Ammonolysis of the epoxide rings of 2,3-anhydro-α-L-guluronic acid residues, generated in alkaline medium from 2-O-sulfated α-L-iduronic acid residues of heparin, quantitatively afforded 2-amino-2-deoxy-α-L-iduronic acid residues.N-sulfation of these residues by TMA·SO3complex led to a formal replacement of the original 2-O-sulfate groups of heparin withN-sulfates, without configurational changes. These modified uronic acid residues (no longer amenable to alkaline epoxidation) can be easilyN-desulfated. The presence of negative or positive charges at position 2 of the newly generated 2-amino-2-deoxy-α-L-iduronic acid residues influences thein vivoantithrombotic activity and haemorrhagic effects in different ways. A free amino group mainly decreases the haemorrhagic properties of heparin, while a negatively chargedN-sulfate group decreases the coagulation parameters.