Liquid chromatographic resolution of racemic amino acids and their derivatives on a new chiral stationary phase based on crown ether

A new high-performance liquid chromatography chiral stationary phase (CSP) was prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to silica gel. The new CSP was employed in separating the two enantiomers of various natural and unnatural racemic alpha-amino acids and their derivatives. All natural acid unnatural racemic alpha-amino acids tested were resolved with reasonable separation factors on the new CSP, except for proline, which does not contain a primary amino group. Racemic alpha-amino acid derivatives were also tested for their separability on the new CSP. In general, N-monoalkyl amides of alpha-amino acids were resolved better than the corresponding free alpha-amino acids. However, N,N-dialkyl amides and esters of alpha-amino acids were not resolved as well as the corresponding free alpha-amino acids, except for phenylglycine derivatives. In the case of phenylglycine, both N-monoalkyl and N,N-dialkyl amides of phenylglycine were resolved better than phenylglycine itself and its ester derivative. (C) 1998 Elsevier Science B.V. All rights reserved.