4-Methylumbelliferyl α-L-Idopyranosiduronic Acid 2-(Hydrogen Sulfate) Methyl Ester is an intermediate used in the synthesis of 4-Methylumbelliferyl α-L-Idopyranosiduronic Acid 2-Sulfate Disodium Salt (M334715), which is a fluorogenic substrate in the assay of α-L-Iduronidase. A fluorimetric enzyme assay for the diagnosis of MPS II (Hunter disease).