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

A novel series of synthetic bantennary tri‐, penta‐ and hepta‐saccharides with terminal β‐GlcNAc, β‐LacNAc and αNeuAc(2,6)βLacNAc residues, respectively, [LacNAc = Galβ(1,4)GlcNAc] connected to a core Gal residue were evaluated for their inhibitory potencies for specific plant and animal lectins. Six isomeric trisaccharides with two β‐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 aganist 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 β‐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‐l 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 α(2,6)NeuAc residues all showed 25‐fold stronger inhibition against the α(2,6)sialicacid‐specific elderberry (Sambucus nigra L.) bark lectin as compared to a monovalent disaccharide αNeuAc(2,6)βGalOR. The lack of inhibition. of αNeuAc(2,6)βGalOR 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 β‐LacNAc which possess different preferred rotamer orientations about the C5‐C6 bond of the Gal residue.