Regioselectivity in the sulfation of some chemically-modified heparins, and observations on their cation-binding characteristics

Abstract Two modified forms of heparin, polymers A and B, have been prepared, one containing residues of nonsulfated α- l -idopyranosyluronic acid ( 3 ) and the other residues of α- l -galactopyranosyluronic acid ( 7 ), in place of the normal α- l -idopyranosyluronic acid 2-sulfate ( 1 ). In addition, both A and B contained 2-acetamido-2-deoxy-α- d -glucopyranosyl 6-sulfate residues ( 6 ) in place of the corresponding N -sulfated residues ( 2 ) of the original heparin. These polymers were subjected to sulfation under various conditions. Examination of the products by NMR spectroscopy showed that polymer A was sulfated initially at position-3 of residue 3 , and that slower substitution occurred at position-3 of 6 . By contrast, polymer B exhibited low regioselectivity, as sulfation occurred with about equal facility at positions-2 and -3 of 7 , and -3 of 6 . The sulfation products had no significant anti Xa activity. Based on the paramagnetic effects of Cu 2+ and chemical shift displacements induced by Ca 2+ , NMR spectroscopy was used to compare cation-binding properties of A and B with those of heparin. In contrast to heparin, which forms a complex with Cu 2+ detectable at a level of ⊃10 −3 mol per dimeric unit of the polymer, neither A nor B exhibited an interaction with the cation. However, polymer A was found to bind Ca 2+ , in this respect being distinct from the related modification, 1 → 6 , which contains a 2-sulfate group in 1 , as well as from polymer B.