Chemoenzymatic synthesis of artificial glycopolypeptides containing multivalent sialyloligosaccharides with a γ-polyglutamic acid backbone and their effect on inhibition of infection by influenza viruses Original Research Article

Highly water-soluble, artificial glycopolypeptides with a γ-polyglutamic acid (γ-PGA) backbone derived from Bacillus subtilis sp. and multivalent sialyloligosaccharide units have been chemoenzymatically synthesized as potential polymeric inhibitors of infection by bird and human influenza viruses. 5-Trifluoroacetamidopentyl β-N-acetyllactosaminide and 5-trifluoroacetamidopentyl β-lactoside were enzymatically synthesized from LacNAc and lactose, respectively, by cellulase-mediated condensation with 5-trifluoroacetamido-1-pentanol. After deacetylation, the resulting 5-aminopentyl β-LacNAc and β-lactoside glycosides were coupled to the α-carboxyl groups of the γ-PGA side chains. The artificial glycopolypeptides carrying LacNAc and lactose were further converted to Neu5Acα2-(3/6)Galβ1–4Glcβ and Neu5Acα2-(3/6)Galβ1–4GlcNAcβ sialyloligosaccharide units by α2,3- and α2,6-sialyltransferase, respectively. The interaction of these glycopolypeptides with various influenza virus strains has been investigated by three different methods. Glycopolypeptides carrying Neu5Acα2,6LacNAc inhibited hemagglutination mediated by influenza A and B viruses, and their relative binding affinities for hemagglutinin were 102- to 104-fold higher than that of the naturally occurring fetuin control. A glycopolypeptide carrying Neu5Acα2,6LacNAc inhibited infection by A/Memphis/1/71 (H3N2) 93 times more strongly than fetuin, as assessed by cytopathic effects on virus-infected MDCK cells. The avian virus [A/duck/Hong kong/4/78 (H5N3)] bound strongly to Neu5Acα2,3LacNAc/Lac-carrying glycopolypeptides, whereas the human virus [A/Memphis/1/71 (H3N2)] bound to Neu5Acα2,6LacNAc in preference to Neu5Acα2,6Lac. Taken together, these results indicate that the binding of viruses to terminal sialic acids is markedly affected by the structure of the asialo portion, in this case either LacNAc or lactose, in the sugar chain of glycopolypeptides.