Chromatographic separation and analysis: chiral ion and ligand exchange stationary phases

Chiral ligand-exchange chromatography (CLEC) was invented in the late 1960s-early 1970s by Davankov and Rogozhin, and can be still considered as the elective choice for the direct enantioseparation of compounds endowed with chelating moieties. Among the numerous chelating species that have been evaluated as chiral selectors in ligand-exchange (LE) chromatography, an outstanding role is played by a group of amino acids encompassing proline, hydroxyproline, cysteine, histidine, phenylalanine, valine, lysine, isoleucine, penicillamine, and few amino alcohols carrying a phenylglycinol or leucinol residual as the basic scaffold. Chiral ion-exchange (IE) based CSPs have been first introduced by Rosini and co-workers, and then largely exploited by Lindner and co-workers at the University of Vienna. Among these phases, it is worth to mention chiral anion-exchangers based on cinchona alkaloid derivatives, chiral cation-exchangers based on chiral amino sulphonic and amino carboxylic acids and zwitterionic ion-exchangers. To date, particularly diffused are the anion-exchange columns, which found their enantiodiscriminating ability upon a modified quinine (QN) or quinidine (QD) scaffold. The effect deriving from a number of focused modifications on the basic chiral selector backbone as well as on the applied immobilization chemistry, have been deeply evaluated along the years.