Methyl glycosides of, oligosaccharides

Table XI. Glycosides of Oligosaccharides Containing Simple Aldohexoses. . 211 Table XII. Methyl Glycosides of Oligosaccharides Containing Galactose and...

A series of methyl glycosides of oligosaccharides having 1— 6 linkage was made by the transfer of glucosyl groups from sucrose to methyl a-D-glucopyranoside (59a). 

The methyl ester of operculinic acid E was obtained by basic hydrolysis and methylation of the crude resin glycoside mixture of 7. murucoides. Mumcoidins XII (53) and XIII (54) afford operculinic acid E as their oligosaccharide core. The lactonization site was placed at C-3 of the first rhamnose unit. These resin glycosides contain an esterifying residue that is composed of n-dodecanoic or (25)-methylbu-tyric acids at the C-2 or C-3 positions on the second rhamnose unit of the oligosaccharide core and (25)-methylbutyric acid at C-4 on the third rhamnose (30). 

The separation of disaccharides and higher oligomers is not essentially different from the separation of monosaccharides, except that the volatility rapidly decreases with increasing molecular weight. Oligosaccharides may be transformed into volatile derivatives, commonly the trimethylsilyl ethers, either directly or after reduction. Other derivatives, such as trifluoroacetates, have been used, but the acetates have low volatility. Oligosaccharides are not usually converted into their methyl glycosides prior to trimethylsilylation. Detailed examples are listed in Table VII (see p. 130). 

The structures of oligosaccharides and polysaccharides are usually determined by a combination of methods specific enzymatic hydrolysis to determine stereochemistry and produce smaller fragments for further analysis methylation analysis to locate glycosidic bonds and stepwise degradation to determine sequence and configuration of anomeric carbons. 

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