Synthetic glycol-split heparin tri- and tetrasaccharides provide new insights into structural peculiarities for antiheparanase activity

Heparanase is the only known endo-β-glucuronidase able to cleave heparan sulfate, participating in degradation and remodelling of the extracellular matrix. Heparanase upregulation promotes tumor growth and metastasis, therefore, its inhibition is a target for anticancer therapies. Heparan sulfate mimetics bearing glycol-split (gs) units are one of the most promising class of heparanase inhibitors. Herein we describe a total synthesis of two trisaccharides (MeO-GlcNS6S-IdoA/GlcA-GlcNS6S-OMe) differing in epimeric uronic acid residues and one tetrasaccharide (MeO-IdoA-GlcNS6S-IdoA-GlcNS6S-OMe), together with their corresponding glycol-split versions, prepared by periodate oxidation and further modified either via reduction or Pinnick oxidation to obtain gs or tricarboxylated saccharides. An intermediate imine was observed during periodate oxidation, which causes formation of byproducts. Evaluation of the heparanase inhibitory activity showed that the glycol-split trisaccharides were more potent than their intact uronic acid congeners. The binding interactions of the glycol-split trisaccharides with heparanase were investigated by a combined STD NMR and molecular docking approach, with good agreement obtained between the STD NMR experimental data, docking calculations and the in vitro activity results, helping to rationalize the observed inhibition data.