Compare alpha Glycosidic bond and beta Glycosidic bond?

Answer 1

A "glycosyl bond" is a generic term and refers to the linkage between the anomeric carbon of a glycosyl moiety and an atom of the aglycon part. A letter in italic placed before the term glycosyl informs about the type of atom linked to the anomeric carbon. For example, in a "N-glycosyl bond" the anomeric carbon of the sugar is linked to a nitrogen atom of the aglycon (for example, the sugar is linked to an amino group of a protein).

The term "glycosidic bond" refers exclusively to the linkage between the anomeric carbon of a glycosyl moiety and an oxygen atom of a hydroxyl compound (an alcohol, another sugar, or the hydroxyl group of serine amino acid). For this reason, to write "O-glycosidic bond" is redundant since the term glycosidic is already indicating that the linkage is with an oxygen atom. Nevertheless, IUPAC accepts the term glycosidic to refer the linkage with sulphur as well. But in this case it is necessary to add the prefix thio- or the letter S (i.e., thio-glycosidic bond or S-glycosidic bond).

Answer 2

Two anomers are designated alpha (α) or beta (β), according to the configurational relationship between the anomeric centre and the anomeric reference atom. The anomeric centre in hemiacetals is the anomeric carbon C-1, which is attached to the hemiacetal oxygen (in the ring) and in hemiketals carbon C-2, attached to the hemiketal oxygen. In aldohexoses and smaller carbohydrates the anomeric reference atom is the furthest chiral centre in the ring (the configurational atom, defining the sugar as D or L). In α-D-glucopyranose the reference atom is C-5.

If the anomeric centre and the anomeric reference atom have opposite stereochemistries, this is an alpha linkage. If they have the same stereochemistry, this is a beta linkage.

eg.

α-D-Glucopyranose has opposite stereochemistry at both C-1 and C-5 (respectively S and R), whereas in β-D-glucopyranose they are the same (both R).

Answer 3

glycocydic bonds are covalent