Hemiacetals glycosidic linkages

Hemiacetal hydroxyl groups of carbohydrate molecules also may be coupled to amine-containing molecules to form N-glycosidic linkages, such as those in nucleic acids and oligonucleotides. 

Only the configuration of the hemiacetal function is affected in this process. The a configuration of the glycosidic linkage remains unchanged. 

Amylose is a polysaccharide. Its glycoside linkages are inert to Benedict s reagent, but the terminal glucose residues at the ends of the chain and its branches are hemiacetals in equilibrium with open-chain structures. A positive test is expected. 

Hemiacetal and Glycosidic Linkages Explain the difference between a hemiacetal and a glycoside. 

Hemiacetals and hemiketals react with alcohols to form acetals and ketals, respectively. When the cyclic hemiacetal or hemiketal form of a monosaccharide reacts with an alcohol, the new linkage is called a glycosidic linkage, and the compound is called a glycoside. 

T-glycosidic linkage. Trehalose is not a reducing sugar because there is no hemiacetal group in this structure. Instead it has two acetal type linkages, much like sucrose. 

The hemiacetal carbons and the acetal carbons to which they are converted are marked with asterisks. Carbohydrate acetals (and ketals) are referred to as glycosides. The acetal (or ketal) carbon and its two OR substituents are referred to as a glycosidic linkage. To name the glycoside of a specific carbohydrate, the -ose ending of the carbohydrate s name is replaced by -oside, as shown above for methyl a- and /3-D-glucosides. 

Is the linkage a- or j8-7 The linkage between the two monosaccharide molecules is always a glycosidic linkage, i.e., one of the monosaccharide molecules is always linked through its hemiacetal (or hemiketal) OH. Naturally occurring disaccharides are either the a- or the /3-glycoside, not a mixture of a- and )8- as formed in the laboratory. 

D-glucopyranose is a cyclic hemiacetal, which is an equilibrium with its open-chain form that contains an active aldehyde group. In contrast, the anomeric carbon atoms of glucose and fructose are joined in an a-glycosidic linkage in sucrose. Hence sucrose is not in equilibrium with an active aldehyde or ketone form. 

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