Oxygen glycosides

Figure 1.17 Examples of (a) oxygen glycosides, (b) nitrogen glycosides and (c) carbon glycosides. The shaded parts of the structures are the aglycone sections...

Polysaccharides (glycans) are carbohydrates whose structures consist of monosaccharide residues joined together by oxygen glycosidic linkages (Figure 1.18). 

These compounds will be dealt with here because of their structural analogy with oxygenated glycosides, although their role is quite different. These intermediates are not often used in synthesis. Universally widespread natural structures are found in this family. Certain transformations described below are good models of well-established biosynthetic pathways. 

Sialidase inhibitors based on the A-acetylneuraminic acid (NeuSAc) template could include substrate-like, product-like, and transition state-like compounds (reviewed [87]). Sialidase-resistant substrate analogs where the natural oxygen glycosidic linkage is replaced with carbon or sulfur (e.g., 9, 10 [88], Figure 22.4)... 

A point to be emphasized about glycoside formation is that despite the presence of a number of other hydroxyl groups m the carbohydrate only the anomenc hydroxyl group IS replaced This is because a carbocation at the anomenc position is stabilized by the nng oxygen and is the only one capable of being formed under the reaction conditions... 

Note. This prefix includes the oxygen of the glycosidic bond. An example is given in 2-Carb-31.2 more are given below. 

Note. This prefix does not include the oxygen of the glycosidic group. This is the appropriate method for naming natural products if the trivial name includes the OH group. The system is also used to name oligosaccharides (see 2-Carb-37). 

Structures in which the linking glycosidic oxygen is replaced by -CH2- may be named by use of the replacement prefix carba- (c/. 2-Carb-34.2) for emphasis of homomorphic relationships. The oxygen replaced is given the locant of the carbon atom to which it is attached in the residue with the lower roman numeral (cited as superscript) (cf 2-Carb-37.2), with suffix a1. 

If the glycosidic oxygen link is replaced by -0-NH-, normal amino sugar nomenclature can be employed. 

Fig. 14.—Catalysis of glycosidic oxygen protonation by hydrated magnesium...

The "lining" of the cavity glycosidic oxygen bridges, high eiect ron density... 

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