The structure of chondroitin sulfate shown in the article is ambiguous in at least two instances. 1) The oxygen linkages on the far right and between rings are actually glycosidic, that is, the oxygens are part of acetal functional groups, and not bonded to a -CH2- as denoted by the "bend" in the line connecting the ring to the oxygen. 2) The stereochemistry at C-4 on the left-hand ring is not specified.

The left ring is is from D-glucuronic acid which is derived from D-glucose. Knowing this, you can draw a Fisher projection of D-glucuronic acid.

How might the carboxylate substituent have been formed from glucose?

The right ring is said to be from N-acetylglucosamine sulfate. Most names of this sort imply an amine salt (R4N+X-), but here the sulfate is a covalently bonded substituent group. Explain why the N-acetyl (amide) group is not basic.

Very probably, the right ring residue is either named incorrectly or drawn incorrectly. If drawn correctly, the residue is N-acetylgalactosamine-4-sulfate. Explain why this might be a better name for the residue (hint: draw the Fisher, then Haworth, structures of glucose and galactose).

Specify the type of glycosidic residue between the two sugar residues (e.g. alpha/beta(n --> n')).