Chiral mobile phase additives macrocyclic glycopeptides

Although the macrocyclic glycopeptide antibiotic CSPs are very effective for the chiral resolution of many racemic compounds, their use as chiral mobile phase additives is very limited. Only a few reports are available on this mode of chiral resolution. It is interesting to note that these antibiotics absorb UV radiation therefore, the use of these antibiotics as the CMPAs is restricted. However, Armstrong et al. used vancomycin as the CMPA for the chiral resolution of amino acids by thin-layer chromatography, which will be discussed in Section 10.7. 

The chiral recognition mechanisms in NLC and NCE devices are similar to conventional liquid chromatography and capillary electrophoresis with chiral mobile phase additives. It is important to note here that, to date, no chiral stationary phase has been developed in microfluidic devices. As discussed above polysaccharides, cyclodextrins, macrocyclic glycopeptide antibiotics, proteins, crown ethers, ligand exchangers, and Pirkle s type molecules are the most commonly used chiral selectors. These compounds... 

Chiral mobile phase additives provide a more versatile and cost-effective approach for enantiomer separations in thin-layer chromatography. Typically, chemically bonded layers with cyclodextrin and its derivatives, bovine serum albumin, or macrocyclic glycopeptides are used as chiral additives in the reversed-phase mode [59,60,172-178]. For [5- and y-cyclodextrins and their derivatives, a 0.1 to 0.5 M aqueous methanol or acetonitrile solution of the chiral selector is used as the mobile phase. Bovine serum albumin is generally used at concentrations of 1-8 % (w/v) in an aqueous acetate buffer of pH 5 to 7 or in a 0.5 M acetic acid solution, in either case with from 3-40 % (v/v) propan-2-ol (or another aliphatic alcohol), added to control retention. Enantioselectivity usually increases with an increase in concentration of the chiral selector, and may be non existent at low concentrations of the chiral selector. 

Figure 4.10 shows the effect of additive concentration on the separation of clen-buterol enantiomers on a polysaccharide-based chiral stationary phase [79]. The peak shapes were dramatically improved by adding an amine additive and the separation time was also reduced from 14 to 7 min when 1.0% amine was added to the mobile phase. Phinney and Sander [100] investigated the effect of amine additives using chiral stationary phases having either a macrocyclic glycopeptide or a... 

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