Macrocyclic Glycopeptide-based Chiral Stationary Phases Research Articles

Enantioseparation of a-substituted proline analogs with macrocyclic glycopeptide-based chiral stationary phases immobilized on superficially porous particles of silica applying liquid chromatography with ultraviolet and mass spectrometric detection

In this study, the liquid chromatography-based direct enantioseparation of the stereoisomers of α-substituted proline analogs has been investigated utilizing chiral stationary phases with UV and/or mass spectrometric (MS) detection. Macrocyclic antibiotics, such as vancomycin, teicoplanin, modified teicoplanin, and teicoplanin aglycone, all covalently immobilized to 2.7 μm superficially porous silica particles have been applied as stationary phases. Mobile phases utilizing mixtures of methanol and acetonitrile with different additives (polar-ionic mode) were optimized during method development. Best separations were achieved with mobile phases of 100% MeOH containing either 20mM acetic acid or 20mM triethylammonium acetate. Special attention was given to the applicability of MS-compatible mobile phases. Acetic acid was found to be advantageous as a mobile phase additive for MS detection. Enantioselective chromatographic behaviors are interpreted based on the explored correlations between the analytes' structural features and those of the applied chiral stationary phases. For the thermodynamic characterization, separations were studied in the temperature range of 5-50°C. Generally, retention and selectivity decreased with increasing temperature, and in most cases, enthalpy-driven enantiorecognition was observed, but entropic contributions also were present. Unexpectedly, unusual shapes for the van Deemter curves were registered in the kinetic evaluations. General trends could be observed in the enantiomeric elution orders: S < R on VancoShell and NicoShell, and opposite R < S on TeicoShell and TagShell columns.

The Enantioselective Potential of NicoShell and TeicoShell Columns for Basic Pharmaceuticals and Forensic Drugs in Sub/Supercritical Fluid Chromatography.

The enantioselective potential of two macrocyclic glycopeptide-based chiral stationary phases for analysis of 28 structurally diverse biologically active compounds such as derivatives of pyrovalerone, ketamine, cathinone, and other representatives of psychostimulants and antidepressants was evaluated in sub/supercritical fluid chromatography. The chiral selectors immobilized on 2.7 μm superficially porous particles were teicoplanin (TeicoShell column) and modified macrocyclic glycopeptide (NicoShell column). The influence of the organic modifier and different mobile phase additives on the retention and enantioresolution were investigated. The obtained results confirmed that the mobile phase additives, especially water as a single additive or in combination with basic and acidic additives, improve peak shape and enhance enantioresolution. In addition, the effect of temperature was evaluated to optimize the enantioseparation process. Both columns exhibited comparable enantioselectivity, approximately 90% of the compounds tested were enantioseparated, and 30% out of them were baseline enantioresolved under the tested conditions. The complementary enantioselectivity of the macrocyclic glycopeptide-based chiral stationary phases was emphasized. This work can be useful for the method development for the enantioseparation of basic biologically active compounds of interest.

Reversed-phase HPLC enantioseparation of pantoprazole using a teicoplanin aglycone stationary phase-Determination of the enantiomer elution order using HPLC-CD analyses.

A direct HPLC method was developed for the enantioseparation of pantoprazole using macrocyclic glycopeptide-based chiral stationary phases, along with various methods to determine the elution order without isolation of the individual enantiomers. In the preliminary screening, four macrocyclic glycopeptide-based chiral stationary phases containing vancomycin (Chirobiotic V), ristocetin A (Chirobiotic R), teicoplanin (Chirobiotic T), and teicoplanin-aglycone (Chirobiotic TAG) were screened in polar organic and reversed-phase mode. Best results were achieved by using Chirobiotic TAG column and a methanol-water mixture as mobile phase. Further method optimization was performed using a face-centered central composite design to achieve the highest chiral resolution. Optimized parameters, offering baseline separation (resolution = 1.91 ± 0.03) were as follows: Chirobiotic TAG stationary phase, thermostated at 10°C, mobile phase consisting of methanol/20mM ammonium acetate 60:40 v/v, and 0.6 mL/min flow rate. Enantiomer elution order was determined using HPLC hyphenated with circular dichroism (CD) spectroscopy detection. The online CD signals of the separated pantoprazole enantiomers at selected wavelengths were compared with the structurally analogous esomeprazole enantiomer. For further verification, the inline rapid, multiscan CD signals were compared with the quantum chemically calculated CD spectra. Furthermore, docking calculations were used to investigate the enantiorecognition at molecular level. The molecular docking shows that the R-enantiomer binds stronger to the chiral selector than its antipode, which is in accordance with the determined elution order on the column-S- followed by the R-isomer. Thus, combined methods, HPLC-CD and theoretical calculations, are highly efficient in predicting the elution order of enantiomers.

High-Performance Liquid Chromatography Enantioseparations Using Macrocyclic Glycopeptide-Based Chiral Stationary Phases: An Overview.

Since their introduction by Daniel W. Armstrong in 1994, antibiotic-based chiral stationary phases have proven their applicability for the chiral resolution of various types of racemates. The unique structure of macrocyclic glycopeptides and their large variety of interactive sites (e.g., hydrophobic pockets, hydroxy, amino and carboxyl groups, halogen atoms, aromatic moieties) are the reasons for their wide-ranging selectivity. The commercially available Chirobiotic™ phases, which display complementary characteristics, are capable of separating a broad variety of enantiomeric compounds with good efficiency, good column loadability, high reproducibility, and long-term stability. These are the major reasons for the frequent use of macrocyclic antibiotic-based stationary phases in HPLC enantioseparations.This overview chapter provides a brief summary of general aspects of antibiotic-based chiral stationary phases including their preparation and their application to direct enantioseparations of various racemates focusing on the literature published since 2004.

Direct analysis of chiral active pharmaceutical ingredients and their counterions by ultra high performance liquid chromatography with macrocyclic glycopeptide-based chiral stationary phases

In this work the simultaneous separation of chiral active pharmaceutical ingredients (API) in salt form from their counterions has been performed by using different high-efficiency macrocyclic glycopeptide-based chiral stationary phases (CSPs). Not only a new zwitterionic vancomycin-based CSP has been prepared (similarly to what was done for teicoplanin) but macrocyclic selectors have also been bonded to sub-2 μm fully porous silica particles through traditional ureidic linkage to obtain versions of CSPs suitable for ultra-high performance applications. The direct separation of chiral APIs and counterions is particularly attracting since it simplifies the workflow traditionally used with reduction of analysis time and costs. The wide selection of macrocyclic antibiotics CSPs now available has allowed to manage different cases that can happen in the simultaneous separation of APIs and their counterions (either cations or anions). Indeed, while inorganic cations are retained on traditional vancomycin- and teicoplanin-based CSPs, inorganic anions are almost unretained (due to Donnan’s effect). On the other hand, cations and anions can be both retained on the zwitterionic versions of these CSPs. Afterwards, zwitterionic CSPs allowed the separation of other compounds including N-derivative amino-acids, profens, polyols, sugar anomers, oligosaccharides and inorganic anions/cations opening new perspectives in the use of this family of CSPs.

Chiral Method Development Strategies for HPLC using Macrocyclic Glycopeptide-Based Stationary Phases

Chiral HPLC methods using macrocyclic glycopeptide-based chiral stationary phases have been widely used and reported; however, the development of efficient methods to separate and quantify the analytes with high resolution is a challenging task. Therefore, the knowledge regarding the optimization of chromatographic parameters regarding this type of chiral chromatography is essential. This review presents and discusses the optimization of HPLC conditions and parameters for the chiral resolution of racemic drugs on macrocyclic glycopeptide-based chiral stationary phases. Strategies for chiral method development are presented, using polar ionic, reversed phase, normal phase and polar organic modes. The effect of the most important chromatographic parameters, such as mobile phase composition, flow rate and temperature on the enantioseparation are discussed aiming the adequate screening and optimization protocol for each mode.

Enantiomeric Separations of N–H/N–Me Aziridines Utilizing GC and HPLC

High-performance liquid chromatographic (HPLC) and gas chromatographic (GC) methods were developed for the separation of enantiomers of 12 novel aziridines. The HPLC separations were performed on cyclodextrin, cyclofructan, amylose, cellulose and macrocyclic glycopeptide-based chiral stationary phases, whereas the GC separations were performed only on cyclodextrin-based chiral stationary phases. The amylose-based HPLC chiral stationary phases showed good selectivity toward the aziridines, while having low retention factors. It was shown that the HPLC generally provided better separations for most of the compounds as compared to GC. Effective enantiomeric separations for ten aziridines were developed.

Comparison of Separation Efficiency of Macrocyclic Glycopeptide-Based Chiral Stationary Phases for the LC Enantioseparation of β-Amino Acids

Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of eighteen unnatural β-amino acids, including several β-3-homo-amino acids. The direct separations of the underivatized analytes were performed on chiral stationary phases containing macrocyclic glycopeptide antibiotics such as teicoplanin (Chirobiotic T and T2), teicoplanin aglycone (Chirobiotic TAG), vancomycin (Chirobiotic V and V2), and ristocetin A (Chirobiotic R) as chiral selectors. The effects of the organic modifier, mobile phase composition and pH on the separations were investigated. A comparison of the separation performances of the macrocyclic glycopeptide stationary phases revealed that the Chirobiotic T2 column exhibited better selectivity than the Chirobiotic T column for the separation of β-3-homo-amino acid enantiomers; vancomycin or ristocetin A exhibited lower selectivity. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers, with the exception of the Chirobiotic R column, where the elution sequence R < S was observed.

Transforming chiral liquid chromatography methodologies into more sensitive liquid chromatography–electrospray ionization mass spectrometry without losing enantioselectivity

LC–electrospray ionization (ESI) MS conditions were optimized for the individual chiral separation of 19 compounds of pharmaceutical interest using the macrocyclic glycopeptide-based chiral stationary phases in both polar organic and reversed-phase modes (RPM). The influence of mobile phase composition and MS additive type on sensitivity was investigated for all classes of compounds tested. Compounds with amine or amide groups were efficiently separated, ionized, and detected with the addition of 0.1% (w/w) ammonium trifluoroacetate to the solvent system in either the reversed-phase or polar organic mode (POM). Macrocyclic glycopeptide coupled column technology was initially used to screen all chiral compounds analyzed. Baseline resolution of enantiomers was then achieved with relatively short retention times and high efficiencies on Chirobiotic T, Chirobiotic V or Chirobiotic R narrow bore chiral stationary phases. The polar organic mode offered better limits of detection (as low as 100 pg/ml) and sensitivity over reversed-phase methods. An optimum flow-rate range of 200–400 μl/min was necessary for sensitive chiral LC–ESI-MS analysis.

Enantiomeric separations by HPLC using macrocyclic glycopeptide-based chiral stationary phases: an overview.

Enantiomeric separations by HPLC using macrocyclic glycopeptide-based chiral stationary phases: an overview.