Click chemistry immobilization strategies in the development of strong cation exchanger chiral stationary phases for HPLC.

Enantioseparation of chiral amines with HPLC has developed into a widely used analytical and preparative tool. Chiral basic molecules, which act as cationic species upon protonation, are suited for an enantioselective cation exchange process. Novel strong cation exchangers (SCX) based on different 3,5-disubstituted benzoic acids functionalized with trans-(R,R)- and trans-(S,S)-2-aminocyclohexanesulfonic acid as the chiral selector (SO) and ion exchange unit were synthesized. Employing 1,3-dipolar cycloaddition (azide-yne click chemistry), the SOs were immobilized onto azidopropyl-modified silica gel. This immobilization strategy enables controlled loading of the SO, and especially, high SO density on the silica surface compared to the thiol-ene click immobilization. The performance of the novel SCX chiral stationary phases was evaluated under polar organic mode conditions with different ratios of methanol and acetonitrile, thereby changing the polarity of the bulk mobile phase. The type of co- and counterion additives employed in the mobile phase was varied as well. The influence of the formed 1,2,3-triazol spacer as well as different substitution patterns in the benzene unit on the chiral recognition properties of the SOs is discussed.