Direct enantioseparation of underivatized aliphatic 3-hydroxyalkanoic acids with a quinine-based zwitterionic chiral stationary phase

Diastereo- and enantioseparation of a Nα-Boc amino acid with a zwitterionic quinine-based stationary phase: Focus on the stereorecognition mechanism

“…PI environments are expected to effectively suppress hydrophobic-type SO-SA contacts, attenuate all polar interactions, but still preserve strong electrostatic attraction between SO-SA substructure elements, such as H-bonding and ion pairing [21,35]. Acidic and basic additives in PI eluent systems help to control the ionization status of charged SOs and SAs by protonation and/or support the formation of well defined ion pairs.…”

“…Nonaqueous polar organic mobile phases enriched with acid and basic additives (polar-ionic mode of elution, PI) revealed the elective choice for the separation of acidic, basic and zwitterionic SAs on the ZWIX CSPs [18][19][20][21][22]. PI environments are expected to effectively suppress hydrophobic-type SO-SA contacts, attenuate all polar interactions, but still preserve strong electrostatic attraction between SO-SA substructure elements, such as H-bonding and ion pairing [21,35].…”

“…The ZWIX SOs are zwitterionic molecules with pseudo-enantiomeric character that incorporate both an anion-and a cation-exchange functional group [18][19][20][21]. In CSP 1 ( Fig.…”

“…Owing to the zwitterionic nature of the two SOs, the corresponding CSPs exhibit excellent enantioseparation capability towards amphoteric molecules of a wide structural variety as well as chiral bases and acids [18][19][20][21]. Besides the strong coulombic attraction, which is the major driving force for intermolecular SO-SA interaction, a series of further superimposed and potentially stereoselective contacts (including H-bonding-, dipole-dipole-, van der Waals-, and p-p-interactions) can be activated during the course of the enantiorecognition event.…”

“…A considerable increase in terms of overall stereoselectivity towards acidic compounds is exhibited by the second generation of this class of CSPs based on Cinchona alkaloids: the zwitterionic (ZWIX) CSPs, prepared by the rational fusion of the QN-or quinidine (QD)-based scaffold (that is, the WAX site) with aminocyclohexanesulfonic acid residues (acting as strong cation-exchange sites, SCX) ( Fig. 1, CSP 1 and CSP 2, respectively) [18][19][20][21][22].…”