Question

Following is a chair conformation for the repeating disaccharide unit in chondroitin 6-sulfate. This biopolymer acts as the flexible connecting matrix between the tough protein filaments in cartilage. It is available as a dietary supplement, often combined with D-glucosamine sulfate. Some believe this combination can strengthen and improve joint flexibility. (a) From which two monosaccharide units is the repeating disaccharide unit of chondroitin 6-sulfate derived? (b) Describe the glycosidic bond between the two units.

Short answer

(b) Describe the glycosidic bond between the two monosaccharide units of chondroitin 6-sulfate.

Step-by-step solution

Identifying monosaccharides of chondroitin 6-sulfate

To find the two monosaccharides that form the repeating disaccharide unit of chondroitin 6-sulfate, we must look at the chemical structure of this biopolymer. Chondroitin 6-sulfate is a disaccharide formed from two monosaccharides: glucuronic acid and N-acetylgalactosamine.

Substituent groups on monosaccharides

In chondroitin 6-sulfate, the glucuronic acid has a carboxylate group on carbon 1 and a sulfate group on carbon 6. N-acetylgalactosamine has an N-acetyl group on its nitrogen and a sulfate group on carbon 6.

Describing the glycosidic bond

The glycosidic bond that links the two monosaccharide units in chondroitin 6-sulfate is a β(1→4) glycosidic linkage. This means that the bond is formed between the carbon 1 of the glucuronic acid and the carbon 4 of the N-acetylgalactosamine. The β configuration indicates that the hydroxyl group linked to carbon 1 of glucuronic acid is in the axial position.