Streamlined synthesis of core disaccharide building blocks from natural polysaccharides for the generation of heparan sulfate libraries

Heparan sulfate (HS) glycosaminoglycans (GAGs) are linear, diversely sulfated polysaccharides that regulate a wide range of essential biol. processes, including growth factor signaling, blood coagulation, viral infection, neural development, and cancer. HS chains consist of repeating disaccharide units of glucosamine (GlcN) joined via a-1,4-linkages to either D-glucuronic acid (GlcA) or L-iduronic acid (IdoA). Sulfation at the 3-O-, 6-O-, and N-positions of GlcN and the 2-O-position of IdoA or GlcA creates many different sulfation sequences that are tightly regulated in vivo. The diverse biol. functions of HS GAGs are thought to stem from their complex sulfation patterns. However, understanding their structure-activity relationships (SAR) has been hampered by a lack of methods to synthesize large collections of HS oligosaccharides with defined sulfation sequences. A major obstacle is the prepn. of differentially protected disaccharide building blocks, which typically require 20-30 chem. steps. Here, we report a new approach to access all four of the core disaccharides required for HS assembly from natural heparin and heparosan (K5) polysaccharides. The use of disaccharides rather than monosaccharides as minimal synthetic precursors greatly accelerates the synthesis of HS GAGs, providing easier access to core building blocks for the assembly of strategically protected HS tetrasaccharides in significantly fewer steps. Rapid access to such building blocks promises to significantly expand the scope of HS synthesis, enabling the future generation of large libraries of compds. for detailed investigations into the 'sulfation code' and its roles in biol