a][] Samuele Staderini, [a] Nathalie Berthet, [b] Pascal Dumy, [b][] Olivier Renaudet, [b] and Alessandro Dondoni* [a] Keywords: Carbohydrates / Cluster compounds / Glycoconjugates / Click chemistry / Radical reactions / Alkynes / Photochemistry A new polyhedral oligomeric silsesquioxane (POSS) deriva-tive with a periphery of eight PEGylated chains function-alized with terminal propargyl groups was synthesized start-ing from commercially available octavinyl-POSS. The photo-induced free-radical coupling of this octapropargyl POSS de-rivative with various sugar thiols enabled the preparation of globular hexadecavalent glycoclusters. Thus, it appears that according to the alkyne hydrothiolation mechanism, two thiyl radicals were added across each triple bond of the POSS scaffold side-chains. The affinities of some of the densely glycosylated clusters towards certain lectins were measured by the Enzyme-Linked Lectin Assay (ELLA). The binding selectivity of Concanavalin A between the hexadecavalent