Some Important Oligosaccharides

When animals consume sucrose, it is hydrolyzed to glucose and fructose, which are then degraded by metabolic processes to provide energy. Humans consume large quantities of sucrose, and excess consumption can contribute to health problems this feet has led to a search for other sweetening agents. One 

Fruits, Flowers, Striking Colors, and Medicinal Uses Too 

Many flavors involve sugar glycosides. Two familiar ones are cinnamon and vanilla, in which the sugars bond to cinnamaldehyde (3-phenyl-2-propenal) and vanillin, respectively. Both of these compounds are aromatic aldehydes. The distinctive taste of the kernel in a peach or apricot pit (a bitter-almond flavor) is due to laetrile, a controversial substance suggested as a cancer treatment by some. 

The disaccharide sucrose is common table sugar. It consists of glucose and fructose linked by a glycosidic bond. 

Lactose, found in milk, and maltose, obtained from starch, are two other common disaccharides. 

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In addition, the CB glycoside method has been successfully applied to the synthesis of some important oligosaccharides, trisaccharide 89, tetrasaccharide 98, and octaarabinofbranoside 112 as the latent-active glycosylation method, which is a valuable strategy for the rapid assembly of oligosaccharides. 

Some important contributions to the conformational analysis of oligosaccharides have come from the determination of the structure of oligosaccharides which form complexes with protein. In this context the complex of lysozyme with chitohexaose [40] and the phosphorylase complex with maltoheptaose [41, 42] and maltopentaose [43] have been resolved to atomic resolution. 

The molecular mass of a oligosaccharide can be calculated from residue masses of individual sugar units in the molecule from M = 18 + S (Residue masses of monomeric units). Residue masses of some important monomeric units are given in Table 20.1. Relevant sugar monomer stmctures are shown in Figure 20.1. 

Specific rotation constants, designated as [a] for sodium D-line light at 20-25°C, are listed in Table 4.8 for some important mono- and oligosaccharides. The specific rotation constant [a] at a selected wavelength and temperature is calculated from the angle of rotation, a, by the equation ... 

Due to the strongly acidic conditions usually required for their activation, the ox-azoline method has not found broad application in the field of oligosaccharide synthesis. They are incompatible with acid-sensitive protecting groups and with poorly nucleophilic acceptors. Their employment seems to be restricted to reactive acceptors. Despite these severe limitations, some important examples of the application of the oxazoline method have been reported [136]. 

Oligosaccharide side chains of glycoproteins play an important role in recognition processes (Hubbard and Ivatt, 1981). Some phosphorylated oligosaccharides have been found to date, and by means of P NMR it has been possible to differentiate among phosphomonoesters, phosphodiesters, and artifacts like cyclic phosphates that are introduced by harsh purification methods (Hashimoto et al, 1980). Further studies should allow insight into the motional characteristics of such protein-bound moieties. 

Oligosaccharides also occur widely as components (via glycosidic bonds) of antibiotics derived from various sources. Figure 7.20 shows the structures of a few representative carbohydrate-containing antibiotics. Some of these antibiotics also show antitumor activity. One of the most important of this type is bleomycin A2, which is used clinically against certain tumors. 

Several enzymatic routes with sucrase-type enzymes have been established for oligosaccharide synthesis, some of which are applied industrially for food and feed ingredients, and important examples are compiled.5 Convenient routes for new oligosaccharides, however, are rarely available. 

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