Enantiomeric analysis of the five major monohydroxylated metabolites of methaqualone in human urine by chiral capillary electrophoresis

Methaqualone (MQ; 2-methyl-3-o-tolylquinazolin-4(3H)-one) is a hypnotic and anticonvulsive drug in which the rotation about the nitrogen-to-aryl bond between the planar 2-methyl-quinazolin-4(3H)-one structure and the o-tolyl moiety is sterically hindered at body temperature. MQ and its five major mo nohydroxylated metabolites found in urine, 4'-hydroxymethaqualone (4'OH-MQ) , 2'-hydroxymethaqualone (2'-OH-MQ), 3'-hydroxymethaqualone (3'OH-MQ), 2-hy droxymethaqualone (2OH-MQ) and 6-hydroxymethaqualone (6OH-MQ), are thus chi ral substances whose enantiomers are shown to be separable by chiral capill ary electrophoresis at pH 2.1 in the presence of 50 mM (2-hydroxypropyl)-be ta -cyclodextrin (OHP-beta -CD). Other neutral derivatives of P-CD, namely (2-hydroxypropyl)-gamma -CD, (2,3,6-trimethyl)-beta -CD, and (2,6-di-O-meth yl)P-CD were found to be able to resolve the enantiomers of some but not al l of these six components. With OHP-beta -CD, simultaneous analysis of the enantiomers of MQ and its five metabolites is hampered by the difficulty in separating MQ and 4'OH-MQ, the major urinary metabolite. A two-step solid phase extraction process is shown to permit discrimination between these tw o compounds and thus analysis of MQ enantiomers in unhydrolyzed urines that were collected overnight after administration of 250 mg of racemic MQ. Fur thermore, analysis of liquid/liquid or solid-phase extracts of enzymaticall y hydrolyzed urines reveals the distribution of the enantiomers of the five hydroxymetabolites of MQ and, for the first time, insight into the stereos electivity of the MQ metabolism. The major metabolite, 4'OH-MQ, is shown to be excreted almost exclusively as single enantiomer. The two urinary enant iomers of 6OH-MQ are present at about equal amounts, whereas unequal amount s are noted for the enantiomers of 3'OH-MQ, 2OH-MQ, and 2'OH-MQ.