Preparation of a stilbene diamido-bridged bis(β-cyclodextrin)-bonded chiral stationary phase for enantioseparations of drugs and pesticides by high performance liquid chromatography

Short bridging and partial derivatization synergistically modified β-cyclodextrin bonded chiral stationary phases for improved enantioseparation

β-Cyclodextrin (β-CD) and its derivatives have been widely employed in the field of chiral separation, but they are still faced the limitation of low enantioselectivity and complex processes. Derivatization with functional molecules or preparation as bridging dimers are the two main modifications for β-CD to obtain chiral recognition compounds. Herein, a partially derived bridged β-CD (CPI-EBCD) bonded chiral stationary phases was prepared to improve enantioseparation. The chiral recognition moiety was synthesized by a bridged β-cyclodextrin dimer using a short-chain bridging agent (ethylenediamine) and then modifying the bridged cyclodextrin with a 4-chlorophenylisocyanate (CPI) containing a benzene ring and polar group. Compared with natural β-CD, dual-chambered CPI-EBCDs have better encapsulation synergies and more recognition sites with the guest molecule, while the short flexible bridging groups make the double cavities closer and more easily recognizable as linear molecules. The introduction of derived groups CPI provided more recognition sites and more types of interactions, including π-π interaction force, hydrogen bonding effect, and dipole-dipole interaction, thus improving the enantiomer-specific chirality recognition effect. The chiral stationary phase CPI-EBCDP was obtained by connecting CPI-EDCB with mesoporous silica microspheres by simple photochemical reaction using a green non-toxic diazo resin as coupling agent, simplifying preparation process. In the reversed phase mode of liquid chromatography, CPI-EBCDP has excellent chiral recognition ability, and 12 chiral compounds are successfully isolated by optimizing mobile phase conditions, with good reproducibility and stability. The successful preparation of this new chiral stationary phase provides an important reference for the subsequent development of cyclodextrin-like chiral stationary phases.

Preparation of a bis-triazolyl bridged β-cyclodextrin stationary phase and its application for enantioseparation of chiral compounds by HPLC

A novel bis-triazolyl bridged β-cyclodextrin was first synthesized by the Click reaction between azido-β-cyclodextrin and 1,6-heptadiyne. Then it was bonded onto silica gel to obtain a bis-triazolyl bridged β-cyclodextrin-based chiral stationary phase (BCDP). After structure characterization, the HPLC performance of BCDP was systematically evaluated by using different types of compounds as probes. The results showed that BCDP could well separate 18 kinds of achiral aromatic compounds (homologues, positional isomers, etc.) and 35 kinds of chiral drugs or pesticides, such as triazoles (Rs = 1.33-3.15), flavanones (Rs = 1.49-2.62), dansyl amino acids (Rs = 0.96-1.99), and β-blocker drugs (Rs = 0.68-2.78). BCDP could separate a wider range of compounds (53 kinds); especially, some chiral substance pairs that were difficult to be resolved on the ordinary cyclodextrin CSPs, including triazoles containing two chiral carbons (triadimenol, bitertanol, metconazole, and triticonazole), strongly ionized amino acids (acidic Asp, alkalic Arg, and polar Thr) and β-blockers with bulky groups (carvedilol, propranolol, and pindolol). Obviously, the unique synergistic inclusion effect of bridged cyclodextrin with double cavities and the bis-triazole bridging group could provide multiple action sites, such as hydrogen bonding, π-π stacking and acid-base action sites, thus improving its chiral chromatographic performance.

Investigation of the chiral recognition role of cyclodextrin hydroxyl moieties via high performance liquid chromatography

Cyclodextrin (CD) is known to afford excellent enantioselectivities due to its hydrophobic cavity and external H-bonding sites from hydroxyl moieties. However, there is still a lack of direct and comprehensive evidence clearly illustrating the origin of the important H-bonding effect. Regarding this issue, herein, four allylimidazole CD derivatives by selective substitution of the primary (6-position) and/or secondary (2,3-position) CD were synthesized and clicked onto silica surfaces to afford the corresponding chiral stationary phases (CSPs). The chiral chromatographic performances were systematically evaluated by separating 35 racemic analytes including isoxazolines, dansyl-amino acids, flavonoids and other racemates under reversed-phase HPLC. The chiral selection factors (α) and retention times (k) of the analytes on the as-prepared CSPs were comprehensively compared and it reveals that the enantioseparation ability was significantly altered due to the selective substituents of CD hydroxyl groups. The natural allylimidazole CD CSP (AICDCSP) was superior to the 6-O-tert-butyldimethylsilyl AICDCSP (6-TBDMAICDCSP) for most analytes. Dansyl amino acids and Ar-Pys were well separated on AICDCSP and 6-TBDMAICDCSP, where dansyl amino leucine gained the highest resolution up to 4.72 on AICDCSP, and flavonoids and Ar-Oprs were only separated on AICDCSP. These interesting separation results demonstrate that the secondary hydroxyl groups play a pivotal role in the separation of chiral compounds. In addition, the size of the CD cavity and the choice of solute also have an effect on the separation of substances. The mechanism involved in enantioselective discrimination of the selectively substituted CDs was further investigated by the molecular docking simulation.

Recent advances in chiral selectors immobilization and chiral mobile phase additives in liquid chromatographic enantio-separations: A review

For decades now, the separation of chiral enantiomers of drugs has been gaining the interest and attention of researchers. In 1991, the first guidelines for development of chiral drugs were firstly released by the US-FDA. Since then, the development in chromatographic enantioseparation tools has been fast and variable, aiming at creating a suitable environment where the physically and chemically identical enantiomers can be separated. Among those tools, the immobilization of chiral selectors (CS) on different stationary phases and the chiral mobile phase additives (CMPA) which have been progressed and studied extensively. This review article highlights the major advances in immobilization of CS together with their different recognition mechanisms as well as CMPA as a cheaper and successful alternative for chiral stationary phases. Moreover, the role of molecular modeling tool as a pre-step in the choice of CS for evaluating possible interactions with different ligands has been pointed up. Illustrations of reported methods and updates for immobilized CS and CMPA have been included.

A novel pillar[3]trianglimine macrocycle with a deep cavity used as a chiral selector to prepare a chiral stationary phase by thiol-ene click reaction for enantioseparation in high-performance liquid chromatography

A chiral pillar[3]trianglimine (C60 H72 N6 O6 ) with a deep cavity has been developed as a chiral selector and bonded to thiolated silica by thiol-ene click reaction to fabricate a novel chiral stationary phase for enantioseparation in high-performance liquid chromatography. The enantioseparation performance of the fabricated chiral stationary phase has been evaluated by separating various racemic compounds, including alcohols, esters, amines, ketones, amino acids, and epoxides, in both normal-phase and reversed-phase elution modes. In total, 14 and 17 racemates have been effectively separated in these two separation modes, respectively. In comparison with two widely used chiral columns (Chiralcel OD-H and Chiralpak AD-H), our novel chiral stationary phase offered good chiral separation complementarity, separating some of the tested racemates that could not be separated or were only partially separated on these two commercial columns. The influences of analyte mass, mobile phase composition, and column temperature on chiral separation have been investigated. Good repeatability, stability, and column-to-column reproducibility of the chiral stationary phase for enantioseparation have been observed. After the fabricated column had been eluted up to 400 times, the relative standard deviations (n = 5) of resolution (Rs) and retention time of the separated analytes were < 0.39% and < 0.20%, respectively. The relative standard deviations (n = 3) of Rs and retention time for column-to-column reproducibility were < 4.6% and < 5.2%, respectively. This study demonstrated that the new chiral stationary phase has great prospects for chiral separation in high-performance liquid chromatography.

Preparation and Evaluation of an Azobenzenediamide Bridged bis(β-Cyclodextrin)-Bonded Chiral Stationary Phase for HPLC

An azobenzenediamide bridged bis(β-cyclodextrin) chiral stationary phase (AZCDP) was prepared, and its high-performance liquid chromatography performance in reversed-phase and polar organic modes was evaluated by chiral probes, including triazoles, flavanones, amino acids and β-blockers. The results showed that AZCDP had strong chiral separation ability and the 40 chiral compounds were successfully resolved, of which 32 were completely separated (Rs ≥ 1.5) and the best enantioresolution was up to 3.93 within 20 min under a wide range of pH value and temperature. The separation ability of AZCDP with double cavities was significantly better than common CD-CSPs with single cavity, which was related to the synergistic inclusion effect. Compared with the previously reported stilbene (C=C)-bridged CSP, AZCDP with azobenzene (N=N)-bridged had a wider resolution range. For example, it could resolve myclobutanil, pindolol, carteolol, betaxolol, bevanolol and bitertanol, which could not be resolved before, and should be related to the fact that the flexible N=N was more compatible with the synergistic inclusion between cavities than the rigid C=C bridge group. The azobenzenediamide bridging group could also provide hydrogen bond, π-π and other sites, which was conducive to chiral separations.

Vacuum-assisted thermal bonding of β-cyclodextrin and its derivatives as chiral stationary phases for high-performance liquid chromatography

In this work, the vacuum-assisted thermal bonding method was proposed for the covalent coupling of β-cyclodextrin (β-CD) (CD-CSP), hexamethylene diisocyanate cross-linked β-CD (HDI-CSP) and 3, 5-dimethylphenyl isocyanate modified β-CD (DMPI-CSP) onto the isocyanate silane modified silica gel. Under vacuum conditions, the side reaction due to the water residue from the organic solvent, air, reaction vessels and silica gel could be avoided, and the optimal temperature and time of vacuum-assisted thermal bonding method were determined as 160°C and 3 h. These three CSPs were characterized by FT-IR, TGA, elemental analysis and the nitrogen adsorption-desorption isotherms. The surface coverage of CD-CSP and HDI-CSP on silica gel was determined as ∼0.2 μmol m^-2, respectively. The chromatographic performances of these three CSPs were systematically evaluated by separating 7 flavanones, 9 triazoles and 6 chiral alcohols enantiomers under the reversed-phase condition. It was found that the chiral resolution ability of CD-CSP, HDI-CSP and DMPI-CSP was complementary to each other. Among them, CD-CSP could separate all 7 flavanones enantiomers with the resolution of 1.09-2.48. HDI-CSP had a good separation performance for triazoles enantiomers with one chiral center. DMPI-CSP showed excellent separation performance for chiral alcohol enantiomers, among which the resolution of trans-1, 3-diphenyl-2-propen-1-ol reached 12.01. Generally, the vacuum-assisted thermal bonding had been demonstrated as a direct and efficient method for the preparation of chiral stationary phases of β-CD and its derivatives.

Protein synergistic action-based development and application of a molecularly imprinted chiral sensor for highly stereoselective recognition of S-fluoxetine

In order to improve the recognition performance of MIPs sensors in chiral drug enantiomers, a novel a highly selective molecular recognition method based on protein-assisted immobilization of chiral molecular conformation was developed. S-fluoxetine (S-FLX) as the target chiral molecule, human serum albumin (HSA), which has a high affinity and strong interactions with S-FLX, was screened from 11 proteins to serve as an auxiliary recognition unit for the fixation of chiral conformation. By incorporating HSA into the preparation of molecularly imprinted polymers (MIPs), the natural chirality and high stereoselectivity of the protein were leveraged for the induction and fixation of the stereo conformation of S-FLX, refinement of internal structures of the imprinted cavities. The sensor exhibited excellent chiral recognition ability and high detection sensitivity. The changes of probe signal intensity of the MIPs/HSA sensor were positively correlated with the logarithmic concentration of S-FLX in the range of 1.0 × 10^-16-1.0 × 10^-11 mol L^-1, where a detection limit of 6.43 × 10^-17 mol L^-1 was achieved (DL = 3δ_b/K). The selectivity of MIPs/HSA sensor in recognizing S-FLX was increased by 18.5 times and the sensitivity was increased by 2.6 times after the incorporation of HSA. The developed sensor was successfully used for the analysis of S-FLX in fluoxetine hydrochloride capsules.

Green β-cyclodextrin-based corrosion inhibitors: Recent developments, innovations and future opportunities

β-Cyclodextrin-based compounds are used to develop and innovate materials that protect against corrosion due to their sustainability, low cost, environmental friendliness, excellent water solubility and high inhibition efficiency. However, corrosion potentials of β-CD-based compounds were not reviewed with the modern trends. The essence of the problem is that a deep understanding of the development and innovation of β-CD-based compounds as corrosion inhibitors is very important in creating next-generation materials for corrosion protection. In this review, the fundamental behaviour, importance, developments and innovations of β-CD modified with natural and synthetic polymers, β-CD grafted with the organic compounds, β-CD-based supramolecular (host-guest) systems with organic molecules, polymer β-CD-based supramolecular (host-guest) systems, β-CD-based graphene oxide materials, β-CD-based nanoparticle materials and β-CD-based nanocarriers as corrosion inhibitors for various metals were reviewed and discussed with recent research works as examples. In addition, the corrosion inhibition of β-CD-based compounds for biocorrosion, microbial corrosion and biofouling was reviewed. It was found that (i) these compounds are sustainable, inexpensive, environmentally friendly, and highly water-soluble and have high inhibition efficiency; (ii) the molecular structure of β-CD makes it an excellent molecular container for corrosion inhibitors compounds; (iii) the β-CD is excellent core to develop the next generation of corrosion inhibitors. It is recommended that (i) β-CD compounds would be synthesized by green methods, such as using biological sustainable catalysts and green solvents, green methods include irradiation or heating, energy-efficient microwave irradiation, mechanochemical mixing, solid-state reactions, hydrothermal reactions and multicomponent reactions; (ii) this review will be helpful in creating, enhancing and innovating the next green and efficient materials for future corrosion protection in high-impact industries.

Preparation and evaluation of a perylenediimide bridged bis(β-cyclodextrin) chiral stationary phase for HPLC

A large π-conjugated perylenediimide bridged bis(β-cyclodextrin)-bonded stationary phase (PBCDP) was first prepared and characterized. The chiral HPLC performance was systematically evaluated using a series of chiral probes. The results showed that PBCDP could resolve 36 kinds of chiral compounds in reversed-phase and polar organic modes with high resolutions (Rs) 1.48-3.28 for profens, 1.25-2.85 for triazoles, 1.34-5.29 for flavanones, 1.66-4.58 for amino acids and 1.22-1.97 for β-blockers. Especially, PBCDP could completely resolve acidic non-steroidal chiral drugs (profens) and simultaneously resolve basic five triazole pesticides, which were difficult to separate by ordinary CDCSP. Compared with CDCSP (15 kinds), the new stationary phase has a wider resolution range (36 kinds). Obviously, the synergistic inclusion of the two cavities of bridged cyclodextrin, as well as the large π-π stacking, hydrogen bond, dipole-dipole and basic primary amine site (-NH-) provided by the perylenediimide bridging group contributed together to the improvement of the above chiral separations. PBCDP was a new type of versatile chiral separation material without port derivatization.

Enantioselective separation, analysis and stereoselective dissipation of the chiral pesticide cloquintocet-mexyl using a modified QuEChERS method by high-performance liquid chromatography tandem mass spectrometry

An efficient and novel enantioseparation method was successfully developed and validated to quantify the enantiomers of cloquintocet-mexyl in soil, millet, enoki mushroom, oilseed rape, and watermelon using a modified QuEChERS technique combined with HPLC-MS/MS. This method showed reliable performances for determining both enantiomers of cloquintocet-mexyl in all five matrices. The limits of detection and limits of quantification were in the range of 0.06-0.15 μg kg^-1 and 0.2-0.5 μg kg^-1, respectively. Good linearities were obtained with correlation coefficients ≥0.9954. The mean recoveries were between 84.1% and 111.5%, with relative standard deviations ranging from 1.2% to 9.8% at three spiked levels. Additionally, the study of stereoselective dissipation of cloquintocet-mexyl in soil indicated that (R)-cloquintocet-mexyl was preferentially degraded. This work is the first to describe a chiral analytical method and enantioselective behavior of cloquintocet-mexyl and provide basic data for the risk evaluation of cloquintocet-mexyl in food and environmental safety.

Cyclodextrin-dendrimers nanocomposites functionalized high performance liquid chromatography stationary phase for efficient separation of aromatic compounds

In this work, novel cyclodextrin-dendrimers nanocomposites functionalized high performance liquid chromatography stationary phases were developed for efficient separation of aromatic compounds. β-cyclodextrin was grafted onto the surface of silica gel matrix with poly (amidoamine) dendrimers as spacers. Scanning electron microscope, fourier transform infrared spectroscopy, element analysis and Brunner-Emmet-Teller measurement proved the successful grafting of cyclodextrin-dendrimers nanocomposites. The obtained stationary phases showed satisfactory separation effects for alkylbenzenes and benzenesulfonic acid substituents in reverse phase liquid chromatography mode. Weak hydrophilic and ion exchange interactions were also confirmed at the same time. Meanwhile, the effects of dendrimers and cyclodextrin on the chromatography performance were discussed. Separation mechanism of the stationary phases were verified by two-dimensional nuclear magnetic resonance technology, and the result implied that the proposed cyclodextrin-dendrimers nanocomposites functionalized stationary phases have significant prospects for separation and determination of more aromatic compounds in future.

Preparation of a novel bridged bis(β-cyclodextrin) chiral stationary phase by thiol-ene click chemistry for enhanced enantioseparation in HPLC

A bridged bis(β-cyclodextrin) ligand was firstly synthesized via a thiol–ene click chemistry reaction between allyl-ureido-β-cyclodextrin and 4-4′-thiobisthiophenol, which was then bonded onto a 5 μm spherical silica gel to obtain a novel bridged bis(β-cyclodextrin) chiral stationary phase (HTCDP). The structures of HTCDP and the bridged bis(β-cyclodextrin) ligand were characterized by the ¹H nuclear magnetic resonance (¹H NMR), solid state ¹³C nuclear magnetic resonance (¹³C NMR) spectra spectrum, scanning electron microscope, elemental analysis, mass spectrometry, infrared spectrometry and thermogravimetric analysis. The performance of HTCDP in enantioseparation was systematically examined by separating 21 chiral compounds, including 8 flavanones, 8 triazole pesticides and 5 other common chiral drugs (benzoin, praziquantel, 1-1′-bi-2-naphthol, Tröger's base and bicalutamide) in the reversed-phase chromatographic mode. By optimizing the chromatographic conditions such as formic acid content, mobile phase composition, pH values and column temperature, 19 analytes were completely separated with high resolution (1.50–4.48), in which the enantiomeric resolution of silymarin, 4-hydroxyflavanone, 2-hydroxyflavanone and flavanone were up to 4.34, 4.48, 3.89 and 3.06 within 35 min, respectively. Compared to the native β-CD chiral stationary phase (CDCSP), HTCDP had superior enantiomer separation and chiral recognition abilities. For example, HTCDP completely separated 5 other common chiral drugs, 2 flavanones and 3 triazole pesticides that CDCSP failed to separate. Unlike CDCSP, which has a small cavity (0.65 nm), the two cavities in HTCDP joined by the aryl connector could synergistically accommodate relatively bulky chiral analytes. Thus, HTCDP may have a broader prospect in enantiomeric separation, analysis and detection.

Separation of chiral compounds on HTCDP.

Recent progress in the development of chiral stationary phases for high-performance liquid chromatography

Separations and analyses of chiral compounds are important in many fields, including pharmaceutical production, preparation of chemical intermediates, and biochemistry. High-performance liquid chromatography using a chiral stationary phase is regarded as one of the most valuable methods for enantiomeric separation and analysis because it is highly efficient, is broadly applicable, and has powerful separation capability. The focus for development of this method is the identification of novel chiral stationary phases with superior recognition performance and good stability. The present article reviews recent progress in the development of new chiral stationary phases for high-performance liquid chromatography between January 2018 and June 2021. These newly reported chiral stationary phases are divided into three categories: small organic molecule-based (cyclodextrin and its derivatives, macrocyclic antibiotics, cinchona alkaloids, and other low molecular weight chiral molecules), macromolecule-based (cellulose and amylose derivatives, chitin and chitosan derivatives, and synthetic helical polymers) and chiral porous material-based (chiral metal-organic frameworks, chiral covalent organic frameworks, and chiral inorganic mesoporous silicas). Each type of chiral stationary phase is discussed in detail.

Strategies for Preparation of Chiral Stationary Phases: Progress on Coating and Immobilization Methods

Enantioselective chromatography is one of the most used techniques for the separation and purification of enantiomers. The most important issue for a specific successful enantioseparation is the selection of the suitable chiral stationary phase (CSP). Different synthetic approaches have been applied for the preparation of CSPs, which embrace coating and immobilization methods. In addition to the classical and broadly applied coating and immobilization procedures, innovating strategies have been introduced recently. In this review, an overview of different methods for the preparation of coated and immobilized CSPs is described. Updated examples of CSPs associated with the various strategies are presented. Considering that after the preparation of a CSP its characterization is fundamental, the methods used for the characterization of all the described CSPs are emphasized.

An overview of chiral separations of pharmaceutically active substances by HPLC (2018-2020)

This review provides a brief survey of chiral separation of pharmaceutically active substances published over the last 3 years (2018-2020). Chiral separation of drugs is an important area of research. The control of enantiomeric purity and determination of individual enantiomeric drug molecules is a necessity especially for clinical, analytical, and regulatory purposes. Among chromatographic resolution methods, high-performance liquid chromatography based on chiral stationary phases remains the most popular and effective method used for chiral separation of various drugs. In this review, attention is paid to several classes of chiral stationary phases that have been the most frequently used for drug enantioseparation during this period.

GRAPHIC ABSTRACT

Polysaccharide- and β-Cyclodextrin-Based Chiral Selectors for Enantiomer Resolution: Recent Developments and Applications

Polysaccharides, oligosaccharides, and their derivatives, particularly of amylose, cellulose, chitosan, and β-cyclodextrin, are well-known chiral selectors (CSs) of chiral stationary phases (CSPs) in chromatography, because they can separate a wide range of enantiomers. Typically, such CSPs are prepared by physically coating, or chemically immobilizing the polysaccharide and β-cyclodextrin derivatives onto inert silica gel carriers as chromatographic support. Over the past few years, new chiral selectors have been introduced, and progressive methods to prepare CSPs have been exploited. Also, chiral recognition mechanisms, which play a crucial role in the investigation of chiral separations, have been better elucidated. Further insights into the broad functional performance of commercially available chiral column materials and/or the respective newly developed chiral phase materials on enantiomeric separation (ES) have been gained. This review summarizes the recent developments in CSs, CSP preparation, chiral recognition mechanisms, and enantiomeric separation methods, based on polysaccharides and β-cyclodextrins as CSs, with a focus on the years 2019-2020 of this rapidly developing field.

Natural and Artificial Chiral-Based Systems for Separation Applications

Chiral separation has attracted much attention for basic research and industrial applications in analytical chemistry. Generally, chiral separations use natural or artificial chiral-based materials as adsorbents. To improve the precision and efficiency of chiral separation, focus has shifted from natural and synthetic adsorbents to binary combinations of materials. This review specifically summarizes the significant advancements made in natural and artificial chiral adsorbents as promising candidates for diverse drug and biomolecule separation applications as well as the remaining drawbacks and challenges for research on chiral separations. The mechanisms of chiral-based recognition and separation and history and development of natural and artificial chiral-based systems are the focus of this review. Future directions in natural and artificial chiral-based systems for practical separations and other applications are also presented.

A novel electronic nose for the detection and classification of pesticide residue on apples

Excessive pesticide residues are a serious problem faced by food regulatory authorities, suppliers, and consumers. To assist with this challenge, this work aimed to develop a method of detecting and classifying pesticide residue on fruit samples using an electronic nose, through the application of three different data-recognition algorithms. The apple samples carried various concentrations of two known pesticides, namely cypermethrin and chlorpyrifos. Data collection was performed using a PEN3 electronic nose equipped with 10 metal oxide semiconductor (MOS) sensors. In order to classify and analyze these pesticide residues on the apple samples, principal component analysis (PCA), linear discriminant analysis (LDA), and support vector machine (SVM) results were combined with sensor output responses to realize MOS sensor array data visualization. The results indicated that all three data-recognition algorithms accurately identified the pesticide residues in the apple samples, with the PCA algorithm exhibiting the best classification and discrimination ability. Consequently, this work has shown that the MOS electronic nose, in combination with data-recognition algorithms, can provide support for the rapid and non-destructive identification of pesticide residues in fruits and can provide an effective tool for the detection of pesticide residues in agricultural products.

The MOS electronic nose in combination with data-recognition algorithms can provide an effective tool for the detection of pesticide residues in agricultural products.

Anhydride-linked β-cyclodextrin-bonded silica stationary phases with enhanced chiral separation ability in liquid chromatography

β-Cyclodextrin can be functionalized by derivation of reactive hydroxyl on the ring due to its special chiral environment and structural characteristics, which can be used to identify or separate a variety of chiral substance. In this manuscript, a series of excellent chiral stationary phases for high-performance liquid chromatography were developed for enantioseparation by using anhydride modified β-cyclodextrin bearing chiral (R/S)-α-phenethylamine or (S)-(+)-2-amino-1-propanol. They were characterized by elemental analysis, Fourier transform infrared spectra (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and BET. These chiral stationary phases presented good resolution and repeatability, about 17 kinds of enantiomers were effectively separated. And most of enantiomers were separated better than those reported in the literature in the same both normal and reversed phase modes. The RSD values of R_s for repeatability and column-to-column were below 0.44% and 2.83%, respectively. All results revealed that these new CSPs show great prospect for chiral separation in actual applications.

Cyclodextrins-Peptides/Proteins Conjugates: Synthesis, Properties and Applications

Cyclodextrins (CDs) are a family of macrocyclic oligosaccharides mostly composed of six, seven, or eight α-D-glucopyranose units with α-1,4-glycosidic bonds to form toroidal structures. The CDs possess a hydrophilic exterior and hydrophobic interior with the ability to form an inclusion complex, especially with hydrophobic molecules. However, most existing studies are about conjugation CDs with peptide/protein focusing on the formation of new systems. The CD-peptide/protein can possess new abilities; particularly, the cavity can be applied in modulation properties of more complexed proteins. Most studies are focused on drug delivery, such as targeted delivery in cell-penetrating peptides or co-delivery. The co-delivery is based mostly on polylysine systems; on the other hand, the CD-peptide allows us to understand biomolecular mechanisms such as fibryllation or stem cell behaviour. Moreover, the CD-proteins are more complexed systems with a focus on targeted therapy; these conjugates might be controllable with various properties due to changes in their stability. Finally, the studies of CD-peptide/protein are promising in biomedical application and provide new possibilities for the conjugation of simple molecules to biomolecules.

Enantioseparation on a new synthetic β-cyclodextrin chemically bonded chiral stationary phase and molecular docking study

A novel β-cyclodextrin derivative chemically bonded chiral stationary phase (EDACD) was synthesized by the reaction of mono-6-ethylenediamine-β-cyclodextrin with the active alkyl isocyanate, anchoring to silica gel. After the successful analysis and characterization using scanning electron microscopy, Fourier transform infrared spectra, solid-state nuclear magnetic resonance spectra, elemental analysis, and thermogravimetric analysis techniques, the enantioselective performance of the as-prepared EDACD column was evaluated by non-steroidal antiinflammatory drugs and flavonoids under the reversed-phase HPLC condition. The factors that affected enantioseparation including mobile phase compositions and buffers were investigated in more detail. As a result, EDACD showed a satisfactory enantioselectivity for the tested drugs. With the mobile phase of acetonitrile and 20-mM ammonium formate adjusted to pH 4.0 using formic acid (85:15, v/v) at the flow rate of 0.6 mL min^-1, the enantiomers of ibuprofen, carprofen, naproxen, indoprofen, ketoprofen, eriocitrin, naringin, and narirutin were separated with the best resolutions of 1.53, 1.64, 3.72, 2.40, 0.50, 0.61, 0.58, and 0.52. To adjust the proportion of acetonitrile to 80% (by volume), the enantiomers of pranoprofen and flurbiprofen were completely resolved with the best resolutions of 1.60 and 1.59. Additionally, by the study of the molecular docking, hydrogen bonding and inclusion complexation were believed to play an important role in chiral recognition. As a new material, EDACD will have a wider application in the analysis of chiral compounds.

Synthesis and Chiral Separation of Some 4-thioflavones

A thionation reaction was performed on some chiral flavanones using Lawesson's reagent (LR) and leads to the formation of new chiral thiocarbonyl flavanes. LR in this thionation reaction with Hesperetin and Naringenin gives new flavan-4-thiones with yields ranged between 41 and 52%. Based on the Wittig reaction principle, LR is currently the most widely used reagent for this type of reaction. Enantiomeric separation by high-performance liquid chromatography methods was then set-up using three different polysaccharide-based chiral stationary phases (CSPs). Chiral separations were successfully accomplished with high resolution (1.22 ≤ Rs ≤ 5.23). The chiral discrimination mechanism(s) between the analytes under study, mobile phase, and the CSPs were discussed.

Progress in the Enantioseparation of β-Blockers by Chromatographic Methods

β-adrenergic antagonists (β-blockers) with at least one chiral center are an exceedingly important class of drugs used mostly to treat cardiovascular diseases. At least 70 β-blockers have been investigated in history. However, only a few β-blockers, e.g., timolol, are clinically marketed as an optically pure enantiomer. Therefore, the separation of racemates of β-blockers is essential both in the laboratory and industry. Many approaches have been explored to obtain the single enantiomeric β-blocker, including high performance liquid chromatography, supercritical fluid chromatography and simulated moving bed chromatography. In this article, a review is presented on different chromatographic methods applied for the enantioseparation of β-blockers, covering high performance liquid chromatography (HPLC), supercritical fluid chromatography (SFC) and simulated moving bed chromatography (SMB).

Rapid preparation and characterization of a bridged bis(β-cyclodextrin) functionalized urea–formaldehyde monolithic column by a “one-pot” approach

A new bridged-CD monolith was prepared by “one-pot” method within 30 minutes. The obtained bridged-CD monolith showed satisfactory enantioselectivity compared to a native-CD monolith.

Simultaneous enantiomeric determination of multiple triazole fungicides in fruits and vegetables by chiral liquid chromatography/tandem mass spectrometry on a bridged bis(β-cyclodextrin)-bonded chiral stationary phase

A LC-MS/MS method for simultaneous determination of twelve triazole enantiomers (hexaconazole, tebuconazole, triticonazole, flutriafol, diniconazole, paclobutrazol) in six fruits and vegetables was established based on a stable and self-made bridged bis(β-cyclodextrin)-bonded chiral stationary phase. Simultaneous enantio-separation of multiple analytes was achieved with resolution ca. 1.67-2.14. Magnetically assisted QuECHERS was used to simplify and optimize sample pre-treatment. The new method was validated (accuracy, precision, matrix effect, etc.). Good linearity (0.5-20 μg/L, R² > 0.99) and high recoveries (76.1-103.4%) based on intra- and inter-day relative standard deviation (RSDs) (2.6-11.9%), were obtained. Furthermore, a total of 90 samples were analyzed using this method and enantiomeric fractions (EF) for tebuconazole in strawberry and cucumber (0.63 and 0.43, respectively) were determined as well as 0.57 for flutriafol in tomato. This high-throughput detection method supported a convenient enantiomeric monitoring for chiral pesticides in fruits and vegetables.

Stereoisomer separation of flavanones and flavanone-7-O-glycosides by means of nanoliquid chromatography employing derivatized β-cyclodextrins as mobile-phase additive

A nanoliquid chromatographic method for the stereoisomer separation of some flavanone aglycones and 7-O-glycosides has been proposed employing a C18 capillary column and a chiral mobile-phase additive such as cyclodextrin. The chiral separation of eriodictyol, naringenin, and hesperitin was obtained by addition of carboxymethyl-β-cyclodextrin to the mobile phase, whereas eriocitrin, naringin, narirutin, and hesperidin diastereoisomers were resolved by using sulfobutyl ether-β-cyclodextrin. The influence of the composition of the mobile phase, the length of the capillary column, and the flow rate on the chiral recognition were investigated. At optimum conditions, baseline separation for the selected aglycones and glycosylated forms were achieved with a mobile phase consisting of 50 mM sodium acetate buffer pH 3 and 30% methanol containing 20 mM of carboxymethyl-β-cyclodextrin and 10 mM of sulfobutyl ether-β-cyclodextrin, respectively. Precision, linearity, and sensitivity of the method were tested. Limits of detection and quantification for the studied flavanone glycosides were in the range 1.3-2.5 and 7.5-12.5 µg/mL, respectively. The method was used for the determination of the diastereomeric composition of the flavanone-7-O-glycosides in Citrus juices after solid-phase extraction procedure.