tWhile aliphatic 2-hydroxyalkanoic acids have been more or less successfully enantioseparated withvarious chiral stationary phases by HPLC and GC, analogous applications on underivatized aliphatic 3-hydroxyalkanoic acids are completely absent in the scientific literature. With the aim of closing thisgap, the enantioseparation of 3-hydroxybutyric acid, 3-hydroxydecanoic acid and 3-hydroxymyristicacid has been performed with two ion-exchange type chiral stationary phases (CSPs): one containing theanion-exchange type tert-butyl carbamoyl quinine chiral selector motif (Chiralpak QN-AX), and the othercarrying the new zwitterionic variant based on trans-(S,S)-2-aminocyclohexanesulfonic acid-derivatizedquinine carbamate (Chiralpak ZWIX(+)) as the chiral selector and enantiodiscriminating element, respec-tively. The zwitterionic enantiorecognition material provided better results in terms of enantioselectivityand resolution compared to the anion-exchanger CSP at reduced retention times due to the intramolecularcounterion effect imposed by the sulfonic acid moiety and its competition with the 3-hydroxyalkanoicacid analyte for ionic interaction at the quininium-anion exchanger site. It is thus recommended as theCSP of first choice for enantioseparations of the class of aliphatic 3-hydroxyalkanoic acids. With use ofpolar organic eluent composed of ACN/MeOH/AcOH – 95/5/0.05 (v/v/v), a good compromise in terms ofanalysis time and enantioresolution quality was accomplished. The major experimental variables havebeen investigated for optimization of the resolution and allowed to derive information on the enan-tiorecognition mechanism. Corresponding Chiralpak ZWIX(−), based on pseudo-enantiomeric selectorderived from quinidine and trans-(R,R)-2-aminocyclohexanesulfonic acid with opposite configurationsprovided reversed enantiomer elution orders. It has further to be stressed that these separations can beobtained with mass spectrometry compatible mobile phases.
Direct enantioseparation of underivatized aliphatic3-hydroxyalkanoic acids with a quinine-based zwitterionic chiralstationary phase
IANNI, FEDERICA;SARDELLA, Roccaldo;NATALINI, Benedetto;
2014
Abstract
tWhile aliphatic 2-hydroxyalkanoic acids have been more or less successfully enantioseparated withvarious chiral stationary phases by HPLC and GC, analogous applications on underivatized aliphatic 3-hydroxyalkanoic acids are completely absent in the scientific literature. With the aim of closing thisgap, the enantioseparation of 3-hydroxybutyric acid, 3-hydroxydecanoic acid and 3-hydroxymyristicacid has been performed with two ion-exchange type chiral stationary phases (CSPs): one containing theanion-exchange type tert-butyl carbamoyl quinine chiral selector motif (Chiralpak QN-AX), and the othercarrying the new zwitterionic variant based on trans-(S,S)-2-aminocyclohexanesulfonic acid-derivatizedquinine carbamate (Chiralpak ZWIX(+)) as the chiral selector and enantiodiscriminating element, respec-tively. The zwitterionic enantiorecognition material provided better results in terms of enantioselectivityand resolution compared to the anion-exchanger CSP at reduced retention times due to the intramolecularcounterion effect imposed by the sulfonic acid moiety and its competition with the 3-hydroxyalkanoicacid analyte for ionic interaction at the quininium-anion exchanger site. It is thus recommended as theCSP of first choice for enantioseparations of the class of aliphatic 3-hydroxyalkanoic acids. With use ofpolar organic eluent composed of ACN/MeOH/AcOH – 95/5/0.05 (v/v/v), a good compromise in terms ofanalysis time and enantioresolution quality was accomplished. The major experimental variables havebeen investigated for optimization of the resolution and allowed to derive information on the enan-tiorecognition mechanism. Corresponding Chiralpak ZWIX(−), based on pseudo-enantiomeric selectorderived from quinidine and trans-(R,R)-2-aminocyclohexanesulfonic acid with opposite configurationsprovided reversed enantiomer elution orders. It has further to be stressed that these separations can beobtained with mass spectrometry compatible mobile phases.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
