Novel cyclic phosphate-linked oligosaccharides (CyPLOS) covalently immobilized on solid supports for potential cation scavenging

For potential cation scavenging both from water and from organic solvents, here we propose a synthetic procedure for functionalization of a Tentagel solid support with novel cyclic phosphate-linked oligosaccharide (CyPLOS) analogues. To establish the feasibility of the synthetic strategy, the cyclic dimer was the model compound selected to be incorporated onto the solid support. This functionalization was achieved through a stepwise solid-phase synthesis of the linear dimer, obtained by standard phosphoramidite protocols, followed by a synthesis of the cyclic molecule on the resin. The key intermediate in our synthetic strategy was a suitably derivatized sugar phosphoramidite building block, with the secondary hydroxy functions masked as TBDMS ethers. This proved to be an orthogonal protection with respect to the DMT ether, fully compatible with the phosphoramidite and the phosphotriester chemistry used for the oligomerization and the cyclization process onto the solid support, respectively. Conditions for the total unmasking of the hydroxy groups of the cyclic dimer, not affecting the integrity of the cyclic structure nor its linkage with the solid matrix, have been optimized. Gel-phase 31P NMR spectroscopy has been used extensively here to monitor the efficiency of the reactions carried out on the solid support.