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Stereospecific Gas chromatographic/mass Spectrometric Assay of the Chiral Labetalol Metabolite 3-amino-1-phenylbutane

Stereospecific Gas chromatographic/mass Spectrometric Assay of the Chiral Labetalol Metabolite 3-amino-1-phenylbutane

A Changchit, J Gal, J A Zirrolli

Biol Mass Spectrom. 1991 Dec;20(12):751-8.

PMID: 1812984

Abstract:

We previously identified 3-amino-1-phenylbutane (APB) as an oxidative N-dealkylated, metabolite of the antihypertensive agent labetalol. Labetalol has two asymmetric centers and is used clinically as a mixture of the four possible stereoisomers; APB has one asymmetric center. We now report an enantiospecific gas chromatographic/mass spectrometric assay for APB in urine. After adding the internal standard 1-methyl-2-phenoxyethylamine and alkalinizing, the urine samples were extracted with ether. The extracts were derivatized with the optically active acid chloride prepared from (S)-alpha-methoxy-alpha-trifluoromethylphenylacetic acid. The derivatives were separated by capillary gas chromatography and detected by electron capture negative ion chemical ionization mass spectrometry with selected ion monitoring. The derivative of the R enantiomer eluted first, and the [M--32]- ions were monitored for both the drug and the internal standard. The method was linear in the 0.05-2.5 micrograms enantiomer-1 ml-1 range and had inter-assay and intra-assay coefficients of variation of less than 6%. The assay was used in the analysis of urine samples from a patient in labetalol therapy and no interference was found. Further studies are needed to elucidate the oxidative metabolism of labetalol and its stereochemical aspects.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP17257715	(S)-(−)-α-Methoxy-α-trifluoromethylphenylacetic acid		17257-71-5	Price

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