Separation and determination of cinchona alkaloids by ligand-exchange capillary electrophoresis using a Cu(II)–l-lysine complex as selector

Splitting and separation mechanism of tenofovir alafenamide fumarate chiral isomers based on indirect chiral ligand exchange chromatography

The isolation and analysis of chiral isomers are critical parts of the drug development process to ensure effective and safe drug administration to patients. Indirect chiral ligand exchange chromatography (ICLEC) was developed to separate and determine tenofovir alafenamide fumarate (TAF) and its diastereoisomer GS-7339, with a hypothesized separation mechanism. The effect of using a chiral column versus a standard C18 column on the separation of the TAF chiral isomer mixture was investigated. Various factors in ICLEC, including ligand type, ligand ratio, mobile phase composition, and column temperature, were optimized. The separation of TAF and GS-7339 was successfully achieved by selecting L-phenylalanine as the chiral selective agent and Cu(II) as the central metal ion, using a C18 column as the analytic column and a mobile phase of 20 mM ammonium dihydrogen phosphate buffer (pH = 4.0)-acetonitrile (79 : 21, v/v). The corresponding linearity range for TAF and GS-7339 indicated a good correlation with R2 > 0.9960. The average recoveries of TAF and GS-7339 ranged from 98.2% to 106.9%. None of the eight manufacturers detected GS-7339, and the percentage of TAF-labeled amounts in the drugs ranged from 95.0% to 98.5%. TAF tablets from eight manufacturers were of satisfactory quality. The separation mechanism of TAF and GS-7339 by ICLEC is due to the different spatial configurations of the two ternary complexes formed by the two chiral isomers, leading to differences in their thermodynamic stability and retention behavior. The established ICLEC method is economical, simple, and flexible, providing an effective strategy for studying chiral drug separation and analysis.

Chiral ligand exchange capillary electrophoresis with L-dipeptides as chiral ligands for separation of Dns-D,L-amino acids

Herein, D- and L-oligopeptides were explored for the first time as chiral ligands in a chiral ligand exchange capillary electrophoresis (CLE-CE) protocol with Zn(II) as central ion for separation of derived d,l-amino acid enantiomers (Dns-D,L-AAs). The effect of four D- and L-oligopeptides, including glycine-l-lysine (Gly-L-Lys), glycine-d-lysine (Gly-D-Lys), l-lysine-lysine-OH and l-lysine-lysine-lysine-lysine-OH on the CLE-CE separation efficiency were evaluated. Thermodynamic calculations and circular dichroism spectra properties showed that the ternary species [(Gly-L-Lys)Zn(II)(D-AAs)] and [(Gly-L-Lys)Zn(II)(L-AAs)] presented the best stereoselectivity, possibly due to entropic effects. Notably, the migration order of Dns-D-AAs and Dns-L-AAs could be tuned by using Gly-D-Lys as the ligand for the CLE-CE system. To obtain satisfactory CLE-CE performance, the concentration ratio of Zn(II) to Gly-L-Lys, the pH of the buffer solution, and the concentration of Zn(II) were investigated. Under the optimized CLE-CE conditions using 100.0 mM H₃BO₃, 10.0 mM NH₄Ac, 3.0 mM Zn (II) and 12.0 mM Gly-L-Lys as the buffer solution at pH 8.30, nine pairs of Dns-D,L-AAs achieved baseline separation, with the partial separation of another five pairs. Furthermore, the proposed CLE-CE protocol, which presented a good linear relationship with the concentration of the test analytes in the range of 75.0-625.0 μM (r² ≥ 0.994) and the limit of detection of the method was 5.0 μM, was successfully applied in the kinetics study of l-asparaginase using l-asparagine as the substrate. Our strategy shows the great potential of L-dipeptides in the CLE-CE separation of D,L-AAs enantiomers and bio-applications.