In the monosaccharide derivatives known as sugar alcohols,...

Name: Problem 1, Chapter 7: Lehninger Principles of Biochemistry
Uploaded: 2023-12-10T14:21:24-08:00
Duration: 2 min 26 s
Channel: Anand Jangid
Description: In the monosaccharide derivatives known as sugar alcohols, the carbonyl oxygen is reduced to a hydroxyl group. For example, D-glyceraldehyde can be reduced to glycerol. However, this sugar alcohol is no longer designated D or L. Why?

In the monosaccharide derivatives known as sugar alcohols, the carbonyl oxygen is reduced to a hydroxyl group. For example, D-glyceraldehyde can be reduced to glycerol. However, this sugar alcohol is no longer designated D or L. Why?

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Key Concepts

Loss of Stereochemical Reference in Sugar Alcohols

Sugar alcohols, being the reduced forms of sugars, often exhibit symmetry or have differently defined stereocenters that do not correspond to the original configuration seen in the parent sugars. This change means that the molecule might no longer be accurately described by the D or L system, as the essential reference chirality is removed or altered.

Reduction of the Carbonyl Group

The process of reducing the carbonyl group (aldehyde or ketone) to a hydroxyl group alters the pivotal reference point used in determining the D or L configuration. Since the carbonyl oxygen is replaced with a hydroxyl, the molecule no longer has the same stereochemical reference, rendering the original D or L designation inapplicable.

D and L Configuration in Carbohydrates

The D and L system in carbohydrates is defined by the configuration of the chiral carbon farthest from the carbonyl group in the open-chain form of the sugar. This notation is based on the arrangement of groups relative to the reference carbon, which is preserved in the intact aldose or ketose but is lost when the carbonyl is converted to another functional group.

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