Enantioseparation Of Analytes Research Articles

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.

Enantioseparation of basic drugs by reverse phase high-performance liquid chromatography system using carboxymethyl-β-cyclodextrin as chiral mobile phase additive.

A rapid and efficient method was developed for enantioseparation of basic drugs, using carboxymethyl-β-cyclodextrin (CM-β-CD) as chiral mobile phase additive, rather than involving costly chiral column in high-performance liquid chromatography (HPLC) system. Four of the six basic drug enantiomers investigated were successfully separated. The highest resolution reaches 2.15 for threo-(1S,2S)-2-amino-l-p-nitrophenyl-1,3-propanediol. The effects of the organic modifier, pH value, concentration of chiral additive, column temperature, and flow rate of mobile phase on the enantioseparation of analytes were researched. The apparent formation constants of inclusion and the thermodynamic parameters were evaluated to explain the mechanism of chiral recognition.

Simultaneous enantiomeric determination of multiple triazole fungicides in fruits and vegetables by chiral liquid chromatography/tandem mass spectrometry on a bridged bis(β-cyclodextrin)-bonded chiral stationary phase

A LC-MS/MS method for simultaneous determination of twelve triazole enantiomers (hexaconazole, tebuconazole, triticonazole, flutriafol, diniconazole, paclobutrazol) in six fruits and vegetables was established based on a stable and self-made bridged bis(β-cyclodextrin)-bonded chiral stationary phase. Simultaneous enantio-separation of multiple analytes was achieved with resolution ca. 1.67–2.14. Magnetically assisted QuECHERS was used to simplify and optimize sample pre-treatment. The new method was validated (accuracy, precision, matrix effect, etc.). Good linearity (0.5–20 μg/L, R2 > 0.99) and high recoveries (76.1–103.4%) based on intra- and inter-day relative standard deviation (RSDs) (2.6–11.9%), were obtained. Furthermore, a total of 90 samples were analyzed using this method and enantiomeric fractions (EF) for tebuconazole in strawberry and cucumber (0.63 and 0.43, respectively) were determined as well as 0.57 for flutriafol in tomato. This high-throughput detection method supported a convenient enantiomeric monitoring for chiral pesticides in fruits and vegetables.

Approaching over 10000-fold sensitivity increase in chiral capillary electrophoresis: Cation-selective exhaustive injection and sweeping cyclodextrin-modified micellar electrokinetic chromatography.

A novel and simple method that combines an online concentration technique with an enantioseparation technique for capillary electrophoresis-namely, cation-selective exhaustive injection and sweeping cyclodextrin-modified micellar electrokinetic chromatography (CSEI-sweeping CD-modified MEKC)-realizes the effective enantioseparation of cationic analytes while keeping a significant increase of detection sensitivity. This technique consists of a slight modification of the basic CSEI-sweeping MEKC. The main idea is to simply add an anionic CD as a chiral selector into the micellar buffer including sodium dodecyl sulfate, but not to change any other buffers in order to preserve the online concentration mechanism. When applied to analysis of the street drug, methamphetamine, the method achieved not only a baseline enantioseparation but also limits of detection (LODs; S/N = 3) of 70-90 pg/mL (ppt) for each isomer. This translates to a more than 10000-fold improvement compared to the LODs by the usual injection method. The present technique, which was made from a slight modification of CSEI-sweeping MEKC, would give an attractive approach that is applicable to almost any analytes for which CSEI-sweeping MEKC is applicable; all that is required is the selection of an appropriate anionic CD to be added to the micellar buffer.

Combined use of cyclofructans and an amino acid ester-based ionic liquid for the enantioseparation of huperzine A and coumarin derivatives in CE.

Cyclofructans (CFs) and their derivatives have recently been proven to be efficient chiral selectors (CSs) for the enantioseparation of several analytes in CE, HPLC, and GC. In this study, the chiral separation ability of a number of native and derivatized CFs was examined in CE. Particularly, six different CFs, with different derivatization groups and cavity sizes [native CF-6 and CF-7, isopropyl cyclofructan-6 (IPCF-6), IPCF-7, sulfated cyclofructan-6 (SCF-6), and SCF-7] were used as CSs for the enantioseparation of huperzine A, warfarin, and coumachlor. Almost all of the examined CFs, except from SCF-6 & -7, demonstrated relatively low and sometimes no chiral separation ability for huperzine A. In an effort to improve both resolution and efficiency, the chiral ionic liquid D-Alanine tert butyl ester lactate (D-AlaC4Lac) was added into the BGE. In most of the cases, the combination of CF with D-AlaC4Lac resulted in an improvement in peak efficiency and/or resolution. When CF-6 was utilized with D-AlaC4Lac, a resolution of 1.4 was obtained, while the use of IPCF-6/D-AlaC4Lac provided a baseline enantioseparation. Although the combination of SCF-7 and 40 mM D-AlaC4Lac did not affect resolution, it dramatically increased peak efficiency from 24,000 to 117,000. In the case of warfarin and coumachlor, IPCF-6 and IPCF-7 proved to be the most effective CSs. It is, therefore, concluded that the size of the cavity and the CF derivatization are the key parameters for the chiral separation capability. It is also clear from this study that D-AlaC4Lac is necessary for improved peak efficiencies and resolutions.

Clarithromycin as a chiral selector for enantioseparation of basic compounds in nonaqueous capillary electrophoresis.

The first use of macrolide antibiotic clarithromycin (CLM) in nonaqueous media for enantioseparation (partial or baseline) of the following compounds: alprenolol, atenolol, metoprolol, clenbuterol, methoxyphenamine, pindolol, propranolol, sotalol, synephrine, labetalol, and fenoterol is reported. Each analysis took less than 15 min. To find optimal separation conditions, some properties of CLM (adsorption, solubility), as well as the effect of experimental parameters on the enantioseparation of analytes (background electrolyte composition, chiral selector concentration, temperature, and applied voltage) were studied. The best chiral resolution was achieved in methanolic solution of 100 mM citric acid, 10mM NaOH, 240-300 mM H3 BO3 , and 60-75 mM CLM. Using the proposed procedure, adsorption of CLM on the capillary wall was negligible and the repeatability of the migration times (RSD) was as good as 1.6%. For the analysis of propranolol, the linearity was achieved in the concentration range 2.5 × 10(-2) - 3.0 × 10(-1) mg/mL with the LODs (3 × S/N) being equal 2.6 × 10(-3) mg/mL and 2.8 × 10(-3) mg/mL for the first and the second enantiomers, respectively. Linear range for metoprolol enantiomers was 1.0 × 10(-2) -1.6 × 10(-1) mg/mL. The LODs (3 × S/N) were determined as 2.8 × 10(-3) and 3.0 × 10(-3) mg/mL for the first and the second enantiomers, respectively.

(S)‐Naproxen as a platform to develop chiral derivatizing reagent for reversed‐phase high‐performance liquid chromatographic enantioseparation of analytes having a carbonyl functional group

(S)-Naproxen was used to synthesize a chiral reagent, (S)-2-(6-methoxynaphthalen-2-yl)propanehydrazide, by itsreaction with hydrazine hydrate in the presence of dicyclohexylcarbodiimide as coupling agent. The reagent was characterized and its chiral purity was established. It was used as a chiral derivatizing reagent for the synthesis of hydrazone diastereomers, under microwave irradiation, of certain chiral aldehydes and ketones. The respective diastereomers were separated by reversed-phase high-performance liquid chromatography using a binary solvent combination containing trifluoroacetic acid. The diastereomers were detected at 231 nm. The method was validated for accuracy, precision, and limit of detection (LOD). For a series of hydrazones the LOD was found to be in the range 1.62-1.65 pmol/mL.

Enantiomeric separation in high-performance liquid chromatography using novel β-cyclodextrin derivatives modified by R-configuration groups as chiral stationary phases

Two new chiral stationary phases (CSP) were successfully prepared through bonding β-cyclodextrin (CD) derivatives modified by R-configuration groups (R-CPGCD, R-HMPGCD) to silica gel. Nineteen chiral nitro aromatic alcohol derivatives were separated under the polar organic and the reversed phase modes. Better enantioseparation was obtained in the reversed phase mode. The resolution values of the analytes ranged from 1.98 to 7.57 and from 2.19 to 8.14 on R-CPGCD and R-HMPGCD CSPs, respectively, using a mobile phase composed of methanol/water (v/v, 40/60). Better enantioseparation was obtained on R-HMPGCD CSP than on R-CPGCD CSP because of stronger hydrogen bonding and π–π interactions between the substituents on the cyclodextrin derivatives and the analytes. For different analytes, the increasing electronic density of the benzene ring was found to be favorable to the enantioseparation of the test analytes. The thermodynamic parameters showed that the enantioseparation of analytes was enthalpy-controlled and a lower temperature aided the enantiomeric separation of the solutes on the two CSPs. MD simulations were used to investigate the recognition mechanism between the chiral selectors and the analyte using R-, S-2-naphthalenemethanol and R-CPGCD and R-HMPGCD complexes as examples. S-2-naphthalenemethanol had the stronger interactions with R-CPGCD and R-HMPGCD than the R-isomer. The substituent derivatized on R-CPGCD and the cyclodextrin cavity contributed to the discrimination of the S-isomer, but only the derivatized group on R-HMPGCD was found to play a major role in separating prosess. In addition, the larger free energy deviation of the R- and S-isomers in the R-HMPGCD system brought about a higher resolution value (Rs=8.14).

Novel β-cyclodextrin derivative functionalized polymethacrylate-based monolithic columns for enantioselective separation of ibuprofen and naproxen enantiomers in capillary electrochromatography

A novel enantioselective polymethacrylate-based monolithic column for capillary electrochromatography was prepared by ring-opening reaction of epoxy groups from poly(glycidyl methacrylate- co-ethylene dimethacrylate) monolith with a novel β-cyclodextrin derivative bearing 4-dimethylamino-1,8-naphthalimide functionalities. Conditions for the ring-opening reaction with respect to different reaction parameters were thoroughly optimized to obtain high electroosmotic flow, separation efficiency and enantioselectivity for the analytes. The nonaqueous mobile phase composition regarding acetonitrile–methanol ratio and the concentration of electrolyte were examined to manipulate the hydrophobic inclusion and anion-exchange interaction between the analytes and chiral stationary phase. It was observed that in addition to β-cyclodextrin cavity, the electrostatic interaction exhibited pronounced influence on the enantioseparation of acidic analytes. Acidic enantiomers (ibuprofen and naproxen) could be separated with separation factor ( α) values up to 1.08 and a maximum separation efficiency of 86 000 plates/m could be achieved.

The effect of acidic and basic additives on the enantioseparation of basic drugs using polysaccharide‐based chiral stationary phases

The enantioseparation of nine commercially available basic drugs was achieved on polysaccharide-based chiral stationary phases with the acidic additive ethanesulfonic acid and the basic additive butylamine. Seven different commercially available CSPs were used for the study (AD, AS, OD, OJ, OG, OB, and OC). Mobile phase additives have been proven to be essential in obtaining satisfactory enantio-resolution in terms of both efficiency and selectivity. Significantly improved selectivities were obtained for the basic probe drugs with the acidic additive, ethanesulfonic acid, rather than the basic additive, butylamine. This is best seen with Chiralpak AS CSP. No enantioseparation for the nine drugs was observed when butylamine was used as an additive; however, satisfactory enantioseparation for the nine drugs was achieved using ethanesulfonic acid. Higher column efficiencies were observed with the acidic additive, especially when isopropanol was used as a modifier. Higher sensitivity was also achieved with ethanesulfonic acid because of the significantly lower background at the UV detection wavelength. The acidic additive was demonstrated to be superior to the basic additive for the enantioseparation of basic drugs using seven different polysaccharide-based CSPs. These results are counterintuitive to the common "rule of thumb" in enantioseparation that states acidic additives work best for acidic analytes and basic additives work best for basic analytes. The beneficial effects of acidic additive in enantioseparations observed in this study could significantly improve the applicability of polysaccharide-based CSPs for the enantioseparation of basic analytes.

Analytical and semipreparative high performance liquid chromatography enantioseparation of new substituted 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-(1 H)-pyrazoles on polysaccharide-based chiral stationary phases in normal-phase, polar organic and reversed-phase conditions

The direct HPLC enantioseparation of five pairs of new chiral pyrazole derivatives on coated cellulose- and amylose-based chiral stationary phases (Chiralpak AD, Chiralcel OJ and Chiralcel OJ-RH) and new immobilised amylose-based Chiralpak IA CSP was performed. Very high enantioselectivity factor ( α) values were achieved in polar organic and reversed-phase conditions by using OJ-RH as CSP. Chiralpak IA exhibited an excellent chiral resolving ability in normal-phase mode and it allowed the enantioseparation of analytes investigated with resolution factors (Rs) >20. Due to its bonded nature, it was successfully employed at analytical and semipreparative scale in combination with normal-phase eluents containing “non-standards” solvents such as acetone.

Enantioselective separation in capillary electrophoresis using a novel mono-6 A-propylammonium-β-cyclodextrin as chiral selector

The chiral resolving ability of a novel single-isomer cationic β-cyclodextrin (CD), mono-6 A-propylammonium-6 A-deoxy-β-cyclodextrin chloride (PrAMCD), as a chiral selector in capillary electrophoresis (CE) is reported in this work for the enantioseparation of hydroxy, carboxylic acids and amphoteric analytes. The effect of chiral selector concentration on the resolution was studied. Good resolutions were achieved for hydroxy acids. Optimum resolutions were obtained even at 3.5 mM CD concentration for carboxylic acids. The electrophoretic method showed good linearity and reproducibility in terms of migration times and peak areas, which should make it suitable for routine analysis. In addition, baseline chiral separation of a six-acid mixture was achieved within 20 min. PrAMCD proved to be an effective chiral selector for acidic analytes.

Enantioseparation of acidic enantiomers in capillary electrophoresis using a novel single-isomer of positively charged β-cyclodextrin: Mono-6 A- N- pentylammonium-6 A-deoxy-β-cyclodextrin chloride

The new single-isomer of positively charged β-cyclodextrin, mono-6 A- N-pentylammonium-6 A-deoxy-β-cyclodextrin chloride (PeAM-β-CD), was employed for the first time for the enantioseparation of anionic and ampholytic analytes by capillary electrophoresis (CE). The synthesis and characterization of PeAM-β-CD were reported. The effect of background electrolyte (BGE) pH and selector concentration on the enantioseparation was investigated. Good separation was obtained at low BGE pH (ca. 5.0–6.0). The effective mobilities of all analytes were found to decrease with increasing CD concentration. PeAM-β-CD proved to be an effective chiral selector for most studied anionic analytes.

Comparative study on the enantioseparation of glutethimide using dual cyclodextrin systems and cyclodextrin modified MEKC in capillary electrophoresis

In order to critically evaluate the potential of dual cyclodextrin (CD) systems in CE, enantioseparation of the neutral chiral analyte glutethimide (GT) was performed using: (a) charged CDs; (b) combinations of charged and neutral CDs (dual CD systems), and (c) CD-modified micellar electrokinetic chromatography (CD-MECK). The results of this comparative study indicate that properly designed dual CD systems may in certain cases represent a valuable alternative to CD-MEKC and electrokinetic chromatography involving charged CDs for enantioseparation of neutral analytes.

Enantioseparation of anionic analytes by non-aqueous capillary electrophoresis using quinine and quinidine derivatives as chiral counter-ions

A non-aqueous capillary electrophoretic method developed for the enantioseparation of N-protected amino acids has been applied to the investigation of five new quinine and quinidine derivatives as chiral selectors: 1-adamantyl carbamoylated quinine, 3,4-dichlorophenyl carbamoylated quinidine, allyl carbamoylated dihydroquinine, allyl carbamoylated dihydroquinidine and 1-methyl quininium iodide. The composition of the background electrolyte was 12.5 m M ammonia, 100 m M octanoic acid in an ethanol–methanol (60:40 v/v) mixture containing a 10 m M concentration of the chiral selector. Under these conditions, the enantioseparation of a series of various benzoyl, 3,5-dinitrobenzoyl and 3,5-dinitrobenzyloxycarbonyl amino acid derivatives was studied with respect to selectand–selector relationship and enantioselectivity.