Cyclodextrins as Chiral Selectors in Capillary Electrophoresis Enantioseparations

Capillary electrokinetic chromatography for chiral separation of potential SARS-CoV-2 3CL protease inhibitors

In this work, a capillary electrophoresis method was developed as a quality control tool to determine the enantiomeric purity of a series of five chiral compounds evaluated as potential severe acute respiratory syndrome coronavirus 2 3CL protease inhibitors. The first cyclodextrin tested, that is, highly sulfated-β-cyclodextrin, at 6% (m/v) in a 25 mM phosphate buffer, using a capillary dynamically coated with polyethylene oxide, at an applied voltage of 15 kV and a temperature of 25°C, was found to successfully separate the five derivatives. The limits of detection and quantification were calculated together with the greenness score of the method in order to evaluate the method in terms of analytical and environmental performance. In addition, it is noteworthy that simultaneously high-performance liquid chromatography separation of the enantiomers of the same compounds with two different columns, the amylose tris(3,5-dimethylphenylcarbamate)-coated and the cellulose tris(3,5-dichlorophenylcarbamate)-immobilized on silica stationary phases, was studied. Neither the former stationary phase nor the latter was able to separate all derivatives in a mobile phase consisting of n-heptane/propan-2-ol 80/20 (v/v).

Improvement of chemo- and stereoselectivity for phosphorothioate oligonucleotides in capillary electrophoresis by addition of cyclodextrins

Phosphorothioate (PS) modification is one of the most widely used oligonucleotide chemical alterations in the oligonucleotide backbone. It has proven to be crucial in the field of therapeutic oligonucleotides regarding the optimization of their physicochemical and biological properties. In this study, a capillary electrophoresis (CE) method with an acidic background electrolyte (BGE) containing a combination of β- and γ-cyclodextrins derivatives as chiral selectors is proposed for the diastereomeric separation of 5-mer oligonucleotides containing 0, 1, 2, or 3 phosphorothioate linkages (5´-TCGTG-3´). The effects of the BGE pH, organic modifier addition, and type of cyclodextrin (CD) on chemo- and stereoselectivity and resolution were studied. A mixture of 25 mM (2-hydroxy-3-N,N,N-trimethylamino)propyl-γ-CD and 10 mM carboxymethyl-β-cyclodextrin in a pH 3 buffer was found to be the most appropriate system for the qualitative evaluation of the short oligonucleotides investigated. These phosphorothioate oligonucleotides were separated with high efficiency in less than 11 min with no capillary treatment. The suggested approach can be the basis for purity testing of this new generation of therapeutics.

Chiral separation of lansoprazole and rabeprazole by capillary electrophoresis using dual cyclodextrin systems

Novel capillary electrophoresis methods using CDs as chiral selectors were developed and validated for the chiral separation of lansoprazole and rabeprazole, two proton pump inhibitors. Fourteen different neutral and anionic CDs were screened at pH 4 and 7 in the preliminary analysis. Sulfobutyl-ether-β-CD with a degree of substitution of 6.5 and 10 at neutral pH proved to be the most suitable chiral selector for both compounds. Various dual CD systems were also compared, and the possible mechanisms of enantiomer separation were investigated. A dual selector system containing sulfobutyl-ether-β-CD degree of substitution 6.5 and native γ-CD proved to be the most adequate system for the separations. Method optimization was carried out using an experimental design approach, performing an initial fractional factorial screening design, followed by a central composite design to establish the optimal analytical conditions. The optimized methods (25 mM phosphate buffer, pH 7, 10 mM sulfobutyl-ether-β-CD/20 mM γ-CD, +20 kV voltage; 17°C temperature; 50 mbar/3 s injection, detection at 210 nm for lansoprazole; 25 mM phosphate buffer, pH 7, 15 mM sulfobutyl-ether-β-CD/30 mM γ-CD, +20 kV voltage; 18°C temperature; 50 mbar/3 s injection, detection at 210 nm for rabeprazole) provided baseline separation for lansoprazole (R_s = 2.91) and rabeprazole (R_s = 2.53) enantiomers with favorable migration order (in both cases the S-enantiomers migrates first). The optimized methods were validated according to current guidelines and proved to be reliable, linear, precise, and accurate for the determination of 0.15% distomer as chiral impurity in dexlansoprazole and dexrabeprazole samples.