NMR studies of chiral discrimination relevant to the liquid chromatographic enantioseparation by a cellulose phenylcarbamate derivative

Chromatographic enantioseparation of-1,1'-bi-2-naphthol (2) and its mono- and di-O-methylated derivatives (3a, 3b), 2,2'-dihydroxy-6,6'-dimethylbiphenyl (4), and 10,10'-dihydroxy-9,9'-biphenanthryl (5) has been performed on cellulose tris(5-fluoro-2-methylphenylcarbamate) (1) as a chiral stationary phase for high-performance liquid chromatography (HPLC). The complete base-line separation of 2 and 4 was achieved with the elution order of enantiomers such that the (R)-isomers eluted first followed by the (S)-isomers, The resolution of 5 and the O-methylated 3 was difficult on 1. The cellulose derivative 1 dissolved in chloroform also exhibited a chiral discrimination for 2 and 4 in H-1 and C-13 NMR spectroscopies as well as in HPLC. The hydroxy and some aromatic protons and carbon resonances of 2 and 4 were clearly separated into a pair of peaks due to enantiomers in the presence of 1. The binding geometry and dynamics between 1 and the enantiomers of 2 were investigated on the basis of spin-lattice relaxation time, H-1 NMR titrations, and intermolecular NOEs in the presence of 1. These NMR data are fully consistent with the chromatographic elution order. These results, combined with molecular modeling, reveal the chiral discrimination rationale.