Carbohydrates sugar substitutes

The incorporation of heteroatoms can result in stereoelectronic effects that have a pronounced effect on conformation and, ultimately, on reactivity. It is known from numerous examples in carbohydrate chemistry that pyranose sugars substituted with an electron-withdrawing group such as halogen or alkoxy at C-1 are often more stable when the substituent has an axial, rather than an equatorial, orientation. This tendency is not limited to carbohydrates but carries over to simpler ring systems such as 2-substituted tetrahydropyrans. The phenomenon is known as the anomeric ect, because it involves a substituent at the anomeric position in carbohydrate pyranose rings. Scheme 3.1 lists... 

K. Aoi, K. Tsutsumiuchi, A. Yamamoto, and M. Okada, Globular carbohydrate macromolecule sugar balls 3. Radial-growth polymerization of sugar-substituted x-amino acid N-carboxyanhydrides (glyco-NCAs) with a dendritic initiator, Tetrahedron, 53 (1997) 15415-15427. 

This technique has been successfully used with 2,3- 3,4-, and 4,5- unsaturated sugars to form C-2, C-3, and C-4 branched-chain carbohydrates. Oxygen-substituted double bonds are also good radical acceptors [74,78]. Radicals also add to a glycal double bond to form C-2 branched-chain sugars [79]. 

The brominated sugars are usually quite stable and can be useful for a variety of purposes [151]. Substitution of bromine with deuterium can be used for preparation of labeled carbohydrates, while substitution with hydrogen sometimes can be used for inverting the stereochemistry. Noteworthy is the conversion of D-glucuronic acid derivative 61 into the corre-... 

Sugar alcohol (e.g., the sugar substitute sorbitol) Other carbohydrate % Vitamin A as beta-carotene Other essential vitamins and minerals... 

The incorporation of heteroatoms can result in stereoelectronic effects that have a pronounced effect on conformation and, ultimately, on reactivity. It is known from numerous examples in carbohydrate chemistry that pyranose sugars substituted... 

Sorbitol, with its many hydroxyl groups, is water soluble. It is almost as sweet as cane sugar and is used in candy making and as a sugar substitute for diabetics. In Chapter 16, we will see that carbohydrates, for example, sucrose (table sugar), starch, and cellulose, have many hydroxyl groups. 

Liquid phase catalytic processing is a promising biorefinery process that produces functionalized hydrocarbons from biomass-derived intermediates (e.g., intermediate hydroxymethylfurfural or HMF). Renewable furan derivatives can be used as substitute building blocks for fossil fuels, plastics, and fine chemicals, ° or to develop biofuels based on C5 and C6 carbohydrates (sugars, hemicellulose, cellulose). Currently, Avantium Chemicals in the Netherlands is developing chemical catalytic routes to generate furanics for renewable polymers, bulk and specialty chemicals, and biofuels. ... 

Very little is known about a possible role of carbohydrates in these diseases only a few general remarks can be made that may be important. Excess carbohydrates are converted into fat, which in turn is deposited in the tissues. The fatty acids produced in this way are of the saturated type, or may have one double bond. Quantitatively the most important are palmitic, stearic, and oleic acid. The higher unsaturated fatty acids cannot be produced from sugars. Laurent (1958) recently reported a very marked elevation of plasma triglyceride when carbohydrate is substituted for fat in the diet, but no effect on the cholesterol level was seen, indicating an acceleration of lipogenesis. 

The widespread occurrence and biological significance of polyoxygenated carbocycles provided the impetus to apply RCM to sugar-derived dienes. Carbohydrate carbocyclization based on a sequence of Vasella reductive opening of iodo-substituted methyl glycosides [25], and RCM of the dienes available from the resulting unsaturated aldehydes, were used to prepare a series of natural compounds (Schemes 5-7). 

Note 2. To maintain integrity of carbohydrate names, it is sometimes helpful to overstep the strict order of principal group preference specified in general organic nomenclature [13,14]. For example, a carboxymethyl-substituted sugar can be named as such, rather than as an acetic acid derivative (see 2-Carb-31.2). 

Where the new bridge is attached to oxygen (or a replacement heteroatom, e.g. nitrogen in an amino sugar) already indicated in the name of the unbridged carbohydrate, the bivalent substituent prefix denotes substitution at two heteroatoms as outlined in 2-Carb-24.1 and 2-Carb-25 [method (b)]. Heteroatoms not directly bonded to the carbohydrate chain are regarded as part of the bridge. 

An extreme example of slime production is found in Leuconostoc dextranicum and L. mesenteroides where so much carbohydrate, called dextran, may be produced that the whole medium in which these cells are growing becomes almost gel-like. This phenomenon has caused pipe blockage in sugar refineries and is deliberately encouraged for the production of dextran as a blood substitute (Chapter 25). 

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