Chiral Separation of the Enantiomers of Metoprolol and Its Metabolites by High Performance Liquid Chromatography

(1'R, 2R)-, (1'R, 2S)-, (1'S, 2R)- and (1'S, 2S)-$\alpha$-hydroxymetoprolol; (2R)- and (2S)-O-des-methylmetoprolol; and (2R)- and (2S)-metoprolol acid are major metabolites of (2R)-and (2S)-metoprolol, $\beta$-adrenergic antagonist. The focus of most chiral separation methods until now has been on determination of the enantiomeric parent drug. However, it is just as important to be able to follow the metabolism of the enantiomers and their possible chiral metabolites. Therefore, for the study of stereoselective metabolism and pharmacokinetics of metoprolol, the chiral separation of the enantiomers of metoprolol and its metabolites has been investigated using four chiral stationary phases, i.e., Chiralcel OD, Chiral-AGP, Cyclobond I and Sumichiral OA-4900 columns. Metoprolol acid was resolved only by Sumichiral OA-4900. Chiralcel OD provided the highest separation factor and resolution value for metoprolol and O-desmethylmetoprolol and partially resolved the four stereoisomers of $\alpha$-hydroxymetoprolol. Diastereomeric $\alpha$-hydroxymetoprolols were resolved using the coupled column chromatographic system of two chiral stationary phases, Sumichiral OA-4900 column and Chiralcel OD column.