Iduronic acid
IUPAC name	(2S,3R,4R,5S)-2,3,4,5- tetrahydroxy-6-oxohexanoic acid
Other names	L-Iduronic acid, D-ido-Hexuronic acid, IdoA
Identifiers
CAS number	[3402-98-0]
PubChem	18845
KEGG	C06472
MeSH	Iduronic+acid
ChEBI	28481
SMILES	C(=O)C(C(C(C(C(=O)O)O)O)O)O or [H]C(=O)[C@]([H])(O)[C@@]([H])(O) [C@]([H])(O)[C@@]([H])(O)C(O)=O
Properties
Molecular formula	C6H10O7
Molar mass	194.139 g/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

L-Iduronic acid (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 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.

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

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

Proton NMR spectroscopy can be used to track changes in the balance of this equilibrium.^[1]

IdoA(2S)1C4 conformation

IdoA(2S)2S0 conformation

References

1. Ferro, D. R. Provasoli, A. (1990). "Conformer populations of L-iduronic acid residues in glycosaminoglycan sequences". Carbohydr. Res. 195: 157–167. doi:10.1016/0008-6215(90)84164-P. PMID 2331699. 

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Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Iduronic acid". Image Credit.