Enantioseparation of amino acids and amino alcohols on chiral stationary phases derived from alpha-amino acid- and pyrrolidinyl-disubstituted cyanuric chloride

Three silica-based chiral stationary phases (CSPs) derived from L-alpha-amino acid- and pyrrolidinyl-disubstituted cyanuric chloride were prepared. The alpha-amino acids norvaline, valine, and phenylalanine were selected as the chiral moiety of CSPs. These CSPs provide effective recognition and separation of enantiomers of both methyl esters of N-(3,5-dinitrobenzoyl) amino acids, except that of proline, and N-(3,5-dinitrobenzoyl) amino alcohols by high-performance liquid chromatography. Amino acids, except phenylglycine, were generally separated more effectively than amino alcohols. Separation factors obtained for norephedrine on these CSPs, except CSP-2, are the best among reported values. Although the enantioselectivity depends mainly on three preferential interactions described previously which include a pi-pi interaction and two hydrogen-bonding interactions, steric interaction between substituents attached to chiral centers of chiral selectands and chiral selectors plays a significant role in the mechanism of chiral recognition. The phenyl ring in the phenylalanyl moiety of CSP-3 neither plays an electronic role in chiral recognition nor makes a significant contribution to chiral recognition. Comparison of chromatographic results shows that a CSP of a covalent type was more effective than the corresponding ionic type.