Of methyl glycopyranosides

The characteristic feature of the mass spectra of methyl glycopyranosides is the presence of peaks M+l. 

The reaction of methyl glycopyranosides with sulfuryl chloride has also provided a route to 6-chloro (and other monochloro, dichloro, and trichloro) derivatives. 44 Schlubach and Wagenitz 44 observed that reaction of /3-d-galactopyranose pentaacetate with hydrogen bromide affords a 1,6-dibromo derivative which they converted into crystalline D-fucose in two steps. 

Molecular Rotations of Anoniers of Methyl Glycopyranosides and of Methyl 2-Desoxyglycopyranosides... 

The continued use of pyridine as the usual solvent for sulfonyla-tions is justified by the well known catalytic effect of pyridine on esterification of alcohols. A discussion of such reactions has been presented by Foster and coworkers in which the possibility is considered that complexes of pyridine with sulfonyl chlorides are responsible for the catalytic effect of pyridine. In a study of the reaction of l,2 5,6-di-0-isopropylidene-a-D-glucofuranose with methanesulfonyl chloride, the corresponding 3-methanesulfonate was formed in 88% yield widi pyridine as solvent, but in only 45% yield with triethylamine or tributylamine. In some methanesulfonylations of methyl glycopyranosides, mixtvures of pyridine and triethylamine, and of pyridine and N,2V-dimethylformamide, have been used " to... 

The oxidation of methyl glycopyranosides with periodic acid in DMSO is unusual in that only 1 mole of oxidant is consumed. Most of the stereoselective oxidation observed can be explained on the assumption that nic-cis-diols (axial-equatorial) are more reactive than ei c-tra/w-diols (diequatorial ordiaxial).10h... 

The introduction into a sugar of a halogen atom in place of a hydroxyl group might influence the general reactivity either by steric or electronic effects. Such effects have been extensively discussed with respect to the acid hydrolysis of methyl glycopyranosides, and it is generally considered that, except for substituents at C-2, steric factors predominate. 

R. J. Yu and C. T. Bishop, Novel oxidations of methyl glycopyranosides by periodic acid in... 

K. M. Aalmo and T. J. Painter, Periodate oxidation of methyl glycopyranosides Rate coefficients and relative stabilities of intermediate hemiacetals, Carbohydr. Res., 89 (1981) 73-82. 

Mixtures of O-methyl ethers obtained by partial methylation of a number of methyl glycopyranosides have been acetylated and the products identified by g.l.c.-m.s. The use of partially ethylated alditol acetates for the analysis by g.I.c. of the components of polysaccharides has been described. The ethyl analogues are eluted before the corresponding methyl derivatives, and this often allows the separation of many polysaccharide components by g.l.c. that are not separable as their partially methylated alditol acetates. The use of molar flame-responses calculated on the basis of effective carbon responses has been advocated for the accurate determination of partially methylated and partially ethylated alditol acetates by g.I.c. ... 

In their study of Bronsted acid induced cleveage of a [with axial C(l)-OMe] and (3 [with equatorial C(l)-OMe] glycopyranosides, Fraser-Reid et al.46 demonstrated that the (3/a rate ratios for hydrolysis of methyl pyranosides (Table 5) can be explained by the different intermediates and transition-state structures through which proceed the heterolysis of a and [3 isomers (Fig. 18). 

J. M. Williams and A. C. Richardson, Selective acylation of pyranosides I. Benzoylation of methyl a-D-glycopyranosides of mannose, glucose and galactose, Tetrahedron, 23 (1967) 1369-1378. 

R. U. Lemieux, A. A. Pavia, J. C. Martin, and K. A. Watanabe, Solvation effects on conformational equilibria. Studies related to die conformational properties of 2-methoxytetrahydropyran and related methyl glycopyranosides, Can. J. Chem., A1 (1969) 4427-4439. 

The first synthesis of methyl 4-thiomaltoside (36b) (34%), 4-thiocellobioside (39d) (52%) and 4-thiodigalactobioside (86) (56%) was reported 18 years ago by using the Sn2 displacement of 1,2-cis- or 1,2-trans- glycosyl halides (9 a), (7 a) and (7c) with methyl 4-thio-a-D-glycopyranoside sodium salts generated from the acetylated methyl glycosides (84) and (85a) (Scheme 25) [14a]. 

In the absence of this information, early attempts at rationalization of the experimental results were based on a detailed investigation of enzymatic substrate specificity. For instance, acylation of enantiomeric methyl glycopyranosides by different lipases was focused on the characterization of the reaction outcomes (percentage of the formed regioisomers after the complete disappearance of starting materials or after a fixed reaction time), and the results obtained were interpreted on the basis of the relative orientation of hydroxyls at C-2, C-3, and C-4 [97]. 

One common structural feature is the presence of a xylose unit attached to C-3 of the aglycone and substituted at C-2 with a quinovose unit. As shown in Table 2, carbons involved in the interglycosidic linkages show chemical shifts at 5 ca. 82-88 ppm, shifted downfield from those expected for the corresponding methyl glycopyranosides. 

The first application of GLC in carbohydrate chemistry was to separate fully methylated methyl glycopyranosides of simple pentoses and hexoses (10), and much literature now covers these derivatives (II, 12, 13, 14). Shortly after this work, acetate derivatives were examined by various workers (15, 16), and a little later another development was the use of these acetates with thin-film columns containing liquid phases of high thermal stability such as silicone polymers (e.g., SE-30) and fluoro-alkyl silicone polymers (e.g., QF-1) (17). 

T. Ziegler, M. Vollmer, S. Oberhoffner, and E. Eckhardt, Unexpected formation of 3,6-anhydrofuranoses by acid treatment of methyl 2,3-di-O-acyl-D-glycopyranosides, Liebigs Ann. Chem., (1993) 255-260. 

In Ref. 1 (pp. 1114-1115) the effect of the axial or equatorial orientation of the aglycon in the rate of oxidation of a number of /f-D-glycopyranosides is described. When the aglycon adopts an equatorial orientation [a / anomer in the 4Ci(d) conformation] the oxidation takes place at a higher rate (two to ten times) than for the a anomer. In the case of methyl L-arabinopyranosides, the a-L anomer, which, in the (l) conformation has an equatorially attached group at C-l, is oxidized more rapidly. 

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