Versatile functionalization of polylysine: Synthesis, characterization, and use of neoglycoconjugates

Glycopolymers are useful macromolecules with a non-carbohydrate backbone fo r presenting saccharides in a multivalent form. Here, a new methodology is described which allows easy access to water-soluble, biodegradable glycopol ymers with both predeterminable composition and molecular weight distributi on. Thus, chloroacetylation of commercially available polylysine hydrobromi de 3 gave the reactive homopolymer 4, whose chloroacetamide functions allow ed subsequent coupling with thiol-containing components. Water-soluble homo polymers such as 8 and 13 were available by treatment with an excess of hyd rophilic thiols. Heteroglycopolymers were obtained via quantitative incorpo ration of substoichiometric amounts of carbohydrates with a mercapto functi onality linked to the reducing end; the remaining chloroacetamide groups we re capped with an excess of thioglycerol. A variety of glycopolymers with u p to four different components was prepared. The composition and purity of the products were reliably analyzed by H-1 NMR. Generally, the quantitative incorporation of substoichiometric components was verified. The polymer ba ckbone 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. Gly copolymer 25, containing sialyl Lewis(a) and biotin as a functional group f or enzyme linked immune sorbent assay, was used for developing cell-free se lectin ligand binding assays. The inhibition of E-selectin by glycopolymers 1.6, containing sialyl Lewis(x) (sLe(x)), was evaluated in a cell adhesion assay under flow conditions using activated human umbilical vein endotheli al cells and polymorphonuclear neutrophils. The sLe(x) polymers 16 showed n o significant inhibition, whereas conjugates with additional charged groups (carboxylates 18, sulfonates 21) in addition to sLe(x) gave 30-35% reducti on of the number of interacting cells at the same concentration of 100 mu M sLe(x).