Enantioseparation of phenothiazines in CD-modified CZE using single isomer sulfated CD as a chiral selector

Enantioseparations of five chiral phenothiazines in CD-modified CZE using the single isomer sulfate-substituted beta-CD (heptakis(2,3-dihydroxy-6-O-sulfo)-beta-CD, SI-S-beta-CD) and dual CD systems consisting of SI-S-beta-CD and a neutral CD as chiral selectors in a citrate buffer at pH 3.0 were investigated. The results indicate that SI-S-beta-CD is an excellent chiral selector for enantioseparation of promethazine. The enantiomers of trimeprazine were well separated, while those of ethopropazine could also be baseline-resolved with SI-S-beta-CD. With dual CD systems, especially with hydroxypropyl-beta-CD (HP-beta-CD) as neutral CD, the enantioselectivity of thioridazine and ethopropazine was considerably enhanced. Effective enantioseparation of phenothiazines, except for methotrimeprazine, could thus be favorably and simultaneously achieved. Moreover, reversal of the enantiomer migration order of ethopropazine and thioridazine occurred by varying the concentration of gamma-CD in the presence of SI-S-beta-CD. These phenomena may be attributable to the opposite effects of sulfated beta-CD and gamma-CD on the mobility of the enantiomers of ethopropazine and of thioridazine. Comparative studies on the enantioseparations of phenothiazines with single CD and dual CD systems containing SI-S-beta-CD and randomly sulfate-substituted beta-CD (MI-S-beta-CD) were made.     

Sample stacking in laboratory-on-a-chip devices

In this study, enantioseparations of five phenothiazines, including promethazine, ethopropazine, trimeprazine, methotrimeprazine, and thioridazine, in cyclodextrin (CD)-modified capillary zone electrophoresis were investigated using a phosphate buffer (40 mM) at pH 3.0. We focussed on the separation of phenothiazines with the use of CDs at low concentrations. Three different CDs, including β-CD, hydroxypropyl-β-CD (HP-β-CD) and γ-CD, were chosen as chiral selectors. The results indicate that effective enantioseparation of phenothiazines, except for methotrimeprazine, is simultaneously achievable with addition of γ-CD at a concentration of 2.5–6.0 mM. The enantiomers of ethopropazine and trimeprazine are effectively separated with addition of HP-β-CD at low concentrations, in the range 0.4–6.0 mM, whereas those of promethazine and trimeprazine are baseline resolved with β-CD at much lower concentrations (0.02–3.0 mM) than with HP-β-CD. The results also confirm that the separation window is greatly enlarged at low CD concentrations. Moreover, the drastic variations of the electrophoretic mobility of phenothiazines as a function of CD concentration reveal that phenothiazines interact very strongly with CDs in the order γ-CD相似文献   

Enantioseparation of phenothiazines in cyclodextrin-modified micellar electrokinetic chromatography

In this study, enantioseparations of five phenothiazines in cyclodextrin (CD)-modified micellar electrokinetic chromatography (MEKC) were investigated using a citrate buffer containing tetradecyltrimethylammonium bromide (TTAB) as a cationic surfactant at low pH. Beta-cyclodextrin (beta-CD) and hydroxylpropyl-beta-CD (HP-beta-CD) were selected as chiral selectors. The results indicate that the separation window is greatly enlarged by beta-CD concentration and that the separability and selectivity of phenothiazines are remarkably influenced by the concentrations of both beta-CD and TTAB, as well as buffer pH. The interaction of thioridazine with beta-CDs is considerably reduced in the presence of TTAB micelles due to competitive complexation of thioridazine with TTAB micelles, which is pH-dependent. As a result, effective enantioseparation of thioridazine is simultaneously achievable with that of trimeprazine and promethazine or ethopropazine in MEKC with addition of either beta-CD or HP-beta-CD, respectively, to a micellar citrate buffer containing TTAB at pH 3.5. Better enantioresolution of thioridazine in MEKC than in capillary zone electrophoresis can be obtained.     

Enantioseparations of hydrobenzoin and structurally related compounds in capillary zone electrophoresis using heptakis(2,3-dihydroxy-6-O-sulfo)-beta-cyclodextrin as chiral selector and enantiomer migration reversal of hydrobenzoin with a dual cyclodextrin system in the presence of borate complexation

We investigated the enantioseparations of racemic hydrobenzoin, together with benzoin and benzoin methyl ether, in capillary electrophoresis (CE) using the single-isomer heptakis(2,3-dihydroxy-6-O-sulfo)-beta-cyclodextrin (SI-S-beta-CD) as a chiral selector in the presence and absence of borate complexation and enantiomer migration reversal of hydrobenzoin with a dual CD system consisting of SI-S-beta-CD and beta-CD in the presence of borate complexation at pH 9.0 in a borate buffer. The enantioselectivity of hydrobenzoin increased remarkably with increasing SI-S-beta-CD concentration and the enantioseparation depended on CD complexation between hydrobenzoin-borate and SI-S-beta-CD. The (S,S)-enantiomer of hydrobenzoin-borate complexes interacted more strongly than the (R,R)-enantiomer with SI-S-beta-CD. The enantiomers of hydrobenzoin could be baseline-resolved in the presence of SI-S-beta-CD at a concentration as low as 0.1% w/v, whereas the three test analytes were simultaneously enantioseparated with addition of 0.3% w/v SI-S-beta-CD or at concentrations >2.0% w/v in a borate buffer and 0.5% w/v in a phosphate background electrolyte at pH 9.0. Compared with the results obtained previously using randomly sulfated beta-CD (MI-S-beta-CD) in a borate buffer, enantioseparation of these three benzoin compounds is more advantageously aided by SI-S-beta-CD as the chiral selector. The enantioselectivity of hydrobenzoin depended greatly on the degree of substitution of sulfated beta-CD. Moreover, binding constants of the enantiomers of benzoin compounds to SI-S-beta-CD and those of hydrobenzoin-borate complexes to SI-S-beta-CD were evaluated for a better understanding of the role of CD complexation in the enantioseparation and chiral recognition. Enantiomer migration reversal of hydrobenzoin could be observed by varying the concentration of beta-CD, while keeping SI-S-beta-CD at a relatively low concentration. SI-S-beta-CD and beta-CD showed the same chiral recognition pattern but they exhibited opposite effects on the mobility of the enantiomers.     

Enantioseparation of phenothiazines in cyclodextrin-modified capillary zone electrophoresis: reversal of migration order

Enantioseparations of phenothiazines with gamma-cyclodextrin (gamma-CD) as a chiral selector were investigated using citrate and phosphate buffer electrolytes at pH 3.0. Reversal of the enantiomer migration order of promethazine, ethopropazine, and trimeprazine was observed by varying gamma-CD concentration in the range of 5-9 mM, 2.5-4.5 mM and 1.5-2.8 mM, respectively, using 100 mM citrate buffer at pH 3.0. As in the case of beta-CD, the (+)-enantiomers of phenothiazines possess greater binding strength to gamma-CD than the (-)-enantiomers. The evaluation of the binding constants and limiting mobility of the complexes formed between the enantiomers of phenothiazines and gamma-CD reveals that the binding strength of phenothiazines to gamma-CD and the differences in the binding constants and limiting mobility of the complexes are responsible for the enantiomer migration reversal. Both the binding constants and limiting mobility of the complexes between the (+)-enantiomers of phenothiazine and gamma-CD are greater than those of the corresponding (-)-enantiomers in a citrate buffer, while the binding constants of the complexes primarily determined the migration order of the enantiomers in a phosphate buffer. Compared with the results obtained using a phosphate buffer, we may conclude that citrate buffer which involves competitive complexation with chiral selector plays a significant role in the enantiomer migration reversal.     

Enantioseparation of chiral benzimidazole derivatives by electrokinetic chromatography using sulfated cyclodextrins

Baseline separation of 18 new substituted benzimidazole derivatives, potent AMP‐activated protein kinase (AMPK) activators, with one chiral center, was achieved by CD‐EKC using sulfated and highly sulfated CDs (SCDs and HS‐CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The SCDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times around 6 min using 25 mM phosphate buffer at pH 2.5 containing either β‐S‐CD, HS‐β‐CD, HS‐γ‐CD (3 or 4% w/v) at 25°C, with a voltage of 20 kV. The apparent association constants of the inclusion complexes were calculated. The study of the solute structure‐enantioseparation relationships seems to show the high contribution of the interactions between the solutes phenyl ring and the CDs to the enantiorecognition process. The optimized method was briefly validated (LOD less than 1%) and the purity of enantiomers of compound 3 was determined. The enantiomer migration shows reversal order depending on the kind of CD.     

Evaluation of enantioselective binding of basic drugs to plasma by ACE

The present paper deals with the evaluation of the stereoselective binding of antihistamines (brompheniramine, chlorpheniramine, hydroxyzine, orphenadrine and phenindamine), phenothiazines (promethazine and trimeprazine) and a local anesthetic (bupivacaine) to human plasma proteins. Since all of them are drugs highly bound to proteins, a methodology to determine the bound fraction of each drug enantiomer was proposed. This methodology includes the incubation of samples containing plasma and racemic drug, ultrafiltration of the mixture and the chiral separation of enantiomers in the bound drug fraction using affinity EKC (AEKC)-partial filling technique and HSA as chiral selector. The results shown in this paper represent the first evidence of the enantioselective binding of some antihistamines such as brompheniramine, hydroxyzine, orphenadrine and phenindamine and the phenothiazines, promethazine and trimeprazine, to human plasma proteins. The binding of phenindamine to plasma presented the highest enantioselectivity (ES) (ES = 2.5) followed by trimeprazine (ES = 1.5) and promethazine (ES = 1.4).     

The Use of Dual Cyclodextrin Chiral Selector Systems in the Enantioseparation of Pharmaceuticals by Capillary Electrophoresis: An Overview

Cyclodextrin (CD) derivatives are the most efficient and frequently used chiral selectors (CSs) in capillary electrophoresis (CE). There are situations when the use of a single CD as CS is not enough to obtain efficient chiral discrimination of the enantiomers; in these cases, sometimes this problem can be resolved using a dual CD system. The use of dual CD systems can often dramatically enhance enantioseparation selectivity and can be applied for the separation of many analytes of pharmaceutical interest for which enantioseparation by CE with another CS systems can be problematic. Usually in a dual CD system an anionic CD is used together with a neutral one, but there are situations when the use of a cationic CD with a neutral one or the use of two neutral CDs or even two ionized CDs can be an efficient solution. In the current review we present general aspects of the use of dual CD systems in the analysis of pharmaceutical substances. Several examples of applications of the use of dual CD systems in the analysis of pharmaceuticals are selected and discussed. Theoretical aspects regarding the separation of enantiomers through simultaneous interaction with the two CSs are also explained. Finally, advantages, disadvantages, potential and new direction in this chiral analysis field are highlighted.     

Simultaneous enantioseparation of cyproconazole,bromuconazole, and diniconazole enantiomers by CD‐modified MEKC

An efficient method for the simultaneous enantioseparation of cyproconazole, bromuconazole, and diniconazole enantiomers was developed by CD‐modified MEKC using a dual mixture of neutral CDs as chiral selector. Three neutral CDs namely hydroxypropyl‐β‐CD, hydroxypropyl‐γ‐CD, and γ‐CD were tested as chiral selectors at different concentrations ranging from 10, 20, 30 and 40 mM, but enantiomers of the studied fungicides were not completely separated. The best dual chiral recognition mode for the simultaneous separation of cyproconazole, bromuconazole, and diniconazole enantiomers was achieved with a mixture of 27 mM hydroxypropyl‐β‐CD and 3 mM hydroxypropyl‐γ‐CD in 25 mM phosphate buffer (pH 3.0) containing 40 mM SDS to which methanol‐acetonitrile (10%:5% v/v) was added as organic modifiers. The best separation was based on the appearance of 10 peaks simultaneously, with good resolution (R_s 1.1–15.9), and peak efficiency (N>200 000). Good repeatabilities in the migration time, peak area, and peak height were obtained in terms of RSD ranging from (0.72 to 1.06)%, (0.39 to 3.49)%, and (1.90 to 4.84)%, respectively.     

Enantioseparation of chiral N-imidazole derivatives by electrokinetic chromatography using highly sulfated cyclodextrins: mechanism of enantioselective recognition

Baseline separation of ten new substituted [1-(imidazo-1-yl)-1-phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives, with one chiral center, was achieved by CD-EKC using highly sulfated CDs (alpha, beta, gamma highly S-CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The highly S-CDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times inferior to 2.5 min and resolution factors R(s) of 3.73, 3.90, 1.40, and 4.35 for compounds 1, 2, 3, and 5, respectively, using 25 mM phosphate buffer at pH 2.5 containing either highly S-alpha-CD, highly S-beta-CD, and highly S-gamma-CD (3 or 4% w/v) at 298 K, with an applied field of 0.30 kV/cm. The determination of the enantiomer migration order for the various analytes and the study of the analyte structure-enantioseparation relationships display the high contribution of the interactions between the analytes phenyl ring and the CDs to the enantiorecognition process. The thermodynamic study of the analyte-CD affinities permits us to improve our knowledge about the enantioseparation mechanism.     

Enhancement of second-migrating enantiomer peak symmetry of basic drugs by using dual-cyclodextrin system in capillary electrophoresis

Today, chiral separations of cationic drugs by capillary electrophoresis are generally carried out by adding negatively charged cyclodextrins (CDs) to the running buffer while anionic or neutral drug separations require the use of dual-CD systems (mixtures of neutral and charged CDs). Chiral separation of some basic drugs (idazoxan, efaroxan, milnacipran) has been studied by using mixtures of sulfated-beta-CD (S-beta-CD) and hydroxypropyl-gamma-CD (HP-gamma-CD). The influence of the following parameters (nature and concentration of neutral CD, concentration of S-gamma-CD) on many separation factors (electrophoretic mobility, selectivity, efficiency, asymmetry factor, resolution) demonstrated that dual-CD systems are useful for chiral separation of basic drugs in order to improve the symmetry of the second-migrating enantiomer. Indeed, the neutral CD reduces the extent of electromigration dispersion by mobility tuning. Finally, the 0.5 mg/mL S-beta-CD/5 mg/mL HP-gamma-CD dual system has allowed the chiral separation of idazoxan, efaroxan and milnacipran enantiomers in less than 9 min.     

Enantioseparation of phenotiazines by affinity electrokinetic chromatography using human serum albumin as chiral selector: application to enantiomeric quality control in pharmaceutical formulations

Nowadays, there is a special interest within the pharmaceutical laboratories to develop single enantiomer formulations and consequently a need for analytical methods to determine the enantiomeric purity of drugs. The present paper deals with the enantiomeric separation of promethazine and trimeprazine enantiomers by affinity electrokinetic chromatography (AEKC)-partial filling technique using human serum albumin (HSA) as chiral selector. A multivariate optimization of the most critical experimental variables in enantioresolution, running pH, HSA concentration and plug length, is carried out to obtain enantioresolution of promethazine and trimeprazine. The estimated maximum and optimum resolution of trimeprazine and prometazine enantiomers (Rs = 1.74 and 2.01, respectively) corresponded to the following experimental conditions: pH 7.5; [HSA] 170 μM and plug length 190 s and pH 7.6; [HSA] 170 μM and plug length 170 s, for trimeprazine and prometazine, respectively. The developed methodologies were applied for the enantiomeric quality control of promethazine and trimeprazine enantiomers in commercially available pharmaceutical formulations. Resolution, accuracy, reproducibility, cost and sample throughput of the proposed methodologies make it suitable for quality control of the enantiomeric composition of promethazine and trimeprazine in pharmaceutical preparations.     

Influence of the amino acid sequence and nature of the cyclodextrin on the separation of small peptide enantiomers by capillary electrophoresis using randomly substituted and single isomer sulfated and sulfonated cyclodextrins

The separation of dipeptide and tripeptide enantiomers using negatively charged single isomers as well as randomly sulfated and sulfonated cyclodextrins (CDs) was investigated with respect to the amino acid sequence of the peptides and the nature of the CDs. Standardized conditions concerning buffer pH and molarity, CD concentration, and separation voltage were applied. Compared to suffobutylether-beta-CD and heptakis-(2,3-dimethyl-6-sulfato)-beta-CD, randomly sulfated beta-CD as well as the single isomer derivatives heptakis-6-sulfato-beta-CD and heptakis-(2,3-diacetyl-6-sulfato)-beta-CD were the more universal CDs for enantioseparations. The enantiomer migration order depended to a greater extent on the CD than on the amino acid sequence of the peptide although small structural differences such as formation of a peptide amide or ester affected the chiral recognition by the randomly substituted CD derivatives. Using sulfobutylether-beta-CD or heptakis-(2,3-diacetyl-6-sulfato)-beta-CD the DD enantiomers migrated before the LL enantiomers for most peptides while the opposite migration order, i.e. LL before DD, was observed when heptakis-6-sulfato-beta-CD was applied as chiral selector.     

Chiral separation of hydroxyflavanones in cyclodextrin-modified capillary zone electrophoresis using sulfated cyclodextrins as chiral selectors

Chiral separations of three hydroxyflavanone aglycones, including 2'-, 3'-, and 4'-hydroxyflavanone, in capillary zone electrophoresis (CZE) using randomly sulfate-substituted beta-cyclodextrin (S-beta-CD) or dual cyclodextrin (CD) systems consisting of S-beta-CD and a neutral CD at low pH were investigated. The results indicate that S-beta-CD is an excellent chiral selector for enantioseparation of 2'-hydroxyflavanone and is a good chiral selector for 3'-hydroxyflavanone. Depending on the concentration of S-beta-CD ranging from 2.0 to 0.75% (w/v), the enantioresolution values were 10.5-19.5 and 1.8-3.4 for 2'- and 3'-hydroxyflavanone, respectively. The enantiomers of 4'-hydroxyflavanone could be effectively separated with S-beta-CD at a concentration of 2.0% (w/v) within 20 min. The enantioselectivity and enantioresolution follow the order 2'-hydroxyflavanone>3'-hydroxyflavanone>4'-hydroxyflavanone. Alternatively, with the addition of sodium dodecyl sulfate (SDS) monomers at low concentrations in the electrophoretic system, enantioselectivity of these hydroxyflavanone aglycones could be enhanced with dual CD systems. In this case, SDS monomer acted as a complexing agent probably first with S-beta-CD and then subsequently with the analytes for increasing the effective electrophoretic mobility of the analytes towards the anode and as a selectivity controller for affecting the selectivity of hydroxyflavanones. Better enantioseparation between 2'-hydroxyflavanone and 3'-hydroxyflavanone could be achieved with a dual CD system consisting of S-beta-CD and gamma-CD than that with S-beta-CD and beta-CD. In addition, possible chiral recognition mechanisms of hydroxyflavanones are discussed.     

Study of the enantioseparation capability of chiral dual system based on chondroitin sulfate C in CE

It has been reported that chiral dual system is able to improve the enantioseparation of enantiomers in many cases. Currently, the dual systems involved in CE chiral separation are mostly dual CDs systems, and the polysaccharides‐based chiral dual system was reported in only one paper. To the best of our knowledge, the use of chondroitin sulfate C (CSC)‐based dual system for enantiomeric separation has not been reported previously. Herein, four CSC‐based chiral dual systems, namely CSC/glycogen, CSC/chondroitin sulfate A (CSA), CSC/hydroxypropyl‐β‐CD (HP‐β‐CD), as well as CSC/β‐CD (β‐CD), were evaluated for the first time for their enantioseparation capability by CE in this paper. During the course of the work, the influences of chiral selector concentration and buffer pH values on enantioseparation in dual systems were systematically investigated. Under the optimized conditions, the dual system consisting of CSC and glycogen exhibited better separations toward nefopam, duloxetine, sulconazole, atenolol, laudanosine, and cetirizine enantiomers compared to the single CSC or glycogen system. The combination of CSC and HP‐β‐CD improved the separation of amlodipine and chlorphenamine enantiomers. However, no synergistic effect was observed in the CSC/CSA and CSC/β‐CD systems.     

Enantiomeric separation of glycidyl tosylate by CE: Application to the study of catalytic asymmetric epoxidation of allyl alcohol

A CE method using CDs as chiral selectors was developed and validated to achieve the separation of glycidyl tosylate enantiomers originated by in situ derivatization of glycidol enantiomers obtained in asymmetric epoxidation of allyl alcohol with chiral titanium‐tartrate complexes as catalysts. The effects of the nature, pH and concentration of the buffer, the nature and concentration of chiral selector, the addition of SDS, methanol, ethanol or 2‐propanol, the capillary temperature, the effective capillary length and the applied voltage on the chiral resolution of glycidyl tosylate enantiomers were investigated. The best separation conditions were achieved using a Tris‐borate buffer mixture (50 and 25 mM, respectively) at pH=9.3 with a dual CD system consisting of 2.5% succinyl‐β‐CD and 1.0% β‐CD w/v at 15°C. A baseline separation (resolution～2.0) of the glycidyl tosylate enantiomers was obtained in a relatively short time (less than 12 min). Satisfactory results were obtained in terms of linearity (r>0.99) and intermediate precision (RSD below 8.5%). The LOD and LOQ were 3.0 and 10.0 mg/L, respectively, and the recoveries ranged from 99.8 to 108.8%. Finally, the method was applied to the determination of the enantiomeric excess and the yield obtained in the asymmetric epoxidation of allyl alcohol employing chiral titanium‐tartrate complexes as catalysts after an in situ derivatization of glycidol enantiomers to glycidyl tosylate.     

Enantioselectivity of basic analytes in CZE enantioseparation under reversed-polarity mode using sulfated beta-cyclodextrins as chiral selectors: An unusual temperature effect

Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted beta-CDs (MI-S-beta-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octopamine and norephedrine) were selected as test compounds in an electrophoretic system at low pH. The mobility differences between the (+)-enantiomers and the (-)-enantiomers of the two catecholamines and dopamine at 40 degrees C are greater than those at 25 degrees C with MI-S-beta-CD, even at a concentration as low as 0.3% w/v. Thus the enantioselectivity of these three basic analytes increases with increasing temperature. This phenomenon results from the inequality of the temperature effect on the mobility of the two enantiomers. In contrast, norephedrine behaves differently. The (+)-enantiomers of these basic analytes were found to migrate faster than the (-)-enantiomers. Consequently, the unusual temperature effect on the enantioselectivity can be observed when the mobility difference of the (+)-enantiomer between 40 and 25 degrees C is greater than that of the (-)-enantiomer using MI-S-beta-CD at a concentration greater than about 0.7% w/v for enantioseparation of isoproterenol, 0.4% w/v for epinephrine, and 0.3% w/v for octopamine. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times.     

Enantiomer separation of drugs by capillary electrophoresis using mixtures of beta-cyclodextrin sulfate and neutral cyclodextrins

Direct separation of enantiomers of drugs was investigated by capillary electrophoresis employing mixtures of charged cyclodextrin derivatives (CDs) and electrically neutral CDs (i.e., dual CD system). Among various charged CDs employed, it was found that beta-CD sulfate showed relatively wide enantioselectivity for a wide variety of drugs under acidic conditions. Then separation of enantiomers was performed by employing beta-CD sulfate and the effect of the addition of electrically neutral CDs to the buffers containing beta-CD sulfate was investigated. Through the addition of electrically neutral CDs to the buffers containing the charged CD, resolution of most of the enantiomers was improved, compared with those with the charged CD alone. It was also found that the ring size (alpha, beta, gamma,), the substitution groups and the concentration of the additional electrically neutral CDs affected the enantioselectivity. For example, alpha-CD addition was effective for the separation of enantiomers of chlorpheniramine and hydroxypropyl-beta-CD was effective for the enantiomer separation of trimetoquinol isomer. The application of the method in optical purity testing is also briefly mentioned.     

Strategies for enantioseparations of catecholamines and structurally related compounds by capillary zone electrophoresis using sulfated beta-cyclodextrins as chiral selectors

Strategies for simultaneous enantioseparations of three catecholamines (DL-norepinephrine, DL-epinephrine, and DL-isoproterenol) and three structurally related compounds (DL-octopamine, DL-synephrine, and DL-norephedrine) by CZE using sulfated beta-CDs as chiral selectors were investigated. Four different separation modes were attempted: (I) using randomly sulfate-substituted beta-CD (MI-S-beta-CD) at relatively low concentrations in a high-concentration phosphate buffer at low pH in the normal polarity mode, (II) using MI-S-beta-CD at high concentrations at low pH in the reversed polarity mode, (III) using MI-S-beta-CD at moderately high concentrations in a phosphate buffer at neutral pH in the normal polarity mode, and (IV) using the single isomer heptakis(2,3-dihydroxy-6-O-sulfo)-beta-CD (SI-S-beta-CD) at low to moderately high concentrations in a high-concentration BGE at low pH in the normal polarity mode. Among them, enantioseparation of these cationic solutes was best achieved under the conditions of mode (II). In mode (II) and mode (III), temperature is an important factor affecting the enantioresolution of norepinephrine. In mode (I) and mode (IV), the use of a high-concentration BGE (150-200 mM) is crucial for effective enantioseparation of these cationic solutes with sulfated beta-CDs. Comparative studies of enantioseparations of these cationic solutes with MI-S-beta-CD and SI-S-beta-CD reveal that the sulfate substituents of MI-S-beta-CD located at the C(2)- position interact strongly with the diol moiety of catecholamines.     

Determination of enantiomeric excess by chiral liquid chromatography without enantiomerically pure starting standards

A facile approach for the enantiomeric excess determination of enantiomeric mixtures without the necessity of pure enantiomer standards is presented. Promethazine and trimeprazine commercial nonracemic mixtures were used as cases study to probe the validity of the method. Chromatographic resolutions obtained with a chiral column AGP in reverse phase mode were 1.32–1.16 (promethazine) and 1.20–0.93 (trimeprazine) for the three detectors (circular dichroism, photometric and fluorimetric) in series. Results obtained showed that enantiomeric excess was 10.4, 8.71 and 8.58% for promethazine and 1.60, 1.23 and 1.80% for trimeprazine (medium values of 9.23 ± 1.01% and 1.54 ± 0.29%, respectively). Recovery assay over human serum samples, at three concentration levels, spiked with prometazine and submitted to solid‐phase extraction, gave values of 99.09–93.48% [S‐(?) enantiomer] and 98.51–91.89% [R‐(+)‐enantiomer]. Detection limits of promethazine enantiomers were between 0.02 µg (fluorimetric) and 1 µg (circular dichroism), and 0.02–1.1 µg for trimeprazine. Copyright © 2012 John Wiley & Sons, Ltd.