Vancomycin, structure

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Schafer M, Schneider TR, Sheldrick GM (1996) Crystal Structure of Vancomycin. Structure 4 1509... 

Scheme 2-3. Stereochemical features of the vancomycin structure. The AB-ring (chiral axis) and the C-O-D-O-E-rings (chiral planes) fixate the heptapeptide aglycon in a rigid comformation.

The first structural work on vancomycin were degradation studies carried out by Marshall [208] followed by extensive NMR examinations in the laboratory of Williams [209]. On the basis of these pioneering studies and on the X-ray analysis of the degradation product CDP-1 [210], Harris and Harris published the complete structure of vancomycin in 1982 [211]. The determination of the vancomycin structure then served as the basis for the structural characterization of hundreds of natural and semisynthetic glycopeptide antibiotics. 

Vancomycin is an antibiotic isolated from Strep, orientalis and has an empirical formula of C66H75CI2N9O4 (mol. wt 1448) it has a complex tricyclic glycopeptide structure. Modern chromatographically purified vancomycin gives rise to fewer side-effects than the antibiotic produced in the 1950s. 

The answer is c. (Hardman, pp 1143-1144.) Bacitracin, cycloserine, cephalothin, and vancomycin inhibit cell-wall synthesis and produce bacteria that are susceptible to environmental conditions. Polymyxins disrupt the structural integrity of the cytoplasmic membranes by acting as cationic detergents. On contact with the drug, the permeability of the membrane changes. Polymyxin is often applied in a mixture with bacitracin and/or neomycin for synergistic effects. 

In an attempt to change and broaden the capabilities of the vancomycin CSP, the glycopeptide was derivatized with (R)- and (S )-(l-naphthylethyl) isocyanate (NEIC) and then bonded to a silica-gel support [48]. A variety of chiral compounds was tested on the two composite stationary phases and the results were compared with the ones obtained using the underivatized vancomycin CSP. The advantages of the NEIC derivatization were not as obvious or substantial as they were in the case of cyclodextrin phases [49]. Moreover, the exact chemical structures of the synthesized NEIC derivatives of vancomycin were not reported. 

In the case of vancomycin [72], an original study was performed to obtain a well-defined stationary phase structure, since it was reasonably assumed that the antibiotic is randomly linked to the silica by one or both of its amino groups, one belonging to the disaccharide portion (primary), and the other one to the heptapeptide core (secondary). Thus, alternate fluorenylmethyloxycarbonyl (FMOC)-amino-protected derivatives were prepared and immobilized in a packed column, and then vancomycin was recovered by cleavage of the protecting groups. The two defined CSPs obtained, when compared with the CSP produced from native randomly linked vancomycin, showed lower retention and enantioselectivity, also if they still separated the same compounds. Thus, no advantages could be found to choose these phases as an alternative to the native vancomycin CSP. 

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