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A glycosidic bond is a covalent bond that joins a carbohydrate to another functional group or molecule. A substance containing a glycosidic bond is termed a glycoside. Glycosides may be categorized according to elements involved in the chemical bond.
Glycosidic Bond Example
An N-glycosidic bond connects the adenine and ribose in the molecule adenosine. The bond is drawn as a vertical line between the carbohydrate and the adenine.
O-, N-, S-, and C-glycosidic Bonds
Glycosidic bonds are labeled according to the identity of the atom on the second carbohydrate or the functional group. The bond formed between the hemiacetal or hemiketal on the first carbohydrate and the hydroxyl group on the second molecule is an O-glycosidic bond. There are also N-, S-, and C-glycosidic bonds. Covalent bonds between the hemiacetal or hemiketal to -SR form thioglycosides. If the bond is to SeR, then selenoglycosides form. Bonds to -NR1R2 are N-glycosides. Bonds to -CR1R2R3 are termed C-glycosides.
The term aglycone refers to any compound ROH from which a carbohydrate residue has been removed, while the carbohydrate residue may be referred to as the glycone. These terms are most commonly applied to naturally occurring glycosides.
Α- and β-glycosidic Bonds
The orientation of the bond may be noted, too. α- and β-glycosidic bonds are based on the stereocenter furthest from saccharide C1. An α-glycosidic bond occurs when both carbons share the same stereochemistry. Β-glycosidic bond forms when the two carbons have different stereochemistry.