Use of homologous series of analytes as mechanistic probes to investigate the origins of enantioselectivity on two chiral stationary phases

Abstract

The normal-phase liquid chromatographic behavior of two homologous series of racemic carbamate derivatives of leucine anilides was examined on two chiral stationary phases, one of which has not been described heretofore. These chiral stationary phases are related structurally to the N-(3,5-dinitrobenzoyl)leucine chiral stationary phases originally developed in these laboratories, but differ from each other principally in the manner in which the chiral selector is attached to the silica gel support. While these selectors utilize the same interaction sites for bonding, the length of the analyte's linear alkoxyl substituent strongly influences enantioselectivity on only one of the chiral stationary phases. Similar but substantially less severe trends are noted as the length of a p-alkyl substituent on the second series of anilides is increased. Inferences concerning possible chiral recognition mechanisms are drawn from these observations.