Wonjae Lee

Liquid chromatographic resolution of racemic amino acids and their derivatives on a new chiral stationary phase based on crown ether

Abstract A new high-performance liquid chromatography chiral stationary phase (CSP) was prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to silica gel. The new CSP was employed in separating the two enantionmers of various natural and unnatural racemic α-amino acids and their derivatives. All natural and unnatural racemic α-amino acids tested were resolved with reasonable separation factors on the new CSP, except for proline, which does not contain a primary amino group. Racemic α-amino acid derivatives were also tested for their separability on the new CSP. In general, N-monoalkyl amides of α-amino acids were resolved better than the corresponding free α-amino acids. However, N,N-dialkyl amides and esters of α-amino acids were not resolved as well as the corresponding free α-amino acids, except for phenylglycine derivatives. In the case of phenylglycine, both N-monoalkyl and N,N-dialkyl amides of phenylglycine were resolved better than phenylglycine itself and its ester derivative.

Liquid chromatographic resolution of racemic amines and amino alcohols on a chiral stationary phase derived from crown ether

Abstract A chiral stationary phase (CSP) prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to silica gel was successfully employed in resolving various racemic amines and amino alcohols including therapeutically active compounds such as amphetamine, phenylethanolamine, octopamine and norepinephrine. Related compounds such as α-amino carbonyl compounds were also resolved on the CSP. In order to see the effect of organic and acidic modifiers in the mobile phase and the temperature of the column on the enantioselectivity exerted by the CSP, four racemic compounds which resolved well on the CSP were selected and their resolutions were investigated with the variation of organic and acidic modifiers in the mobile phase and the temperature of the column. From the results, the chromatographic factors such as capacity factors ( k ′), separation factors ( α ) and resolution factors ( R s ) were expected to be controlled to some extent by varying organic and acidic modifiers in the mobile phase and the temperature of the column.

Direct liquid chromatographic enantiomer separation of new fluoroquinolones including gemifloxacin

The enantiomers of gemifloxacin mesylate (formerly LB20304a), a new fluoroquinolone compound with potent in vitro and in vivo antibacterial profile were resolved on a commercially available Crownpak CR chiral stationary phase (CSP). All of the fluoroquinolones, including gemifloxacin used in this study, were well enantioseparated on Crownpak CR(+) column. These results are the first reported for the direct separation of the enantiomers of quinolones on chiral crown ether coated Crownpak CR CSP. The behavior of chromatographic parameters by the change of mobile phase additives for the resolution of gemifloxacin was investigated. Also, the effect of structural change of gemifloxacin on chiral recognition was described.

Liquid chromatographic resolution of racemic compounds containing a primary amino group on a dynamic chiral stationary phase derived from chiral crown ether

A dynamic chiral stationary phase (CSP) prepared by hydrophobically bonding N-dodecyl diamide of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to octadecyl silica gel was successfully employed in resolving various racemic compounds containing a primary amino functional group. The racemic compounds resolved on the CSP include α-amino acids, α-amino esters, amino alcohols, amines, α-aminocarbonyl compounds, and fluoroquinolone antibacterial agents. In order to see the effect of organic and acidic modifiers in the mobile phase and the temperature of the column on the enantioselectivity exerted by the CSP, five racemic compounds that resolved well on the CSP were selected and their resolutions were investigated with the variation of organic and acidic modifiers in the mobile phase and the temperature of the column. The results demonstrate that the chromatographic factors such as capacity factors (k), separation factors (α), and resolution factors (RS) might be controlled, to some extent, by varying organic and acidic modifiers in the mobile phase and the temperature of the column.