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A glycosidic bond or glycosidic linkage is a type of ether bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. Formation of ethyl glucoside: Glucose and ethanol combine to form ethyl glucoside and water .
The formation of a glycosidic linkage results in the formation of a new stereogenic centre and therefore a mixture of products may be expected to result. The linkage formed may either be axial or equatorial (α or β with respect to glucose). To better understand this, the mechanism of a glycosylation reaction must be considered.
The glycosidic bond is formed from a glycosyl donor and a glycosyl acceptor. There are four types of glycosidic linkages: 1, 2-trans-α, 1, 2-trans-beta, 1, 2-cis-α, and 1, 2-cis-beta linkages. 1, 2-trans glycosidic linkages can be easily achieved by using 2-O-acylated glycosyl donors (neighboring group participation).
Depending on whether the glycosidic bond lies "below" or "above" the plane of the cyclic sugar molecule, glycosides are classified as α-glycosides or β-glycosides. Some enzymes such as α-amylase can only hydrolyze α-linkages; others, such as emulsin, can only affect β-linkages. There are four type of linkages present between glycone and ...
The other challenge of chemical glycosylation is the stereoselectivity that each glycosidic linkage has two stereo-outcomes, α/β or cis/trans. Generally, the α- or cis-glycoside is more challenging to synthesis. [19]
This β-linkage is similar to glycosidic bond between the sugar moieties in the glycan structure as described above. Instead of being attached to a sugar hydroxyl group, the anomeric carbon atom is attached to an amide nitrogen. The energy required for this linkage comes from the hydrolysis of a pyrophosphate molecule. [4]
When the glycosidic linkages and configurations of the monosaccharides are known, they may be included as a prefix to the name, with the notation for glycosidic linkages preceding the symbols designating the configuration. [3] The following example will help illustrate this concept: (1→4)-β-D-Glucan
They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with water using amylase enzymes as catalyst, which produces constituent sugars (monosaccharides or oligosaccharides). They range in structure from linear to highly branched.