Isolation, characterisation and synthesis of a new quinidine metabolite

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Abstract
In addition to the well-known quinidine metabolites, 2’-quinidinone and 3-hydroxy-quinidine, a third metabolic product was detected in the plasma of cardiac patients receiving quinidine therapy. Mass spectroscopic,13C- and1H-NMR studies, together with information on UV and IR properties of the isolated and also synthetically accessible compound, suggested the presence of an aliphatic N-oxide group. The structure of quinidine-N-oxide for the hitherto unknown metabolite was finally confirmed by X-ray diffraction analysis. Evidence was found to indicate that a contaminant in quinidine preparations, dihydro-quinidine, is metabolized with respect to N-oxidation in the same way as quinidine.