half-lives. The chromatograms were modeled with the computer program SIMUL. Also determined were the rate constants for enantiomerization and the corresponding Gibbs free energies of activation, all at varying temperatures. At 37°C, the rate constant and activation energy respectively equaled 0.213 min-1 and 21.6 kcal mole-1. An Arrhenius plot was linear. The intractably brief life spans necessitated development of the racemic drug, rather than advancement of one enantiomer only. The pharmacological, biological, and chemical consequences of molecular asymmetry inherent to the drug were therefore nil. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 86
    ISSN: 0899-0042
    Keywords: thalidomide enantiomers ; TNF-α ; lipopolysaccharide ; immunomodulation ; optically pure drugs ; stereochemistry ; structure activity relations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The question whether the immunomodulating activity of rac-thalidomide resides in either the (-)-(S)- or the (+)-(R)-enantiomer was addressed by synthesis and separation of pure enantiomers of thalidomide-analogues which carry a methyl-group at the asymmetric carbon atom and are thus prevented from racemization. The effect of the pure enantiomers of the thalidomide-analogues and also of the enantiomers of thalidomide on relapse of TNF-α was tested in vitro by using stimulated peripheral mononuclear blood cells. Both enantiomers of thalidomide inhibited the release of TNF-α equally well at low concentrations (5 and 12.5 μg/ml) but at higher concentrations (25 and 50 μg/ml) there was a weak but statistically significant selectivity towards the (-)-(S)-enantiomer. In the case of the configuration-stable thalidomide-analogues there was a very pronounced and statistically significant enantioselectivity towards the (S)-form even at lower concentrations (≥5 μg/ml). The (S)-enantiomers of the thalidomide-analogues differed in their inhibitory potency from (-)-(S)-thalidomide suggesting that the introduction of the methyl-group increases the TNF-α-inhibitory activity while the reduction of one of the carbonyl-functions in the glutarimide-moiety to a methylene-group decreases activity. The effect of these small molecular alterations on activity and the enantioselectivity towards the (S)-enantiomers may indicate that thalidomide and its analogues directly interact with one or several cellular target-proteins. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 87
    ISSN: 0899-0042
    Keywords: flurbiprofen ; β-cyclodextrin ; chiral discrimination ; nuclear magnetic resonance ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sodium salts of (+)-(S)- and (-)-(R)-2-(2-fluoro-4-biphenylyl)propionic acid (flurbiprofen, FBP) form 1:1 inclusion complexes with β-cyclodextrin (β-CD) having different association constants. Proton selective relaxation rate measurements revealed the existence of superior aggregated forms for both complexes (+)-FBP/β-CD and (-)-FBP/β-CD; information about their stereochemistry has been obtained by 2D ROESY analysis. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 88
    ISSN: 0899-0042
    Keywords: capillary zone electrophoresis ; axially chiral biphenyls ; energy barrier ; cyclodextrin derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new technique is presented for the investigation of the rotational energy barrier of axially chiral biphenyls, based on capillary zone electrophoresis using cyclodextrin derivatives as chiral selectors. Only minute amounts are required for the investigation of dynamic processes with energy barriers of 100-130 kJ/mol. The influence of the chiral selector on the conformational stability of atropisomers can be determined separately for each enantiomer. Additionally, segmentation of the capillary into different buffer zones allows us to exclude any influence of the chiral selector on the rotational energy barrier. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 89
    ISSN: 0899-0042
    Keywords: chirality of agonist-efficacy ; β-adrenoceptor ; stereoselective change of receptor ; epinephrine enantiomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The presence of β-adrenoceptor in a rat lung membrane preparation was confirmed by stereoselective competition of enantiomers of epinephrine with labeled iodocyanopindolol. The receptor-rich protein fraction, when combined with the pharmacologically active (-)-epinephrine, exhibited specific changes in the 205-220 nm region of circular dichroism spectra, indicating that the receptor helices may be perturbed. The (+)-epinephrine combined with the lung protein produced little or no change of the spectra. Bovine serum albumin, when combined with either enantiomer of epinephrine, produced nonstereoselective alterations of the spectra. Thus, the data provide important evidence for the higher intrinsic pharmacologic activity of the natural (-)-epinephrine over the unnatural (+)-enantiomer. © 1996 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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  • 90
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 83-88 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Balance of Transesterification of Natural Oils to BiodieselTheoretic relations were derived, which are necessary for the calculation of the optimal course of transesterification of plant oils and animal fats to form ecological products such as biodiesel fuel or lubricants. Advantages of one- and two-step transesterification courses are discussed. The relations derived were practically used for the model system rape oil-methanol-potassium hydroxide.
    Additional Material: 5 Ill.
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  • 91
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 92
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 1,2-diaminoethane (5) with malonic acid derivatives (6, 7, 8, 10) gives oligo- and polymers that were characterized by MALDI-ToF mass spectrometry. Literature reports that claimed the formation of the title compound in these reactions were critically evaluated and could not be confirmed.
    Additional Material: 2 Ill.
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  • 93
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 146-150 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Dibenzo-tetrathiafulvalenes Containing 1,3-Dithiol-2-yl-phosphonic Ester Structures1,3-Dithiol-2-ylphosphonate esters (3a-d) with a dibenzo-tetrathiafulvalene unit were synthesized directly from trialkylphosphite and 6,6′-dioxo- (2a, c) and 6,6′-dithioxo-4,4′,8,8′-tetrakis(alkylthio)-2,2′-bi-1,3,5,7-tetrathia-s-indacenylidenes (2b, d). The influence of the type of trialkylphosphite, of the reaction temperature and the solvent on the regioselectivity of the reaction was studied. In toluene the tristetrathiafulvalene (4c) was exclusively obtained from 2c.
    Additional Material: 1 Tab.
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  • 94
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 165-168 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several diesters of dicarboxylic acids with pendant sterically hindered amines of the piperazine type were prepared from α-bromo- and α,α′-dibromosubstituted dicarboxylic acid esters by reactions with 14,16-dioxo-7,15-diaza-dispiro[5,1,5,3]hexadecane and 7,15-diazadispiro [5,1,5,3] hexadecane.
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  • 95
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 320-326 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Chiral Multifunctional Polycyclic Furanoids via Annulation of PyranosidesA new strategy to chiral polyfunctionalized furanoids from 2, 3, 4, 7, 8, 9, 11, 12, 14, 15, 17 and 18 from cis-orientated epoxypyranosetriflates 1 and 6 and dianions of β-dicarbonyl compounds 10, 13 and 16 is described. The control of the substituents in the satellite ring through acid catalysis is discussed.
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  • 96
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of Bisvinamidinium Salts of 1,1-Dioxo-1,2-thiazine-6-aldehydes with Hydroxylamine to Substituted Pyrido[4,3-e]-1,2-thiazine-1,1-dioxidesBerichtigung der Struktur vom Typ 3 in [2]The formylation of 2-aryl-3,5-dimethyl-1,1-dioxo-1,2-thiazines with POCl3/DMF leads to the thiazine-6-aldehydes 1 and to the bis-vinamidinium salts 2. The reaction of 2a,b with hydroxylamine results in the formation of the pyrido-thiazine-N-oxides 5a,b, which give with PCl3 the 5-cyano-3-isoxazol-4-yl-pyrido[4,3-e]thiazines 6a,b. The pyridothiazines 9a and 10a are obtained by base-induced opening of the isoxazolyl-ring in 5a and 7a to the cyanoformylmethyl group. The compounds 6a and 7a were characterized by X-ray structure analysis.
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  • 97
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 386-389 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 98
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis-(1-chloro-3-phenoxy-prop-2-yl)-sulfanes - Nucleophilic Displacement and Regiochemistry. Separation and Assignment of Diastereomers. Synthesis of Diastereomerically Pure TrithiacyclesThe title compounds 1 were substituted by a series of O-, N- and S-nucleophiles (H2O solvolysis, AgOAc, NaN3, KSCN, NaSPh, thiourea). A strong tendency to β-elimination of HCl depending on the kind of the attacking nucleophile was found. In most cases no regioisomerization could be detected in the isolated products of the nucleophilic displacement. Best results were obtained with sulfur nucleophiles. The separation of the diastereomeric mixture of the p-kresyl derivative 1b into the individual diastereomers 1bA and 1bB in a preparative scale was achieved. These 3-thia-1,5-dichlorides and several products of substitution could be assigned to the meso- or (±)-form by examination of the stereochemistry and symmetry of the corresponding sulfoxides.The 1,5-dimercapto derivatives 8 are convenient as structural units for the synthesis of diastereomerically pure cis- or trans-disubstituted trithiacycles e.g. 15bA, 15bB. The (±)-form of the 4,6-disubstituted 2,5,8-trithia[9]-(2,6)-pyridinophane 16bA was characterized by X-ray crystal structure determination.
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  • 99
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 374-375 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NMR-Spectroscopic Investigations of Chiral Carboxylic Acids via Their Tributyltin Derivatives
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  • 100
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    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 383-385 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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