Versatile Functionalization of Polylysine: Synthesis, Characterization, and Use of Neoglycoconjugates

Abstract

Glycopolymers are useful macromolecules with a non-carbohydrate backbone for presenting saccharides in a multivalent form. Here, a new methodology is described which allows easy access to water-soluble, biodegradable glycopolymers with both predeterminable composition and molecular weight distribution. Thus, chloroacetylation of commercially available polylysine hydrobromide 3 gave the reactive homopolymer 4, whose chloroacetamide functions allowed subsequent coupling with thiol-containing components. Water-soluble homopolymers such as 8 and 13 were available by treatment with an excess of hydrophilic thiols. Heteroglycopolymers were obtained via quantitative incorporation of substoichiometric amounts of carbohydrates with a mercapto functionality linked to the reducing end; the remaining chloroacetamide groups were capped with an excess of thioglycerol. A variety of glycopolymers with up to four different components was prepared. The composition and purity of the products were reliably analyzed by 1H NMR. Generally, the quantitative incorporation of substoichiometric components was verified. The polymer backbone was not altered under the applied reaction conditions, as indicated by very similar polydispersities and degrees of polymerization of starting polylysine 3 and functionalized homo- and heteropolymers 8, 13, and 14. Glycopolymer 25, containing sialyl Lewisa and biotin as a functional group for enzyme-linked immuno sorbent assay, was used for developing cell-free selectin ligand binding assays. The inhibition of E-selectin by glycopolymers 16, containing sialyl Lewisx (sLex), was evaluated in a cell adhesion assay under flow conditions using activated human umbilical vein endothelial cells and polymorphonuclear neutrophils. The sLex polymers 16 showed no significant inhibition, whereas conjugates with additional charged groups (carboxylates 18, sulfonates 21) in addition to sLex gave 30−35% reduction of the number of interacting cells at the same concentration of 100 μM sLex.