Retention of fluorinated chiral selectors in biphasic fluorinated solvent systems and its application to the separation of enantiomers by countercurrent chromatography

Ethoxynonafluorobutane (ENFB) has been used as a component of new biphasic solvent mixtures. The suitability of several mixtures as solvent systems in countercurrent chromatography was tested. The applicability of the ENFB/2-PrOH/H₂O mixture to the separation of enantiomers, in combination with a fluorinated chiral selector (CS), was evaluated. N-Perfluoroundecanoyl-l-proline-3,5-dimethylanilide (2), analogous to the previously used N-dodecyl-l-proline-3,5-dimethylanilide (1), was synthesized for this purpose. The capacity of the new solvent system to retain the fluorinated CS in the fluorinated phase used as stationary was examined. Chiral selector 1 was applied in analogous conditions for comparative purposes. Additionally, MTBE/phosphate buffer solvent system was also used with the two CSs. The ENFB/2-PrOH/H₂O (25:35:40) mixture was found to be adequate in the enantioseparation of DNB-Leu and DNB-Leu-tBu. Enantioselectivity was maintained in the fluorinated solvent system without compromising eluting time. The complete separation of DNB-Leu-tBu was achieved and no leaks of CS to the mobile phase were detected.