Crystalline degradation products of vancomycin as chiral stationary phase in microcolumn liquid chromatography

Enantioseparation of β-Blockers Using Silica-Immobilised Eremomycin Derivatives as Chiral Stationary Phases in HPLC

The regularities of chromatographic retention and separation enantioselectivity of the selected β-blockers (propranolol, pindolol, alprenolol, atenolol, oxprenalol, metoprolol, clenbuterol, sotalol, pronethalol, salbutamol, and labetalol) were studied with eight chiral stationary phases (CSPs) in polar ionic mode (PIM) elution system. A range of novel CSPs was prepared by immobilisation of macrocyclic glycopeptide antibiotic eremomycin (E-CSP); structurally related antibiotics chloreremomycin (Chloro-E-CSP) and semi-synthetic oritavancin (O-CSP); and five eremomycin derivatives including amide- (Amide-E-CSP), adamantyl-2-amide- (Adamantylamide-E-CSP), eremomycin aglycon (EAg-CSP), eremosaminyl eremomycin aglycon (EEA-CSP), and des-eremosamynyl eremomycin (DEE-CSP) onto microspherical silica (Kromasil, particle size 5 micron, pore size 11 nm). The effect of different functional groups in eremomycin structure on chiral recognition of β-blockers was studied. The original E-CSP revealed moderate enantioseparation for all studied β-blockers. The presence of a free carboxylic group in a chiral selector molecule is found to be critical for the general retention of enantiomers as no separation enantioselectivity was recorded for Amide-E-CSP and Adamantyl-E-CSP. Modification of the aromatic system of eremomycin by the introduction of a chloro- substituent in the aromatic ring (Chloro-E-CSP) or a hydrophobic 4’-chlorobiphenylmethyl substituent to the disaccharide sugar residue (O-CSP) resulted in decreased enantioselectivity. The best enantioseparation of β-blockers was obtained for CSPs with eremosaminyl eremomycin aglycon and des-eremosamynyl eremomycin as chiral selectors.

Silica Immobilised Chloro- and Amido-Derivatives of Eremomycine as Chiral Stationary Phases for the Enantioseparation of Amino Acids by Reversed-Phase Liquid Chromatography

Macrocyclic glycopeptide antibiotics immobilized on silica are one of the effective classes of stationary phases for chiral recognition and HPLC separation of a wide range of optically active compounds. Enantioselectivity primarily depends on the chemical structure of the chiral ligand, immobilization chemistry, and separation conditions. In the present work, three new chiral stationary phases (CSPs) based on macrocyclic antibiotic eremomycin were prepared and investigated for enantioseparation of amino acids. Two eremomycin derivatives, including simple non-substituted amide and bulky adamantyl amide, provided important information on the role of the carboxylic group in the eremomycin structure in the chiral recognition mechanism concerning amino acid optical isomers. One more CSP having a chlorine atom in the same position elucidates the role of the first aromatic ring in the eremomycin structure as a crucial point for chiral recognition. CSP with immobilized chloreremomycin was the most successful among the phases prepared in this work. It was additionally investigated under various separation conditions, including the type and content of the organic solvent in the eluent, the effects of different additives, and the concentration and pH of the buffer. Importantly, an efficient enantioselective separation of amino acids was achieved with pure water as the eluent.

A new chiral stationary phase based on noscapine: Synthesis, enantioseparation, and docking study

Noscapine is an isolated compound from the opium poppy, with distinctive chiral structure and chemistry, interacts with other compounds due to having multiple π-acceptors, hydrogen bond acceptors, and ionic sites. Therefore, it has promising applicability for the enantioselective separation of a wide range of polar, acidic, basic, and neutral compounds. A new noscapine derivative chiral stationary phase (ND-CSP) has been synthesized by consecutive N-demethylation, reduction, and N-propargylation of noscapine followed by attachment of a solid epoxy-functionalized silica bed through the 1,3-dipolar Huisgen cycloaddition. The noscapine derivative-based stationary phase provides a considerable surface coverage, which is greater than some commercial CSPs and can validate better enantioresolution performance. The major advantages inherent to this chiral selector are stability, reproducibility after more than 200 tests, and substantial loading capacity. The characterization by Fourier transform infrared (FTIR) spectroscopy and elemental analysis indicated successful functionalization of the silica surface. Chromatographic method conditions like flow rate and mobile phase composition for enantioseparation of various compounds such as warfarin, propranolol, mandelic acid, and a sulfanilamide derivative were optimized. Comparing the experimental results with docking data revealed a clear correlation between the calculated binding energy of ND-CSP and each enantiomer with the resolution of enantiomer peaks.

Simultaneous separation and determination of vancomycin and its crystalline degradation products in human serum by ultra high performance liquid chromatography tandem mass spectrometry method and its application in therapeutic drug monitoring

A rapid and simple ultra high performance liquid chromatography with tandem mass spectrometry method was developed and validated for the simultaneous separation and determination of vancomycin and its crystalline degradation products in human serum. Vancomycin and two isomers of the degradants were extracted from human serum with a protein precipitation method. The compounds were separated on an Acquity BEH C18 column (2.1 × 50 mm, 1.7 μm) eluted with a gradient mixture of acetonitrile and 0.1% formic acid as the mobile phase. Norvancomycin was used as the internal standard. The linear ranges of vancomycin and two degradant isomers were 1.057-105.7, 0.1437-14.37, and 0.2540-25.40 μg/mL, respectively. The established methods were validated and successfully applied to a therapeutic drug monitoring study of vancomycin in patients with renal insufficiency.

Two Synthetic Methods for Preparation of Chiral Stationary Phases Using Crystalline Degradation Products of Vancomycin: Column Performance for Enantioseparation of Acidic and Basic Drugs

Two chiral stationary phases (CSPs) based on crystalline degradation products (CDPs) of vancomycin by using different synthetic methods were prepared and compared. Crystalline degradation products of vancomycin were produced by hydrolytic loss of ammonia from vancomycin molecules. Performances of two chiral columns prepared with these degradation products were investigated using several acidic and basic drugs as model analytes. Retention and resolution of these analytes on the prepared columns, as two main parameters, in enantioseparation were studied. The results demonstrated that the stationary phase preparation procedure has a significant effect on the column performance. The resolving powers of prepared columns for enantiomers resolution were changed with the variation in vancomycin-CDP coverage on the silica support. Elemental analysis was used to monitor the surface coverage of silica support by vancomycin-CDP. The results showed that both columns can be successfully applied to chiral separation studies.

Chiral capillary electrophoresis-mass spectrometry of 3,4-dihydroxyphenylalanine: evidence for its enantioselective metabolism in PC-12 nerve cells

A fully automated chiral capillary electrophoresis-tandem mass spectrometry (CE-MS/MS) method was developed for enantiomeric quantification of 3,4-dihydroxyphenylalanine (DOPA) and its precursors, phenylalanine (Phe) and tyrosine (Tyr). To avoid MS source contamination, a negatively charged chiral selector, sulfated β-cyclodextrin (sulfated β-CD), that migrated away from the detector was used in combination with the partial filling technique. The six stereoisomers were simultaneously quantified in less than 12 min. Detection limits were 0.48 and 0.51 μM for l- and d-DOPA enantiomers, respectively. Assay reproducibility values (relative standard deviations [RSDs], n=6) were 4.43, 3.15, 4.91, 5.16, 3.96, and 3.25% for l- and d-DOPA, l- and d-Tyr, and l- and d-Phe at 10 μM, respectively. Thanks to the high enantioseparation efficiency, detection of trace d-DOPA in l-/d-DOPA mixtures could be achieved. The assay was employed to study the metabolism of DOPA, a well-known therapeutic drug for treating Parkinson's disease. It was found that l-DOPA was metabolized effectively in PC-12 cells. Approximately 88% of l-DOPA disappeared after incubation at a cell density of 2×10(6)cells/ml for 3 h. However, d-DOPA coexisting with l-DOPA in the incubation solution remained intact. The enantiospecific metabolism of DOPA in this neuronal model was demonstrated.