Recently, we have discovered a new member of the macrocyclic chiral selector family called cyclofructan.  Cyclofructans are cyclic oligosaccharides consisting of a crown ether core with pendent fructofuranose units spiro-anealated around its exterior.   In their native forms, cyclofructans show little enantioselectivity when used as chiral selectors.  However, when cyclofructans are derivatized and bonded to silica, they make exceptional chiral stationary phases for HPLC.  Specifically, aliphatic (i.e. isopropyl) derivatized cyclofructan 6 exhibits tremendous enantioselectivity toward chiral primary amines primarily in the polar organic mode.  Aromatic derivatized cyclofructans (i.e. dimethylphenyl and naphthylethyl) prove to be broadly selective for a wide range of types of racemates and typically perform optimally in the normal phase.  In this study, the chiral recognition capabilities of three cyclofructan based chiral selectors, namely LARIHC CF6-P, LARIHC CF6-RN, and LARIHC CF7-DMP, were evaluated with supercritical and subcritical fluid mobile phases. The usage of carbon dioxide as a mobile phase component to replace either heptane (for transferring normal phase separations) or acetonitrile (for transferring polar organic separations) is evaluated. Using carbon dioxide as a replacement solvent allows for faster separations as well as huge operating cost savings. Direct comparisons between SFC and HPLC using the cyclofructan based chiral stationary phases will be made. Technical aspects of HPLC to SFC method transfer will be discussed in terms of flow rate, temperature, and mobile phase additives. Lastly, the applicability of semi-preparative SFC chiral separation on the LARIHC columns will be presented.

Super/subcritical fluid chromatographic chiral separations with cyclofructan based stationary phases

247th National Meeting (2014)

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