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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 78-83 
    ISSN: 0899-0042
    Keywords: (-)-(S)-scopolamine ; (-)-(S)-hyoscyamine ; racemization ; hydrolysis ; α-cyclodextrins ; β-cyclodextrins ; γ-cyclodextrins ; β-cyclodextrin derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Because of the constantly increasing demand for optically pure drugs it is of great importance to elucidate factors affecting stereochemistry, in order to provide a stable formulation with a high chiral quality of the desired isomer. Therefore, the effects of cyclodextrins (CyDs) and their alkylated and hydroxyalkylated derivatives on racemization and hydrolysis of (-)-(S)-hyoscyamine and (-)-(S)-scopolamine were examined kinetically and spectroscopically (NMR). Direct methods, based on a chiral and achiral chromatographic phase system, were used to determine their degradation products and enantiomer composition during stability tests. All different CyDs, except α-CyD, retarded racemization and hydrolysis. The inclusion of the drug substances in CyDs inhibits the attack of hydroxyl ions and/or water molecules and thus retards the racemization and hydrolysis. The racemization of the tropic acid alkaloids is dependent on the pH and temperature. NMR studies were used to evidence the formation of a soluble 1:1 complex in aqueous solution. © 1993 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 370-374 
    ISSN: 0899-0042
    Keywords: (+)-chlorthalidone ; racemization ; pH profile ; influence of liposomes ; reaction kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The extent of racemization of (+)-chlorthalidone as a function of pH is examined. The minimum of the log K/pH curve is pH 3. The reaction mechanism of inversion is postulated to involve a carbenium cation over the entire pH range and a ring opening reaction in the alkaline range. The influence of liposomes on the inversion rate is also studied, retardation of the racemization rate being observed with increasing liposome concentration. A model of drug distribution between liposome phase and aqueous phase based on the Nernst distribution principle is presented and reaction kinetic aspects are considered. © 1993 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 3
    ISSN: 0899-0042
    Keywords: zopiclone ; chiral liquid chromatography ; enantioseparation ; fractional crystallization ; cyclopyrrolone ; benzodiazepine receptor binding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report the preparative separation of rac-zopiclone using malic acid as the resolving agent. Furthermore, two different methods for the analytical determination of zopiclone enantiomers by HPLC on chiral stationary phases are described. The benzodiazepine receptor binding of the isolated enantiomers was investigated. Half-maximal inhibitory concentrations of (+)- and (-)-zopiclone were 21 or 1,130 nmol/liter, respectively, indicating a more than 50 times higher affinity of the (+)-enantiomer toward the receptor. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0899-0042
    Keywords: thalidomide enantiomers ; HPLC ; hydroxylated metabolites ; mass spectrometry ; EM 12 ; in vitro metabolism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselective metabolism of the former sedative thalidomide and the metabolism of its analogue EM 12 were studied in vitro with liver homogenates. In our study we focused on hydroxylated nonhydrolyzed metabolites of thalidomide. An analytical HPLC method was developed to determine these metabolites directly. The investigations showed a highly stereoselective biotransformation of thalidomide. 5-Hydroxy thalidomide was preferentially formed by (-)-(S)-thalidomide, whereas (+)-(R)-thalidomide was metabolized to two hitherto unknown compounds (Met A and B). Mass spectrometry of these metabolites Met A and B indicated that oxidation or hydroxylation took place in the glutarimide moiety. Biotransformation studies with the more stable thalidomide analogue EM 12 revealed four new metabolites (Met C—F) whose quantities differed in the selected liver homogenate. © 1994 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 5
    ISSN: 0899-0042
    Keywords: configurational stability ; pH ; temperature ; ionic strength ; phosphate buffer concentration ; plasma protein affinity ; native cyclodextrins ; cyclodextrin derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational stability of (+)- and (-)-diethylpropion [(+)- and (-)-2-(diethyl)-1-phenyl-1-propanone or (+)- and (-)-DEP] was investigated systematically from chemical, pharmaceutical, and pharmacological aspects. The enantiomeric ratio was monitored directly with a recently developed stability-indicating enantioselective HPLC method.In aqueous solutions, the rate of racemization increased non-linearly with increasing pH and with increasing phosphate buffer concentration. The racemization rate showed a positive slope with increasing temperature and decreasing ionic strength.The racemization rates of (+)- and (-)-DEP in the presence of cyclodextrins (CDs) did not differ significantly. CDs that were added to (+)- and (-)-DEP in a molar ratio 5:1 showed the following effects after dissolution in 10 mM phosphate buffer (final pH 6.7): sulfobutyl ether-β-CD (SBE-β-CD) and methylated-β-CD (Me-β-CD) retarded racemization; whereas hydroxypropyl-β-CD (HP-β-CD), acetyl-γ-CD (Ac-γ-CD), acetyl-β-CD (Ac-β-CD), γ-CD, and β-CD showed a weak destabilising effect. In contrast to the described CDs, α-CD distinctly accelerated the rate of racemization.The configurational stability of (+)- and (-)-DEP was also studied under physiological conditions. The half-life of racemization in heparinised human plasma was for both enantiomers determined to be approximately 23-25 min.In phosphate buffer (10 mM, pH 7.4), rac-DEP showed a high, but unselective affinity towards human α1-acid glycoprotein (orosomucoid) immobilised on silica (Chiral AGP).The rate of racemization of the free base of (-)-DEP dissolved in organic solutions generally increases with the polarity of the solvating agent. Chirality 10:307-315, 1998. © 1998 Wiley-Liss, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 109 (1976), S. 1967-1975 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigation of Chromatographic Resolutions of Racemates, VI. Polymeric Amino Acid Derivatives as Optically Active AdsorbensStarting with optically active amino acids, the polyacrylamides 3a-h, 5a-d and 6a, b the polymethacrylamides 8a-c and the polyacrylic ester 6f were synthesized. The separation efficiencies of these polymers were determined by chromatography of racemic mandelic acid and mandelamide, respectively. The best separations of the enantiomers of both racemates were observed on the phenylalanine derivatives 3e and 5a.
    Notes: Die Polyacrylamide 3a-h, 5a-d und 6a, b die Polymethacrylamide 8a-c und der Polyacrylsäureester 6f wurden aus optisch aktiven Aminosäurederivaten hergestellt und auf ihre Trennwirkung durch Chromatographie racem. Mandelsäure sowie racem. Mandelamids geprüft. Die beste Trennung der Enantiomeren beider Racemate wurde an den Phenylalaninderivaten 3e und 5a beobachtet.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 4616-4619 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation, Optical Purity and Configuration of the Enantiomers of FlecainideThe chiral antiarrhythmic drug flecainide (rac-1) was resolved by fractional crystallization of the diastereomeric salts with optically active mandelic acid. Derivatization with (+)-1-phenylethyl isocyanate and analytical separation of the diastereomers 3 by HPLC on silica gel confirmed the optical purity of the enantiomers. CD-Spectra of the N-chloro derivatives established the absolute configuration: (-)-1 is R-, (+)-1 S-configurated.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 1188-1197 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigation of Chromatographic Resolutions of Racemates, IV. Separation Efficiency of Optically Active poly [N-((S)-1-phenylethyl)acrylamide] Depending on the Polymerisation ProcedureThe optically active suspension polymers 2a-o were synthesized from N-[(S)-1-phenylethyl]-acrylamide [(S)-1] by systematic variation of the polymerisation procedure. These adsorbents whose separation efficiencies were determined by chromatography of racemic mandelic acid separated the enantiomers with very different results. Depending on the synthesis of 2, the optical yields were between 0(2e, f, n, o) and 43% (2i, j). Additionally, 2d separated the enantiomers of mandelamide, the optical yield being 35%. Furthermore, investigations on the particle structure of these adsorbents and the preparative partial separation of 3 are reported.
    Notes: Die optisch aktiven Suspensionspolymerisate 2a-o wurden aus N-[(S)-1-Phenyläthyl]acrylamid [(S)-1] unter systematischer Variation der Versuchsbedingungen hergestellt und auf ihre Trennwirkung durch Chromatographie racem. Mandelsäure geprüft. Die Enantiomeren wurden sehr unterschiedlich getrennt. Je nach Herstellung von 2 schwankten die optischen Ausbeuten von 0 (2e, f, n, o) bis 43% (2i, j). Bei der Trennung von racem. Mandelamid an 2d betrug sie 35%. Ferner wird über Untersuchungen zur Kornstruktur der Polymeren sowie über die präparative Anreicherung der Enantiomeren von 3 berichtet.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 111 (1978), S. 2732-2734 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chloroquine Enantiomers by Chromatographic Resolution and SynthesisThe chromatographic resolution of the antimalarial drug chloroquine (1) on an optically active polyamide is described. The results reveal that the optical purity of chloroquine formerly resolved with d-bromocamphorsulfonic acid was 12% only. A facile synthesis of the enantiomers via the optically active diamine 4 is given.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 2031-2035 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromatographie Resolutions of Racemates, IX. Chlorotalidone-, Chlorotalidone Methyl Ether-, and Oxazepam EnantiomersThe racemic drugs chlorotalidone (2a) and oxazepam (3) are completely, chlorotalidone methyl ether (2b) partially resolved by chromatography on the optically active amide 1. 2a and 3 racemize under the influence of acids and bases.
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