Hexosamine

Hexosamine is a class of hexose sugars in which one hydroxyl group is replaced by an amino group. The most common forms are amino sugars with the amino group at C-2, such as glucosamine (2-amino-2-deoxy-D-glucose), galactosamine, and mannosamine. These can also exist as N-acetyl derivatives, notably N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), and N-acetylmannosamine (ManNAc).

In nature, hexosamines occur as free sugars and as components of glycoconjugates. GlcNAc and GalNAc are common in glycoproteins and proteoglycans; GlcNAc is also found in chitin. UDP-N-acetylglucosamine, produced by the hexosamine biosynthetic pathway from fructose-6-phosphate, serves as a donor for N- and O-glycosylation of proteins and lipids; the O-GlcNAc modification of nuclear and cytosolic proteins is a dynamic regulatory process.

Industrial and medical relevance: Hexosamines are used in research as substrates and in the synthesis of glycoconjugates. Glucosamine supplements are marketed for joint health, but evidence for clinical benefit is mixed. Peracetylated hexosamines are used to improve cellular uptake in experiments.

Chemically, these compounds can adopt ring forms and exist as various isomers; the amino group is typically configured as part of an acetamido group in the N-acetyl derivatives. The term hexosamine often refers to the amino sugars derived from hexoses, especially GlcNAc and GalNAc, which are key constituents of cellular surfaces and extracellular matrices.