d-Glucuronate and l-iduronate containing disaccharides related to the antithrombin-binding pentasaccharide of heparin, in which one of the sulfate esters is systematically replaced by a sodium sulfonatomethyl moiety, were synthesized. The sulfonic acid group was introduced by stereoselective radical addition onto the exomethylene moiety of the appropriate glycoside derivatives, and the resulting sulfonatomethyl