Vancomycin Chiral Stationary Phase Research Articles

New enantioselective liquid chromatography method development and validation of dipeptidyl peptidase IV inhibitors using a macrocyclic glycopeptide (vancomycin) chiral stationary phase under polar ionic mode condition.

The direct separation of dipeptidyl peptidase IV (DPP-4) inhibitors such as Sitagliptin (STG), Linagliptin (LIG), and Saxagliptin (SAG) enantiomers in normal phase conditions have been achieved on immobilized polysaccharide-based chiral stationary phases (CSPs), as well as on the macrocyclic glycopeptide vancomycin chiral stationary phase (Chirobiotic V2) under polar ionic mode. The enantiomers of these targets could be separated completely (resolution factor Rs > 2) using the Chirobiotic V2 column in polar ionic mode with the mobile phase (MeOH/AcOH/TEA 100/0.3/0.1 v/v/v) in an isocratic elution at 1.0 ml min-1 . The effect of the mobile phase composition on separation, including buffer salts, acid-base modifiers, and analyte structures, was evaluated. The developed technique was validated in the polar ionic mode according to the International Conference on Harmonization (ICH) Q2R1 guidelines in terms of accuracy, precision, selectivity, linearity, limit of detection (LOD), and limit of quantification (LOQ). The calibration curve was linear in a concentration range from LOQ to 3.75 μg/ml. The LOD and LOQ of STG, LIG, and SAG were 0.15 and 0.45, 0.15 and 0.50, 0.16 and 0.50, respectively. The proposed method is said to be selective, accurate, and precise. Finally, the validated method was used successfully for the quantitative determination of DPP-4 enantiomers in pharmaceutical analytes.

Enantioseparation of mandelic acid on vancomycin column: Experimental and docking study.

So far, no detailed view has been expressed regarding the interactions between vancomycin and racemic compounds including mandelic acid. In the current study, a chiral stationary phase was prepared by using 3-aminopropyltriethoxysilane and succinic anhydride to graft carboxylated silica microspheres and subsequently by activating the carboxylic acid group for vancomycin immobilization. Characterization by elemental analysis, Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance, and thermogravimetric analysis demonstrated effective functionalization of the silica surface. R and S enantiomers of mandelic acid were separated by the synthetic vancomycin column. Finally, the interaction between vancomycin and R/S mandelic acid enantiomers was simulated by Auto-dock Vina. The binding energies of interactions between R and S enantiomers and vancomycin chiral stationary phase were different. In the most probable interaction, the difference in mandelic acid binding energy was approximately 0.2 kcal/mol. In addition, circular dichroism spectra of vancomycin interacting with R and S enantiomers showed different patterns. Therefore, R and S mandelic acid enantiomers may occupy various binding pockets and interact with different vancomycin functions. These observations emphasized the different retention of R and S mandelic acid enantiomers in vancomycin chiral column.

Enantioseparation of chiral pharmaceuticals by vancomycin-bonded stationary phase and analysis of chiral recognition mechanism.

The drug chirality is attracting increasing attention because of different biological activities, metabolic pathways, and toxicities of chiral enantiomers. The chiral separation has been a great challenge. Optimized high-performance liquid chromatography (HPLC) methods based on vancomycin chiral stationary phase (CSP) were developed for the enantioseparation of propranolol, atenolol, metoprolol, venlafaxine, fluoxetine, and amlodipine. The retention and enantioseparation properties of these analytes were investigated in the variety of mobile phase additives, flow rate, and column temperature. As a result, the optimal chromatographic condition was achieved using methanol as a main mobile phase with triethylamine (TEA) and glacial acetic acid (HOAc) added as modifiers in a volume ratio of 0.01% at a flow rate of 0.3mL/minute and at a column temperature of 5°C. The thermodynamic parameters (eg, ΔH, ΔΔH, and ΔΔS) from linear van 't Hoff plots revealed that the retention of investigated pharmaceuticals on vancomycin CSP was an exothermic process. The nonlinear behavior of lnk' against 1/T for propranolol, atenolol, and metoprolol suggested the presence of multiple binding mechanisms for these analytes on CSP with variation of temperature. The simulated interaction processes between vancomycin and pharmaceutical enantiomers using molecular docking technique and binding energy calculations indicated that the calculated magnitudes of steady combination energy (ΔG) coincided with experimental elution order for most of these enantiomers.

Enantioseparation of Cinacalcet, and its Two Related Compounds by HPLC with Self-Made Chiral Stationary Phases and Chiral Mobile Phase Additives

Background:Cinacalcet is one of the second-generation calcimimetics which consists of a chiral center. The pharmacological effect of R-cinacalcet is 1000 times greater than that of the Scinacalcet. As mentioned in many literatures, 1-(1-naphthyl)ethylamine is used as the starting material for the synthesis of cinacalcet. The absolute structure of cinacalcet is influenced by the starting materials.Methods:We present the chiral separation of cinacalcet and its starting material, 1-(1-naphthyl) ethylamine along with one of its intermediates, N-(1-(naphthalen-1-yl) ethyl)-3- (3-(trifluoromethyl) phenyl) propanamide by high-performance liquid chromatography with chiral stationary phase and chiral mobile phase additives.Results:On vancomycin and cellulose tri 3,5-dimethylphenylcarbamate) chiral stationary phase, cinacalcet and 1-(1-naphthyl)ethylamine achieved enantioseparation under normal phase with addition of triethylamine additives, respectively. Meanwhile, 1-(1-naphthyl)ethylamine and N-(1-(naphthalen-1- yl)ethyl)-3-(3-(trifluoromethyl) phenyl) propanamide achieved enantioseparation on 1-napthalene vancomycin chiral stationary phase using D-tartaric acid, diethyl L-tartrate and diethyl D-tartrate as chiral mobile phase additives.Conclusion:The chiral recognition in our experiment was based on the hydrogen-bonding, dipoledipole and π-π interactions among the solutes, chiral stationary phases and chiral mobile phase additives. In addition, the space adaptability of chiral stationary phases also affected the separation efficacy.

Mass spectrometry detection of basic drugs in fast chiral analyses with vancomycin stationary phases

Current trends in chiral analysis of pharmaceutical drugs are focused on faster separations and higher separation efficiencies. Core-shell or superficially porous particles (SPP) based chiral stationary phases (CSPs) provide reduced analysis times while maintaining high column efficiencies and sensitivity. In this study, mobile phase conditions suitable for chiral analyses with electrospray ionization LC-MS were systematically investigated using vancomycin as a representative CSP. The performance of a 2.7 µm SPP based vancomycin CSP (SPP-V) 10 cm × 0.21 cm column was compared to that of a corresponding 5 µm fully porous particles based analogue column. The results demonstrated that the SPP-V column provides higher efficiencies, 2–5 time greater sensitivity and shorter analysis time for a set of 22 basic pharmaceutical drugs. The SPP-V was successfully applied for the analysis of the degradation products of racemic citalopram whose enantiomers could be selectively identified by MS.

Light-assisted preparation of vancomycin chiral stationary phase based on diazotized silica and its enantioseparation evaluation by high-performance liquid chromatography

Owing to enantiomers’ identical physical and chemical properties, separation work in the chiral environments is still a great challenge.and chemical properties. Chromatographic techniques employing chiral stationary phases (CSPs) have been developed as powerful tools for the chiral analysis and preparation of pure enantiomers. Here we report a facile synthesis of vancomycin stationary phase based on diazotized silica. Monodisperse silica particles were synthesized by a modified Stöber method. The obtained silica particles were modified by self-assembly photosensitive diazoresin (DR) and vancomycin on the surface. After treatment with UV light, the ionic bonding was converted into covalent bonding through a unique photochemistry reaction of DR. Baseline separation of chiral drugs was achieved by using the vancomycin@SiO2 particles as packing materials in high performance liquid chromatography (HPLC). The effects of separation parameters including elution mode, flow rate and analyte mass on the enantioselectivity of the CSP were investigated in detail. Due to the replacement of highly toxic and moisture sensitive silane agent by water soluble non-toxic DR in the modification of silica microspheres, this method provides a green and easy way to manufacture packing materials for chromatography applications.

Determination of trantinterol enantiomers in human plasma by high-performance liquid chromatography - tandem mass spectrometry using vancomycin chiral stationary phase and solid phase extraction and stereoselective pharmacokinetic application.

A sensitive and enantioselective vancomycin chiral stationary phase high-performance liquid chromatography-tandem mass spectrometry method was developed for the determination of trantinterol enantiomers in human plasma. Baseline resolution was achieved using the vancomycin chiral stationary phase known as Chirobiotic V with polar ionic mobile phase consisting of acetonitrile-methanol (60:40, v/v) containing 0.01% ammonia and 0.02% acetic acid at a flow rate of 1.0 mL/min. Waters Oasis HLB C18 solid phase extraction cartridges were used in the sample preparation of trantinterol samples from plasma. The detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring mode via electrospray ionization. The calibration curve was linear in a concentration range from 0.0606 to 30.3 ng/mL in plasma, with the lower limit of quantification of 0.0606 ng/mL. The intra- and interday precision (relative standard deviation) values were within 9.7% and the accuracy (relative error) was from -6.6 to 7.2% at all quality control levels. The method was successfully applied to a study of stereoselective pharmacokinetics in human.

Single-step approach for fabrication of vancomycin-bonded silica monolith as chiral stationary phase

A vancomycin-bonded silica monolithic column for capillary electrochromatography (CEC) was prepared by a single-step in situ sol–gel approach. This sol–gel process incorporates a synthetic sol–gel precursor which contains a macrocyclic antibiotic, vancomycin, to form a porous silica network inside a fused-silica capillary. To avoid degradation of vancomycin during the column fabrication, a mild step was adopted into the sol–gel process. The performance of the vancomycin chiral stationary phase was investigated by CEC in both the reversed-phase mode and the normal-phase mode. The vancomycin chiral stationary phase was optimized with respect to vancomycin loading in the reversed-phase mode for chiral separation of thalidomide enantiomers. The best efficiency and resolution values of 94600plates/m and 5.79, respectively, were achieved. The optimized column was further applied to chiral separation of alprenolol enantiomers. A plate height of less than 7μm for the first eluted enantiomer of alprenolol was obtained in an aqueous mobile phase at a flow rate of 0.74mm/s. Using enantiomers of seven β-blockers and some other basic enantiomers as test analytes, separation efficiencies of up to 148100plates/m in the reversed-phase mode and up to 138100plates/m in the normal-phase mode were achieved.

Microwave-assisted preparation of a vancomycin modified open tubular capillary electrochromatography column for chiral separation

A vancomycin chiral stationary phase modified open tubular capillary electrochromatography (OT-CEC) column has been prepared using a microwave irradiation method. Compared with the use of conventional heating, the microwave-assisted process improved the efficiency of the synthesis, led to a significant increase in the rate of the reaction, and reduced the preparation time from 12 h to 55 min. Four aromatic racemates were selected as model compounds to evaluate the performance of the vancomycin modified OT-CEC column. Using the optimized conditions, all four of these racemic compounds were successfully separated with a baseline resolution (RS) of more than 1.75. These results demonstrated that the vancomycin modified OT-CEC column prepared using the microwave-assisted process possessed excellent chiral recognition properties towards aromatic racemates, as well as showed good levels of stability and repeatability. This column is therefore suitable for use in chiral separations by CEC.

Development of a chiral micellar electrokinetic chromatography–tandem mass spectrometry assay for simultaneous analysis of warfarin and hydroxywarfarin metabolites: Application to the analysis of patients serum samples

The enantioseparation of warfarin (WAR) along with the five positional and optical isomers is challenging because of the difficulty to simultaneously separate and quantitate these chiral compounds. Currently, no effective chiral CE–MS methods exist for the simultaneous enantioseparation of WAR and all its hydroxylated metabolites in a single run. Polymeric surfactants (aka. molecular micelles) are particularly compatible with micellar electrokinetic chromatography–mass spectrometry (MEKC–MS) because they have a wider elution window for enantioseparation and do not interfere with the MS detection of chiral drugs. Using polysodium N-undecenoyl-l,l-leucylvalinate (poly-l,l-SULV) as a chiral pseudophase in MEKC–MS baseline separation of WAR, its five metabolites along with the internal standard was obtained in 45min. This is in comparison to 100min required for separation of the same mixture with packed column CEC–MS using a vancomycin chiral stationary phase. Serum samples were extracted with mixed-mode anion-exchange (MAX) cartridge with recoveries of greater than 85.2% for all WAR and hydroxywarfarin (OH-WAR) metabolites. Utilizing the tandem MS and multiple reaction monitoring mode, the MEKC–MS/MS method was used to simultaneously generate calibration curves over a concentration range from 2 to 5000ng/mL for R- and S-warfarin, 5 to 1000ng/mL for R- and S-6-, 7-, 8- and 10-OH-WAR and 10 to 1000ng/mL for R and S-4′-OH-WAR. For the first time, the limits of detection and quantitation for most WAR metabolites by MEKC–MS/MS were found to be at levels of 2 and 5ng/mL, respectively. The method was successfully applied for the first time to analyze WAR and its metabolites in plasma samples of 55 patients undergoing WAR therapy, demonstrating the potential of chiral MEKC–MS/MS method to accurately quantitate with high sensitivity.

Separation and Determination of Clenbuterol by HPLC Using a Vancomycin Chiral Stationary Phase

Enantiomers of clenbuterol were separated by a new HPLC method on a chiral column. Enantiomeric resolution was achieved on a vancomycyin macrocyclic antibiotic chiral stationary phase known as chirobiotic V with UV detection at 247 nm. The polar ionic mobile phase consisting of methanol-triethylamine-glacial acetic acid (100 + 0.05 + 0.025, v/v/v), was used at a flow rate of 1.0 mL/min. The method was validated for linearity, accuracy, precision, and robustness. Standard linear calibration curves were established for the R-(-) and S-(+) enantiomers over the range of 0.2-20 microg/mL, and an average recovery of 98.0% and a mean relative standard deviation of 1.5% were obtained at 5.0 microg/mL. The lower limit of detection was 0.05 microg/mL for each enantiomer. The mean recovery for R-(-) and S-(+)-clenbuterol enantiomers from plasma was 91.0-97.0% at 0.20-20 microg/mL. The method was successfully used to identify and quantify the clenbuterol enantiomers in human plasma.

Enantioselective HPLC Analysis and In-vitro Kinetic Study Decomposition of Potential β-Blocker Drug in Guinea Pig Serum

A method using off-line solid-phase extraction and liquid chromatography has been developed for the analysis of enantiomers of derivatives of aryloxyaminopropanol in guinea pig blood serum. The paper presents the results of HPLC enantioseparation of the derivative of aryloxyaminopropanol obtained by using of four chiral stationary phases [macrocyclic antibiotic (vancomycin, teicoplanin, teicoplanin aglycone, and methylated teicoplanin aglycone)] and the mixture of methanol/acetonitrile/acetic acid/triethylamine (45:55:0.3:0.2, v/v/v/v) as mobile phase for all tested stationary phases. The presence of saccharide moieties in the chiral stationary phase (vancomycin and teicoplanin chiral stationary phases) plays an important role, together with charge interactions and steric interactions, in the separation of enantiomers of derivatives of aryloxyaminopropanol. The in-vitro degradation studies of individual (R)-enantiomer and (S)- enantiomer in blood serum demonstrated a difference in the final concentration of the enantiomers after the incubation at 37°C. It was found that the rate constant of the (R)-enantiomer is lower than the (S)-enantiomer.

Chiral Separation of Duloxetine and Its R-Enantiomer by LC

The direct enantioseparation of duloxetine and its R-enantiomer was achieved by HPLC using hydroxypropyl-β-cyclodextrin (HP-β-CD) as a chiral selector and a vancomycin chiral stationary phase (Chirobiotic V). Operational parameters, such as the concentration of HP-β-CD, buffer pH, organic modifiers, temperature and flow rate, were varied in order to achieve the desired retention time and resolution. These two enantioseparation methods developed gave a baseline resolution of the enantiomers. Finally, the HPLC-CSP method was selected to determine the enantiomeric purity of duloxetine drug substance due to its much shorter analysis time and better resolution. The limit of detection of this method was 0.06 μg mL−1.

HPLC separation technique for analysis of bufuralol enantiomers in plasma and pharmaceutical formulations using a vancomycin chiral stationary phase and UV detection

A sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of bufuralol enantiomers in plasma and pharmaceutical formulations. Enantiomeric resolution was achieved on a vancomycin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic V with UV detection set at 254 nm. The polar ionic mobile phase (PIM) consisting of methanol–glacial acetic acid–triethylamine (100:0.015:0.010, v/v/v) has been used at a flow rate of 0.5 ml/min. The method is highly specific where other coformulated compounds did not interfere. The stability of bufuralol enantiomers under different degrees of temperature was also studied. The results showed that the drug is stable for at least 7 days at 70 °C. The method was validated for its linearity, accuracy, precision and robustness. An experimental design was used during validation to evaluate method robustness. The calibration curves in plasma were linear over the range of 5–500 ng/ml for each enantiomer with detection limit of 2 ng/ml. The mean relative standard deviation (RSD) of the results of within-day precision and accuracy of the drug were ≤10%. There was no significant difference ( p > 0.05) between inter- and intra-day studies for each enantiomer which confirmed the reproducibility of the assay method. The mean extraction efficiency for S-(−)- and R-(+)-bufuralol from plasma was in the range 97–102% at 15–400 ng/ml level for each enantiomer. The overall recoveries of bufuralol enantiomers from pharmaceutical formulations was in the range 99.6–102.2% with %RSD ranging from 1.06 to 1.16%. The assay method proved to be suitable as chiral quality control for bufuralol formulations by HPLC and for therapeutic drug monitoring.

Study of the Mechanism of Enantioseparation. Part XII. Comparison Study of Thermodynamic Parameters on Separation of Phenylcarbamic Acid Derivatives by HPLC using Macrocyclic Glycopeptide Chiral Stationary Phases

Four macrocyclic glycopeptide chiral stationary phases (CSPs) based on native teicoplanin (Chirobiotic T), methylated teicoplanin aglycone (Chirobiotic m‐TAG), teicoplanin aglycone (Chirobiotic TAG), and vancomycin (Chirobiotic V) were compared for the high performance liquid chromatographic (HPLC) separation of enantiomers of 1‐methyl‐2‐piperidinoethylesters of 2‐, 3‐and 4‐ alkoxyphenylcarbamic acid (potential local anaesthetic drugs). The enthalpies (ΔH i ), entropies (ΔS i ), and Gibbs energies (ΔG i ) of transfer were evaluated for the separation of these compounds. The enantiomers were separated isothermally in the range of 0–50°C with 10°C increments, in the polar organic mode. The thermodynamic parameters were calculated in order to gain an understanding of the driving forces for retention in this chromatographic system. From these results, it is evident that the elongation of the alkoxy‐chain has major influence on the values of (ΔS i ) when using the vancomycin CSP and on the values of (ΔH i ) using the teicoplanin‐type CSPs.

Simultaneous enantioseparation and sensitive detection of eight β‐blockers using capillary electrochromatography‐electrospray ionization‐mass spectrometry

The feasibility of using vancomycin chiral stationary phase (CSP) and polar organic eluent is investigated for simultaneous enantioseparation of eight beta-blockers using CEC coupled to ESI mass spectrometric detection (ESI-MS). The internally tapered capillaries were utilized to pack CEC-MS columns. As compared to externally tapered columns, the use of internally tapered columns demonstrated enhanced stability, durability, and reproducibility. A mixture containing methanol/ACN/acetic acid/triethylamine at 70:30:1.6:0.2 v/v/v/v was considered as optimum mobile phase since it provided a good compromise between resolution and analysis time. As expected, sheath liquid and ESI-MS parameters mainly influenced the detection sensitivity. Interestingly, structural information of beta-blockers was available by varying the MS fragmentor voltage using in-house CID in the scan mode. In order to maximize the chiral/achiral resolution, various column-coupling approaches using teicoplanin as complementary CSP to vancomycin were tested. Several changes in the elution order of beta-blockers were observed using multimodal CSPs with some improvement in chiral or achiral resolution. The quantitative aspects of the CEC-MS method were demonstrated using R- and S-talinolol as internal standards. The calibration curves of beta-blockers showed good linearity in the range of 3-600 microM. The enantiomer of beta-blockers at a concentration of 30 nM was detectable. Furthermore, both 0.1 and 1% of the S-enantiomer could be precisely quantified in the presence of 99.9 and 99% of the R-isomer of beta-blocker.

Vancomycin as chiral selector for enantioselective separation of selected profen nonsteroidal anti‐inflammatory drugs incapillary liquid chromatography

The chiral selector vancomycin was used either as mobile phase additive or bound as a chiral stationary phase (CSP) for the stereoselective separation of seven racemic nonsteroidal anti-inflammatory drugs (NSAIDs), fenoprofen, carprofen, flurbiprofen, indoprofen, flobufen, ketoprofen, and suprofen, by capillary liquid chromatography. The effect of the type of stationary phase, the chiral column Chirobiotic V or the achiral stationary phases Nucleosil 100 C8 HD and Nucleosil 100 C18 HD, and the concentration of vancomycin in the mobile phase on separation of the drug enantiomers were evaluated. All the drugs, except flobufen, were successfully enantioseparated on Nucleosil 100 C8 HD with 4 mM vancomycin present in the mobile phase (composed of methanol and buffer) in the reversed phase mode. On the vancomycin-bonded chiral stationary phase, it was difficult to get enantioseparations of the profen NSAIDs. However, flobufen gave better enantioseparation on the vancomycin CSP. The better enantioresolution of the majority of profen derivatives on the achiral columns with vancomycin added to the mobile phase can be attributed in particular to the higher separation efficiency of this capillary chromatographic system. In addition, vancomycin dimers, formed in the mobile phase, seem to offer a better steric arrangement for stereoselective interaction to these analytes than the vancomycin bonded on the CSP. These substantial differences in the CS structure significantly influence the chiral discrimination mechanism.

Use of vancomycin chiral stationary phase for the enantiomeric resolution of basic and acidic compounds by nano-liquid chromatography

In this paper we studied the potentiality of nano-liquid chromatography (nano-LC) for the enantiomeric resolution of both basic and acidic compounds of pharmaceutical interest using a vancomycin modified silica stationary phase. Experiments were carried out in a fused silica capillary of 75 μm I.D. packed with chiral modified silica particles of 5 μm diameter, the detection, was done on-line at 195 nm. Enantiomeric resolution of alprenolol, atenolol, metoprolol, oxprenolol, pindolol, propranolol (basic compounds) and some acidic analytes, namely 2-[(5′-benzoyl-2′-hydroxy)phenyl]propionic acid (DF1738Y), 2-[(4′-benzoyloxy-2′-hydroxy)phenyl]propionic acid (DF1770Y), ketoprofen, indoprofen and suprofen was studied by nano-LC utilizing mobile phases containing methanol-acetonitrile-ammonium formate or acetate. The effect of mobile phase composition (buffer type and concentration, organic modifier type and concentration) on chiral resolution ( Rs), retention factor ( k) and retention time ( t R) was also investigated. Good enantiomeric resolution was achieved for basic compounds utilizing the mobile phase containing 90% (MeCN–MeOH)/5% water/5% of 100 mM ammonium acetate pH 4.5. Acidic compounds such as DF1738Y and DF1770Y were better resolved at lower pH 3.5 while ketoprofen, indoprofen and suprofen exhibited the highest resolution at pH 4.5; in this case the mobile phase contained MeOH or MeCN (90%), 5% buffer and 5% of water. The nano-LC method was validated using R-(+)-propranolol as an internal standard finding good repeatability, detection limit, correlation coefficient and recovery and applied to the assay of a pharmaceutical formulation containing a racemic mixture of metoprolol.

A validated LC method for the determination of vesamicol enantiomers in human plasma using vancomycin chiral stationary phase and solid phase extraction

An enantioseparation high performance liquid chromatographic (HPLC) method was developed and validated to determine d-(+)- and l-(−)-vesamicol in human plasma. The assay involved the use of a solid phase extraction for plasma sample clean up prior to HPLC analysis utilizing a C18 Bond-Elute column. Chromatographic resolution of the vesamicol enantiomers was performed on a vancomycin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic V with a polar ionic mobile phase (PIM) consisting of methanol:glacial acetic acid:triethylamine (100:0.1:0.05 (v/v/v)) at a flow rate of 1.0 ml/min and UV detection set at 262 nm. All analyses were conducted at ambient temperature. The method was validated over the range of 1–20 μg/ml for each enantiomer concentration ( R 2>0.999). Recoveries for d-(+)- and l-(−)-vesamicol enantiomers were in the ranges of 96–105% at 3–16 μg/ml level. The method proved to be precise (within-run precision ranged from 1.3 to 2.7% and between-run precision ranged from 1.5 to 3.4%) and accurate (within-run accuracies ranged from 0.8 to 3.4% and between-run accuracies ranged from 1.7 to 5.0%). The limit of quantitation (LOQ) and limit of detection (LOD) for each enantiomer in human plasma were 1.0 and 0.5 μg/ml ( S/ N=3), respectively.

Study of the Mechanism of Enantioseparation. X. Comparison Study of Thermodynamic Parameters on Separation of Phenylcarbamic Acid Derivatives Using Vancomycin and Teicoplanin CSPs

The enantiomers of 1‐methyl‐2‐piperidinoethylesters of 3‐ and 4‐alkoxyphenylcarbamic acid were separated on vancomycin (CHIROBIOTIC V) and teicoplanin (CHIROBIOTIC T) columns isothermally in the range of 0–50°C at 10°C increments, using methanol containing 17.5 mmol/L acetic acid and 4.8 mmol/L diethylamine as the mobile phase. Lower temperatures produced the expected increase in retention of the studied enantiomers and improved their separation. The retention factors k i (as well as the resolutions R ij ) were higher on the teicoplanin chiral stationary phase (CSP) compared with the vancomycin CSP. Van't Hoff plots (dependence of ln k i on 1/T) were linear within the temperature interval studied, and they also were used to determine thermodynamic data, such as the (ΔH i ) and (ΔS i ) of transfer of the enantiomers between mobile and stationary phases. From these results, it is evident that the prolongation of carbon atoms in the alkoxy‐chain has a major influence on the values of Δ(ΔS 2,1) using the vancomycin CSP, and on the values of Δ(ΔH 2,1) using the teicoplanin CSP. However, when the alkoxy‐substituent on the phenylcarbamic acid ring system is in the 3‐ and 4‐positions, there seems to be little difference in the thermodynamic parameters.