Chemistry Reference
In-Depth Information
Figure 13.6 The structure of the G(3)-poly(propylene imine) dendrimers.
Fr´chet and coworkers have popularized poly(aryl ether) dendrimers and polyester
dendrimers (Fig. 13.7), which have been widely used (Hawker and Fr´chet 1990; Ihre
et al. 1998). Addition of the aromatic rings adds rigidity to the dendrimer framework
that is lacking in the PPI and PAMAM dendrimers. The polyester dendrimers may be
more like the PPIs and PAMAMs in terms of rigidity, but the ester linkages enable
degradation of the polyester dendrimers by esterases in vivo. Thus, the biological
stability of the PAMAMs and the polyester frameworks is quite different.
The remaining dendrimer frameworks that are being applied to a wide range
of biological problems including protein-carbohydrate interactions include the
polylysine dendrimers used by Starpharma Ltd (Melbourne, Australia; Fig. 13.8;
Denkewalter et al. 1981) and the phosphorus-containing dendrimers developed by
Majoral's group (Fig. 13.9; Launay et al. 1996; Servin et al. 2007). The polylysine
systems are elegant in their simplicity, whereas the strength of the Majoral dendrimers
is that they achieve an unusually high density of branches. Because they are so highly
branched, small generation Majoral dendrimers can be used where larger generation
PAMAMs or PPIs would be required to achieve the same degree of functionalization.
Having many dendrimer frameworks available is critical, because dendrimers are
currently being used for a variety of biological applications. Different applications
will necessitate different levels of structural rigidity and stability, end-group mobility,
and end-group density. New dendritic systems, such as the new PrioStar dendrimers
(www.dnanotech.com), continue to emerge as the needs of different user commu-
nities become clear.
Drug and DNA delivery, photodynamic therapy, boron neutron capture therapy,
and magnetic resonance imaging are some areas in which appropriately functiona-
lized dendrimers are being evaluated (Jang and Kataoka 2005; Svenson and
Tomalia 2005; Yang and Kao 2006). In one particularly nice example, polylysine
