Chemistry Reference
In-Depth Information
Homopolymers are the result of self-condensation of monomeric carbohydrate
derivatives in the absence of any other added molecules. The polymerizable func-
tionality can be placed at the anomeric center (for further details on strategies,
please see Chapter 3) or at any other position on the carbohydrate ring. They can
be prepared from fully protected carbohydrate monomers or undeprotected deriva-
tives and polymerization processes are initiated or triggered by suitable catalysts
or by heating, and their isolation remains easy by precipitation or dialysis. This
strategy has allowed the successful synthesis of a variety of glycopolymers with
polyvinyl, polystyrene or poly(iminomethylene) backbones with potential biologi-
cal applications as biocompatible glycopolymers, drug delivery carriers and immu-
nodiagnostics [8] .
Heteropolymers constitute the most abundant and most useful form of glyco-
polymers, since they are built with added noncarbohydrate comonomers which
confer special physical and biophysical properties. Copolymers can be synthesized
by direct copolymerization of two different monomers or, alternatively, using the
grafting strategy in a postpolymerization modifi cation approach. The advantages
result from the possibility to control the incorporation of the desired ratios of the
two monomers and thus the saccharide density. In order to increase the number
and complexity of the functionalities on the polymer backbone to better fi t some
of the desired properties, custom-designed hybrid glycopolymers have been syn-
thesized by copolymerization of three distinct components (terpolymerization)
[9-11]. Typically, reaction mixtures are composed of carbohydrate haptens, probes
(or effectors molecules), drugs, solubility enhancers containing suitable polymer-
izable function and monomers (acrylamide, methacrylamide, and so on) that can
be incorporated as polymer backbones.
Although a wide variety of methods are available for the construction of multi-
valent structures based on proteins, lipids and polymers, serious limitations arise
with these neoglycoconjugates in relation to the heterogeneity of their structures
or molecular weight. For this reason, strategies and procedures to obtain structur-
ally well - defi ned and smaller multivalent glycoconjugate systems have become an
important area of research activity in recent years. This has led to the newly designed
family of glycodendrimers that can better mimic multiantennary glycans.
4.6
Glycodendrimers
Dendrimers are synthetic highly branched monodisperse polyfunctional macro-
molecules that are constituted by repetitive units that are chemically bound to each
other by an arborescent process around a multifunctional central core (please see
Figure 4.1 for natural examples). Thus, as opposed to traditional polymers, which
often have poorly defi ned molecular structures that clearly represent an important
disadvantage for medical application in terms of reproducibility, dendrimers are
structurally well defi ned and can be synthesized by a fully controlled iterative
approach (please see Info Box for details on historic development). Although dif-
