Efficient solid-phase synthesis of dendritic a-thiosialoside inhibitors of influenza A virus haemagglutinin are described using hyperbranched L-lysine core structures.
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. α-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 α-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 α-sialodendrimer 29 had a greater affinity towards dimeric wheat germ agglutinin (WGA) and the lectin from the slug Limaxflavus (LFA) than the corresponding trivalent glycodendrimers 21 and 22. Keywords: carbohydrate, dendrimer, sialic acid, gallic acid, lectin, wheat germ agglutinin, Limaxflavus.
Starting from peracetylated chloro- or bromo-glycosyl donors of N-acetylneuraminic acid, N-acetylglucosamine, glucose and lactose, the corresponding p-formylphenyl glycosides were synthesized stereospecifically under phase transfer catalysed conditions at room temperature in yields of 38-67%. After Zemplén de-O-acetylation, the formyl groups were directly and chemoselectively coupled to the lysine residues of bovine serum albumin by reductive amination using sodium cyanoborohydride. The conjugation reactions were followed as a function of time and under a series of different molar ratios of the reactants to provide glycoconjugates of varying degree of antigenicities. Thus, carbohydrate protein conjugates were made readily available using essentially two key reactions.
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