Separation of unmodified α-amino acid enantiomers by reverse phase HPLC

Summary A novel chiral phase system is presented for the resolution of unmodified α-amino acid racemates which is composed of a reverse phase packing coated with N-alkyl-L-hydroxyproline (where alkyl is n-C₇H₁₅-, n-C₁₀H₂₁- and n-C₁₆H₃₃-) and a hydro-organic eluent containing copper(II)acetate. The factors controlling retention and enantioselectivity such as concentration of Cu(II)ion and pH of the eluent, addition of NH₄Ac to the eluent, type and content of organic solvent of hydro-organic eluent and column temperature were examined. The extremely high enantioselectivity observed (α up to 16) is assumed to be caused by a three site sorbate-sorbent interaction involving bidentate coordination of two amino acids to a Cu(II)ion and hydrophobic attractions between hydrocarbon side chains of amino acids and the n-octadecyl groups of the support. The efficiency and selectivity of the system permits resolution of up to 7 racemic amino acids into enantiomers within 35 minutes on a conventional HPLC apparatus. 13th publication in the series dealing with the ligand-exchange chromatography. Previous publication: ref. 1].