Mannose

Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose.

Structure
Two of the cyclic mannose isomers possess a pyranose (six-membered) ring, two have a furanose (five-membered) ring.

Metabolism
Mannose is not well metabolized in humans. Therefore, it does not significantly enter the carbohydrate metabolism when taken orally, and although traces of exogeneously introduced mannose have been detected in all body tissues, using radioactive markers, in a well hydrated mammal, although further studies are necessary, 90% of mannose ingested is excreted unconverted into the urine within 30 – 60 minutes, with 99% of the remainder being excreted within the following 8 hours. There is no significant increase in blood-glucose levels during this time.

Mannose is present in numerous glycoconjugates including N-linked glycosylation of proteins. C-mannosylation is also abundant and can be found in collagen-like regions. Mannose is a C-2 epimer of glucose and displays a $$^4C_1$$ pucker in the solution ring form.

Recombinant proteins produced in yeast may be subject to mannose addition in patterns different from those used by mammalian cells. This difference in recombinant proteins from those normally produced in mammalian organisms may influence the effectiveness of vaccines.

Formation
Mannose can be formed by the oxidation of mannitol.

It can also be formed from glucose in the Lobry-de Bruyn-van Ekenstein transformation

D-mannose is sold as a naturopathic remedy for urinary tract infections, and it is claimed to work through the disruption of adherence of bacteria in the urinary tract.

Etymology
The root of both "mannose" and "mannitol" is manna, which the Bible records as the food supplied to the Israelites during their journey through the Sinai Peninsula. Manna is a sweet secretion of several trees and shrubs, such as Fraxinus ornus.

Configuration
Mannose differs from glucose by inversion of the C-2 chiral center. This apparently simple change leads to the drastically different chemistry of the two hexoses, as it does the remaining six aldohexoses.