Disaccharide fragments

In Fig. 3 all conformers are plotted within 3 kcal/mol above, the global minimum found by CICADA for each of the glycosidic torsions, superimposed on the corresponding disaccharide relaxed map. Fig. 4 clearly indicates that most of the local minima present in the corresponding disaccharide fragments are also explored along the PES of the pentasaccharide by CICADA... 

Approximately 400 different glycosyltransferases are necessary in order to ensure the synthesis of those bacterial polysaccharides whose structures have thus far been elucidated. This estimate is based on the results of an analysis of the structures, made in order to ascertain how many different disaccharide fragments are present. An example of such an analysis is shown in Table V for the disaccharide sequences L-rhamnopyranosyl-D-galacto-pyranose, D-mannopyranosyl-L-rhamnopyranose, and D-galactopyranosyl-D-mannopyranose that are characteristic for the O-specific polysaccharides of Salmonella serogroups A, B, D, and E, the objects of many biosynthetic studies. Full details of similar analyses for other disaccharide sequences will be published elsewhere, as the resulting Tables are too voluminous for inclusion in this Chapter, but the most interesting results are summarized in Tables VI and VII. 

The disaccharide fragments listed in this Table are not found in the polysaccharides of Gram-positive cell-walls. For references on the structures of O-specific and capsular polysaccharides mentioned in this Table, see Refs. 98 and 276. b The total number of isomeric, disaccharide fragments identified in different polymers is shown in parentheses. 

The list of the most common monosaccharide components of bacterial polysaccharides, shown in Table VI, includes the sugars that were found at the nonreducing end of nine or more different disaccharide fragments of the polymers. The right-hand column of the Table, which shows the total number of such fragments, gives an estimate of the number of different glycosyltransferases that use the activated form of the monosaccharides as... 

Total Number of Isomeric Disaccharide Fragments of the Polysaccharides Composed of the Most Common Monosaccharides"... 

The disaccharide fragment of tricolorin A 110, which is a 19-membered macrolactone, was synthesized by efficient RCM of terminal diene 108 to give 109 and its hydrogenation in 77% yield [39]. The presence of sugar groups as a polar relay substituent, its proper distance to the alkene groups, and low steric hindrance close to the double bonds are decisive parameters for the efficient RCM of 108. 

Assuming rigid monosaccharide rings, the source of flexibility in carbohydrates is the glycosidic linkage characterized by the /T torsion angles. In this approximation the complete information about the conformation of a disaccharide fragment is embodied in the conformational distribution function It has been... 

The methyl a-glycoside (82) of the disaccharide fragment, which appears to be thermodynamically the more stable, was formed preponderantly on... 

With tri- and oligo-saccharides, partial acid hydrolysis offers a useful means of determining the nature of at least some of the links. Much milder hydrolytic conditions are required and these must be determined experimentally for each compound studied. The disaccharide fragments of... 

Fujimoto and coworkers determined that the order of stabilities to acid hydrolysis of D-glucopyranosidic linkages is reversed under the conditions of acetolysis this may be due to steric factors affecting the acetylium ion. In consequence, acetolytic, degradative procedures have enabled secondary-linked disaccharide fragments to be obtained from a large number of native dextrans. The o-D-linked disaccharides obtained by acetolysis and deacetylation of a cross-section of dextrans are listed in Table II. The results may be seen to complement data from periodate... 

Compounds having GlcNAc a-(l- 4) linked to 2,3-diacetamido-2,3-dideoxy-a-D-mannose, and to the corresponding mannuronic acid, have been made as 2-phenylethyl glycosides to represent spacer group-containing disaccharide fragments of the lipopolysaccharide of Bordetella pertussis. ... 

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