Glycoside and peptide clustering around the octasilsesquioxane scaffold via photoinduced free-radical thiol–ene coupling. The observation of a striking glycoside cluster effect

Two series of multivalent octasilsesquioxane glyco- and peptido-conjugates were synthesized using the photoinduced free-radical thiol-ene coupling (TEC). The first series was obtained by coupling C-glycosylpropyl thiols and cysteine containing peptides with the known octavinyl octasilsesquioxane while the second series was obtained by reacting glycosyl thiols with a new octasilsesquioxane derivative displaying eight PEGylated chains functionalized with terminal allyl groups. The evaluation of the binding properties of mannoside and glucoside clusters toward Concanavalin A by Enzyme-Linked Lectin Assay (ELLA) revealed a modest glycoside cluster effect. On the other hand, the PEGylated POSS-based glycocluster featuring eight N-acetyl-glucosamine residues showed high affinity toward Wheat Germ Agglutinin to give a measured IC(50) at 3 nM. The calculated relative potency per number of sugar unit (rp/n) was superior to a value of 10(6), thus revealing the occurrence of a striking glycoside cluster effect.