Effective Synthesis of α‐ d ‐GlcN‐(1→4)‐ d ‐GlcA/ l ‐IdoA Glycosidic Linkage under Gold(I) Catalysis

An effective glycosylation procedure for the stereoselective construction of the α‐ d ‐GlcN‐(1→4)‐ d ‐GlcA/ l ‐IdoA glycosidic linkage found in heparin and heparan sulfate is reported. The condensation occurs between 2‐deoxy‐2‐azido‐ d ‐glucopyranosyl ( d ‐GlcN) ortho ‐hexynylbenzoate donors and uronate acceptors ( d ‐GlcA/ l ‐IdoA) under mild gold(I)‐catalyzed conditions. Optimal results are obtained when performing the reaction in CH 2 Cl 2 , from −72 °C to room temperature in the presence of 4 Å molecular sieves and under the promotion of [Ph 3 PAuCl]/AgOTf or [(1,1‐bis‐(diphenylphosphino)methane)(AuCl) 2 ]/AgOTf as a source of the gold(I) catalyst. A donor/acceptor ratio of 3:1 as well as a loading of 0.6 equivalents of the gold(I) catalyst are essential to attain high yields and α selectivity, particularly for the [1+1] and [1+2] glycosylations.