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 an O-sulfate group at carbon position 2 to form 2-O-sulfo-L-iduronic acid (IdoA2S). Dermatan sulfate and heparan sulfate were the only GAGs containing IdoA, and they were the only ones that inhibited RSV infection in cell culture.
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