L-Fucose is one of the naturally occurring L monosaccharides. It is present in the short chains of monosaccharides by which blood groups are classified. Compare the structure of L-fucose shown in the margin with the structures of α- and β-D-galactose and answer the following questions.
d. "Fucose” is a common name. Is 6-deoxy-L-galactose a correct name for fucose? Why or why not?

Question

L-Fucose is one of the naturally occurring L monosaccharides. It is present in the short chains of monosaccharides by which blood groups are classified. Compare the structure of L-fucose shown in the margin with the structures of α- and β-D-galactose and answer the following questions.
d. "Fucose” is a common name. Is 6-deoxy-L-galactose a correct name for fucose? Why or why not?

d. "Fucose” is a common name. Is 6-deoxy-L-galactose a correct name for fucose? Why or why not?

Structural diagram of l-Fucose, a monosaccharide, with labeled carbon atoms and hydroxyl groups.

Accepted Answer

Hi, everybody. And welcome back. Let's look at our next problem. L Ram nose is a deoxy sugar that can be found in various plants. Compare the structure of rams with the structure of alpha L manos. And answer the following question is six deoxy L manos, an appropriate name for L rams. Explain why or why not. And we're given the structures of both L rams and alpha L manos. Both are six carbon sugars. They are drawn as Hayworth structures. So we see they're in the ring form and we can see whether the groups are above or below the plane of the ring. So we just need to look at the differences between them and we know we'll need to look at where this deoxy nomenclature would be with. The name suggested is six deoxy al Manos. So we'll need to find carbon six. So what's the convention for numbering the rings when we have this cyclical sugar form? Well, we start with the anomic carbon, which is the only carbon in the ring attached to two oxygens. So find the oxygen in the ring and there will be a carbon attached to it that also has a hydroxyl group. So we see that carbon, it has two oxygens. The carbon on the other side has one oxygen and a carbon and another carbon. So it doesn't have two oxygens attached to it. So this anomic carbon is carbon one and then you proceed clockwise or I'll say number clockwise from the anomic carbon. So we have carbon one, go around our ring clockwise 345 and then carbon six is attached to carbon five projecting below the plane of the ring. I did the numbering here on alpha L manos. Let's do it on ram nose. So the same position for the anomic carbon number 12345 carbon six projecting below the ring just as with alpha al Manos. So when we look at each of those carbons, all of the hydroxyl groups are in the same orientation with respect to the plane of the ring, either above or below. So hydroxyl at carbon one above at carbon two below carbon three below at carbon four above. And then when we look at our carbon six, because that is the one of interest since we see the name proposed has six deoxy L ram nose. That carbon six is highlight that in pink part of a methyl group, there's no oxygen there. Whereas in alpha Al Manos, carbon six has a hydroxyl group. So we can see that the only difference between these two molecules is the missing hydroxyl group on carbon six. So is this an appropriate name? Yes, is our answer because six deoxy indicates that the only difference between L rams and L Manos is a missing hydroxyl group on carbon six. So that will be our answer. And the reason why the answer is yes. See you in the next video.

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Key Concepts

Monosaccharide Structure

Deoxy Sugars

Nomenclature in Biochemistry