Monosaccharides ethers, formation

A disaccharide is derived from two monosaccharides by the formation of an ether (usually, acetal) bridge (Sections 17-7 and 24-11). Hydrolysis regenerates the monosaccharides. Ether formation between a mono- and a disaccharide results in a trisaccharide, and repetition of this process eventually produces a natural polymer (polysaccharide). Polysaccharides constitute the framework of cellulose and starch (Section 24-12). 

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

Because carbohydrates are so frequently used as substrates in kinetic studies of enzymes and metabolic pathways, we refer the reader to the following topics in Ro-byt s excellent account of chemical reactions used to modify carbohydrates formation of carbohydrate esters, pp. 77-81 sulfonic acid esters, pp. 81-83 ethers [methyl, p. 83 trityl, pp. 83-84 benzyl, pp. 84-85 trialkyl silyl, p. 85] acetals and ketals, pp. 85-92 modifications at C-1 [reduction of aldehydes and ketones, pp. 92-93 reduction of thioacetals, p. 93 oxidation, pp. 93-94 chain elongation, pp. 94-98 chain length reduction, pp. 98-99 substitution at the reducing carbon atom, pp. 99-103 formation of gycosides, pp. 103-105 formation of glycosidic linkages between monosaccharide residues, 105-108] modifications at C-2, pp. 108-113 modifications at C-3, pp. 113-120 modifications at C-4, pp. 121-124 modifications at C-5, pp. 125-128 modifications at C-6 in hexopy-ranoses, pp. 128-134. 

Abstract The telomerization of butadiene with alcohols is an elegant way to synthesize ethers with minimal environmental impact since this reaction is 100% atom efficient. Besides telomerization of butadiene with methanol and water that is industrially developed, the modification of polyols is still under development. Recently, a series of new substrates has been involved in this reaction, including diols, pure or crude glycerol, protected or unprotected monosaccharides, as well as polysaccharides. This opens up the formation of new products having specific physicochemical properties. We will describe recent advances in this field, focusing on the reaction of renewable products and more specifically on saccharides. The efficient catalytic systems as well as the optimized reaction conditions will be described and some physicochemical properties of the products will be reported. 

Meso-tartrate is joined to glucuronic acid in glycosidic linkage and by acetal formation to the aldehyde gly-oxylic acid, HOOC—CHO, which is also joined in an ether linkage to the next repeating unit.130 Similar open acetal linkages join monosaccharide units in some bacterial lipopolysaccharides and may occur more widely.1303... 

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. 

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

The ability of compounds 109 and 109a to function as glycosyl donors has been evaluated.62 The choice of solvent was of prime importance to avoid formation of the a anomer. For example, reaction of 109 with monosaccharide derivatives B and D in diethyl ether, in the presence of a catalytic... 

The use of gas chromatography requires volatile compounds, of course, and derivatives must be made of the hydrolyzed monosaccharides. Many investigators have used methylation or acetylation to produce these derivatives (10,16). However, both of these methods require more steps than are desirable with a small sample. In addition, the reaction time required for quantitative conversion to the derivative may be a problem. The use of trimethylsilyl ethers makes the derivatization exceedingly simple and relatively fast. Formation of these derivatives in the absence of water has been shown to occur without anomerization and to proceed quantitatively (30,31). The reaction mixture is chromatographed directly (Figure 9). 

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