High-performance liquid chromatography for analytical and small-scale preparative separation of (R,S)-mexiletine using (S)-(—)-(N)-trifluoroacetyl-prolyl chloride and (1S)-(—)-camphanic chloride and recovery of native enantiomer by detagging

Abstract

A reversed phase high-performance liquid chromatographic method has been established for enantioseparation of (R, S)-mexiletine. Two volatile and thermally stable acyl chlorides, viz., (S)-(—)-(N)-trifluoro acetyl prolyl chloride and (1S)-(—)-camphanic chloride, were used as chiral derivatizing reagents. Binary composition of aqueous trifluoroacetic acid (0.1%)-acetonitrile as mobile phase was successful with ultraviolet (UV) detection at 210 nm. The method was optimized and validated for accuracy, precision, and limit of detection. The limit of detection was found to be 45 ng mL−1 and 80 ng mL−1 for the two types of diastereomers. Besides, kinetic resolution was achieved, and the experimental conditions optimized for this purpose provided diastereomeric excess up to 74% for (R)-isomer. On achieving a resolution value greater than 2, the optimized method for analytical enantioseparation was scaled-up to smallscale preparative level, and the native (R)-mexiletine was recovered by acid hydrolysis of the diastereomer.