Crystallographic studies for the chiral recognition of the novel chiral stationary phase derived from (+)-(R)-18-crown-6 tetracarboxylic acid

Abstract

Chiral discrimination observed in high-performance liquid chromatography (HPLC) with the novel chiral stationary phase (CSP-18C6I) derived from (+)-(R)-18-crown-6 tetracarboxylic acid [(+)-18C6H4] was investigated by X-ray crystallographic analysis of the complex composed of the R-enantiomer of 1-(1-naphthyl)ethylamine (1-NEA) and (+)-18C6H4. Mixtures of 1-NEA (the R- or S-enantiomer) and (+)-18C6H4 were dissolved in methanol-water (1:1) solution and allowed to stand for crystallization. The R-enantiomer crystallized with (+)-18C6H4 as a co-crystal, although the S-enantiomer did not. This result was in good agreement with the enantiomer elution order of 1-NEA in CSP-18C6I. The apparent binding constants (Ka) of the enantiomers to the (+)-18C6H4 obtained from 1H-NMR experiments also supported the above-mentioned result. The X-ray crystal structure of the 1:1 complex of the R-enantiomer and (+)-18C6H4 indicated the four sets of hydrogen bond association between the naphthylethylammonium cation and oxygen of polyether ring or carbonyl group of (+)-18C6H4. Chirality 11:173–178, 1999. © 1999 Wiley-Liss, Inc.