Novel strong cation-exchange type chiral stationary phase for the enantiomer separation of chiral amines by high-performance liquid chromatography

The preparation of novel brush-type chiral cation-exchange materials based on de novo designed synthetic low molecular mass selectors (SOs) and their evaluation for enantioselective separation of chiral amines by HPLC are presented. The SO as the functional unit for enantioselectivity contains a β-aminocyclohexanesulfonic acid moiety and is readily accessible via straightforward synthesis in both enantiomeric forms yielding chiral stationary phases (CSPs) with opposite configurations, CSPs 1 and 2, and reversed elution orders. For the evaluation of these novel CSPs by HPLC a sound set of chiral amines, mainly amino-alcohol type drug molecules, was selected. The chromatographic evaluations were carried out using polar organic mobile phase conditions. All of the analytes could be baseline separated, compared to common CSPs in parts with excellent peak efficiencies (up to 70 000 theoretical plates per meter for the second eluted enantiomer). A number of experimental parameters have been varied to look at and prove the underlying ion-exchange process on CSPs 1 and 2, and to reveal suitable conditions for their operation. In this context, the influence of proton activity in the mobile phase and the effects of varying concentration and type of the counterion as well as type of co-ion and of bulk solvent components were thoroughly investigated.