Selective inhibition of N‐acetylglucosamine and galactose‐specific lectins including the 14‐kDa vertebrate lectin by novel synthetic biantennary oligosaccharides

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Abstract
A novel series of synthetic biantennary tri-, penta- and hepta-saccharides with terminal beta-GlcNAc, beta-LacNAc and alpha NeuAc(2,6)beta LacNAc residues, respectively, [LacNAc = Gal beta (1,4)Glc-NAc] connected to a core Gal residue were evaluated for their inhibitory potencies for specific plant and animal lectins. Six isomeric trisaccharides with two beta-GlcNAc residues at the 2,3-, 2,4-, 2,6-, 3,4-, 3,6-, or 4,6-positions of the core Gal were tested for their hemagglutination inhibition activities against two GlcNAc-specific lectins, Griffonia simplicifolia II (GS II) and wheat germ agglutinin (WGA). The 2,3-, 2,4-, 2,6- and 3,6-trisaccharides inhibited WGA 12-50 times more strongly than GlcNAc, whereas only weak or no inhibition was observed with GS II. The 3,4- and 4,6-trisaccharides did not inhibit either of the lectins. Six biantennary isomeric pentasaccharides containing two terminal beta-LacNAc residues with branching patterns similar to the trisaccharides showed selective hemagglutination inhibition of five Gal/GalNAc-specific plant lectins and the 14-kDa Gal-specific calf spleen lectin. The plant lectins include the soybean agglutinin (SBA), ricin agglutinin-I (RCA-I), and three Erythrina lectins with similar specificities: Erythrina indica (EIL), E. corallodendron (ECorL), and E. cristagalli (ECL). The 2,3-pentasaccharide inhibited only SBA and the 14-kDa lectin, and thus was a selective inhibitor among the plant lectins. The 2,6-pentasaccharide inhibited SBA, ECL and the 14-kDa lectin, but not RCA-I or the two other Erythrina lectins. The 4,6-pentasaccharide did not inhibit any of the plant lectins, but was a specific inhibitor of the 14-kDa calf spleen lectin. Synthetic heptasaccharides analogs with 2,4-, 2,6-, 3,6- and 4,6-branching patterns and terminal alpha(2,6)NeuAc residues all showed 25-fold stronger inhibition against the alpha(2,6)sialic-acid-specific elderberry (Sambucus nigra L.) bark lectin as compared to a monovalent disaccharide alpha NeuAc(2,6)beta GalOR. The lack of inhibition of alpha NeuAc(2,6)beta GalOR derivatives methylated at the C6 of the Gal residue and a sulfur-linked thiosialoside derivative demonstrates that the 2,6-anomeric linkage region is important for lectin recognition. Selective inhibition of the Gal/GalNAc-specific lectins was observed for two isomeric C6 methyl-substituted Gal derivatives of methyl beta-LacNAc which possess different preferred rotamer orientations about the C5-C6 bond of the Gal residue.

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