Electrophoretic separation of multiple chiral center analyte with a three cyclodextrins mixture.

A capillary electrokinetic chromatography method (CEKC) was developed for complete stereoisomeric separation of a neutral, hydrophobic, multiple chiral center dihydropyridone analogue, a drug candidate proposed in type 2 diabetes treatment. A background electrolyte comprising three cyclodextrins was found to successfully separate the eight isomers. First an anionic cyclodextrin, the SBE-ß-CD, was selected to allow the chiral separation of our neutral compound and partial resolutions of the eight isomers were obtained. Then, the effects of different parameters such as the nature and concentration of the other cyclodextrins added and pH of the buffer were examined. Finally, a triple CD-system consisted of 15 mM SBE-ß-CD plus 15 mM Î³-CD and 40 mM HP-γ-CD in a 50 mM borate background electrolyte at pH 10, was found to successfully separate the eight isomers. Last, the selectivity and limits of detection and quantification were evaluated for this optimized method.

Measurement of NLG207 (formerly CRLX101) nanoparticle-bound and released camptothecin in human plasma.

Camptothecin (CPT), a potent inhibitor of topoisomerase I and HIF-1α, failed to demonstrate utility as an anti-cancer agent in early clinical trial investigations, primarily due to limited clinical activity and significant toxicity attributable to unfavorable physicochemical properties (e.g. low plasma solubility, pH-labile lactone ring). NLG207 (formerly CRLX101), a nanoparticle-drug conjugate (NDC) of CPT designed to optimize plasma pharmacokinetics and facilitate drug delivery to tumors, is included as part of combination treatment in two Phase II clinical trials ongoing at the National Cancer Institute (NCT02769962 and NCT03531827). To better understand the potential for drug-drug interactions and to correlate drug exposure to clinical outcomes and pharmacodynamic biomarkers, a robust analytical method was developed to measure CPT in human plasma. Two sample processing methods were developed to quantify both NDC-bound CPT and free CPT, primarily via alteration of pH conditions. A solid-phase extraction recovered >79 % of CPT prior to quantitative analysis by ultra HPLC-MS/MS. Dynamic calibration ranges of 10 to 10,000 ng/mL and 1 to 1000 ng/mL for total and free CPT, respectively were utilized to capture clinical ranges. NLG207 NDCs demonstrated significant rates of CPT release in human plasma at room temperature after 2 h but were shown to be stable at 4 °C for 24 h and through 4 freeze/thaw cycles. This assay was used to quantitate CPT plasma concentrations in clinical samples to confirm clinical utility following NLG207 treatment in subjects with advanced prostate cancer.

Sonochemically-Promoted Preparation of Silica-Anchored Cyclodextrin Derivatives for Efficient Copper Catalysis.

Silica-supported metallic species have emerged as valuable green-chemistry catalysts because their high efficiency enables a wide range of applications, even at industrial scales. As a consequence, the preparation of these systems needs to be finely controlled in order to achieve the desired activity. The present work presents a detailed investigation of an ultrasound-promoted synthetic protocol for the grafting of ß-cyclodextrin (ß-CD) onto silica. Truly, ultrasound irradiation has emerged as a fast technique for promoting efficient derivatization of a silica surface with organic moieties at low temperature. Three different ß-CD silica-grafted derivatives have been obtained, and the ability of ß-CD to direct and bind Cu when CD is bonded to silica has been studied. A detailed characterization has been performed using TGA, phenolphthalein titration, FT-IR, diffuse reflectance (DR), DR UV-Vis, as well as the inductively-coupled plasma (ICP) of the ß-CD silica-grafted systems and the relative Cu-supported catalysts. Spectroscopic characterization monitored the different steps of the reaction, highlighting qualitative differences in the properties of amino-derivatized precursors and final products. In order to ensure that the Cu-ß-CD silica catalyst is efficient and robust, its applicability in Cu(II)-catalyzed alkyne azide reactions in the absence of a reducing agent has been explored. The presence of ß-CD and an amino spacer has been shown to be crucial for the reactivity of Cu(II), when supported.

Modeling of chiral gas chromatographic separation of alkyl and cycloalkyl 2-bromopropionates using cyclodextrin derivatives as stationary phases.

Chiral 2-bromopropionates are widely used as raw materials or intermediates for synthesis of chiral pesticides and medicines with high biological activities. Enantioseparation of 2-bromopropionates is crucial for evaluating the optical purity of chiral 2-bromopropionates. In this study, the enantioseparation of 8 pairs of alkyl 2-bromopropionates and 5 pairs of cycloalkyl 2-bromopropionates were examined using 7 different cyclodextrin derivatives (CDs). For the enantiomers of methyl, ethyl, bromoethyl and prop-2-yn-1-yl 2-bromopropionates, three different kinds of enantioseparation results including baseline separation, partial separation and no separation, are obtained on the 7 different CDs. Besides the baseline enantioseparation of methyl and ethyl 2-bromopropionates on some CDs, baseline enantioseparation of 2-bromoethyl 2-bromopropionate on 2,3,6-tri-O-methyl-ß-CD with resolution as 1.78, prop-2-yn-1-yl 2-bromopropionate on 2,3,6-tri-O-methyl-ß-CD and 2,3-di-O-pentyl-6-O-propyl-ß-CD with the resolution as 3.45 and 1.77, respectively, are also obtained, and can be used for determination of the optical purity. However, for the enantiomers of isopropyl, isobutyl, tert-butyl and 3-methylbut-2-en-1-yl 2-bromopropionates, only partial enantioseparation are obtained on 5 CDs, meaning that these methods cannot be used for determination of the optical purity. To 5 pairs of cycloalkyl 2-bromopropionates, the 7 CDs exhibit low enantioseparation abilities. While the investigated 5 cycloalkyl-2-bromopropionates don't result in baseline enantioseparation when they are analyzed on the 7 CDs, partial enantioseparation of 4 cycloalkyl 2-bromopropionates, cyclopentyl, cyclohexyl, cyclohexylmethyl and benzyl 2-bromopropionates, are obtained on some CDs, and no any enantioseparation of phenyl 2-bromopropionates are observed on the 7 CDs. The baseline enantioseparation methods for methyl, ethyl, bromoethyl, and prop-2-yn-1-yl 2-bromopropionates have been validated for the parameters linearity, limit of detection, limit of quantification, recovery, intra-day and inter-day precision. Moreover, the validated baseline enantioseparation methods for methyl 2-bromopropionate using columns coated with 4 different CDs have been successfully applied on the determination of optical purity of chiral methyl 2-bromopropionate sample. Furthermore, molecular docking study is performed to investigate the 2,3,6-tri-O-methyl-ß-cyclodextrin (PM-ß-CD) inclusion complexes with various 2-bromopropionates. The docking results show the contribution of differences of geometry and interaction energy between the inclusion complexes of two enantiomers with PM-ß-CD to enantioseparation of some 2-bromopropionates, however the docking results cannot explain the enantioseparation mechanism of other 2-bromopropionates, especially cycloalkyl 2-bromopropionates. This study provides information on the selection of chiral stationary phase CDs for the optimal GC enantioseparation conditions of some new 2-bromopropionates. The methodology of this study can be applied to evaluate the optical purity of some chiral 2-bromopropionates.

Combination of capillary electrophoresis and molecular modeling to study the enantiomer affinity pattern between ß-blockers and anionic cyclodextrin derivatives in a methanolic and water background electrolyte.

In order to have deep insights into the mechanisms of enantiomer affinity pattern in both aqueous and non-aqueous systems, an approach combining capillary electrophoresis and molecular modeling was undertaken. A chiral ß-blocker; acebutolol, was enantioseparated in aqueous capillary electrophoresis and non-aqueous capillary electrophoresis using two anionic ß-cyclodextrin derivatives. The enantiomer affinity pattern of acebutolol was found to be opposite when an aqueous background electrolyte was replaced with non-aqueous background electrolyte in the presence of heptakis(2,3-di-O-acetyl-6-sulfo)-ß-cyclodextrin but remained the same in the presence of heptakis(2,3-di-O-methyl-6-sulfo)-ß-cyclodextrin. Molecular docking of acebutolol into two ß-cyclodextrin derivatives indicated two distinct binding modes called 'up' and 'down' conformations. After structure optimization by molecular dynamics and energy minimization, both enantiomers of acebutolol were preferred to the 'up' conformation with heptakis(2,3-di-O-methyl-6-sulfo)-ß-cyclodextrin while 'down' conformation with heptakis(2,3-di-O-acetyl-6-sulfo)-ß-cyclodextrin. The further calculation of the complex energy with solvent effect indicated that heptakis(2,3-di-O-acetyl-6-sulfo)-ß-cyclodextrin had higher affinity to S-acebutolol than R-acebutolol in non-aqueous capillary electrophoresis while it showed better binding to R-acebutolol in aqueous capillary electrophoresis. However, the heptakis(2,3-di-O-methyl-6-sulfo)-ß-cyclodextrin bound better to R-acebutolol in both aqueous and non-aqueous capillary electrophoresis, implying that the binding mode played more important role in chiral separation of heptakis(2,3-di-O-methyl-6-sulfo)-ß-cyclodextrin while the solvent effect had prevailing impact on heptakis(2,3-di-O-acetyl-6-sulfo)-ß-cyclodextrin.

Associated-Extraction Efficiency of Six Cyclodextrins on Various Flavonoids in Puerariae Lobatae Radix.

Puerariae Lobatae Radix (PLR), a well-known herbal medicine, is the root of Pueraria lobata (Willd.) Ohwi and has been employed for the treatment and prevention of cardiovascular and cerebrovascular diseases. The purpose of this study was to compare the associated-extraction efficiency of six cyclodextrins (CDs) on five flavonoids in PLR, namely puerarin, daidzein, daidzin, genistein and genistin, which are the major secondary metabolites, and exhibit low water solubility. The six CDs applied were ß-cyclodextrin (ß-CD), γ-cyclodextrin (γ-CD), hydroxypropyl-ß-cyclodextrin (HP-ß-CD), hydroxypropyl-γ-cyclodextrin (HP-γ-CD), carboxymethyl-ß-cyclodextrin (CM-ß-CD), and sulfobutyl ether ß-cyclodextrin (SBE-ß-CD). They can be grouped into one of the following three categories: traditional cyclodextrins (ß-CD and γ-CD), water-soluble cyclodextrin derivatives (HP-ß-CD and HP-γ-CD) and ionic cyclodextrin derivatives (SBE-ß-CD and CM-ß-CD). High-performance liquid chromatography (HPLC) was used to analyze the five flavonoids in the original aqueous extracts (OAE) in the presence or absence of various CDs. The associated-extraction efficiency of the various CDs followed the ranking: SBE-ß-CD > HP-ß-CD > CM-ß-CD > HP-γ-CD > γ-CD > ß-CD. It was clear that SBE-ß-CD presented the highest associated-extraction capability, and it was used to extract the four flavonoids from three PLR products, including raw product, stir- fried product, and product simmered with wheat bran. The results showed that SBE-ß-CD could improve the extraction capability of flavonoids, both from the raw product and in processed products of PLR. In conclusion, CDs, especially SBE-ß-CD, have a promising application for the associated-extraction of flavonoids from PLR.

Polarity tuned perphenylcarbamoylated cyclodextrin separation materials for achiral and chiral differentiation.

Phenylcarbamoyls are known to remarkably accentuate cyclodextrin's enantioselectivities. In this work, by inducing electron-donating methoxyl or electron-withdrawing bromine/trifluoromethyl moieties, three novel cyclodextrin enantioseparation materials including per(4-trifluoromethoxy) phenylcarbamoylated-ß-CD CSP (CSP1), per(4-bromo)phenylcarbamoylated-ß-CD CSP (CSP2) and per(4-methoxy)phenylcarbamoylated-ß-CD CSP (CSP3) were prepared via thiol-ene click chemistry. The polarity tuning decorations are found to significantly influence the CSPs' achiral and chiral separation performance. The three CSPs can easily separate toluene, 1,2-xylene and 1,3,5-trimethylbenzene with the strongest retention on CSP3. In reversed-phase mode, the three CSPs exhibited completely different enantioseparation ability towards specific isoxazolines and flavonoids. 4'-hydroxyflavanone was separated on CSP1 with a resolution of 9.24 while 6-methoxyflavanone was best separated on CSP2 (Rs = 9.98). CSP3 exhibited the strongest differentiation ability towards 4NPh-2Py (Rs = 9.69). The comparison study may provide some insight into the design of functional cyclodextrin materials.

Different strategies for cyclodextrin production: Ultrafiltration systems, CGTase immobilization and use of a complexing agent.

The study comparatively evaluated diverse strategic models of cyclodextrin (CD) production by the CGTase of Bacillus firmus strain 37: continuous production and repetitive batches in ultrafiltration systems; immobilization of CGTase on curdlan and vegetable sponge natural supports; the use of the glycyrrhizin complexing agent to modulate CGTase selectivity in favor of γ-CD production. All strategies had in common the possibility of separation of CGTase from its inhibitory products and its reuse. In the continuous production model, at 48 h of assay, the highest productivity and selectivity for ß-CD were obtained, 1.47 mmol/L/h and 92.8%, respectively. Glycyrrhizin was able to modulate the production of γ-CD with selectivity of 61.2% for 30-h batches. The comparative evaluation of the different strategic models for obtaining CDs showed particularities that should be considered, and most of the models studied returned satisfactory yields as well as excellent selectivity.

Two-Dimensional Capillary Electrophoresis with On-Line Sample Preparation and Cyclodextrin Separation Environment for Direct Determination of Serotonin in Human Urine.

An advanced two-dimensional capillary electrophoresis method, based on on-line combination of capillary isotachophoresis and capillary zone electrophoresis with cyclodextrin additive in background electrolyte, was developed for effective determination of serotonin in human urine. Hydrodynamically closed separation system and large bore capillaries (300-800 µm) were chosen for the possibility to enhance the sample load capacity, and, by that, to decrease limit of detection. Isotachophoresis served for the sample preseparation, defined elimination of sample matrix constituents (sample clean up), and preconcentration of the analyte. Cyclodextrin separation environment enhanced separation selectivity of capillary zone electrophoresis. In this way, serotonin could be successfully separated from the rest of the sample matrix constituents migrating in capillary zone electrophoresis step so that human urine could be directly (i.e., without any external sample preparation) injected into the analyzer. The proposed method was successfully validated, showing favorable parameters of sensitivity (limit of detection for serotonin was 2.32 ng·mL-1), linearity (regression coefficient higher than 0.99), precision (repeatability of the migration time and peak area were in the range of 0.02-1.17% and 5.25-7.88%, respectively), and recovery (ranging in the interval of 90.0-93.6%). The developed method was applied for the assay of the human urine samples obtained from healthy volunteers. The determined concentrations of serotonin in such samples were in the range of 12.4-491.2 ng·mL-1 that was in good agreement with literature data. This advanced method represents a highly effective, reliable, and low-cost alternative for the routine determination of serotonin as a biomarker in human urine.

Functionalities tuned enantioselectivity of phenylcarbamate cyclodextrin clicked chiral stationary phases in HPLC.

The mixed chloro- and methyl- functionalities can greatly modulate the enantioselectivities of phenylcarbamate cyclodextrin (CD) clicked chiral stationary phases (CSPs). A comparison study is herein reported for per(4-chloro-3-methyl)phenylcarbamate and per(2-chloro-5-methyl)phenylcarbamate ß-CD clicked CSPs (i.e., CCC4M3-CSP and CCC2M5-CSP). The enantioselectivity dependence on column temperature was studied in both normal-phase and reversed-phase mode high performance liquid chromatography (HPLC). The thermodynamic study revealed that the stronger intermolecular interactions can be formed between CCC4M3-CSP and chiral solutes to drive the chiral separation. The higher enantioselectivities of CCC4M3-CSP were further demonstrated with the enantioseparation of 17 model racemates in HPLC.

Nano-liquid chromatography applied to enantiomers separation.

This paper presents the state of the art concerning the separation of chiral compounds by means of nano-liquid chromatography (nano-LC). The enantiomers' separation and determination are a subject of fundamental importance in various application fields such as pharmaceutical industry, biomedicine, food, agrochemical etc. Nano-LC is a miniaturized chromatographic technique offering some advantages over conventional ones such as low consumption of mobile phase, sample volume and amount of chiral stationary phase, reduced costs etc. This is reported in the first part of the paper illustrating the features of the nano-LC. In addition, chiral resolution methods are briefly illustrated. Some chiral selectors, used in high-performance liquid chromatography have also been applied in nano-LC including cyclodextrins, glycopeptide antibiotics, modified polysaccharides etc. This is discussed in the second part of the review. Finally some examples of the applications available in literature are reported.

Enantiomer Separations by Capillary Electrophoresis.

Capillary electrophoresis (CE) is a versatile and flexible technique for analytical enantioseparations. This is due to the large variety of chiral selectors as well as the different operation modes including electrokinetic chromatography, micellar electrokinetic chromatography, and microemulsion electrokinetic chromatography. The chiral selector, which is added to the background electrolyte, represents a pseudostationary phase with its own electrophoretic mobility allowing a variety of different separation protocols. The present chapter briefly addresses the basic fundamentals of CE enantioseparations as well as the most frequently applied chiral selectors and separation modes. The practical example illustrates the separation of the enantiomers of a positively charged analyte using native and charged cyclodextrin derivatives as chiral selectors.

Separation of sulfoalkylated cyclodextrins with hydrophilic interaction liquid chromatography.

Determination of the charged state distributions of partially- and fully-substituted sulfoalkylated cyclodextrins was achieved using hydrophilic interaction liquid chromatography (HILIC). HILIC analysis of a spiked sample of the partially sulfopropylated cyclodextrins was achieved using a gradient to baseline resolve the charged states from -1 to -14. The fully-substituted CDs yielded a major peak with some trace impurities and the partially-substituted sulfopropylated cyclodextrins showed a wide range of charge states present in the mixture. Small changes in the structure of the cyclodextrins have a significant impact on the retention times of the various types of cyclodextrins investigated.

The enantiomeric separation of tetrahydrobenzimidazoles cyclodextrins- and cyclofructans.

High performance liquid chromatography (HPLC) and capillary electrophoresis (CE) were used to examine the enantiomeric separation of a series of 17 racemic tetrahydrobenzimidazole analytes. These compounds were prepared as part of a synthetic program directed towards a select group of pyrrole-imidazole alkaloids. This group of natural products has a unique framework of pyrrole- and guanidine-containing fused rings which can be constructed through the intermediacy of a tetrahydrobenzimidazole scaffold. Several bonded cyclodextrin- (both native and derivatized) and derivatized cyclofructan-based chiral stationary phases were evaluated for their ability to separate these racemates via HPLC. Similarly, several cyclodextrin derivatives and derivatized cyclofructan were evaluated for their ability to separate this set of chiral compounds via CE. Enantiomeric selectivity was observed for the entire set of racemic compounds using HPLC with resolution values up to 3.0. Among the 12 different CSPs, enantiomeric recognition was most frequently observed with the Cyclobond RN and LARIHC CF6-P, while the Cyclobond DMP yielded the greatest number of baseline separations. Fifteen of the analytes showed enantiomeric recognition in CE with resolution values as high as 5.0 and hydroxypropyl-γ-cyclodextrin was the most effective chiral additive.

Recent advances in electrodriven enantioseparations.

Capillary electromigration techniques have developed into significant analytical separation tools especially for enantioseparations. While CE can be considered a mature technique as documented by its wide applications, CEC is still in a developmental state despite many research efforts. The success of stereospecific CE separation methods is due to the high specificity and flexibility of the technique as well as the availability of many types of chiral selectors. Thus, numerous methods have been developed for the analysis of chiral compounds in chemical, biochemical, pharmaceutical, environmental, and forensic sciences. However, most reported applications deal with pharmaceuticals. The search for new chiral selectors also continued despite the fact that most applications were performed using cyclodextrins. Furthermore, CE has been combined with spectroscopic and molecular modeling studies in attempts to understand the interactions between chiral selectors and analytes. The present review focuses on recent examples of mechanistic aspects of capillary enantioseparations with regard to mathematical modeling of enantioseparations, investigations of the analyte-complex structures as well as new chiral selectors and applications of chiral analyses by CE and CEC. It covers the literature published between January 2011 and August 2012.

A multifunctional test mixture for chiral cyclodextrin GC columns.

Gas chromatography (GC) is a powerful tool in the separation science of chiral analytes. The development of a new chiral test mixture for cyclodextrin (CD) coated GC columns allows comparing, choosing and identifying most suitable columns for a given separation challenge. This test mixture contains 12 enantiomer pairs of a broad range of functional groups and it is the first mixture suitable for all types of modified cyclodextrin capillary columns. Column changes can be observed and system performance can be monitored by means of this test mixture, which is therefore a base for reliable results. Furthermore, this publication is thought to be a start-up aid for chiral GC.

Isolation of cycloamylose by iodine affinity capillary electrophoresis.

In contrast to α-, ß- and γ-cyclodextrins, little information is available on the isolation and separation of cycloamylose (CA) with degree of polymerization (DP) larger than 22. The objective of the current study was to develop a new iodine affinity capillary electrophoresis (CE) for separation of CA with DP of 22-42, which was based on the formation of CA-iodine inclusion complexes, CA with twisted conformations made complicated mobility behaviors on CE instead of merely size dependent. The influences of iodide/iodine ratio, iodine concentration, pH, ion strength of running phosphate buffer, voltage, and temperature on the peak resolution and electrophoretic mobility were further investigated. Our results suggest that iodine affinity capillary electrophoresis provides a versatile and selective tool for the isolation and analysis of CA with DP from 22 to 42.

Electrokinetic remediation and microbial community shift of ß-cyclodextrin-dissolved petroleum hydrocarbon-contaminated soil.

Electrokinetic (EK) migration of ß-cyclodextrin (ß-CD), which is inclusive of total petroleum hydrocarbon (TPH), is an economically beneficial and environmentally friendly remediation process for oil-contaminated soils. Remediation studies of oil-contaminated soils generally prepared samples using particular TPHs. This study investigates the removal of TPHs from, and electromigration of microbial cells in field samples via EK remediation. Both TPH content and soil respiration declined after the EK remediation process. The strains in the original soil sample included Bacillus sp., Sporosarcina sp., Beta proteobacterium, Streptomyces sp., Pontibacter sp., Azorhizobium sp., Taxeobacter sp., and Williamsia sp. Electromigration of microbial cells reduced the biodiversity of the microbial community in soil following EK remediation. At 200 V m(-1) for 10 days, 36% TPH was removed, with a small population of microbial cells flushed out, demonstrating that EK remediation is effective for the present oil-contaminated soils collected in field.

Separation of Tic-hydantoin enantiomers, potent sigma-1 agonists, by high performance liquid chromatography and capillary electrophoresis.

Stereospecific separations of seven Tic-hydantoin sigma-1 agonists were performed by both HPLC method using derivatized cellulose and amylose chiral stationary phases and capillary electrophoresis (CE) method using neutral and anionic cyclodextrins added in the background electrolyte (BGE). An optimal baseline separation (R(s)>3.3 with analysis times<25min) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. CE was used as an alternative technique to HPLC for the Tic-hydantoin derivatives separation. The enantiomers were fully resolved with highly sulfated beta-cyclodextrins at pH 2.5 (R(s)>1.5 with analysis times <11min). Both methods were validated in terms of linearity, detection and quantification limits. They were used to check the enantiomeric purity of the enantiomers.