Enantioseparation of paroxetine intermediate on an amylose-derived chiral stationary phase by supercritical fluid chromatography

The enantioseparation of trans-3-ethoxycarbonyl-4-(4′-fluorophenyl)-1-methyl piperidine-2,6-dione (3), which is one of the important racemic precursors of trans-(−)-paroxetine, has been investigated using supercritical fluid chromatography on a Daicel Chiralpak AD column. Supercritical CO₂ modified with methanol, ethanol and 2-propanol were used as mobile phase. The influence of type and concentration of alcohol modifier on retention factor, enantioselectivity and resolution were studied. Among methanol, ethanol and 2-propanol, 2-propanol was proved to be the most favorable modifier, and 9.5% (v/v) of 2-propanol was the preferred concentration at which racemate 3 could be separated with resolution of 15.86 and retention factor of 6.323. The effects of pressure and temperature were investigated at 9.5% (v/v) of 2-propanol in the pressure range of 12–24 MPa and temperature range of 303.15–318.15 K. It was found that the lower pressure and temperature were favorable to the enantioseparation. Using van’t Hoff plot, the isoenantioselective temperature was calculated to be 410 K. The enantioseparation process was “enthalpically driven” under experimental conditions. Finally, the retention factors were satisfactorily correlated by a simplified lattice–fluid model with average absolute relative deviation (AARD%) of both enantiomers smaller than 1.76%.