Synthesis of lactosylated glycoclusters and inhibition studies with plant and human lectins

Under microwave activation, the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) between an azido-functionalized lactoside and tetra-alkynylated core scaffolds (one porphyrin and three topological conformers of calix[4]arenes) afforded four lactosylated glycoclusters in high yields. The glycoclusters were then evaluated and compared to a monovalent probe as ligands of two lectins: ECA from legume plant Erythrina cristagalli and recombinant human galectin-1. Micromolar inhibition concentrations and IC50 values were measured by inhibition of hemagglutination (HIA) or enzyme-linked lectin assays (ELLA), respectively for these glycoclusters for binding to ECA. A slight binding preference was identified for the porphyrin and the 1,3-alternate calixarene scaffolds. Similar inhibition studies were performed for galectin-1 by HIA and surface plasmon resonance (SPR) analyses. A strong selectivity was observed for the porphyrin and cone conformer topologies under HIA experimental conditions but these could not be confirmed using SPR analysis. This difference in the inhibitory properties based on two techniques confirmed the need for multiple complementary analyses for in-depth and accurate analysis of the inhibitory properties of multivalent glycoconjugates to multivalent lectins.