Separation Of Chiral Compounds Research Articles

Flow-modulation comprehensive two-dimensional enantio-gas chromatography: A valid and flexible alternative to heart-cutting multidimensional enantio-gas chromatography

The present research is focused on the proposal of use of flow-modulation comprehensive two-dimensional enantio-gas chromatography (FM eGC × GC) as a valid, flexible, and possibly superior alternative to heart-cutting multidimensional enantio-GC (eMDGC). The latter, a technique of demonstrated utility, is used specifically for the targeted separation of chiral compounds, whereas FM eGC × GC can produce both targeted and high-resolution untargeted information in a single run. It is clearly possible to use eMDGC for untargeted analysis, often with a flame ionization detector (stand-by analysis), to monitor a first-dimension (1D) separation, of much lower peak capacity compared to FM eGC × GC. If eMDGC is used with mass spectrometry (MS), it is normally exploited to monitor the second-dimension (2D) separation.The analytical instrument consisted of automated solid-phase microextraction (SPME), and a low duty-cycle FM eGC × GC system (with time-of-flight MS), equipped with an enantioselective 1D column (2,3-di-O-methyl-6-t-butyl silyl β-cyclodextrin derivative) and a 2D polyethylene glycol one. Ten Marsala wines were subjected to analysis, for the determination of chiral lactones (many at the low ppb level, due to the high concentration capacity of SPME) and for general analyte profiling. In many instances, highly complex chromatograms were attained, with statistical analysis (ANOVA-simultaneous component analysis and partial least squares discriminant analysis) used for sample differentiation.

Isocyanate‐chitin modified microspheres for chiral drug separation in high performance liquid chromatography

AbstractIn this work, a two‐step activated swelling technique was effectively employed to successfully synthesize monodisperse porous poly(styrene‐divinylbenzene) (PS‐DVB) particles. Diazoresin (DR) transform an ionic bond into a covalent bond by photoreaction. Under ultraviolet irradiation, DR was used to covalently attach dichlorophenyl isocyanate to sulfonated PS‐DVB microspheres. The novel photo‐crosslinking reaction effectively overcomes the toxicity issues associated with conventional coupling agents and enables green production of chromatographic fillers. Modified PS‐DVB particles were indeed commonly used as filler material for the separation of chiral compounds by high performance liquid chromatography (HPLC). The porous modified microspheres designed effectively separate benzoone, DL‐mandelic acid, 2‐phenylcyclohexanone, ibuprofen, 2‐hydroxyl flavone, DL‐cysteine, chloraniline maleate, hesperidin, and other chiral compounds by 100 mm column. It is noteworthy that the isocyanate‐chitin modified microspheres are effective in separating chiral drugs (1000 μg/mL) within 5 min. Compared with ordinary microspheres, porous isocyanate‐chitin modified microspheres showed better separation efficiency under the same conditions. The enhancement is attributed to the increase in their specific surface area. Consequently, they are a better choice of chromatographic packing matrix.

Sesquiterpene coumarins from Ferula sinkiangensis and their anti-pancreatic cancer effects

Eight previously unreported sesquiterpene coumarins, namely (+)- and (−)-ferulasinkian A (1), (−)-fukanefuromarin M (2), (±)-ferulasinkian C (3), (±)-ferulasinkian D (4), ferulasinkian E (5), ferulasinkian F (7), and ferulasinkian G (8), together with two known compounds, (+)-fukanefuromarin M (2) and 7-hydroxyferprenin (6), have been isolated from the roots of Ferula sinkiangensis (Umbelliferae). The structures of all compounds were elucidated by spectroscopic analysis, along with ECD calculations and optical rotation calculations. Compounds 1–6 are dimers consisting of a chain sesquiterpene and a coumarin with an oxygen-containing six-membered ring connected from coumarin C-3 and C-4. Currently, there are only seven such structures reported in the genus Ferula, and their absolute configurations have not yet been determined. Compounds 7–8 are sesquiterpene coumarin derivatives with a chain sesquiterpene connected with coumarin C-4. In the present study, the chiral separation of compounds (±)-1 and (±)-2 was successfully carried out, and the absolute configurations of compounds (±)-1, (±)-2, 5, 7 and 8 were determined. The isolates were evaluated for their cytotoxic activity against human pancreatic cancer cell lines including CFPAC-1, PANC-1, CAPAN-2 and SW 1990. Compounds (+)-1, (−)-1 and 7 exhibited potent cytotoxicity against pancreatic cancer cells with IC50 values ranging from 4.57 ± 0.94 to 14.01 ± 1.03 μM. Furthermore, the primary mechanistic study of (−)-1 demonstrated that it could induce apoptosis in CFPAC-1 cells.

Separation of chiral compounds using high performance liquid chromatography stationary phase based on covalent organic framework material TpPa-NH<sub>2</sub>-Glu

Covalent organic frameworks （COFs） are an emerging class of porous crystalline materials composed of multidentate organic units connected by covalent bonds. COFs have been demonstrated to exhibit great potential and research value in many fields， including gas storage and separation， photoelectric devices， fluorescence sensors， catalysis， drug delivery， dye and pollutant adsorption， and electronic devices， and so on. The COFs obtained by post-synthesis modification tend to exhibit high crystallinities and porosities， thereby rendering them suitable materials for use in the fields of chiral resolution， asymmetric catalysis， and chromatography. In this work， TpPa-NO2 was synthesized from 1，3，5-tricarbaldehyde phloroglucinol and 2-nitro-1，4-phenylenediamine， which was then reduced to TpPa-NH2. Subsequently， this material was modified with D-glucose via a post-synthesis modification strategy to obtain the TpPa-NH2-Glu. TpPa-NH2-Glu were characterized by nuclear magnetic resonance （NMR） spectroscopy， Fourier transform-infrared （FT-IR） spectroscopy， X-ray powder diffraction （XRD） analysis， etc. In the XRD pattern， the peaks observed at 4.7°， 8.1°， 11.1°， and 27° were attributed to the TpPa-NH2-Glu， and these peaks are consistent with previous reports， thereby confirming the successful synthesis of this derivative. In addition， circular dichroism experiments indicated that the TpPa-NH2-Glu exhibited a Cotton effect， further confirming the chiral COF was prepared. Subsequently， this material was immobilized on the surface of spherical silica gel particles via the net-wrapping method to prepare a stationary phase for high performance liquid chromatographic column. Using n-hexane-isopropanol （9∶1， v/v） or methanol-water （9∶1， v/v） as mobile phases at a flow rate of 0.5 mL/min， 16 racemates and two benzene-based positional isomers （o，m，p-nitroaniline and o，m，p-Iodoaniline） were successfully resolved by this chiral column. In addition， under methanol-water （9∶1， v/v） mobile phase conditions， five racemates were separated， among which propranolol hydrochloride， warfarin， and metoprolol reached baseline separation. Furthermore， under n-hexane-isopropanol （9∶1， v/v） mobile phase conditions， 11 racemates were resolved， among which ethyl 2-bromopropionate and 3-butyn-2-ol reached baseline separation. Meanwhile， the effect of temperature on the TpPa-NH2-Glu liquid chromatography column and the repeatability of the TpPa-NH2-Glu liquid chromatography column were also explored. The HPLC column prepared by TpPa-NH2-Glu had good repeatability， and its relative standard deviation （RSD） was 1.55% and 1.46%， respectively. It is demonstrated that the TpPa-NH2-Glu material has good resolution ability for chiral compounds.

Crystallization in Fluidized Bed Reactors: From Fundamental Knowledge to Full-Scale Applications

A review is presented on fifty years of research on crystallization in fluidized bed reactors (FBRs). FBRs are suitable for recovery of slightly soluble compounds from aqueous solutions, as it yields large, millimeter sized particles, which are suitable for reuse and permits low liquid residence times in the timescale of minutes. Full-scale applications for water softening have been applied since the 1980s, and since then, new applications have been developed or are in development for recovery of phosphorus, magnesium, fluoride, metals, sulfate, and boron. Process integration with membrane, adsorption, and biological processes have led to improved processes and environmental indicators. Recently, novel FBR concepts have been proposed, such as the aerated FBR for chemical-free precipitation of calcium carbonate, the seedless FBR to yield pure particulate products, a circulating FBR for economic recovery and extended use of seeds, as well as coupled FBRs for separation of chiral compounds and FBRs in precipitation with supercritical fluids. Advances are reported in the understanding of elementary phenomena in FBRs and on mathematical models for fluid dynamics, precipitation kinetics, and FBR systems. Their role is highlighted for process understanding, optimization and control at bench to full-scale. Future challenges are discussed.

One-stage chiral enrichment process by continuous flow electrodialysis with molecularly imprinted membrane

The purification and separation of amino acid enantiomeric compounds, such as dl-phenylalanine (dl-Phe), are attracting increasing attention in the biomedical and pharmaceutical fields. In this study, an enantioselective l-Phe molecularly imprinted membrane (l-Phe-MIM) was prepared via a surface grafting reaction. The membrane performances in the separation and enrichment of dl-Phe were investigated by using a continuous-flow electrodialysis system. The synthesis and electrodialysis parameters were optimized to obtain the maximum separation ratio. The selectivity for dl-Phe can be switched by changing the template from l-Phe to d-Phe. This suggests that the MIM is controlling the selectivity in the continuous flow electrodialysis system. The membrane prepared via a layer-by-layer process gave improved selectivity. The results show that excellent chiral separation and high stability were achieved, with a selectivity (l/d) of 2.95 ± 0.34. The results of this study offer new insights into, and perspectives on, obtaining enhanced chiral compound separation by continuous electrodialysis with a MIM in a single-pass process within ∼ 10 s.

Preparation and chromatographic application of β‐cyclodextrin modified poly (styrene‐divinylbenzene) microspheres

AbstractIn order to better realize the separation of chiral enantiomers and prevent chiral compounds with toxic side effects from causing harm to human beings, porous microspheres were modified to improve their chromatographic separation performance. In this paper, in order to verify the chromatographic performance of porous polymer microspheres, the precise and controllable synthesis of poly (styrene‐divinylbenzene) (PS‐DVB) microspheres was realized based on the two‐step swelling method. Then, the porous PS‐DVB microspheres were sulfonated with concentrated sulfuric acid. The sulfonated microspheres were grafted with diazo resin (DR), and then the 3,5‐dichlorobenzene isocyanate modified β‐cyclodextrin (β‐CD‐DCIPI) was bonded to the sulfonated PS‐DVB microspheres by the DR. Finally, the bond inversion occurred after UV irradiation. We have successfully solved the toxic effect of traditional coupling agents by using the unique photo‐crosslinking reaction of DR. This novel and environmentally friendly chromatographic packing can be used to separate chiral compounds. The results showed that all of the eight compounds (chlorpheniramine; ibuprofen; benzoin; 2‐phenylcyclohexanone; trans‐stilbene oxide; Cobalt [III] acetylacetonate; Hesperetin; DL‐Mandelic acid) can be separated. It is worth noting that the modified microspheres can achieve good separation of chiral compounds with the concentration of 1 mg/ml in 3 min.

Highly Improved Chiral-Selective Resolution in Pillar[5]arene-Functionalized Molecularly Imprinted Membranes

It is a challenging task to achieve the effective separation of chiral compounds under simple and rapid conditions. In order to solve this problem, this study used the molecularly imprinted membrane (MIM) technology developed on the basis of biological semi-permeable membranes, using S-triadimefon as the template molecule, and successfully prepared MIMs by photo-initiated polymerization. By adding macrocyclic molecular 1,4-bis(allyloxy)pillar[5]arene as a functional monomers, the effectiveness of the chiral recognition sites of the target molecules is improved, thereby improving the chiral selectivity of the MIM and optimizing the molar ratio of template molecules, monomers, and cross-linkers. On this basis, the separation effect of non-MIM (NIM), single-monomer MIM (MIM-I), and two-monomer MIM (MIM-II) on triadimefon enantiomers was investigated. It was found that the enantiomer excess (e. e.) % value of MIM-I is larger than that of NIM, but the value of MIM-I is still very low. When pillar[5]arene, a macrocyclic molecule was added as the second monomer, its e. e. % increased from 27.4 to 84.8%.

High mechanical strength conductive inorganic–organic composite membranes for chiral separation and in situ cleaning

Enantiomeric separation based on membrane techniques has the advantages of energy efficiency, sustainable operation, and no additives, but there are no commercially available chiral membranes. The main reasons restricting the development of chiral membranes are separation specificity, poor mechanical properties, and membrane fouling. Therefore, we developed a novel chiral membrane with a stainless steel mat mesh as the base and β-cyclodextrin blended in cellulose acetate as the functional layer. The organic layer was loaded on the inorganic base by nonsolvent-induced phase inversion, and the two post treatments were optimized. The results indicate that the optimal percent enantiomeric excess (ee%) was 96.98 ± 5.22 % for d,l-tryptophan, 46.38 ± 1.65 % for d,l-phenylalanine, 11.50 ± 2.52 % for (RS)-propranolol, and 5.16 ± 0.88 % for (RS)-warfarin. The mechanical properties of stainless steel chiral composite membranes are better than those of other chiral membranes, and the Young's modulus values reached 3234 MPa. In addition, ultrasonic cleaning and electrolytic cleaning were successfully tested to solve the membrane fouling problem, and a comparative study indicated that electrolytic cleaning has low energy consumption and is a fast and effective cleaning method that can achieve flux recovery. These results indicate that conductive chiral membranes can achieve long-term separation of chiral compounds and have great potential for industrial applications.

The progress on porous organic materials for chiral separation

Chiral compounds have similar structures and properties, but their pharmacological action is very different or even opposite. Therefore, the separation of chiral compounds has great significance in pharmaceutical and agriculture. Porous organic materials are novel crystalline porous materials, which possess high surface area, controllable pore size, and favorable functionalization. Therefore, porous organic materials are considered to be an ideal material for chiral separation. In this review, we summarized the progress of chiral porous organic materials for chiral separation in recent years. Furthermore, the applications of chiral porous organic materials as chiral separation medias (chromatography stationary phases and membrane materials) in enantioseparation were highlighted. Finally, the remaining challenges and future directions for porous organic materials in chiral separation were also briefly outlined further to promote the development of porous organic materials in chiral separation.

Simultaneous and rapid analysis of chiral Danshensu and its ester derivatives by supercritical fluid chromatography

The analysis and separation of chiral compounds with wide polar range by supercritical fluid chromatography is of major importance in the process of drug development and quality control. In this work, a fast and reliable enantioselective method for the simultaneous quantitative determination of 8 DBZ-related enantiomers has been successfully developed by supercritical fluid chromatography using an amylose-based reversed-chiral stationary phase. Within less than seven minutes all target compounds could be baseline resolved, using a mobile phase comprising supercritical carbon dioxide and methanol with 0.05 % H3PO4. The optimum chiral stationary phase showed to be a CHIRALPAK® AD-RH column, operated at flow rate of 3.0 mL/min, back pressure of 150 bar and temperature of 40 °C. Method validation confirmed that the developed procedure was selective, linear (r2 > 0.998), accurate (recovery rates: 98.02–100.02 %), and precise (intra-day: 0.05–1.98 %, inter-day: 0.08–1.98 %); the limit of detection and limit of quantification were 0.13–0.55 μg/mL and 0.37–1.68 μg/mL on column, respectively. After initial evaluation of stability according to the ICH Q1A (R2) guideline, R-DBZ showed good stability. Thus, this developed method can be used for assessing the stability of bulk DBZ samples, dosage forms of DBZ and also for monitoring the synthetic procedures of DBZ.

Advances in chiral separation and analysis by capillary electrophoresis-mass spectrometry

目前使用的绝大多数药物为手性化合物,它们具有相似的物理和化学性质,但药理活性不同,且常以外消旋混合物的形式存在,因此对手性化合物的分离在生物、环境、食品和医药等领域一直备受关注。与广泛使用的液相色谱-质谱(LC-MS)相比,毛细管电泳-质谱(CE-MS)作为一种新型分离分析技术,具有分离效率高、样品和试剂消耗量低、选择性高和分离模式多样化等诸多优势,已经发展成为手性分析领域中有广阔应用前景的分析方法之一。CE-MS结合了CE的高分离效率和低样品消耗以及MS的高灵敏度和强结构解析能力,在蛋白质组学和代谢组学等领域发挥了重要作用。CE杰出的手性拆分能力与MS优势的结合,亦使CE-MS成为实现手性化合物高效分离分析的完美组合。在过去的十几年里,基于不同CE-MS分离模式的高性能手性分析体系层出不穷,如电动色谱-质谱(EKC-MS)、胶束电动色谱-质谱(MEKC-MS)和毛细管电色谱-质谱(CEC-MS)等,并成功应用于医药、生物、食品和环境科学等领域的手性化合物分析。该文主要综述了2011~2021年,CE-MS在手性化合物分析领域的技术、手性选择剂(如改性环糊精和聚合物表面活性剂等)的使用以及在医药等领域应用方面的研究进展,并讨论了不同手性分析模式的局限性,为未来的CE-MS手性分离分析技术发展及应用提供借鉴。

Synthesis of 3,5-dichlorobenzene isocyanate-derived β-cyclodextrin and 3,5-dimethyl phenyl isocyanate-derived β-cyclodextrin chiral stationary phases and their applications in the separation of chiral compounds

β-Cyclodextrin (β-CD) has a unique three-dimensional structure and chemical properties, and has a strong chiral separation ability. In this study, we linked 3,5-dichlorobenzene isocyanate to β-cyclodextrin and named this newly synthesized molecule β-CD-DCIPI. 3,5-Dimethylbenzene isocyanate was attached to β-cyclodextrin and named β-CD-DPIC. A modified polymerization-induced colloidal aggregation (PICA) method and self-made silica sol were used to synthesize mesoporous silica microspheres with a particle size of 2.38 μm-5.51 μm. A green non-toxic diazoresin (DR) is used as a coupling agent, which is connected to the surface of silica microspheres through electrostatic interaction. After ultraviolet light irradiation, ionic bonds are transformed into covalent bonds, and a new chiral stationary phase with chiral separation properties (β-CD-DCIPI@SiO2 and β-CD-DPIC@SiO2) is constructed. This article first characterizes the properties of mesoporous silica microspheres and β-CD-DCIPI@SiO2 and β-CD-DPIC@SiO2. Through reversed-phase high-performance liquid chromatography (RP-HPLC), the separation performance of two new chiral stationary phases in chiral compounds was explored and compared, and five chiral enantiomers were effectively separated.

Sub/supercritical Fluid Chromatography for Chiral Compounds Analysis

Chirality is an essential feature of nature as it is common for many biologically active compounds. The different biological effects of individual enantiomers in a chiral environment are generally known. Therefore, there is a need for fast, efficient, and robust methods for their separation, quantification, and purification, too. The easiest way is to use chromatographic methods utilizing chiral stationary phases. Sub/supercritical fluid chromatography has become popular in the field of enantioselective separations in various scopes and, in some cases, has become a method of the first choice.
 Therefore, this review article covers actual trends and possibilities of sub/supercritical fluid chromatography in enantioseparations. Ways to influence enantioselectivity of the separation system by column coupling, screening approaches, and processes of methodical development for fast and efficient analyses are discussed.
 Sub/supercritical fluid chromatography under suitable experimental conditions provides fast and highly efficient separation of chiral compounds.

Evaluation of homochiral zeolitic imidazolate framework-8 supported open-tubular column by miniaturized capillary electrochromatography with amperometric detection.

A novel kind of chiral open-tubular (OT) column was established with homochiral zeolitic imidazolate framework-8 nanomaterials using L-histidine as the chiral carbon center (L-His-ZIF-8). The morphologies of L-His-ZIF-8 nanoparticles and chiral OT column were characterized by scanning electron microscopy. The effects of L-His-ZIF-8 concentrations, pH values, and concentrations of the running buffer on the resolution of the selected chiral compounds were investigated based on miniaturized capillary electrochromatography with amperometric detection system (mini-CEC-AD), respectively. The separation performances of the prepared L-His-ZIF-8@OT chiral columns were explored under the optimal conditions, and the RSDs of run-to-run, day-to-day, and column-to-column reproducibility were less than 6.7% using salbutamol raceme as the model enantiomers. The prepared chiral OT columns have been successfully applied to the enantioseparation of one pair of amino acid enantiomers, two pairs of racemic drugs, and three pairs of neurotransmitter enantiomers. Under the optimum conditions, the prepared OT columns were applied to real-world sample analysis of salbutamol aerosol. The limits of detection of salbutamol raceme were 0.90μg·mL-1 (S/N = 3), and the recovery was 80.4-82.7%. The assay results indicated that this kind of chiral OT column modified with homochiral L-His-ZIF-8 possesses good reproducibility and stability. This developed mini-OT-CEC-AD system has some attractive characteristics of sensitivity and low cost, providing a potential way for the separation of chiral compounds.

A chiral metal-organic framework core-shell microspheres composite for high-performance liquid chromatography enantioseparation.

The unique features of uniform and adjustable cavities, abundant chiral active sites, and high enantioselectivity make chiral metal-organic frameworks popular as an emerging candidate for enantioselective separation. However, the wide particle size distribution and irregular shape of as-synthesized metal-organic frameworks result in low column efficiency, undesired chromatographic peak shape, and high column backpressure of such metal-organic frameworks packed columns. Herein, we report the fabrication of chiral core-shell microspheres [Cu2 (d-Cam)2 (4,4'-bpy)]n @SiO2 composite for high-performance liquid chromatography enantioseparation to overcome the above-mentioned problems. The [Cu2 (d-Cam)2 (4,4'-bpy)]n @SiO2 packed column gave high-resolution separation of racemates under low column backpressure (10-22bar), indicating its synergistic effect of the good column packing property of the SiO2 microspheres and the chiral recognition ability of [Cu2 (d-Cam)2 (4,4'-bpy)]n crystals. Thirteen kinds of chiral compounds including alcohols, amines, ketones, epoxides, and organic bases were well separated with good peak shapes and high column efficiency (18200 plates/m for 1-(9-anthryl)-2,2,2-trifluoroethanol) on the [Cu2 (d-Cam)2 (4,4'-bpy)]n @SiO2 packed column. Among them, seven pairs of enantiomers achieved baseline separation and the resolution value for 1-(9-anthryl)-2,2,2-trifluoroethanol reached 11.22. Some effects such as column temperature, and analytes mass on the enantioseparations have been investigated. In addition, the [Cu2 (d-Cam)2 (4,4'-bpy)]n @SiO2 packed column exhibited good stability and repeatability for the separation of chiral compounds. The relative standard deviations for five replicate separations of 1-phenylethanol were less than 1.0, 1.5, 3.0, and 2.0% for the retention time, peak area, number of theoretical plates, and resolution, respectively. The research results demonstrated the development of chiral metal-organic frameworks core-shell microspheres composite provide a promising platform for their practical application in chiral separation fields.

Chiral polyaniline modified Metal-Organic framework Core-Shell composite MIL-101@c-PANI for HPLC enantioseparation

Metal-organic frameworks (MOFs) have attracted a substantial amount of attention due to special properties, such as gas adsorption, chromatographic separation, and catalytic activity. Herein, a post-modification method was used to modify the surface of achiral MOFs using chiral polyaniline to synthesize a chiral core–shell composite (MIL-101@c-PANI), which was used for the first time as a stationary phase for the separation of chiral compounds. Twelve kinds of chiral compounds, including alcohols, ketones, esters, aldehydes, organic acids and amines were separated on the MIL-101@c-PANI packed column. Moreover, the column also showed good selectivity for the separation of positional isomers. Some chiral compounds that cannot be separated using a commercially available tris(3,5-dimethylphenylcarbamoyl) amylose-packed column (AD column), could be separated on the MIL-101@c-PANI column. The effects of the analyte mass and column temperature on the separation efficiency were investigated. The column exhibited good stability and reproducibility during the enantioseparation of chiral compounds. The MIL-101@c-PANI composite gives rise to a synergistic effect by combining the advantages of c-PANI and MIL-101, which is favorable for an improvement in the chiral separation performance. Therefore, this work shows that such composite materials will be very attractive in the field of separation science.

Role of Chromatograph-based Analytical Techniques in Quantification of Chiral Compounds: An Update

Background: Chiral purity is a critical quality attribute of pharmaceutical materials as chiral compounds are known to exhibit different pharmacological and toxicological properties as compared to those of their enantiomers (or diastereomers for molecules with multiple chiral centers). It is important to note that about 40% of the synthetic drugs are chiral, 60% of all pharmaceuticals are chiral and 45% chiral drugs are sold as racemates. The objective of the current review is to discuss various chromatographic techniques used for the separation of chiral compounds. Methods: Various bibliographic databases of previously published peer-reviewed research papers were explored and systematic data has been compiled in terms of various chromatographic techniques used for chiral compounds’ separation. A comparison of different techniques as well as their advantages is also discussed. Results: A comprehensive review of 130 papers including both, research and review articles, was carried out. The analytical techniques have been discussed in detail. Apart from chromatographic techniques, other techniques such as circular dichroism, nuclear magnetic resonance, UV-visible spectroscopy using cyclodextrin derivatives have also been highlighted. Conclusion: The pharmaceutical industries need analytical methods to conclude enantiomeric concentration and obtain a drug with a single stereo configuration. Sensitive techniques such as HPLC, GCMS and LCMS, etc. are used for identification and quantification of single enantiomers, specifically in drug discovery and development.

Conversion of S-2-amino-1-butanol-l-tartrate to S-2-amino-1-butanol by Using Bipolar Membrane Electrodialysis for Post-treatment of Direct Enantioseparation

In this work, a green route for the preparation of S-2-amino-1-butanol in the post-treatment for direct enantioseparation for the antituberculosis drug ethambutol hydrochloride has been explored. Therein, OH– produced from bipolar membrane electrodialysis (BMED) technology was used to in situ converse diastereomeric salt S-2-amino-1-butanol-l-tartrate to S-2-amino-1-butanol, rather than directly adding the chemical reagent of NaOH or Na2CO3 in a traditional way. For realization of the process, laboratory-scale BMEDs with two membrane stack configurations were fabricated, followed by an investigation of the effect of ion-exchange membrane types, initial feed concentrations, voltages, etc. As a result, under optimized conditions, the concentration of as-obtained S-2-amino-1-butanol (the final purity of the product: ca. 98.2%) can achieve 1.04 mol·L–1, and the conversion rate is 92.28%. The cost is estimated at approximately $2.22 kg–1. Accordingly, the current efficiency and energy consumption are 54.05% and 1.88 kW·h·kg–1, respectively. The investigation has verified the feasibility of BMED for the conversion of S-2-amino-1-butanol-l-tartrate to S-2-aminobutanol and also demonstrates potential application in the field of chiral compound separation.

Molecular Cages Self‐Assembled by Imine Condensation in Water

AbstractSelf‐assembly by imine condensation in aqueous media is a formidable task because of the labile nature of imines in the presence of water. Here, by taking advantage of multivalence and ligand preorganization, basket‐shaped triscationic cage molecules are self‐assembled in high yields in both water and organic solvent, by condensing a hexaformyl and bisamine. These cages, especially the chiral ones, are stable or inert in aqueous solution, that is, no decomposition was observed upon dilution, precipitation, or exposure to competitive amines or aldehydes. Such water‐compatibility allows the hosts to take advantage of the hydrophobic effect to accommodate hydrophobic guests. The chiral cage S‐23+ selectively binds and distinguishes one of two enantiomers, opening up opportunities for applications such as chiral compound separation. Chiral narcissistic self‐sorting and sergeants‐and‐soldiers effects occur during cage formation when two amino precursors are involved in self‐assembly.