Enantiomeric Analysis of Chiral Drugs Using Mass Spectrometric Methods: A Comprehensive Review.

Chirality plays a crucial role in the drug development process, influencing fundamental chemical and biochemical processes and significantly affecting our daily lives. This review provides a comprehensive examination of mass spectrometric (MS) methods for the enantiomeric analysis of chiral drugs. It thoroughly investigates MS-hyphenated techniques, emphasizing their critical role in achieving enantioselective analysis. Furthermore, it delves into the intricate chiral recognition mechanisms inherent in MS, elucidating the fundamental principles that govern successful chiral separations. By critically assessing the obstacles and potential benefits associated with each MS-based method, this review offers valuable insights for researchers navigating the complexities of chiral analysis. Both qualitative and quantitative approaches are explored, presenting a comparative analysis of their strengths and limitations. This review is aimed at significantly enhancing the understanding of chiral MS methods, serving as a crucial resource for researchers and practitioners engaged in enantioselective studies.

Expanding the Role of Chiral Drugs and Chiral Nanomaterials as a Potential Therapeutic Tool.

Chirality, the property of molecules having mirror-image forms, plays a crucial role in pharmaceutical and biomedical research. This review highlights its growing importance, emphasizing how chiral drugs and nanomaterials impact drug effectiveness, safety, and diagnostics. Chiral molecules serve as precise diagnostic tools, aiding in accurate disease detection through unique biomolecule interactions. The article extensively covers chiral drug applications in treating cardiovascular diseases, CNS disorders, local anesthesia, anti-inflammatories, antimicrobials, and anticancer drugs. Additionally, it explores the emerging field of chiral nanomaterials, highlighting their suitability for biomedical applications in diagnostics and therapeutics, enhancing medical treatments.

Bionic nanopore recognition receptors for single-molecule enantioselectivity studies of chiral drugs.

BACKGROUND: Enantiodiscrimination of chiral drugs is critical for understanding physiological phenomena and ensuring medical safety. Although enantiomers of these drugs share identical physicochemical properties, they exhibit significant differences in pharmacodynamic, pharmacokinetic, and toxicological properties due to the differences in their three-dimensional shapes. Therefore, the development of effective methods for chiral recognition is of great significance and has been a hot topic in chemo/biological studies. RESULTS: In this study, we designed a recognition receptor comprising a α-hemolysin (α-HL) nanopore and sulfobutyl ether-ß-cyclodextrin (SBEßCD) for identifying the enantiomers of the antidepressant duloxetine at the single-molecule level. Chiral molecules were discriminated based on the different current blockages within the recognition receptor. The results indicated a strong interaction between R-duloxetine and the recognition receptor. By combining the experimental data and molecular docking results, we explored the recognition mechanism of the designed nanopore recognition receptor for chiral drug molecules. It was found that hydrophobic and electrostatic interactions play key roles in chiral recognition. Additionally, by comparing the binding kinetics of enantiomers to cyclodextrins in confined nanospace and bulk solution, we found that enantiomeric identification was better facilitated in the confined nanospace. Finally, the enantiomeric excess (ee) of the enantiomeric duloxetine mixture was measured using this recognized receptor. SIGNIFICANCE: This strategy has the advantages of low cost, high sensitivity, and no need for additional derivative modifications, providing a new perspective on the development of chiral recognition sensors with excellent enantioselectivity in drug design, pharmaceuticals, and biological applications.

Dextrin-assisted gel electromembrane extraction of chiral drugs: Improving the extraction efficiency and investigation of enantioselectivity of extraction.

The present study investigates the use of dextrins (maltodextrin, ß-cyclodextrin, and hydroxypropyl-ß-cyclodextrin) to improve the efficiency of the agarose-based gel electromembrane extraction technique for extracting chiral basic drugs (citalopram, hydroxyzine, and cetirizine). Additionally, it examines the enantioselectivity of the extraction process for these drugs. To achieve these, dextrins were incorporated into either the sample solution, the membrane, or the acceptor solution, and then the extraction procedure was performed. Enantiomers were separated and analyzed using a capillary electrophoresis device equipped with a UV detector. The results obtained under the optimal extraction conditions (sample solution pH: 4.0, acceptor solution pH: 2.0, gel membrane pH: 3.0, agarose concentration: 3 % w/v, stirring rate: 1000 rpm, gel thickness: 4.4 mm, extraction voltage: 62.3 V, and extraction time: 32.1 min) indicated that incorporating dextrins into either the sample solution, membrane or the acceptor solution enhances extraction efficiency by 17.3-23.1 %. The most significant increase was observed when hydroxypropyl-ß-cyclodextrin was added to the acceptor solution. The findings indicated that the inclusion of hydroxypropyl-ß-cyclodextrin in the sample solution resulted in an enantioselective extraction, yielding an enantiomeric excess of 6.42-7.14 %. The proposed method showed a linear range of 5.0-2000 ng/mL for enantiomers of model drugs. The limit of detection and limit of quantification for all enantiomers were found to be < 4.5 ng/mL and <15.0 ng/mL, respectively. Intra- and inter-day RSDs (n = 4) were less than 10.8 %, and the relative errors were less than 3.2 % for all the enantiomers. Finally, the developed method was successfully applied to determine concentrations of enantiomers in a urine sample with relative recoveries of 96.8-99.2 %, indicating good reliability of the developed method.

Chiral zeolite beta used as stationary phase for enantioseparation in miniaturized open tubular capillary electrochromatography with amperometric detection.

BACKGROUND: With the rapid growth of the demand for optically pure compounds in the fields of biology, medicine and stereospecific synthesis, it is of great importance to develop efficient, economical, simple enantioseparation and analysis methods. Open tubular capillary electrochromatography (OT-CEC) has attracted much attention in the field of chiral separation, but its column capacity and the sensitivity of common-used optical detection are relatively low. Zeolite beta nanomaterial is both enantioselective and size-selective, providing suitable chiral microenvironment for chiral recognition, and amperometric detection (AD) avoids the low sensitivity caused by the short optical path in optical detection to some extent. RESULTS: Zeolite beta nanomaterials with different particle sizes (25, 50 and 200 nm) were synthesized, and the morphology and structure were characterized by scanning electron microscopy and X-ray diffraction. Then, a novel chiral OT column was prepared by one-step method using zeolite beta nanomaterial as chiral stationary phase, and its separation performance was characterized by miniaturized CEC with AD (mini-CEC-AD) device. Under the optimum conditions, six groups of chiral drugs achieved baseline separation. Norepinephrine enantiomers were used for evaluating the inter-day, intra-day and inter-column reproducibility of the prepared open-tubular column. The relative standard deviations of migration time, peak area, resolution and selectivity factor were within 8.7 %. The limits of detection for norepinephrine enantiomers were 0.18 µg mL-1 (S/N = 3), and the average recoveries were in range of 96.7-105.0 %. This developed method has been successfully applied to the analysis of impurity enantiomer in potassium dichromate (+)-norepinephrine injection sample. SIGNIFICANCE: Zeolite beta nanomaterial was used as the stationary phase to prepare chiral OT columns for the first time, and this one-step preparation method is simple and easy. The introduction of zeolite beta enriches the types of chiral stationary phase materials in electrochromatographic columns, and mini-OT-CEC-AD system provides an alternative for fast enantioseparation of chiral compounds.

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

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

[Preparation of porous organic cage and its use as chiral stationary phase for capillary electrochromatography].

Porous organic cages (POCs) are a unique type of microporous materials composed of discrete molecules with internal cavities that are accessible to various compounds. In this study, a prismatic chiral POC with good thermochemical stability was synthesized by condensing (1R,2R)-diaminocyclohexane and 3,3',5,5'-teturonic-4,4'-biphenediol via the Schiff base reaction and characterized by proton nuclear magnetic resonance spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy. The IR spectrum of the POC revealed a strong characteristic absorption peak at 1635 cm-1, indicating that it formed imine bonds (C=N). The absorption peak at 3425 cm-1 was attributed to the stretching vibrations of -OH, the absorption peaks at 2925 and 2858 cm-1 were attributed to the stretching vibrations of N=C-H and C-H, and the absorption peaks at 1446 and 1383 cm-1 were attributed to the stretching vibrations of C=C-H and C=C in the benzene ring. High-resolution mass spectral analysis of the POC showed a molecular ion peak at m/z 1363.7228, indicating its successful synthesis. TGA was performed from 25 to 800 ℃ at a rate of 10 ℃/min, and the results of this analysis showed that the POC was stable up to approximately 300 ℃. The POC was dissolved in dichloromethane and uniformly coated on the inner wall of a quartz capillary via the dynamic coating method to prepare a capillary electrochromatographic column. The experimental results revealed that the chiral electrochromatographic column could not only resolve ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol but also separate the isomers of o-, m-, and p-toluidine and o-, m-, and p-chloroaniline, indicating its good chiral separation ability. Investigation of the optimal separation conditions for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol revealed that the voltage, buffer solution concentration, and pH significantly affected their separation degree. In particular, the optimal separation voltage for ofloxacin, Troger's base, and 2-amino-1-butanol was 15 kV, while that for 1-phenyl-1-amyl alcohol was 17 kV. The optimal buffer concentration and pH for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol were 0.100 mol/L and 7.5. Under optimal chromatographic conditions, the resolution values for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-pentanol were 1.80, 3.33, 1.69, and 1.18, respectively. The results collectively demonstrate that the prepared POC may serve as a good chiral stationary phase for capillary electrochromatography with a certain chiral resolution ability and has good application prospects in chromatographic separation.

Emerging Developments in Separation Techniques and Analysis of Chiral Pharmaceuticals.

Chiral separation, the process of isolating enantiomers from a racemic mixture, holds paramount importance in diverse scientific disciplines. Using chiral separation methods like chromatography and electrophoresis, enantiomers can be isolated and characterized. This study emphasizes the significance of chiral separation in drug development, quality control, environmental analysis, and chemical synthesis, facilitating improved therapeutic outcomes, regulatory compliance, and enhanced industrial processes. Capillary electrophoresis (CE) has emerged as a powerful technique for the analysis of chiral drugs. This review also highlights the significance of CE in chiral drug analysis, emphasizing its high separation efficiency, rapid analysis times, and compatibility with other detection techniques. High-performance liquid chromatography (HPLC) has become a vital technique for chiral drugs analysis. Through the utilization of a chiral stationary phase, HPLC separates enantiomers based on their differential interactions, allowing for the quantification of individual enantiomeric concentrations. This study also emphasizes the significance of HPLC in chiral drug analysis, highlighting its excellent resolution, sensitivity, and applicability. The resolution and enantiomeric analysis of nonsteroidal anti-inflammatory drugs (NSAIDs) hold great importance due to their chiral nature and potential variations in pharmacological effects. Several studies have emphasized the significance of resolving and analyzing the enantiomers of NSAIDs. Enantiomeric analysis provides critical insights into the pharmacokinetics, pharmacodynamics, and potential interactions of NSAIDs, aiding in drug design, optimization, and personalized medicine for improved therapeutic outcomes and patient safety. Microfluidics systems have revolutionized chiral separation, offering miniaturization, precise fluid control, and high throughput. Integration of microscale channels and techniques provides a promising platform for on-chip chiral analysis in pharmaceuticals and analytical chemistry. Their applications in techniques such as high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) offer improved resolution and faster analysis times, making them valuable tools for enantiomeric analysis in pharmaceutical, environmental, and biomedical research.

A Theoretical Analysis of the Differential Chemical Reaction Results Caused by Chirality Induction.

The theory of electron spin has been proposed for a century, but the study of quantum effects in biological molecules is still in its infancy. Chirality-induced spin selectivity (CISS) is a very modern theory that can explain many biochemical phenomena. In this paper, we propose a new theoretical model based on CISS theory and quantum chemistry theory, which can well explain the theoretical explanation of the chiral selectivity of chiral proteins. Moreover, this theory can predict the spin state of corresponding chiral molecules. Taking the L-DOPA and AADC enzymes as examples, this theoretical model elucidates the AADC enzyme's chiral catalysis selectivity and successfully predicts the spin state of L-DOPA and D-DOPA's valence electrons.

Exploration of chiral drugs as references for chiral discrimination of valsartan and voriconazole by tandem mass spectrometry.

The use of mass spectrometry for chiral recognition and quantification has attracted great interest owing to its speed, sensitivity, specificity, and tolerance. However, searching for chiral selectors in chiral analyses using mass spectrometry is still problematic. In this study, chiral drugs could be applied as references for the chiral recognition and enantiomeric quantification of valsartan and voriconazole. Two novel pairs of metal-bound diastereomeric complex ions were detected by mass spectrometry, namely, nickel (II)-bound dimeric ions [NiII (2R,5S-emtricitabine) (S-valsartan)-H]+ and [NiII (2R,5S-emtricitabine) (R-valsartan)-H]+ and copper (II)-bound dimeric ions [CuII (S,S,S-enalaprilat) (2S,3R-voriconazole)-H]+ and [CuII (S,S,S-enalaprilat) (2R,3S-voriconazole)-H]+ . The resulting diastereomers were successfully identified based on the relative intensities of their characteristic fragments using tandem mass spectrometry. The logarithm of the characteristic fragment ion abundance ratio exhibited a good linear relationship with the enantiomeric excess. Density functional theory calculations were also performed to elucidate the mechanism of the structural differences observed in the MS results. This established approach proves that chiral drugs can serve as ligands for the rapid recognition and quantitative analysis of other chiral drugs without a chiral chromatographic column or complex sample pretreatment.

Chiral Inversion of Pharmaceutical Drugs - Mini Review.

2-Arylpropionic acid nonsteroidal anti-inflammatory drugs (NSAIDs) provide one of the most demonstrated pharmaceutical examples of chiral inversion. Chiral inversion depends on various factors (viz. biological-, solvent-, light-, temperature-induced, etc.) and the energy barrier associated with the stereogenic element present in the chiral molecule. The pharmacological properties of chiral drugs depend on the activity of one enantiomer or both the enantiomers targeting different biological targets. Consequently, chiral inversion can alter the biological activities of the pharmaceutical drug. Hence a better understanding of chiral inversion, factors facilitating such inversion, and the tools employed to determine chiral inversion are of great significance from a pharmacological and toxicological perspective.

Asymmetric organocatalysis in drug discovery and development for active pharmaceutical ingredients.

INTRODUCTION: Over the last 20 years, it has become clear that organocatalysis is the third pillar of catalysis. The low reactivity in the early days of organocatalysis has been overcome with the invention of more efficient catalysts, and by harnessing enabling technologies like continuous-flow chemistry and photo-redox catalysis. AREAS COVERED: The main focus of this review is on the development over the last 10-15 years of key APIs using asymmetric organocatalysis. Due to significant engineering advances, and also due to the need for continuous manufacturing, flow and photo-redox approaches are becoming more widespread. EXPERT OPINION: Over the last 20 years, organocatalysis has been used on various occasions for accessing chiral drugs. The great advantage of using these catalysts is that the final active pharmaceutical ingredient (API) is metal-free. Also due to their inherent stability in air and water, they are very amenable to recovery via attachment to appropriate solid supports and also application in continuous flow systems. In recent years, more efficient organocatalysts have been developed, which includes the photoredox types, with much potential for chiral API synthesis.

Chiral Sensing as a Future Challenge in Electroanalytical Chemistry: Cyclodextrin-Based Chiral Sensors.

Chirality is an academically exciting and interesting topic, as most active ingredients have chirality. Chiral enantiomers with the same molecular shape show different effects from each other in terms of pharmacological, pharmacokinetic, and toxicology. There are many examples of these differences that have caused dramatic, even fatal damage. For these reasons, it is of great importance to developing an effective method to achieve chiral identification and separation, and chiral separation methods are becoming increasingly important in both the pharmaceutical industry and clinical studies. Electrochemical techniques, which can provide many advantages over other classical methods, have attracted great interest in chiral recognition in recent years. In this review, extensive and critical research of the trends in chiral recognition in recent studies is explained. Especially the role of cyclodextrins derivatives in chiral analysis has been investigated and the studies related to this are explained and given in the tables. In addition, some remarks and future perspectives in the field of chiral recognition are also discussed in the concluding part.

4-Isobutylmethcathinone-A Novel Synthetic Cathinone with High In Vitro Cytotoxicity and Strong Receptor Binding Preference of Enantiomers.

New psychoactive substances and among them synthetic cathinones represent a significant threat to human health globally. However, within such a large pool of substances derived from a natural compound ((S)-cathinone), substances with important pharmaceutical uses can be identified, as already documented by bupropione. Therefore, this work aimed to find a synthetic pathway for a novel synthetic cathinone, namely 4-isobutylmethcathinone, and describe its spectroscopic properties and biological activity in vitro. Since cathinones comprise a chiral center in their structure, a method for chiral separation of the substance was elaborated using high-performance liquid chromatography on an analytical and preparative scale. Preparative enantioseparation on a polysaccharide column provided a sufficient amount of the drug for the chiroptical studies leading to the determination of the absolute configuration of enantiomers as well as for their subsequent in vitro cytotoxicity study. The cytotoxicity induced by 4-isobutylmethcathinone was determined in human cells derived from the urinary bladder (5637), neuroblastoma (SH-SY5Y), microglia (HMC-3), and hepatocellular carcinoma (Hep G2), in which the IC50 values after 72 h reached an 18-65 µM concentration. This is significantly higher cytotoxicity in comparison with other synthetic cathinones. In the receptor binding studies, a significant difference in the agonistic effect on dopamine and adrenergic receptors of individual enantiomers was observed. The lack of binding affinity towards the serotonin receptors then relates 4-isobutylmethcathinone to the family of monoamine drugs, such as 3,4-methylenedioxymathamphetamine (ecstasy, MDMA).

Advances and challenges in the pharmacokinetics and bioanalysis of chiral drugs.

Enantioselective analytical approaches are essential for monitoring pharmacokinetics and acquiring accurate data to better understand the role of stereochemistry in pharmacokinetics. Enantioselectivity significantly impacts the pharmacokinetics of chiral drugs, especially in metabolic profile, leading to toxicity of enantiomer. Consequently, there is a need to study the pharmacokinetics of enantiomerically pure drugs and racemates as they differ in affinity with enzymes and proteins. Combining the best enantioseparation conditions with the specified biological matrix and the intended purpose of the analysis is a challenging task. This review discusses the importance of chirality in stereoselective pharmacokinetics with more relevant examples, various enantioselective analytical techniques, and stationary phases employed. Challenges such as lack of universal chiral columns, biological inversion of the isomers, and others have been discussed. Further presented the recent advances in the screening of chiral drugs and innovative improvements in the analytical approaches for chiral molecule analysis such as supercritical fluid chromatography, simulated moving bed chromatography, and other techniques are discussed.

The Use of Antibiotics as Chiral Selectors in Capillary Electrophoresis: A Review.

Chirality is becoming an essential issue in modern pharmaceutical research as regulatory agencies emphasize the safety and efficiency of enantiomers in drug development. The development of efficient and reliable chiral separation methods became a necessity in the last 30 years, and capillary electrophoresis (CE), due to its relatively low costs and "green" features, is attracting increased attention. Cyclodextrin (CD) and their derivatives are the most frequently used chiral selectors (CSs) in CE, however, the use of antibiotics as CSs represents an interesting alternative. Various classes of antibiotics (aminoglycosides, ansamycins, glycopeptides, lincosamides, macrolides, tetracyclines) have been used more or less successfully for the enantio-separation of pharmaceuticals. Antibiotics offer the possibility of a multitude of potential interactions (electrostatic, inclusion, hydrogen bonding, etc.) due to their chemical diversity, allowing the enantio-separation of analytes with a wide range of structural characteristics. This article aims to review the application of various classes of antibiotics in the CE enantio-separation of pharmaceuticals. Antibiotic physiochemical characteristics, variables impacting enantio-separation, advantages, and disadvantages when certain antibiotics are used as CSs in CE are also explored.

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

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

Chiral Covalent Organic Framework Packed Nanochannel Membrane for Enantioseparation.

A nanochannel membrane has the prospect of large-scale separation. However, selectivity in enantioseparation is a challenge, due to the size difference between nanochannels and enantiomers. Here, we compartmented nanochannels by the in situ synthesis of a L-tyrosine functionalized covalent organic framework (L-Tyr-COF). The L-Tyr-COF decreased the pore size of channels to match with naproxen enantiomers (S/R-NPX) and improved the enantioselective gating. In contrast to the surface-functionalized nanochannels (L-Tyr channel), the L-Tyr-COF packed nanochannels (L-Tyr-COF channel) exhibited high enantioselectivity for S-NPX and realized the enantioseparation with the enantiomer excess value up to 94.2 %. The separation flux through the highly porous L-Tyr-COF channel was 1.33 mmol m-2 h-1 . This study provided a size-matching strategy and the chiral covalent organic framework packed nanochannel membrane to realize enantioseparation with high selectivity and flux.

Chiral Switch: Between Therapeutical Benefit and Marketing Strategy.

Chirality of pharmaceutical substances is an important aspect in drug research because it determines how enantiomers will interact with chiral biological targets. Enantiomers of a chiral drug can have different pharmacokinetic and pharmacological profiles; consequently, using a single pure enantiomer instead of a racemate can enhance the effectiveness and/or safety of the treatment. The tendencies of modern pharmaceutical industry regarding the current market of chiral drugs are divided between the chiral switch of previously used racemates and the development of new enantiopure drugs. The term chiral switch refers to the replacement on the market of a previously approved racemate with its single enantiomer version. The potential advantages of chiral switch can be related to a higher therapeutic index due to better potency, selectivity and fewer adverse effects, faster onset of action and exposure of the patient to lower drug dosages. However, chiral switch is also a strategy that permits manufacturers to keep market exclusivity for chiral pharmaceuticals that have lost their patent protection, even if the pure enantiomers have not demonstrated higher effectiveness or safety profile compared with the racemates.

Progress of molecular imprinting technique for enantioseparation of chiral drugs in recent ten years.

The existence of chiral compounds is a very common phenomenon in the field of medicine, and nearly 60% of drugs are chiral. The separation of racemic drugs is the key to safe use of drugs. Molecularly imprinted technique (MIT) has attracted wide attention in the separation of chiral drugs in recent years due to its simple operation and strong specific recognition ability of target molecules. Molecularly imprinted polymers (MIPs) have been used as selective adsorbents in a variety of analytical techniques, and excellent progress has been made in the separation of chiral drugs. In this paper, the MIT for the separation of drug in recent ten years is reviewed. We will introduce how to achieve chiral drug resolution in different chromatographic techniques based on the morphological differences of MIPs (micron-sized particles, nanoparticles and monolithic column materials) as the classification criteria. Furthermore, the contributions of surface molecularly imprinted technique (SMIT) and molecularly imprinted membrane (MIM) technology in racemic drug resolution are also introduced. Finally, the main application challenges of chiral MIT are briefly introduced, and the future development direction of this field is prospected.