Ligand-exchange chromatographic separation of DL-amino acids on aminopropylsilica-bonded chiral s-triazines

Chiral stationary phases (CSPs) were synthesized by reaction of aminopropylsilica (APS) with chiral monochloro-s-triazines (MCTs). MCTs were obtained by reaction of 2,4,6-trichloro-s-triazine (cyanuric chloride) with one equivalent of methanol and, subsequently, with one equivalent of L-proline tert butyl ester (H-Pro-OtBu) or N-tert butyloxycarbonyl-L-lysine tert butyl ester (Boc-Lys-OtBu). End-capping of unreacted amino groups of APS with acetic anhydride, followed by trifluoroacetolytic cleavage of the protecting groups of amino acids (AAs), afforded two chiral stationary phases bearing either L-proline (CSP3) or L-lysine (CSP-4) as chiral selector. Using ligand-exchange chromatography with addition of Cu2+ to the mobile phase, enantiomers of free DL-AAs and a few N-(2,4-dinitrophenyl)-DL-AAs were separated on CSP3, whereas N-(dansyl)-DL-AAs were separated on CSP-4.