Synthesis of new unsymmetrical polyarylester dendrimers

Article abstract of DOI:10.1016/j.tet.2004.03.024

Preparation of polyarylester dendrimers containing 2-(hydroxymethyl)-1,4- butanediol and 2,2-bis(hydroxymethyl)-1,4-butanediol cores is described. These polyarylester dendrimers are unsymmetrical with respect to chain lengths and function as model systems for studying in vitro controlled drug release systems. Reaction conditions for deprotection of trichloroethyl group of the dendritic wedges have been improved.

Full text of DOI:10.1016/j.tet.2004.03.024

Tetrahedron 60 (2004) 3739–3744
Synthesis of new unsymmetrical polyarylester dendrimers
*
Srinagesh Kumar Potluri, A. Raghu Ramulu and M. Pardhasaradhi
Gas Based Chemicals and Organic Intermediates Division, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 14 March 2003; revised 3 March 2004; accepted 8 March 2004
Abstract—Preparation of polyarylester dendrimers containing 2-(hydroxymethyl)-1,4-butanediol and 2,2-bis(hydroxymethyl)-1,4-
butanediol cores is described. These polyarylester dendrimers are unsymmetrical with respect to chain lengths and function as model
systems for studying in vitro controlled drug release systems. Reaction conditions for deprotection of trichloroethyl group of the dendritic
wedges have been improved.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Dendrimers are globular, highly branched, monodisperse
macromolecules with a well-defined three-dimensional
shape, size, and molecular weight. Although, dendrimer
chemistry is more than two decades old, new synthetic
strategies and experimental conditions get evolved, keeping
in view their numerous applications; for instance, as slow
drug releasing systems, catalysts, physiological and electro-
chemical devices, and liquid crystals.1 – 7 In general,
dendrimers consist of core, branching structure, and
periphery. Physio-chemical properties, and hence appli-
cations depend on the nature of these basic constituents.
The synthetic strategy presented in this paper describes the
synthesis of new polyarylester dendrimers possessing
unsymmetric aliphatic cores viz., 2-(hydroxymethyl)-1,4-
butanediol (2) and 2,2-bis(hydroxymethyl)-1,4-butanediol
(3). Consequently, ester dendrimers possessing these
cores14,15 are unsymmetrical with respect to chain lengths,
and to the best of our knowledge triol (2) and tetrol (3) were
hitherto not used for the preparation of dendrimers.
Accordingly, G0-acid and G1-acid wedges were syn-
thesized as shown in Scheme 1 and by adopting a fine
combination of both convergent and divergent approaches;
synthesis of the unsymmetrical dendrimers was
accomplished.
Polyester dendrimers were demonstrated as suitable
candidates for drug delivery8 applications; furthermore,
with their chemistries well developed,9–13 it was envisaged
to prepare structures having functionalities that undergo
hydrolytic cleavage at different rates. To enable this,
polyester dendrimers built on unsymmetric cores were
chosen; by virtue of their unequal chain lengths, these
dendrimers may get hydrolyzed by the enzymes at different
rates. It is hypothesized that the differential rates of
hydrolysis would release the dendrimer bound/entrapped
drugs gradually, thus sustaining the availability of the drug
for longer periods. To study this phenomenon in vitro,
herein, synthesis of some model systems is reported.
2,2,2-Trichloroethyl-3,5-dihydroxy benzoate (1) was pre-
pared in 60% yield by the reaction of 3,5-dihydroxybenzoic
acid with a mixture of 2,2,2-trichloroethanol and concen-
trated H2SO4. However, isolation of ester (1) was done by
slightly modifying the literature procedure.9 Removal of
H2SO4 through aqueous NaHCO3 wash, prior to the removal
of trichloroethanol solvent and recrystallization from 1:1
hexane/benzene gave trichloroethyl ester (1) as white solid
having mp of 70 8C. On the contrary, the literature reports9
indicated this compound to be a liquid. In the preparation of
G1-acid, trichloroethyl group was selectively deprotected in
presence of other ester groups using zinc and acetic acid.
Deprotection following the literature procedure9 resulted in
an impure product. However, decreasing the mole ratio of
Zn and acetic acid by three times solved this problem.
Keywords: Dendrimers; Convergent-divergent approach; Dendritic wedge;
Unsymmetrical; Polyaryl ester; Trichloroethyl protection.
G0-acid was coupled to cores 2 and 3 using a combination
of dicyclohexylcarbodiimide (DCC) and 4-(dimethylami-
no)pyridinium p-toluenesulfonate (DPTS). Thus, first gen-
eration polyarylester dendrimers 4 and 5 were isolated in 95
and 93% yield respectively, as shown in Scheme 2.
*
Corresponding author. Address: Department of Chemistry Southern
Methodist University, Fondren Science Bldg. 3215 Daniel Avenue,
Dallas TX 75275, USA. Tel.: þ1-214-768-4392; fax: þ1-214-768-4089;
e-mail addresses: spotluri@smu.edu; psnkumar@hotmail.com
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.03.024

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S. K. Potluri et al. / Tetrahedron 60 (2004) 3739–3744
Scheme 1.
Surprisingly, the above mentioned reaction conditions did
not yield second-generation dendrimers 6 and 7 (Scheme 3).
On the other hand, mixtures of inseparable products were
obtained; despite running the reaction for longer times and
at higher temperatures.
hydroxyl groups were very close to the center of the core.
Second, the ester formation is considered relatively sluggish
with aliphatic hydroxyl groups. However at this point,
changing the strategy to a divergent approach solved these
problems. The periphery of dendrimers 4 and 5 consist of
six and eight benzyloxy groups respectively; accordingly,
debenzylation of compounds 4 and 5 using Pd/C and H2
resulted in hexahydroxy (8) and octahydroxy (9) intermedi-
ates (Scheme 4). With out further purification and
Failure of the reaction of G1-acid wedge with cores 2 and 3
is attributed, first, to crowding in the formation of
dendrimers 6 and 7. This is because the reacting aliphatic
Scheme 2.

S. K. Potluri et al. / Tetrahedron 60 (2004) 3739–3744
3741
Scheme 4.
characterization, phenols 8 and 9 were reacted with G0-acid
in presence of DCC/DPTS to give second-generation
dendrimers 6 and 7 in 69 and 70% yields respectively
(Scheme 5).
Similarly, following the above strategy, G1-acid wedge was
reacted with intermediates 8 and 9 to produce third
generation dendrimers 10 and 11 in 25 and 10% yields,
respectively.
The divergent approach to synthesize the dendrimers 6, 7
10, and 11 was successful because the reacting hydroxyl
groups were phenolic and farther separated from the center
of the core.
The values of the chemical shifts in the NMR spectra were
in well agreement with those reported in the literature for
similar dendritic polyarylesters.9 To establish the extent of
reaction and the generation number, the integration of
ethereal hydrogens of the core (d: 4.6) was compared with
the peripheral benzylic hydrogens (d: 4.9–5.0). MS
techniques, FAB and MALDI were used to establish the
molecular weight of the dendritic wedges and dendrimers.
However, elemental analysis data of third generation
dendrimers showed slight deviation from the calculated
values. This discrepancy may be assumed originating from
some kind of intramolecular transesterification reactions
occurring when the reactions were performed for extended
periods of time (72 and 96 h).
3. Conclusion
Synthesis of new unsymmetrical polyarylester dendrimers,
by a combination of convergent and divergent approaches,
was well demonstrated. Although the concept of differential
hydrolytic cleavage for controlled drug delivery, as
propounded in this paper, is new; its success depends
greatly on the availability of new and diverse unsymme-
trical dendrimers. To explore this phenomenon further,
Scheme 3.

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S. K. Potluri et al. / Tetrahedron 60 (2004) 3739–3744
Scheme 5.
synthesis of S-(þ)-Naproxen based unsymmetrical poly-
arylester dendrimers10 was also achieved. In vitro
enzymatic hydrolysis of the ester dendrimers is under way
and the findings at this stage are somewhat provisional.
into 10% aqueous NaHCO3 solution (100 ml) and extracted
with benzene (3£200 ml). The combined extracts were
washed with distilled water, and evaporated to dryness
under reduced pressure. The crude dark brown colored
product was purified by recrystallization from 1:1 benzene/
hexane to give 2,2,2-trichloroethyl-3,5-dihydroxybenzoate
(1) (4.9 g) as a white crystalline solid. Yield: 60%; mp
70 8C. 1H NMR (CDCl3) d: 4.90 (s, 2H, CH2CCl3), 5.1 (bs,
2H, D2O exchangeable, 2£OH), 6.68 (t, 1H, J¼3 Hz, ArH),
and 7.10 (d, 2H, J¼3 Hz, ArH); MS (EI) m/z (%): 284 (Mþ,
10), 137 (100), 109 (30).
4. Experimental
4.1. General directions
All the melting points reported are uncorrected and were
1
determined using Buchi 525 instrument. H NMR and 13C
4.1.2. G1-ester dendritic wedge. To a solution of 3,5-
dibenzyloxybenzoic acid (5.64 g, 16.8 mmol), 2,2,2-tri-
chloroethyl-3,5-dihydroxybenzoate (2.0 g, 7.0 mmol) in
dry dichloromethane (25 ml) was added 4-(dimethyl-
amino)pyridinium p-toluenesulfonate (DPTS) (0.820 g,
2.7 mmol) and the mixture was stirred at room temperature
under nitrogen atmosphere for 15 min. Dicyclohexylcarbo-
diimide (DCC) (3.40 g, 7.0 mmol) was then added and
stirring continued at room temperature until the reaction had
reached completion (16 h), a precipitate of dicyclohexyl-
urea appeared during this time. The reaction mixture was
filtered, and the filtrate was evaporated to dryness under
reduced pressure. The crude product was then purified by
column chromatography. Eluting with 1:1 CHCl3/benzene
and gradually increasing the polarity to CHCl3 gave the G1-
ester (5.9 g). Yield: 92%; mp 142–146 8C. 1H NMR
NMR spectra were recorded on Varian FT 200 MHz
(Gemini) instrument, using tetramethyl silane (TMS) as
the internal standard. The chemical shifts are expressed in d
scale. The abbreviations such as s, d, t, m, and b refer to
singlet, doublet, triplet, multiplet, and broad respectively.
The trisubstituted benzene is indicated as an aryl ring and is
abbreviated as Ar and the monosubstituted benzene is
indicated as a phenyl ring and is abbreviated as Ph. Mass
spectra were recorded on VG Micromass 7070 H (EI and
CI), Autospec (FAB), and Kratos Kompact SEQ (MALDI)
instruments. Elemental analyses were recorded on a
Perkin–Elmer 240C-CHN analyzer. Completion of the
reaction and purity of the synthesised compounds were
checked by TLC performed on silica gel (acmes) plates,
using iodine and H2SO4 for visualizing the spots.
(CDCl3)
d 5.00 (s, 2H, CH2CCl3), 5.12 (s, 8H,
4.1.1. 2,2,2-Trichloroethyl-3,5-dihydroxybenzoate (1).
To freshly distilled 2,2,2-trichloroethanol (25 ml) was
added 3,5-dihydroxybenzoic acid (4.5 g, 29.2 mmol) fol-
lowed by concentrated sulphuric acid (1.0 ml), and the
mixture was stirred vigorously and heated at 90 8C for 48 h
under nitrogen. The reaction mixture was cooled, poured
4£PhCH2O), 6.85 (t, 2H, J¼3 Hz, 2£ArH), 7.30–7.45 (m,
20H, 4£PhH; 7H, 3£ArH), and 7.88 (d, 2H, J¼3 Hz, ArH);
13C NMR (CDCl3) d 70.3, 74.6, 76.3, 108.2, 109.0, 120.8,
121.4, 127.5, 128.1, 128.6, 130.5, 130.8, 136.2, 151.4,
159.9, 163.2, and 164.1; MS (FAB) m-nitrobenzyl alcohol

S. K. Potluri et al. / Tetrahedron 60 (2004) 3739–3744
3743
(matrix) m/z (%): 919 [(M)þ, 22]. Anal. Calcd for
C51H39O10Cl3: C, 66.71; H, 4.28. Found: C, 66.69; H, 4.30.
131.3, 136.5, 159.8, and 165.6; MS (MALDI) m/z (%): 1415
(Mþ, 28); 1439 [(Mþ23)þ, 100]; 1455 [(Mþ39)þ, 58].
Anal. Calcd for C90H78O16: C, 76.36; H, 5.55. Found: C,
76.27; H, 5.44.
4.1.3. G1-acid dendritic wedge. To a solution of G1-ester
(2.2 g, 2.4 mmol) in THF (15 ml) was added glacial acetic
acid (5 ml) and the solution was stirred at room temperature
under nitrogen atmosphere. Zinc dust (0.46 g, 7.2 mmol)
was added and the reaction stirred vigorously at room
temperature for 2.0 h. Then the reaction mixture was filtered
and the filtrate poured into water (50 ml) and extracted with
diethyl ether (3£50 ml). The combined extracts were
washed with water, dried over anhydrous Na2SO4 and
evaporated to dryness under reduced pressure. The crude
product was purified by column chromatography. Eluting
with CH2Cl2 and gradually increasing the polarity to 1:9
MeOH/CH2Cl2 gave G1-acid (1.52 g) as a white solid.
Yield: 81%; mp 92–95 8C. 1H NMR (acetone-D6) d 5.20 (s,
8H, 4£OCH2Ph), 7.05 (m, 2H, ArH), 7.30–7.60 (m, 20H,
4£PhH; 5H, 3£ArH), and 7.88 (d, 2H, J¼3 Hz, HAr-
COOH); MS (FAB) benzyl alcohol (matrix) m/z (%): 809
[(Mþ23)þ, 10], 786 (Mþ, 10). Anal. Calcd for C49H38O10:
C, 74.80; H, 4.87. Found: C, 74.68; H, 4.76.
4.1.6. Hexahydroxy intermediate (8). Dendrimer (4)
(0.400 g, 0.36 mmol) was dissolved in ethyl acetate (3 ml)
and Pd/C (0.100 g) was then added. The reaction mixture
was stirred in presence of H2 for 16 h. Pd–C was filtered off,
the filtrate concentrated to dryness under reduced pressure
to give 8 (0.180 g) as a white solid.
4.1.7. Octahydroxy intermediate (9). This compound was
prepared from polyarylester dendrimer (5) (0.200 g,
0.14 mmol) in ethylacetate (5 ml) and Pd/C (0.100 g) was
then added. The reaction mixture was stirred in presence of
H2 for 24 h to give 9 (0.096 g) as a white solid.
4.1.8. Second generation polyarylester dendrimer (6).
This compound was prepared from 3,5-dibenzyloxybenzoic
acid (0.507 g, 1.52 mmol), the hexahydroxy intermediate
(8) (0.100 g, 0.189 mmol), DPTS (0.090 g, 0.30 mmol) and
DCC (0.313 g, 1.52 mmol) by following the procedure as
described for 4. The reaction was carried out for 72 h and
the crude product was purified by column chromatography.
Eluting with benzene and gradually increasing the polarity
to 1:1 CHCl3/benzene gave the second generation ester
dendrimer (6) (0.250 g) as a white solid. Yield 69%; mp
58–64 8C. 1H NMR (CDCl3) d: 2.1 (b, 2H, CH2CH), 2.6 (m,
1H, CHCH2), 4.50–4.59 (m, 6H, 3£OCH2), 5.0 (s, 24H,
12£OCH2Ph), 6.75 (d, 6H, J¼2 Hz, 6£ArH), 7.35–7.50 (m:
60H, 12£PhH; 15H, 9£ArH), and 7.72–7.78 (two d, 6H,
(ArH)3core); 13C NMR (CDCl3) d 27.8, 35.1, 63.1, 65.2,
70.3, 108.2, 108.9, 120.4, 127.5, 128.0 128.5, 130.6, 131.9,
136.2, 151.2, 159.8, 164.1, and 164.6; MS (MALDI) m/z
(%): 2449 [(Mþ23)þ, 100], 2465 [(Mþ39)þ, 5]. Anal.
Calcd for C152H120O30: C, 75.24; H, 4.98. Found: C, 75.14,
H, 4.87.
4.1.4. First generation polyarylester dendrimer (4). To a
solution of 3,5-dibenzyloxybenzoic acid (3.60 g,
10.7 mmol), 2-hydroxymethyl-1,4-butanediol (2) (0.430 g,
3.6 mmol) in dry dichloromethane (25 ml) was added DPTS
(0.200 g, 0.72 mmol). The mixture was stirred at room
temperature under nitrogen atmosphere for 15 min. DCC
(2.20 g, 10.7 mmol) was then added and stirring continued
at room temperature for 16 h, during this time a precipitate
of dicyclohexylurea appeared. The reaction mixture was
filtered and the filtrate was evaporated to dryness under
reduced pressure, the crude product was then purified by
column chromatography. Eluting with 1:1 benzene/CHCl3
and gradually increasing the polarity to CHCl3 gave the first
generation ester dendrimer (4) (3.1 g) as a white solid.
Yield: 95%; mp 108 8C. 1H NMR (CDCl3) d: 2.05 (m, 2H,
CH2CH), 2.52 (m, 1H, CHCH2), 4.42–4.55 (m, 6H,
3£OCH2), 5.0 (s, 12H, 6£OCH2Ph), 6.75 (m, 3H,
3£ArH), 7.2 (d, 6H, 6£ArH), and 7.3–7.4 (m, 30H,
6£PhH). 13C NMR (CDCl3) d: 27.9 35.2, 62.7, 64.7, 70.1,
107.3, 108.3, 127.4, 128.0, 128.5, 131.6, 131.9, 136.0,
159.7, 165.9, and 165.99; MS (FAB) m-nitrobenzyl alcohol
(matrix) m/z (%): 1091 [(Mþ23)þ, 58]. Anal. Calcd for
C68H26O12: C, 78.92; H, 2.43. Found: C, 78.92; H, 2.28.
4.1.9. Second generation polyarylester dendrimer (7).
This compound was prepared from 3,5-dibenzyloxybenzoic
acid (0.481 g, 1.44 mmol), the octahydroxy intermediate (9)
(0.100 g, 0.144 mmol), DPTS(0.100 g, 0.028 mmol) and
DCC (0.296 g, 1.44 mmol) by following the procedure as
described for 4. The reaction was carried out for 72 h and
the crude product was purified by column chromatography.
Eluting with benzene and gradually increasing the polarity
to 1:1 chloroform/benzene gave the second generation
polyarylester dendrimer (7) (0.320 g) as a white solid. Yield
70%; mp 88–92 8C. 1H NMR (CDCl3) d 2.29 (b, 2H,
CH2C), 4.60–4.69 (b, 8H, 4£CH2O), 4.92 (s, 8H,
4£OCH2Ph), 4.98 (s, 24H, 12£OCH2Ph), 6.69–6.76 (m,
8H, 8£ArH), 7.30–7.42 (m, 80H, 16£PhH; 20H, 12£ArH),
and 7.70–7.75 (d, 8H, J¼2 Hz, (ArH)4 core); 13C NMR
(CDCl3) d 30.2, 41.2, 65.2, 70.3, 108.3, 109.0, 120.4, 127.5,
128.1, 128.6, 130.7, 131.6, 136.40, 151.3, 151.3, 159.9
164.0, and 164.1; MS (MALDI) m/z (%): 3248 [(Mþ23)þ,
23], 3264 [(Mþ39)þ, 06]. Anal. Calcd for C202H158O40: C,
75.22; H, 4.94. Found: C, 75.02, H, 4.82.
4.1.5. First generation polyarylester dendrimer (5). This
compound was prepared from 3,5-dibenzyloxybenzoic acid
(2.77 g, 8.3 mmol), 2,2-bis(hydroxymethyl)-1,4-butanediol
(3) (0.250 g, 1.66 mmol), DPTS (0.100 g, 0.33 mmol).and
DCC (1.70 g, 8.3 mmol) in dry dichloromethane (25 ml)
following the procedure described for 4. The reaction was
carried out for 24 h. The crude product was then purified by
column chromatography. Eluting with benzene gave the first
generation polyarylester dendrimer (5) (2.20 g) as a white
solid. Yield: 93%; mp 76–80 8C. 1H NMR (CDCl3) d: 2.15
(m, 2H, CH2C), 4.52 (s, 6H, 3£OCH2C), 4.62 (m, 2H,
OCH2CH2), 4.98 (s, 4H, 2£OCH2Ph), 5.02 (s, 12H,
6£OCH2Ph), 6.72 (t, 1H, J¼2 Hz, ArH), 6.80 (t, 3H,
J¼2 Hz 3£ArH), 7.22 (d, 8H, J¼2 Hz, 4£ArH), and 7.32–
7.45 (m, 40H, 8£PhH); 13C NMR (CDCl3) d 30.3, 41.3,
65.1, 70.1, 70.2, 107.7, 108.1, 108.3, 127.4, 128.0, 128.5,
4.1.10. Third generation polyarylester dendrimer (10).
This compound was prepared from G1-acid (1.2 g,
1.52 mmol), the hexahydroxy intermediate (8) (0.102 g,

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S. K. Potluri et al. / Tetrahedron 60 (2004) 3739–3744
0.193 mmol), DPTS (0.100 g, 0.308 mmol) and DCC
(0.318 g, 1.54 mmol) by following the procedure as
described for 4. The reaction was carried out for 72 h and
the crude product was purified by column chromatography.
Eluting with benzene and gradually increasing the polarity
to 3:7 benzene/chloroform gave the third generation ester
dendrimer (10) (0.196 g) as a white solid. Yield: 25%; mp
Acknowledgements
We are grateful to UGC-New Delhi for providing fellow-
ships to S.K.P. and A.R. We thank CSIR-New Delhi and
IICT-Hyderabad for providing the facilities to work. We
acknowledge John E. Wheeler, Dedman college, SMU,
Dallas TX.
1
94–100 8C. H NMR (CDCl3) d 2.25 (bm, 2H, CH2CH),
2.60 (bm, 1H, CHCH2), 4.55 (bm, 6H, 3£CH2O), 4.95 (bs,
48H, 24£PhCH2O), 6.70 (t, 12H, 12£PhCH2OArH), 7.20–
7.40 (m: 120H, 24£PhH; 24H 12£ArH; 6H, 6£ArH; 3H,
3£ArH), 7.75 (d, 4H, J¼2.5 Hz; 2£ester-ArH), 7.80 (d, 2H,
ester-ArH), and 7.88 (m, 12H, ester-ArH). 13C NMR
(CDCl3) d 27.7, 35.2, 63.2, 65.5, 70.2, 108.2, 108.8,
120.5, 121.0, 121.3, 127.5, 128.0, 128.5, 130.4, 130.9,
131.0, 132.1, 132.2, 136.2, 150.9, 151.3, 159.8, 162.7,
164.0, and 164.40. MS (MALDI) m/z: 5164 [(Mþ23)þ].
Anal. Calcd for C320H240O66: C, 74.76; H, 4.71. Found: C,
74.34: H, 4.57.
References and notes
¨
1. Newkome, G. R.; Moorefield, C. N.; Vogtle, F. Dendritic
molecules. Concepts, synthesis, perspectives; VCH: Wein-
heim, 1996.
2. Mathews, O. A.; Shipway, A. N.; Stoddart, J. F. Prog. Polym.
Sci. 1998, 23, 1.
3. Chow, H. F.; Mong, T. K. K.; Nongrum, M. F.; Wan, C. W.
Tetrahedron 1998, 54, 8543.
¨
4. Vogtle, F.; Fischer, M. Angew. Chem., Int. Ed. 1999, 38, 884.
4.1.11. Third generation polyarylester dendrimer (11).
This compound was prepared from G1-acid (1.13 g,
1.44 mmol), the octahydroxy intermediate (9) (0.100 g,
0.144 mmol), DPTS (0.084 g, 0.028 mmol) and DCC
(0.296 g, 1.44 mmol) by following the procedure as
described for 4. The reaction was carried out for 96 h and
the crude product was purified by column chromatography.
Eluting with benzene and gradually increasing the polarity
to 3:7 benzene/CHCl3 gave the third generation ester
dendrimer (11) (0.098 g) as a white solid. Yield: 10%; mp
92–94 8C. 1H NMR (CDCl3) d 2.30 (b, 2H, CH2C), 4.68 (b,
8H, 4£CH2O), 4.95 (s, 64H, 32£OCH2Ph), 6.72 (m, 16H,
16£ArH), 7.20–7.42 (m, 160H, 32£PhH; 32H, 16£ArH;
8H, 8£ArH; 4H, 4£ArH), 7.75 (d, 6H, J¼2 Hz; 3£ester
ArH), 7.79 (d, 2H, J¼2 Hz; ester ArH), and 7.90 (m, 16H,
8£ester ArH).13C NMR (CDCl3) d: 29.6, 41.3, 65.2, 70.2,
108.2, 108.9, 120.5, 121.0, 121.2, 127.5, 128.0, 128.5,
130.5, 131.0, 131.1, 131.6, 136.3, 151.0, 151.3, 159.8,
162.6, 164.0, and 164.2; MS (MALDI) m/z (%): 6883
[(Mþ39)þ, 100]. Anal. Calcd for C426H318O88: C, 74.74; H,
4.69. Found: C, 75.12; H, 4.11.
5. Majoral, J. P.; Caminade, A. M. Chem. Rev. 1999, 99, 845.
6. Newkome, G. R.; He, E.; Moorfield, C. N. Chem. Rev. 1999,
99, 1689.
7. Astruc, D. Acc. Chem. Res. 2000, 33, 287.
8. Padilla, D. J.; Omayra, L.; Ihre, H. R.; Gagne, L.; Frechet, J. M.
J.; Szoka, F. C. Bioconjugate Chem. 2002, 13, 453.
9. Hawker, C. J.; Frechet, J. M. J. J. Am. Chem. Soc. 1992, 114,
8405.
10. Zhai, X.; Peleshanko, S.; Klimenko, N. S.; Genson, K. L.;
Vaknin, D.; Vortman, M. Ya.; Shevchenko, V. V.; Tsukruk,
V. V. Macromolecules 2003, 36, 3101.
11. Lambrych, K. R.; Gitsov, I. Macromolecules 2003, 36, 1068.
12. Gillies, E. R.; Frechet, J. M. J. J. Am. Chem. Soc. 2002, 124,
14137.
13. Nithyanandhan, J.; Jayaraman, N. J. Org. Chem. 2002, 67,
6282.
14. Potluri, S. K. PhD Thesis, Chemistry Departmrnt Osmania
University, Hyderabad, India, 2000.
15. Raghu Ramulu, A. PhD Thesis, Chemistry Department
Osmania University, Hyderabad, India, 2000.