Ethers of monosaccharides

Table III. Methyl Ethers of Monosaccharides from the Hydrolyzate of Methylated LCC Oligomers (A-ESD)...

A large number of a>a-dideuterlobenzyl (i.e. PhCD2 ) ethers of monosaccharides have been prepared so that their n.m.r. spectra could be compared with those of normal benzyl ethers.Partial benzylation of methyl a-D-mannopyranoside yielded either the 2,3,6-... 

The analysis of carbohydrates continues to be of considerable importance in the biological sciences. The diversity of structure and function of carbohydrates in organisms contributes to the difficulty of analysis of these materials. There exist a number of techniques for the analysis of carbohydrates, but no single technique has universal applicability. For the identification of carbohydrates, trimethylsilyl ethers are widely used in GC/MS. Veness and Evans " showed that GC/FTIR can also be used, with some advantages, for this purpose. A selection of 42 monosaccharides and related compounds were examined and, in each case, unique spectra were obtained for the differing compounds and their isomeric forms, allowing unambiguous identification. These results indicate that GC/FTIR of trimethylsilyl ethers of monosaccharides is a useful analytical technique for their identification. The resultant spectra are unique, easy to interpret, and stereo-isomeric forms are readily differentiated. 

Aspects of chemical methods used in the structural elucidation of polysaccharides and complex carbohydrates have been reviewed. In a critical examination of the use of g.l.c.-m.s. in the identification of TMS ethers of monosaccharides, a standardized method, which uses a medium resolution mass spectrometer and short chromatographic columns, has been proposed. TMS Ethers of monosaccharides have been characterized by g.l.c.-chemical ionization m.s. with ammonia as reagent gas. Molecular weights were determined, and fragment ions were produced in a quantity high enough to differentiate between stereoisomers (epimers and anomers). Disaccharides have been determined by permethylation followed by g.l.c. The method has been used in the detection of carbohydrate intolerance secondary to intestinal disaccharidase deficiency. 

Because of their multiple hydroxy groups, sugars can be converted into alcohol derivatives. This section explores the fonnation of simple esters and ethers of monosaccharides and also addresses selective reactions at the anomeric hydroxy group in their cyclic isomers. 

Because monosaccharides contain only two kinds of functional groups, hydroxyls and carbonyls, most of the chemistry of monosaccharides is the familiar chemistry of these two groups. Alcohols can be converted to esters and ethers... 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

Stevens and coworkers used their c.d. data on the various D-glucans to assign, tentatively, the bands to specific chromophores. They found that derivatives of these polysaccharides that have all of their hydroxyl groups acetylated still exhibit the 177-nm band. They assigned this band (which occurs at somewhat shorter wavelengths for the helical polymers) to the ether of the acetal chromophore. This assignment is essentially consistent with the results obtained by Johnson and coworkers on unsubstituted monosaccharides. 

In this article, the authors have endeavored to summarize the methods of synthesis and the proofs of constitution of all the known methyl ethers of D-glucopyranose and D-glucofuranose. Acyclic glucose ethers are not considered in this review. Later articles will deal with monosaccharides other than glucose. It has not been possible to discuss in full all the reactions involved, but to offset this disadvantage the bibliography has been made as complete as possible and tables have been compiled of the physical properties of the methyl-D-glucoses and of their more important derivatives. 

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). 

When methyl a-D-glucopyranoside (an acetal) is treated with dimethyl sulphate in presence of aqueous sodium hydroxide, the methyl ethers of the alcohol functions are formed. The methyl ethers formed from monosaccharides are stable in bases and dilute acids. 

As for the first application considered in Section III,2d, the method for identification of methyl ethers using trideuteriomethyl- derivatives has already been demonstrated to be valid for all of the major types of monosaccharides, and is now receiving practical application.98 We hope that the increasing availability of mass spectrometers will facilitate the introduction... 

Two known types of modification of monosaccharide units with formation of ether bonds include O-methylation and 0-(l-carboxyethyl)ation both (R)- and (S)-lactyl ethers have been identified. 

Similar enol ethers probably serve as intermediates in another common modification-reaction of monosaccharide units especially characteristic of exocellular polysaccharides, namely, the formation of cyclic acetals of pyruvic acid. 

Manninotriose (0.8 g.) was heated with 1.44 g. of phenylhydrazine hydrochloride, 0.22 g. of o-phenylenediamine, and 0.5 g. of glacial acetic acid in 20 ml. of water at 100° in a stoppered tube. After 3 hours, the reaction mixture was cooled and neutralized with 40 ml. of 0.5 N sodium hydroxide. The trisaccharide flavazole was isolated by fractional extraction of the solution with ether (to remove organic bases and colored impurities), ethyl methyl ketone (to remove traces of monosaccharide and disaccharide flavazoles, as well as other colored impurities), and butanol (which extracted the trisaccharide flavazole). Each step in the fractionation process was followed by... 

For the automated synthesis of CS hexasaccharides, Peter Seeberger s group designed a photolabile nitrobenzyl ether-based linker to the Merrifield resin (Scheme 10.15) [31]. Their advanced strategy also differs by the use of monosaccharide donors for the... 

Oxidation of Monosaccharides Reducing Sugars 1117 23-11 Nonreducing Sugars Formation of Glycosides 1119 23-12 Ether and Ester Formation 1121... 

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