Iduronic acid
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 C4 or C1. L-iduronate is different and adopts more than one solution conformation, with an equilibrium existing between three low-energy conformers. These are the C4 and C1 chair forms and an additional S0 skew-boat conformation.