Chitosan-Sialic Acid Hybrid Using Convergent Grafting of Preassembled Dendrons Built on Gallic Acid and Tri(ethylene glycol) Backbone

Sialic acid dendrons bearing a focal aldehyde end group were synthesized by a reiterative amide bond strategy. Polyamine-ending trivalent (G ) 1) and nonavalent (G ) 2) dendrons having gallic acid as branching unit and tri(ethylene glycol) as spacer arm were prepared and initially attached to a sialic acid p-phenylisothiocyanate derivative. The focal aldehyde sialodendrons were then convergently grafted onto the polysaccharide chitosan backbone by reductive amination in 76-80% yields. The degrees of substitution (DS) of the sialodendrimer in the hybrids were 0.13 (G ) 1) and 0.06 (G ) 2), which indicates that 87% and 40% of the sialodendrons were attached to the primary amino groups of chitosan. The water solubility of these novel hybrids was further improved by N-succinylation of the remaining amine functionality.