Vancomycin enantioseparation

As previously observed, for most free amino acids and small peptides unbuffered hydroorganic mixtures are enough to yield good enantioseparations however, for some bifunctional amino acids and most other compounds, an aqueous buffer is usually necessary to enhance resolution. TEAA and ammonium nitrate are the most effective buffer systems, while sodium citrate was also effective for the separation of 2-arylpropionic acids (profens) on vancomycin CSPs [78], and ammonium acetate is the most widely used and appropriate in view of LC-MS applications (see Section 2.3.1.4). Small changes in ammonium acetate concentration of MeOH-water (90 10) mobile phases scarcely affected retention and— to a lesser extent—enantioselectivity of carnitine derivatives [61]. 

Avery recent study [128] deals with the comparison of two commercially available vancomycin-based CSPs with different surface coverage of the chiral selector in the enantioseparation of P-blockers and profens, by RP and POM separation modes. Higher retention and better resolution were obtained on the CSP with higher coverage of vancomycin in both the separation modes. However, in the case of pro fens, higher retention was not always accompanied by an improvement of the enantioselectivity in the RP mode. An accurate study of the influence of the mobile phase composition was also performed in both the separation modes. 

The [ -adrenoreceptors antagonists (also called [)-blockers) comprise a group of chiral drugs that are mostly used in the treatment of cardiovascular disorders such as hypertension, cardiac arrhythmia, or ischemic heart disease. Teicoplanin is the chiral selector most exploited for the enantioseparation of this class of compounds, followed by vancomycin. Several P-blockers have been analyzed, particularly in the... 

Enantioseparation of nine amphetamine derivatives, methorphan, and propoxyphene was studied by comparing two different CSP typologies, a macrocyclic antibiotic CSP (vancomycin) and a native P-cyclodextrin CSP [123]. The suitability of the eluent systems to ESI interfacing was discussed, and a tandem mass spectrometric (MS/MS) detection method was developed. 

Rojkovieova, T. et al.. Study of the mechanism of enantioseparation. X. Comparison study of thermodynamic parameters on separation of phenylcarbamic acid derivatives using vancomycin and teicoplanin CSPs, J. Liq. Chrom. Rel. TechnoL, 27, 3213, 2004. 

Tesafova, E., Zaruba, K., and Flieger, M., Enantioseparation of semisynthetic ergot alkaloids on vancomycin and teicoplanin stationary phases, J. Chromatogr. A, 844, 137, 1999. 

Glycopeptide antibiotics have been found to be very effective chiral selectors in the enantiomeric separation of racemic pharmaceutical compounds. Vancomycin, ristocetin A, rifamycins, teicoplanin, kanamycin, streptomycin, and avoparcin have been added to the running buffer to obtain enantioseparation (161,203— 207). A few technical modifications, such as coated capillaries and separation conditions in the reverse polarity mode (as opposed to normal polarity mode, where the flow is from anode to cathode) were found to improve sensitivity and increase efficiency (116,208). 

MP Gasper, A Berthod, UB Nair, DW Armstrong. Comparison and modeling study of vancomycin, ristocetin A, and teicoplanin for CE enantioseparations. Anal Chem 68 2501-2514, 1996. 

Fanah, S., Cracianelh, M., De Angelis, R, and Presutti, C., Enantioseparation of amino acid derivatives by capillary zone electrophoresis using vancomycin as chiral selector. Electrophoresis, 23,3035, 2002. 

Since first demonstration in 1994 of the potential use of macrocyclic antibiotics as chiral selectors in analysis, glycopeptide antibiotics have been successfully applied for enantiomer separations by liquid chromatography, as recognition components of chiral stationary phases, and by capillary electrophoresis (CE) as soluble chiral selec-tors. Four chiral stationary phases for chromatography with the selectors vancomycin, ristocetin, teicoplanin, and the teicoplanin aglycone are commercialized under the trade name Chirobiotic by Astec and Supelco. Various aspects of analytical applications of glycopeptide antibiotics have been extensively covered in the recent reviews cited above. As an example. Table 2 shows some representative results for CE enantioseparations with vancomycin, ristocetin A, and teicoplanin, which were taken from Ref. 39. 

The macrocyclic glycopeptide chiral selectors are now a very important class of CSPs that must be part of the column set of any laboratory involved in enantiomeric separations. The variety of functionalities found in these relatively small molecules allow for many different interactions leading to successful enantioseparations [29]. The similarities between members of this class of chiral selectors produced the complementary separation property [14, 30, 31]. If a partial separation of an enantiomeric pair is observed on a macrocyclic selector, say vancomycin, a baseline separation may very likely be observed on a different selector, say teicoplanin. This interesting property in method development illustrates the large number of selector-selectand possible interactions. Such complementarities are due to the... 

An inverse relationship between enantioselectivity and temperature was observed while enantioseparation was only detected within the pH 4.0—6.0 range for DNS-( )-Nle. However, in spite of the narrow range of conditions in which vancomycin can be used as a CS in CCC, the major drawbacks for its extensive use are the high molecular weight combined with the involvement of more than one molecule of vancomycin in the solute-CS complex which compromises loading capacity. 

Macrocyclic antibiotics, for example, erythromycin and vancomycin, have also been used as impregnating agents for TLC resolution of enantiomers of dansyl amino acids by Bhushan and Parshad [6] and Bhushan and Thiong o [7]. Separation in this case is due to chirality of macrocyclic antibiotic molecule, which is ionizable and contains hydrophobic and hydrophilic moieties as well providing enantioseparation via n-n complexation, H-bonding, inclusion in a hydrophobic pocket, dipole stacking, steric interactions, or combination thereof. In view of the scope of the chapter and nonavailability of reports related to NSAIDs, these are not being discussed here. 

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