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dendritic polyester chemistry [124,125]. In short, a Boltorn
-type core polyol reacted
with several types of fatty acids (with various chain lengths) under variable stoi-
chiometric ratios. The analysis of their degradation was followed after using a series
of six lipases. The parameters considered were end groups, temperatures, lipases,
degree of esterification, and the dendritic core degradation alone. The latter was not
significantly degraded probably because of some steric hindrance and the absence of
hydrophobic binding interactions. Therewas an influence on the type of alkane chains
and their length. The degradation was dependent on the number of fatty acid chains
bound to the dendritic core versus the remaining hydroxyl functions, it may be related
to a good balance for hydrophilicity/hydrophobicity.
Another study from some poly(
-caprolactone)s with a dendritic PAMAM-OH
core was pursued [126]. The conclusion reinforced the results from Hill's on the
delicate balance of a hydrophilic/lipophilic composition of the dendrimer, upon its
degradation. A certain number of hydroxyl functions on the core helped in the
degradation rate.
A PEGylated bow-tie polyester dendrimer also containing some carbamate
linkages was tested against a slow hydrolytic degradation under physiological pH
at 7.4 or at pH5.0 (at 37
C) [127]. The PEG chains linked via a carbamate function to a
Boltorn
-type core were probably cleaved at pH 5.0. However, at higher pH, it seems
that some ester and carbamate functions could have been cleaved. The important point
is a selective excision of some constitutive elements (PEG chains) from the dendrimer
according to the pH and the choice of the labile functions.
Several drugs conjugated to some polyester dendrimers were tested for a slow drug
release. The syntheses of some star-shape and polyester dendrimers incorporating the
drug naproxenwere achieved. However, the authors mentioned some enzymatic assays
but they were not included in the communication [128]. Similarly, some poly(ester)
star-shape dendrimers functionalized by
L
-Dopa at their periphery were synthesized
with some hydrolyzable diester linkages [129].
L
-Dopa is a drug prescribed to treat the
Parkinson disease. However, the authors only mentioned a sequential degradation of
this prodrug. An anticancer drug such as paclitaxel conjugated to a G4 PAMAM-OH
dendrimer via a succinic acid diester linker was released with the help of an
esterase [130]. Finally, an antidepressant drug, venlafaxine, was conjugated to a
G2.5 PAMAM-CO
2
H via some esters linkages for releasing the drug at pH 7.4 [93].
Additionally, this conjugate was incorporated to an hydrogel, made from a polyacryl-
amide cross-linked with PEG, for a drug diffusion through this matrix.
As shown in a Section 13.3.11 on some applications in carbohydrate chemistry,
some examples of hydrolytic cleavages using a Boltorn
-type core as a soluble
support for carbohydrate synthesis and combinatorial chemistry were reported.
Another example on the cleavage of some carbohydrate units from a solid phase was
also reported with some photocleavable o-nitrobenzylic groups (see Section 13.3.11).
Among other researchers, Shabat and coworkers made uses of carbonate linkers
incorporated in some cleaving units for a cascade disassembly [131,132]. Similarly,
carbamates were also often described in the literature [133]. The latter two functions
are complementary and as useful as the ester linkage in the degradation of
dendrimers [134].
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