Optical Resolution of Racemic α-Amino Acids on a Dynamic Chiral Stationary Phase by Ligand Exchange Chromatography

Effect of analyte lipophilicity on the resolution of α‐ and β‐amino acids on liquid chromatographic ligand exchange chiral stationary phases

“…In the resolution of alanine (3), aspartic acid (4), and glutamic acid (5) on CSP 1, the retention factors (k 1 ) increase as the methanol concentration in the aqueous mobile phase increases. In the resolution of asparagine (6), glutamine (7), and methionine (8) on CSP 1, the retention factors (k 1 ) do not show any significant trends as the methanol concentration in the aqueous mobile phase increases. In the resolution of a-amino acids 9 -14, which contain a relatively lipophilic side chain at the chiral center, on CSP 1, retention factors (k 1 ) decrease as the methanol concentration in the aqueous mobile phase increases.…”

Dynamic ligand‐exchange chiral stationary phase from S‐benzyl‐(R)‐cysteine

“…11,12 An interesting alternative was produced by introducing chiral alkyl groups onto the glycine nitrogen; in this case, there is no asymmetric carbon atom within the chelate ring, chirality being introduced with the Nsubstituent. [13][14][15][16] Following the observation that the presence of a phenyl ring in previously utilized selectors like N,N-dimethyl-(S)-phenylalanine (S-DMP) 17 and O-benzyl-(S)-serine (S-OBS) 18 results in a mixed, dynamically coated CSP, and with the aim to evaluate the influence of structural features on chiral differentiation and hence contribute to the understanding of the process and widen its scope, we have substituted the serine oxygen for a sulfur atom, thus affording S-benzyl-(R)-cysteine (R-SBC, Fig. 1), a new, rather inexpensive chiral selector endowed with a strong lipophilic character that comes through the combination of the sulfur atom and the aromatic ring.…”

High‐performance liquid chromatographic enantioseparation of unusual secondary amino acids on a D‐penicillamine‐based chiral ligand exchange column

“…9,11 Applying copper(II) as the metal ion, the formation of a five-member chelate ring is normally expected and a square planar structure is usually proposed for the ternary complexes involving Cu(II) and chelating ligands. 7,8,12 Penicillamine theoretically may interact via its N-, O-, and S-atom acting as a tridentate ligand. Zheng et al 14 used penicillamine as chiral ligand for ligand-exchange micellar electrokinetic chromatography and suggested that the pencillamine acts as a bidentate chelate, coordinating with Cu(II) via the amino nitrogen and the carboxyl oxygen (the -SH group does not participate in the chiral recognition process).…”

“…Chromatographic separation occurs if the complexes of enantiomers have different stabilities. Several chiral ligand-exchange stationary phases have been applied so far with different chiral selectors, e.g., proline, 5,7 leucinol derivative, 13 norephedrine, 8 and penicillamine. 9,11 Applying copper(II) as the metal ion, the formation of a five-member chelate ring is normally expected and a square planar structure is usually proposed for the ternary complexes involving Cu(II) and chelating ligands.…”