Chiral characterization of deprenyl‐ N ‐oxide and other deprenyl metabolites by capillary electrophoresis using a dual cyclodextrin system in rat urine

A chiral capillary electrophoresis method has been developed for the simultaneous separation of the enantiomers of deprenyl and eight of its metabolites, among them the recently described metabolite deprenyl‐ N ‐oxide. Although heptakis‐(2,6‐di‐ O ‐methyl)‐β‐cyclodextrin (DIMEB) was suitable for the enantioresolution of deprenyl and its dealkylated derivatives, the enantiomers of deprenyl‐ N ‐oxide were just partly resolved. Carboxymethyl‐β‐cyclodextrin (CMBCD) in as low as 2 m M concentration was capable of the enantiomer separation of all the nine examined compounds, however co‐migration of 1 R ,2 S ‐(−)‐norephedrine and 1 R ,2 R ‐(−)‐pseudoephedrine, as well as 1 S ,2 R ‐(+)‐ephedrine and R ‐(−)‐amphetamine was observed. This problem could be overcome by the use of a dual cyclodextrin system containing 4 m M DIMEB in addition to 2 m M CMBCD; simultaneous separation of all the compounds could be achieved. The optimized method was used for the analysis of rat urine samples after 10 days of treatment of animals with either R ‐(−)‐ or S ‐(+)‐deprenyl. The stereospecific biotransformation of both deprenyl enantiomers was confirmed, and the stereoselectivity of N ‐oxide formation was demonstrated.