Département de chimie moléculaire

A new polyhedral oligomeric silsesquioxane (POSS) deriv. with a periphery of eight PEGylated chains functionalized with terminal propargyl groups was synthesized starting from com. available octavinyl-POSS. The photoinduced free-radical coupling of this octapropargyl POSS deriv. with various sugar thiols enabled the prepn. 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 Con A between the hexadecavalent mannosylated and glucosylated clusters was much higher than the selectivity obsd. for the corresponding octavalent glycoclusters (ref.4). Moreover, the affinity of the N-acetylglucosamine-based cluster towards wheat germ agglutinin (WGA) revealed a remarkable glycoside cluster effect with up to a 9.0 × 105-fold increase in binding compared to monovalent GlcNAc. As a multivalent effect of the same order of magnitude was reported for an octavalent GlcNAc cluster towards the same lectin (ref.4), it is concluded that increasing the no. of sugar units around the cubic platform does not lead systematically to an enhancement of binding affinity. [on SciFinder(R)]