Experiments and Models in Enantiorecognition by Chiral Pirkle-type Stationary Phases Containing Aromatic π-Acid Branching Units

An overview of the projects in the authors\u27 laboratory aimed at developing novel chiral stationary phases (CSPs) is presented. Emphasis is put on the origin of the concept of using 2,4,5,6-tetrachloro-1,3-dicyanobenzene (TCDCB) and 4-chloro-3,5-dinitrobenzoic acid (CDNB) as the branching units in the Pirkle-type (brush-type) CSPs. Preparations of nearly a hundred novel CSPs, requiring synthesis of almost three hundred new compounds as intermediates or model structures, are described. Specific recognition properties and enantioselection efficacy of individual CSPs is demonstrated for various sets of test racemates (TR). Correlation between the structure and conformational properties of chiral selectors and racemic analytes is discussed. Specific properties of some CSPs, such as enhancement of their capacity by introducing the tweezer unit in the chiral selector, and catalysis of the enantiomerization process of configurationally unstable analyte are discussed. The mechanism of enantiorecognition of some TRs by structurally related CSPs is suggested