The Development of One New Normal Phase Liquid Chromatography Method and Thermodynamic Investigation of Olodaterol Hydrochloride Enantiomer

In order to improve and replace the enantiomer method outlined in the olodaterol hydrochloride draft monograph (From the European Pharmacopoeia forum), one new, simple, and fast enantioselective normal phase high-performance liquid chromatography chiral method was developed on polysaccharide-based Chiral MX (2) (4.6 × 250 mm, 5 μm) column. n-Hexane, ethanol, and diethylamine in the ratio of 40:60:0.1 (V/V/V) were selected as mobile phase at a flow rate of 0.8 mL/min, and the detection was performed on a photodiode array detector at 225 nm with 5 μL injection volume. The column temperature was set at 40°C for better peak shape and sensitivity. The analysis time can be shortened to 15 min, whereas the resolution between enantiomer and olodaterol was found to be even more than 10.0, which was far better than that obtained with the reported method in this draft monograph. The developed chiral method was validated in accordance with ICH Q2 (R1), including specificity, LOD&LOQ, precision, linearity, accuracy, and robustness. Thereby, the proposed method was demonstrated to be suitable for the determination of enantiomer in olodaterol hydrochloride bulk drug and drug product. Besides, the thermodynamic parameters were evaluated on the basis of Van't Hoff plots that was used to explain correlative chiral recognition mechanisms with the chiral stationary phase.

Valbenazine isomers and enantiomer determination by chiral normal phase liquid chromatography

A novel, simple, specific, rapid, enantioselective normal phase chiral high-performance liquid chromatographic method with amylose-based Chiral Pak IG-3(250 × 4.6 mM) 3.0 μM column was developed and validated for separation and quantification of isomers and enantiomer of Valbenazine. The mobile phase composed of n-Heptane, isopropyl alcohol, dichloromethane, ethanol, and diethylamine in the ratio of 70:10:15:5:0.1 (V/V/V/VV) with a gradient flow rate was applied. The injection volume was 10 μl, and detection was carried out using a photodiode array detector at 282 nM. The column compartment was set at 35°C. The resolution between the enantiomer and isomers was found to be more than 2.0. The method was linear over the concentration range of limit of quantitation to 250% for isomers and enantiomers. The method was found to be robust with column temperature. The proposed chiral method is applicable for the determination of isomers and enantiomer of Valibenazine and was successfully used in the quality control of bulk drug manufacturing and pharmaceuticals.

Application of Polysaccharide-Based Chiral High-Performance Liquid Chromatography Columns for the Separation of Regio-, E/Z-, and Enantio-Isomeric Mixtures of Allylic Compounds

Daicel Chiralpak IA, IB, and IC, which are the polysaccharide-based chiral stationary phase (CSP) columns for high-performance liquid chromatography (HPLC), were applied in the separation of the non-enantiomeric isomeric mixtures obtained by the various allylation reactions and were highly effective in separating the regio- and (E)/(Z)-isomers in the allylation products. Due to the close structural similarity of the isomeric allylic compounds in the reaction mixtures, separations of the isomers are laborious and could not be accomplished by the conventional methods such as silica gel column chromatography, silica gel HPLC, preparative GPC, distillation, and so forth. This study has shown potential advantages of using the polysaccharide-based CSP columns in the separation of not only enantiomeric but also non-enantiomeric isomeric mixtures.

Impact of cyclofructan derivatives as efficient chiral selector in chiral analysis: An overview

The development of chiral selectors for the separation and analysis of chiral molecules has been an evolving process happening over three decades, since the introduction of the first chiral stationary phase (CSP) in 1938. The main impetus for designing new chiral selectors is to get to most promising one which has a broad chiral recognition property, separation capability for a wide range of chiral analytes, and the cost-effective CSP, which is also a major concern. Today, we have more than 100 commercially available CSPs, and these are prepared by coating or immobilizing the classical chiral selectors on to the chromatographic support, normally, silica gel. The purpose of this review is to look at progress and the impact of cyclofructan derivatives, a novel chiral selector introduced recently, for performing chiral analysis.

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

The planning and development of new chiral stationary phases (CSPs) for liquid chromatography (LC) are considered as continuous and evolutionary issues since the introduction of the first CSP in 1938. The main objectives of the development strategies were to attempt the improvement of the chromatographic enantioresolution performance of the CSPs as well as enlarge their versatility and range of applications. Additionally, the transition to ultra-high-performance LC were underscored. The most recent strategies have comprised the introduction of new chiral selectors, the use of new materials as chromatographic supports or the reduction of its particle size, and the application of different synthetic approaches for preparation of CSPs. This review gathered the most recent developments associated to the different types of CSPs providing an overview of the relevant advances that are arising on LC.

Chiral separation of 12 pairs of enantiomers by capillary electrophoresis using heptakis-(2,3-diacetyl-6-sulfato)-β-cyclodextrin as the chiral selector and the elucidation of the chiral recognition mechanism by computational methods

Chiral separation of 12 pairs of basic analyte enantiomers including oxybutynin, bambuterol, tradinterol, clenbuterol, clorprenaline, terbutaline, tulobuterol, citalopram, phencynonate, fexofenadine, salbutamol, and penehyclidine was conducted by capillary electrophoresis using a single-isomer anionic β-cyclodextrin derivative, heptakis-(2,3-diacetyl-6-sulfato)-β-cyclodextrin as the chiral selector. Parameters influencing separation were studied, including background electrolyte pH, heptakis-(2,3-diacetyl-6-sulfato)-β-cyclodextrin concentration, buffer concentration, and separation voltage. A background electrolyte consisting of 50 mM Tris-H₃ PO₄ and 6 mM heptakis-(2,3-diacetyl-6-sulfato)-β-cyclodextrin at pH 2.5 was found to be highly efficient for the separation of most enantiomers, with other conditions of normal polarity mode at 10 kV, detection wavelength of 210 nm using hydrodynamic injection for 3 s. Under the optimal conditions, baseline resolution (>1.50) for 11 pairs of enantiomers and somewhat lower resolution for penehyclidine enantiomers (1.17) were generated. Moreover, the possible mechanism of separation of clenbuterol, oxybutynin, salbutamol, and penehyclidine was investigated using a computational modeling method.

Optically active distorted cyclic triptycenes: chiral stationary phases for HPLC

A pair of optically active triptycene derivatives ((R,R)- and (S,S)-8) with a distorted cyclic structure were synthesized via an intramolecular etherification and evaluated as a novel chiral selector for high-performance liquid chromatography. The (R,R)- and (S,S)-8-based chiral stationary phases (CSPs) were found to be particularly effective in the resolution of axially chiral biaryl compounds. The importance of the distorted cyclic structure present in 8 for chiral recognition was demonstrated by comparisons with the corresponding non-cyclic model compound ((R,R)-9), which did not display enantioselectivity in the separation of the test racemates.

We have succeeded in developing triptycene-based chiral stationary phases with a distorted cyclic structure, which can resolve a series of axially chiral compounds.

New chiral stationary phases based on xanthone derivatives for liquid chromatography

Six chiral derivatives of xanthones (CDXs) were covalently bonded to silica, yielding the corresponding xanthonic chiral stationary phases (XCSPs). The new XCSPs were packed into stainless-steel columns with 150 x 4.6 mm i.d. Moreover, the greening of the chromatographic analysis by reducing the internal diameter (150 x 2.1 mm i.d.) of the liquid chromatography (LC) columns was also investigated. The enantioselective capability of these phases was evaluated by LC using different chemical classes of chiral compounds, including several types of drugs. A library of CDXs was evaluated in order to explore the principle of reciprocity as well as the chiral self-recognition phenomenon. The separation of enantiomeric mixtures of CDXs was investigated under multimodal elution conditions. The XCSPs provided high specificity for the enantiomeric mixtures of CDXs evaluated mainly under normal-phase elution conditions. Furthermore, two XCSPs were prepared with both enantiomers of the same xanthonic selector in order to confirm the inversion order elution.

Chromatographic enantioseparation by poly(biphenylylacetylene) derivatives with memory of both axial chirality and macromolecular helicity

Novel poly(biphenylylacetylene) derivatives bearing two acetyloxy groups at the 2- and 2'-positions and an alkoxycarbonyl group at the 4'-position of the biphenyl pendants (poly-Ac's) were synthesized by the polymerization of the corresponding biphenylylacetylenes using a rhodium catalyst. The obtained stereoregular (cis-transoidal) poly-Ac's folded into a predominantly one-handed helical conformation accompanied by a preferred-handed axially twisted conformation of the biphenyl pendants through noncovalent interactions with a chiral alcohol and both the induced main-chain helicity and the pendant axial chirality were maintained, that is, memorized, after complete removal of the chiral alcohol. The stability of the helicity memory of the poly-Ac's in a solution was lower than that of the analogous poly(biphenylylacetylene)s bearing two methoxymethoxy groups at the 2- and 2'-positions of the biphenyl pendants (poly-MOM's). In the solid state, however, the helicity memory of the poly-Ac's was much more stable and showed a better chiral recognition ability toward several racemates than that of the previously reported poly-MOM when used as a chiral stationary phase for high-performance liquid chromatography. In particular, the poly-Ac-based CSP with a helicity memory efficiently separated racemic benzoin derivatives into enantiomers.

Chiral stationary phases consisting of π-conjugated polymers bearing glucose-linked biphenyl units: reversible switching of resolution abilities based on a coil-to-helix transition

We have succeeded in developing a novel chiral stationary phase that can reversibly switch resolution abilities based on a coil-to-helix transition in a column.

Application of click chemistry on preparation of separation materials for liquid chromatography

With the increasing requirement for analysis and separation of samples related to genomics, proteomics, metabolomics, pharmacology and agrochemistry, diverse stationary phases for liquid chromatography have been prepared by Cu(i)-catalyzed 1, 3-dipolar azide-alkyne cycloaddition reaction (CuAAC). It has been proved that CuAAC is a powerful tool for preparing covalently bonded stationary phases. In this tutorial review, we highlighted the preparation of separation materials by immobilization of functional groups on silica beads, polymer beads and agarose via CuAAC and their applications in liquid chromatography and related purposes, such as separation of polar compounds, enrichment of valuable bio-samples, orthogonal two-dimensional HPLC and chiral separation. Meanwhile, agarose-based separation materials for affinity chromatography are reviewed.

Structures of water molecules at solvent/silica interfaces

The adsorption of water at solvent/silica interfaces was studied using IR-visible sum frequency generation (SFG) vibrational spectroscopy. We discovered a water layer between toluene and silica with no detectable free OHs. The water layer without free OHs showed resistance against further adsorption of water molecules. This "water-resistant" water surface was very stable at room temperature and did not become a regular water layer with free OH over a period of 12 h in water-saturated toluene. However, this special structure of water was not observed at heptane/silica interfaces, at which free OHs were observed. The study indicates that interactions between solvents and water molecules can significantly change the interfacial water properties.

Application of Click-chemistry-based perphenylcarbamated beta-CD chiral stationary phase in CEC

A novel chiral stationary phase (CSP) was prepared by anchoring mono-6-azido-6-deoxyperphenylcarbamated beta-CD onto omega-alkynyl functionalized silica (5 microm) via organic soluble Cu(I)-catalyzed Click chemistry. The obtained CSP was thereafter packed into fused-silica capillary (100 microm id) with an effective length of 9 cm and tested in aqueous CEC to separate a series of racemic aryl alcohols. High separation factors with good resolution were achieved using the current novel CSP. Some pharmaceutical compounds could also be well resolved on this newly derived CSP. The analytical results demonstrate that Click-chemistry-based perphenylcarbamated CSP affords high stability in high electric field and depicts excellent enantioseparation in CEC. The effects of pH value, buffer concentration, applied voltage, concentration of organic modifier and analyte structure on the enantioseparation are also discussed.

Rapid chiral separation and impurity determination of levofloxacin by ligand-exchange chromatography

A sensitive, simple, and accurate method for determination of levofloxacin and its (R)-enantiomer was developed to determine the chiral impurity of levofloxacin in Cravit Tablets material by ligand-exchange high performance liquid chromatography. The effects of different kinds of ligands, concentration of ligands in mobile phase, organic modifier, pH of mobile phase, and temperature on enantioseparation were investigated and evaluated. Chiral separation was performed on a conventional C(18) column, where the mobile phase consisted of a methanol-water solution (containing 10 mmol L(-1)l-leucine and 5 mmol L(-1) copper sulfate) (88:12, v/v) and its flow-rate was set at 1.0 mL min(-1). The conventional C(18) column offers baseline separation of two enantiomers with a resolution of 2.4 in less than 20 min. Thermodynamic data (DeltaDeltaH and DeltaDeltaS) obtained by Van't Hoff plots revealed the chiral separation is an enthalpy-controlled process. The standard curves showed excellent linearity over the concentration range from 0.5 to 400 mg L(-1) for levofloxacin and its (R)-enantiomer. The linear correlation equations are: y=1.33 x 10(5)x+6297 (r=0.9991) and y=1.34 x 10(5)x+3565 (r=0.9997), respectively. The relative standard deviation (RSD) of the method was below 2.3% (n=3).

Immobilized polysaccharide derivatives: chiral packing materials for efficient HPLC resolution

Polysaccharide-based chiral packing materials (CPMs) for high-performance liquid chromatography have frequently been used not only to determine the enantiomeric excess of chiral compounds but also to preparatively resolve a wide range of racemates. However, these CPMs can be used with only a limited number of solvents as mobile phases because some organic solvents, such as tetrahydrofuran, chloroform, and so on, dissolve or swell the polysaccharide derivatives coated on a support, e.g., silica gel, and destroy their packed columns. The limitation of mobile phase selection is sometimes a serious problem for the efficient analytical and preparative resolution of enantiomers. This defect can be resolved by the immobilization of the polysaccharide derivatives onto silica gel. Efficient immobilizations have been attained through the radical copolymerization of the polysaccharide derivatives bearing small amounts of polymerizable residues and also through the polycondensation of the polysaccharide derivatives containing a few percent of 3-(triethoxysilyl)propyl residue.