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  • 1
    Electronic Resource
    Electronic Resource
    Enantioselective aliphatic hydroxylations of racemic 1-hydroxy-3-methylcholanthrene by rat liver microsomes (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 141-149 
    Details
    ISSN: 0899-0042
    Keywords: 3-methylcholanthrene ; 1-hydroxy-3-methylcholanthrene ; 1-hydroxy-3-hydroxymethylcholanthrene ; 3-methylcholanthrene trans-1,2-diol ; 3-methylcholanthrene cis-1,2-diol ; high-performance liquid chromatography ; chiral stationary phase ; resolution of enantiomers ; absolute configuration ; circular dichroism spectra ; enantioselective hydroxylation ; rat liver microsomes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric pairs of 1-hydroxy-3-hydroxymethylcholanthrene (1-OH-3-OHMC), 3-methylcholanthrene (3MC) trans- and cis-1,2-diols, and 1-hydroxy-3-methylcholanthrene (1-OH-3MC) were resolved by HPLC using a covalently bonded (R)-N-(3,5-dinitrobenzoyl)phenylglycine chiral stationary phase (Pirkle type 1A) column. The absolute configuration of an enantiomeric 3MC trans-1,2-diol was established by the exciton chirality CD method following conversion to a bis-p-N,N-dimethylaminobenzoate. Incubation of an enantiomeric 1-OH-3MC with rat liver microsomes resulted in the formation of enantiomeric 3MC trans- and cis-1,2-diols; the absolute configurations of the enantiomeric 1-OH-3MC and 3MC cis-1,2-diol were established on the basis of the absolute configuration of an enantiomeric 3MC trans-1,2-diol. Absolute configurations of enantiomeric 1-OH-3-OHMC were determined by comparing their CD spectra with those of enantiomeric 1-OH-3MC. The relative amount of three aliphatic hydroxylation products formed by rat liver microsomal metabolism of racemic 1-OH-3MC was 1-OH-3-OHMC 〉 3MC cis-1,2-diol 〉 3MC trans-1,2-diol. Enzymatic hydroxylation at C2 of racemic 1-OH-3MC was enantioselective toward the 1S-enantiomer over the 1R-enantiomer (∼3/1); hydroxylation at the C3-methyl group was enantioselective toward the 1R-enantiomer over the 1S-enantiomer (∼58/42). Rat liver microsomal C2-hydroxylation of racemic 1-OH-3MC resulted in a 3MC trans-1,2-diol with a (1S,2S)/(1R,2R) ratio of 63/37 and a 3MC cis-1,2-diol with a (1S,2R)/(1R,2S) ratio of 12/88, respectively.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020304
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  • 2
    Electronic Resource
    Electronic Resource
    Stereoselectivity in acid-catalyzed heteronucleophilic substitution of enantiomeric 3-O-methyloxazepam and 3-O-ethyloxazepam (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 34-39 
    Details
    ISSN: 0899-0042
    Keywords: 1,4-benzodiazepines ; oxazepam ; 3-O-methyloxazepam ; 3-O-ethyloxazepam ; stereoselectivity ; racemization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetics of acid-catalyzed heteronucleophilic substitution and racemization of enantiomeric MeOX in ethanol and enantiomeric EtOX in methanol were studied by quenching reaction products at various times by neutralization. Enantiomeric contents of remaining substrate and reaction product were determined by chiral stationary phase high-performance liquid chromatography. The experimental procedure allowed the determination of the stereoselectivity (i.e., the enantiomeric ratio of a substitution product formed from an enantiomerically pure substrate) involved in the heteronucleophilic substitution reactions. The stereoselectivity was found to vary between 58:42 and 87:13, depending on the acid concentration, substrate, solvent, and temperature. The enantiomeric purity of remaining substrates was identical to that of the starting substrate, indicating that the enantiomeric substrates did not undergo a ring-opening reaction. The results provided additional evidence supporting the mechanism proposed earlier in acid-catalyzed stereoselective heteronucleophilic and homonucleophilic substitutions and the resulting racemization of enantiomeric 3-alkoxy-1,4-benzodiazepines in alcoholic solvents. © 1995 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070107
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  • 3
    Electronic Resource
    Electronic Resource
    Absolute configuration ofcis-5,6-dihydrodiol enantiomers derived from helical conformers of 1,12-dimethylbenz[a]anthracene (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 58-64 
    Details
    ISSN: 0899-0042
    Keywords: 1,12-dimethylbenz[α]anthracene ; helical conformers ; cis-5,6-dihydrodiol ; high-performance liquid chromatography ; chiral stationary phase ; optical isomers ; resolution of enantiomers ; absolute configuration ; circular dichroism spectra ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,12-Dimethylbenz[α]anthracene (1,12-DMBA) cis-5,6-dihydrodiol was synthesized by oxidation of 1,12-DMBA with osmium tetroxide in pyridine in low yield (≤3%) and was purified by sequential use of reversed-phase and normal-phase HPLC. Two pairs of 1,12-DMBA cis-5,6-dihydrodiol enantiomers, derived from P (right-handed helix) and M (left-handed helix) conformers, were eluted as a single chromatographic peak on both reversed-phase and normal-phase HPLC. However, these four enantiomers were resolved by sequential use of two chiral stationary phase (CSP) HPLC columns. CSP (Pirkle type I) columns were packed with either (R)-N-(3,5-dinitrobenzoyl)phenylglycine or (S)-N-(3,5-dinitrobenzoyl)leucine, which is ionically bonded to γ-aminopropylsilanized silica. Absolute configurations of enantiomers were determined by comparing their circular dichroism spectra with those of conformationally similar cis-5,6-dihydrodiol enantiomers of 4-methylbenz[α]anthracene and 7,12-dimethylbenz[α]-anthracene with known absolute stereochemistry.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020109
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  • 4
    Electronic Resource
    Electronic Resource
    Highly stereoselective acid-catalyzed homonucleophilic substitution reactions (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 525-530 
    Details
    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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chiral stationary phase high-performance liquid chromatographic resolution and absolute configuration of enantiomeric benzo[a]pyrene diol-epoxides and tetrols (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 276-283 
    Details
    ISSN: 0899-0042
    Keywords: benzo[a]pyrene diol-epoxides ; benzo[a]pyrene tetrols ; high-performance liquid chromatography ; chiral stationary phase ; optical isomers ; resolution of enantiomers ; absolute configuration ; circular dichroism spectra ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomers of diastereomeric benzo[a]pyrene (BP) diol-epoxides, r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydro-BP (BP 7,8-diol-anti-9,10-epoxide), r----7,t-8-dihydroxy-c-9,10-epoxy-7,8,9,10-tetrahydro-BP (BP 7,8-diol-syn-9,10-epoxide), r-9,t-10-dihydroxy-t-7,8-epoxy-7,8,9,10-tetrahydro-BP (BP 9,10-diol-antiy7,8-epoxide), and several 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrenes (BP tetrols) were resolved by high-performance liquid chromatography (HPLC) using columns packed with either (R)-N-(3,5-dinitrobenzoyl)phenylglycine[(R)-DNBPG] or (S)-N-(3,5-dinitrobenzoyl)leucine [(S)-DNBL], which is either ionically or covalently bonded to γ-aminopropylsilanized silica. Resolution of enantiomers was confirmed by ultraviolet-visible absorption and circular dichroism spectral analyses. Resolved enantiomers of BP diol-epoxides were each hydrolyzed in acidic solution to a pair of diastereomeric tetrols which were separated by reversed-phase HPLC. Absolute stereochemistries of enantiomeric diol-epoxides were deduced by the absolute configuration of their hydrolysis products.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010406
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  • 6
    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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