Of methylated glycosides

The present work involves the study of methyl glycosides and O-isopropylidene ketals of various isomeric deoxy sugars by mass spectrometry. Several of the compounds selected for the present study have free hydroxyl groups, and interpretation of their mass spectra shows the scope of the study of these and related deoxy sugar derivatives by mass spectrometry without prior substitution of all hydroxyl groups. Some of the candidates (compounds 4, 7, 8 and 10) are structurally related to biologically-derived deoxy sugars. 

The study of monosaccharides subjected to conditions of methanolysis is considered for two reasons. First, the decomposition of monosaccharides is indicative of the decomposition of monosaccharides liberated during methanolysis second, the ratio of methyl glycosides of a particular standard monosaccharide is the same for the same monosaccharide released during methanolysis (for a particular set of methanolysis conditions), provided that the concentration of sugars is relatively low. Up to four methyl glycosides (the a and )8 anomers of the pyranoside and furan-oside forms) of a particular monosaccharide may be formed the acyclic dimethyl acetal is an additional possibility. The ratios of methyl glycosides of 10 monosaccharides subjected to methanolysis with M hydrogen chloride for 24 h at 80° has been reported. Similar information is also available in another study."... 

Table 3. Compositions of methyl glycoside mixtures at equilibrium (35°C)...

However, two recent papers suggest that DMF is also a good solvent for this type of condensation under appropriate activation conditions of the donor. A simple and efficient method for the preparation of thioglycosides of N-acetyl-neuraminic acid has been developed [30]. This procedure involves the selective in situ S-deacetylation and activation of the 2-S-acetyl NeuSAc (24a) and the displacement of primary bromide of methyl glycosides (28a, 28b). The desired a(2->6) thioglycosides (29a,29b) were obtained in 75 and 82% yield. Condensation of the sodium salt (24b), freshly derived from (24 a) by selective S-deacetylation with sodium methoxide [16], with (28c) in DMF at 45 °C also gave the expected compound (29c) in 76% yield (Scheme 8) [31]. 

The use of methyl glycoside of hemithiocellodextrin (40c) and tetrasaccharide (44j) as inhibitors of cellulases belonging to various families has also been investigated. These compounds were not split under the experimental conditions used, and were effective inhibitors (Kj in pmol/1 range) [67]. 

Trimethylsilyl ethers of methyl glycosides have been used in analyzing bacterial endotoxins that contain 3,6-dideoxyhexoses, and, because of the volatility of such glycosides, careful temperature-programming is essential.373 Methyl D-glucosides and analogs have been... 

Additional examples of the resolution of mixtures of methyl glycosides, as trimethylsilyl ethers, peracetates, and as O-methylated derivatives are given in Table IV (p. 115). 

TableXIV. Acetates of Methyl Glycosides of Oligomers of Xylose. 215...

The rates of methyl glycosidation are approximately proportional to the concentration of acid catalyst. In the early part of the glycosidation, a single reaction is predominant and can be characterized as first order. A cyclic, carbonium intermediate (13) was proposed for the mechanism of the anomerization of the furanosides. 

M. Schamann and H. J. Schafer, TEMPO-mediated anodic oxidation of methyl glycosides and 1-methyl and 1-azido disaccharides, Eur. J. Org. Chem. (2003) 351-358. 

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