Modular Synthesis of Heparan Sulfate Oligosaccharides Having -Acetyl and -Sulfate Moieties.

Heparan sulfates are structurally diverse sulfated polysaccharides that reside at the surface of all animal cells where they can interact with a multitude of proteins, thereby modulating a wide range of physiological and disease processes. We describe here a modular synthetic methodology that can provide libraries of heparan sulfate oligosaccharides that have glucosamine residues modified by different patterns of -acetyl and -sulfate moieties. It is based on the use of glycosyl donors that are modified at C2 by an azido- or trifluoromethylphenyl-methanimine moiety, which allowed the selective installation of α-glycosides. The amino protecting groups can be selectively unmasked by a reduction or acid treatment, allowing the installation of -acetyl and -sulfate moieties, respectively. In combination with the orthogonal hydroxyl protecting groups levulinic (Lev) ester, thexyldimethylsilyl (TDS) ether, allyloxycarbonate (Alloc), and 9-fluorenylmethyl carbonate (Fmoc), different patterns of -sulfation can be installed. The methodology was applied to prepare four hexasaccharides that differ in the pattern of - and -sulfation. These compounds, together with a number of previously prepared HS oligosaccharides, were printed as a glycan microarray to examine the binding selectivities of several HS-binding proteins.