title: Enantiospecific quantification of hexobarbital and its metabolites in biological fluids by gas chromatography/electron capture negative ion chemical ionization mass spectrometry.
abstract: A highly sensitive and specific assay based on gas chromatography/electron capture negative ion chemical ionization mass spectrometry has been developed for the analysis of the enantiomers of hexobarbital and its major metabolites in human urine and plasma. S-(+)-(5-2H3)hexobarbital and R-(-)-(5-2H3)hexobarbital were synthesized for clinical studies along with (+/-)-(1,5-2H6)hexobarbital and the deuterated major metabolites for use as internal and reference standards. Hexobarbital enantiomers and their metabolites were analyzed after pentafluorobenzyl and trimethylsilyl derivatization, following solid-phase extraction from plasma and urine. Intense negative ion spectra were observed for all of the derivatives. The base peak in the spectra corresponded to the M-pentafluorobenzyl anion [M-PFB]- except for 1,5-dimethylbarbituric acid, where M-. was the most abundant ion. The applicability of the method was demonstrated by following the plasma concentration-time profiles and urinary excretion in a male extensive metabolizer of mephenytoin who was given a pseudoracemic oral dose of hexobarbital containing equal 50 mg amounts of S-(+)-2(H0)hexobarbital and R-(-)-(2H3)hexobarbital. Marked stereoselective disposition was observed, with the R-(-)-enantiomer being more efficiently metabolized, primarily by alicyclic oxidation and ring cleavage.
authors.affiliation: Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: C
authors.initials: C
authors.lastname: Prakash
authors.forename: A
authors.initials: A
authors.lastname: Adedoyin
authors.forename: G R
authors.initials: GR
authors.lastname: Wilkinson
authors.forename: I A
authors.initials: IA
authors.lastname: Blair
mesh_terms: D000328:Adult; D004563:Electrochemistry; D008401:Gas Chromatography-Mass Spectrometry; D006591:Hexobarbital / Q000032:analysis* / Q000097:blood / Q000652:urine; D006801:Humans; D008297:Male; D008617:Mephenytoin / Q000378:metabolism; D010084:Oxidation-Reduction; D013237:Stereoisomerism
chemical_list: D006591:Hexobarbital; D008617:Mephenytoin