Chiral recognition using a conformationally rigid chiral stationary phase derived from amino-ε-carprolactam

The mechanisms underlying chiral recognition of enantiomer separation using a conformationally rigid chiral stationary phase (CSP 2) derived from N-3,5-dinitrobenzoyl (DNB) amino-ε-carprolactam, a CSP structurally related to DNB leucine derived CSP 1, were investigated. Chromatographic comparisons of the resolution for two typical types of analytes were made on CSPs 1 and 2. For enantioseparation of N-acyl derivatives of 1-(1-or 2-naphthyl)ethylamine, all separation factors for DNB leucine derived CSP 1 were greater than those for DNB ε-carprolactam derived CSP 2. On the other hand, all separation factors for CSP 2 were much greater than those for CSP 1 when resolving DNB leucine derivatives. In any case, the overall chiral recognition mechanism of CSP 2 might be similar to that of CSP 1. However, it is thought that the conformationally rigid structure and/or enhanced electron density of the carbonyl group as a tertiary amide of CSP 2 could be responsible for different levels of chiral recognition relative to CSP 1, depending upon the analytes examined.