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Intramolecular Aglycon Delivery
Intramolecular aglycon delivery is a synthetic strategy for the construction of glycans. This approach is generally used for the formation of difficult glycosidic linkages. Introduction Glycosylation reactions are very important reactions in carbohydrate chemistry, leading to the synthesis of oligosaccharides, preferably in a stereoselective manner. The stereoselectivity of these reactions has been shown to be affected by both the nature and the configuration of the protecting group at C-2 on the glycosyl donor ring. While 1,2-''trans''-glycosides (e.g. α-mannosides and β-glucosides) can be synthesised easily in the presence of a participating group (such as OAc, or NHAc) at the C-2 position in the glycosyl donor ring, 1,2-''cis''-glycosides are more difficult to prepare. 1,2-''cis''-glycosides with the α configuration (e.g. glucosides or galactosides) can often be prepared using a non-participating protecting group (such as Bn, or All) on the C-2 hydroxy group. However, 1,2-''ci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycan
The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan, even if the carbohydrate is only an oligosaccharide. Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan (or, to be more specific, a glucan) composed of β-1,4-linked D-glucose, and chitin is a glycan composed of β-1,4-linked ''N''-acetyl-D-glucosamine. Glycans can be homo- or heteropolymers of monosaccharide residues, and can be linear or branched. Glycans and proteins Glycans can be found attached to proteins as in glycoproteins and proteoglycans. In general, they are found on the exterior surface of cells. O- and N-linked glycans are very common in eukaryotes but may also be found, although ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |