Clazolam

Seven new stationary phases with different number of proline units and/or different linkage to silica gel were prepared and evaluated in order to improve the performance of proline chiral stationary phases. The average separation factor achieved with the 53 analytes increases with the number of proline units in the stationary phases. When the proline peptides are directly attached to the 3-methylaminopropyl silica gel without using the 6-methylaminohexanoic acid linker, the stationary phases perform better overall. For decaproline chiral stationary phase 8, the separation also depends on the mobile phase system used. For this stationary phase, the CH2Cl2/hexanes/2-propanol system significantly outperforms the 2-propanol/hexanes system. For the 53 analytes tested, the separation factors achieved with this stationary phase compare well with those for three commercial columns.

The role of 9-fluorenylmethoxycarbonyl (Fmoc) in previously reported proline enantioselective stationary phases was investigated. Seven stationary phases in which the Fmoc group was replaced by other groups were prepared and evaluated in normal phase mode. The Fmoc group proved nonessential for the broad enantioselectivity observed, as the stationary phase with a trimethylacetyl (Tma) group proved much more effective than the one with the Fmoc group. For the 53 analytes studied, the stationary phase with the Tma group resolved 39, while the one with the Fmoc group resolved 19. Separation factors achieved for the stationary phase with the Tma group are also significantly higher than those for the stationary phase with the Fmoc group. The stationary phase with the (-)-2-(2,4,5,7-tetranitro-9-fluorenylideneaminooxy)propionyl (Tapa) group provides very different selectivity profile when compared to the one with the Tma group. In most of the proline stationary phases studied, pi-pi interaction is not the dominant interaction for the enantioselective recognition.