Chiral separation of phospine‐containing α‐amino acid derivatives using two complementary cellulosic stationary phases in supercritical fluid chromatography

Abstract

Enantiomeric separations of six amino-acid derivatives have been studied using packed-column supercritical fluid chromatography with two polysaccharide-based enantioselective stationary phases: cellulose tris(3,5-dimethylphenylcarbamate) and cellulose tris(3-chloro-4-methylphenylcarbamate) (Lux Cellulose-1 and -2). The effect of analyte structure on retention and separation was studied. Varied mobile phase compositions were investigated: alcohol modifier percentage was increased from 3 to 40% but smaller amounts were most effective in separating these compounds. Besides, ethanol was preferred to methanol or isopropanol as it proved to be a good compromise to achieve sufficient resolution in a reasonable analysis time. Moreover, a carbon dioxide-ethanol mixture allows performing analyses in safe and green conditions. The effect of temperature at constant mobile phase composition was explored between 10 and 40 degrees C. In most cases, increasing the temperature improved the chiral separation, up to an optimum temperature. The results are discussed in line with the structure variation of the racemic derivatives analyzed and the two columns are compared. The two columns were shown to provide complementary selectivities for the investigated solutes: whereas Lux 1 provided separation for five of the six racemates, Lux 2 could resolve the last racemic mixture. Finally, optimized conditions of separation are defined.

Thermodynamic enantioseparation behavior of phenylthiohydantoin‐amino acid derivatives in supercritical fluid chromatography on polysaccharide chiral stationary phases

“…The first two have short hydrophobic chains (one or two carbon atoms) while the latter two have hydrogen‐bonding groups (acidic function for PTH‐Aspartic acid and phenol group for PTH‐Tyrosine). U‐shaped curves were observed in past studies and may be explained by a change in conformation of the CSP in the range of temperature. For all pairs of enantiomers in this group, similar retention behavior was observed for the two enantiomers.…”

Enantiomeric separation of citalopram base by supercritical fluid chromatography

“…On the other hand, as temperature increases, thermal desorption of the solute is improved, which contributes to decreased retention. U‐shaped curves of retention with a minimum point were observed in some cases . In this work, the column temperatures were varied between 20 and 40°C.…”

“…Polar modifiers are often added to increase solvent strength, especially when polar solutes are to be separated. The addition of a polar modifier has numerous impacts on separation and retention . Firstly, the modifiers alter the solvent strength and density of the mobile phase.…”

Synthesis of optically active macroporous poly(N-isopropylacrylamide) hydrogels with helical poly(N-propargylamide) for chiral recognition of amino acids

“…Now it is widely accepted that only one of the enantiomers can be effective to cure diseases, while the other is less effective, sometimes ineffective, or even toxic. Accordingly, chiral recognition/resolution is thus of great interest and of ever-increasing importance, and large efforts have been paid to novel chiral separation techniques [1][2][3][4][5][6][7][8][9]. In addition, helical polymers were found to exhibit chiral recognition ability toward a wide range of chiral compounds [10][11][12][13].…”