Galactosamine

Replace the hydroxyl group on carbon-2 of galactose with an amino group and the result is galactosamine, a derivative found in glycolipids, mucopolysaccharides and chondroitin sulfate. It builds the cartilage and connective-tissue polysaccharides, and its N-acetylated form decorates cell-surface glycans involved in recognition. Analytical chemists release and quantify it when profiling glycosaminoglycans in foods and supplements. Its presence marks the amino-sugar family that gives structural polysaccharides their charge and water-binding power. Supplement makers list it among the building blocks of joint-health products.