Synthesis of New α-Thiosialodendrimers and Their Binding Properties to the Sialic Acid Specific Lectin from Limax flavus

Abstract

Carbohydrate−protein binding interactions can be greatly amplified using the cluster or multivalent effect. In previous studies, sialylated multibranched l -lysine dendrimers were found to be potent inhibitors of the hemagglutination of human erythrocytes by Influenza viruses. In order to further the understanding of multivalency and its role in carbohydrate−protein interactions, glycoconjugates with differing carbohydrate densities, conformations, and interglycosidic spacings must be prepared. The synthesis and biological testing of structurally similar divergent and tethered α-sialodendrimers are presented herein. α-Thiosialoside-containing dendrimers scaffolded on an orthogonally protected 3,3‘-iminobis(propylamine) core were efficiently prepared via Cbz-protecting group and HOBt/DIC coupling strategies. The potential of these sialodendrimers to cross-link and precipitate Limax flavus lectin (LFA) was confirmed by turbidimetric analysis. When tested in enzyme-linked lectin inhibition assays using human α 1 -acid glycoprotein (orosomucoid) as coating antigen and horseradish peroxidase-labeled LFA for detection di- ( 31 ), tetra- ( 32 ), octa- ( 33 ), and hexadecavalent ( 34 ) divergent dendrimers showed IC 50 values of 176, 11.8, 206, and 425 nM while the tethered structures with valencies of four ( 14 ), six ( 20 ), eight ( 25 ), and twelve ( 30 ) exhibited IC 50 values of 58.7, 16.9, 17.5, and 8.22 nM, respectively. These data represent 3.5 ( 34 ) to 182 ( 30 ) fold increases in inhibitory potential over monovalent 5-acetamido-5-deoxy- d -glycero-α- d -galacto-2-nonulopyranosyl azide used as a standard (IC 50 1500 nM). The tethered α-sialodendrimers appeared to have structural organizations more suitable than the divergent dendrimers for the solid phase inhibition of the binding of human α 1 -acid glycoprotein to LFA. All α-sialodendrimers are currently being evaluated as inhibitors of human erythrocyte hemagglutination by Influenza viruses.