CHIRAL SEPARATION OF IBUTILIDE ENANTIOMERS BY DERIVATIZATION WITH 1-NAPHTHYL ISOCYANATE AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY ON A PIRKLE COLUMN

The enantiomers of ibutilide fumarate, a new antiarrhythmic agent with a single secondary alcohol chiral center, were solid-phase extracted, derivatized with I-naphthylisocyanate, and separated by high-performance liquid chromatography on a chiral Pirkle column (covalent 3,5-dinitrobenzoyl-D-phenyl-glycine stationary phase) with UV detection. Due to the strong interaction between the ibutilide derivatives and the stationary phase, a mobile phase containing 0.05% trifluoroacetic acid and 0.05% triethylamine in methanol was used. The assay was accurate to within 0.2% absolute error for samples ranging from primarily one enantiomer to racemic mixtures, measured as the percentage of peak area of one enantiomer relative to the total peak area of the two enantiomer peaks. The day-to-day reproducibility (standard deviation) ranged from +/- 0.03% relative peak area for samples containing primarily one enantiomer to +/- 0.2% for racemic mixtures. Accurate results over a wide range of enantiomer ratios were dependent on the method used to draw high-performance liquid chromatography peak baselines. The method was applied to racemization studies of ibutilide enantiomers in formulations and gastric fluid.