Chemistry Reference
In-Depth Information
dendrimers). The second-generation dendrimers were formed by treating the
peripheral functional groups with complementary chemical functions present on
the branching building blocks. Chemical transformations of the newly formed
surface groups with, for example, sugars resulted in the desired second- generation
glycodendrimers. The generation growth can quickly allow exponential multiplica-
tion of active terminal functions and the process is repeated until the required
degree of branching (multivalency) is obtained.
Several dendrimers having various surface functionalities and building blocks
are commercially available: poly(amidoamine) (PAMAM) (Starburst; Dendritic
Nanotechnologies), poly(propylene)imine (Astramol; DSM Fine Chemicals), poly-
glycerols and Boltorn dendrimers are most commonly used as multibranched
dendritic core or glycodendron precursors, most of them being known to be
nontoxic and nonimmunogenic. One of the most striking examples is represented
by the largest glycodendrimer built so far containing 256 mannoside residues
that was prepared on generation G6-PAMAM dendrimer using thiourea
linkages.
The convergent strategy was fi rst reported in 1990 by Fréchet [13], using the
symmetrical nature of these structures to its advantage, in order to overcome some
of the synthetic and purifi cation problems associated with the divergent methodol-
ogy. It involves preliminary synthesis of peripheral branched dendritic arms
named ' dendrons ' or ' glycodendrons ' from the ' outside - in ' (Figure 4.7). The advan-
tages of the convergent strategy lie with the reduced number of reactions carried
out at each step. Moreover, purifi cation of the desired dendrimer becomes easier
than that in the divergent case, since the fi nal products are structurally different
from the corresponding smaller precursors.
Glycodendrimers may constitute an arsenal of novel principles for the treat-
ment of infectious agents by the inhibition of attachment of the infecting
Figure 4.7
Schematic representation of the two major strategies for glycodendrimer growth.
