Sugar Substitution

In homo-DNA (h-DNA) and pyranosyl-RNA (p-RNA), the hexitol ring is frozen in a single y-endo- ke eonformation, as opposed to the multiple conformations accessible to the furanose of DNA and RNA. The h-DNA duplexes have a quasi-linear orientation as opposed to the superhelical structure of DNA duplexes, and the distance between the base stacking planes is larger relative to that of DNA. The h-DNA duplexes also have different pairing stability, e.g., the pairing priorities of A-A exceeds that of A-T. In contrast to h-DNA, p-RNA, which is also quasi-linear, does not show altered pairing priorities. 

The hexose rings in these analogues have a different regiochemistry of attachment to the backbone - C-6, C-4 in h-DNA and C-4, C-2 in p-RNA - and the base stacking is different. For example, studies of self-complementary sequences, such as 5 -TTTTAAAA-3 and 5 -AAAATTTT-3, which show equivalent energies with native duplexes, are quite different with the modified backbones. In p-RNA, the for the duplex of the first sequence is much higher than that of the second. In h-DNA, the situation is reversed and the duplex of the second sequence is more stable than the first. The different backbones have been proposed to alter the inclination between the backbone 

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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... 

The system shown is heavily used in food processing applications such as milk or chocolate crumb production, sugar substitutes, modified starch, and alginates. In addition to food processing applications, such a system is used in the processing of heat-sensitive pharmaceuticals, polymer suspensions like latex, in processing pigments and dyestuffs, and pesticides. 

D-Glucitol, the alditol produced by reduction of D-glucose, is itself a naturally occurring substance present in many fruits and berries. It is used under its alternative name, D-sorbitol, as a sweetener and sugar substitute in foods. 

Table 25.2 Sweetness of Some Sugars and Sugar Substitutes...

Preparation of TMS derivative To derivatize the amino sugars as well as the nonamino sugars, substitute TRI-SIL TBT or TRI-SIL/BSA (Formula P) reagent for TRI-SIL Z and follow the procedure given in Section I,A,1. 

Allcock, H, R., and Scopelianos, A. G., Sjmthesis of sugar-substituted cyclic and polymeric phosphazenes, and their oxidation, reduction, and acetylation reactions. Macromolecules. 36. 715, 1983. 

Four cyanidins with 4 -glucosidation were recently isolated in minor amounts from pigmented scales of red onion. Two were the only anthocyanins with B ring sugar substitutions and no glycosyl moieties in anthocyanidin position 3, whereas the other two were also glycosilated at the usual position 3. ... 

Sugar Substitutes Americans Opt for Sweetness and Lite. John Henkel, FDA Consumer Magazine, November-December 1999, http //www.fda.gov/fdac/features/1999/699 sugar.html... 

F. Paul, A. Lopez-Munguia, M. Remaud, V. Pelenc, and P. Monsan, Process for the enzymatic preparation of oligodextrans useful in the production of sugar substitutes, and these oligodextrans, (1992). U.S. Patent 5,141,858. 

M. Gottschaldt, D. Koth, D. Muller, I. Klette, S. Rau, H. Gorls, B. Schafer, R. P. Baum, and S. Yano, Synthesis and structure of novel sugar-substituted bipyridine complexes of rhenium and 99m-technetium, Chem. Eur. 13 (2007) 10273-10280. 

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. 

A large number of sweet-tasting substances has been described in the scientific literature, most of them in the course of the last 20 to 30 years. The number of substances having an intense sweetness is by far higher than the number of products with a sweetening power similar to sucrose which could therefore be used as bulking sugar substitutes. Only a small number of these has found... 

Lavigne JJ, Broughton DL, Wilson JN, Erdogan B, Bunz UHF (2003) Surfactochromic conjugated polymers surfactant effects on sugar-substituted PPEs. Macromolecules 36 7409-7412... 

Phillips RL, Kim I-B, Carson BE, Tidbeck B, Bai Y, Lowary TL, Tolbert LM, Bunz UHF (2008) Sugar-substituted poly(p-phenyleneethynylene)s sensitivity enhancement toward lectins and bacteria. Macromolecules 41 7316-7320... 

Sugars substituted by a functionalized fluoroalkyl chain have been used to glycosylate proteins, such as albumin (BSA, HSA) and haptenes. In the latter case, the fluorine atoms can be used as probes in F NMR to determine quantitatively the bonding of the haptene. " ... 

Alkylation of 2-methoxycarbonyl-l-oxoindane with these sugar-substituted sulfonium salts gives the (/f)-2-alkyl derivatives with enantiomeric excesses up to 12%, while alkylation of ethyl 2-methyl-3-oxobutanoate with allyl or benzyl(aryl)sulfonium perchlorates gives 2-allyl-(or benzyl)-substituted ethyl 2-methyl-3-oxobutanoates 5 with enantiomeric excess up to 25%12. 

C-3 in the unsubstituted compound.176,177 However, at the time of these experiments, only C-3 substitution had been observed with 2,3-anhydropentofuranosides, and the results of investigation of this reaction suggest that the amino sugar substituted at C-2 is the major product.184 With thiocyanate ion, substitution also occurs at C-3, leading to the thietane derivative, namely, methyl 3,5-anhydro-3-thio-a-D-xylofuranoside (59) but, as this compound was obtained in only 25% yield, the major pathway may involve 2-substitution, leading to products not characterized.178... 

In view of the appearance ol neuraminic acid in evolution, the question must be posed as to which molecule pre-existed, and may still be found, in those primitive animals unable to synthesize sialic acids where comparable functions might be expected, for example, in cell membranes, or in the nervous system. Are such molecules uronic acids, or neutral sugars, substituted by such acids as phosphoric or sulfuric acid At this point, the present essay may he concluded by point-... 

The prototype industrial process based on this concept is the Ruhrchemie-Rhone Poulenc process for the hydroformylation of propylene to butanal94,219,220 (see Section 7.3.1). Because of the use of appropriately modified water-soluble ligands, the catalyst resides and operates in the aqueous phase. The particular features of this process are the positive energy balance and easy catalyst recovery, namely, the simply circulation of the aqueous catalyst solution. New types of water-soluble Ir and Rh complexes with tris(hydroxymethyl)phosphine222 were described, and the biphasic hydroformylation of 1-hexene was accomplished in ionic liquids.223 A cationic sugar-substituted Rh complex displays high regioselectivity to branched aldehydes.224... 

Xylitol is as sweet as sucrose and has been used as a food additive. Because it does not induce formation of dental plaque, it is used as a replacement for sucrose in chewing gum. It appeared to be an ideal sugar substitute for diabetics. However, despite the fact that it is already naturally present in the body, ingestion of large amounts of xylitol causes bladder tumors as well as oxalate stones in rats and mice. Its use has, therefore, been largely discontinued. A possible source of the problem may lie in the conversion by fructokinase of some of the xylitol to D-xylulose 1 -P, which can be cleaved by the xylulose 1-P aldolase to dihydroxy acetone P and glycolaldehyde. 

Polyols are frequently used sugar substitutes and are particularly suited to situations where their different sensory and functional properties are attractive. In addition to sweetness, some of the polyols have other useful properties. For example, although it contains the same number of calories/gram as other sweeteners, sorbitol is absorbed more slowly from the digestive tract than is sucrose. It is, therefore, useful in making foods intended for special diets. When consumed in large quantities (1-2 oz 25,059 g)/dav, sorbitol can have a laxative effect, apparently because of its comparatively slow intestinal absorption. 

Fructose can also be used as a sugar substitute in crystalline or syrup form. It is present naturally in many fruits and in honey, but commercially it is manufactured using sucrose as a stalling material. Sucrose is fust hydrolysed to... 

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