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  • 1
    Electronic Resource
    Electronic Resource
    Acid-Catalyzed nucleophilic substitution and racemization of 3-methoxy-N-desmethyldiazepam enantiomers in methanol (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 91-96 
    Details
    ISSN: 0899-0042
    Keywords: 1,4-benzodiazepines ; oxazepam ; 3-O-methyloxazepam ; stereoselective nucleophilic substitution ; kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: pKa1 values of 3-methoxy-N-desmethyldiazepam in acetonitrile and methanol containing various acid concentrations were determined by spectrophotometry to be 3.5 and 1.3, respectively. Temperature-dependent racemization of enantiomeric 3-methoxy-N-desmethyldiazepam in methanol containing 0.5 M H2SO4 was studied by circular dichroism spectropolorimetry and the racemization reactions were found to follow apparent first-order kinetics. Thermodynamic parameters of the racemization reaction were found to be: Eact = 18.8 kcal/mol, and at 25°C: ΔH
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050209
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  • 2
    Electronic Resource
    Electronic Resource
    Resolution and stability of oxazepam enantiomers (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 443-446 
    Details
    ISSN: 0899-0042
    Keywords: oxazepam ; chiral stationary phases ; high-performance liquid chromatography ; enantiomer separation ; enantiomer stability ; racemization ; kinetics of racemization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A solvent mixture containing dioxane, acetonitrile, and hexane was found to be suitable as a mobile phase to resolve oxazepam enantiomers by chiral stationary phase high performance liquid chromatography using covalent Pirkle columns. The resolved oxazepam enantiomers in this solvent mixture had a racemization half-life greater than 3 days at 23°C. When desiccated at 0°C as dried residue, OX enantiomers were stable for at least 50 days with less than 2% racemization. The conditions which stabilized OX enantiomers significantly facilitated the determination of racemization half-lives of OX enantiomers in a variety of aqueous and nonaqueous solvents and at different temperatures. © 1992 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530040708
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  • 3
    Electronic Resource
    Electronic Resource
    N,N-dimethylcarbamyl derivatives of oxazepam (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 212-219 
    Details
    ISSN: 0899-0042
    Keywords: oxazepam ; demoxepam ; 3-O-acyl-1-(N,N-dimethylcarbamyl)oxazepam ; 1-(N,N-dimethylcarbamyl)oxazepam ; 3-O-(N,N-dimethylcarbamyl)oxazepam ; camazepam ; norcamazepam ; 1,3-O-bis(N,N-dimethylcarbamyl)oxazepam ; kinetics of racemization ; enantioselectivity of esterases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three N,N-dimethylcarbamyl derivatives of oxazepam {1-(N,N-dimethylcarbamyl)oxazepam, 3-O-(N,N-dimethylcarbamyl)oxazepam, and 1,3-O-bis(N,N-dimethylcarbamyl)oxazepam} and a 3-O-acyl-1-(N,N-dimethylcarbamyl)-oxazepam were synthesized from either oxazepam or demoxepam. Enantiomeric pairs of these derivatives and of camazepam were resolved by high-performance liquid chromatography on at least two of three commercially available chiral stationary phase columns employed. Absolute configurations of resolved enantiomers were established by comparing their circular dichroism spectra to those of enantiomeric oxazepams with known absolute stereochemistry. Similar to those of oxazepam, enantiomers of 1-(N,N-dimethylcarbamyl)oxazepam undergo rapid racemization (t½ 1.9 min at 23°C and 0.9 min at 37°C) in an aqueous solution at pH 7.5. The (R)-enantiomer of rac-3-O-acyl-1-(N,N-dimethylcarbamyl)oxazepam was hydrolyzed ∼4.6-fold faster than the (S)-enantiomer by esterases in rat liver microsomes, whereas the (S)-enantiomer was hydrolyzed ∼43-fold faster than the (R)-enantiomer by esterases in rat brain S9 fraction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030313
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  • 4
    Electronic Resource
    Electronic Resource
    Metabolism of halazepam by rat liver microsomes: Stereoselective formation and n-dealkylation of 3-hydroxyhalazepam (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 1-9 
    Details
    ISSN: 0899-0042
    Keywords: halazepam ; 3-hydroxyhalazepam ; diazepam ; N-desmethyldiazepam ; oxazepam ; enantiomers ; rat liver microsomes ; stereoselectivity ; enantioselectivity ; hydroxylation ; enantioselective N-dealkylation ; kinetics of racemization ; circular dichroism spectra ; chiral stationary phase ; high-performance liquid chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metabolism of halazepam [7-chloro-1,3-dihydro-5-phenyl-1-(2,2,2-trifluoroethyl)-2H-1,4-benzodi epin-2-one, HZ] was studied by incubation with liver microsomes prepared from untreated, phenobarbital (PB)-treated, and 3-methylcholanthrene (3MC)-treated male Sprague-Dawley rats. Metabolites of HZ were separated by normal-phase HPLC. Relative rates of HZ metabolism by liver microsomes prepared from untreated and treated rats were PB-treated ≫ untreated 〉 3MC-treated at low concentration of microsomal enzymes (0.25 mg protein per ml of incubation mixture) and PB-treated ≫ 3MC-treated ≈ untreated at high concentration of microsomal enzymes (2 mg protein per ml of incubation mixture). The relative amounts of major metabolites were found to be 3-hydroxy-HZ (3-OH-HZ) 〉 N-desalkylhalazepam (NDZ, also known as N-desmethyldiazepam and nordiazepam) ≫ oxazepam (OX) for all three rat liver microsomal preparations and the distribution of metabolites was independent of microsomal enzyme concentrations. Enantiomers of 3-OH-HZ were resolved by HPLC on a Chiralcel OC column (cellulose trisphenylcarbamate coated on silica gel, particle size 10 μm). 3-OH-HZ enantiomeres have racemization half-lives of ∼ 150 min in pH 4,7.5, and 10 aqueous solutions. 3-OH-HZ formed in the metabolism of HZ by liver microsomes prepared from untreated and treated rats were found to have 3R/3S enantiomer rations of 37/63 (untreated), 55/45 (PB-treated), and 36/64 (3MC-treated), respectively. N-dealkylation of 3-OH-HZ by liver microsomes from PB-treated rats was substrate enantioselective; the 3R-enantiomer was N-dealkylated faster than 3S-enantiomer. The results indicated that the stereoselective C3-hydroxylation of HZ is dependent on the cytochromes P-450 present in the rat liver microsomal preparations; pro-R in liver microsomes from PB-treated rats and pro-S in liver microsomes from untreated and 3MC-treated rats, respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020102
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