Nuclear magnetic resonance studies for the chiral recognition of the novel chiral stationary phase derived from 18-crown-6 tetracarboxylic acid

Enantioselectivities observed in high-performance liquid chromatography (HPLC) with the novel chiral stationary phase (CSP-18C6I) derived from (+)-18-crown-6 tetracarboxylic acid (18C6H₄) were investigated by using nuclear magnetic resonance (NMR) spectrometry. The elution orders in CSP-18C6I, that is, the S-enantiomer of 1-(1-naphthyl)ethylamine (1-NEA) and the

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-enantiomer (S-form) of alanine-β-naphthylamide (Ala-β-NA) eluted prior to each corresponding enantiomer, were successfully explained on the basis of the apparent binding constants (K_a) of the enantiomers to the CSP moiety which were calculated from ¹H-NMR experiments. Detailed HPLC and NMR studies for the chiral recognition of racemic amino compounds with 18C6H₄ hosts showed that ¹H-NMR spectrometry is a useful technique for the investigation of the chiral recognition mechanism in HPLC. Additionally, it was found 18C6H₄ can be recommended as a useful chiral shift reagent for the enantiomeric excess determination by ¹H-NMR.