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In the process of studying for my upcoming biochemistry exam, I have stumbled over the classification of glycosidic bonds. I want to be able to distinguish $\alpha$- from $\beta$-glycosidic bonds. Unfortunately, even after reading through this page, I don't really understand how to go about classifying the bonds in e.g. an oligosaccharide.

Oligosaccharide (Source)

Now, I am inclined to say that both of these anomeric linkages are of type $\alpha$, because the O-glycosidic bond is axial to the respective sugar rings. Is that a correct way of reasoning?

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up vote 1 down vote accepted

Here's my interpretation, as far as I can get, which agrees with your deduction that both of the O-glycosidic bonds involve α epimers. (If the epimeric carbon has an -OH in the axial direction then this is the α anomer.)

Do you have the name of this compound?

Let's hope that a real glycobiologist comes along.

Supplementary I'm now not sure that it is even possible to assign an anomeric state to the sugar marked as ?. There is no indication in the diagram of the presence of a -CH2OH substituent on the ring - it appears to have a methyl group instead. If that group was a -CH2OH then the putative anomeric C would indeed be in the α form since it is pointing in the opposite direction from the "-CH2OH" (c.f. the two galactose residues). If ? is a deoxy- derivative of a sugar then it may be that the convention still holds.

enter image description here

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Unfortunately, I don't have a name for the compound, I just grabbed an image from the internet that looked roughly like the exam problem I was trying to solve. – tschoppi Jan 30 '14 at 19:56

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