-Iduronic acid (IUPAC abbr.: IdoA) is the major uronic acid component of the glycosaminoglycans (GAGs) dermatan sulfate, and heparin. It is also present in heparan sulfate, although here in a minor amount relative to its carbon-5 epimer glucuronic acid.
IdoA is a pyranose sugar. Most pyranoses are stable in one of two chair conformations <sup>1</sup>C<sub>4</sub> or <sup>4</sup>C<sub>1</sub>. -iduronate is different and adopts more than one solution conformation, with an equilibrium existing between three low-energy conformers. These are the <sup>1</sup>C<sub>4</sub> and <sup>4</sup>C<sub>1</sub> chair forms and an additional <sup>2</sup>S<sub>0</sub> skew-boat conformation.
IdoA may be modified by the addition of an O-sulfate group at carbon position 2 to form 2-O-sulfo--iduronic acid (IdoA2S).
In 2000, LK Hallak described the importance of this sugar in respiratory syncytial virus (RSV) infection. 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 <sup>1</sup>C<sub>4</sub> and <sup>2</sup>S<sub>0</sub> conformations (shown below for IdoA2S) predominate.
Proton NMR spectroscopy can be used to track changes in the balance of this equilibrium.
Iduronic acid can be detected colorimetrically.