Meso Carbohydrates?

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Is it true that carbohydrates cannot exist as meso compounds? I read this somewhere in EK Bio Lecture 1?
 
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They absolutely can. When you take orgo you use the ability to make some sugars meso through fischer kiliani and whatnot.... I'll have to look at that since i have the book
 
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Well aldoses cannot.

Since on one end, the carbon has an aldehyde, and on the other end, the carbon has a hydroxyl group.

Ketoses cannot either, because of the ketone and and hydroxyl group, pretty much for the same reason.
 
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Doodl3s said:
They absolutely can. When you take orgo you use the ability to make some sugars meso through fischer kiliani and whatnot.... I'll have to look at that since i have the book
Click to expand...

Dr Gerrard said:
Well aldoses cannot.

Since on one end, the carbon has an aldehyde, and on the other end, the carbon has a hydroxyl group.

Ketoses cannot either, because of the ketone and and hydroxyl group, pretty much for the same reason.
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Gotchya, thanks. Also, I know that humans can only absorb D sugars. Does this mean that we can't absorb L sugars at ALL? Also, I know that the 20 amino acids have the L configuration. Does this mean that we cannot absorb D amino acids? Thanks.
 
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pookiez88 said:
Gotchya, thanks. Also, I know that humans can only absorb D sugars. Does this mean that we can't absorb L sugars at ALL? Also, I know that the 20 amino acids have the L configuration. Does this mean that we cannot absorb D amino acids? Thanks.
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So what's the consensus on meso carbs? I figured it would be quite difficult to be meso. I was mentally picturing cutting a carb in half vertically to see if it would work as I know cutting it horizontally definitely wouldnt (in my mind i have the chain of carbons being vertical). If I had to say I would say they cannot be meso.

As for your L and D questions: I beleive you are right. I had a question in TPR about the sugars and we can't absorb L sugars. I haven't got confirmation on the D aa's - i know we don't have them.......and i highly doubt we can absorb them (i think bacteria can....). And for sugars know that lactose is an annomoly as we shouldn't be able to digest it but some humans can.
 
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sv3 said:
So what's the consensus on meso carbs? I figured it would be quite difficult to be meso. I was mentally picturing cutting a carb in half vertically to see if it would work as I know cutting it horizontally definitely wouldnt (in my mind i have the chain of carbons being vertical). If I had to say I would say they cannot be meso.

As for your L and D questions: I beleive you are right. I had a question in TPR about the sugars and we can't absorb L sugars. I haven't got confirmation on the D aa's - i know we don't have them.......and i highly doubt we can absorb them (i think bacteria can....). And for sugars know that lactose is an annomoly as we shouldn't be able to digest it but some humans can.
Click to expand...

Why an anomaly? It is made up of D-glucose and D-galactose.
 
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sv3 said:
So what's the consensus on meso carbs? I figured it would be quite difficult to be meso. I was mentally picturing cutting a carb in half vertically to see if it would work as I know cutting it horizontally definitely wouldnt (in my mind i have the chain of carbons being vertical). If I had to say I would say they cannot be meso.

As for your L and D questions: I beleive you are right. I had a question in TPR about the sugars and we can't absorb L sugars. I haven't got confirmation on the D aa's - i know we don't have them.......and i highly doubt we can absorb them (i think bacteria can....). And for sugars know that lactose is an annomoly as we shouldn't be able to digest it but some humans can.
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Yeah, why is lactose an anomaly? I know some people are lactose intolerant but I am thinking that has more to do with genetics.
 
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sv3 said:
animals dont digest B-glucosidic linkages and thats how the monomers are linked. Some humans happen to have lactase though.
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I think you meant most humans have lactase? As some people lack lactase and are lactose intolerant?
 
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pookiez88 said:
I think you meant most humans have lactase? As some people lack lactase and are lactose intolerant?
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yeah some have it and some don't. Sure perhaps "most" is a better word? I just know it stands out since we can't generally digest sugars with B-links
 
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sv3 said:
yeah some have it and some don't. Sure perhaps "most" is a better word? I just know it stands out since we can't generally digest sugars with B-links
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Yeah, I think most would be a better word....almost most humans have it, but you're right about the beta linkages.
 
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pookiez88 said:
Yeah, I think most would be a better word....almost most humans have it, but you're right about the beta linkages.
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i think most humans think they have it. If most really did, stomach issues wouldnt be as prevelent.......but whateva........the B link thing is the key!
 
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So what's the consensus on meso carbs? I figured it would be quite difficult to be meso. I was mentally picturing cutting a carb in half vertically to see if it would work as I know cutting it horizontally definitely wouldnt (in my mind i have the chain of carbons being vertical). If I had to say I would say they cannot be meso.
Click to expand...

I think that they can be. I think ketotriose and ketopentose are both good examples.

I just did EK orgo problem that I think is wrong in saying they can't be. (page 87 # 85.)
 
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tvrb said:
I think that they can be. I think ketotriose and ketopentose are both good examples.

I just did EK orgo problem that I think is wrong in saying they can't be. (page 87 # 85.)
Click to expand...

The ones you listed there are not meso, because there are no chiral centres.

But, there definitely are meso carbohydrates. For example, inositol.
 
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Thanks for the response!
Also thanks for the example with inositol.

i realized right after i posted that ketotriose has no chiral center like you said. :-/
I still don't really see, however, why 3-ketopentose isn't both chiral and meso.
H2COH-HCOH-CO-HCOH-H2COH
aren't both c2 and c4 chiral centers?
 
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