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  • Articles: DFG German National Licenses  (6)
  • antimalarial agents  (2)
  • column liquid chromatography  (2)
  • stereoselectivity  (2)
  • 1
    Electronic Resource
    Electronic Resource
    The stereochemical resolution of the enantiomers of aspartame on an immobilized α-chymotrypsin hplc chiral stationary phase: The effect of mobile-phase composition and enzyme activity (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 32-37 
    Details
    ISSN: 0899-0042
    Keywords: aspartame stereoisomers ; chiral separations ; column liquid chromatography ; chymotrypsin on silica ; binding sites ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselective and diastereoselective resolutions of the stereoisomers of Nα-aspartyl-phenylalanine 1-methyl ester (APME) have been accomplished on an HPLC chiral stationary phase based upon α-chymotrypsin (the ACHT-CSP) with observed enantioselectivities (α1) for the DL-/LD-enantiomers of as high as 29.17 and for the DD-/LL-enantiomers of as high as 28.97. In addition, the effect on the chromatographic retention of the APME stereoisomers of the activity of the ACHT and the composition of the mobile phase - structure of the anionic component, molarity, and pH - have been studied. The results of this study suggest that the aspartyl moiety and/or the aspartyl-phenylalanine amide linkage play key roles in the observed enantioselectivity; the APME stereoisomers containing L-phenylalanine, i.e., DL- and LL-APME, bind at a different site in the ACHT molecule (the L-Phe site) than the APME stereoisomers containing D-phenylalanine (the D-Phe site); and the observed enantioselectivity is a measure of the difference in the binding affinities at the two sites rather than the consequence of differential affinities at a single site.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020105
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Enantioselective chromatography of the antimalarial agents chloroquine, mefloquine, and enpiroline on a α1 -acid glycoprotein chiral stationary phase: Evidence for a multiple-site chiral recognition mechanism (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 30-35 
    Details
    ISSN: 0899-0042
    Keywords: chiral liquid chromatography ; α1 -acid glycoprotein ; antimalarial agents ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of mobile phase pH and dimethyloctylamine (DMOA) on the retention (k') and stereoselectivity (α) of antimalarial agents mefloquine, enpiroline, and chloroquine on the α1-acid glycoprotein chiral stationary phase (AGP-CSP) was investigated. An increase of k' with increasing pH was observed while the effect on α was a function of the solute. The magnitude and direction of changes induced by DMOA depended on pH and the structure of the solute.The results of this study are consistent with a change of the conformation of the AGP between pH 5 and 7. At pH 7, the effect of DMOA on mefloquine was relatively well described by a competitive displacement from one enantioselective site. The effect on chloroquine and enpiroline suggests a multiple-site mechanism in which both competitive and allosteric interactions are involved.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530040108
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Chiral resolution of some antimalarial agents by sub- and supercritical fluid chromatography on an (S)-naphthylurea stationary phase (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 173-180 
    Details
    ISSN: 0899-0042
    Keywords: (S)-naphthylurea chiral stationary phase ; subcritical fluid chromatography ; supercritical fluid chromatography ; antimalarial agents ; enantiomeric separations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The behavior of mefloquine, halofantrine, enpiroline, quinine, quinidine, chloroquine and primaquine is studied by subcritical fluid chromatography on a (S)-naphthylurea column (250 mm × 4.6 mm ID) with a subcritical mobile phase composed of carbon dioxide, methanol and triethylamine (flow rate of 3 ml/min). Except for primaquine and chloroquine, each enantiomer was separated at a temperature between 40 and 60°C, and at a pressure below 15 MPa. A 98/2, v/v CO2/methanol 0.1% triethylamine mixture allowed the separation of halofantrine enantiomers while the enantiomers of the more polar metabolite (N-desbutylhalofantrine) were separated with a 80-20 v/v mixture as used for mefloquine, enpiroline, quinine and quinidine. The influence of temperature, pressure and of the nature of the mobile phase is discussed. © 1993 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050313
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The stereochemical resolution of enantiomeric free and derivatized amino acids using and hplc chiral stationary phase based on immobilized α-chymotrypsin: Ciral separation due to solue structure or enzyme activity (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 38-44 
    Details
    ISSN: 0899-0042
    Keywords: column liquid chromatography ; chiral separations ; chymotrypsin on silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical separation of free and derivatized amino acids on active α-chymotrypsin bonded to silica is governed by two mechanisms based on the structure of the solutes or on the enzymatic activity of the enzyme. Te deactivation of the hydrolytically active site of the enzyme demonstrated that a significant portion of the retention on this support is due to hydrophobic interactions at other sites. These sites appear to be stereoselective for the ester derivatives of amino acids but not for the other studied solutes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010109
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Immobilized serum albumin: Rapid HPLC probe of stereoselective protein-binding interactions (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 263-268 
    Details
    ISSN: 0899-0042
    Keywords: protein binding ; stereoselectivity ; immobilized human serum albumin ; HPLC chiral stationary phase ; chiral drugs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A human serum albumin-based HPLC chiral stationary phase (HSA-CSP) has been examined as a tool to investigate binding of chiral drugs to HSA and drug-drug protein-binding interactions. Rac-oxazepam hemisuccinate (OXH) was used as a model compound and the chromatographic retention (k′) of its enantiomers was determined after addition of displacers to the mobile phase. Compounds known to bind at the same site as OXH and at different sites were tested for their displacing capacities. Competitive binding interactions between the OXH enantiomers and displacers in the mobile phase were reflected by decreases in the k′s of (R)- and (S)-OXH. The results indicate that retention on the HSA-CSP accurately reflects binding to native HSA and the technique can determine enantioselective and competitive binding interactions at specific sites on HSA. The HSA-CSP was also able to recognize separate binding areas for (S)- and (R)-OXH.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020412
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Stereoselective distribution of hydroxychloroquine in the rabbit following single and multiple oral doses of the racemate and the separate enantiomers (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 337-346 
    Details
    ISSN: 0899-0042
    Keywords: hydroxychloroquine ; enantiomers ; stereoselectivity ; distribution ; interconversion ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxychloroquine (HCQ) stereoselective distribution was investigated in rabbits after 20 mg/kg po of racemic-HCQ (rac-HCQ) and 20 mg/kg po of each enantiomer, 97% pure (-)-(R)-HCQ and 99% pure (+)-(S)-HCQ. Concentrations were 4 to 6 times higher in whole blood than in plasma. Melanin did not affect plasma and whole blood levels since concentrations did not differ between pigmented and nonpigmented animals. After single and multiple doses of the separate enantiomers, only 5-10% of the antipode could be measured, in blood or plasma. Therefore, there was no significant interconversion from one enantiomer into the other. Following rac-HCQ, plasma (+)-(S)-levels always surpassed (-)-(R)-ones while in whole blood, (-)-(R)-HCQ concentrations were always the highest. When the enantiomers were administered separately, blood concentrations achieved after (-)-(R)-HCQ were higher, especially after multiple doses. These observations suggest that (-)-(R)-HCQ is preferentially concentrated by cellular components of blood. This enantioselective distribution of HCQ could be secondary to a stereoselective protein binding to plasma proteins, although a more specific binding of (-)-(R)-HCQ to blood cells cannot be ruled out. Since in whole blood (-)-(R)-HCQ is retained in cellular components, metabolism would favour the more available (+)-(S)-enantiomer. © 1994 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530060418
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    Paper (German National Licenses)
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