Glucosamine is an essential, endogenous amino acid sugar with high structural viscosity (malleability), and is a precursor of hyaluronic acid. Glucosamine is considered the main building block for the synthesis of proteoglycans. D-glucosamine sulfate is the bioactive sulfuric acid salt of the aminosaccharide D-glucosamine and, unlike glucosamine HCl, contains organically bound sulfur.
Chondroitin is also an important component of proteoglycans and especially of cartilage tissue. Unlike glucosamine, chondroitin is a long-chain sugar molecule.