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Chemical structures of the repeat units of heparin (1); the FGF-1 binding trisaccharide of heparin (2) and the synthetic antithrombotic fondaparinux (3). The typical substitution patterns in 1 are as follows: R1, R3 = H or SO3‾; R2 = H, C(O)CH3 or SO3‾; and R4 = H (common) or SO3‾ (rare).
