Mechanistic evaluation of the resolution of α-amino acids on dynamic chiral stationary phases derived from amino alcohols by ligand-exchange chromatography

Two dynamic chiral stationary phases CSP 7 and 12) were prepared starting from R-2-amino-1-propanol and (R)-α-phenylethylamine. The resolution of racemic α-amino acids on the two dynamic CSPs thus prepared were compared with previously reported resolution data on a dynamic CSP (2) derived from (1S,2R)-norephedrine. The enantioselectivity for the two enantiomers of α-amino acids on CSP 7 was found to be comparable to or better than that on CSP 2 while the enantioselectivity for the two enantiomers of α-amino acids on CSP 12 was much worse than that on CSPs 2 or 7. From these results, we concluded that the phenyl functionality at the first chiral center of CSP 2 is not essential in the chiral recognition. However, the hydroxy functionality of CSPs 2 or 7 does play a very important role in the chiral recognition.