Enantiomeric Separation of (±)-Amino Acid Esters on (−)-Phenylurea Chiral Stationary Phase

The 3,5-dinitrobenzoyl (±)-amino acid esters were successfully resolved on (−)-phenylurea chiral stationary phases (CSPs) in a normal phase mode by high-performance liquid chromatography (HPLC). The alcohols used for esterification were methanol, ethanol, and n-propanol. The effects of esterification were studied via retention and optical resolution. The solvent and its concentration effect on enantioselectivity have been investigated based on the binary or ternary solvent system. The alcohol used in the binary or ternary solvent system was critical to the enantiomeric resolution of 3,5-dinitrobenzoyl amino acid esters while the nonalcoholic solvent was not suitable. The optical condition of the enantiomeric resolution is discussed in terms of the solvent composition and structure of the amino acid esters. The main chiral recognition mechanism based on the π–π interaction of the nitrobenzoyl group of the amino acid derivatives with the π-basic phenyl group of CSPs is described.