alpha vs. beta link: what's the difference?

[SaintJude]

What's the difference b/w an alpha glycosidic linkage and a beta glycosidic linkage?

For example, who can guess which is alpha & beta below?

View attachment Picture 23.png

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[kasho11]

I think it's just alpha glycosidic linkage points down, and beta glycosidic linkage points up, the same as in alpha and beta sugars.

So would the first one be alpha and the second beta?

 

[SaintJude]

Yeah you're right, but WHAT points down and up? Sorry, I'm still confused.

 

[dmf2682]

What's the difference b/w an alpha glycosidic linkage and a beta glycosidic linkage?

For example, who can guess which is alpha & beta below?

View attachment 18902

To answer your question I need samples of both, a jar of spit, and proton nmr apparatus.

 

[MedPR]

What's the difference b/w an alpha glycosidic linkage and a beta glycosidic linkage?

For example, who can guess which is alpha & beta below?

View attachment 18902

Looks alpha and beta to me. Alpha = the bond comes from an alpha monomer. Beta = the bond comes from a beta monomer.

For example, alpha-1,4 means the anomeric carbon (carbon 1) of one monosaccharide is in the alpha configuration and binds to C-4 of a second monosaccharide.

 

[kasho11]

In sugars it's the hydroxyl group on the primary carbon, if the OH connected to Carbon #1 points up, it's beta, if it points down, it's alpha. Look at the picture of alpha and beta glucopyranose here http://en.wikipedia.org/wiki/Anomer

So it's the same idea for a glycosidic linkage, but instead of a hydrogen attached to the oxygen (making it a hydroxyl group) there are additional molecules attached.

To put it simply if the attached oxygen points up its beta, if the attached oxygen points down its alpha.

 

[MedPR]

Yeah you're right, but WHAT points down and up? Sorry, I'm still confused.

The hydroxyl group on the anomeric carbon. "up" = faces same direction as the CH2OH group = Beta. You can think of it as "BZ on the same side" in reference to E,Z isomerism where Z is on the "zame zide" and since B kind of rhymes with Z, it makes it easy to remember (for me, at least).

Alpha is just the opposite, the hydroxyl on C-1 (the anomeric carbon) points "down" or away from the alcohol group.

 

[SaintJude]

Where is the hydroxyl group you guys are referring to in those molecules? All I see are ethers...

Wait! Let me label the carbons in this picture...

View attachment Picture 26.png

Ok, how what's up and down again?

 

[MedPR]

Where is the hydroxyl group you guys are referring to in those molecules? All I see are ethers...

Condensation reaction combines the two monosaccharides. Trace the shared oxygen back to the group on the left. See how it is pointing away from where the CH2O would be if it were included in the picture? That makes it alpha.

 

[SaintJude]

Condensation reaction combines the two monosaccharides. Trace the shared oxygen back to the group on the left. See how it is pointing away from where the CH2O would be if it were included in the picture? That makes it alpha.

So are you saying, b/c the carbon 3 and carbon 4 are situated "above" the shared oxygen, it's an alpha linkage? So it looks like the shared oxygen is opening it's arms up like this clapping emoticon?

 

[MedPR]

So are you saying, b/c the carbon 3 and carbon 4 are situated "above" the shared oxygen, it's an alpha linkage? So it looks like the shared oxygen is opening it's arms up like this clapping emoticon?

Sorry, I thought I already put this image up.

That should clear it up.

 

[chiddler]

I think you guys are complicating it. If the two sugars are in plane, then it's beta. If they are out of plane, then it's alpha.

An easy way to remember this is to think of cellulose. Cellulose is in plane and is very tough. Notice how all the sugars stand in a line like little soldiers. Beta.

Glycogen is similar to cellulose but is alpha.

In stjude's image, first is alpha second is beta.

edit: "bulky" is not accurate.

 

[MedPR]

I think you guys are complicating it. If the two sugars are in plane, then it's beta. If they are out of plane, then it's alpha.

An easy way to remember this is to think of cellulose. Cellulose is in plane and is very tough. Notice how all the sugars stand in a line like little soldiers. Beta.

Glycogen is similar to cellulose but is alpha.

In stjude's image, first is alpha second is beta.

edit: "bulky" is not accurate.

What makes something in plane vs out of plane?

 

[SaintJude]

Ok, sorry! Let me try this again. You're in plane and out of plane don't make sense to me yet.

I understand that on the left, c-1 and c-2 are up so it's alpha.

On the right c-1 and c-2 are on opposite sides, down and up, so it's beta ?

 

[MedPR]

Ok, sorry! Let me try this again. You're in plane and out of plane don't make sense to me yet.

I understand that on the left, c-1 and c-2 are up so it's alpha.

On the right c-1 and c-2 are on opposite sides, down and up, so it's beta ?

As far as I know, alpha and beta depends only on the configuration of the anomeric carbon in the bond.

 

[SaintJude]

Oh! If they're both the same configuration it's alpha and if not it's beta...

 

[chiddler]

What makes something in plane vs out of plane?

if the two sugars are on the same plane, like

x ---- x

out of plane is like

x ---
aaaa----
aaaaaaa---x

 

[SaintJude]

As far as I know, alpha and beta depends only on the configuration of the anomeric carbon in the bond.

if the two sugars are on the same plane, like

x ---- x

out of plane is like

x ---
aaaa----
aaaaaaa---x

Love that shortcut! Thank you so much for taking the time to write that out.

Alpha "out of plane"

beta " same plane"

 

[MedPR]

Oh! If they're both the same configuration it's alpha and if not it's beta...

Probably, but I don't know if that's always the case. If the anomeric carbon in the bond is alpha, the linkage is alpha. If the anomeric carbon is beta, the linkage is beta.

if the two sugars are on the same plane, like

x ---- x

out of plane is like

x ---
aaaa----
aaaaaaa---x

Huh? I think I know what you mean.. Does that method work if things are twisted around? What are the two linkages in this one.. I guess if you are good at manipulating and rotating in your head then that in/out of plane works. It's easier for me to use the anomeric though.

 

[chiddler]

Probably, but I don't know if that's always the case. If the anomeric carbon in the bond is alpha, the linkage is alpha. If the anomeric carbon is beta, the linkage is beta.





Huh? I think I know what you mean.. Does that method work if things are twisted around? What are the two linkages in this one.. I guess if you are good at manipulating and rotating in your head then that in/out of plane works. It's easier for me to use the anomeric though.

Under what circumstances are the sugars twisted? I've never seen it drawn like that.

But knowing that it's a trick question, I can tell you that the upper link is beta and the bottom one is alpha lol

 

[MedPR]

Under what circumstances are the sugars twisted? I've never seen it drawn like that.

But knowing that it's a trick question, I can tell you that the upper link is beta and the bottom one is alpha lol

It's not a trick. It's amylopectin; alpha 1,6 and alpha 1,4

http://discovery.kcpc.usyd.edu.au/9.5.1/9.5.1_starch1.html

Both anomeric carbons are alpha!

 

[chiddler]

It's not a trick. It's amylopectin; alpha 1,6 and alpha 1,4

http://discovery.kcpc.usyd.edu.au/9.5.1/9.5.1_starch1.html

Both anomeric carbons are alpha!

then my intuitive guess would have been correct. check out the wiki, which is much more predictable with what i wrote.

yeah =/

have you seen it drawn like that before? (or anybody else reading)

 

[MedPR]

then my intuitive guess would have been correct. check out the wiki, which is much more predictable with what i wrote.

yeah =/

have you seen it drawn like that before? (or anybody else reading)

I haven't seen it drawn that way before, but it looks like a legit way to draw it. Whoever made the image seems to have wanted to keep the axial/equatorial pointing in the way you normally would draw them in chair conformers.

 

[Godric]

What's the difference b/w an alpha glycosidic linkage and a beta glycosidic linkage?

For example, who can guess which is alpha & beta below?

View attachment 18902

Ok so I am taking this from TBR Orgo Book 2. First you should know that the -OH on Alpha rings are axial, on Beta rings they are equatorial. So by knowing that you can figure out what type of bond you have.

Hope that helps.

Edit, the second picture is Amylopectin with the main linkages being alpha-1-->4 and the branching being alpha 1-->6
Edit, for some reason someone reported the photo, I've re-uploaded it. If someone has an issue with it I suggest you message me.