BASE-CATALYZED CONVERSION OF THE ALPHA-L-IDURONIC ACID 2-SULFATE UNIT OF HEPARIN INTO A UNIT OF ALPHA-L-GALACTURONIC ACID, AND RELATED REACTIONS

Residues of a-l-idopyranosyluronic acid 2-sulfate in heparin undergo a loss of the sulfate group, by intramolecular displacement in sodium carbonate solution at 100°, leading to the formation of a heparin analog containing residues of a-l-galactopyranosyluronic acid (4). The configuration of these latter residues, which was determined by chemical evidence in combination with n.m.r. and c.d. spectroscopic data, is accounted for by selective hydrolysis of the oxirane ring of 2,3-anhydro-a-l-guluronic acid (3), a transient intermediate formed during the desulfation step. Regio- and stereo-selective aspects of ring-opening reactions of 3 are described. Several observations suggest that the reaction temperature is critical in determining whether the nucleophilic attack on the anhydro ring occurs at C-2 or C-3. Among these is the finding that, in contrast to the conditions used in the formation of the a-l-agalacto diastereomer (4), ammonolysis of 3 at room temperature gives rise to a 2-amino-2-deoxyaldohexuronic acid having the a-l-ido configuration. © 1990.