Separation of the enantiomers of amino and amide compounds on novel chiral stationary phases derived from a crown ether

The enantiomers of primary amino compounds have previously been resolved on a chiral stationary phase (CSP) CSP-18C6I, prepared by immobilizing (+)-18-crown-6 tetracarboxylic acid. In this study related chiral stationary phases were prepared in an effort to broaden the scope of CSP18CGI. CSP-18C6II, synthesized to investigate the effect of spacer length, resolved the enantiomers of 2-amino-1,2-diphenylethanol and 1-(1-naphthyl)ethylamine (1-NEA) (hydrophobic amino compounds) with the larger alpha values and smaller a values than on CSP-18C6I, probably because of the greater hydrophobicity of CSP-18C6II. Use of CSP-18C6III, synthesized by modification of carboxylic acid functionality of CSP-18C6II by introduction of another chiral moiety, S-1-NEA, resulted in larger a values for 2-amino-1 -phenylethanol and 2-amino-1-phenylpropanol than on CSP-18C6II, but the enantiomers of 1-NEA were not resolved, because of steric hindrance between 1-NEA and the chiral moiety. The amide derivative N-3,5 -dinitrobenzoyl-1-(alpha-naphthyl) ethylamine (DNN) as pi-acceptor (3,5-dinitrobenzoyl function) or pi-donor (naphthylethylamide function), and no primary amino functionality, was resolved on CSP-18C6III. The mechanism of separation of the enantiomers of DNN was assumed to be the pi-pi: interaction between the 3,5-dinitrobenzoyl function (pi-acceptor) of DNN and the S-1-NEA moiety ( pi-donor) of CSP-18C6III.