Exploring adsorption-desorption kinetics and eddy dispersion in enantioselective hydrophilic interaction chromatography using teicoplanin-based chiral stationary phase.

Multimodal cation exchange-type tyrosine-based chiral stationary phases: Synthesis and applications in high-performance liquid chromatography.

1-(9H-Fluoren-9-ylidene)-2,3-dihydro-2-methyl-1H-benz[e]indene (short as FMB) as one of second-generation light-driven molecular motors contains a chiral carbon atom, and has attracted considerable attentions due to macroscopic chiral structures and light-driven behaviors through supramolecular assembly and cooperative effects. Herein, chiral analysis and semi-preparative separation of FMB enantiomers have been studied by high-performance liquid chromatography (HPLC) on polysaccharide-derived chiral stationary phases (CSPs). Effects of factors on chiral separation of FMB enantiomers, including type of CSP, composition and ratio of mobile phase, temperature, and flow rate, have been discussed in detail. Best separation of racemic FMB was achieved on cellulose tri(3,5-dimethylphenylcarbamate)-coated CSP with the resolution of 2.50 using the hexane-ethanol mixture (99:1, v/v). Then, each FMB enantiomer was obtained through semi-preparative separation with enantiomeric purity over 99%, and their absolute configurations as well as elution order were determined by electronic circular dichroism spectroscopy. Surprisingly, elution reversal phenomenon of FMB enantiomers was observed on cellulose- and amylose- tri(3,5-dimethylphenyl carbamate)-coated CSPs, in which (S)-FMB was eluted first on cellulose tri(3,5-dimethylphenylcarbamate)-coated CSP, and (R)-enantiomer was eluted first on the other. Moreover, molecular docking simulation has been employed to explain the recognition mechanism and elution reversal of FMB enantiomers on these two CSPs. The docking results revealed that π-π stacks, π-lone pair interactions, π- σ, and π-alkyl interactions between FMB and CSPs were the primary forces driving chiral separation, and the differences between them led to the enantiomer elution reversal on these two CSPs. Briefly, this work would provide valuable information for the separation and elution mechanisms of chiral molecular motors on polysaccharide-based CSPs.

The synthesis of molecularly imprinted polymer (MIP)-based chiral stationary phases (CSPs) by precipitation polymerization or multistep swelling and polymerization and their application are described. Monodisperse, spherical MIP particles, whose diameters are about 5μm, are prepared by those methods using a chiral template molecule. The obtained MIPs are suitable for enantioseparation of the target compound(s) in liquid chromatography (LC). Specifically, procedures for the synthesis of MIP-based chiral stationary phases by precipitation polymerization and multistep swelling and polymerization, respectively, for the enantioseparation of nicotine and warfarin, as well as the latter derivatives, are described.

Given the strict regulations governing the introduction of new drugs, chirality and related issues have garnered increasing attention in both modern pharmaceutical industries and academic research settings worldwide, especially in the realm of medicinal chemistry projects. Considering the crucial chirality-related issues, the necessity to establish suitable methodologies for determining and monitoring enantiomeric composition in either medicinal products or drug candidates becomes apparent. Among these methods, those utilizing the high-performance liquid chromatography (HPLC) technique through the "direct approach" with chiral stationary phase (CSP) currently offer distinct advantages over the others due to their efficiency and reliability. Hundreds of CSPs are now available on the market, with around 20-30 CSPs, or even fewer, being most commonly utilized to address the majority of enantiomer separation challenges across various compound classes. In this chapter, six separate examples concerning the enantioseparation of medicinal chemistry-relevant compounds of varying chemical and physicochemical nature are presented. In this framework, the use of both high-molecular-weight (polysaccharide- and glycopeptide-based) and low-molecular-weight (amino acid-, Cinchona alkaloid- and fully synthetic-based) chiral selectors is described under the most relevant elution regimens for liquid chromatography (i.e., reversed-phase (RP), normal-phase (NP), and polar organic (PO)/polar ionic (PI)modes).

By the early 2000s, chromatographic methods applying chiral stationary phases (CSPs) became the most effective techniques for the resolution of chiral compounds on both analytical and preparative scales. Nowadays, high-performance liquid chromatography (HPLC) employing various types of chiral selectors covalently bonded to silica-based supports, leading to the respective CSPs and the packed chromatographic columns thereof, offers a state-of-the-art methodology for enantioselective "chiral analysis." Although a large number of CSPs are commercially available, the design and development of new "chiral columns" are still mandatory since it is obvious that in practice one needs an even more well-balanced portfolio of different "chiral columns" to face the challenging tasks of enantiomeric resolutions. The development of the unique chiral anion, cation, and zwitterion exchangers achieved by Lindner and his partners serves as an expansion of the range of efficiently applicable CSPs.In this chapter, we present an updated and, in parts, text-wise renewed overview of our earlier chapter of this book series (Ilisz et al. (2019) Cinchona alkaloid-based zwitterionic chiral stationary phases applied for liquid chromatographic enantiomer separations: an overview. In: Scriba GKE (ed) Chiral seperations. Methods and protocols. Humana Press, pp 251-277. https://doi.org/10.1007/978-1-4939-9438-0 ) in discussing and summarizing direct enantiomer separations achieved by zwitterionic ion exchangers derived from Cinchona alkaloids, focusing on the literature published between 2018 and 2023. This article aims to provide comprehensive information on practical solutions for challenging enantiomer separations while discussing more generally the molecular recognition and methodological variables of these particular types of CSPs.

The resolution of chiral compounds into optically pure enantiomers is very important in various fields, such as pharmaceutical, chemical, agricultural, and food industries. Chiral gas chromatography (GC) is one of the efficient methods for enantioseparations of volatile compounds. In recent years, porous materials as stationary phases for chromatographic separations have gained increasing attention. Porous organic cages (POCs) represent an emerging class of porous materials, which are assembled by discrete organic molecules with shape-persistent and permanent cavities through weak intermolecular forces. The present chapter describes several chiral porous organic cages as chiral stationary phases (CSPs) for GC enantioseparations of racemic compounds.

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 the large variety of their interactive sites (e.g., hydrophobic pockets, hydroxyl, amino and carboxyl groups, halogen atoms, aromatic moieties, etc.) are the reasons for their wide-ranging selectivity. The commercially available columns based on antibiotic selectors, which display complementary characteristics, are capable of separating a wide variety of enantiomeric compounds with good efficiency, good column loadability, high reproducibility, and long-term stability. These are the main reasons for the frequent use of macrocyclic antibiotic-based stationary phases in enantioselective liquid chromatography.This overview chapter provides a summary of general aspects of antibiotic-based chiral stationary phases, including their preparation and their application to direct enantioseparations of various chiral compounds, focusing on the literature published between 2018 and 2023.

L-Cys-Functionalized Zr-Based MOF NU-1000: Fabrication and Application as Chiral Stationary Phase in Open Tubular Capillary Electrochromatography for Chiral Separation

Enzymatic reactions usually occur with a high substrate, product, or substrate-product stereoselectivity. In many instances, information on the stereochemical disposition of biologically active metabolites is indispensable for a complete understanding of biological processes and metabolic states. This raised interest in structural isomerism and stereoisomerism in metabolomics and lipidomics. While structural and geometrical isomers, as well as diastereomers, can be principally distinguished by achiral liquid chromatography (LC) and also ion-mobility mass spectrometry (MS), enantiomers require enantioselective separation methods. While untargeted enantioselective metabolomics is mostly based on the derivatization of metabolites with a chiral derivatizing agent, followed by LC separation on achiral columns and hyphenation with high-resolution mass spectrometry, targeted enantioselective LC with chiral stationary phases mostly employs robust triple quadrupole (QqQ) mass spectrometry for detection. It is a powerful technology, yet it focuses primarily on a broad, metabolite class-wide coverage. This chapter describes four distinct fields of application of targeted enantioselective LC-tandem mass spectrometry assays for important and representative metabolite classes. The first one deals with the enantioselective analysis of oxylipins using polysaccharide-based chiral columns, with protocols applicable for platelets and plasma; the second focuses on 3-hydroxyfatty acid enantiomer separations in plasma and platelets; the third application provides two workflows for proteinogenic enantioselective amino acid analysis; and the fourth application proposes methodologies for enantioselective short branched-chain fatty acid analysis. Critical aspects are discussed.

Polysaccharide-based chiral selectors are in wide use in chiral chromatography, both in the analysis and in the purification of chiral compounds. The use of superficially porous silica (SPS) particles, proven successful in various modes of liquid chromatography, is an obvious opportunity to elevate the performance of polysaccharide-based chiral stationary phases as well. In this chapter, the preparation, characterization, and chromatographic evaluation of chiral stationary phases made by combining superficially porous silica with polysaccharide-based chiral selectors are described.

This chapter illustrates the versatility of high-performance liquid chromatography (HPLC) chiral separation techniques to analyze chiral agrochemicals, often applied as racemic mixtures, and useful mathematical tools for the evaluation of stereoisomer degradation routes in the environment. Among the several chiral stationary phases, polysaccharide-based carbamate- or ester-functionalized ones are the most popular and effective, both in terms of enantioselectivity and chemoselectivity, proving to be potent analytical tools for studying chiral pesticides. In recent years, the tendency promoted by the European policies has led to the development of agrochemical formulations containing a single active enantiomer. The actual purity of such preparations and the degradation pathways of the involved chiral species can be studied through the procedures described here. In this perspective, enantioselective analyses allow one to verify the quality of the commercialized products and the degradation processes of involved stereoisomers in environmental and food samples. As a model analytical workflow, an enantioselective chromatographic method for the detection and quantitative assessment of quizalofop-ethyl and quizalofop, a post-emergence herbicide and its main metabolite, respectively, is presented here. The analytical procedure aims at following the chiral signature of these contaminants in the environmental sector, giving tools for the investigation of dispersive dynamics and natural degradation pathways of chiral species.

Stereoselective HPLC separation and configurational stability study of the N-nitrosamine impurity of indapamide.

Synthetic cathinones represent one of the largest groups of new psychoactive substances (NPS), compounds that are being distributed as temporarily legal alternatives to illicit drugs. Apart from this aspect, synthetic cathinones have been intensively studied for their potential medicinal use. Hereby, we discuss some basic considerations for their chiral resolution, which enables the assessment of the biological effect of the individual enantiomers of these drugs. The examples illustrate the utilization of two versatile polysaccharide-based chiral stationary phases (CSPs) in different mobile phases (MPs). Protocols for easy and scalable harvesting of the separated enantiomers are also provided.

A widely targeted analytical method for oxylipins including enantiomers using chiral liquid chromatography tandem mass spectrometry.

In the contemporary landscape, polysaccharide-based chiral stationary phases have garnered significant popularity for several reasons: (i) their broad application range, (ii) the availability of diverse chemistry options in both coated and immobilized forms, and (iii) their substantial loading capacity, advantageous for preparative-scale operations. Undoubtedly, chiral separations continue to be a focal point, especially within the pharmaceutical sector, where supercritical fluid chromatography is swiftly gaining traction. However, its utilization presents greater complexity compared to high-performance liquid chromatography. The provided examples serve to elucidate the development of analytical-scale chiral separation methods and the impact of each operational parameter, such as flow rate, outlet pressure, and temperature variations, on chiral separation.

Capillary electrochromatography is a miniaturized technique offering some advantages over conventional ones in separation science. It combines the best features of capillary zone electrophoresis (high efficiency of separation) and liquid chromatography (high selectivity). Because of the low flow rates, minute volumes of mobile phases can be applied, and therefore, it can be considered a green analytical technique. Capillary electrochromatography has been successfully used to separate many classes of compounds, including peptides, proteins, drugs, antibiotics, pollutants, enantiomers, etc. In this overview chapter, the main features of this technique are summarized. Its potential for the separation of enantiomers of chiral compounds and the main chiral stationary phases employed are presented. Finally, some selected applications in this field, reported in the literature in the period 2020-2024, are presented.

Lipase-based HKUST-1 (Cu) biocomposites as chiral stationary phase for enantiomer separation in capillary electrochromatography

Development of a Reversed-Phase Chiral HPLC Method for Concurrent Chiral, Achiral, Assay, and Identification Analysis of Boc-L-Valine

Hop bitter acids from the pistillate flower of Humulus lupulus L. and their anti-inflammatory and anti-dengue virus activities.