The Convergent Synthesis of Poly(glycerol-succinic acid) Dendritic Macromolecules

Article abstract of DOI:10.1002/chem.200305172

The high-yield convergent synthesis of dendrons, dendrimers, and dendritic-linear hybrid macromolecules composed of succinic acid, glycerol, and poly(ethylene glycol) (PEG) is described. This convergent synthesis relies on two orthogonal protecting groups

Full text of DOI:10.1002/chem.200305172

FULL PAPER
The Convergent Synthesis of Poly(glycerol-succinic acid) Dendritic
Macromolecules
[a]
Nathanael R. Luman,Kimberly A. Smeds,and Mark W. Grinstaff*
Abstract: The high-yield convergent
synthesis of dendrons, dendrimers, and
dendritic linear hybrid macromolecules
composed of succinic acid, glycerol,
and poly(ethylene glycol) (PEG) is de-
scribed. This convergent synthesis
relies on two orthogonal protecting
groups; namely, the benzylidene acetal
(bzld) for the protection of the 1,3-hy-
droxyls of glycerol and the tert-butyldi-
phenylsilyl (TBDPS) ester for protec-
tion of the carboxylic acid of succinic
acid. These novel polyester dendritic
macromolecules are composed entirely
of building blocks known to be bio-
compatible or degradable in vivo to
give natural metabolites. Derivatization
of the dendritic periphery with a meth-
acrylate affords a polymer that can be
subsequently photo-cross-linked. The
three-dimensional cross-linked gels
formed by ultraviolet irradiation are
optically transparent, with mechanical
properties dependent on the initial
cross-linkable dendritic macromole-
cule.
Keywords: biomaterials ¥ chemical
biology ¥ dendrimers ¥ gels
Introduction
function of the scaffold is multifaceted. Scaffolds should be
biocompatible, degrade over time, promote cell growth and
proliferation, and possess mechanical properties reminiscent
Dendrimers are three-dimensional, globular macromolecules
possessing distinct concentric branching layers emanating
27]
of the original host native tissue.[21 Ideally, the formation
from a focal point.[1 As a consequence of the multiple pe-
of the natural extracellular matrix should be synchronized
with loss of the scaffold. Polymers under investigation as
scaffold materials include natural polymers such as colla-
16]
ripheral chain ends, globular shape, low viscosity, high solu-
bility, and miscibility, dendritic macromolecules have in-
creasingly attracted scientific attention.[13
Furthermore,
gen[28 and alginate,[31 as well as synthetic polymers such
16]
30]
33]
38]
the structural and derivatizational control afforded by den-
drimers and dendrons provides synthetic opportunities to
explore unique polymer architectures, to create larger supra-
molecular assemblies, or to prepare interfacial materials. We
are investigating aliphatic dendrons, dendrimers, and dendri-
tic linear hybrid macromolecules composed of glycerol, suc-
cinic acid, and poly(ethylene glycol) (PEG) for potential use
as temporary biodegradable scaffolds for wound heal-
as poly(glycolic acid) and poly(lactic acid).[34 The synthet-
ic polymers are advantageous for this application, since the
degradation rate, hydrophobicity/hydrophilicity, and me-
chanical strength can be varied by controlling the polymer
molecular weight, crystallinity, and composition. Of the scaf-
fold formats being investigated, hydrogels resemble the
physical characteristics of soft tissues, can be molded or
shaped into specific objects, and can be prepared under
physiological conditions.[39,40] Furthermore, these hydrogels
are of interest for in situ applications whereby the photo-
cross-linkable hydrogel precursors are injected in vivo and
then subsequently cross-linked. In situ photopolymerization
20]
ing.[17
Polymeric biomaterials that supplement or replace dam-
aged or diseased tissue with functional synthetic constructs
are of widespread interest and represent an emerging indus-
try sector that offers tremendous potential for advancing
healthcare practices. These constructs provide a temporary
scaffold for cells until the native tissue is remodeled. The
43]
46]
is being explored in the dental,[41
drug delivery,[44
cell
transplantation,[47
biological adhesive,[50
and ophthal-
49]
52]
mology fields.[19,53,54]
Dendrimers may provide unique advantages where
linear polymers have limitations due to the spatial orienta-
tion and high ligand density that are desired characteristics
of good gelators.[18,19,55 59] Multiple interactions between indi-
vidual building blocks are critical in the gel-formation proc-
ess; with dendrimers the number of functional groups can
be controlled by generation number and by the composition
of the core and branching arms. Dendrimers are synthesized
[a] Prof. M. W. Grinstaff, N. R. Luman, K. A. Smeds
Departments of Chemistry and Biomedical Engineering
Duke University
and Departments of Chemistry and Biomedical Engineering
Boston University, Boston MA 02215 (USA)
Fax : (+1)617-353-6466
E-mail: mgrin@bu.edu
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200305172
Chem. Eur. J. 2003, 9, 5618 5626
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5618 5626
by means of either an iterative
65]
divergent[60
or
conver-
73]
gent[66 approach. The conver-
gent approach enables differen-
tiated functionalities to be in-
corporated at the focal point
and periphery of the macromol-
ecule, as well as the preparation
of more intricate multifunction-
alized macromolecules, includ-
ing segment-block and surface-
block dendrimers, and dendri-
tic linear hybrids.[11,66] More-
over, the dendrons synthesized
can be handled in a manner
typical for the isolation, purifi-
cation, and characterization of
small molecules. The conver-
gent synthesis described herein
relies on two orthogonal pro-
tecting groups; namely, benzyli-
dene acetal (bzld) for the pro-
tection of the 1,3-hydroxyl
groups of glycerol and tert-bu-
tyldiphenylsilyl (TBDPS) ester
for protection of the carboxylic
acid of succinic acid. The bzld
group can be selectively re-
moved under hydrogenolysis
conditions, while the TBDPS
group can be selectively cleaved
with tetrabutylammonium fluo-
ride. By using this strategy we
present the convergent synthe-
sis of poly(glycerol succinic
Scheme 1. Synthesis of the [G3]-PGLSA dendron. Reagents and conditions: a) succinic anhydride, pyridine,
RT, 18 h, 95% yield; b) TBDPSi-Cl, imidazole, DMF, RT, 48 h, 86% yield; c) 20% Pd(OH)2/C, 50 psi. H2,
THF, RT, 3 h, 95% yield; d) 2, DCC, DPTS, DCM, RT, 18 h, 88% yield; e) TBAF, THF, 1 h, RT, 87% yield;
acid) (PGLSA) dendrons,
a
PGLSA dendrimer, and a den- f) 20% Pd(OH)2/C, 50 psi. H2, THF, RT, 3 h, 95% yield; g) 4, DCC, DPTS, DCM, RT, 18 h, 83% yield; h) 2,
DCC, DPTS, DCM, RT, 18 h, 54% yield; i) TBAF, THF, 1 h, RT, 83% yield.
dritic(PGLSA)-linear(poly(eth-
ylene glycol)) hybrid macromo-
lecule, the modification with
methacrylate, and the formation of cross-linked dendritic
gels.
fluoride, respectively. In comparison to the use of the tert-
butyldiphenylsilyl ester protecting group in the synthesis of
natural products and analogues, this group has been under
utilized in macromolecular chemistry.
Results and Discussion
cis-1,3-O-Benzylidene glycerol (1) was synthesized from
benzaldehyde and glycerol by using a catalytic amount of
sulfuric acid.[74] The cis isomer was preferentially isolated by
recrystallization in cold diethyl ether. The glycerol succinic
acid monoester 2 was synthesized by the addition of succinic
anhydride to 1 in pyridine. The acid functionality of 2 was
subsequently protected with tert-butyldiphenylsilyl chloride
(TBDPS-Cl) to form the bi-protected bzld-[G1]-PGLSA-
TBDPS dendron 3 in 86% yield. The bzld protecting group
was removed by hydrogenolysis with a palladium catalyst
(20% Pd(OH)2/C or 10% Pd/C)[75] to yield a hydroxy termi-
nated HO-[G1]-PGLSA-TBDPS dendron 4. The silyl pro-
tecting group does not cleave under these mild conditions;
however, it is selectively cleaved with tetrabutylammonium
fluoride (TBAF). Compound 4 was then coupled to 2 with
The polyester dendrons and dendrimers are composed of
glycerol and succinic acid, whereas the polyester ether den-
dritic linear hybrid macromolecules are composed of glycer-
ol, succinic acid, and polyethylene glycol. The generation
one (G1) through four (G4) poly(glycerol succinic acid)
(PGLSA) dendrons are prepared as shown in Schemes 1
and 2. Both the divergent and convergent synthesis are
shown for the dendrons. The convergent approach relies on
the bzld protecting group for the 1,3-hydroxyl groups of
glycerol and the TBDPS ester protecting group for the car-
boxylic acid of succinic acid. As mentioned above, the bzld
and TBDPS group can be selectively removed by using hy-
drogen with a palladium catalyst and tetrabutylammonium
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¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. W. Grinstaff et al.
FULL PAPER
(16) to create a dendrimer or a
dendritic linear hybrid, respec-
tively (Scheme 3). For example,
a [G3]-PGLSA-bzld dendrimer
(13) was synthesized by DCC
coupling dendron 9 to the tetra-
functional core 12. The tetra-
functional core was synthesized
in two steps; succinic acid was
first coupled to two equivalents
of cis-1,3-O-benzylidene glycer-
ol in the presence of DCC and
DPTS (90% yield), followed by
catalytic hydrogenolysis (97%
yield). The dendritic linear
hybrid molecule bzld-[G3]-
PGLSA-PEG-OMe (17) was
prepared by DCC coupling of
dendron 9 to a linear poly(ethy-
lene glycol)-monomethyl ether
(PEG-OMe)
macromolecule
(16) with a molecular weight of
approximately 5000 gmolꢀ1.
The esterification and de-
protection reactions were easily
monitored by the appearance
and disappearance of the ben-
zylidene protons in the aromat-
ic region, as well as the relative
integrated areas of the benzyli-
dene, glycerol, succinic acid,
and TBDPS protons in the 1H
NMR spectra. The molecular
weights of the synthesized mac-
romolecules were determined
by FAB- or MALDI-MS, and
size exclusion chromatography
Scheme 2. Synthesis of the [G4]-PGLSA dendron. Reagents and conditions: a) 20% Pd(OH)2/C, 50 psi. H2,
THF, RT, 3 h, 97% yield; b) 2, DCC, DPTS, DCM, RT, 48 h, 60% yield; c) 6, DCC, DPTS, DCM, RT, 72 h,
75% yield.
dicyclohexylcarbodiimide (DCC) and 4-(dimethylamino)-
pyridinium p-toluenesulfonate (DPTS)[76] to afford a bi-pro-
tected G2 dendron (bzld-[G2]-PGLSA-TBDPS, 5) in 88%
yield. At this stage, either the carboxylic acid was deprotect-
ed to afford the bzld-[G2]-PGLSA-acid dendron 6 (87%
yield), or the bzld groups were removed to yield a HO-
[G2]-PGLSA-TBDPS dendron 7 (95% yield). The bzld-
[G3]-PGLSA-TBDPS dendron 8 was synthesized conver-
gently by coupling 6 to 4 (83% yield). Alternatively, in a di-
vergent manner, 7 was coupled to 2 to give 8 (73% yield).
As shown in Scheme 2, these iterative steps (benzylidene
acetal deprotection followed by esterfication) were repeated
to synthesize a bzld-[G4]-PGLSA-TBDPS 11, from the HO-
[G3]-PGLSA-TBDPS dendron 10 and 2 (60% yield). The
dendron 11 was also synthesized in a convergent manner by
coupling dendron 6 to 7 in the presence of DCC and DPTS
(75% yield). The convergent pathway afforded the G4 den-
dron in seven reactions and a higher overall yield (42% vs
27%) as opposed to the divergent pathway, which involved
eight reactions.
(SEC). Data in Table 1 show that each increase in genera-
tion number corresponds to an approximate doubling of mo-
lecular weight. This trend is observed in both the FAB/
MALDI-MS and SEC data. The synthesized dendrons, den-
drimers, and dendritic linear hybrids possess relatively low
polydispersity indices, a characteristic of dendritic polymers.
This synthetic route provides access to a diverse set of
structurally different dendritic macromolecules that possess
a high number of surface end groups for further derivatiza-
tion with cross-linking moieties, biological recognition li-
gands, or pharmaceuticals. As discussed earlier, we are inter-
ested in photo-cross-linkable macromolecules as temporary,
resorable scaffolds that can fill irregular wounds or defects
in vivo, and aid in wound healing. Ideally, these synthetic
tissue scaffolds will perform a number of biological func-
tions, including mimicking the physical and mechanical
properties of native, healthy tissue. Swelling and mechanical
studies on photo-cross-linked constructs of a methacrylated
[G3]-PGLSA dendrimer (15) and a [G3]-PGLSA-PEG-
OMe dendritic linear hybrid macromolecule (19) show dra-
matically different properties. The cross-linkable methacry-
lated (MA) dendritic macromolecules were prepared by
The dendrons were coupled to a multi-functional core
(12) or linear poly(ethylene glycol) (PEG) macromolecule
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2003, 9, 5618 5626
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Dendritic Macromolecules
5618 5626
of dendritic gels can be tuned.
Our aim is to match the me-
chanical properties of the
native host tissue through opti-
mization of the polymer archi-
tecture, molecular weight, con-
centration in water, and cross-
linking density of the dendritic
macromolecule. For comparison
with natural gel systems, the dy-
namic shear modulus of a 3.7%
collagen solution is ꢁ150 Pa,
the eye lens and nucleus pulpo-
sus are ꢁ15000 Pa, and the
meniscus is ꢁ100000 Pa. A de-
scription and detailed analysis
of the rheological properties of
a series of dendritic gels will be
described elsewhere.[77]
Conclusion
The synthesis and characteriza-
tion of glycerol and succinic
acid dendrons and dendrimers
as well as dendritic linear
hybrid macromolecules com-
posed of glycerol, succinic acid,
and poly(ethylene glycol) are
described. This synthesis capi-
talizes on the differential chem-
ical reactivity of the benzyli-
dene acetal and TBDPS pro-
tecting groups for the 1,3-hy-
droxyls of glycerol and the car-
boxylic acid of succinic acid,
respectively. Since both the pe-
ripheral end groups and focal
point are available for subse-
Scheme 3. Synthesis of the [G3]-PGLSA dendrimer and dendritic linear hybrid. Reagents and conditions. a)
DCC, DPTS, DCM, RT, 72 h, 73% yield; b) 20% Pd(OH)2/C, 50 psi. H2, THF, RT, 3 h, 97% yield; c) metha-
crylic anhydride, DMAP, DCM, 4.5 h, RT, 64% yield; d) DCC, DPTS, DCM, RT, 168 h, 89% yield; e) 20%
Pd(OH)2/C, 50 psi. H2, THF, RT, 3 h, 83% yield; f) methacrylic anhydride, DMAP, DCM, RT, 18 h, 96% yield.
MA = methacrylate.
treating the hydroxylated terminated macromolecules (14 or
18) with methacrylic anhydride and DMAP as shown in
Scheme 3. These cross-linkable derivatives were then irradi-
ated with ultraviolet light to form gels (gels contained 2,2-
dimethoxy-2-phenylacetophenone as the photoinititator).
The photo-cross-linked construct composed of the methacry-
lated dendrimer (50% modified) 15 was hydrophobic (equi-
librium water content; 2.6% w/w water) and possessed a
low swelling ratio (q) in water (q=1.5). The gel was rela-
tively stiff, and possessed a dynamic shear modulus jG*j of
9.6î106 Pa (at 10 radsꢀ1). However, the gel prepared from
the dendritic linear hybrid 19 (ꢁ25% w/v) was hydrophilic
(equilibrium water content; 91% w/w water) and swelled in
water (q=11.4). This gel was elastic and very soft to the
touch. The jG*j was 180 Pa (at 10 radsꢀ1) and approximate-
ly 104-fold less in magnitude than the construct composed of
dendrimer 15. Both the hydrophilicity and elasticity of the
gels are significantly different between the dendrimer 15
and hybrid 19. These data demonstrate that the properties
quent chemical reactions, this convergent synthetic approach
is highly amenable to the preparation of a wide variety of
dendritic macromolecules from biocompatible building
blocks. Studies with the photo-cross-linked dendritic gels
demonstrate that the mechanical properties of these con-
structs can be altered, and our current effort is aimed at syn-
thesizing additional water-soluble dendritic macromolecules
that upon photo-cross-linking afford a specific gel property.
In summary, these biodendritic macromolecules are of inter-
est for fundamental physiochemical studies and as new tai-
lored materials for applications in drug delivery and tissue
engineering.
Experimental Section
All solvents were dried and freshly distilled prior to use (DCM and pyri-
dine with CaH, and THF with Na). All chemicals were purchased from
Aldrich or Acros as highest purity grade and used without further purifi-
5621
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M. W. Grinstaff et al.
FULL PAPER
Table 1. FAB/MALDI MS and SEC data for dendrons, dendrimers, and dendritic linear hybrid macromolecu-
les.[a]
white powder (95% yield). 1H NMR
(CDCl3): d=2.68 2.72 (m, 4H; -CH2-
CH2-), 4.11 4.14 (m, 2H; -CH2-CH-
CH2-), 4.24 4.27 (m, 2H; -CH2-CH-
CH2-), 4.71 4.72 (m, 1H; -CH2-CH-
CH2-), 5.53 (s, 1H; CH), 7.34 7.36 (m,
3H; arom. CH), 7.48 7.50 ppm (m,
2H; arom. CH); 13C NMR (CDCl3):
d=29.05 (CH2), 29.24 (CH2), 66.57
(CH), 69.15 (CH2), 101.43 (CH),
126.26 (CH), 128.51 (CH), 129.33
(CH), 137.95 (CH), 172.38 (COOR),
178.07 ppm (COOH); GC-MS: m/z
No.
Macromolecules
Calcd MW
FAB/MALDI MW
SEC Mw
SEC PDI
dendrons
5
6
7
8
9
bzld-[G2]-PGLSA-TBDPS
955.08
716.68
779.5
1827.9
1588.50
1475.47
3573.54
955.3
715.2
778.3
1825.6
1587.5
1475.56
3574.54
940
810
800
1830
1650
2101
3420
1.01
1.01
1.01
1.01
1.02
1.05
1.02
bzld-[G2]-PGLSA-acid
HO-[G2]-PGLSA-TBDPS
bzld-[G3]-PGLSA-TBDPS
bzld-[G3]-PGLSA-acid
HO-[G3]-PGLSA-TBDPS
bzld-[G4]-PGLSA-TBDPS
10
11
dendrimers
calcd 280 [M]+ ; found 281 [M+H]+
;
13
14
15
[G3]-PGLSA-bzld
6552.2
5142.5
6231.6
6553.4
5144.8
6224.6
4740
4764
3525
1.01
1.01
1.30
[G3]-PGLSA-OH
elemental analysis calcd (%):C 59.99,
H 5.75; found: C 60.07, H 5.80.
[G3]-PGLSA-MA[b]
dendritic linear hybrids
bzld-[G1]-PGLSA-TBDPS (3): Com-
pound 2 (4.00 g, 0.014 mol) and imid-
azole (3.24 g, 0.048 mol) were stirred
in DMF (150 mL). Next, diphenyl-tert-
butyl silyl chloride (6.4 mL, 0.024 mol)
was added, and the reaction was stir-
red for 48 h. The DMF was removed,
the product was dissolved in CH2Cl2,
washed with sat. NaHCO3 and water,
dried over Na2SO4, filtered, concen-
trated, and dried on the vacuum line.
The product was purified by column
chromatography (4:1 hexanes/EtOAc)
affording 6.38 g of product as a viscous
17
18
19
bzld-[G3]-PGLSA-PEG-OMe
6588
6136
6780
Mn =6628
Mw =6671
PDI=1.01
Mn =6260
Mw =6302
PDI=1.01
Mn =7008
Mw =7080
PDI=1.01
6990
6660
6918
1.04
1.03
1.07
HO-[G3]-PGLSA-PEG-OMe
MA-[G3]-PGLSA-PEG-OMe
[a] Relative molecular weights by size exclusion chromatography were compared to polystyrene samples, with
the exception of the PEG linear hybrids, which were compared to PEG standards. [b] 50% methacrylated.
opaque oil (86% yield). Rf =0.13 (4:1 hexanes/EtOAc); 1H NMR
(CDCl3): d=1.09 (s, 9H; tBu), 2.78 2.84 (m, 4H; -CH2-CH2), 4.11 4.15
(m, 2H; -CH2-CH-CH2-), 4.23 4.26 (m, 2H; -CH2-CH-CH2-), 4.70 4.71
(m, 1H; -CH2-CH-CH2-), 5.54 (s, 1H; CH), 7.33 7.42, 7.48 7.50, 7.67
7.68 ppm (m, 15H; arom. bzld and phenyl CH); 13C NMR (CDCl3):
d=19.34 (-C-(CH3)3), 27.07 (-C-(CH3)3), 29.72, 30.96 (succ. -CH2-), 66.46,
69.18 (glycerol, 2C, -CH2-), 101.39 (O-CH-O), 126.23, 127.94, 128.50,
129.28, 130.29, 131.93, 135.51 (arom. CH), 137.99 (arom. bzld -C-),
cation (DCC 99%; DMAP 99%) except methacrylic anhydride, which
was distilled prior to use, and poly(ethylene glycol) monomethyl ether
(PEG-OMe) 5000 MW, which was purchased from Polysciences and
dried under vacuum at 1208C for 3 h. All polymer molecular weights are
based on a PEG chain of 113 ethylene glycol units to calculate yields and
molecular weights. All reactions were performed under nitrogen atmos-
phere at room temperature unless specified otherwise. NMR spectra
were recorded on a Varian INOVA spectrometer (for 1H and 13C NMR,
400 MHz and 100.6 MHz, respectively) or a GE QE-300 (for HETCOR
with APT) spectrometer. Fast atom bombardment mass spectra
(FABMS) were obtained on a JEOL JMS-SX102A spectrometer using a
3-nitrobenzyl alcohol matrix. MALDI-TOF mass spectra were obtained
using a PerSpective Biosystems Voyager-DE Biospectrometry Worksta-
tion operating in the positive ion mode using 2-(4-hydroxyphenylazo)-
benzoic acid (HABA). Each polymer had an approximate 2000 molecular
weight range. Elemental analysis was obtained from Atlantic Microlab.
Size exclusion chromatography was performed with THF as the elutent
on a Polymer Laboratories PLgel 3 mm MIXED-E column (3 mm bead
171.53, 172.52 ppm (succ. -C(=O)-); GC-MS: m/z calcd: 518.2 [M]+
;
found: 519.2 [M+H]+ ; HR-FAB: m/z calcd: 518.2125 [M]+ ; found:
517.2028 [MꢀH]+ ; elemental analysis calcd (%): C 69.47, H 6.61; found:
C 69.18, H 6.69.
HO-[G1]-PGLSA-TBDPS (4): Compound 3 (2.41 g, 4.65 mmol) was dis-
solved in THF (45 mL), and 20% Pd(OH)2/C (1.0 g) was added. The sol-
ution was then placed in a Parr tube on a hydrogenator, evacuated, flush-
ed with hydrogen, and shaken under 50 psi H2 for 3 h. The solution was
then filtered over wet Celite and the solvent removed by rotoevapora-
tion. The product was purified by column chromatography (1:1 hexanes/
EtOAc increasing to 1:4 hexanes/EtOAc) to yield 1.9 g of a clear oil
(95% yield). Rf =0.24 (1:4 hexanes/EtOAc); 1H NMR (CDCl3): d=1.08
(s, 9H; tBu), 2.02 (brs, 2H; -OH), 2.64 2.85 (m, 4H; -CH2-CH2), 3.70
3.72, 4.07 4.14 (m, 4H; -CH2-CH-CH2-), 4.83 4.86 (m, 1H; -CH2-CH-
CH2-), 7.33 7.44, 7.62 7.65 ppm (m, 10H; arom. phenyl CH); 13C NMR
(CDCl3): d=19.30 (-C-(CH3)3), 27.03 (-C-(CH3)3), 29.77, 31.37 (succ.
-CH2-), 62.45 (glycerol, -CH2-), 75.86 (CH2-CH-CH2), 127.97, 130.36,
132.67, 135.49 (phenyl CH), 172.65, 178.24 ppm (succ. -C(=O)-); FAB-
MS: m/z calcd: 430.57 [M]+ ; found: 431 [MꢀH]+.
Acetyl derivative of compound 4: Compound 4 was a hydroscopic oil and
repeated attempts to obtain satisfactory elemental analysis failed. Thus,
we decided to prepare the acetyl analogue for elemental analysis. Com-
pound 4 (0.44 g, 1.02 mmol) was stirred in CH2Cl2 (30 mL) with DPTS
(0.30 g, 1.02 mmol), freshly distilled acetic acid (0.15 mL, 2.66 mmol), and
DCC (0.63 g, 3.07 mmol). The solution was stirred for 18 h. The DCU
precipitate was filtered and the solvent was evaporated. A solution of 1:1
hexanes/EtOAc was added and impurities precipitated. The solution was
filtered, concentrated and further purified by column chromatography
(3:1 hexanes/EtOAc), to afford 0.44 g of product (83% yield). Rf =0.19
(4:1 hexanes/EtOAc); 1H NMR (CDCl3): d=1.08 (s, 9H; tBu), 1.87 1.93
(m, 6H; -CH3), 2.50 2.71 (m, 4H; -CH2-CH2), 3.96 4.19 (m, 4H; -CH2-
CH-CH2-), 5.06 5.18 (m, 1H; -CH2-CH-CH2-), 7.22 7.33, 7.51 7.56 ppm
(m, 10H; phenyl CH); 13C NMR (CDCl3): d=19.10 (-C-(CH3)3), 20.61
size) and
a Rainin HPLC system (temp=258C; flow rate=1.0
mLminꢀ1). Polystyrene standards (0.60 K, 1.00 K, 4.00 K, 20 K; PDI=
1.04 1.30; Polysciences) were used for calibration of compounds 5 11
and 13 15; and polyethylene glycol standards (0.93 K, 4.45 K, and 12 K;
PDI=1.03 1.05; Polymer Standards Service-USA Inc.) were used for cal-
ibration of compounds 17 19. Equilibrium water content was determined
by TGA (TA TGAQ500). The swelling ratio was determined by weighing
the cross-linked gels after formation and then after being suspended in
0.1m HEPES buffer solution for 24 h. Acetylated derivatives were syn-
thesized and characterized for compounds 4,7 , and 10, since these com-
pounds were hydroscopic oils. Abbreviations: DCM=dichloromethane,
THF=tetrahydrofuran, DCC=dicyclohexylcarbodiimide, DMAP=4-(di-
methylamino)pyridine, DCU=1,3-dicyclohexylurea, Pd(OH)2/C=20%
palladium hydroxide on activated carbon, Pd/C=10% palladium on acti-
vated carbon, DPTS=4-(dimethylamino)-pyridinium p-toluenesulfonate.
2(cis-1,3-O-Benzylidene glycerol)succinic acid monoester (2): cis-1,3-O-
Benzylidene glycerol (1; 17.0 g, 0.094 mol) and succinic anhydride (14.42 g,
0.144 mol) were stirred in pyridine (150 mL) for 18 h. The pyridine was
removed and the white powder was dissolved in H2O. The pH of the
water was adjusted to 7.0 with 1n NaOH. The water layer was washed
with CH2Cl2 to remove impurities. The water layer was then adjusted to
pH 4.0 with 1n HCl. The product was extracted with CH2Cl2, dried over
Na2SO4, filtered, and concentrated to yield 25.02 g of pure product as a
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5618 5626
5622

Dendritic Macromolecules
5618 5626
(OC-CH3), 26.82 (-C-(CH3)3), 29.14, 30.62 (succ. -CH2-), 62.12, 69.28
(glycerol, -CH2-), 127.71, 130.09, 131.65, 135.27 (arom. CH), 170.52,
171.19, 171.58 ppm ( -C(=O)-); FAB-MS: m/z calcd: 514.6 [M]+ ; found:
515.4 [M+H]+ ; elemental analysis calcd (%): C 63.01, H 6.66; found: C
62.76, H 6.69; SEC: Mw =547, Mn =528, PDI=1.04.
[M]+ ; found: 947.9 [M+H]+ ; elemental analysis calcd (%):C 57.07, H
6.17; found: C 57.15, H 6.26; SEC: Mw =1075, Mn =1041, PDI=1.03.
bzld-[G3]-PGLSA-TBDPS (8): Dendron 8 was synthesized by two meth-
ods, first by coupling dendron 6 to dendron 4 convergently, and second
by coupling compound 2 to dendron 7 divergently.
bzld-[G2]-PGLSA-TBDPS (5): Compound 4 (1.90 g, 4.41 mmol) was stir-
red in CH2Cl2 (100 mL) with DPTS (1.30 g, 4.41 mmol), compound 2
(2.72 g, 9.70 mmol), and DCC (2.00 g, 9.70 mmol). The solution was stir-
red for 18 h. The DCU precipitate was filtered and the solvent was
evaporated. A solution of 1:1 hexanes/EtOAc was added and impurities
precipitated. The solution was filtered, concentrated and further purified
by column chromatography (1:1 hexanes/EtOAc) to afford 3.70 g of
product (88% yield). Rf =0.22 (1:1 hexanes/EtOAc); 1H NMR (CDCl3):
d=1.08 (s, 9H; tBu), 2.57 2.79 (m, 12H; -CH2-CH2), 4.08 4.14, 4.16 4.22
(m, 12H; -CH2-CH-CH2-), 4.70 4.71 (m, 2H; -CH2-CH-CH2-), 5.21 (m,
1H; CH), 5.49 5.54 (m, 1H; CH), 7.32 7.41, 7.47 7.49, 7.62 7.67 ppm
(m, 20H; arom. bzld and phenyl CH); 13C NMR (CDCl3): d=19.31 (-C-
(CH3)3), 27.04 (-C-(CH3)3), 28.98, 29.33, 30.81 (succ. -CH2-), 62.48, 66.50,
69.16, 69.43 (glycerol, -CH2-), 101.33 (O-CH-O), 126.22, 127.95, 128.49,
129.26, 130.32, 131.92, 135.49 (arom. CH), 138.02 (arom. bzld -C-),
Convergent synthesis: Compound 6 (1.05 g, 1.47 mmol) was stirred in
CH2Cl2 (75 mL), and compound 4 (0.29 g, 0.67 mmol), DPTS (0.20 g,
0.67 mmol), and DCC (0.41 g, 2.00 mmol) were added. The solution was
stirred for 48 h. The DCU precipitate was filtered and the solvent was
evaporated. The product was purified by column chromatography (3:7
hexanes/EtOAc) to afford 0.99 g of product (82% yield).
Divergent synthesis: Compound
7 (0.55 g, 0.71 mmol) was stirred in
CH2Cl2 (50 mL), and DPTS (0.42 g, 1.41 mmol), compound 2 (0.87 g,
3.11 mmol), and DCC (0.64 g, 3.12 mmol) were added. The solution was
stirred for 18 h. The DCU precipitate was filtered and the solvent was
evaporated. The product was purified by column chromatography (3:7
hexanes/EtOAc) to afford 0.71 g of product (54% yield). Rf =0.08 (3:7
hexanes/EtOAc); 1H NMR (CDCl3): d=1.08 (s, 9H; tBu), 2.54 2.92 (m,
28H; -CH2-CH2), 4.08 4.15, 4.22 4.27 (m, 28H; -CH2-CH-CH2-), 4.71 (s,
4H; -CH2-CH-CH2-), 5.21 5.24 (m, 3H; CH), 5.52 (s, 4H; CH), 7.31
7.42, 7.45 7.49, 7.65 7.67 ppm (m, 30H; arom. bzld and phenyl CH); 13C
NMR (CDCl3): d=19.31 (-C-(CH3)3), 27.04 (-C-(CH3)3), 29.35, 30.81
(succ. -CH2-), 62.49, 66.53, 69.16, 69.47 (glycerol, -CH2-), 101.33 (O-CH-
O), 126.21, 127.94, 128.48, 129.26, 130.32, 135.47 (arom. CH), 138.02
(arom. bzld -C-), 171.90, 172.28 ppm (succ. -C(=O)-); GC-MS: m/z calcd:
1827.9 [M]+ ; found: 1825.6 [MꢀH]+ ; HR-FAB: m/z calcd: 1826.6233
[M]+ ; found: 1825.6124 [MꢀH]+ ; elemental analysis calcd (%):C 61.11,
H 5.85; found: C 60.66, H 5.85; SEC: Mw =1830, Mn =1810, PDI=1.01.
171.93, 172.28 ppm (succ. -C(=O)-); GC-MS: m/z calcd: 954.4 [M]+
;
found: 955.3 [M+H]+ ; elemental analysis calcd (%): C 64.14, H 6.12;
found: C 64.35, H 6.29; SEC: Mw =940, Mn =930, PDI=1.01.
bzld-[G2]-PGLSA-acid (6): Compound 5 (1.00 g, 1.04 mmol) was dis-
solved in THF (75 mL). Next, tetrabutylammonium fluoride trihydrate
(1.25 g, 3.96 mmol) was added to the solution and it was stirred for 1
hour, after which the reaction was complete as indicated by TLC. The
solution was diluted with H2O (25 mL) and acidified with 1n HCl to pH
3. The product was extracted into CH2Cl2, dried over Na2SO4, concentrat-
ed, and dried on the vacuum line. The product was purified by column
chromatography (0 5% MeOH in CH2Cl2) for 0.65 g of product (87%
bzld-[G3]-PGLSA-acid (9): Compound 8 (2.00 g, 1.09 mmol) was dis-
solved in THF (125 mL). Next, tetrabutylammonium fluoride trihydrate
(1.3 g, 4.1 mmol) was added to the solution. The mixture was stirred for
1 hour, after which the reaction was complete as indicated by TLC. The
solution was diluted with H2O (25 mL) and acidified with 1n HCl to pH
3. The product was extracted into CH2Cl2, dried over Na2SO4, concentrat-
ed, and dried on the vacuum line. The product was purified by column
chromatography (0 5% MeOH in CH2Cl2) to afford 1.44 g of product
(83% yield). Rf =0.21 (5% MeOH in CH2Cl2); 1H NMR (CDCl3): d=
2.58 2.75 (m, 28H; -CH2-CH2), 4.11 4.16, 4.19 4.27 (m, 28H; -CH2-CH-
CH2-), 4.71 4.72 (m, 4H; -CH2-CH-CH2-), 5.21 5.28 (m, 3H; CH), 5.52
5.53 (m, 4H; CH), 7.32 7.37, 7.46 7.49 ppm (m, 20H; arom. bzld CH);
13C NMR (CDCl3): d=29.05, 29.36 (succ. -CH2-), 62.51, 66.58, 69.16
(glycerol, -CH2-), 101.36 (O-CH-O), 126.21, 128.49, 129.29 (arom. CH),
137.95 (arom. bzld -C-), 171.83, 173.01 ppm (succ. -C(=O)-); GC-MS: m/z
calcd: 1588.5 [M]+ ; found: 1587.5 [MꢀH]+ ; elemental analysis calcd
(%):C 58.18, H 5.58; found: C 58.02, H 5.60; SEC: Mw =1650, Mn =1620,
PDI=1.02.
1
yield). Rf =0.24 (5% MeOH in CH2Cl2). H NMR (CDCl3): d=2.55 2.77
(m, 12H; -CH2-CH2), 4.10 4.17, 4.24 4.31 (m, 12H; -CH2-CH-CH2-),
4.74 4.75 (m, 2H; -CH2-CH-CH2-), 5.28 5.31 (m, 1H; CH), 5.52 5.54 (m,
2H; CH), 7.33 7.38, 7.47 7.49 ppm (m, 10H; arom. bzld CH); 13C NMR
(CDCl3): d=28.72, 29.03, 29.38 (succ. -CH2-), 62.68, 66.56, 69.16 (glycer-
ol, -CH2-), 101.44 (O-CH-O), 126.23, 128.50, 129.33 (arom. CH), 137.75
(arom. bzld -C-), 172.67, 175.16 (succ. -C(=O)-); GC-MS: m/z calcd:
716.2 [M]+ ; found: 715.2 [MꢀH]ꢀ; elemental analysis calcd (%):C 58.66,
H 5.63; found: C 58.71, H 5.82; SEC: Mw =810, Mn =800, PDI=1.01.
HO-[G2]-PGLSA-TBDPS (7): Compound 5 (1.55 g, 1.62 mmol) was dis-
solved in THF (40 mL) and 20% Pd(OH)2/C (1.0 g) was added. The solu-
tion was then placed in a Parr tube on a hydrogenator and shaken under
50 psi H2 for 4 h. The solution was then filtered over wet Celite, concen-
trated, and purified by column chromatography (0 25% acetone in
EtOAc) to yield 1.12 g of product (95% yield). Rf =0.25 (1:3 acetone/
EtOAc). 1H NMR (CDCl3): d=1.07 (s, 9H; tBu), 2.25 (brs, 4H; -OH),
2.58 2.82 (m, 12H; -CH2-CH2), 3.71 3.74, 4.09 4.26 (m, 12H; -CH2-CH-
CH2-), 4.87 4.99, 5.24 5.25 (m, 3H; -CH2-CH-CH2-), 7.34 7.43, 7.63 7.68
ppm (m, 10H; phenyl CH); 13C NMR (CDCl3): d=14.52 (-C-(CH3)3),
25.78 (-C-(CH3)3), 26.99, 29.30, 30.51, 30.81 (succ. -CH2-), 62.08, 63.44,
68.17, 70.23 (glycerol, -CH2-), 125.71, 127.96, 130.35, 135.45 (phenyl),
171.94, 172.40 (succ. -C(=O)-); GC-MS: m/z calcd: 778.3 [M]+ ; found
779.5 [M+H]+ ; SEC: Mw =800, Mn =792, PDI=1.01
HO-[G3]-PGLSA-TBDPS (10): Compound 8 (0.53 g, 0.29 mmol) was
dissolved in THF (50 mL) in a Parr tube. 20% Pd(OH)2/C (0.4 g) was
added and the flask was evacuated and filled with 50 psi of H2. The mix-
ture was shaken for 8 h, then filtered over wet Celite. The filtrate was
dried to produce a clear oil, which was purified by column chromatogra-
phy (0 50% acetone in EtOAc) to afford 0.38 g of product (88% yield).
Rf =0.23 (1:1 acetone/EtOAc); 1H NMR (CDCl3): d=1.3 (s, 9H; tBu),
2.52 2.86 (m, 28H; -CH2-CH2), 3.44 3.94 (m, 24, -CH2-CH-CH2- and
-OH), 4.10 4.38, (m, 12H; -CH2-CH-CH2-), 4.82 4.92 (m, 4H; CH),
5.18 5.30 (m, 3H; CH), 7.28 7.43, 7.50 7.54, 7.60 7.66 ppm (m, 10H;
phenyl CH); 13C NMR (CDCl3): d=19.04 (-C-(CH3)3), 24.44 (-C-(CH3)3),
26.76, 27.12, 28.82, 28.97, 29.10, 30.57 (succ. -CH2-), 61.17, 62.33, 63.21,
69.30, 75.52 (glycerol, -CH2-), 127.72, 130.11, 131.57, 134.36, 135.20
(arom. CH), 171.66, 171.72, 171.99, 172.27, 172.38, 172.46 ppm (succ.
-C(=O)-); MALDI-MS: m/z calcd: 1475.5 [M]+ ; found: 1475.56 [M+H]+
; SEC: Mw =2101, Mn =1994, PDI=1.05.
Acetyl derivative of compound 7: Compound 7 was a hydroscopic oil and
repeated attempts to obtain satisfactory elemental analysis failed. Thus,
we decided to prepare the acetyl analogue. Compound 7 (0.55 g, 0.70
mmol) was stirred in CH2Cl2 (40 mL) with DPTS (0.39 g, 1.34 mmol),
freshly distilled acetic acid (0.19 mL, 3.36 mmol), and DCC (0.87 g, 4.20
mmol). The solution was stirred for 18 h. The DCU precipitate was fil-
tered and the solvent was evaporated. The residue was resuspended in a
minimum of CH2Cl2, cooled to 108C and filtered. The resulting solution
was concentrated and further purified by column chromatography (0 5%
acetone in CH2Cl2) to afford 0.49 g of product (66% yield). Rf =0.17
Acetyl derivative of compound 10: Compound 10 was a hydroscopic oil
and repeated attempts to obtain satisfactory elemental analysis failed.
Thus, we decided to prepare the acetyl analogue. Compound 10 (0.24 g,
0.16 mmol) was stirred in CH2Cl2 (40 mL) with DPTS (0.19 g, 0.65
mmol), freshly distilled acetic acid (0.09 mL, 1.55 mmol), and DCC (0.40
g, 1.94 mmol). The solution was stirred for 18 h. The DCU precipitate
was filtered and the solvent was evaporated. The residue was resuspend-
ed in a minimum of CH2Cl2, cooled to 108C and filtered. The resulting
1
(5% acetone in CH2Cl2); H NMR (CDCl3): d=1.07 (s, 9H; tBu), 2.04 (s,
12H; -CH3), 2.55 2.83 (m, 12H; -CH2-CH2), 4.09 4.32 (m, 12H; -CH2-
CH-CH2-), 5.20 5.29 (m, 3H; -CH2-CH-CH2-), 7.32 7.44, 7.61 7.67 ppm
(m, 10H; phenyl CH); 13C NMR (CDCl3): d=19.10 (-C-(CH3)3), 20.67
(OC-CH3), 26.82 (-C-(CH3)3), 28.60, 28.80, 29.10, 30.59 (succ. -CH2-),
62.11, 62.31, 69.39 (glycerol, -CH2-), 127.72, 130.09, 131.67, 135.27 (arom.
CH), 170.50, 171.33, 171.61 ppm ( -C(=O)-); FAB-MS: m/z calcd: 947.0
5623
Chem. Eur. J. 2003, 9, 5618 5626
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. W. Grinstaff et al.
FULL PAPER
solution was concentrated and further purified by column chromatogra-
phy (4:1 hexanes/EtOAc increasing to 3:7 hexanes/EtOAc) to afford
0.18 g of product (63% yield). Rf =0.15 (3:7 hexanes/EtOAc); 1H NMR
(CDCl3): d=1.10 (s, 9H; tBu), 1.99 (s, 24H; -CH3), 2.48 2.78 (m, 28H;
-CH2-CH2), 4.02 4.30 (m, 28H; -CH2-CH-CH2-), 5.12 5.26 (m, 7H; -CH2-
CH-CH2-), 7.25 7.38, 7.55 7.61 ppm (m, 10H; phenyl CH); 13C NMR
(CDCl3): d=18.87 (-C-(CH3)3), 20.46 (OC-CH3), 26.61 (-C-(CH3)3),
26.95, 28.47, 28.55, 28.64, 28.90, 30.39 (succ. -CH2-), 61.90, 62.10, 69.02,
69.22 (glycerol, -CH2-), 127.52, 129.90, 131.48, 135.05 (arom. CH), 170.26,
filtered. The product was purified by column chromatography (0 5%
MeOH in CH2Cl2) to yield 0.40 g of product (73% yield). 1H NMR
(CDCl3): d=2.60 2.74 (m, 116H; -CH2-CH2), 4.08 4.17 (m, 60H; -CH2-
CH-CH2-), 4.22 4.26 (m, 60H; -CH2-CH-CH2-), 4.70 (s, 16H; -CH2-CH-
CH2-), 5.20 5.23 (m, 14H; CH), 5.51 (s, 16H; CH), 7.32 7.36, 7.46 7.48
ppm (m, 80H; arom. bzld CH); 13C NMR (CDCl3): d=29.02, 29.35 (succ.
-CH2-), 62.47, 66.54, 69.16 (glycerol, -CH2-), 101.31 (O-CH-O), 126.21,
128.48, 129.26 (arom. CH), 138.01 (arom. bzld -C-), 171.83, 172.29 ppm
(succ. -C(=O)-); MALDI: m/z calcd: 6552.2 [M]+
; found: 6553.4
[M+H]+ ; elemental analysis calcd (%):C 58.29, H 5.57; found: C 58.50,
H 5.48; SEC: Mw =4740, Mn =4590, PDI=1.01.
171.14, 171.40, 171.46 ppm ( -C(=O)-); FAB-MS: m/z calcd: 1811.8 [M]+
;
found: 1812.2 [M+H]+ ; elemental analysis calcd (%):C 53.70, H 5.90;
found: C 53.95, H 6.12; SEC: Mw =1943, Mn =1882, PDI=1.03.
[G3]-PGLSA-OH dendrimer (14): Compound 13 (0.33 g, 0.051 mmol)
was dissolved in a 9:1 solution of THF and MeOH (50 mL) in a Parr
tube. Next, 20% Pd(OH)2/C (0.50 g) was added, and the flask was evacu-
ated and filled with 50 psi of H2. The mixture was shaken for 7 h, then fil-
tered over wet Celite. The filtrate was dried to produce 0.25 g of a clear
oil (0.049 mmol, 97% yield). 1H NMR (CD3OD): d=2.64 (m, 116, -CH2-
CH2-), 3.51 (m, 26, -CH2-CH-CH2-), 3.67 (m, 28, -CH2-CH-CH2-), 3.80
(m, 12, -CH2-CH-CH2-), 4.05 (m, 14, -CH2-CH-CH2-), 4.14 (m, 14, -CH2-
CH-CH2-), 4.22 (m, 22, -CH2-CH-CH2-), 4.30 (m, 22, -CH2-CH-CH2-),
5.26 ppm (m, 14, -CH2-CH-CH2); 13C NMR (CD3OD): d=28.61 (CH2),
62.41 (CH2), 62.87 (CH2), 65.67 (CH2), 67.64 (CH), 69.91 (CH), 172.86
ppm (COOR); MALDI-MS: m/z calcd: 5142.5 [M]+ ; found: 5144.8
[M+H]+ ; elemental analysis calcd (%):C 48.11, H 5.84; found: C 48.07,
H 5.84; SEC Mw: 5440; Mn: 5370; PDI: 1.01.
bzld-[G4]-PGLSA-TBDPS (11): Dendron 11 was synthesized by two
methods, first by coupling dendron 6 to dendron 7 convergently, and sec-
ondly by coupling the monoester 2 to dendron 10 divergently.
Convergent synthesis: Compound 7 (0.14 g, 0.18 mmol) was dissolved in
CH2Cl2 (30 mL). Next, DPTS (0.05 g, 0.18 mmol), compound 6 (0.82 g,
1.10 mmol), and DCC (0.22 g, 1.10 mmol) were added. The solution was
stirred for 72 h. The DCU was filtered, the filtrate was concentrated to
dryness, and the residue was resuspended in a minimum of cold THF.
The solution was filtered, concentrated, and purified by column chroma-
tography (1:1 hexanes/EtOAc increasing to 1:4 hexanes/EtOAc) to afford
0.48 g of product (75% yield).
Divergent synthesis: Compound 10 (0.38 g, 0.26 mmol) was dissolved in
CH2Cl2 (50 mL). Next, compound 2 (1.00 g, 3.57 mmol), DPTS (0.10 g,
0.34 mmol), and DCC (0.66 g, 3.57 mmol) were added to the mixture.
The solution was stirred for 48 h. The solution was filtered to remove the
DCU precipitate, concentrated, and then purified by column chromatog-
raphy (1:1 hexanes/EtOAc increasing to 1:4 hexanes/EtOAc) to afford
0.57 g of product (60% yield). Rf =0.14 (1:4 hexanes/EtOAc). 1H NMR
(CDCl3): d=1.07 (s, 9H; tBu), 2.55 2.77 (m, 60H; -CH2-CH2), 4.07 4.15,
4.22 4.25 (m, 60H; -CH2-CH-CH2-), 4.70 (s, 8H; -CH2-CH-CH2-), 5.19
5.21 (m, 7H; CH), 5.51 (s, 8H; CH), 7.30 7.40, 7.46 7.48, 7.63 7.65 ppm
(m, 50H; arom. bzld and phenyl CH); 13C NMR (CDCl3): d=14.40 (-C-
(CH3)3), 27.03 (-C-(CH3)3), 29.02, 29.35 (succ. -CH2-), 62.47, 66.53, 69.16,
69.49 (glycerol, -CH2-), 101.31 (O-CH-O), 126.21, 127.94, 128.48, 129.26,
135.47 (arom. CH), 138.03 (arom. bzld -C-), 171.50, 171.90, 172.27 ppm
(succ. -C(=O)-); MALDI-MS: m/z calcd: 3573.54 [M]+ ; found: 3574.54
[M+H]+ ; elemental analysis calcd (%):C 59.19, H 5.74; found: C 59.49,
H 5.70; SEC: Mw =3420, Mn =3350, PDI=1.02.
[G3]-PGLSA-MA dendrimer (50% derivatized) (15): Compound 14
(0.22 g, 0.041 mmol) was dissolved in DMF (5 mL). Next, DMAP (0.20 g,
1.66 mmol) was added followed by methacrylic anhydride (0.10 mL, 0.67
mmol, 0.5 equivof the peripheral hydroxyl groups on 14). After 4.5 h the
reaction was complete as indicated by TLC. MeOH (0.03 mL, 0.67 mmol)
was added to the reaction, and the mixture was stirred for an additional
20 minutes. The solution was precipitated into cold diethyl ether (300
mL). The diethyl ether was decanted and the remaining oily residue was
diluted with CH2Cl2 (20 mL). The organic phase was washed with 1n
HCl and brine. The organic phase was dried over Na2SO4, filtered, and
concentrated to approximately 2 mL. This concentrated solution was pre-
cipitated in cold diethyl ether (300 mL). The diethyl ether was decanted
and the resulting oily residue was dried under reduced pressure to yield
1
0.20 g of product (78% yield). H NMR (CDCl3): d=1.90 (s, 42H; -CH3),
2.55 2.77 (m, 116H; -CH2-CH2), 3.61 3.78 (m, 30H; -CH2-CH-CH2-),
4.07 4.30 (m, 120H; -CH2-CH-CH2-), 5.58 5.62 (m, 16H;=CH), 6.03
6.16 ppm (m, 16H;=CH); 13C NMR (CDCl3): d=18.24 (-CH3), 29.56,
29.75 (succ. -CH2-), 61.52, 62.09, 62.14, 65.17, 65.83, 69.39, 69.56, 70.04,
73.23, 75.89 (glycerol -CH2-), 171.04, 171.25, 171.37, 171.58, 171.79,
172.14, 172.51 ppm; MALDI-MS: m/z calcd: 6231.6 [M]+ ; found: 6224.6
[M+H]+ ; SEC: Mw =3525, Mn =2708, PDI=1.30.
Tetrafunctional G0 Core ([G0]-PGLSA-bzld): Succinic acid (1.57 g, 13.3
mmol), compound 1 (5.05 g, 28.0 mmol), and DPTS (4.07 g, 13.8 mmol)
were dissolved in CH2Cl2 (100 mL). Next, DCC (8.19 g, 39.7 mmol) was
added and the reaction was stirred for 18 h. The DCU was filtered and
the filtrate was concentrated and purified by column chromatography (0
3% MeOH in CH2Cl2) to afford 5.28 g of product (90% yield). Rf =0.69
(3% MeOH in CH2Cl2); 1H NMR (CDCl3): d=2.78 (s, 4H; -CH2-CH2-),
4.07 4.11 (m, 2H; -CH2-CH2-CH2-), 4.23 4.26 (m, 2H; -CH2-CH2-CH2-),
4.70 (s, 2H; -CH2-CH2-CH2-), 5.51 (s, 2H; CH), 7.31 7.37 (m, 6H; arom.
CH), 7.47 7.49 ppm (m, 4H; arom. CH); 13C NMR (CDCl3): d=29.57
(CH2), 66.49 (CH), 69.17 (CH2), 101.35 (CH), 126.23 (CH), 128.48 (CH),
129.25 (CH), 138.05 (CH), 172.35 ppm (COOR); GC-MS: m/z calcd: 442
[M]+ ; found: 443 [M+H]+ ; HR-FAB: m/z calcd: 442.1628 [M]+ ; found:
442.1635 [M]+ ; elemental analysis calcd (%): C 65.15, H 5.92; found: C
65.25, H 5.85.
bzld-[G3]-PGLSA-PEG-OMe (17): Compound 9 (0.29 g, 0.18 mmol) was
dissolved in CH2Cl2 (75 mL). Next, 5000 MW poly(ethylene glycol)
mono-methyl ether (PEG-OMe; 0.45 g, 0.09 mmol; MALDI-MS: Mw =
5147, Mn =5074, PDI=1.01), DCC (0.037 g, 0.18 mmol), and DPTS
(0.026 g, 0.09 mmol) were added to the solution. The solution was stirred
for 168 h. The DCU was filtered and the filtrate was concentrated to dry-
ness. The resulting residue was resuspended in THF and cooled, and the
DCU was filtered. The resulting solution was precipitated in diethyl
ether. The solid was dissolved in THF, stirred with Amberlyst A-21 ion-
exchange resin (Aldrich) (weakly basic resin) to eliminate excess 9. The
solution was filtered and the filtrate was dried over Na2SO4, dissolved in
CH2Cl2, washed with 0.1n HCl, dried over Na2SO4, and concentrated to
dryness to yield 0.53 g of a solid white product (89% yield). 1H NMR
(CDCl3): d=2.60 2.73 (m, 28H; -CH2-CH2), 3.36 (s, MME CH3), 3.57
3.64 (m, 406H; PEG CH2), 4.11 4.26 (m, 28H; -CH2-CH-CH2-), 4.71 (m,
4H; -CH2-CH-CH2-), 5.21 5.23 (m, 3H; CH), 5.52 5.54 (m, 4H; CH),
7.32 7.37, 7.46 7.49 ppm (m, 20H; arom. bzld CH); 13C NMR (CDCl3):
d=29.36, 29.90 (succ. -CH2-), 62.48, 66.53, 69.17 (glycerol, -CH2-), 70.77
(PEG, -CH2-), 101.33 (O-CH-O), 126.21, 128.48, 129.26 (arom. CH),
137.80 (arom. bzld -C-), 171.90 ppm (succ. -C(=O)-); MALDI-MS: Mw =
6671, Mn =6628, PDI=1.01 (theoretical MW =6588); SEC: Mw =6990,
Mn =6670, PDI=1.04.
[G0]-PGLSA-OH (12): [G0]-PGLSA-bzld (1.00 g, 0.0023 mol) was dis-
solved in THF (40 mL) in a Parr tube. Next, 20% Pd(OH)2/C (0.50 g)
was added. The Parr tube was evacuated, and filled with 50 psi of H2.
The solution was shaken for 3 h. The catalyst was filtered through wet
Celite and washed with THF. The filtrate was evaporated to give 0.57 g
of a clear oil (95% yield). 1H NMR (CDCl3): d=2.67 (s, 4H; -CH2-CH2-
), 3.64 (m, 8, -CH2-CH2-CH2-), 4.87 ppm (m, 2H; -CH2-CH2-CH2-); 13C
NMR (CDCl3): d=28.96 (CH2), 60.41 (CH), 75.85 (CH2), 172.78 ppm
(COOR); GC-MS: m/z calcd: 266 [M]+ ; found: 284 [M+NH4]+ ; elemen-
tal analysis calcd (%):C 45.11, H 6.81; found: C 44.94, H 6.87.
[G3]-PGLSA-bzld dendrimer (13): Compound 12 (0.019 g, 0.084 mmol)
was dissolved in CH2Cl2 (50 mL). Next, compound 9 (0.64 g, 0.40 mmol),
DPTS (0.074 g, 0.25 mmol), and DCC (0.10 g, 0.50 mmol) were added.
The solution was stirred for 72 h. The DCU was filtered and the filtrate
was concentrated. The additional DCU was precipitated in cold THF and
HO-[G3]-PGLSA-PEG-OMe (18): Compound 17 (0.52 g) was dissolved
in THF (40 mL). Next, 20% Pd(OH)2/C (0.10 g) was added. The reaction
vessel was evacuated and flushed with hydrogen. The solution was
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2003, 9, 5618 5626
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Dendritic Macromolecules
5618 5626
shaken for 3 h under 50 psi H2. The Pd(OH)2/C was removed by filtering
over wet Celite. The filtrate was dried and precipitated in diethyl ether
to yield 0.40 g of an opaque hydroscopic solid (83% yield). 1H NMR
(CDCl3): d=2.60 2.70 (m, 28H; -CH2-CH2), 3.36 (s, MME CH3) 3.53
3.78 (brm, 422H; PEG CH2 and -CH2-CH-CH2-), 4.17 4.27 (m, 12H;
-CH2-CH-CH2-), 4.92 (m, 4H; -CH2-CH-CH2-), 5.21 5.23 ppm (m, 3H;
CH); 13C NMR (DMSO): d=29.14, 29.36 (succ. -CH2-), 60.25 (-CH3
OMe), 63.22, 66.54, 69.87 (glycerol, -CH2-), 70.43 (PEG, -CH2-), 172.35,
172.57 ppm (succ. -C(=O)-); MALDI-MS: Mw =6302, Mn =6260, PDI=
1.01 (theoretical MW =6136); SEC: Mw =6660, Mn =6460, PDI=1.03.
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1
0.41 g of product (96% yield). H NMR (CDCl3): d=1.92 (s, 24H; -CH3-
methacrylate), 2.63 (m, 28H; -CH2-CH2), 3.36 (s, MME CH3) 3.59 3.67
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Acknowledgement
This work was supported by the Pew Scholars Program in the Biomedical
Sciences, the Johnson and Johnson Focused Giving Program, and the
NIH (R01 EY13881). We thank Dr. Steve Aubuchon of TA Instruments
for help with the mechanical studies. N.R.L. and K.A.S. gratefully ac-
knowledge the NIH Biological Chemistry Training Grant Program at
Duke University. M.W.G. also thanks the Dreyfus Foundation for a Ca-
mille Dreyfus Teacher-Scholar, the 3M corporation for a Non-Tenured
Faculty Award, and the Alfred P. Sloan Foundation for a Research Fel-
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Received: May 23, 2003 [F5172]
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