Chiral Recognition of Binaphthyl Derivatives: A Chiral Recognition Model on the Basis of Chromatography, Spectroscopy, and Molecular Mechanistic Calculations for the Enantioseparation of 1,1'-Binaphthyl Derivatives on Cholic Acid-Bonded Stationary Ph

摘要

In an effort to elucidate the mechanism of chiral discrimination of cholic acid-based stationary phases, the enantiomeric recognition ability of six chiral stationary phases (CSPs), prepared from differently substituted cholic acid derivatives, was evaluated in normal phase high-performance liquid chromatography (HPLC) with a series of 1,1'-binaphthyl compounds. The influence of structural variations of analytes on retention and enantioselectivity was investigated. Particularly high values of enantioselectivity were observed for the binaphthol enantiomers on a CSP prepared from the allyl 7α,12α-dihydroxy-3α-phenylcarbamoyloxy-5β-cholan-24-oate. The complexes of this chiral selector with both enantiomers of binaphthol were studied as models for the interactions responsible for the enantioseparation with the cholic acid-based stationary phases. The 1:1 stoichiometry of the complex in solution wa determined by UV titration. The chiral selector dissolved in chloroform exhibited a chiral discrimination for the binaphthol in ~1H and ~(13)C nuclear magnetic resonance (NMR) spectroscopies. Some aromatic proton and carbon resonances of binaphthol were clearly separated into a pair of peaks due to enantiomers in the presence of the chiral selector. Moreover, on the basis of molecular mechanics calculation, a chiral discrimination model was proposed which nicely explains the relevant chromatographic behavior of the 1,1'-binaphthyl derivatives.