Study of chromatographic enantioseparation of the esters of N-dinitrobenzoyl (N-DNB) and N-benzoyl (N-B) alpha-amino acids on novel chiral stationary phases containing structurally matching N-DNB and N-B-alpha-AA amides in the chiral selector

摘要

Enantioseparation ability and enantiopreference of chiral stationary phases CSP 1-CSP 3, containing a terminal N-3,5-dinitrobenzoyl (N-DNB) unit, and CSP 4, containing a terminal N-benzoyl (N-B) unit, are studied. Separation factors (a) for the two sets of test racemates (TR) that structurally match the chiral selector of these CSPs have been determined. The first set consists of seven N-DNB alpha-amino acid isopropylesters (TR 1A-TR 7A), and the second one of their N-B analogues (TR 1-TR 7). The best enantioseparation (alpha(average) 1.27) is obtained when pi-acceptor DNB unit is present in both TR and CSP. One pi-acceptor unit, either in the analyte or in CSP, suffices for efficient enantioseparation (aaverage L 19). Interaction between pi-neutral units in the CSP and test racemate does not afford effective enantioseparation (alpha(average) 1.03). Using (S)-enantiomers of all TRs as standards, CID detection has revealed regular preference of the CSPs for the enantiomers containing amino acid amide of the same absolute configuration. The possible origin of such enantiopreference is discussed.