Glycopeptides derivatization

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. 

A simple and efficient alternative to the traditional UV detection of amino acids and related compounds is nowadays represented by the evaporative light scattering (ELS) detector, which allows the direct chromatographic separation, with no need for preliminary derivatization. In the field of glycopeptides-based CSPs, it was applied for the first time in the chromatographic resolution of carnitine and 0-acylcarnitine enantiomers on a TE CSP [61]. The considered compounds are nonvolatile solids and gave optimal ELS response under a variety of experimental conditions (buffered and unbuffered mobile phases, flow-rates from 0.5 to 1.5 mL/min, different kind and... 

Another study focused on aryl-substituted P-lactams, using the same set of teicoplanin-based CSPs and variable-temperature conditions [99]. Tricyclic P-lactams were investigated by the same group of authors, together with some bicyclic P-amino acids, on five different commercially available glycopeptides CSPs, namely ristocetin A, TE, TAG, vancomycin, and VAG, and on a new dimethylphenyl carbamate-derivatized 5-cyclodextrin-based CSP. The chromatographic results, achieved with different methods, were compared in systematic examinations [170]. 

Wamke, M.M. et al.. Use of native and derivatized cyclodextrin based and macrocychc glycopeptide based chiral stationary phases for the enantioseparation of pterocarpans by HPLC, J. Liq. Chrom. Rel. TechnoL, 28, 823, 2005. 

Derivatization of the C-Terminus The derivatization of glycopeptides has been performed with various amines to yield the corresponding amides. An early example is the synthesis of vancomycin propanamide, histamide, and 3-aminopropana-mide with DCC/HOBt. " Solution and solid-phase synthesis protocols were developed to yield similar derivatives as mentioned above, but also C-terminally elongated nonapeptide and decapeptide derivatives have been obtained. The glycopeptide eremomycin was C-terminally converted to the methylester, the hydra-zide, some urea derivatives, and the amide along with the methylamide and the benzylamide. The latter two derivatives were more active than eremomycin. 

Recently, another cysteine-free ligation strategy has been reported for the synthesis of glycopeptides. The method, dubbed sugar assisted ligation (SAL), utilizes a peptide thioester and a glycopeptide in which the carbohydrate is derivatized with a thiol auxiliary at the C-2 acetamide [52,53]. The proposed mechanism of this ligation, depicted in Scheme 7, involves... 

Biotin-derivatized carbohydrates can be immobilized on a streptavidin-coated substrate through the affinity interaction of the streptavidin-biotin pair to create carbohydrate microarrays. Biotin-derivatized carbohydrates include carbohydrate hgands that are biotinylated via a short aliphatic spacer or at the peptide part of glycopeptides. Several commercially available streptavidin-coated microweU plates can be apphed when biotin-derivatized carbohydrates are available, such as the streptavidin-coated 384-well plate with a well volume 25 pi (4,18) and a streptavidin-coated 192-spot shde format (27). The first was designed to be in maximal proximity to the traditional immunochemical assay using commercial streptavidin-coated black 384-well plates. 

Experiments were conducted to determine the free amino groups available for reaction with dansyl chloride. Only one faint fluorescent area in the region of dansyl-lysine was observed. No dansyl-ethanolamine was observed. However, if the pol3nner was first treated with 6 N HCl to hydrolyze the amino acids, dansyl amino acids were obtained. Quantitative analysis for ethanolamine from the amino acid analyzer gave 1.3 ethanolamine residues for 2 proline residues. The low solubility of the polymer in aqueous solution may have been the primary factor leading to lack of derivatization of the intact glycopeptide. 

Free sugars have been determined without derivatization by high performance capillary electrophoresis with refractometric detection. Complex carbohydrates, such as 0-glycosylated amino acids and glycopeptides, in urine have been... 

The modification and biological profiling of potentially useful bio active natural products is a very important goal. By applying CuAAC in the last step of derivatization, Walsh et al. prepared a library of the glycopeptide antibiotic tyrocidine [80]. 

Oligosaccharides from glycopeptides by hydarazinolyses Derivatization 2-pyridylamine dimethylamine/borane D FI Aex = 320 nm Aem = 380 nm C Fused silica (60 cm x 50 pm i.d.) polyimine coated E 100 mmol 1 phosphate, pH 2.5 200 mmol I borate V 20 kV Glycopeptides obtained by trypsine digestion of human transferrin, serum fetuin, human immunoglobulin, bovine, spleen ribonuclease, yeast invertase... 

Many matrices have been used for carbohydrate analysis but 2,5-DHB has proved to be the most versatile and widely used. Esculetin is more specific, however, and ionizes sugars in preference to peptides and glycopeptides in mixtures of these compounds (Figure 4). Carbohydrates form [M -I- Na] ions with most matrices but other adducts can be produced if the matrix is doped with the appropriate salt. Anionic carbohydrates additionally form [M — H] ions. Sensitivity in both modes is lower than with peptides as the latter can be efficiently protonated because of their high proton affinity. However, sensitivity can be increased by permethylation or derivatization at the reducing terminus with a compound that can be protonated, such as a tertiary amine or one that possesses a constitutive charge. Alkyltrimethylammonium compounds have been used in the latter context. 

Malabarba A. Modulation of the antibacterial activity of glycopeptide antibiotics by chemical derivatization. On the Frontier of Anti-Bacterial Discovery. New York Strategic Research Institute L.P.. 1995. 

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