title: Assessment of the stereoselective metabolism of methaqualone in man by capillary electrophoresis.
abstract: Methaqualone (MQ) and its hydroxylated metabolites are quinazoline derivatives that exhibit atropisomerism. As a continuation of our previous work with these compounds (Electrophoresis 2001, 22, 3270-3280), chiral capillary zone electrophoresis with hydroxypropyl-beta-cyclodextrin as buffer additive and multiwavelength absorbance detection is shown to be an effective tool to provide insight into the stereoselectivity of the MQ metabolism. The five major monohydroxy MQ metabolites formed during biotransformation do not show enantiomerization at temperatures up to 85 degrees C. Enzymatic and acidic hydrolysis of urines that were collected after concomitant administration of 250 mg of MQ and 25 mg diphenhydramine (DH) chloride are both shown to provide stereoselective metabolic patterns with 4'-hydroxymethaqualone, the major urinary metabolite, being excreted almost exclusively as a single enantiomer. A stereoselectivity in the formation of 2'-hydroxymethaqualone and 2-hydroxymethaqualone was also observed in vitro using human liver microsomes and preparations containing the cytochrome P450 enzyme (CYP) CYP3A4 only. The presence of DH during incubation with human liver microsomes did not reveal a difference in the metabolic pattern obtained. Furthermore, CYP2D6 and CYP2C19 do not significantly contribute to the metabolism of MQ. This was independently observed in vitro and via analysis of urines of individuals that are either efficient metabolizer phenotypes or poor metabolizer phenotypes for the two polymorphic enzymes. Although interindividual differences in the monitored metabolic patterns were noted, no marked difference could be related to a CYP2D6 or CYP2C19 polymorphism.
authors.affiliation: Department of Clinical Pharmacology, University of Bern, Murtenstrasse 35, CH-3010 Bern, Switzerland.
authors.forename: Francine
authors.initials: F
authors.lastname: Prost
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Thormann
mesh_terms: D001711:Biotransformation; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D019075:Electrophoresis, Capillary / Q000379:methods*; D006801:Humans; D008702:Methaqualone / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D011110:Polymorphism, Genetic; D011799:Quinazolines; D013237:Stereoisomerism
chemical_list: D011799:Quinazolines; D008702:Methaqualone; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human