Cation‐enhanced capillary electrophoresis separation of atropoisomer anions

Abstract

CE was used to study the separation of the atropoisomers of four phosphoric acids and two sulfonic acids and the enantiomers of two phosphoric acids. All solutes are in their anionic forms in aqueous electrolytes. The chiral additives were two hydroxypropyl cyclodextrins (CDs) and cyclofructan 6 (CF6). The CDs were able to separate four solutes and the CF6 additive could separate only one: 1,1'-binaphthyl-2,2'-diyl hydrogenphosphate (BHP). Since CF6 is able to bind with cations, nitrate of alkaline metals, Ba(2+) , and Pb(2+) were added, greatly improving the BHP separation at the expense of longer migration times. There seems to be a link between CF6-cation-binding constants and BHP resolution factors. Cation additions were also performed with CD selectors that are less prone to form complexes with cations. Significant improvements of enantiomer or atropoisomer separations were observed also associated with longer migration times. It is speculated that the anionic solutes associate with the added cations forming larger entities better differentiated by CDs.

Recent trends and applications in liquid‐phase chromatography enantioseparation of atropisomers

“…In this review, new applications, covering years 2010–2016, are described and discussed with a specific focus on current topics and trends concerning HPLC enantioseparations. Indeed, despite electromigration techniques have been shown to be a powerful tool also for atropisomers separation , HPLC is still the most commonly used technique due to its widespread popularity. At the same time, supercritical fluid chromatography (SFC) has been developed both for analytical and preparative purposes, receiving special attention by pharmaceutical industry and becoming the preferred technique for enantioseparation and purification in drug discovery research.…”

Chiral selectors in CE: Recent development and applications (mid‐2014 to mid‐2016)

“…In other studies, HP‐β‐CD was successfully used as a CS for the separation of catechins and propranolol enantiomers , and the methods were applied in green tea leave samples and human body fluids, respectively. In another study , hydroxypropyl‐γ‐CD (HP‐γ‐CD) was able to separate 1,1′‐binaphtyl‐2,2′‐diyl hydrogenphosphate (BHP) enantiomers, while HP‐β‐CD separated BHP, 2‐(2‐isopropylphenyl)‐3,5,6‐trimethyl‐phenyl sulfonic acid, and 2‐naphthyl‐3,5,6‐trimethyl‐phenyl sulfonic acid enantiomers. The addition of either Ba 2+ or Pb 2+ in the BGE improved the separations.…”

“…Na et al. studied the enantioseparation ability of native CF6 with and without the addition of metal cations. The only compound that was partially separated ( R S = 1.0) was BHP.…”