Macrocyclics glycopeptides

The column was 25 cm long, 4.6 mm I.D. and packed with Partisil 10. It is seen that linear curves were obtained for three different solutes and two different moderators in n-heptane. Scott and Beesley [14] obtained retention data for the two enantiomers, (S) and (R) 4-benzyl-2-oxazolidinone. The column chosen was 25 cm long, 4.6 mm I.D. packed with 5 mm silica particles bonded with the stationary phase Vancomycin (Chirobiotic V provided by Advanced Separations Technology Inc., Whippany, New Jersey). This stationary phase is a macrocyclic glycopeptide Vancomycin that has a molecular weight of 1449.22, and an elemental composition of 54.69% carbon. 

Method Development and Optimization of Enantiomeric Separations Using Macrocyclic Glycopeptide Chiral Stationary Phases... 

The macrocyclic glycopeptides CSPs arc capable of operating in three different mobile phase systems reversed phase, normal phase, and the new polar organic mode. The new polar organic mode refers to the approach when methanol is used as the mobile phase with small amounts of acid and/or base as the modifier to control... 

Statistically, of the compounds enantioresolved by macrocyclic glycopeptide CSPs, new polar organic mode accounts for more than 40 %, balanced by reversed-phase mode, while typical normal-phase operation resulted in approximately 5 % of separations. Some categories of racemic compounds that are resolved on the glycopeptide CSPs at different operating modes are listed in Table 2-4. 

Macrocyclic glycopeptides. The first of these CSPs - based on the cavity of the antibiotic vancomycin bound to silica - was introduced by Armstrong [25]. Two more polycyclic antibiotics teicoplanin and ristocetin A, were also demonstrated later. These selectors are quite rugged and operate adequately in both normal-phase and reversed-phase chromatographic modes. However, only a limited number of such selectors is available, and their cost is rather high. 

Chirobiotic Handbook, Guide to using macrocyclic glycopeptide bonded phases for chiral LC separations, Advanced Separation Technologies Inc. (ASTEC), 2nd Ed. Whippany, New York... 

Fig. 2-1 Proposed structures of three macrocyclic glycopeptides. On teicoplanin, R = 8-methyl-nonanoic acid.

Because plasma and urine are both aqueous matrixes, reverse-phase or polar organic mode enantiomeric separations are usually preferred as these approaches usually requires less elaborate sample preparation. Protein-, cyclodextrin-, and macrocyclic glycopeptide-based chiral stationary phases are the most commonly employed CSPs in the reverse phase mode. Also reverse phase and polar organic mode are more compatible mobile phases for mass spectrometers using electrospray ionization. Normal phase enantiomeric separations require more sample preparation (usually with at least one evaporation-to-dryness step). Therefore, normal phase CSPs are only used when a satisfactory enantiomeric separation cannot be obtained in reverse phase or polar organic mode. 

Owing to flexibility in the substrate, the TycATE was also used to synthesize a variety of novel cyclic structures. Inclusion of a propargylated amino acid into the linear substrate allowed the synthesis of over 247 macrocyclic glycopeptides, where azido-sugars were coupled onto the cyclized alkyne via copper-catalyzed 1,3-dipolar cycloaddition [44] (Figure 13.12). 

Ahoul-Enein, H.Y. and Ali, I. Macrocyclic glycopeptide antihiotics-hased chiral stationary phase, in Chiral Separation by Liquid Chromatography and Related Technologies, Marcel Dekker New York, 2003, chap. 2. 

Staroverov, S.M. et al.. New chiral stationary phase with macrocyclic glycopeptide antibiotic eremomycin chemically bonded to sihca, J. Chromatogr. A, 1108, 263, 2006. 

Petrusevska, K. et al.. Chromatographic enantioseparation of amino acids using a new chiral stationary phase based on a macrocyclic glycopeptide antibiotic, J. Sep. ScL, 29, 1447, 2006. 

Berthod, A. et al.. Evaluation of the macrocyclic glycopeptide A-40,926 as a high-performance liquid chromatographic chiral selector and comparison with teicoplanin chiral stationary phase, J. Chromatogr. A, 897, 113, 2000. 

Beesley, T.E., Lee, J.T., and Wang, A.X., Method development and optimization of enantiomeric separations using macrocyclic glycopeptide chiral stationary phases, in Chiral Separation Techniques, Second completely revised and updated edition, Subramanian, G., Ed., Wiley-VCH Weinheim, 2001, 25. 

Xiao, T.L., Reversal of enantiomeric elution order on macrocyclic glycopeptide chiral stationary phases, J. Liq. Chrom. Rel. TechnoL, 24, 2673, 2001. 

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