Separation of enantiomers of drugs by capillary electrophoresis. Part 4: hydroxypropyl-gamma-cyclodextrin as chiral solvating agent

Preparation of a novel hydroxypropyl-γ-cyclodextrin functionalized monolith for separation of chiral drugs in capillary electrochromatography

In this study, a novel hydroxypropyl-γ-cyclodextrin (HP-γ-CD) functionalized monolithic capillary column was prepared by one-pot sequential strategy and used for chiral separation in capillary electrochromatography for the first time. In one pot, GMA-HP-γ-CD as functional monomer was allowed to be formed via the ring opening reaction between HP-γ-CD and glycidyl methacrylate (GMA) catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and then copolymerized directly with ethylene dimethacrylate (EDMA) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) in the presence of porogenic solvents via thermally initiated free radical polymerization. The preparation conditions of monoliths were optimized. Enantiomer separations of six chiral drugs including pindolol, clorprenaline, tulobuterol, clenbuterol, propranolol, and tropicamide were achieved on the monolith. Among them, pindolol, clorprenaline, and tropicamide were baseline separated with resolution values of 1.62, 1.73, and 1.55, respectively. The mechanism of enantiomer separation was discussed by comparison of the HP-γ-CD and HP-β-CD functionalized monoliths.

Enantioseparation and determination of orphenadrine in rat plasma and its application to a stereoselective pharmacokinetic study

Chiral separation and stereoselective pharmacokinetics study of orphenadrine enantiomers in rats by HPLC-MS/MS.

Chiral separation of quinolones by liquid chromatography and capillary electrophoresis

The quinolones are derivatives of oxoquinolines and mostly known for their antibacterial and antiviral activities. Many quinolones are chiral compounds having asymmetric centers and important due to their enantioselective biological activities. In order to study the biological activities of quinolone enantiomers, to control the manufacturing of homochiral drugs and to prepare necessary quantities of pure enantiomers for preclinical or clinical trials, respective chiral separation methods are urgently needed. In this context, the present review discusses chromatographic and electrophoretic methods for the enantioseparation of chiral quinolones and provides some useful information on their physical and pharmaceutical properties. The drawbacks of currently used techniques are revealed and ways to overcome them are outlined. Moreover, recommendations for an optimal choice of a separation protocol are given.

[Roles of bacterial and mammalian siderophores in host-pathogen interactions]

Iron is an essential nutriment for almost all forms of life, from bacteria to humans. Despite its key role in living organisms, iron becomes toxic at high concentrations. In the body, to circumvent this toxicity, almost all the intracellular iron is bound to proteins (especially to ferritin, a protein able to bind up to 4000 atoms of iron) and a small proportion (0.2% to 3%) to low molecular weight ligands (less than 2 kDa) constituting a free iron pool able to ensure the traffic of intracellular iron. A number of small molecules (citrate, phosphate, phospholipid, polypeptide) able to chelate iron, with variable affinities, have been known for a long time. In 2010, two teams have identified new mammal endogen chelators able to bind iron with similar chemical properties as bacterial siderophores. Recently, a few publications emphasized that most of the free iron present in the body cells is indeed linked to these siderophores, which play a key role in infected-host protection mechanisms during bacterial infections, through iron homeostasis and oxidative stress regulation.

Comparative enantioseparation of talinolol in aqueous and non-aqueous capillary electrophoresis and study of related selector-selectand interactions by nuclear magnetic resonance spectroscopy

The enantiomers of the chiral β-blocker drug talinolol were separated with two single component sulfated β-cyclodextrin (CD) derivatives, namely heptakis (2,3-di-O-methyl-6-sulfo)-β-CD) (HDMS-β-CD) and heptakis (2,3-di-O-acetyl-6-sulfo)-β-CD) (HDAS-β-CD), in aqueous and non-aqueous capillary electrophoresis (CE). The enantiomer affinity pattern of talinolol toward these two CDs was opposite in both aqueous and non-aqueous CE. However, the enantiomer affinity pattern for a given CD derivative did not change when aqueous buffer was replaced with non-aqueous background electrolyte. The structures of the analyte-selector complexes in both, aqueous and non-aqueous electrolytes were studied using rotating frame nuclear Overhauser effect (ROESY) NMR spectroscopy. Inclusion complex formation between the enantiomers of talinolol and HDAS-β-CD was confirmed in aqueous buffer, while the complex between the enantiomers of talinolol and HDMS-β-CD was of the external type. The complex of the talinolol enantiomers with HDAS-β-CD in non-aqueous electrolyte was also of the external type. In spite of external complex formation excellent separation of the enantiomers was observed in non-aqueous CE.

The role of cyclodextrins in chiral capillary electrophoresis

The members of the enantiomeric pairs frequently show rather different biological effects, so their chiral selective synthesis, pharmacological studies and analysis are necessary. CE has unique advantages in chiral analysis. The most frequently used chiral selectors are CDs in this field. This paper gives a short view on the advantages on CE in direct chiral separations, emphasizing the role of CDs. The reason for the broad selectivity spectra of CDs is discussed in detail. The physical background of chiral selective separations is briefly shown in CE. Their interaction mechanisms are shortly defined. The general trend of their use is statistically evaluated. Most frequently used CDs and CD derivatives are characterized. Advantages of ionizable CDs and single-isomer derivatives are shown. The general trend of their use is established.

Enantioseparation in capillary electrophoresis using 2-O-(2-hydroxybutyl)-β-CD as a chiral selector

The resolving ability of 2-O-(2-hydroxybutyl)-beta-CD (HB-beta-CD) with different degrees of substitution (DS = 2.9 and 4.0) as a chiral selector in CZE is reported in this work. Fourteen chiral drugs belonging to different classes of compounds of pharmaceutical interest such as beta-agonists, antifungal agents, ageneric agents, etc., were resolved. The effects of the DS of HB-beta-CD on separations were also investigated. The chiral resolution (R(s)) was strongly influenced by the concentrations of the CD derivative, the BGE, and the pH of the BGE. Under the conditions of 50 mmol/L Tris-phosphate buffer at pH 2.5 containing 5 mmol/L HB-beta-CD, all 14 analytes were separated. The very low concentration necessary to obtain separation was particularly impressive. The DS had a significant effect on the resolution of the chiral drugs and the ionic strength of the separation media; hence, the use of a well-characterized CD derivative is crucial.

Simultaneous enantioselective separation of azelastine and three of its metabolites for the investigation of the enantiomeric metabolism in rats. I. Liquid chromatography-ionspray tandem mass spectrometry and electrokinetic capillary chromatography

Enantioselective separation methods and the enantioselective determination of the anti-allergic drug azelastine and of three of its main phase I metabolites in a biological matrix underwent chromatographic and electrophoretic investigations. An enantioselective assay of a coupling of HPLC using a beta-cyclodextrin chiral stationary phase to ionspray tandem mass spectrometry is presented. Additionally, this assay is compared to another enantioselective assay using electrokinetic capillary chromatography with beta-cyclodextrin and carboxymethyl-beta-cyclodextrin in polyacrylamide-coated capillaries. For capillary electrophoresis (CE) the importance of polyacrylamide coating for the validation of this separation method is highlighted. Extracted rat plasma samples of enantioselective metabolism studies were measured by both validated assays. Differences in the pharmacokinetics and pharmacodynamics were evaluated for the main substance azelastine and its main metabolite demethylazelastine. So, a first hint about the enantioselectivity of biotransformation of azelastine in rats was seen after oral application of either enantiomer or the racemate to rats.

Enantioseparation of erythro-mefloquine and its analogues in capillary electrophoresis

The enantioseparations of the chiral antimalaria drug (R,S)-erythro-alpha-(2-piperidyl)-2,8-bis(trifluoromethyl)4-quinolinemethanol (erythro-mefloquine, erythro-MQ) and its analogues were studied by capillary electrophoresis (CE) using cyclodextrins (CDs) as chiral selectors. The emphasis was put on the enantiomer affinity pattern of MQ towards different CDs as well as on simultaneous enantioseparations of erythro-MQ and its structural analogues. All three native CDs resolved the enantiomers of erythro-MQ and the enantiomer affinity pattern was the same, i.e. (+)-erythro-MQ was the more tightly bond enantiomer. However, the affinity pattern of erythro-MQ enantiomers was opposite in the case of heptakis-(2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD), heptakis-(2,3-di-O-methyl-6-sulfo)-beta-CD (HDMS-beta-CD), heptakis-(3-O-methyl-2,6-di-O-sulfo)-beta-CD (HMdiSu-beta-CD) and randomly sulfated beta-CD (SU-beta-CD). Randomly hydroxyalkylated and acetylated derivatives of CDs appeared to be suitable chiral selectors for simultaneous enantioseparation of erythro-MQ and its analogues.

Stereoselective determination of ofloxacin and its metabolites in human urine by capillary electrophoresis using laser-induced fluorescence detection

A capillary electrophoresis method for the simultaneous separation and enantioseparation of the antibacterial drug ofloxacin and its metabolites desmethyl ofloxacin and ofloxacin N-oxide in human urine has been developed and validated. Enantioseparation was achieved by adding sulfobutyl beta-cyclodextrin to the running buffer. The detection of the analytes was performed by laser-induced fluorescence (LIF) detection using a HeCd-laser with an excitation wavelength of 325 nm. In comparison with conventional UV detection, LIF detection provides higher sensitivity and selectivity. The separation can be performed after direct injection of urine into the capillary without any sample preparation, because no matrix compounds interfere with the assay. Additionally, the high sensitivity of this method allows the quantification of the very low concentrations of enantiomers of both metabolites. The limit of quantification was 250 ng/ml for ofloxacin enantiomers and 100 ng/ml for each metabolites' enantiomers. This method was applied to the analysis of human urine samples collected from a volunteer after oral administration of 200 mg of (+/-)-ofloxacin to elucidate stereoselective differences in the formation and excretion of the metabolites. It could be demonstrated that the renal excretion of the S-configured metabolites, especially S-desmethyl ofloxacin, within the first 20 h after dosage, is significantly lower than that of the R-enantiomers.

New single-isomer chiral selector for capillary electrophoresis: the highly water-soluble heptakis(2-N,N-dimethylcarbamoyl)-beta-cyclodextrin

A new single isomer beta-cyclodextrin, the heptakis(2-N,N-dimethylcarbamoyl)-beta-cyclodextrin (HDMC-beta-CD), has been synthesized and spectroscopically characterized. The outstanding feature of the new neutral beta-CD derivatives is their high solubility in water (>100 mM) and methanol. The resolution of chiral drugs can take advantage of this property. The resolution power of the new HDMC-beta-CD is demonstrated by a selection of acidic and basic compounds using standard conditions.

Separation of drug enantiomers by capillary electrophoresis in the presence of neutral cyclodextrins

This is a selected review, highlighting our results obtained in an extended screening program ("The German-Chinese Drug Screening Program"), with a focus on a set of original data obtained with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD) as the chiral solvating agent (CSA). The enantioseparation of 86 drugs by capillary zone electrophoresis in the presence of this CSA was successful for 47 drugs. The migration separation factors (alpham) and the migration retardation factors (Rm) were compared with those found for native beta-cyclodextrin (beta-CD). The patterns thus obtained were also compared with those observed for hexakis(2,3,6-tri-O-methyl)-alpha-CD (TM-alpha-CD) and octakis(2,3,6-tri-O-methyl)-gamma-CD (TM-gamma-CD), respectively. From the statistical data, it can be concluded that there is a remarkable influence of the analyte structure on the electrophoretic data. A substructure 4H was found in the analyte structure that has a significant influence on the analytes' behaviour. Thus, analytes bearing the substructure 4H do not only have a strong affinity to the CDs but also a high rate of success of chiral separation in all systems reviewed. In light of this, the different ring sizes of native cyclodextrins (alpha-, beta- and gamma-CD) readily explain their behaviour towards a limited test set of chiral drugs. Sterical considerations point to the significance of side-on-binding versus inclusion in the cavity of the host. In addition to the findings from the screening program, numerous references to the literature are given.

Chiral separations in capillary electrophoresis

The marked increase in the number of communications on the utilization of electrophoresis for practical chiral separations within the last three years is the most evident, and the most important fact. It reveals that the basic period of intensive research in the field is finished. The search for chiral selectors discriminating racemates in a reasonably analytical manner and the study of both the mechanism and physicochemical aspects of the chiral discrimination process were the main features of that period. Here, we review the state of the art in the field and state the references of the related literature up to the end of 1998.

Study of enantioselective interactions between chiral drugs and serum albumin by capillary electrophoresis

The separation of the enantiomers of three basic drugs, i.e., ofloxacin, propranolol and verapamil, was achieved by affinity capillary electrophoresis (ACE), with human serum albumin (HSA) and bovine serum albumin (BSA) as chiral selectors in phosphate buffer at pH 7.4. Ofloxacin was only separated in the presence of BSA, and verapamil only with HSA, while propranolol was separated with either HSA or BSA. The effects of protein concentration and column wall adsorption on the degree of separation were investigated. Two displacers, ketoprofen and warfarin, respectively, when added to the protein containing buffer, both showed significant effects on the separation behavior. From these data it was argued that verapamil may bind to HSA at both locations known, the warfarin binding site (I) and the ketoprofen binding site (II). While with BSA, binding of ofloxacin may also occur at site I, the preferential binding site for propanolol remains controversial. A drug-drug interaction between propranolol and ketoprofen due to opposite charges was concluded from the increase in migration time in BSA solution. The unbound concentration of verapamil enantiomers in solution in the presence of HSA, as estimated from CD-modified capillary zone electrophoresis, was triggered not only by the HSA concentration but also by the coadditive concentration.

Separation of drugs by capillary electrophoresis, Part 10. Permethyl-alpha-cyclodextrin as chiral solvating agent

Following the German-Chinese Drug Screening Program, 86 racemic drugs were investigated in capillary zone electrophoresis in the presence of the chiral solvating agent (CSA) hexakis-(2,3,6-tri-O-methyl)-alpha-cyclodextrin (TM-alpha-CD). Of the 86 drugs, 23 were separated into enantiomeric pairs. A comparison of the migration separation factors (alpha(m)) and the migration retardation factors (Rm) with previously published data for native alpha-CD revealed that the 'upper-rim' hydroxyl groups do not necessarily facilitate the recognition of the drug enantiomers by the chiral host. In contrast, an overall increase in affinity for the permethylated host led to a higher rate of successful enantiomer separations. A key substructure (4H) was identified in the analyte structure domain, with a crucial influence on the behavior of a particular drug.

Use of cyclodextrins in capillary electrophoresis: resolution of tramadol enantiomers

Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol. Both uncoated and polyacrylamide-coated capillaries were tested for method optimization using either negatively charged or native cyclodextrins (CD) added to the background electrolyte (BGE). The resolution was strongly influenced by the CD type and concentration as well as by the pH and the concentration of the BGE. Among the CDs tested, carboxymethylated-beta-cyclodextrin allowed the baseline separation of tramadol enantiomers. After the method was optimized, it was validated in a coated capillary for enantiomeric analysis of tramadol enantiomers in pharmaceutical formulation, including specificity and elution order, linearity, accuracy and precision, determination of limit of detection (LOD) and quantification (LOQ), enantiomeric purity linearity, freedom from interference, and stability of sample solutions. Precision at the target concentration was less than 2%, with an accuracy higher than 99%. Furthermore, the method was able to detect 0.3% and to quantify 1% of the minor enantiomer in the presence of the major one at the target value.