Separation of phenylsuccinic acid enantiomers using biphasic chiral recognition high-speed countercurrent chromatography

Lipase-based MIL-100(Fe) biocomposites as chiral stationary phase for high-efficiency capillary electrochromatographic enantioseparation

A novel chiral porous column was fabricated by lipase immobilized MIL-100(Fe) biocomposites as chiral stationary phase through covalent coupling and applied to capillary electrochromatographic enantioseparation. MOF-based lipase biocomposites not only enhance stereoselective activities but also improve the stability and applicability of the enzyme. The functionalized porous columns were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and powder X-ray diffraction. The performance of the porous column was evaluated by enantioseparating amino acid enantiomers, affording high resolution over 2.0. Besides, the enantio-resolutions of phenylephrine, phenylsuccinic acid, chloroquine, and zopiclone were also greater than 2.0. The relative standard deviations of run-to-run, intra-, and inter-day repeatability were within 4.0% in terms of resolution and retention time, exhibiting excellent stability of the column. Conceivably, the results show that MOF-based lipase composites as chiral stationary phase offer a highly efficient means for enantioseparation in capillary electrochromatography, attributing to the enhanced enantioselective activities of lipase by highly ordered frameworks.

Open tubular capillary column immobilized with sulfobutylether-β-cyclodextrin for chiral separation in capillary electrochromatography

A novel chiral open tubular capillary column was fabricated with sulfobutylether-β-cyclodextrin and glycidyl methacrylate for enantioseparation in capillary electrochromatography. First, the pretreated silica-fused capillary was treated with 3-trimethoxysilyl propyl methacrylate to attach double bond ligand onto the surface. A copolymer layer was formed on the surface of capillary using glycidyl methacrylate and ethylene dimethacrylate by in situ one-pot polymerization. Sulfobutylether-β-cyclodextrin was encapsulated inside the copolymerized layer. The morphology of the developed column was characterized by field emission scanning electron microscopy. The effect of organic percentage and pH value of the mobile phase on electroosmotic flow and resolution was also investigated. The performance of the fabricated column was validated by separation of amlodipine besilate, 2,3-diphenylpropionic acid, tropic acid, and pantoprazole enantiomers with good resolutions of 3.67, 4.82, 3.34, and 2.61, respectively. The repeatabilities of column-to-column and day-to-day through relative standard deviation were found better than 4%, exhibiting satisfactory repeatability of the developed column. The results reveal that open tubular capillary columns modified with β-cyclodextrin show a great prospect for enantioseparation of chiral drugs in capillary electrochromatography.

Hydroxypropyl-β-cyclodextrin encapsulated stationary phase based on silica monolith particles for enantioseparation in liquid chromatography

Hydroxypropyl-β-cyclodextrin-encapsulated stationary phase incorporated on silica monolith particles was prepared by physical embedding, providing a new method for the development of chiral stationary phase for enantioseparation in liquid chromatography. Ground silica monolith particles of about 2.0 μm were prepared via sol-gel reaction followed by differential sedimentation. Initially, the silica monolith particles were pretreated with 3-trimethoxysilyl propyl methacrylate to attach double-bonded ligands onto the surface, then a network structure was formed onto the surface of the particle using N-isopropyl acrylamide as functional monomer. Hydroxypropyl-β-cyclodextrin was encapsulated inside N-isopropyl acrylamide copolymerized layer on the surface of silica monolith particles. The effect of the amount of chiral selector on the chromatographic efficiency of the chiral stationary phase was examined. The glass lined stainless steel columns (1 mm internal diameter, 300 mm length) were packed with the stationary phase for estimation of the efficiency by separation of phenylsuccinic acid, oxybutynin, equol, and naproxen enantiomers in high-performance liquid chromatography, with the resolutions of 1.54, 1.72, 2.54, and 2.31, respectively. The column to column repeatabilities through relative standard deviation were found better than 3%. The experimental results indicate that the sol-gel ground silica particles modified with β-cyclodextrin provide a promising way for the separation of chiral enantiomers.

Enantioseparation of 2-(4-chlorophenyl)succinic acid by countercurrent chromatography and investigation of injection volume on resolution

2-(4-Chlorophenyl)succinic acid was successfully enantioseparated by countercurrent chromatography using hydroxypropyl-β-cyclodextrin as chiral selector. A two-phase solvent system composed of n-hexane-ethyl acetate-0.1 mol/L phosphate buffer with pH 2.65 (5:5:10, v/v) was selected. Enantioselective liquid-liquid extraction was used to optimize the enantioseparation conditions. Meanwhile, the influence of injection volume on resolution in countercurrent chromatography was investigated and a linear relationship between the inflection point of injection volume and sample loading was tentatively obtained. The peak resolution will decrease significantly when the injection volume over the inflection point was used. In addition, it could be found that the smaller amount of sample loading, the larger impact of injection volume on resolution could be observed, which might serve as a good reference for the selection of sample volume in enantioseparations by countercurrent chromatography. Under optimized conditions, 20 mg of 2-(4-chlorophenyl)succinic acid racemate dissolved in 10 mL of aqueous phase was successfully enantioseparated by countercurrent chromatography. The recovery for both of the enantiomer of (±)-2-(4-chlorophenyl)succinic acid reached within 70-75% with a purity of 99.0%.

Chiral counter-current chromatography: A survey of its instrument, mechanism, procedure, and applications

The chiral separation by counter-current chromatography has made great progress in the past three decades. It has become increasingly popular in the field of chiral separation, and many applications have been introduced during the last years. This review mainly focuses on the current topics, applications, and trends in chiral separation by counter-current chromatography. It contains the development of modern counter-current chromatography apparatus, theory of counter-current chromatography, overview of applications of chiral counter-current chromatography enantioseparation, its current situation, and challenges. At last, some conclusions and perspectives also have been discussed in this review.

Isolation and purification of four phenolic glycoside isomers from the leaves of Idesia polycarpa Maxim. by high-speed counter-current chromatography and preparative high-performance liquid chromatography

We established an efficient method using high-speed counter-current chromatography (HSCCC) combined with preparative high-performance liquid chromatography (prep-HPLC) for isolating and purifying phenolic glycoside isomers. The method involves a rapid and sensitive ultra-performance liquid chromatography-under voltage(UPLC-UV) technique using a sub-2 μm core-shell particle column for qualitative and quantitative analysis of four phenolic glycoside isomers from Idesia polycarpa Maxim. leaves. The partially purified samples from ethyl acetate extraction of ethanol extracts of I. polycarpa Maxim. leaves were obtained by HSCCC with a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water solution (3:5:3:5, v/v/v/v) to obtain fractions I and II, which contain two phenolic glycoside isomers. The two fractions were further isolated by prep-HPLC to yield compounds 1, 2, 3, and 4 with purities of 98.29%, 98.71%, 98.49% and 98.52%, and total recoveries of 93.5%, 72.2%, 75.5% and 88.3%, respectively. Compound 1 was first isolated from I. polycarpa Maxim., while compound 2 was reported to be a new phenolic glycoside, which is 1-[(6'-O-(Z)-p-coumaroyl)-β-D-glucopyranosyl]-oxy-2-phenol. The chemical structures of the four phenolic glycoside isomers were analyzed and confirmed by UPLC, UV, electrospray ionization mass spectrometry (ESI-MS), fourier transform infra-red (FT-IR), 1H-nuclear magnetic resonance (1H NMR), 13C-nuclear magnetic resonance (13C NMR) and 2D nuclear magnetic resonance (2D NMR) spectra. This study opens prospects for broad industrial applications of HSCCC/prep-HPLC for the isolation and purification of isomers.

Enantioseparation of acetyltropic acid by countercurrent chromatography with sulfobutyl ether-β-cyclodextrin as chiral selector

Acetyltropic acid is an important synthetic intermediate for preparation of tropane alkaloid derivatives, which can be used as anticholinergic drugs, deliriants, and stimulants. In the present work, acetyltropic acid was successfully enantioseparated by countercurrent chromatography using sulfobutyl ether-β-cyclodextrin as chiral selector. A biphasic solvent system composed of n-butyl acetate/n-hexane/0.1 mol/L citrate buffer at pH = 2.2 containing 0.1 mol/L of sulfobutyl ether-β-cyclodextrin (7:3:10, v/v) was selected, which produced a suitable distribution ratio D_S  = 1.14, D_R  = 2.31 and a high enantioseparation factor α = 2.03. Baseline separation was achieved for preparative enantioseparation of 50 mg of racemic acetyltropic acid. A method for chiral analysis of acetyltropic acid by conventional reverse phase liquid chromatography with hydroxylpropyl-β-cyclodextrin as mobile phase additive was established, and formation constants of inclusion complex were determined. It was found that different substituted β-cyclodextrin should be selected for enantioseparation of acetyltropic acid by countercurrent chromatography and reverse phase liquid chromatography.

The development of biphasic chiral recognition in chiral separation

In chiral separation, enantioseparation factor is an important parameter which influences the resolution of enantiomers. In this current overview, a biphasic chiral recognition method is introduced to the readers. This method can significantly improve the enantioseparation factor in two-phase solvent through adding lipophilic and hydrophilic chiral selectors which have opposite chiral recognition ability to organic and aqueous phases, respectively. This overview presents the development and applications of biphasic chiral recognition in liquid-liquid extraction and counter current chromatography. It mainly focuses on the topics of mechanism, advantages and limitations, applications, and key factors of biphasic chiral recognition. In addition, the future outlook on development of biphasic chiral recognition also has been discussed in this overview.

An overview of recent progress in solvent systems, additives and modifiers of counter current chromatography

Solvent systems are critical to counter current chromatography (CCC). Appropriate additives and modifiers can be used to improve the separation efficiency of CCC.

Separation of caffeoylquinic acids and flavonoids from Asteris souliei by high-performance counter-current chromatography and their anti-inflammatory activity in vitro

Eleven compounds were successfully separated from Asteris souliei by using a two-step high-performance counter-current chromatography method. The first step involved a reversed phase isocratic counter-current chromatography separation using hexane/ethyl acetate/methanol/water (1:0.8:1:1 v/v/v/v), which produced three fractions, the first two of which were mixtures. The second step used step-gradient reversed-phase counter-current chromatography with hexane/butanol/ethyl acetate/methanol/water (1:0.5:3.5:1:4 v/v/v/v/v) initially followed by hexane/ethyl acetate/methanol/water (1:2:1:2 v/v/v/v) to separate Fraction 1 into seven compounds; and hexane/ethyl acetate/methanol/water (1:1:1:1.2 v/v/v/v) to separate Fraction 2 into three further compounds. The chemical structures of the separated compounds were identified by ESI-MS and NMR spectroscopy (¹ H and ¹³ C). Baicalin (5), eriodictyol (7), apigenin-7-glycoside (8), quercetin (9), luteolin (10), and apigenin (11) showed obvious inhibitory effects on lipopolysaccharide-induced nitric oxide production in RAW264.7 cells at a concentration of 10 μg/mL.

Development of a method to screen and isolate potential α-glucosidase inhibitors from Panax japonicus C.A. Meyer by ultrafiltration, liquid chromatography, and counter-current chromatography

A new assay based on ultrafiltration, liquid chromatography and mass spectrometry was developed for the rapid screening and identification of the ligands for α-glucosidase from the extract of Panax japonicus. Six saponins were identified as α-glucosidase inhibitors. Subsequently, the specific binding ligands, namely, notoginsenoside R1 , ginsenoside Rb1 , chikusetsusaponin V, chikusetsusaponin IV, chikusetsusaponin IVa, and ginsenoside Rd (the purities were 94.18, 95.43, 96.09, 93.26, 94.50, 93.86%, respectively) were separated by counter-current chromatography using two-phase solvent systems composed of tert-butyl methyl ether, acetonitrile, 0.1% aqueous formic acid (3.8:1.0:4.4, v/v/v) and the solvent system composed of methylene chloride, isopropanol, methanol, 0.1% aqueous formic acid (5.8:1.0:6.0:2.2, v/v/v). The results demonstrate that ultrafiltration, liquid chromatography and mass spectrometry combined with high-speed counter-current chromatography might provide not only a powerful tool for screening and isolating α-glucosidase inhibitors in complex samples but also a useful platform for discovering bioactive compounds for the prevention and treatment of diabetes mellitus.

Application and comparison of high-speed countercurrent chromatography and high performance liquid chromatography in preparative enantioseparation of α-substitution mandelic acids

Preparative enantioseparations of α-cyclopentylmandelic acid and α-methylmandelic acid by high-speed countercurrent chromatography (HSCCC) and high performance liquid chromatography (HPLC) were compared using hydroxypropy-β-cyclodextrin (HP-β-CD) and sulfobutyl ether-β-cyclodextrin (SBE-β-CD) as the chiral mobile phase additives. In preparative HPLC the enantioseparation was achieved on the ODS C₁₈ reverse phase column with the mobile phase composed of a mixture of acetonitrile and 0.10 mol L^-1 phosphate buffer at pH 2.68 containing 20 mmol L^-1 HP-β-CD for α-cyclopentylmandelic acid and 20 mmol L^-1 SBE-β-CD for α-methylmandelic acid. The maximum sample size for α-cyclopentylmandelic acid and α-methylmandelic acid was only about 10 mg and 5 mg, respectively. In preparative HSCCC the enantioseparations of these two racemates were performed with the two-phase solvent system composed of n-hexane-methyl tert.-butyl ether-0.1 molL^-1 phosphate buffer solution at pH 2.67 containing 0.1 mol L^-1 HP-β-CD for α-cyclopentylmandelic acid (8.5:1.5:10, v/v/v) and 0.1 mol L^-1 SBE-β-CD for α-methylmandelic acid (3:7:10, v/v/v). Under the optimum separation conditions, total 250 mg of racemic α-cyclopentylmandelic acid could be completely enantioseparated by HSCCC with HP-β-CD as a chiral mobile phase additive in a single run, yielding 105-110 mg of enantiomers with 95-98% purity and 85-90% recovery. But, no complete enantioseparation of α-methylmandelic acid was achieved by preparative HSCCC with either of the chiral selectors due to their limited enantioselectivity. In this paper preparative enantioseparation by HSCCC and HPLC was compared from various aspects.