Oligosaccharides trimethylsilyl ethers

Although several advantages of dimethylsilyl (Me2HSi) ethers have been claimed,191 few examples of their use have been reported, except for the separation of cycloamyloses.133 Thus, dimethylsilyl derivatives (which are more volatile than trimethylsilyl ethers) require lower column-temperatures and have shorter retention times for example, for glucose, the per(trimethylsilyl) derivative has a retention time of 11.4 min, and the per(dimethylsilyl) derivative, 5.10 min. Both types of derivative may be analyzed on the same column, and, in certain cases, compounds inseparable as their O-trimethylsilyl derivatives may be separated as their dimethylsilyl ethers. The potential of di-methylsilylation for converting oligosaccharides into volatile derivatives should be examined. 

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). 

Tsai551 has proposed a method for determining the degree of polymerization of oligosaccharides from chitin wherein they are reduced with sodium borohydride, methanolyzed, and the content of 2-acetamido-2-deoxy-D-glucitol determined as the trimethylsilyl ether. 

Mass spectrometry provides a rapid, sensitive method for the structural analysis of oligosaccharides and, especially in combination with g.l.c., offers a valuable technique for the analysis of oligosaccharides from natural sources and from polysaccharide hydrolyzates. Methyl ethers " or trimethylsilyl ethers are suitable derivatives for the g.l.c. separation of oligosaccharides. 

A series of aldoses has been reductively aminated (NaBH3CN) with octadecylamine to give hydrophobic conjugates as model compounds in the g.c.-m.s. analysis (as the N-acetylated O-trimethylsilyl ether derivatives) of reductivety aminated oligosaccharides from the Streptococcus pneumoniae capsular polysaccharide. Isosorbide dinitrate and its metabolites have been assayed in plasma by g.c. with electron-capture detection. ... 

Another hybrid protecting group is the p-[(trimethylsilyl)ethoxy]methoxy benzyl (p-SEM-benzyl) ether354 Phenolate anions generated by treatment of p-SEM-benzyl ethers with TBAF in DMF at 80 °C eliminate to give the deprotected alcohol as illustrated in Scheme 4.303 p-SEM-benzyl ethers are compatible with many of the standard manipulations in oligosaccharide synthesis and they arc orthogonal to benzyl and p-methoxybenzyl ethers. 

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