Monosaccharides anomeric configuration

An important characterization parameter for ceUulose ethers, in addition to the chemical nature of the substituent, is the extent of substitution. As the Haworth representation of the ceUulose polymer shows, it is a linear, unbranched polysaccharide composed of glucopyranose (anhydroglucose) monosaccharide units linked through thek 1,4 positions by the P anomeric configuration. 

The anomeric configurations of the sugar residues were determined by chromium trioxide oxidation [14], Oxidation of the fully acetylated polysaccharide and subsequent monosaccharide analysis by GLC indicated that the D-Xyl units are P-linked (oxidized more rapidly) and that die D-GlcA are a-linked (Table II). 

It may be seen that only several elements of the trisaccharide structure seem to be strictly controlled by the specificity of the enzymes. These include the anomeric configuration of the terminal monosaccharide residue of the glycosyl acceptor and the configuration of C-4 of the D-mannopyranosyl... 

To fully establish the structure of a disaccharide, we must determine (1) the identity of the component monosaccharides (2) the type of ring junction, furanose or pyranose, in each monosaccharide, as it exists in the disaccharide (3) the positions that link one monosaccharide with the other and (4) the anomeric configuration (a or fi) of this linkage. 

Introduction to 2-D NMR experiments The purpose of the standard 1-D H NMR experiment is to achieve structure-related information about sample protons (i.e., chemical shifts, spin-spin couplings, and integration data) describing the relative number of protons. Applied to anthocyanins, this information may help to identify the aglycone (anthocyanidin), number of monosaccharides present, and anomeric configuration of the monosaccharides. However, for most anthocyanins, the information gained by a standard 1 -D H NMR experiment is insufficient for complete structure elucidation. In recent years, various 2-D NMR experiments have evolved as the most powerful tools for complete structure elucidation of anthocyanins. 

Table Fl.4.7 contains typical H- H coupling constants for the monosaccharides commonly identified in anthocyanins. When the ring size of the anthocyanin monosaccharides has been reported, all but one have been reported as pyranoses (arabinofuranosyl has been identified in zebrinin Idaka et al., 1987). When examined, the anomeric configurations of the glucosyl, galactosyl, xylosyl and glucuronyl...

A. S. Shashkov, A. I. Usov, Y. A. Knirel, B. A. Dmitriev, and N. K. Kochetkov, Determination of absolute and anomeric configurations of monosaccharides in oligo- and poly-saccharides by glycosylation effects in 13C-NMR spectra, Bioorg. Khim., 7 (1981) 1364-1371. 

Nuclear magnetic resonance (NMR) spectroscopy is a very powerful tool for analyzing the conformation and molecular architecture of carbohydrate molecules. Both one- and two-dimensional (ID and 2D) methodologies have provided valuable information about small and large molecules, ranging from the anomeric configuration of a monosaccharide to the sequence of monosaccharide residues that constitute an oligo- or polysaccharide. 

Designation of the bond between two monosaccharides should specify the first residue, its anomeric configuration (a or J3), the position of attachment on both sugar residues, and the second residue. Additional locants and configurational descriptors may be present but are not required. A number of variations may be used. 

Wen et al. (1993) showed the ROA spectra of 15 monosaccharides in aqueous solution. They found three main regions of interest, were ROA spectra should provide insights into local stereochemistry. The first is the region of 750 to 950 cm reflecting anomeric configuration, the second at 950 to 1200 cm gives information about ring structure and... 

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