Synthesis of hyperbranched glycodendrimers incorporating α-thiosialosides based on a gallic acid core

Hyperbranched glycodendrimers containing sialic acid residues were synthesized in order to further understand the multivalency effect and its role in carbohydrate-protein interactions. Gallic acid 7 as trivalent core and oligoethylene glycol derivatives as hydrophilic spacers were used to scaffold the dendritic backbones. alpha-Thiosialoside 16 was conjugated onto N-chloroacetylated dendritic precursors 13, 14, and 26 by nucleophilic substitution to afford trivalent 17, 18, and nonavalent 27 sialodendrimers. Complete sugar deprotection furnished water-soluble alpha-thiosialodendrimers 21, 22, and 29, which were used in protein-binding studies. Turbidimetric analysis confirmed the strong potential of sialodendrimers 29 having nine readily accessible sialic acid residues to bind, cross-link, and precipitate two different lectins. Preliminary results indicated that nonavalent alpha-sialodendrimer 29 had a greater affinity towards dimeric wheat germ agglutinin (WGA) and the lectin from the slug Limax flavus (LFA) than the corresponding trivalent glycodendrimers 21 and 22.