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Species variability in the stereoselective N-oxidation of pargyline
M R Hadley1, E Svajdlenka, L A Damani
1Department of Pharmacy, King's College London, England.
Abstract:
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 stereoselective 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.
Insights
Monoamine oxidase inhibitor pargyline undergoes N-oxidation by flavin-containing monooxygenase (FMO) enzymes. This process is stereoselective, preferentially forming the (+)-enantiomer of pargyline N-oxide (PNO).
Area of Science:
- Pharmacology
- Biochemistry
- Enzymology
Background:
- Pargyline, a monoamine oxidase inhibitor, undergoes N-oxidation in vitro.
- This metabolism is primarily mediated by flavin-containing monooxygenase (FMO) enzymes.
- N-oxidation of pargyline generates a chiral metabolite, pargyline N-oxide (PNO), allowing for asymmetric oxidation.
Purpose of the Study:
- To develop and validate analytical methods for quantifying pargyline N-oxide (PNO).
- To determine the enantiomeric ratio of PNO formed from pargyline N-oxidation.
- To investigate the stereoselectivity of pargyline N-oxidation in various species and with purified FMO.
Main Methods:
- Development of a reverse-phase high-performance liquid chromatography (HPLC) method for PNO quantitation.
- Establishment of a chiral-phase HPLC method for determining the enantiomeric ratio of PNO.
- In vitro microsomal N-oxidation assays using liver microsomes from different species and purified porcine hepatic FMO.
Main Results:
- The in vitro microsomal N-oxidation of pargyline demonstrated high stereoselectivity across multiple species.
- The (+)-enantiomer of PNO was preferentially formed.
- The metabolic transformation was found to be stereospecific when using purified porcine hepatic FMO.
Conclusions:
- Pargyline N-oxidation by FMO enzymes is a stereoselective process.
- The (+)-enantiomer of PNO is the major metabolite formed.
- Purified FMO exhibits stereospecificity in pargyline metabolism, highlighting its role in asymmetric oxidation.