Validation of a gas chromatographic/mass spectrometric method for the determination of (E)-beta-fluoromethylene-m-tyrosine and its active metabolite in human plasma and urine.

(E)-beta-Fluoromethylene-m-tyrosine (FMMT, MDL 72394) represents a prodrug approach to site-selective, irreversible inhibition of monoamine oxidase. A sensitive and specific method for the quantification of FMMT and its active metabolite (MDL 72392) in human plasma and urine has been developed for future pharmacokinetic studies. The procedure consists of a liquid-liquid extraction of plasma and urine samples, esterification with HCl/butanol and, subsequently, N-acylation with pentafluoropropionic anhydride. This is followed by gas chromatography/mass spectrometry employing negative ion chemical ionization. The precision and the accuracy of the method have been optimized by using two internal standards: MDL 72661 (a methyl homologue of FMMT) for the quantification of FMMT, and MDL 72761 (a methyl homologue of MDL 72392) for the quantification of MDL 72392. The method has been validated for FMMT and MDL 72392 over the concentration range 2.5-400 pmol ml-1 with a limit of quantification for both compounds of 2.5 pmol ml-1. Sample clean-up and selected ion monitoring by mass spectrometry ensured the specificity and sensitivity required for the pharmacokinetic evaluation of FMMT and MDL 72392.