Vancomycin layer

Figure 2.17 Cumulative vancomycin release of single-layer coatings as a function of antibiotic concentration. (Reproduced from ref. 12, with permission.)...

Figure 2.18 Fourier transform infrared spectrum of sol-gel film composed of three layers and containing 10% vancomycin after 14 days of immersion in phosphate-buffered saline (weight measurements and release study showed 90% weight loss and 80% release). Intense silica bands and the bands associated with vancomycin (centred at 1660,1500 and 1397 cm-1) suggest the presence of a sol-gel film with vancomycin that remains after 14 days of immersion. (Reproduced from ref. 13, with permission.)...

The glycopeptides include vancomycin and teico-planin. They are bactericidal antibiotics. Their mechanism of action is based on inhibition of bacterial cell-wall synthesis by blocking the polymerization of glycopeptides. They do not act from within the peptidoglycan layer, as the beta-lactam antibiotics do, but intracellularly. The indications are mainly restricted to the management of severe or resistant staphylococcal infections, especially those caused by coagulase negative staphylococcal species such as S. epidermidis. 

Vancomycin acts by inhibiting the correct synthesis of cell walls in gram-positive bacteria by specifically inhibiting the incorporation of V-acetylmuramic acid (NAM) and A-acetylglucosamine (NAG), two important peptide subunits that are present in the peptidoglycan layer of these types of bacteria. 

Bhushan and Parsad [65] resolved dansyl amino acids on erythromycin impregnated thin-layer chromatographic (TLC) silica plates. The mobile phase used was different ratios of 0.5 M aqueous NaCl-acetonitrile-methanol. Further, Bhushan and Thiong o [66] achieved the chiral resolution of dansyl amino acids on silica TLC plates impregnated with vancomycin chiral selector. The mobile phase used for this study was acetonitrile-0.5 M aqueous NaCl (10 4 and 14 3, v/v). The chiral recognition mechanisms of antibiotic CSPs in sub-SFC, SFC, CEC, and TLC modes of chromatography were found to be similar to HPLC. 

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 peptidoglycan layer confers mechanical stability to the cell wall of the bacteria. An important intermediate of the peptidoglycan biosynthesis is the GlcNAc- MurNAc-L-Ala-D-y-Gln-L-Lys-D-Ala-D-Ala peptide (muramyl-pentapeptide), which is in its lipid-carrrier bound form transglycosylated to a linear polysaccharide. The linear polysaccharide is then cross-linked to peptidoglycan by transpeptidation reactions. Perkins observed that vancomycin binds to the Lys-D-Ala-D-Ala peptide motif of bacterial cell wall intermediates. This observation was later investigated on a mole-cular level by NMR and by x-ray crystallographic studies. ... 

For the separation of anionic analytes, the positively charged macrocyclic antibiotic vancomycin is one of the most commonly used chiral selectors. It was introduced by Armstrong and coworkers as a new class of chiral selector in CE, HPLC and thin-layer chromatography for the separation of a wide range of enantiomers [29, 47-52]. It contains multiple stereogenic centers and a variety of functional groups. 

Olalde, B., Garmendia, N., Saez-Martinez, V., Argarate, N., Nooeaid, P., Morin, F., Boccaccini, A.R., 2013. Multifunctional bioactive glass scaffolds coated with layers of polyfD, L-lactide-co-glycolide) and poly(n-isopropylacrylamide-co-acrylic acid) microgels loaded with vancomycin. Mater. Sci. Eng. C Mater. Biol. Appl. 33, 3760-3767. 

Impregnation of layers with a chiral selector for use in enantiomer separations has usually been carried out by mixing the compound with silica gel to prepare a slurry for in-house preparation of the layer. For example, Bhushan and Martens [18] reported use of this method for preparing layers containing selectors such as (-F)-tartaric acid or (-F)-ascorbic acid, erythromycin, vancomycin, L-lysine and L-arginine, and (—)-brucine. 

Whatman RP diphenylsiloxane-bonded silica gel plates have 8.5% carbon loading and 10-14 /rm average particle size they are endcapped but still contain a relatively high concentration of silanol groups [27]. These layers were used with the macrocyclic antibiotic, vancomycin, as a mobile phase additive to resolve 6-aminoquinolyl-Ai-hydroxysuccinimidyl carbamate (AQC) derivatized amino acids, racemic drugs, and dansyl amino acids. The mobile phase was acetonitrile-0.6 M NaCl-1% triethylammonium acetate buffer (pH 4.1) with 0.025-0.08 M vancomycin in various ratios. The development distance was 10 cm, development time 1-3 h, and detection by fluorescence at 245 and 365 nm. Typical Rf values were bendroflumethiazide (0.02/0.06), AQC-a//o-isoleucine [0.14 (l)/0.21 (d)], and dansyl-norleucine [0.04 (l)/0.16 (d)] [40]. 

The layers coated with (—)-vancomycin were also successfully used for the separation of enantiomers of verapamil, a calcium channel blocker usually administered as racemic compound, even though the 5-(—)-isomer was 20-30 times pharmacologically more active than the i -(+)-form [42], The results are reported in Table 5.13. Amounts as low as 0.075 /rg of each enantiomer were detected by iodine vapor at working temperature 18 C. 

Erythromycin and vancomycin possess multiple stereogenic centers and a variety of functional groups, which can interact with functional groups of solute to create diastereomeric complex. Layers impregnated with antibiotics show good selectivity for acidic solutes, where interaction between the carboxylate group of the solute and amino group of chiral selector can occur. 

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