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Bezhan Chankvetadze

Publications and source records attributed to Bezhan Chankvetadze.

At least 19 recordsLinked to original sources
PubMed2006

High-performance liquid chromatographic enantioseparations on capillary columns containing monolithic silica modified with amylose tris(3,5-dimethylphenylcarbamate).

Monolithic capillary columns containing native silica were modified by in situ coating with amylose tris(3,5-dimethylphenylcarbamate) and applied for enantioseparations in capillary liquid chromatography. Capillary columns were examined for 10 standard racemic compounds in order to compare the performance of monolithic silica columns with the common, 4.6mm I.D. high-performance liquid chromatographic columns packed with particulate silica. The effects of polysaccharide coating and of the linear velocity of the mobile phase on peak performance were studied. Enantioseparations with an analysis time below 1min were achieved for some chiral analytes.

Amylose↗
PubMed2006

High-performance liquid chromatographic enantioseparations on capillary columns containing crosslinked polysaccharide phenylcarbamate derivatives attached to monolithic silica.

Monolithic capillary columns containing native silica gel were covalently modified with 3,5-disubstituted phenylcarbamate derivatives of cellulose and amylose and applied for enantioseparations in capillary LC. The method previously used for covalent immobilization of polysaccharide phenylcarbamate derivatives onto the surface of microparticulate silica gel was successfully adapted for in situ modification of monolithic fused-silica capillary columns. The effects of the nature of polysaccharide and the substituents, as well as of multiple covalent immobilization of polysaccharide derivative on chromatographic performance of capillary columns were studied. The capillary columns obtained using this technique are stable in all solvents commonly used in LC and exhibit promising enantiomer resolving ability.

Amylose↗
PubMed2005

High performance liquid chromatographic separation of dipeptide and tripeptide enantiomers using a chiral crown ether stationary phase.

A chiral stationary phase (CSP) based on (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was evaluated for the direct resolution of the enantiomers of dipeptides and tripeptides. The type and concentration of the acid and the methanol content were optimized with regard to retention time and resolution using Ala-Phe as model peptide. A mobile phase consisting of 10 mM sulfuric acid in 70% aqueous methanol was applied to the separation of a set of 16 structurally diverse dipeptides and tripeptides. Generally, the configuration of the amino acid at the N-terminus determined the enantiomer elution order. With a few exceptions the LL- and LD-enantiomers interacted stronger with the CSP compared to the corresponding DD- or DL-enantiomers. The experimental conditions also allowed the simultaneous separation of all four stereoisomers of Ala-Phe. Addition of ammonium sulfate generally reduced retention times and enantiomer resolution. Addition of triethylamine as modifier led to an overall increase of the retention times while the resolution did not show a general trend, increasing in the case of Ala-Ala but decreasing in the case of Ala-Phe.

Ammonium Sulfate↗
PubMed2005

Evaluation of cyclodextrins modified with dichloro-, dimethyl-, and chloromethylphenylcarbamate groups as chiral stationary phases for capillary electrochromatography.

Capillary electrochromatography using cyclodextrins modified with dichloro-, dimethyl-, and chloromethylcarbamate groups were used for the enantiomeric separation of standard analytes. The chiral selector was chemically bonded to aminopropylsilanized silica particles, and these chiral stationary phases (CSPs), mixed with aminopropylsilanized silica (1:1 wt:wt), were packed into 100-microm-i.d. fused-silica capillaries. The effect of the type of cyclodextrin, the nature and position of the substituents on the phenyl ring, and the binding mode of cyclodextrin phenylcarbamates onto the silica gel surface on the chiral recognition were studied. Experimental parameters such as organic solvent concentration were varied in order to better understand the mechanism contributing to the chiral recognition of these CSPs. Good enantioseparations were achieved for a racemic flavanone (FLA) and trans-cyclopropanedicarboxylic acid dianilide (CAD).

Carbamates↗
PubMed2004

Enantiomer separations in capillary electrophoresis in the case of equal binding constants of the enantiomers with a chiral selector: commentary on the feasibility of the concept.

It is generally acknowledged that enantiomer separations in capillary electrophoresis are based on differences in the affinities of the analyte enantiomers toward the chiral selector expressed as equilibrium constants of the resulting temporary diastereomeric associates. However, as can be derived from theoretical considerations, a separation of enantiomers by CE is in principle also possible solely based on differences in the mobilities of the temporary diastereomeric complexes per se, when equal binding constants between analyte enantiomers and the chiral selector are assumed and observed.

Journal Article↗
PubMed2004

High-performance liquid chromatographic enantioseparations on monolithic silica columns containing a covalently attached 3,5-dimethylphenylcarbamate derivative of cellulose.

Covalent immobilization of 3,5-dimethylphenylcarbamate derivative of cellulose was performed in situ onto native silica monoliths cladded in a 50 mm x 4.6 mm polyether ether ketone high-performance liquid chromatographic (HPLC) column. The covalent attachment of cellulose derivative in the range of 16-19% (w/w) was performed via an epoxide moiety. The column obtained by this technique combines the high enantiomer-resolving ability of the polysaccharide derivative with favourable dynamic properties of monolithic HPLC columns. The covalent attachment of the cellulose derivative enables this column to be used in combination with the mobile phases which are incompatible with coated-type polysaccharide columns due to solubility of chiral selector in some organic solvents.

Carbamates↗
PubMed2004

Combined approach using capillary electrophoresis and NMR spectroscopy for an understanding of enantioselective recognition mechanisms by cyclodextrins.

This tutorial review describes the contribution of chiral capillary electrophoresis in combination with other instrumental techniques, especially nuclear magnetic resonance spectroscopy, to a better understanding of the chiral recognition mechanisms by cyclodextrins. Aspects such as affinity pattern of enantiomers towards various cyclodextrins as well as the stoichiometry of the resulting complexes, the equilibrium constants and the structure of complexes are addressed. In addition to the aforementioned techniques, the usefulness of complementary instrumental and molecular modeling techniques for an understanding of the chiral recognition mechanisms of cyclodextrins is also illustrated.

Cyclodextrins↗
PubMed2004

Separation of tocopherols by nano-liquid chromatography.

Nanoliquid chromatography (nano-LC) was used for the separation of tocopherols (delta-, gamma-, alpha-TOH), alpha-tocopherol acetate (alpha-TOH-Ac) and an antioxidant compound, namely butylated hydroxytoluene (BHT) used to prevent TOHs autoxidation. The separation was carried out in a fused silica capillary of 100 microm I.D. and 375 microm O.D. packed in our laboratory with RP18 silica stationary phase of either 5- or 3-microm diameter (23-cm long). The mobile phase was composed by mixtures of methanol (MeOH), acetonitrile (MeCN) and water. Typical analyses time for the separation of all the five components of the mixture were 6-9 min depending on the composition of the mobile phase. Efficiency and resolution were strongly influenced by the particle diameter and the highest Rs and N/m values were observed using 3-microm RP18 particles. Experiments performed with capillaries packed with 3-microm RP18 particles provided good limit of detection (LOD) and limit of quantification (LOQ) (for delta-, gamma-TOH, alpha-TOH-Ac were 4 and 8 microg/ml, while for alpha-TOH were 6 and 10 microg/ml, respectively). The optimized method was applied to extracts of serum and pharmaceutical preparation containing alpha-TOH and alpha-TOH-Ac.

Chromatography, Liquid↗
PubMed2004

High-performance liquid chromatographic enantioseparations on capillary columns containing monolithic silica modified with cellulose tris(3,5-dimethylphenylcarbamate).

Monolithic capillary columns containing native silica gel were modified with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and used for enantioseparations in capillary liquid chromatography. The method adopted for in situ enantioselective modification of monolithic fused silica capillary columns by coating with CDPMC appears to be fairly simple and fast. High efficiency enantioseparations of test racemic compounds and s(everal chiral drugs were achieved in a short time. It was possible to increase the amount of chiral selector present by multiple coating of monoliths with CDMPC. The baseline enantioseparation of 2,2,2-trifluoro-1-(9-anthryl)ethanol was achieved in an analysis time less than 30 s with this capillary column. In addition, reproducible enantioseparations were obtained when the chiral selector was removed from the monolithic column by flushing it with appropriate solvent and the column recoated.

Carbamates↗
PubMed2003

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.

Antimalarials↗
PubMed2003

Comparative study on the application of capillary liquid chromatography and capillary electrochromatography for investigation of enantiomeric purity of the contraceptive drug levonorgestrel.

In the last few years, it has been shown that capillary electrochromatography (CEC) is a promising technique for enantioseparations. However, to date almost no studies are published on a critical comparison of CEC and its pressure-driven counterpart, capillary liquid chromatography (CLC) for real samples. In this study, the goal was to compare CLC and CEC for the determination of the enantiomeric purity of the contraceptive drug levonorgestrel and its pharmaceutical formulation. The study prevailed that not all potential advantages of CEC over CLC can easily be transformed in a real gain of detection limit of the enantiomeric impurity. However, certain advantages of CEC over CLC have been unambiguously shown.

Chromatography, Liquid↗
PubMed2003

Comparative enantioseparations with native beta-cyclodextrin, randomly acetylated beta-cyclodextrin and heptakis-(2,3-di-O-acetyl)-beta-cyclodextrin in capillary electrophoresis.

Comparative enantioseparations were performed with three neutral cyclodextrins (CDs) in capillary electrophoresis (CE). In particular, native beta-CD was compared with single component heptakis(2,3-di-O-acetyl)-beta-CD (HDA-beta-CD) and randomly acetylated beta-CD (Ac-beta-CD) with the emphasis on the enantiomer migration order. The opposite affinity of the enantiomers of several chiral analytes was observed towards native beta-CD and its acetylated derivatives. The enantiomer affinity pattern of some chiral analytes was also opposite towards the two acetylated derivatives of beta-CD. In the case of the chiral drug clenbuterol (CL) an attempt was made to evaluate the possible structural reasons of the affinity reversal using one- and two-dimensional as well as transverse rotating frame nuclear Overhauser effect spectroscopy (ROESY). Significant differences were observed between the structure of the CL complexes with beta-CD and HDA-beta-CD.

Acetylation↗
PubMed2002

Comparative enantioseparation of selected chiral drugs on four different polysaccharide-type chiral stationary phases using polar organic mobile phases.

The enantiomers of randomly selected chiral drugs and drug analogs of various structural and pharmacological groups were resolved on four different polysaccharide-type chiral stationary phases (CSP) using pure methanol and acetonitrile as mobile phases. Polysaccharide phenylester type CSP, Chiralcel-OJ although resolving the enantiomers of some chiral drugs was less universal in the combination with methanol and acetonitrile as mobile phases. Among polysaccharide phenylcarabamates amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak-AD) was superior over the corresponding cellulose derivative, cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel-OD). However, another derivative of cellulose, namely, cellulose tris(3,5-dichlorophenylcarbamate) (CDCPC) exhibited higher chiral recognition ability compared to Chiralpak-AD material. This study confirms previous findings about the applicability of polysaccharide type CSPs in so called polar organic mode as well as shows high potential of CDCPC as a practically useful CSP for High performance liquid chromatography (HPLC) enantioseparations.

Chromatography, High Pressure Liquid↗
PubMed2002

Comparative HPLC enantioseparation of new chiral hydantoin derivatives on three different polysaccharide type chiral stationary phases.

The enantioseparation of eighteen new chiral hydantoin derivatives was studied on three different polysaccharide type chiral stationary phases (CSP) Chiralpak AD, Chiralcel OD and Chiralcel OJ in the normal-phase HPLC mode. Chiralpak AD material exhibited the most universal chiral resolving ability and allowed the enantioseparation of 17 out of 18 compounds followed by Chiralcel OD (10 enantioseparations of 12 tested compounds) and Chiralcel OJ (eight enantioseparation from 13 tested analytes). Some complementary separations were observed and all of 18 compounds could be resolved at least with one of the three chiral CSP under the conditions of this study. With regard to the structure of the analytes, bulky electron rich substituents at C5 of the hydantoin nucleus appear to favor stereoselective interactions.

Chromatography, High Pressure Liquid↗
PubMed2002

Enantioseparation of chiral vasodilator drug isoxsuprine in high-performance liquid chromatography and capillary electrophoresis.

Two independent methods using high-performance liquid chromatography (HPLC) on polysaccharide type chiral stationary phase (CSP) and capillary electrophoresis (CE) with native and derivatised cyclodextrins (CD) have been proposed for the enantioseparation of chiral vasodilator drug isoxsuprine (ISP). The methods have been compared from the viewpoint of separation characteristics (efficiency, sensitivity, analysis time, costs, etc.).

Chromatography, High Pressure Liquid↗
PubMed2002

Simultaneous enantioseparation of cis-diltiazem hydrochloride and its metabolite cis-desacetyldiltiazem using high-performance liquid chromatography and capillary electrophoresis.

Two alternative methods were developed using high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) for a simultaneous enantioselective determination of Ca(2+) blocking chiral drug cis-diltiazem hydrochloride (DLT) and its degradation product and metabolite cis-desacetyldiltiazem (Desac-DLT). The methods were compared from the viewpoint of analytical performance. The identification of HPLC peaks were performed using off-line electrospray ionization mass spectrometry. In addition, CE method was evaluated for quantitative determination of minor enantiomeric impurities in pharmacologically active (+)-cis-DLT.

Calcium Channel Blockers↗
PubMed2002

Enantioseparations in nonaqueous capillary liquid chromatography and capillary electrochromatography using cellulose tris(3,5-dimethylphenylcarbamate) as chiral stationary phase.

The potential of the widely used chiral stationary phase for high-performance liquid chromatography (HPLC) enantioseparations, cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC, sold under the trade name Chiralcel OD) was evaluated under the conditions of nonaqueous capillary electrochromatography (CEC). The effect of the particle size of the silica gel, the loading of CDMPC on the silica gel and nature of the organic solvent, as well as electrolyte salts on the separation characteristics were investigated. This study illustrates the applicability of CDMPC for obtaining highly efficient enantioseparations under the conditions of nonaqueous CEC. Comparative study of enantioseparations in capillary liquid chromatography (CLC) and CEC indicated the significant advantages of CEC such as higher plate number at the similar linear flow rates of the mobile phase as well as better tolerance of higher linear flow rates.

Carbamates↗