Comparative studies of immobilized polysaccharide derivatives chiral stationary phases for enantioseparation of furanocoumarins and dihydroflavones and discussion on chiral recognition mechanism

Abstract

Enantiomeric separation of furanocoumarins and dihydroflavones compounds were systematically studied in the normal‐phase mode using four different polysaccharide‐type chiral stationary phases, namely, Chiralpak IA, Chiralpak IC, Chiralpak IG, and Chiralpak IK‐3 by high‐performance liquid chromatography. The effect of alcohol modifiers and alcohol content on enantiomeric separation was evaluated for the separation of furanocoumarins and dihydroflavones. All the eight compounds have achieved baseline separation with the resolutions ranging between 1.52 and 23.11. For a better insight into the enantiorecognition mechanisms, thermodynamic analysis was carried out. The mechanisms of chiral recognition have been discussed. Among four chiral columns, Chiralpak IG exhibited the most universal and the best enantioseparation ability toward furanocoumarins and dihydroflavones when used n‐hexane‐isopropanol and n‐hexane‐ethanol as mobile phase, respectively. The steric hindrance, hydrogen bonding, and π‐π interaction played major roles in chiral recognition on Chiralpak IG. By comparing four chiral columns, this work systematically analyzed the separation methods of furanocoumarins and dihydroflavones for the first time and reported some active chiral ingredients of traditional Chinese medicine that have never been separated, which provided a further insight into the enantioseparation of furanocoumarins and dihydroflavones on chiral stationary phases.

Update on chiral recognition mechanisms in separation science

“…Recent studies combining HPLC enantioseparations on polysaccharide CSPs with computational modeling techniques have been summarized in Table 1. In contrast to an earlier summary [17], an increasing number of publications studied cellulose-based selectors [66,[71][72][73][74][75][76] compared to amylose-based selectors [69,70,[77][78][79]. Most often the enantioseparations were achieved under normal-phase conditions [70][71][72][73][74][76][77][78][79], but reversedphase elution [75,78] and polar organic mode [66,69] were also applied.…”

“…In contrast to an earlier summary [17], an increasing number of publications studied cellulose-based selectors [66,[71][72][73][74][75][76] compared to amylose-based selectors [69,70,[77][78][79]. Most often the enantioseparations were achieved under normal-phase conditions [70][71][72][73][74][76][77][78][79], but reversedphase elution [75,78] and polar organic mode [66,69] were also applied. The group of Carotti combined circular dichroism with molecular modeling to establish the enantiomer elution order of two tetracyclic quinoline derivatives composed of four stereoisomers when pure enantiomeric standards are not available [71].…”