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  • 1
    ISSN: 0899-0042
    Keywords: pargyline N-oxide ; chiral nitrogen centre ; flavin-containing monooxygenase ; chiral stationary phase ; high-performance liquid chromatography ; Chiralcel OD ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The monoamine oxidase inhibitor pargyline (N-benzyl-N-methyl-2-propynylamine) is known to undergo extensive in vitro microsomal N-oxidation, thought to be mediated predominantly by the flavin-containing monooxygenase (FMO) enzyme system. Formation of the pargyline N-oxide (PNO) metabolite creates a chiral nitrogen centre and thus asymmetric oxidation is possible. This study describes a reverse-phase high-performance liquid chromatographic (HPLC) method for the quantitation of PNO and a chiral-phase HPLC method for the determination of the enantiomeric ratio of PNO. In vitro microsomal N-oxidation of pargyline was found to be highly steroselective in a number of species, with the (+)-enantiomer being formed preferentially. This metabolic transformation was stereospecific when purified porcine hepatic FMO was used as the enzyme source. © 1994 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0899-0042
    Keywords: cimetidine ; sulfoxidation ; urinary metabolite ; enantiomeric composition of cimetidine sulfoxide ; sequential achiral - chiral high-performance liquid chromatography ; preparative chromatographic resolution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The individual enantiomers of cimetidine sulfoxide were resolved by preparative chromatography using a Chiralcel OC stationary phase and were characterized by the determination of optical rotation and circular dichroism spectra. Cimetidine sulfoxide was isolated from the urine of two healthy male volunteers following oral administration of cimetidine (400 mg). Urine was collected every 2 h for 12 h postdosing, after which time HPLC analysis indicated negligible recovery of the drug as the sulfoxide. Some 7% of the dose was recovered as cimetidine sulfoxide over this period. The enantiomeric composition of cimetidine sulfoxide was determined by sequential achiral - chiral chromatography using the OC phase. Over the collection period the enantiomeric ratio was found to be constant in all samples at (+/-) of 71 ± 2.5:29 ± 2.5. The enantiomeric composition of cimetidine sulfoxide was also determined in rat urine (24 h) following the administration of cimetidine (30 mg/kg po) to male Wistar rats (n = 7). The enantiomeric ratio in this case was found to be (+/-) 57 ± 2.3:43 ± 2.3. These preliminary data indicate that sulfoxidation of cimetidine is stereoselective with respect to the (+)-enantiomer and that species variation in enantiomeric composition occurs. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    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.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0899-0042
    Keywords: high-performance liquid chromatography ; chiral stationary-phase ; flavin-containing monooxygenase ; N-ethyl-N-methylaniline N-oxide, Chiralcel OD ; 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 metabolically N-oxygenated in vitro with microsomal preparations. This biotransformation is thought to be mediated predominantly by the flavin-containing monooxygenase (FMO) enzyme system. Microsomal N-oxygenation of EMA is known to be stereoselective and varies between species. In order to further characterise this metabolic transformation, we have examined the in vitro metabolism of EMA using purified porcine hepatic FMO. Following incubation of EMA with purified FMO, EMA N-oxide, the only metabolite detected, was found to be produced stereoselectively [ratio (-)-(S):(+)-(R), ca. 4:1]. The enantiomeric ratio of the N-oxide product did not change markedly with respect to time, enzyme or substrate concentration. Determination of the kinetics of formation of the N-oxide indicated a single affinity for the prochiral substrate with differential rates of formation of the enantiomers. The extent of EMA N-oxide formation was shown to be affected by activators and inhibitors of FMO and pH, but its stereoselectively was unaltered. © 1994 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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