Model-based design of gradient elution in liquid-liquid chromatography: Application to the separation of cannabinoids

Liquid-liquid chromatography (LLC) is a separation technique that utilizes a biphasic solvent system as the mobile and stationary phases. The components are separated solely due to their different distributions between the two liquid phases. Gradient change in the mobile phase composition during the chromatographic process is a powerful method for improving the resolution of separation or shortening the process time. Gradient elution readily applies to LLC with biphasic solvent systems in which the stationary phase composition remains nearly constant when the mobile phase composition changes. This work proposes a model-based approach to optimize gradients in LLC and circumvent tedious trial-and-error experiments. The solutes' distribution constant depends on the mobile phase composition. Thus, the distribution constants were described as a function of the content of one of the solvents (= modifier) in the mobile phase. The dispersive and mass-transfer effects in the tubing and the column are modeled with a stage model. Only a few experiments are required to determine the model parameters. After the validation of the model and its parameters, the model can be used for LLC gradient optimization. The proposed approach was demonstrated for a gradient LLC separation of a mixture of four cannabinoids. Two different gradient shapes, one-step and linear gradient, were considered. For a pre-selected minimal purity requirement, the gradient was optimized for maximum process efficiency, defined as the product of productivity and yield. An experiment conducted with the optimized gradient conditions was in good agreement with the simulation, showing the potential of the proposed method.

Nonlinear liquid-liquid chromatography: Modeling a binary mixture separation

In liquid-liquid chromatography (LLC), mixture components are separated due to their different distribution between the phases of a biphasic liquid system composed of three or four solvents. LLC separations are typically modeled assuming that only the solutes distribute between the two liquid phases and their distribution can be described with a concentration-independent distribution constant. With increasing solute concentration, the physicochemical properties of the biphasic system change, and the distribution of the solutes becomes a function of their concentration. However, the experimental determination of liquid-liquid equilibria in multicomponent systems is time-intensive, and its prediction using thermodynamic models is often not sufficiently accurate for process design purposes. Thus, in this work, we propose a simple approach to model and simulate LLC separations in the nonlinear (concentration-dependent) range of the solutes' distribution equilibria, namely cannabidiol (CBD) and cannabigerol (CBG). Using the inverse method, the distribution equilibrium equation parameters were estimated from pulse injection experiments of single solutes at concentrations ranging from 1 to 100 mg/mL and 1-50 mg/mL for CBD and CBG, respectively. The obtained parameters were then successfully used to predict the elution profiles of binary mixtures of different compositions at 40 mg/mL total cannabinoid concentration. The approach was demonstrated and validated for CBD and CBG as model compounds and n-hexane/methanol/water 10/7.5/2.5 (v/v/v) as the biphasic solvent system. It should be noted that the applicability of the proposed approach is system-dependent, and hence, it should be evaluated for each separation task individually.

Enrichment and structural assignment of geometric isomers of unsaturated furan fatty acids

Furan fatty acids (FuFAs) are valuable minor fatty acids, which are known for their excellent radical scavenging properties. Typically, the furan moiety is embedded in an otherwise saturated carboxyalkyl chain. Occasionally, these classic FuFAs are accompanied by low amounts of unsaturated furan fatty acids (uFuFAs), which additionally feature one double bond in conjugation with the furan moiety. A recent study produced evidence for the occurrence of two pairs of E-/Z-uFuFA isomers structurally related to saturated uFuFAs. Here, we present a strategy that allowed such trace compounds to be enriched to a level suited for structure determination by NMR. Given the low amounts and the varied abundance ratio of the four uFuFA isomers, the isolation of individual compounds was not pursued. Instead, the entire isomer mixture was enriched to an amount and purity suitable for structure investigation with contemporary NMR methods. Specifically, lipid extracted from 150 g latex, the richest known source of FuFAs, was subsequently fractionated by countercurrent chromatography (CCC), silver ion, and silica gel column chromatography. Analysis of the resulting mixture of four uFuFAs isomers (2.4 mg in an abundance ratio of 56:23:11:9) by different NMR techniques including PSYCHE verified that the structures of the two most abundant isomers were E-9-(3-methyl-5-pentylfuran-2-yl)non-8-enoic acid and E-9-(3-methyl-5-pent-1-enylfuran-2-yl)nonanoic acid. Additionally, we introduced a computer-based method to generate an averaged chromatogram from freely selectable GC/MS runs of CCC fractions without the necessity of pooling aliquots. This method was found to be suitable to simplify subsequent enrichment steps.

Retention correlation and orthogonality between reversed phase countercurrent chromatography and liquid chromatography based on solvent strength

Correlation of elution performance between reversed phase countercurrent chromatography and liquid chromatography was investigated using five selected natural components. Theoretical guidance for orthogonality of two-dimensional countercurrent chromatography and liquid chromatography was proposed. The difference in retention behavior between countercurrent chromatography and liquid chromatography was studied when the mobile phase was composed of methanol and water by measuring the partition behavior of five selected compounds in two typical biphasic solvent systems composed of n-hexane-ethyl acetate-methanol-water and chloroform-methanol-water. An orthogonal diagram between countercurrent chromatography and liquid chromatography was obtained by normalized treatment of the measured partition coefficients and capacity factors. The experimental results showed that each biphasic solvent system used for countercurrent chromatography had a high orthogonality with liquid chromatography when a specific volume ratio was used.

Enantioseparation of two antifungal azole drugs by analytical countercurrent chromatography using sulfobutyl ether-β-cyclodextrin as chiral selector

This study reports a successful enantioseparation of two antifungal drugs, Ketoconazole and Voriconazole, using countercurrent chromatography (CCC) with synthesized sulfobutyl ether-β-cyclodextrin (SBE-β-CD) as chiral selector. Two biphasic solvent systems composed of dichloromethane: 0.1 mol L-1 of phosphate buffer solution (pH 3.0) (1:1, v/v) and n-hexane: ethyl acetate: 0.1 mol L-1 phosphate buffer solution (pH 3.0) (1.5:0.5:2, v/v/v) were selected. Influence factors were investigated, including degree of substitution of SBE-β-CD, concentration of SBE-β-CD, equilibrium temperature, and pH of aqueous phase. Under optimized separation conditions, a large enantioseparation factor of α ≥ 3.26 and a high peak resolution Rs= 1.82, was achieved for enantioseparation of Voriconazole by countercurrent chromatography, and purity of two azole stereoisomers collected from CCC separation reached 98.5%, as determined by HPLC. Molecular docking was employed to investigate the formation of inclusion complex.

Sample preparation of free sterols from vegetable oils by countercurrent chromatography in co-current mode

Countercurrent chromatography (CCC) is a preparative instrumental method where both the mobile and stationary phases are liquids and which are predominantly used for the isolation of natural products. In this study, we widened the scope of CCC by using it as an instrumental method for the direct enrichment of the free sterol fraction from plant oils to which they contribute with ~ 1%. For the enrichment of sterols in a narrow band, we employed the so-called co-current CCC (ccCCC) mode in which both liquid phases of the solvent system (here: n-hexane/ethanol/methanol/water (34:11:12:2, v/v/v/v)) are moved at different flow rates in the same direction. Different from previous applications of ccCCC, the lower and predominant "stationary" phase (LP_s) was pumped twice as fast as the mobile upper phase (UP_m). This novel reversed ccCCC mode improved the performance but also required a higher demand of LP_s compared to UP_m. Therefore, the exact phase composition of UP_m and LP_s was determined by gas chromatography and Karl Fischer titration. This step enabled the direct preparation of LP_s which considerably reduced the waste of solvents. Internal standards (phenyl-substituted fatty acid alkyl esters) were synthesised and utilised to frame the free sterol fraction. This approach allowed a fractionation of free sterols based on the UV signal and compensated run-to-run variations. The reversed ccCCC method was then applied to the sample preparation of five vegetable oils. In addition to free sterols, free tocochromanols (tocopherols, vitamin E) were also eluted in the same fraction as free sterols.

Isolation of plastochromanol-8 from flaxseed oil by countercurrent separation methods

The naturally occurring antioxidant plastochromanol-8 (PC-8) is a member of the tocochromanol (vitamin E) family which features eight unsaturated isoprene units in the side chain compared to three in the case of γ-tocotrienol. Due to the lack of a commercially available PC-8 standard, we developed a route to gain relevant amounts of highly pure PC-8. Specifically, ∼320 g flaxseed oil was saponified and the bulky PC-8 was enriched by gel permeation chromatography. It followed countercurrent chromatography using the solvent system n-hexane/benzotrifluoride/acetonitrile (20:7:13, v/v/v). The final purification was achieved by centrifugal partition chromatography using the novel solvent system hexamethyldisiloxane/acetonitrile (1:1, v/v). This step provided ∼26 mg PC-8 (>99.5 %, according to HPLC, GC and NMR analysis). Two further, hitherto unknown minor tocochromanols (<1 % of PC-8) were detected and could be identified to be plastochromanol-7 (PC-7) and plastochromanol-9 (PC-9), i.e. tocochromanols with seven and nine unsaturated isoprene units, respectively, in the side chain.

Nonlinear liquid-liquid chromatography: Beyond a constant distribution coefficient

Liquid-liquid chromatography (LLC) is a technique in which the separation of mixture components is achieved due to their different distribution between the two phases of a pre-equilibrated biphasic solvent system. In this work, the LLC operation in the nonlinear range of the distribution isotherm was systematically examined for the first time. The influence of the feed concentration on the elution profiles of a model component (cannabidiol, CBD) was studied in three LLC units of different types and sizes ranging from ∼20 mL to ∼2 L. A series of pulse injections with CBD concentrations varying from 1 to 300 mg/mL was performed with n-hexane/methanol/water 5/4/1 (v/v/v) in descending mode (lower phase as the mobile phase). The elution profiles were simulated using the equilibrium-cell model and an anti-Langmuir-like equation for describing the CBD distribution equilibria. The distribution equilibria equation parameters were fitted to the CBD elution profiles using the peak fitting method. The model was validated and provided good predictions of the CBD elution profiles in the entire concentration range for all three LLC units.

GUESS - A simple approach to accelerate optimization countercurrent separation

The generally useful estimate of solvent systems (GUESS) method, which is based on thin layer chromatography, is a simple and practical method for selecting solvent systems for countercurrent chromatography (CCC). However, it is rarely used for complex samples derived from natural products. In this study, GUESS was used for CCC solvent system selection and polarity-adjusted CCC separations of several fractions, which were obtained from a silica gel column containing complex compositions with a broad polarity from Salvia bowleyana Dunn. The GUESS method was performed on five fractions based on solvent systems in the n-hexane-ethyl acetate-methanol-water (HEMWat) family. Based on the GUESS results, the optimal solvent systems were selected for CCC separation. Twelve diterpenoids were obtained from the five silica gel column fractions of S. bowleyana Dunn using elution-extrusion countercurrent chromatography (EECCC). These demonstrate that GUESS guidance and the polarity adjustment of the solvent system accelerate the optimization of CCC separation conditions and simplify the process of accommodating a broad polarity of components in complicated mixture fractions. We therefore confirmed the feasibility and advantage of the GUESS method for complex natural chemical component separations.

Degree and distribution of substitution of hydroxypropyl-β-cyclodextrin in enantioselective liquid-liquid extraction and countercurrent chromatographic enantioseparation

Nine types of hydroxypropyl-β-cyclodextrin (HP-β-CD) with different degrees and distributions of substitution were synthesised, and nine racemates were selected to investigate the effect of different degrees and distributions of substitution of HP-β-CD on the enantioseparation factor. ¹H NMR and GC/MS were used to characterise the synthesised HP-β-CD. The degree and distribution of substitution had a significant influence on enantioselective liquid-liquid extraction and enantioseparation by countercurrent chromatography. For most of the tested racemates, increasing both the degree of substitution and distribution of substitution at the C-2 position for HP-β-CD would lead to an increasing enantioseparation factor; the optimal enantioseparation factor of 2-phenylbutyric acid, tropic acid, 2,3-diphenylpropionic acid, 2-(4-hydroxylphenyl) propanoic acid, and naproxen was increased to 1.77, 1.53, 1.67, 1.61, and 1.75, respectively. The enantioseparation of racemic naproxen, 2-(4-hydroxylphenyl) propanoic acid, and 2,3-diphenylpropionic acid by countercurrent chromatography was optimised using HP-β-CD with a degree of substitution of 16.5, and peak resolution was significantly improved to 1.03, 1.35, and 1.01, respectively.

Continuous Countercurrent Chromatography in Protein Purification

Continuous countercurrent chromatography can be applied for both capture and polishing steps in the downstream processing of biopharmaceuticals. This chapter explains the concept of countercurrent operation, focusing on twin-column processes and how it can be used to alleviate the trade-offs of traditional batch chromatography with respect to resin utilization/productivity and yield/purity. CaptureSMB and MCSGP, the main twin-column continuous countercurrent chromatography processes, are explained, and the metrics by which they are compared to single-column chromatography are identified. Practical hints for process design and application examples are provided. Finally, regulatory aspects, scale-up, and UV-based process control are covered.

Relayed chromatography - Countercurrent chromatography in series with liquid chromatography for the separation of natural products

Chromatography is an essential method for separating natural products. In this study, we proposed the concept of 'relayed chromatography', based on the strategy of combining different chromatography with relayed resolution by in-situ concentration technique. The following chromatographic methods were used: high-speed countercurrent chromatography (HSCCC), silica gel liquid chromatography (silica gel LC), and reverse phase liquid chromatography (reverse phase LC). The proposed strategy was effectively applied to the preparative separation of naturally existing naphthaquinones. After the first separation stage (silica gel LC), acetylalkannin (1) was directly collected, while fractions 1, 4 and 5 were collected and respectively subjected to recycling CCC separation after concentration. Thus, deoxyshikonin (2), 8-O-methyl-11-O-acetylshikonin (6), β-acetoxyisovalerylalkannin (7) and alkannin (8) were collected. Fraction 2 was concentrated and injected in reverse phase LC separation. After collection of isobutyrylalkannin (3), the remaining effluent from reverse phase LC retained the peak resolution (R_4,5=0.45) and was injected into a recycling CCC elution. Finally, β, β-dimethylacrylalkannin (4), and isovalerylalkannin (5) were collected with sufficient resolution (R_4,5=1.25). Eight naturally occurring naphthaquinones were thus isolated from Arnebia euchroma. The purities of all the compounds were determined by HPLC to be > 90%, and the chemical structures were determined by spectral method. Among the aforementioned compounds, 8-O-methyl-11-O-acetylshikonin (6) was separated as a new compound from A. euchroma. In conclusion, the relayed strategy that retains the resolution of the previous chromatographic stage can improve CCC separation efficiency, which may expand the range of application of CCC combined with different chromatography to the separation of natural products.

Online hyphenation of centrifugal partition chromatography with countercurrent chromatography (CPC-CCC) and its application to the separation of saturated alkylresorcinols

Centrifugal partition chromatography (CPC) and countercurrent chromatography (CCC) are two preparative techniques mainly used for the isolation and purification of natural products. While CPC benefits from a larger sample capacity, CCC typically provides better peak resolutions and hereby higher purities. In this study, we aimed to combine both advantages by the direct linking of CPC and CCC which was achieved by installation of switching valves and connection tube. The hyphenated CPC-CCC setup was tested with major alkylresorcinols which were obtained from a transesterified and hydrogenated rye extract. Injections of 1- and 5-g samples into the individual CCC system confirmed the limited sample capacity because of immediate flooding with the 5-g sample (total loss of stationary phase). In comparison, the CPC system was stable with 5- and 10-g samples but the peak resolution with 1-g sample was poorer than with the CCC system. Injections of 5- and 10-g samples into the CPC-CCC system were successful. However, a sample load of 10 g resulted in lower purities of the alkylresorcinols (80% or less) due to peak tailing. By contrast, injection of 5-g sample provided high amounts of ~ 1.2 g alkylresorcinols with purities of > 95%.

Fast isolation of the environmentally relevant halogenated natural product MHC-1 by means of countercurrent chromatography

Environmentally relevant halogenated natural products (HNPs) are frequently similarly high concentrated in marine biota as major anthropogenic persistent organic pollutants (POPs). The lack of widely available reference standards, however, hampers the in-depth research of several HNPs. For instance, (1R,2S,4R,5R,1'E)-2-bromo-1-bromomethyl-1,4-dichloro-5-(2'-chloroethenyl)-5-methylcyclohexane (MHC-1), which is produced by species referred to the red seaweed Plocamium cartilagineum has not yet been synthesized due to its complex structure and stereochemistry. For this reason, we aimed to establish a method for fast isolation of mg-amounts of MHC-1 from its natural producer based on countercurrent chromatography (CCC). Five biphasic solvent systems were tested and finally, the solvent system acetonitrile/n-hexane/toluene (9:9:2, v/v/v) was selected for the separations due to its suitable partition coefficient of MHC-1 (K_U/L = 0.52). n-Hexane extracts of dried P. cartilagineum were directly injected into the CCC system. Four subsequent CCC runs from three samples of Plocamium cartilagineum (two from Heligoland, Germany and one from Brittany, France) could be performed with high reproducibility. Together, the main fraction provided ~16 mg MHC-1 in a purity of >97% according to GC/FID, GC/ECNI-MS and NMR analysis. This amount could be used to prepare ~1600 quantitative standard solutions of MHC-1. The high MHC-1 content in the seaweed sample collected at Brittany indicated that this area was another hotspot of MHC-1.

Separation of minor cannabinoids from hemp extract with trapping multiple dual mode liquid-liquid chromatography

Aside from Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), other less common cannabinoids have recently gained an increasing popularity, mostly due to their promising biological potential. However, time-saving and cost-effective methods for their preparative purification are missing. In this study, trapping multiple dual mode (MDM), a flow-reversal liquid-liquid chromatography (LLC) operating mode, was used for the separation of different minor cannabinoids from a hemp extract. Separation task specific biphasic solvent systems were selected for the purification of the target constituents, as follows: n-hexane/methanol/water 10/6.5/3.5 for cannabielsoin (CBE); n-hexane/methanol/water 10/7/3 for cannabidivarin (CBDV) and cannabigerol (CBG); n-hexane/methanol/water 10/8/2 for cannabinol (CBN) and n-hexane/methanol/water 10/9/1 for cannabichromene (CBC) and cannabicylol (CBL). For each separation task, the concentration of the hemp extract in the feed stream and mobile phase flow rate were selected by shake-flask and stationary phase retention experiments, respectively. For the determination of the trapping MDM operating parameters, the short-cut method was implemented and followed by equilibrium-cell model-based simulations. The trapping MDM allowed the separation of the targeted cannabinoids with purities of 93-99%, yields of 73-95%, solvent consumption 2-4-fold lower and productivities almost double than those obtained using batch separation.

Flavonoids from Siparuna cristata as Potential Inhibitors of SARS-CoV-2 Replication

The novel coronavirus SARS-CoV-2 has been affecting the world, causing severe pneumonia and acute respiratory syndrome, leading people to death. Therefore, the search for anti-SARS-CoV-2 compounds is pivotal for public health. Natural products may present sources of bioactive compounds; among them, flavonoids are known in literature for their antiviral activity. Siparuna species are used in Brazilian folk medicine for the treatment of colds and flu. This work describes the isolation of 3,3',4'-tri-O-methyl-quercetin, 3,7,3',4'-tetra-O-methyl-quercetin (retusin), and 3,7-di-O-methyl-kaempferol (kumatakenin) from the dichloromethane extract of leaves of Siparuna cristata (Poepp. & Endl.) A.DC., Siparunaceae, using high-speed countercurrent chromatography in addition to the investigation of their inhibitory effect against SARS-CoV-2 viral replication. Retusin and kumatakenin inhibited SARS-CoV-2 replication in Vero E6 and Calu-3 cells, with a selective index greater than lopinavir/ritonavir and chloroquine, used as control. Flavonoids and their derivatives may stand for target compounds to be tested in future clinical trials to enrich the drug arsenal against coronavirus infections.

GRAPHICAL ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43450-021-00162-5.

Isolation of sesquiterpenoids from Matricaria chamomilla by means of solvent assisted flavor evaporation and centrifugal partition chromatography

The (semi)volatile fraction of Matricaria chamomilla L., an annual herbal plant from the family of Asteraceae, contains high quantities of sesquiterpenes and sesquiterpenoids. A method was developed to achieve isolation and separation of these compounds, using a combination of solvent assisted flavor evaporation (SAFE) and solid support-free liquid-liquid chromatography. The biphasic liquid solvent system n-heptane/ethyl acetate/methanol/water, 5/2/5/2 v/v/v/v (Arizona S) was elaborated as a suitable solvent system for the simultaneous separation of the target compounds. The lab-scale liquid-liquid chromatography separation performed in a countercurrent chromatography (CCC) column was successfully transferred to a semi-preparative centrifugal partition chromatography (CPC) column, which enabled the isolation of artemisia ketone, artemisia alcohol, α-bisabolone oxide A, and (E)-en-yn-dicycloether. α-Bisabolol oxide A and (Z)-en-yn-dicycloether co-eluted, but were successfully separated by subsequent size-exclusion chromatography (SEC). Similarly, spathulenol and α-bisabolol oxide B were obtained as a mixture, and were separated by means of column chromatography using silica gel as stationary phase. The isolated compounds were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gas chromatography–mass spectrometry (GC-MS).

Development of ultrasound-assisted mixture extraction and online extraction solution concentration coupled with countercurrent chromatography for the preparation of pure phytochemicals from Phellinus vaninii

Herein, ultrasound-assisted mixture extraction (UAME) and online extraction solution concentration (OESC) were conducted to extract products from crops and plants. These techniques were coupled with parallel countercurrent chromatography (PCCC) and applied for continuous extraction and online isolation of chemical constituents from Phellinus vaninii. The UAME instrument comprises extraction and solution separation chambers. It provides higher extraction efficiency and fewer impurities and is suitable for processing various sample matrices. The OESC device comprises a spray nozzle, concentrating cylinder, and hot-blast air nozzle. The mechanical parameters for UAME and OESC were optimized, and the operation of online UAME and OESC coupled with PCCC was described. Raw plant materials were extracted using a two-phase extractant comprising petroleum-ethyl acetate-ethanol-water (0.5:2.0:0.5:2.0, v/v/v/v). The aqueous and organic phases were then concentrated using the OESC technique. Two CCC runs were conducted for preparatory work. After extraction and online concentration, the concentrate was pumped into the CCC for separation. During PCCC separation, continuous automated extraction and concentration were still conducted. When the first cycle of the UAME/OESC/PCCC was completed, followed by the initiation of the second cycle, and the process was continued. Six target compounds with purities exceeding 97.22% were successfully separated using the CCC solvent systems comprising n-hexane-ethyl acetate-acetonitrile-water (5.5:2.5:5.0:0.4, v/v/v/v) and n-butanol-ethanol-water (4.5:1.3:6.5, v/v/v). Compared with conventional extraction methods, the proposed UAME/OESC/PCCC method has higher efficiency, facilitates high-purity separation of analytes, and offers opportunity for automation and systematic preparation of natural products.

Partition Efficiency of Eccentric Coil for Countercurrent Chromatographic Separation of Proteins Using Small-scale Cross-axis Coil Planet Centrifuge with Circular and Elliptic Cylindrical Columns

The partition efficiency of the double-spaced coil for eccentric and toroidal coils on countercurrent chromatographic separation of proteins was evaluated using the small-scale cross-axis coil planet centrifuge (CPC) equipped with circular and elliptic cylindrical columns. Standard cytochrome c, myoglobin and lysozyme samples were used for separation with the 12.5% (w/w) polyethylene glycol 1000 and 12.5% (w/w) dibasic potassium phosphate system. In the circular column, the double-spaced eccentric coil yielded better peak resolution than the double-spaced toroidal coil, and the double-spaced eccentric coil yielded better peak resolution than the single-spaced eccentric coil. In the elliptic column, the double-spaced eccentric coil also produced better peak resolution than the double-spaced toroidal coil, but the single-spaced eccentric coil yielded better peak resolution than the double-spaced eccentric coil. The overall results indicated that the double-spaced eccentric coil for the circular column and the single-spaced eccentric coil for the elliptic column yielded better protein separation using the small-scale cross-axis CPC with aqueous two-phase solvent systems.

In vitro human cell-based TTR-TRβ CALUX assay indicates thyroid hormone transport disruption of short-chain, medium-chain, and long-chain chlorinated paraffins

Over the last decades, short-chain chlorinated paraffins (SCCPs), medium-chain chlorinated paraffins (MCCPs), and long-chain chlorinated paraffins (LCCPs) have become the most heavily produced monomeric organohalogen compound class of environmental concern. However, knowledge about their toxicology is still scarce, although SCCPs were shown to have effects on the thyroid hormone system. The lack of data in the case of MCCPs and LCCPs and the structural similarity with perfluoroalkyl substances (PFAS) prompted us to test CPs in the novel TTR-TR CALUX assay for their thyroid hormone transport disrupting potential. Four self-synthesized and additionally purified single chain length CP mixtures (C₁₀-CPs, C₁₁-CPs, C₁₄-CPs and C₁₆-CPs) and two each of industrial MCCP and LCCP products were tested in parallel with PFOA. All CP mixtures influenced the TTR binding of T4, giving activities of 1,300 to 17,000 µg/g PFOA equivalents and lowest observable effect concentrations (LOELs) of 0.95 to 0.029 mM/L incubate. Highest activities and lowest LOELs were observed for C₁₆-CPs (48.3% Cl content, activity 17,000, LOEL 0.047 mM/L) and a LCCP mixture (71.7% Cl content; activity 10,000; LOEL 0.029 mM/L). A trend of higher activities and lower LOELs towards longer chains and higher chlorination degrees was implied, but could not be statistically confirmed. Irrespectively, the less well examined and current-use LCCPs showed the highest response in the TTR-TRβ CALUX assay.

Target separation and antitumor metastasis activity of sesquiterpene-based lysine-specific demethylase 1 inhibitors from zedoary turmeric oil

Lysine-specific histone demethylase 1 (LSD1) was the first histone demethylase identified in epigenetics and has recently emerged as an attractive therapeutic target for treating tumors. To date, almost all reported LSD1 inhibitors have been chemosynthesized; however, natural products possess pharmacological and biological activity and can be sources for drug development. Here, we established a target separation countercurrent chromatography technique to isolate LSD1 inhibitors from zedoary turmeric oil. Four sesquiterpene-based LSD1 inhibitors were efficiently obtained with an inhibition ratio equal to or less than that of the positive control drug. Compound 2 showed the most potent inhibitory activity, with a half-maximal inhibitory concentration of 3.97 μM, and was further tested to determine its ability to inhibit LSD1 and its antitumor metastatic effects in MDA-MB-231 cells. These four compounds are the first sesquiterpene-based natural LSD1 inhibitors to be characterized. Our findings provide a new molecular framework for studying LSD1 inhibitors and offer a template for designing more sesquiterpene-based LSD1 inhibitors with potential antitumor activity.

et Zucc

Off-line two-dimensional countercurrent chromatography has been widely applied to the isolation of complex samples, but little research on the investigation of orthogonality in the selection of biphasic solvent systems is available. In the present work, the orthogonality in the selection of a biphasic solvent system for liquid-liquid chromatographic separation of aqueous extract and ether extract from the traditional Chinese medicinal plant Polygonum cuspidatum Sieb. et Zucc was evaluated by the correlation coefficient and space occupancy rate. In total, 25 different biphasic solvent systems were tested, and 313 system combinations were analysed. A convex hull methodology was used to determine the separation space and to optimize separation conditions. The correlation coefficient matrix was transformed into dendrograms and a colour map to visualize the dissimilarity between, and orthogonality for, all solvent systems. The aqueous extracts from Polygonum cuspidatum were separated using selected biphasic solvent systems with high orthogonality: ethyl acetate-ethanol-water (70:1:70, v/v) and petroleum ether-ethyl acetate-water (1:5:5, v/v). The ether extracts from Polygonum cuspidatum were also separated using selected biphasic solvent systems with high orthogonality: petroleum-ethyl acetate-methanol-aqueous 0.25 M NH₃•H₂O (5:5:5:5, v/v) and petroleum-ethyl acetate-methanol-water (5:5:5:5, v/v). Thirteen compounds were successfully obtained. The experimental results demonstrated that the evaluation of orthogonality provided an alternative strategy to select an applicable solvent system for the separation of complex samples using off-line two-dimensional countercurrent chromatography.

Chromatographic behavior of six lanthanides on a centrifugal mixer-settler extractor cascade

This work furthers the development of counter-current chromatography as an industrial separation process method. It was demonstrated that the industrial counter-current chromatography methods, in particular, for the separation groups of rare earth metals, can be implemented in a modified cascade of centrifugal mixer-settler extractors. The retention behavior of rare earth elements (samarium, europium, gadolinium, terbium, dysprosium and yttrium) on the pilot chromatographic unit consisting of 70 serially connected centrifugal mixer-settler extractors was experimentally studied under isocratic elution conditions using the mixture of 30 vol.% Cyanex^Ⓡ572 + 10 vol.% tributylphosphate in a hydrocarbon diluent as the stationary phase and aqueous nitric acid as the mobile phase. Theoretical analysis of experimental studies showed an acceptable agreement between the assumptions of the theory and experimental results.

Enantioseparation of three constitutional isomeric 2-(methylphenyl)propanoic acids by countercurrent chromatography

2-(3-Methylphenyl)propanic acid and 2-(4-methylphenyl)propanoic acid were successfully enantioseparated by countercurrent chromatography using hydroxypropyl-β-cyclodextrin (HP-β-CD) as a chiral selector. 2-(2-Methylphenyl)propanoic acid was also studied to compare the enantioseparation ability of three isomeric 2-(methylphenyl)propanoic acids. Totally 20 mg of 2-(3-methylphenyl)propanic acid and 20mg of 2-(4-methylphenyl)propanic acid were enantioseparated individually by countercurrent chromatography. Recovery for the (±)-2-(3-methylphenyl)propanic acid enantiomer was in the range of 85%-90% with 98.0%-98.8% purity and recovery for the (±)-2-(4-methylphenyl)propanic acid enantiomer was in the range of 80%-83% with 97.0%-98.0% purity. The enantioseparation factor in countercurrent chromatography for 2-(4-methylphenyl)propanic acid and 2-(3-methylphenyl)propanic acid were 1.31 and 1.26, and the peak resolution in HPLC reached 2.2 and 1.4. However, no enantioseparation could be found for 2-(2-methylphenyl)propanic acid. In addition, the inclusion complexes were investigated by UV spectrophotometer. The inclusion formation constant of inclusion complex between 2-(4-methylphenyl)propanic acid, 2-(3-methylphenyl)propanic acid, 2-(2-methylphenyl)propanic acid and HP-β-CD were determined as 121.73 mol/L, 78.12 mol/L and 53.18 mol/L, respectively. The present results showed that enantiorecognition was greatly affected by substituted positions of methyl group on the benzene ring. Combined with our previous results, the steric hindrance had a significant effect on inclusion interaction between HP-β-CD and racemic 2-(substitutedphenyl)propanoic acids. No enantiorecognition could be achieved for 2-(substitutedphenyl)propanoic acids with ortho-substituent group on benzene, while the influence of meta- and para- group on enantiorecognition varies with different substituent groups on benzene ring.

Symphytum officinale L.: Liquid-liquid chromatography isolation of caffeic acid oligomers and evaluation of their influence on pro-inflammatory cytokine release in LPS-stimulated neutrophils

ETHNOPHARMACOLOGICAL RELEVANCE

Symphytum officinale L. (comfrey, Boraginaceae) has been traditionally used for millennia in joint distortions, myalgia, bone fractures and hematomas. However, key activity-determining constituents and molecular mechanisms underlying its use have not been completely elucidated.

AIM OF THE STUDY

The objective of this study was to isolate and identify the major compounds from a hydroethanolic root extract of S. officinale and evaluate their antioxidant potential, alongside their effect on the cytokine production of ex vivo stimulated neutrophils, thus providing scientific support for the traditional use of comfrey root.

MATERIAL AND METHODS

Four caffeic acid oligomers were isolated from comfrey roots by liquid-liquid chromatography, their structures being established by MS and NMR analyses. In vitro antioxidant evaluation was performed by DPPH and ABTS assays. The cytotoxicity of isolated compounds was established by flow cytometry. The effect on cytokine release, such as interleukin (IL)-1β, IL-8 and tumor necrosis factor alpha (TNF-α), in lipopolysaccharide (LPS)-stimulated neutrophils was determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The main constituents found in comfrey root were represented by four caffeic acid oligomers, namely globoidnan B (1), rabdosiin (2), rosmarinic acid (3) and globoidnan A (4). Rabdosiin, globoidnans A and B were isolated for the first time from S. officinale. In the in vitro antioxidant tests, compound 2 was the most active, with EC₅₀ values in DPPH and ABTS assays of 29.14 ± 0.43 and 11.13 ± 0.39, respectively. Neutrophils' viability over the tested concentration domain of 12.5-50 μM was not altered. At 50 μM, all compounds significantly inhibited IL-1β release, with compound 3 (45.60% release vs. LPS stimulated neutrophils) being the most active, followed by compounds 1 (53.85%), 2 (69.89%) and 4 (60.68%).

CONCLUSIONS

The four caffeic acid oligomers reported in S. officinale root may contribute to the overall anti-inflammatory activity for which comfrey preparations are used in traditional medicine.

Countercurrent chromatographic fractionation followed by gas chromatography/mass spectrometry identification of alkylresorcinols in rye

Alkylresorcinols (5-alkyl-1,3-dihydroxybenzenes, ARs) are bioactive phenolic lipid compounds which are particularly abundant in rye and partly other cereals. In this study on ARs, whole rye grain extracts were gained with cyclohexane/ethyl acetate (46/54, w/w). Silylated extracts were used to develop a gas chromatography with mass spectrometry method in the selected ion monitoring mode (GC/MS-SIM) for the sensitive detection of conventional ARs along with keto-substituted (oxo-AR) and ring-methylated ARs (mAR) with 5-alkyl chain lengths of 14 to 27 carbon atoms and 0 to 4 double bonds in one run. Analysis was performed by countercurrent chromatographic (CCC) fractionation using the solvent system n-hexane/ethyl acetate/methanol/water (9/1/9/1, v/v/v/v). Subsequent GC/MS-(SIM) analysis of 80 silylated CCC fractions enabled the detection of 74 ARs in the sample. The CCC elution of the ARs followed the equivalent chain length (ECL) rule in which one double bond compensated the effect of two (additional) carbon atoms. Novel or rarely reported ARs were detected in virtually all classes, i.e. saturated AR (AR14:0), even-numbered monounsaturated AR isomers (AR16:1-AR26:1), triunsaturated ARs (AR25:3), oxo-ARs (AR17:0 oxo, AR19:1 oxo, AR21:2 oxo, AR23:2 oxo) and odd-numbered methyl-ARs (mAR15:0-mAR23:0). Positions of the double bonds of monounsaturated ARs and oxo-ARs were determined with the help of dimethyl disulfide (DMDS) derivatives.

A biphasic system based on guanidinium ionic liquid: Preparative separation of eicosapentaenoic acid ethyl ester and docosahexaenoic acid ethyl ester by countercurrent chromatography

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are high nutritional components. Evidence for unique effects of them is increasing. Further understanding of their independent biological functions urgently needs more efficient separation techniques. Nowadays, most of the commercially available fish oil products are the mixture of eicosapentaenoic acid ethyl ester (EPAEE) and docosahexaenoic acid ethyl ester (DHAEE). It will be convenient to directly separate esterified EPA and DHA without saponification pretreatment. However, it is of great challenge to separate EPAEE and DHAEE because of their extremely fat-soluble nature and the equivalent chain length rule. In this research, the suitability of green guanidinium ionic liquid (IL) in countercurrent chromatography (CCC) solvent system for the separation of them was evaluated for the first time. Compared with imidazolium IL and phosphonium IL, guanidinium IL based non-aqueous biphasic system showed more outstanding separation performance. The separation mechanism was elucidated in depth through quantum mechanical calculations. It was found that guanidinium IL acted a crucial role in the CCC separation, which resulted in difference of partition behavior of EPAEE and DHAEE via different hydrogen-bonding affinity. EPAEE and DHAEE were successfully separated by solvent system (n-heptane/methanol/propylguanidinium chloride ([C₃Gun]Cl, 1:1:5%, v/v/m)) with high purity (>95%) in one step, which was not achieved beforehand. Moreover, an easy recycling procedure of IL had also been devised, which significantly reduced waste generated. It opens up a new way for reasonable design water-free two-phase solvent system for efficient separation of very non-polar lipid compounds.

Modeling counter-current chromatography with non-ideal injection

In general counter-current chromatography systems, there are several off-column fittings between injector and column inlet, such as bends, valves, connecting tubes and joints. Due to these off-column fittings, the sample will diffuse in the mobile phase and form an irregular distribution when it flows from the injector to the column inlet. Thus, the concentration distribution of the solutes at the column inlet is a continuous curve (called the injection profile). As some previous research reveals, it is necessary to input actual injection profile into the simulation model to mimic elution profile. Therefore, we built a non-ideal CCC model whose initial value is from the actual injection profile, and validated the rationality of this model with iteration method. The simulation analysis of different injection profiles shows the conditions whereby a discrete injection profile can replace the actual injection profile in the non-ideal CCC model for accurate simulation elution. Simulation elution under such conditions reveal that non-ideal injection model can reflect the relationship between the injection profile and elution profile, and help to explain the reasons of irregular change in elution profile, like the tailed peak and flat peak.

Stereoselective separation of isomeric sertraline with analytical countercurrent chromatography

Sertraline is an antidepressant in a group of drugs called selective serotonin reuptake inhibitors. Four stereoisomeric compounds would be produced in its synthetic preparation due to two chiral carbons on its chemical structures. In the present work, stereoselective liquid-liquid extraction of isomeric sertraline with substituted cyclodextrins as stereoselective extractant was investigated. Factors affecting the distribution performance, including organic solvents, types of extractants, pH value, buffer solution of aqueous phase, concentration of extractant and temperature, were investigated. Under optimized conditions, a stereoselectivity of 1.404 was obtained for cis-sertraline and a stereoselectivity of 2.373 was obtained for trans-sertraline when hydroxypropyl-β-cyclodextrin was used as the stereoselective extractant, and a stereoselectivity of 1.685 was achieved for trans-sertraline with methyl-β-cyclodextrin as extractant. An unusual stereoselective combination was observed for trans-sertraline and cis-sertraline when sodium carbonate buffer was used. Successful stereoselective separation of trans-sertraline and cis-sertraline, (1S, 4R) and (1R, 4S)-sertraline by analytical countercurrent chromatography with methyl-β-cyclodextrin as stereoselective selector was achieved, using a biphasic solvent system composed of n-hexane : 0.1 mol L^-1 citrate buffer solution with pH7.6 (1:1, v/v).

Classification of biphasic solvent systems according to Abraham descriptors for countercurrent chromatography

The method development of liquid-liquid chromatography, either countercurrent chromatography or centrifugal partition chromatography, is slowed down by the selection of the biphasic solvent system that constitutes its column. This paper introduces a classification of 19 solvent systems, including the most popular systems based on heptane/ethyl acetate/methanol/water, some non-aqueous systems and some greener systems. This classification is based on Abraham descriptors determined through the partition coefficients of 43 probes. Among 21 determined models, nine of them allow an accurate prediction of partition coefficients from solute descriptors and another ten provide a description of the chromatographic interactions at the 5% significance level. A graphical tool (spider diagram) is built for the comparison of the chromatographic columns previously characterized with the solvation parameter model. The position of a solvent system in this spider diagram relates to the interactions at stake, thus the selection of columns offering similar or orthogonal interactions is facilitated, with no previous knowledge of the solute required. This semi-empirical strategy cannot fully predict the retention behavior but can judiciously orientate the user towards a limited number of solvent systems to be experimentally tested.

Identification of two α-tocodienol isomers in palm oil after countercurrent chromatographic enrichment

Countercurrent chromatography (CCC) was used for the enrichment of α-tocodienol (α-T₂), a rare vitamin E-related minor compound previously tentatively detected in palm oil. Hitherto, only one isomer has been mentioned to occur at traces in palm oil. However, CCC fractionation followed by GC/MS measurements of all fractions resulted in the detection of two α-T₂ isomers in five different palm oil vitamin E dietary supplement capsules. Five repetitive CCC separations of ~ 1 g sample and additional purification steps by column chromatography provided ~ 2 mg of two equally abundant α-T₂ isomers with a purity of ~ 85%. The positions of the double bonds in the alkyl side chain could be assigned by means of two characteristic chemical shifts in the ¹H NMR spectrum. Accordingly, the structures of the α-T₂ isomers were 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridec-3,11-dienyl)chroman-6-ol (double bonds in 3',11'-position) and 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridec-7,11-dienyl)chroman-6-ol (double bonds in 7',11'-position). Natural occurrence of both isomers was proven by GC/MS screening of crude palm oil after saponification and CCC separation. Moreover, GC/MS analysis allowed the tentative assignment of γ-tocomonoenol (γ-T₁) and β-tocomonoenol (β-T₁) as trace compounds in palm oil.

Operating mode and parameter selection in liquid-liquid chromatography

The presence of a liquid stationary phase in liquid-liquid chromatography (LLC) allows for high versatility of operation as well as adaptability to different sample types and separation tasks. LLC, also known as countercurrent chromatography (CCC) or centrifugal partition chromatography (CPC), offers the user a variety of operating modes, many of which have no direct equivalent in conventional preparative liquid-solid chromatography. These operating modes have the potential to greatly improve LLC separation performance compared to the standard "classical" isocratic batch injection mode, and they often require minimal to no addition of equipment to the standard set-up. However, reports of the use of alternative LLC operating modes make up only a fraction of the literature. This is likely due, at least in part, to the lack of clear guidelines and methods for operating mode and parameter selection, leaving alternative process options to be avoided and underutilized. This review seeks to remedy this by providing a thorough overview of the available LLC operating modes, identifying the key characteristics, advantages and disadvantages, and areas of application of each. Additionally, the equations and short-cut models aiding in operating mode and parameter selection are presented and critiqued, and their notation is unified for clarity. By rendering LLC and its alternative operating modes more accessible to current and prospective users, it is hoped to help expand the application of this technology and support the achievement of its full potential.

Screening and isolation of cyclooxygenase-2 inhibitors from the stem bark of Phellodendron amurense Ruprecht by ultrafiltration with liquid chromatography and tandem mass spectrometry, and complex chromatography

Nonsteroidal anti-inflammatory drugs appear to reduce the risk of developing cancer. One mechanism through which nonsteroidal anti-inflammatory drugs act to prevent carcinogenesis is inhibition of the activity of the enzyme cyclooxygenase-2. The cyclooxygenase-2 inhibitors are widely used to reduce the risk of developing cancer. Natural products are considered to be a promising source of several novel cyclooxygenase-2 inhibitors. Ultrafiltration with liquid chromatography and mass spectrometry is an efficient method that can be applied to rapidly screen and identify the ligands from the barks of Phellodendron amurense Ruprecht. A continuous online method comprised of pressurized liquid extraction, countercurrent chromatography, and semi-preparative liquid chromatography was developed for the efficient scaled-up production of eight compounds with high purities. The bioactivities of the separated compounds were assessed by an in vitro enzyme inhibition assay. The use of bioactivity screening method combined with preparation method of bioactive compounds and an in vitro enzyme inhibition assay facilitated the efficient screening and isolation of the cyclooxygenase-2 inhibitors from complex samples. This could be used as an efficient method for the large-scale production of functional ingredients.

A novel combined countercurrent chromatography - inductively coupled plasma mass spectrometry method for the determination of ultra trace uranium and thorium in Roman lead

The concentration of uranium and thorium in lead shields, which are used in underground particle physics research, should be monitored at sub-ppt levels. A combination of extraction chromatography and inductively coupled plasma mass spectrometry can resolve this analytical task. However, a multi-step complicated separation procedure and clean room are required. Besides, the recovery yields for U and Th do not exceed 80% and 60%, correspondingly. We propose an alternative approach. U and Th were pre-concentrated and separated from Pb by countercurrent chromatography, which is a support-free liquid-liquid chromatography. A series of two-phase extraction systems were tested. Under the optimized conditions, U and Th were extracted using a system 1 M HNO₃/0.01 M tetraphenylmethylenediphosphine dioxide in chloroform and then eluted by 0.01 M aqueous solution of etidronic acid and determined by inductively coupled plasma mass spectrometry. The separation is performed in one chromatographic run, takes less than 1 h, and provides the quantitative recovery of U and Th. The limits of detection are 3 and 1 ppt for U and Th, correspondingly. The concentrations of U and Th in Roman lead, which was raised from the sea bottom, were lower than the limits of detection. It sounds unbelievable, nevertheless, the antique lead manufactured by Romans can indeed serve as a high-purity low-background material for the construction of Pb shields. Apart from the analysis of antique lead, the proposed approach can be easily extended to the determination of ultra trace impurities in different materials due to a very wide variety of two-phase extraction systems, which can be used in countercurrent chromatography.

Chiral Separations by Countercurrent Chromatography

Chiral separations by countercurrent chromatography are mainly divided into two types: homogeneous chiral selector addition and interfacial chiral ligand exchange. In this chapter, we describe two methods for the enantioseparation of phenylsuccinic acid and α-hydroxy acids by high-speed countercurrent chromatography using hydroxypropyl-β-cyclodextrin and N-n-dodecyl-L-proline as chiral selectors for both above mentioned modes.

(-)‑Oleocanthal inhibits proliferation and migration by modulating Ca2+ entry through TRPC6 in breast cancer cells

Triple negative breast cancer is an aggressive type of cancer that does not respond to hormonal therapy and current therapeutic strategies are accompanied by side effects due to cytotoxic actions on normal tissues. Therefore, there is a need for the identification of anti-cancer compounds with negligible effects on non-tumoral cells. Here we show that (-)‑oleocanthal (OLCT), a phenolic compound isolated from olive oil, selectively impairs MDA-MB-231 cell proliferation and viability without affecting the ability of non-tumoral MCF10A cells to proliferate or their viability. Similarly, OLCT selectively impairs the ability of MDA-MB-231 cells to migrate while the ability of MCF10A to migrate was unaffected. The effect of OLCT was not exclusive for triple negative breast cancer cells as we found that OLCT also attenuate cell viability and proliferation of MCF7 cells. Our results indicate that OLCT is unable to induce Ca²⁺ mobilization in non-tumoral cells. By contrast, OLCT induces Ca²⁺ entry in MCF7 and MDA-MB-231 cells, which is impaired by TRPC6 expression silencing. We have found that MDA-MB-231 and MCF7 cells overexpress the channel TRPC6 as compared to non-tumoral MCF10A and treatment with OLCT for 24-72 h downregulates TRPC6 expression in MDA-MB-231 cells. These findings indicate that OLCT impairs the ability of breast cancer cells to proliferate and migrate via downregulation of TRPC6 channel expression while having no effect on the biology of non-tumoral breast cells.

Xanthohumol C, a minor bioactive hop compound: Production, purification strategies and antimicrobial test

Hop has been attracting scientific attention due to its favorable bioactivity properties. It is thus desirable to relate these properties to the specific hop compounds and extract these compounds in highly purified form in order to enhance the effect. The aim of the present study is the isolation of a sufficient amount of the highly purified prenylated minor hop compound xanthohumol C (XNC) for characterizing its bioactivity. Two strategies for the production of XNC were evaluated. The first strategy involved a capture of natural XNC from a xanthohumol (XN)-enriched hop extract (XF) by countercurrent chromatography. In the second approach, a one-step semi-synthesis of XNC was performed starting from XN, which had previously been separated from a natural XN-enriched hop extract. Both methods delivered XNC in sufficient amount and purity (>95%, HPLC), whereas the second strategy was preferable in terms of purity (>99%, HPLC) as well as productivity and solvent consumption. The methods were validated by identifying and quantifying XNC using LC-MS, LC-MS/MS and ¹H NMR analysis. The XNC obtained in this way was supplied to several bacterial, yeast and fungal cultures in order to evaluate its antimicrobial effects. For comparison, microorganisms were also treated with the natural XN-enriched hop extract, as well as the prenylated hop compound XN. While still reducing cell proliferation, XNC was found to be less effective than both XF and XN for all studied bacteria and yeasts. Furthermore, for Bacillus subtilis, a strongly pH-dependent minimal inhibition concentration was observed for all three bioactive compounds, lowest at a pH of 5 and highest at a pH of 7.

Comparison between centrifugal partition chromatography and preparative liquid chromatography as first dimensions in off-line two-dimensional separation: Application to the isolation of multi-targeted compounds from Edelweiss plant

Preparative two-dimensional chromatography is gaining interest in the elucidation of complex samples as it allows the recovery of a large number of molecules without the risks inherent to tedious multi-step sample preparation. While the second dimension is often selected to be liquid chromatography, it may be of interest to compare the specificities of two different techniques, namely liquid chromatography and centrifugal partition chromatography, to be used as first dimension. A fair comparison between off-line CPCxLC and prepLCxLC in selective comprehensive mode for preparative purposes is carried out in this study, illustrated by the isolation of five compounds from high-value Edelweiss plant. The method development of each configuration is achieved on laboratory scale instruments. The quality of separation is compared using 2D-contour plots. The prepLCxLC exhibits a large separation space that leads to an overall large peak capacity, which is of great interest for complex samples. But its limited loading capacity involves a large number of 2 D runs increasing the running costs for preparative purposes. On the other hand, CPCxLC provides a low peak capacity due to the poor efficiency provided by CPC. However, this liquid-liquid technique can be finely tuned to generate a high selectivity, decreasing the number of runs necessary to produce a limited number of target solutes.

Continuous and Integrated Expression and Purification of Recombinant Antibodies

This chapter introduces the necessary concepts to design continuous expression and purification processes for monoclonal antibodies. The operation of a perfusion bioreactor is discussed containing the preparation procedures, the seeding train and the preparation and control of a long-term production run. The downstream processes exploit the benefits of countercurrent chromatography. Their design from batch experiments is presented. The CaptureSMB process is introduced for continuous capturing while for polishing applications the design of the two-column MCSGP process is described. The chapter also puts these processes together in the context of their integration to an end-to-end production process.

The 9th International Countercurrent Chromatography Conference held at Dominican University, Chicago, USA, August 1-3, 2016

The 9th International Countercurrent Chromatography Conference (CCC 2016) was held at Dominican University near Chicago, IL (USA), from August 1st-3rd, 2016. The biennial CCC 20XX conferences provide an opportunity for countercurrent chromatography and centrifugal partition chromatography (CCC/CPC) manufactures, marketers, theorists, and research scientists to gather together socially, learn from each other, and advance countercurrent separation technology. A synopsis of the conference proceedings as well as a series of short reviews of the special edition articles is included in this document. Many productive discussions and collegial conversation at CCC 2016 attested to the liveliness, connectivity, and productivity of the global countercurrent research community and bodes well for the success of the 10th conference at the University of Braunschweig, Germany on August 1-3, 2018.

Ionic Liquid-Liquid Chromatography: A New General Purpose Separation Methodology

Ionic liquids can form biphasic solvent systems with many organic solvents and water, and these solvent systems can be used in liquid-liquid separations and countercurrent chromatography. The wide range of ionic liquids that can by synthesised, with specifically tailored properties, represents a new philosophy for the separation of organic, inorganic and bio-based materials. A customised countercurrent chromatograph has been designed and constructed specifically to allow the more viscous character of ionic liquid-based solvent systems to be used in a wide variety of separations (including transition metal salts, arenes, alkenes, alkanes, bio-oils and sugars).

HSCCC separation and enantiomeric distribution of key volatile constituents of Piper claussenianum (Miq.) C. DC. (Piperaceae)

High Speed Countercurrent Chromatography (HSCCC) technique was used for the preparative isolation of the major leishmanicidal compounds from the essential oils of Piper claussenianum species in Brazil. The essential oils from inflorescences of P. claussenianum were analyzed by GC-FID and GC-MS. The enantiomeric ratio of the major constituents of the P. claussenianum essential oils were determined using a Rt-DEXsm chiral capillary column by GC-FID analysis. It was found an enantiomeric excess of (+)-(E)-nerolidol in the leaves, and (+)-linalool and (+)-(E)-nerolidol in the inflorescences essential oil. The major volatile terpenes alcohols were isolated in preparative scale from inflorescences: linalool (320.0 mg) and nerolidol (95.0 mg) in high purity level. The HSCCC, a support-free liquid-liquid partition chromatographic technique, proved to be an effective and useful method for fast isolation and purification of hydrophobic and similarly structured bioactive components from essential oils of Piper species.

Trapping multiple dual mode centrifugal partition chromatography for the separation of intermediately-eluting components: Throughput maximization strategy

Trapping multiple dual mode centrifugal partition chromatography (trapping MDM CPC) is an alternative to isocratic pulse injections for the separation of intermediately-eluting components from complex mixtures using liquid-liquid chromatography. In this work, a throughput maximization strategy is developed and validated to investigate the full potential of trapping MDM CPC as a preparative technique. In the proposed approach, shake flask and stationary phase retention experiments are used to determine the maximum feed concentration and flow rate, respectively. A model-based parameter selection process combining a mathematical short-cut method and simulations based on the equilibrium cell model is used to obtain the column loading and step durations resulting in maximized process throughput. The proposed throughput maximization strategy is experimentally validated for the separation of a ternary model mixture of parabens. A preliminary comparison of trapping MDM CPC separation performance to that of stacked pulse injections is also made.

Enhancing silymarin fractionation using the conductor-like screening model for real solvents

A significant hurdle for discovery of plant-derived products is the numerous trial-and-error experiments required to develop an effective purification strategy. To overcome the experimental burden, a quantum mechanics-based molecular modeling approach - known as the COnductor-like Screening Model for Real Solvents (COSMO-RS) - was used to predict a suitable two-phase solvent system to purify six silymarins from an aqueous mixture. Silymarins, a class of flavonolignans found in milk thistle (Silybum marianum L.), are well suited for assessing the use of a molecular modeling approach to predict partitioning in a countercurrent chromatography (CCC) separation because they are well characterized and previous studies report low purity fractionation in liquid-liquid solvent systems. They also present an opportunity to evaluate the use of COSMO-RS in predicting the partitioning of structurally similar isomeric compounds that are present together in an aqueous solution upon extraction from their native source. The COSMO-RS model results predicted the partition coefficients in: three traditional ARIZONA solvent systems (composed of heptane, ethyl acetate, methanol, and water), nine additional variations of this quaternary solvent system, and two chloroform, methanol, and water solvent systems. Predicted results were concise but not accurate when compared to experimental results determined by the shake flask method. The 1:4:3:5 n-heptane:ethyl acetate:methanol:water (v/v/v/v) system was identified to be an improvement on the 1:4:3:4 system previously reported. The present study verified the ability of COSMO-RS to hone in on one or two solvent systems that will yield the best fractionation using CCC.

Countercurrent chromatography separation of saponins by skeleton type from Ampelozizyphus amazonicus for off-line ultra-high-performance liquid chromatography/high resolution accurate mass spectrometry analysis and characterisation

Ampelozizyphus amazonicus Ducke (Rhamnaceae), a medicinal plant used to prevent malaria, is a climbing shrub, native to the Amazonian region, with jujubogenin glycoside saponins as main compounds. The crude extract of this plant is too complex for any kind of structural identification, and HPLC separation was not sufficient to resolve this issue. Therefore, the aim of this work was to obtain saponin enriched fractions from the bark ethanol extract by countercurrent chromatography (CCC) for further isolation and identification/characterisation of the major saponins by HPLC and MS. The butanol extract was fractionated by CCC with hexane - ethyl acetate - butanol - ethanol - water (1:6:1:1:6; v/v) solvent system yielding 4 group fractions. The collected fractions were analysed by UHPLC-HRMS (ultra-high-performance liquid chromatography/high resolution accurate mass spectrometry) and MSn. Group 1 presented mainly oleane type saponins, and group 3 showed mainly jujubogenin glycosides, keto-dammarane type triterpene saponins and saponins with C31 skeleton. Thus, CCC separated saponins from the butanol-rich extract by skeleton type. A further purification of group 3 by CCC (ethyl acetate - ethanol - water (1:0.2:1; v/v)) and HPLC-RI was performed in order to obtain these unusual aglycones in pure form.

Isolation and in vitro permeation of phenylpropylamino alkaloids from Khat (Catha edulis) across oral and intestinal mucosal tissues

ETHNOPHARMACOLOGICAL RELEVANCE

Khat, the leaves of Catha edulis, is used as a "natural amphetamine-like" stimulant in eastern and southern Africa, as well as in the Arabian Peninsula. Leaves are masticated to elicit a state of euphoria. Although the psychostimulatory effects of the leaves are attributed to the presence of phenylpropylamino alkaloids (i.e. cathinone, cathine and norephedrine), the extent of permeation of these alkaloids across the oral and intestinal mucosa has not been established.

MATERIALS AND METHODS

Cathinone was isolated in the form of the oxalate salt from young buds, following acid-base extraction. High performance countercurrent chromatography (HPCCC) was used to isolate cathine and norephedrine, following borohydride reduction of a mixture of the three alkaloids. The in vitro permeability of these three alkaloids in their pure form, as well as in a crude extract, was evaluated across Caco-2 cell monolayers and across excised porcine intestinal, sublingual and buccal tissues.

RESULTS

The purities of the isolated cathine and norephedrine were in excess of 90%, thereby proving that HPCCC can be applied for efficient separation of these alkaloids from extracts of Khat. The apparent permeability (P_app) coefficients for the Khat alkaloids in their pure form were all above 1.0×10^-6cm/s, indicating that the transport of the three alkaloids across the selected biological membranes is comparable to that of the highly permeable reference compound, caffeine. Although readily transported across the various membranes, the alkaloids were transported to a lesser extent when present in a leaf extract, suggesting that other phytochemicals present in the extract influence their permeation.

CONCLUSIONS

These results provide evidence that chewing of Khat contributes to the buccal and sublingual absorption of the psychoactive alkaloids in the bloodstream directly across the oral mucosal membranes. In addition, it confirms that these metabolites will be readily absorbed from the gastrointestinal tract when swallowed.

Effect of operating parameters on a centrifugal partition chromatography separation

Centrifugal partition chromatography (CPC) is the branch of countercurrent chromatography (CCC) that works with single axis hydrostatic columns with rotary seals. The hydrodynamic of the liquid stationary phase-liquid mobile phase equilibrium in the CPC chambers has been studied theoretically and with specially designed CPC columns. In this work, we selected a simple analytical separation (no loading study) of three test solutes, coccine red, coumarin and carvone, with a commonly used heptane/ethyl acetate/methanol/water 1:1:1:1v/v biphasic liquid system and two different rotors: a commercially available 30-mL CPC instrument and a 80-mL prototype rotor designed for productivity. We fully studied this separation in many possible practical operating conditions of the two rotors, aiming at a generic column characterization. The rotor rotation was varied between 1000 and 2800rpm, the aqueous mobile phase flow rate was varied between 1 and 22mL/min with the 30-mL rotor and 10 and 55mL/min with the 80-mL rotor, the upper limits being mechanical constraints and some liquid stationary phase remaining in the rotor. The variations of Sf, the volume ratio of stationary phase in the rotor, were studied versus mobile phase flow rate and rotor rotation speed. A maximum mobile phase linear velocity was found to depend on the centrifugal field for the 30-mL rotor. This maximum velocity was not observed with the 80-mL rotor. Studying the changes in coumarin and carvone peak efficiencies, it is established that the number of cells required to make one theoretical plate, i.e. one chromatographic exchange, is minimized at maximal rotation speed and, to a lesser extent, at high mobile phase flow rate (or linear velocity). Considering the throughput, there is evidence of an optimal flow rate depending on the rotor rotation that is not necessarily the highest possible.

Countercurrent assisted quantitative recovery of metabolites from plant-associated natural deep eutectic solvents

NAtural Deep Eutectic Solvents (NADES) are chemically simple but physiologically important plant constituents that exhibit unique solubilizing properties of other metabolites, including bioactive constituents. The high polarity of NADES introduces a challenge in the ability of conventional solid-support based chromatography to recover potential bioactive metabolites. This complicates the systematic explanation of the NADES' functions in botanical extracts. The present study utilizes countercurrent separation (CCS) methodology to overcome the recovery challenge. To demonstrate its feasibility, Glucose-Choline chloride-Water (GCWat, 2:5:5, mole/mole) served as a model NADES, and four widely used marker flavonoids with different polarities (rutin, quercetin, kaempferol, and daidzein) were chosen as model target analytes. In order to prepare GCWat with high consistency, a water drying study was performed. The unique capabilities of the recently introduced CherryOne system, offering volumetric phase metering, were used to monitor the CCS operations. The collected fractions were analyzed using UHPLC and NMR/quantitative NMR. CCS was able to recover the analytes from the NADES matrix with quantitative recoveries of 95.7%, 94.6%, 97.0%, and 96.7% for rutin, quercetin, kaempferol, and daidzein respectively. The CCS strategy enables recovery of target metabolites from NADES-containing crude extracts as well as from other chemical mixtures, and moreover offers a means of using NADES as environmentally friendly extraction solvents.

Accelerated separation of GC-amenable lipid classes in plant oils by countercurrent chromatography in the co-current mode

Triacylglycerols represent the major part (>90%) in most plant oils and have to be eliminated, when the minor compounds such as phytosterols or tocopherols should be analyzed. Here, we used an all liquid-liquid chromatographic technique, countercurrent chromatography (CCC), to fractionate the minor lipids before gas chromatography (GC) analysis. To cover the wide range of polarity of the minor compounds, we used the co-current mode, in which both mobile and stationary phase are pumped through the system. This allowed to elute substances which partitioned almost exclusively in the stationary phase within 90 min. After testing with standard compounds, the method was applied to the separation of sesame oil and sunflower oil samples. The abundant triacylglycerols could be effectively separated from tocopherols, phytosterols, diacylglycerols, and free fatty acids in the samples, and these compounds could be analyzed (after trimethylsilylation) by GC coupled with mass spectrometry. After the enrichment caused by the CCC fractionation, we were also able to identify the tocopherol derivative α-tocomonoenol, which had not been described in sunflower oil before. Also, separation of sesame oil yielded a mixture of the polar compounds sesamin and sesamolin without further impurities.

Comparison of twin-cell centrifugal partition chromatographic columns with different cell volume

Two twin-cell centrifugal partition chromatographic columns (SCPC 250 and SCPE-250-BIO, Armen Instrument, France) with the same column volume but different cell size and number were compared in terms of stationary phase retention and column efficiency. The columns were tested with two types of solvent systems: a commonly used organic solvent based biphasic system from the ARIZONA solvent system family and a polymer/salt based aqueous two phase system (ATPS). The efficiency of the columns was evaluated by pulse injection experiments of two benzenediols (pyrocatechol and hydroquinone) in the case of the ARIZONA system and a protein mixture (myoglobin and lysozyme) in the case of the ATPS. As result of high stationary phase retention, the column with the lower number of larger twin-cells (SCPE-250-BIO) is suitable for protein separations using ATPS. On the other hand, due to higher column efficiency, the column with the greater number of smaller cells (SCPC 250) is superior for batch elution separations performed with standard liquid-liquid chromatography organic solvent based biphasic systems.