High-performance liquid chromatographic enantioseparation of azole analogs of monoterpene lactones and amides focusing on the separation characteristics of polysaccharide-based chiral stationary phases.

High-performance liquid chromatography-based enantioseparation of newly prepared azole analogs of monoterpene lactones and amides was studied. Effects of additives and mobile phase composition were evaluated both in normal and polar organic modes. Applying amylose tris-(3,5-dimethylphenylcarbamate) selector in normal and polar organic modes acid and base additives were found to affect the peak profiles, without significantly influencing the enantiorecognition ability of the studied selector. In most cases, differences observed in retention times and enantioselectivities were lower than 10 and 20 % under normal phase and polar organic conditions, respectively. Under normal phase conditions decreased retention was observed for all the studied analytes with increased eluent polarity. Interestingly, enantioselectivity was only slightly (<10 %) influenced by the variation in the n-hexane/2-propanol ratio between 80/20 and 20/80 v/v. In polar organic mode, five different neat solvents (acetonitrile, methanol, ethanol, 1-propanol, and 2-propanol) were tested, and the best results were obtained with acetonitrile and ethanol in the case of Lux Amylose-1 column with enantioresolutions most often above 2. Based on results obtained with amylose and cellulose-based columns the amylose tris-(3,5-dimethylphenylcarbamate) selector is found to offer a superior performance both in normal and polar organic modes. When evaluating the possible effects of the selector immobilization, no striking differences were found in the normal phase. Usually, enantioselectivities and resolutions were higher (10-20 %), while retention factors of the first peaks were lower (20-30 %), on the coated-type column. In contrast, in polar organic mode, the retention characteristics and enantiorecognition ability of the coated and immobilized selectors were heavily affected by the nature of the polar solvent. Special attention has been paid to the history-dependent behavior of polysaccharide-based selectors. A confidence interval-based evaluation is suggested to help comparison of the histereticity observed in different systems. Several examples are shown to confirm that the recently discovered hysteresis is a common characteristic of polysaccharide-based selectors.

Regioselective modification at the 2,3- and 6-positions of chitosan with phenylcarbamates for chromatographic enantioseparation.

Chitosan derivatives with two different phenylcarbamate pendants at the 6-position and 2,3-positions of the glucosamine unit were synthesized by triphenylmethyl as a protective group. The regioselective chitosan derivatives were prepared corresponding to coated-type chiral packed materials (CPMs), which were evaluated with thirteen chiral compounds by high-performance liquid chromatography (HPLC). The regioselective chitosan derivatives (4aⅠ/4aⅡ, 4bⅠ/4bⅡ) bearing electron-withdrawing 3,5­chloro or 4­chloro at the 6-position can recognize 7 or 8 of the 13 enantiomers and achieve baseline separation for enantiomers 5 and 7. They exhibited better chiral recognition abilities than the other derivatives with different substituents at the 6-position and the same 3,5-dimethylphenyl substituent at the 2,3-postion. In comparison to Chit-1 featuring a 3,5-dimethylphenyl substituent at the 2,3- and 6-positions, it was observed that the combination of both an electron-withdrawing and an electron-donating substituent of the regioselective chitosan derivatives (4aⅠ/4aⅡ, 4bⅠ/4bⅡ) showed better or similar enantioseparation abilities for racemic Compounds 7 and 6, respectively. The molecular weight-performance relationship of the regioselective chitosan derivatives was investigated in detail. It was found that with increasing molecular weight, the derivatives 4aⅡ and 4bⅡ all possessed greater enantioseparation power for 4 enantiomers, such as enantiomers 4, 7, 11, and 15, than the corresponding derivatives with low molecular weights. The molecular docking simulation results showed that excellent enantioseparation power significantly depended on the combination and interaction of multiple factors, such as steric hindrance, and polarity of the substituents on the CPMs and enantiomers.

Molecular Dynamics Simulations of Amylose- and Cellulose-Based Selectors and Related Enantioseparations in Liquid Phase Chromatography.

In the last few decades, theoretical and technical advancements in computer facilities and computational techniques have made molecular modeling a useful tool in liquid-phase enantioseparation science for exploring enantioselective recognition mechanisms underlying enantioseparations and for identifying selector-analyte noncovalent interactions that contribute to binding and recognition. Because of the dynamic nature of the chromatographic process, molecular dynamics (MD) simulations are particularly versatile in the visualization of the three-dimensional structure of analytes and selectors and in the unravelling of mechanisms at molecular levels. In this context, MD was also used to explore enantioseparation processes promoted by amylose and cellulose-based selectors, the most popular chiral selectors for liquid-phase enantioselective chromatography. This review presents a systematic analysis of the literature published in this field, with the aim of providing the reader with a comprehensive picture about the state of the art and what is still missing for modeling cellulose benzoates and the phenylcarbamates of amylose and cellulose and related enantioseparations with MD. Furthermore, advancements and outlooks, as well as drawbacks and pitfalls still affecting the applicability of MD in this field, are also discussed. The importance of integrating theoretical and experimental approaches is highlighted as an essential strategy for profiling mechanisms and noncovalent interaction patterns.

Enantiomeric analysis of drugs in water samples by using liquid-liquid microextraction and nano-liquid chromatography.

The nano-LC technique is increasingly used for both fast studies on enantiomeric analysis and test beds of novel stationary phases due to the small volumes involved and the short conditioning and analysis times. In this study, the enantioseparation of 10 drugs from different families was carried out by nano-LC, utilizing silica with immobilized amylose tris(3-chloro-5-methylphenylcarbamate) column. The effect on chiral separation caused by the addition of different salts to the mobile phase was evaluated. To simultaneously separate as many enantiomers as possible, the effect of buffer concentration in the mobile phase was studied, and, to increase the sensitivity, a liquid-liquid microextraction based on the use of isoamyl acetate as sustainable extraction solvent was applied to pre-concentrate four chiral drugs from tap and environmental waters, achieving satisfactory recoveries (>70%).

Exploitation of the enantioselectivity space of coated amylose tris(3,5-dimethylphenylcarbamate) in mixtures of 2-propanol and acetonitrile.

Chiral stationary phases (CSPs) with coated amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) selector have long been recognized for their excellent chiral recognition ability in liquid chromatography. The conformational versatility behind this feature is the source of their known hysteretic behavior, which has been previously observed in polar organic (PO) mode eluents containing 2-propanol (IPA). Mixtures of IPA and acetonitrile (MeCN), a typical PO mode eluent system, have not been examined in this aspect yet, even though hysteresis is promising for finding unique unexplored enantioselectivities. Not only was the hysteresis detectable on ADMPC using mixtures of IPA and MeCN, but it was the typical behavior in a diverse set of test compounds. The difference in the retention time of the same analyte under conditions which only differed in the eluent history on the column can go up to 20-fold. The assumed hindered conformational changes of the selector were reflected in retention drift at certain eluent compositions. On the two sides of the transitions, distinct, useful states of the selector were detected. A series of IPA - MeCN compositions with defined pretreatment was selected and recommended as an extension of the preliminary, first choice method screening set that used only alcohols. The incorporation of a solvent possessing substantially different characteristics enhances the potential in practical applications, while keeping the technical simplicity. Stability and robustness of the additional states of the CSP were characterized. The examined columns of different brands shared the observed behavior. Kinetic stability of a column state is adequate for successful application. The evaluated states of ADMPC provide multiple enantiorecognition potential by using mixtures of IPA and MeCN also considering the pretreatment of the column. Unprecedented double and triple elution order reversals along the composition range supported the versatility of the available states. Our findings further enhance the usefulness of ADMPC-containing CSPs. We provide instructions for the application of the widespread chiral selector in common eluent mixtures to avoid pitfalls regarding reproducibility and robustness.

Modelling the enantiorecognition of structurally diverse pharmaceuticals on O-substituted polysaccharide-based stationary phases.

This study aims to develop models to predict the retention, separation and elution sequence of the enantiomers of structurally diverse pharmaceuticals. More specifically, Quantitative Structure Retention Relationships (QSRR) models are built that describe the relationship between molecular descriptors and retention. Eighteen structurally diverse chiral mixtures, each consisting of a pair of enantiomers, were analyzed on two polysaccharide chiral stationary phases, Chiralcel OD-RH (cellulose tris(3,5-dimethylphenylcarbamate)) and Lux amylose-2 (amylose tris(5-chloro-2-methylphenylcarbamate)), applying either a basic or an acidic mobile phase, and their retention factor and elution sequence were determined. Both achiral and, in-house defined, chiral descriptors were used as descriptive variables to build the models. Linear regression techniques, i.e. stepwise multiple linear regression (sMLR) and partial least squares (PLS) regression, were applied to model the retention or separation as a function of the descriptors. In a first step, models were built with only achiral descriptors to model the global retention of both enantiomers of a chiral molecule. Subsequently, models were built with only chiral descriptors to predict the enantioseparation and elution sequence, and finally, models were considered with both descriptor types to predict the retention, the separation and the elution sequence of the enantiomers. The global retention was predicted well by the sMLR models with only achiral descriptors. The models with only chiral descriptors were not found suitable to predict the enantioseparation and elution sequence. Finally, the models containing both chiral and achiral descriptors allowed predicting the retention well, but their ability to predict the elution sequence and separation of the enantiomers differed widely for the chromatographic systems considered.

Requirements in structure for chiral recognition of chitosan derivatives.

In order to investigate the influence of a minor variation in structure of N-acyl chitosan derivatives on enantioseparation, chiral selectors (CSs) of chitosan 3,6-bis(phenylcarbamate)-2-(phenylacetamide)s and chitosan 3,6-bis(phenylcarbamate)-2-(cyclohexylacetamide)s were synthesized. The corresponding chiral stationary phases (N-PhAc CSPs and N-cHeAc CSPs) were also prepared, respectively, with the two series of CSs. Enantioseparation results revealed that the N-PhAc CSPs were better than the N-cHeAc ones in enantioseparation. Thus, benzyl group (Bn) at C2 should be more preferable to enantioseparation than cyclohexylmethyl (cyclohexyl-CH2-) at the same position. Because N-PhAc CSPs exhibited higher enantioseparation capability than chitosan 3,6-bis(phenylcarbamate)-2-(benzamide) based CSPs (N-Bz CSPs), the Bn should also be more beneficial to enantioseparation than phenyl group (Ph) at C2 in N-Bz CSPs. In addition, it was found that, the cyclohexyl group at C2 in chitosan 3,6-bis(phenylcarbamate)-2-(cyclohexylformamide) CSPs was better than cyclohexyl-CH2- in N-cHeAc CSPs to enantioseparation. In a word, a minor variation at C2 of chitosan derivatives significantly affected enantioseparation. After the prepared CSPs were stood for six months, their enantioseparation capabilities were changed obviously, and the changes were probably related to nature, position and number of a substituent on Ph connected to carbamates at C3 and C6 of the CSs.

Enantioseparation and molecular modeling study of chiral amines as three naphthaldimine derivatives using amylose or cellulose trisphenylcarbamate chiral stationary phases.

This study describes the enantioseparation of three chiral amines as naphthaldimine derivatives, using normal phase HPLC with amylose and cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (CSPs). Three chiral amines were derivatized using three structurally similar naphthaldehyde derivatizing agents, and the enantioselectivity of the CSPs toward the derivatives was examined. The degree of enantioseparation and resolution was affected by the amylose or cellulose-derived CSPs and aromatic moieties as well as a kind of chiral amine. Especially, efficient enantiomer separation was observed for 2-hydroxynapthaldimine derivatives on cellulose-derived CSPs. Molecular docking studies of three naphthaldimine derivatives of leucinol on cellulose tris(3,5-dimethylphenylcarbamate) were performed to estimate the binding energies and conformations of the CSP-analyte complexes. The obtained binding energies were in good agreement with the experimentally determined enantioseparation and elution order.

HPLC Enantioseparation of Rigid Chiral Probes with Central, Axial, Helical, and Planar Stereogenicity on an Amylose (3,5-Dimethylphenylcarbamate) Chiral Stationary Phase.

The chiral resolving ability of the commercially available amylose (3,5-dimethylphenylcarbamate)-based chiral stationary phase (CSP) toward four chiral probes representative of four kinds of stereogenicity (central, axial, helical, and planar) was investigated. Besides chirality, the evident structural feature of selectands is an extremely limited conformational freedom. The chiral rigid analytes were analyzed by using pure short alcohols as mobile phases at different column temperatures. The enantioselectivity was found to be suitable for all compounds investigated. This evidence confirms that the use of the amylose-based CSP in HPLC is an effective strategy for obtaining the resolution of chiral compounds containing any kind of stereogenic element. In addition, the experimental retention and enantioselectivity behavior, as well as the established enantiomer elution order of the investigated chiral analytes, may be used as key information to track essential details on the enantiorecognition mechanism of the amylose-based chiral stationary phase.

Synthesis and application of chitosan thiourea derivatives as chiral stationary phases in HPLC.

Chitosan 2-thiourea derivatives with various substituents, including 3-(methylthio)propyl, phenyl, octyl and ethoxycarbonyl, at the 2-position of the glucosamine skeleton were prepared via isothiocyanates with the above substituents. The obtained chitosan 2-thiourea derivatives without ethoxycarbonyl were then esterified to develop a new series of chitosan 2-thiourea-3,6-diphenylcarbamate derivatives. The enantioseparation properties of the obtained chitosan derivatives were examined by high-performance liquid chromatography (HPLC). These results demonstrated that these chitosan 2-[3-(methylthio)propylthiourea]-3,6-diphenylcarbamate derivatives showed attractive chiral recognition abilities, especially for dihydropyridine calcium antagonist racemates. This result was probably attributed to the fact that the 2-thiourea substituents of this series of chitosan derivatives, as well as the 3,6-phenylcarbamate substituents, provided more favorable sites, which evidently enhanced the interactions between the enantiomers and the chitosan derivatives. The mechanism involved in the enantioseparation of the chitosan 2-[3-(methylthio)propylthiourea]-3,6-diphenylcarbamate derivatives was further discussed by molecular docking simulation.

Low-Frequency Raman Spectroscopy as an Avenue to Determine the Transition Temperature of ß- and γ-Relaxation in Pharmaceutical Glasses.

In an earlier investigation, low-frequency Raman (LFR) spectroscopy was shown to detect the transition temperature of the ß-relaxation (Tß) in both amorphous celecoxib and various celecoxib amorphous solid dispersions [Be̅rzins, K. Mol. Pharmaceutics 2021, 18(10), 3882-3893]. In this study, we further investigated the application of this technique to determine Tß, an important parameter for estimating crystallization potency of amorphous drugs. Alongside commercially available amorphous drugs (zafirlukast and valsartan disodium salt), differently melt-quenched samples of cimetidine were also analyzed. Overall, the variable-temperature LFR measurements allowed for an easy access to the desired information, including the even lesser transition of the tertiary relaxation motions (Tγ). Thus, the obtained results not only highlighted the sensitivity, but also the practical usefulness of this technique to elucidate (subtle) changes in molecular dynamics within amorphous pharmaceutical systems.

Enantioseparation of selected chiral agrochemicals by using nano-liquid chromatography and capillary electrochromatography with amylose tris(3­chloro-5-methylphenylcarbamate) covalently immobilized onto silica.

In this paper enantiomers of selected chiral agrochemicals representing various structural classes were separated by using nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) employing a capillary column packed with silica particles containing immobilized amylose tris(3­chloro-5-methylphenylcarbamate) (i-ADMPC) as a chiral selector (CS). Special attention was paid to peak dispersion in nano-LC and CEC instruments used in order to make comparison between these two techniques more reliable. Enantioseparations were studied utilizing methanol (MeOH) or acetonitrile-water (ACNH2O), both containing 5 mM of ammonium acetate as the mobile phases (MPs). The tested chiral stationary phase (CSP), containing 20% (w/w) of the neutral CS onto native silica, allowed the generation of sufficiently strong electroosmotic flow (EOF) to observe separation of enantiomers of studied agrochemicals in a reasonable time also in CEC mode. Modestly higher efficiencies and enantioresolutions were obtained in CEC than in nano-LC. Just a moderate preference of CEC over nano-LC in this particular study can be explained with a significant mass transfer resistance through the CSP that is caused due to high content of the CS in CSP.

Molecular structure and chiral recognition ability of highly branched cyclic dextrin carbamate derivative.

A hyperbranched polymer, highly branched cyclic dextrin tris(3,5-dimethylphenylcarbamate) (HDMPC), consisting of rigid rodlike subchains was synthesized to investigate dimensional and hydrodynamic properties of HDMPC in methyl acetate and 4-methyl-2-pentanone at 25 °C. Both gyration radii and intrinsic viscosities of the HDMPC sample in the two solvents were much smaller than those for the linear amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) chain with the corresponding molar mass. The chiral column made of the HDMPC sample has chiral separation ability for 8 racemates with a mobile phase of hexane/2-propanol while 6 of them were also separated by our previously investigated linear ADMPC column. These results indicate that HDMPC retains the functionality of the rigid linear ADMPC chain with much smaller chain dimensions and lower solution viscosity than those for the linear chain with the same molar mass.

A protocol to replace dedication to either normal phase or polar organic mode for chiral stationary phases containing amylose tris(3,5-dimethylphenylcarbamate).

Alteration of the enantiorecognition ability of polysaccharide-based chiral columns in the shipping normal phase (NP) eluent after exposition to polar organic (PO) mode eluents can be conceived as an incomplete hysteresis cycle. Non-standard solvents provide a solution to overcome this issue with immobilized stationary phases, but a procedure was missing so far to regenerate coated stationary phases from the altered state. Recent results with alcohol mixtures within the PO mode showed that an appropriate order of standard solvents may also be suitable to complete hysteresis. Using an analogous approach, a simple protocol was established to regenerate the original NP retentions on various stationary phases containing amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) chiral selector after the change induced by flushing with 2-propanol or ethanol. The members of a chemically diverse compound set indicated that alterations in retentions and selectivities using different brands and types of ADMPC-based stationary phases can be quite different, but the recovery of the original state was very good for all of them. The proposed protocol eliminates the need of the costly dedication of a chiral column with ADMPC selector to either NP or PO mode. Furthermore, the limits of the alcohol content in the mobile phase compositions where the system is free of hysteresis were determined.

Comparative study on retention behaviour and enantioresolution of basic and neutral structurally unrelated compounds with cellulose-based chiral stationary phases in reversed phase liquid chromatography-mass spectrometry conditions.

A comparative study on the retention behaviour and enantioresolution of 54 structurally unrelated neutral and basic compounds using five commercial cellulose-based chiral stationary phases (CSPs) and hydro-organic mobile phases compatible with MS detection is performed. Four phenylcarbamate-type cellulose CSPs (cellulose tris(3,5-dimethylphenylcarbamate), Cell1; cellulose tris(3-chloro-4-methylphenylcarbamate), Cell2; cellulose tris(4-chloro-3-methylphenylcarbamate), Cell4 and cellulose tris(3,5- dichlorophenylcarbamate), Cell5) and one benzoate-type cellulose CSP (cellulose tris(4-methylbenzoate), Cell3) are assayed. Mobile phases consist of binary mixtures of methanol (30-90% MeOH) or acetonitrile (10-98% ACN) with 5 mM ammonium bicarbonate (pH = 8.0). The existence of reversed phase (RPLC) and hydrophilic interaction liquid chromatography (HILIC) retention behaviour domains is explored. In MeOH/H2O mobile phases, for all compounds and CSPs, the typical RPLC retention behaviour is observed. When using ACN/H2O mobile phases, for all compounds in all CSPs (even in the non-chlorinated CSPs) a U-shaped retention behaviour depending on the ACN/H2O content is observed which indicates the coexistence of the RPLC- (< 80% ACN) and HILIC- (∼80-98% ACN) domains. The magnitude of retention changes in both domains is related to the hydrophobicity of the compound as well as to the nature of the CSP. The study of the effect of the nature and concentration of the organic solvent, as well as the nature of the CSP on the enantioresolution reveals that: (i) the use of MeOH/H2O or ACN/H2O greatly affects the enantioselectivity and enantioresolution degree of the chromatographic systems, being, in general, better the results obtained with ACN/H2O mobile phases. (ii) The ACN-RPLC-domain provides much better enantioresolution than HILIC-domain. (iii) Cell2, especially with ACN/H2O mobile phases, is the CSP that allows baseline enantioresolution for a higher number of compounds. (iv) Phenylcarbamate-type CSPs do not offer clear complementary enantioselectivity to that of Cell2. (v) Cell3 is the only CSP that provides marked complementary enantioselectivity to that of Cell2, almost orthogonal in MeOH/H2O mobile phases.

Artificial neural networks to model the enantioresolution of structurally unrelated neutral and basic compounds with cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase and aqueous-acetonitrile mobile phases.

Artificial neural networks (ANN; feed-forward mode) are used to quantitatively estimate the enantioresolution (Rs) in cellulose tris(3,5-dimethylphenylcarbamate) of chiral molecules from their structural information. To the best of our knowledge, for the first time, a dataset of structurally unrelated compounds is modelled using ANN, attempting to approach a model of general applicability. After setting a strategy compatible with the data complexity and their relatively limited size (56 molecules), by prefixing initial ANN inner weights and the validation and cross-validation subsets, the ANN optimisation based on a novel quality indicator calculated from 9 ANN outputs allows selecting a proper (predictive) ANN architecture (a single hidden layer of 7 neurons) and performing a forward-stepwise feature selection process (8 variables are selected). Such relatively simple ANN offers reasonable good general performance in predicting Rs (e.g. validation plot statistics: mean squared error = 0.047 and R = 0.98 and 0.92, for all or just the validation molecules, respectively). Finally, a study of the relative importance of the selected variables, combining the estimation from two approaches, suggests that the surface tension (positive overall contribution to Rs) and the -NHR groups (negative overall contribution to Rs) are found to be the main variables explaining the enantioresolution in the current conditions.

Characteristic and complementary chiral recognition ability of four recently developed immobilized chiral stationary phases based on amylose and cellulose phenyl carbamates and benzoates.

To date, various immobilized chiral stationary phases (CSPs) have been developed. The immobilized CSPs have opened up possibilities not only maintaining the high chiral recognition abilities as well as corresponding coated ones but also affording high durability to various mobile phase. This report directed to investigate enantioseparation of recently launched four immobilized CSPs with cellulose and amylose backbones under normal phase liquid chromatography conditions. Their chiral recognition abilities were compared with previously developed six immobilized CSPs. Particularly, we focused on the complementarity for chiral recognitions. Among them, amylose tris(3-chloro-5-methylphenylcarbamate) CSP, namely, CHIRALPAK IG, showed notable chiral recognition abilities to various racemates. As expected, the investigated immobilized CSPs represented remarkable durability to wide range of mobile phases, whereas the corresponding coated CSPs could not be run due to the irreversible degradation. Taking advantage of unrestricted solvent compatibility, chiral separation selectivities were improved for some racemates.

Preparation of cellulose derivative bearing bulky 4-(2-benzothienyl)phenylcarbamate substituents as chiral stationary phase for enantioseparation.

A novel cellulose derivative bearing bulky 4-(2-benzothienyl)phenylcarbamate substituents (Cel-1) was readily synthesized by carbamoylation followed by Suzuki-Miyaura coupling reaction. The corresponding coated-type chiral stationary phase (CSP) was prepared on basis of the derivative, and its chiral recognition ability was then evaluated by high-performance liquid chromatography (HPLC). The chiral recognition ability of the cellulose derivative was greatly influenced by introduction of the bulky benzothienyl pendants on the aromatic moieties of phenylcarbamates, compared with its analog with smaller groups. Many racemates, including the metal tris(acetylacetonate) complexes, chiral drug, and the analyte with axial chirality, were sufficiently separated with good enantioselectivities on Cel-1. Some of them were even higher than those on the commercially powerful Chiralcel OD, which is also a coated-type CSP derived from cellulose phenylcarbamate derivative containing smaller 3,5-dimethyl pendants. The 1 H NMR and circular dichroism (CD) spectra of Cel-1 indicated that the obtained derivative possessed a regular higher order structure, and a strong cotton effect was observed within the absorption range of π-conjugated pendant at 350-500 nm. Impressively, the cellulose derivative bearing the bulky 4-(2-benzothienyl)phenylcarbamates exhibited good enantioselective fluorescence quenching behavior to the enantiomer pair of 1-phenylethylamine, probably suggesting its potential for the application as a chiral fluorescent sensor with high efficiency. The combination of the arrangement of bulky π-conjugated benzothienyl pendants on the phenylcarbamate moieties surrounding the helical backbone and the regular higher order structure of the polymer itself probably played a key role for this high chiral fluorescent recognition ability of Cel-1. The interaction sites of bulky 4-(2-benzothienyl)phenylcarbamate pendants in its excited state can exhibit higher enantioselective discrimination via fluorescent response to the chiral compound Q1, whereas the chiral recognition ability of Cel-1 to the same compound in the ground state had no clear improvement.

A novel stability-indicating HPLC method for the determination of enantiomeric purity of eluxadoline drug: Amylose tris(3,5-dichlorophenyl carbamate) stationary phase.

A simple and sensitive stability-indicating chiral HPLC method has been developed and validated per International Conference on Harmonization guidelines for the determination of enantiomeric purity of eluxadoline (Exdl). The impact of different mobile phase compositions and chiral stationary phases on the separation of Exdl enantiomer along with process- and degradation-related impurities has been studied. Homogeneity of Exdl and stable results of Exdl enantiomer in all degraded samples reveal the fact that the proposed method was specific (stability indicating). Amylose tris(3,5-dichlorophenyl carbamate) stationary phase column Chiralpak IE-3 (150 × 4.6 mm, 3 µm) provided better resolution with polar organic solvents than cellulose derivative, crown ether, and zwitterion stationary phases and nonpolar solvents. The mobile phase consisted of acetonitrile, tetrahydrofuran, methanol, butylamine, and acetic acid in the ratio of 500:500:20:2:1.5 (v/v/v/v/v). Isocratic elution was performed at a flow rate of 1.0 mL/min, column temperature of 35°C, injection volume of 10 µL, and UV detection of 240 nm. The United States Pharmacopeia (USP) resolution of the Exdl enantiomer was found to be more than 4.0 within a 65-min run time. Exdl enantiomer detector response linearity over the concentration range of 0.859-4.524 µg/mL was found to be R2  = 0.9985. The limit of detection, limit of quantification, and average percentage recovery values were established as 0.283 µg/mL, 0.859 µg/mL, and 96.0, respectively.

Preparation and application of 3-(methylene-bis(1',4'-phenylene)dicarbamate-2,3-bis(3,5-dimethylphenylcarbamate)-amylose)-2-hydroxylpropoxy-propylsilyl-appended silica particles as chiral stationary phase for HPLC.

3-(Methylene-bis(1',4'-phenylene) dicarbamate-2,3-bis(3,5-dimethylphenylcarbamate)-amylose)-2-hydroxylpropoxy-propylsilyl-appended silica particles (DMP-AM-HPS), a new type of 2, 3-regioselectively substituted amylose-immobilized chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC), have been prepared by treatment of 3-(2,3-dihydroxyl-propoxy)-propylsilyl silica particles with 2,3-bis(3,5-dimethylphenylcarbamate)-amylose and 4,4'-diphenylmethane diisocyanate. The chemical characterization of the bonded particles DMP-AM-HPS has been carried out by elemental analysis and Fourier transform infrared spectroscopic analysis. The chromatographic performance of the DMP-AM-HPS has been evaluated in HPLC under multi-mode conditions including normal phase, reversed phase, and polar organic mobile phase conditions. The DMP-AM-HPS phase has exhibited excellent selectivity in separating enantiomers of a wide range of chiral drug compounds. The result also suggests that unsubstituted C6 hydroxyl groups in the regioselectively substituted amylose not only have important contributions to chiral recognitions and chromatographic separations, but also allow the DMP-AM-HPS to be used as a new type of amylose-immobilized CSP under multi-mode mobile phase conditions in HPLC.