• oligosaccharides
• Protein tyrosine phosphatase 1B (PTP1B)
• reiterative glycal assembly
• stereospecific synthesis

In eukaryotic cells, phosphorylation is an essential process and is considered critical for biological functions. The balance between phosphorylation and dephosphorylation is under the control of two super enzyme families, protein kinases (PKs) and protein phosphatases (PPs), respectively. Protein tyrosine phosphatase 1B (PTP1B), belonging to the PTP family, is considered a direct negative regulator of numerous receptors and receptor-associated tyrosine kinases becoming a key player in several human diseases and disorders through modulation of different signaling pathways. In the last years PTP1B has attracted attention in the field of neuroscience, indeed its activation in brain cells can lead to schizophrenia-like behavior deficits, anxiety-like effects, neurodegeneration, neuroinflammation and depression. On the contrary its inhibition has been shown potent anti-inflammatory effect and the increase in cognitive process through the stimulation of hippocampal insulin, leptin and BDNF/TrkB receptors. As a result, most research on the clinical efficacy of targeting PTP1B has been developed in the field of obesity and type 2 diabetes mellitus (TD2M). Crystallographic structures of the protein show the presence of hydrophilic active sites containing cysteine and arginine residues and several allosteric sites demonstrating affinity towards lipophilic ligands. The relationship between hydrophilicity and lipophilicity of allosteric sites allows the use of heterogeneous ligands and allosteric inhibition is therefore considered a very promising approach. This is due to a lower sequence conservation of the allosteric site compared to the preserved catalytic site resulting in greater specificity, reduced adverse effects and limited toxicity of the inhibitors. Considering the molecular scaffolds already presents in literature for the inhibition of this protein, the aim of my thesis work has been focused on the synthesis of linear 1,4- stereodefined disaccharides and trisaccharides characterized by a different degree of polarity and their evaluation as ligands of PTP1B.
Our research group recently identified a microwave-activated one-pot reiterative assembly of glycal-derived vinyl epoxides, that allow a substrate-dependent non-catalyzed stereospecific process for the preparation of both β-1,4-D-Gulo- and α-1,4-D-Manno-oligosaccharides. The general procedure involves the addition of a series of previously synthesized glycosyl acceptors to the glycosyl donor vinyl epoxide, generated in situ by cyclization under basic conditions for t-BuOK of its stable precursor hydroxyl mesylate. The distribution of oligosaccharides resulting from the process depends on the relative ratio between the initiator and the vinyl epoxide.
For the synthesis of the disaccharide and trisaccharide, we used 2 equivalents of initiator and 1 equivalent of vinyl epoxide. The advantage of this procedure is to easily assess the 2,3-unsaturated-1,4-disaccharides without any protection/deprotection/activation protocol with the possibility of subsequent functionalization towards less lipophilic derivatives.
Disaccharides and trisaccharides were then purified using preparative HPLC. New and general chromatographic method applicable to oligosaccharides of different sizes has been developed in this regards . In particular, 1,4-alpha-disaccharide was treated with OsO4 in presence of NMO to afford the relative dihydroxylated product with alpha-manno configuration and then deprotected by hydrogenolysis to provide the most hydrophilic disaccharide.
Exploiting this new process and playing with the epoxide/initiatior ratio we prepared a small library of compounds in order to be tested as PTP1B allosteric ligands