Iduronic acid

L-Iduronic acid is the major uronic acid component of the glycosaminoglycans (GAGs) dermatan sulfate

Dermatan sulfate

Dermatan sulfate is a glycosaminoglycan found mostly in skin, but also in blood vessels, heart valves, tendons, and lungs....

, and heparin

Heparin

Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...

. It is also present in heparan sulfate

Heparan sulfate

Heparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...

 although here in a minor amount relative to its carbon-5 epimer

Epimer

In chemistry, epimers are diastereomers that differ in configuration of only one stereogenic center. Diastereomers are a class of stereoisomers that are non-superposable, non-mirror images of one another....

 glucuronic acid

Glucuronic acid

Glucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...

.

IdoA is a hexapyranose sugar. Most hexapyranoses are stable in one of two chair conformations ¹C₄ or ⁴C₁. L-iduronate is different and adopts more than one solution conformation, with an equilibrium existing between three low-energy conformers. These are the ¹C₄ and ⁴C₁ chair forms and an additional 2S₀ skew-boat conformation

Carbohydrate conformation

Carbohydrate conformation is the characteristic 3-dimensional shape of a carbohydrate. Conformations of monosaccharide and oligosaccharide heavily influence their reactivity and recognition by other molecules, which are essential to mammals and other organisms....

.

IdoA may be modified by the addition of an O-sulfate group at carbon position 2 to form 2-O-sulfo-L-iduronic acid (IdoA2S).

In 2000, LK Hallak described the importance of this sugar in respiratory syncytial virus infection

Human respiratory syncytial virus

Human respiratory syncytial virus is a virus that causes respiratory tract infections. It is the major cause of lower respiratory tract infections and hospital visits during infancy and childhood. A prophylactic medication exists for preterm birth infants and infants with a congenital heart...

. Dermatan sulfate and heparan sulfate were the only GAGs containing IdoA, and they were the only ones that inhibited RSV infection in cell culture.

When internally positioned within an oligosaccharide, the ¹C₄ and ²S₀ conformations (shown below for IdoA2S) predominate.

Proton NMR spectroscopy

NMR spectroscopy

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...

can be used to track changes in the balance of this equilibrium.