Synthesis of Poly(propyl ether imine) Dendrimers and Evaluation of Their Cytotoxic Properties

Article abstract of DOI:10.1021/jo035072y

In this paper, we report the synthesis of several poly(propyl ether imine) dendrons and dendrimers. These dendrons and dendrimers were constructed by involving an ether as the linker component and an imine as the branching component. The divergent syntheses of dendrons and dendrimers were established with the aid of two alternate Michael addition reactions and two alternate reduction reactions in a four-step iterative synthetic sequence. Dendrons up to three generations were synthesized and some of the dendrons were attached to a benzenoid core so as to obtain dendrimers up to two generations containing 12 carboxylic acids at the periphery. Divergent synthesis involving ether as the core was found to be more facile, and dendrimers up to three generations having 16 carboxylic acids at the periphery were achieved in good to excellent yields in each individual step. The adopted synthetic sequence allows us to install either alcohol, an amine, or a carboxylic acid at their peripheries. The carboxylic acid-terminated dendrons and dendrimers were evaluated as to their cytotoxic properties, and while most dendrons and dendrimers did not exhibit any measurable cytotoxicity, even up to 100/μg/mL, the second-generation dendrimer with the benzenoid core exhibited a mild toxicity at concentrations above 30/μg/mL.

Full text of DOI:10.1021/jo035072y

Syn th esis of P oly(p r op yl eth er im in e) Den d r im er s a n d Eva lu a tion
of Th eir Cytotoxic P r op er ties
Thatavarathy Rama Krishna and Narayanaswamy J ayaraman*
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
jayaraman@orgchem.iisc.ernet.in
Received J uly 24, 2003
In this paper, we report the synthesis of several poly(propyl ether imine) dendrons and dendrimers.
These dendrons and dendrimers were constructed by involving an ether as the linker component
and an imine as the branching component. The divergent syntheses of dendrons and dendrimers
were established with the aid of two alternate Michael addition reactions and two alternate reduction
reactions in a four-step iterative synthetic sequence. Dendrons up to three generations were
synthesized and some of the dendrons were attached to a benzenoid core so as to obtain dendrimers
up to two generations containing 12 carboxylic acids at the periphery. Divergent synthesis involving
ether as the core was found to be more facile, and dendrimers up to three generations having 16
carboxylic acids at the periphery were achieved in good to excellent yields in each individual step.
The adopted synthetic sequence allows us to install either alcohol, an amine, or a carboxylic acid
at their peripheries. The carboxylic acid-terminated dendrons and dendrimers were evaluated as
to their cytotoxic properties, and while most dendrons and dendrimers did not exhibit any
measurable cytotoxicity, even up to 100 µg/mL, the second-generation dendrimer with the benzenoid
core exhibited a mild toxicity at concentrations above 30 µg/mL.
In tr od u ction
principle of dendritic architecture remains the most
attractive.3 Although large varieties of dendrimers are
reported, only a few represent most of the studies that
have been carried out so far. Primary among them are
poly(amido amine),1b poly(propylene imine),1a,4 poly(ben-
zylaryl ether),5 polysilane,6 and polyphosphine7 dendrim-
ers. Despite the synthesis of these and a number of other
dendrimers,8 identification of new monomers and syn-
theses of new dendrimers are a continuously evolving
interest. A fundamental requirement in the synthesis of
The highly branched, symmetrical, and monodispersed
macromolecules called “dendrimers”1 occupy a consider-
able interest among synthetic chemists in the last two
decades. The uniform branching, large number of pe-
ripheral functionalities, molecular weights of several
kilodaltons, and a globular spherical shape with defined
inner cavities are some of the features of dendrimers,
upon which a large body of investigations is being carried
out at present.2 Numerous dendrimers were synthesized
with an aim to explore their functional properties result-
ing from the unique structural features of dendrimers.
In this context, both endo and exo receptor properties of
dendrimers have been investigated to identify the so-
called “dendritic effect” in chemical, biological, and
materials related studies, establishing the fact that the
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10.1021/jo035072y CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/19/2003
9694
J . Org. Chem. 2003, 68, 9694-9704

Poly(propyl ether imine) Dendrimers
F IGURE 1. Reaction sequence adopted to synthesize poly(propyl ether imine) dendrons and dendrimers.
SCHEME 1 a
a dendrimer is the identification of a suitable monomer,
possessing desirable functionalities that are amenable for
synthetic manipulations. In this respect, a variety of
functionalities have been used to construct dendrimers.
The most commonly used linker functionalities are
amide,1b,c ether,2e,5 ester,9 urethane,10 phosphorus,7 and
silane,6 and the branch junctures are those derived from
amine,1a,4 benzyl,5 phosphorus,7 quarternary carbon,1c
silane,6 and metal ions.11 Noncovalent bonding has also
been explored as branch junctures.8d While tertiary
amine as the branch juncture and the amide as the linker
component or the tertiary amine alone as the branch
juncture constitute the most widely used PAMAM1b and
poly(propylenimine)1a,4 dendrimers, respectively, we de-
sired to explore the synthesis of dendrimers in which the
branch juncture is a tertiary amine and the linker
component is an ether. We report herein the synthesis
of these new types of dendrons and dendrimers in which
3-amino-1-propanol forms the constituent part of the
repeating unit. This monomer unit was chosen so as to
offer a tertiary amine as the branch juncture and an
ether as a linking component. Apart from synthesis and
characterization, we describe evaluation of cytotoxicity
properties relevant to their applicability in biological
studies.
a
Reagents and conditions: (i) cat. NaOH, 6 h, rt; (ii) CoCl2,
NaBH4, MeOH, -78 °C to room temperature; (iii) tert-butyl
acrylate, MeOH, 6 h; (iv) 10% Pd/C, 5 days; (v) LAH, THF, 0 °C.
tion and alkylation of free hydroxyl groups, which often
led to quaternization of the amine and cyclization to form
three-membered aziridine derivatives and six-membered
morpholine derivatives, had prevented effective use of
this monomer to construct the dendrons and dendrimers.
We realized that replacement of the ethyl linker with a
propyl linker would overcome some of the difficulties such
as the cyclization and quaternization. On the basis of the
above preliminary experiments with triethanolamine,
3-aminopropan-1-ol was chosen as the monomer and a
divergent synthetic methodology was found to be most
appropriate to prepare the dendrons and dendrimers. The
reaction sequence was divided into four major iterative
reactions, namely, (i) Michael addition of acrylonitrile to
alcohol; (ii) reduction of the nitrile to amine; (iii) double
Michael addition of amine with tert-butyl acrylate; and
(iv) reduction of the resulting ester to alcohol (Figure 1).
Syn th esis of Den d r on s. In the initial stages of
synthesis, the hydroxyl group, in the O-benzyl-protected
form, served as the focal point functionality. Thus,
reaction of BnOH with acrylonitrile, in the presence of a
catalytic amount of aqueous NaOH (40%) at room tem-
perature, afforded O-benzyl-2-cyano ethanol (1) in nearly
quantitative yield (Scheme 1). The reduction of nitrile 1
with NaBH4/CoCl2 in MeOH, followed by treatment of
the resulting amine with excess tert-butyl acrylate,
afforded the bis(tert-butyl acrylate) (2) in good yields.
Reduction of 2 was performed in the presence of LAH at
0 °C to afford bis-alcohol 3 in nearly quantitative yield
without necessitating column chromatographic purifica-
tion.
Resu lts a n d Discu ssion
The early generation dendrons and dendrimers de-
scribed herein are composed of tertiary amine as the
branch juncture with ether as the linker functionality.
To have such a constitution of dendrimers, we had
attempted initially to utilize triethanolamine as the
monomer. However, difficulties encountered in protecting
one or more of the hydroxyl groups and selective activa-
(8) Many new monomers and synthesis of dendrimers have been
covered in: (a) Seebach, D.; Rheiner, P. B.; Greiveldinger, G.; Butz,
T.; Sellner, H. Top. Curr. Chem. 1998, 197, 125. (b) Astruc, D., Blais,
J .-C., Cloutet, L. Djakovitch, L.; Rigaut, S.; Ruiz, J .; Sartor, V.; Vale´rio,
C. Top. Curr. Chem. 2000, 210, 229. (c) Chow, H.-F.; Leung, C.-F.;
Wang, G, -X.; Zhang, J . Top. Curr. Chem. 2002, 217, 1. (d) Zimmerman,
S. C.; Zeng, F.; Reichert, D. E. C.; Kolotuchin, S. V. Science 1996, 271,
1095. (e) J ayaraman, M.; Fre´chet, J . M. J . J . Am. Chem. Soc. 1998,
120, 12996. (f) Nithyanandhan, J .; J ayaraman, N. J . Org. Chem. 2002,
67, 6282.
(9) (a) Hawker, C. J .; Fre´chet, J . M. J . J . Am. Chem. Soc. 1992, 114,
8405. (b) Twyman, L. J .; Beezer A. E.; Mitchell J . C. J . Chem. Soc.,
Perkin Trans. 1 1994, 407.
(10) Taylor, R. T.; Puapaiboon, U. Tetrahedron Lett. 1998, 39, 8005.
(11) (a) Newkome, G. R.; Cardullo, F.; Constable, E. C.; Moorefield,
C. N.; Cargill, T. A. M. W. J . Chem. Soc., Chem. Commun. 1993, 925.
(b) Campagna, S.; Denti, G.; Serroni, S.; J uris, A.; Venturi, M.;
Ricevuto, V.; Balzani, V. Chem. Eur. J . 1995, 1, 211. (c) Achar, S.;
Puddephatt, R. J . Organometallics 1995, 14, 1681. (d) Cuadrado, I.;
Casado, C. M.; Alonso, B.; Mora´n, M.; Losada, J .; Belsky, V. J . Am.
Chem. Soc. 1997, 119, 7613. (e) Wang, R.; Zheng, Z. J . Am. Chem. Soc.
1999, 121, 3549. (f) Constable, E. C.; Eich, O.; Housecroft, C. E.;
J ohnston, L. A. Chem. Commun. 1998, 2661. (g) Gorman, C. B.;
Parkhurst, B. L. J . Am. Chem. Soc. 1997, 117, 1141. (h) Oosterom, G.
E.; van Haaren, R. J .; Reek, J . N. H.; Kamer, P. C. J .; van Leeuwen,
P. W. N. M. Chem. Commun. 1999, 1119. (i) Cardona, C. M.; Kaifer,
A. E. J . Am. Chem. Soc. 1998, 120, 4023. (j) Rama Krishna, T.;
J ayaraman, N. J . Chem. Soc., Perkin Trans. 1 2002, 746.
In an iterative reaction sequence, bis-alcohol 3 was
subjected to Michael addition with acrylonitrile to afford
5 in nearly quantitative yields (Scheme 2).
It was noticed that vigorous stirring of 3 was required
during the reaction, so as to allow quantitative O-
J . Org. Chem, Vol. 68, No. 25, 2003 9695

Krishna and J ayaraman
SCHEME 2 a
SCHEME 4 a
a
Reagents and conditions: (i) cat. NaOH, 6 h, rt; (ii) CoCl2,
NaBH4, MeOH, -78 °C to room temperature; (iii) tert-butyl
acrylate, MeOH, 6 h; (iv) 10% Pd/C, 5 days.
SCHEME 3 a
a
Reagents and conditions: (i) Raney Co, MeOH/H2O, H2, 40
atm, 70 °C; (ii) tert-butyl acrylate, MeOH, 6 h; (iii) LAH, THF, 0
°C; (iv) cat. NaOH, 15 h, rt; (v) AcCl, H2O, CH2Cl2, 8 h; (vi) CAN,
MeCN-H2O, 15 min.
a
group for the hydroxyl group functionality at the focal
point of dendrons. p-Anisyl protecting was chosen for this
purpose, owing to its stability under strongly acidic, basic,
oxidative, and reductive conditions, yet it can be depro-
tected under mild conditions (CAN, MeCN-H2O).12 3-Ami-
nopropan-1-ol was chosen as the starting material for the
construction of dendrons, which upon exhaustive Michael
addition with tert-butyl acrylate provided bis(tert-butyl
acrylate) (4) in 98% yield (Scheme 3).
Reagents and conditions: (i) tert-butyl acrylate, MeOH, 6 h;
(ii) DIAD, PPh3, p-MeOC6H4OH, THF, 15 min, 80 °C; (iii) LAH,
THF, 0 °C; (iv) cat. NaOH, 15 h, rt; (v) AcCl, H2O, CH2Cl2, 8 h.
alkylation. Reduction of two nitrile groups in 5 (CoCl2,
NaBH4, -78 °C to room temperature) and subsequent
double Michael reaction of the resulting diamine with
tert-butyl acrylate afforded the desired tetrakis(tert-butyl
ester) (6) in an overall moderate yield of 54% for two
steps.
The free hydroxyl group was protected at this stage
by reaction of 4 with p-methoxyphenol, under Mitsunobu
conditions (DIAD, PPh3, THF), to afford 8 (91%). Reduc-
tion of the ester in 8 was conducted adding LAH to the
corresponding bis-alcohol 10 in a nearly quantitative
yield. Michael addition with acrylonitrile to bis-alcohol
10 was accomplished in the presence of a catalytic
amount of aqueous NaOH (40%) to obtain bis-nitrile 11
in 90% yield. Reduction of the nitrile groups in 11 was
An alternate approach was also explored to synthesize
the above dendrons, on account of lower yields encoun-
tered during reduction of multiple nitrile groups to the
corresponding amines by using a CoCl2/NaBH4 reagent
system, while retaining the benzyl protecting group intact
at the focal point of the dendrons. Because of the
requirement that efficient reactions are essential for the
generation of dendrimers, we desired to use Raney Co
catalyst for the reduction of nitrile groups of dendrons,
as adopted by Meijer and de Brabender van den Berg in
their synthesis of poly(propylenimine) dendrimers.4b Use
of this catalyst in turn required an alternate protecting
(12) Fukuyama, T.; Laird, A. A.; Hotchkiss, L. M. Tetrahedron Lett.
1985, 51, 6291.
9696 J . Org. Chem., Vol. 68, No. 25, 2003

Poly(propyl ether imine) Dendrimers
SCHEME 5 a
a
Reagents and conditions: (i) Raney Co, MeOH/H2O, H2, 40 atm, 70 °C; (ii) tert-butyl acrylate, MeOH, 6 h; (iii) AcCl, H2O, CH2Cl2, 8 h.
SCHEME 6 a
carried out effectively with the use of Raney Co and H2
(40 atm) in water at 70 °C, and the resulting amine was
subjected to exhaustive Michael addition to obtain four
tert-butyl ester group terminated dendron 12 with an
overall yield of 89% for two steps (Scheme 4).
The modified route involving the use of Raney Co as
the reducing agent of nitrile groups has improved greatly
the dendron synthesis with excellent yields at each
individual step. Further growth of second- and third-
generation dendrons was accomplished by repetition of
the sequence: (i) reduction of 12 to alcohol 14 (LAH,
THF, 97%); (ii) Michael addition of 14 with acrylonitrile
to afford 15 (aqueous NaOH (40%), 92%); (iii) reduction
of 15 to amine (Raney Co, MeOH-H2O); followed by (iv)
Michael addition of the resulting amine with tert-butyl
acrylate (MeOH, 83% for two steps) to afford octavalent
tert-butyl acrylate 16 (Scheme 5).
Syn th esis of Den d r im er s. Upon synthesis of den-
drons, their attachment to a chosen core was carried out.
The first- (4) and second- (7) generation dendrons were
thus coupled with 1,3,5-benzenetricarbonyl chloride in
the presence of DMAP to afford the first- (18) and second-
a
Reagents and conditions: (i) DMAP, PhMe, 6 h reflux; (ii)
(20) generation dendrimers (Schemes 6 and 7), respec-
tively. tert-Butyl ester protecting groups at the peripher-
ies of these dendrimers were deprotected (AcCl, H2O) to
afford the free carboxylic acid-containing dendrimers 19
and 21, respectively.
AcCl, H2O, CH2Cl2, 8 h.
The required starting material bis-nitrile 22 was obtained
from acrylonitrile and aqueous NaOH (40%) (Scheme 8).
The reaction was facile and could be accomplished in
multigram quantities in quantitative yields. Bis-nitrile
22 was subjected to sequential reactions: (i) reduction
of nitrile in the presence of Raney Co catalyst; (ii) tert-
butyl acrylate addition to afford first-generation tetrakis-
(tert-butyl acrylate) (23); (iii) reduction of peripheral tert-
butyl acrylate with LAH to alcohol 25; and (iv) conversion
of 25 to tetrakis-nitrile 26 by reaction with acrylonitrile.
This synthetic sequence was repeated with nitrile 26 to
afford, respectively, the second-generation octakis(tert-
butyl acrylate) (27), octakis-alcohol (29), and octakis-
With the difficulty that we were unable to remove the
benzyl group at the focal point of dendrons 2 and 6
effectively, presumably due to catalyst poisoning in the
presence of several tertiary amine groups, and also with
the difficulty of removing the p-anisyl group in the
anticipated manner in the higher generation dendron 16,
we focused on synthesis of 3-aminopropan-1-ol-based
dendrimers by adopting a divergent growth methodology.
In principle, the same synthetic sequence was required
as we had followed previously for the dendron synthesis.
J . Org. Chem, Vol. 68, No. 25, 2003 9697

Krishna and J ayaraman
SCHEME 7 a
a
Reagents and conditions: (i) DMAP, PhMe, 6 h reflux; (ii) AcCl, H2O, CH2Cl2, 8 h.
SCHEME 8 a
resulting octakis-amine to afford the third-generation
dendrimer 31 with 16 peripheral tert-butyl ester groups
in excellent yield (Scheme 10). In summary, this sequence
of reactions could be conducted in excellent yields,
characterizing the facile nature of the reactions involved
in the syntheses of dendrimers.
Ch a r a cter iza tion . All the dendrons and dendrimers
were characterized by routine physical methods. Since
the synthetic sequence involved changes in the functional
group at their peripheries, monitoring the progress of
reaction was easy by using IR spectroscopy. Thus, forma-
tion of nitrile (ν 2251), reduction of nitrile to amine (ν
3460), formation of tert-butyl ester (ν 1727), and conver-
sion of the ester to the corresponding alcohol (ν 3390)
could be followed rather comprehensively by IR spectros-
copy for all the dendrons and dendrimers. Characteristics
1
of H NMR spectra were the changes of chemical shifts
of the -CH2- groups at the peripheries, depending on
the functional group present. Thus, disappearance of the
triplet at ∼2.60 ppm of the CH2CN group and appearance
of resonances at ∼1.70 and ∼2.50 ppm, corresponding to
CH2CH2N, were distinct for this nitrile reduction. Like-
wise, disappearance of the resonance at 2.30 ppm of
t
CH2-CO2 Bu and appearance of resonances at ∼1.70 and
∼3.70 ppm of CH2CH2OH could be used comfortably to
monitor the progress of the extent of functional group
conversion and the growth of the dendrons and dendrim-
ers. While the resonances were sharp and distinct for
modifications at the peripheries, the internal CH2 protons
became broader progressively as the generations ad-
vanced, indicating the changing morphologies of the
dendritic architecture.
a
Reagents and conditions: (i) cat. NaOH, 15 h, rt; (ii) Raney
Co, MeOH/H2O, H2, 40 atm, 70 °C; (iii) tert-butyl acrylate, MeOH,
6 h; (iv) LAH, THF, 0 °C; (v) AcCl, H2O, CH2Cl2, 6 h.
nitrile (30) (Scheme 9). Higher generation dendrimer 31
was synthesized, starting from nitrile 30, by performing
reduction of the nitrile groups using Raney Co catalyst,
followed by addition with tert-butyl acrylate to the
9698 J . Org. Chem., Vol. 68, No. 25, 2003

Poly(propyl ether imine) Dendrimers
SCHEME 9 a
a
Reagents and conditions: (i) cat. NaOH, 15 h, rt; (ii) Raney Co, MeOH, H2O, 70 °C, 40 atm; (iii) tert-butyl acrylate, MeOH, 6 h; (iv)
LAH, THF, 0 °C; (v) AcCl, H2O, CH2Cl2, 8 h.
Similar changes in 13C NMR chemical shifts could also
be used to monitor the conversions of functional groups
at the peripheries of dendrons and dendrimers. Thus,
disappearance of the resonance due to the nitrile group
at ∼117 ppm and appearances of the carbonyl resonance
of the ester group at ∼172 ppm and of the CH2OH group
resonance at 62 ppm resulting from the reduction of the
ester group could be observed distinctly, thereby confirm-
ing the required changes in the functionalities as the
generations of dendrons and dendrimers grew. The
constitution of the dendrons and dendrimers was further
ascertained by mass spectrometric analysis. The calcu-
lated molecular ion peak, including in the form of Na and
K adducts, could be obtained as the most intense peak
in almost all the compounds (Figure 2). For smaller
molecular weight dendrons and dendrimers (molecular
weight < 1000 g/mol), high-resolution ES-MS analysis
was performed, and the error between the observed mass
position and the calculated mass position was often less
than 5 ppm. The ES-MS behavior of carboxylic acid-
terminated dendrons and dendrimers was different in
each case, except in those containing a phenyl group,
wherein molecular ion peaks were either Na or K
adducts. In the case of dendrimer 24, the mass spectrum
showed the molecular ion peak along with a few more
peaks corresponding to the addition of 14 molecular mass
units. Whereas in the case of dendrimers 28 and 32, with
free carboxylic acids, it was difficult to analyze by ES-
MS analysis; only a cluster of peaks of much lesser
molecular weights could be seen. Also, elemental analysis
could not be obtained reliably due to the hygroscopic
nature of these dendrons and dendrimers.
Eva lu a tion of th e Cytotoxic P r op er ties of Den -
d r on s a n d Den d r im er s. Dendrons and dendrimers
synthesized herein have molecular features correspond-
ing to polyimines and polyethers, both of which have been
studied in detail for their biological applications.13,14 On
the basis of the properties of the constituent imine and
ether linkages, we tested the cytotoxic properties of some
(13) (a) Ferruti, P.; Knobloch, S.; Ranucci, E.; Duncan, R.; Gianasi.
Macromol. Chem. Phys. 1998, 199, 2565. (b) Wroblewski, S.; Ko-
peckova, J . Macromol. Chem. Phys. 1998, 199, 2601.
J . Org. Chem, Vol. 68, No. 25, 2003 9699

Krishna and J ayaraman
SCHEME 10 a
a
Reagents and conditions: (i) Raney Co, MeOH, H2O, 70 °C, 700 psi; (ii) tert-butyl acrylate, MeOH, 6 h; (iii) AcCl, H2O, CH2Cl2, 6 h.
F IGUR E 2. Low-resolution ES-MS of the third-generation
dendrimer 31.
of the dendrons and dendrimers as a means to evaluate
F IGURE 3. In vitro cytotoxicity studies on the mammalian
their acceptance in the biological studies.15 The cytotox-
CHO cell line (13, 17, 19, 21, and 24) and breast cancer T47D
cell line (28 and 32), at various concentrations of dendrons
and dendrimers.
icity studies were performed using a tetrazolium-based
MTT colorimetric assay. This assay relies on quantitation
of cells surviving after treatment of the live cells by
testing their enzymatic dehydrogenase activity.16 The
assessment of enzymatic activity is based on changes of
the water-soluble tetrazolium salt to a purple, insoluble
formazan derivative, and this change can be monitored
by UV-vis spectroscopy. Either a Chinese hamster
ovarian cell line or breast cancer T47D cell line was used
for testing the cytotoxic properties of a few carboxylic
acid-terminated dendrons and dendrimers. Cells were
incubated for 24 h with increasing concentration of
dendrons and dendrimers in the presence of bovine
serum. The relative cell viability in the presence of
dendrons and dendrimers at different concentrations is
presented in Figure 3. The cell survival rate was more
than 90% in the case of 13, 17, 19, 24, 28, and 32, and
the rate had reduced slightly to 80% in the case of the
second-generation dendrimer 21, for concentrations up
to 100 µg/mL of the solutions. It is clear from this assay
that while no measurable cytotoxicity is observed for 13,
17, 19, 24, 28, and 32, a mild toxicity at concentrations
above 30 µg/mL is shown by 21. The observation that the
dendrons and dendrimers tested herein allow cell sur-
(14) (a) Boussif, O.; Lezoualch, F.; Zanta, M. A.; Mergny, M. D.;
Scherman, D.; Demeneix, B.; Behr, J . P. Proc. Natl. Acad. Sci. U.S.A.
1995, 92, 7297. (b) Elizabeth R. G.; Fre´chet, J . M. J . J . Am. Chem.
Soc. 2002, 124, 14137. (c) Choi, J . S.; J oo, D. K.; Kim, C. H.; Kim, K.;
Park, J . S. J . Am. Chem. Soc. 2000, 122, 474.
(15) For toxicity studies of amine and carboxylic acid terminated
dendrimers, see: Malik, R.; Wiwattanapatapee, R.; Klopsch, R.;
Lorentz, K.; Frey, H.; Weener, J . W.; Meijer, E. W.; Paulus, W.; Duncan,
R. J . Controlled Release 2000, 65, 133.
(16) Mosmann, T. J . Immun. Methods 1983, 65, 55.
(17) For an alternate synthesis of 22, see: Masasane, I.; Kanemitsu,
M.; Akira, I.; Yamauchi, A. J pn. Kokai Tokkyo Koho 1989, 4 (Chem.
Abstr. 1989, 111, 133654y).
9700 J . Org. Chem., Vol. 68, No. 25, 2003

Poly(propyl ether imine) Dendrimers
MeOH was transferred to a hydrogenation reactor vessel and
was admixed with Raney Co catalyst in H2O (40 mL). The
mixture was hydrogenated (H2, 40 atm) at 70 °C for 1 h, cooled,
and decanted, and the solvents were evaporated off to afford
amine as a colorless oil. A solution of the resulting crude amine
in MeOH (5 mL) was treated with tert-butyl acrylate and
stirred for 6 h. Excess tert-butyl acrylate and solvents were
removed in vacuo, and the resulting product was purified
(alumina).
Gen er a l P r oced u r e for th e Atta ch m en t of Den d r on to
th e Tr im esityl Ch lor id e Cor e (VI). A two-necked flask,
fitted with a Dean Stark trap and a condenser, was charged
with dendron and DMAP in PhMe (20 mL), refluxed for 2 h,
then cooled to room temperature. 1,3,5-Benzenetricarbonyl
trichloride was added to the reaction mixture and refluxed for
4 h, and the solvents were removed in vacuo. The product was
purified to afford dendrimer as a colorless liquid.
vival ability of more than 80% indicates that these
compounds are significantly less toxic, are biocompatible,
and thus are suitable for in vitro biological studies.
Con clu sion
We have established a four-step iterative protocol to
synthesize poly(propyl ether imine) dendrons and den-
drimers. The yields of individual reactions are excellent
often, indicating the facile N- and O-alkylations, as well
as the reduction reactions. The facile conversions also
allow us to have either a carboxylic acid, an alcohol, or
an amine easily at their peripheries. In addition, their
molecular features, having the ether and imine function-
alities, are common, as in the case of several polyethers
and polyimines, and thus are likely to have similar
properties for further chemical and other interfacial
studies. Evaluation of the extent of cytotoxicities dem-
onstrates that the toxicity levels of the dendrons and
dendrimers are either nearly none or very mild. These
experiments point to the possibility of incorporation of
these poly(propyl ether imine) dendrons and dendrimers
in biological and related studies as well.
Com p ou n d 1. Acrylonitrile (5.83 g, 0.11 mol) was added
to a mixture of BnOH (10.8 g, 0.1 mol) and aqueous NaOH
(40%) (1 mL), and the mixture was stirred for 6 h and worked
up as described in the general procedure I to obtain 1 as a
colorless liquid (15.9 g, 99%). FT-IR (neat) ν: 2251, 1455, 1363,
1
1104. EI-MS m/z: 161 [M]+. H NMR (CDCl3) δ: 2.62 (t, 2 H,
J ) 6.9 Hz), 3.68 (t, 2 H, J ) 6.9 Hz), 4.58 (s, 2 H), 7.28-7.39
(m, 5 H). 13C NMR (CDCl3) δ: 18.8, 64.5, 73.3, 117.8, 127.7,
128.0, 128.6, 137.2.
Exp er im en ta l Section
Com p ou n d 2. A solution of 1 (1.61 g, 10 mmol) in MeOH
(80 mL) was treated with CoCl2‚6H2O (2.38 g, 10 mmol) and
NaBH4 (7.56 g, 0.2 mol), and the reaction continued as
described in the general procedure II. The amine (1.5 g),
resulting from this reaction, was then treated with tert-butyl
acrylate (3.83 g, 30 mmol) and processed further as described
in the general procedure II to afford, after purification (hexane/
EtOAc, 90:10), 2 as a colorless liquid (2.95 g, 70%). FT-IR (neat)
ν: 1726, 1455, 1367, 1151. EI-MS m/z: 422 [M]+. 1H NMR
(CDCl3) δ: 1.44 (s, 18 H), 1.74 (m, 2 H), 2.35 (t, 4 H, J ) 7.2
Hz), 2.50 (t, 2 H, J ) 6.3 Hz), 2.71 (t, 4 H, J ) 7.2 Hz), 3.50 (t,
2 H, J ) 6.3 Hz), 4.49 (s, 2 H), 7.29-7.34 (m, 5 H). 13C NMR
(CDCl3) δ: 27.7, 28.1, 33.8, 49.4, 50.4, 68.5, 72.9, 80.2, 127.5,
127.6, 128.3, 138.6, 172.1. HRMS m/z: calcd for C24H39O5N
422.2906, found 422.2912.
Gen er a l P r oced u r e for Mich a el Ad d ition of Acr ylon i-
tr ile (I). Acrylonitrile was added to a mixture of alcohol and
aqueous NaOH (40%) while maintaining the temperature
below 30 °C. The reaction mixture was stirred for 6 h at room
temperature, neutralized with aqueous HCL (1 N), and diluted
with CHCl3. The organic layer was washed with 5% aqueous
NaOH followed by brine, evaporated in vacuo, and dried
thoroughly to afford the desired compound.
Gen er a l P r oced u r e for th e Red u ction of Nitr ile Usin g
Na BH4/CoCl2 a n d Mich a el Ad d ition of Resu ltin g Am in es
(II). To a solution of the nitrile compound in MeOH was added
CoCl2‚6H2O followed by addition of NaBH4 in portions at -78
°C (violent gas evolution occurred during addition). The
reaction mixture was gradually brought to room temperature,
stirred for an additional 2 h, and acidified cautiously with
concentrated HCl, and the solvents were removed in vacuo.
The resulting residue was treated with aqueous NH3 solution
(30%) to give a deep-blue solid residue, and the residue was
extracted with CHCl3. The organic extracts were dried and
concentrated to give a crude yellow-colored oil product. A
solution of this crude product in MeOH was added with tert-
butyl acrylate, and the reaction mixture was stirred for 6 h at
room temperature. Excess of tert-butyl acrylate was then
removed in vacuo, and the resulting product was purified by
column chromatography (SiO2).
Gen er a l P r oced u r e for Red u ction of ter t-Bu tyl Ester s
(III). To a suspension of LAH in THF at 0 °C was added
dropwise the ester in THF for ∼30 min. The suspension was
stirred at 0 °C for 30 min and brought to room temperature,
and stirring continued for an additional 1 h. The reaction
mixture was cooled to 0 °C and quenched with ice (∼1 g), solid
Na2SO4 was added, and the mixture was left until LAH was
quenched and the gray residue became a free white suspension
and settled. The suspension was passed through a plug of
Celite, and the filtrate was dried and concentrated to obtain
alcohol as a colorless liquid.
Gen er a l P r oced u r e for Hyd r olysis of ter t-Bu tyl Ester s
(IV). To a solution of the ester in CH2Cl2 were added slowly
AcCl and H2O, and the solution was stirred at room temper-
ature for 8 h. Solvents were removed in vacuo, and the
resulting residue was triturated several times with hexane and
CH2Cl2 to afford the desired acid as a white, foamy solid.
Gen er a l P r oced u r e for Red u ction of Nitr ile Usin g
Ra n ey Coba lt Ca ta lyst a n d Su bsequ en t Mich a el Ad d i-
tion of Resu ltin g Am in es (V). The nitrile derivative in
Com p ou n d 3. To a suspension of LAH (0.10 g, 2.3 mmol)
in THF at 0 °C was added dropwise 2 (0.4 g, 0.95 mmol) in
THF (10 mL), and the reaction continued further as described
in the general procedure III to obtain 3 as a colorless liquid
(0.26 g, 97%). FT-IR (neat) ν: 3390, 1455, 1365, 1069. EI-MS
1
m/z: 282 [M]+. H NMR (CDCl3) δ: 1.72 (q, 4 H, J ) 6.6, 6.9
Hz), 1.81 (q, 2 H, J ) 6.6, 6.9 Hz), 2.53 (t, 2 H, J ) 6.9 Hz),
2.62 (t, 4 H, J ) 6.3 Hz), 3.51 (t, 2 H, J ) 6.6 Hz), 3.72 (t, 4 H,
J ) 6.0 Hz) 4.50 (s, 2 H), 7.27-7.37 (m, 5 H). 13C NMR (CDCl3)
δ: 26.9, 28.5, 51.0, 52.7, 62.5, 68.4, 73.0, 127.6, 127.7, 128.4,
138.3. HRMS m/z: calcd for
C16H27O3N 282.2089, found
282.2074.
Com p ou n d 4. A mixture of 3-aminopropan-1-ol (4.91 g, 65.4
mmol) and tert-butyl acrylate (21.87 g, 171.0 mmol) in MeOH
(25 mL) was stirred at room temperature for 6 h. Excess tert-
butyl acrylate and solvents were removed in vacuo, the crude
product was diluted with CHCl3 and washed with brine, and
the organic portion was dried and concentrated to afford 4 as
a
colorless viscous liquid (21.3 g, 98%). Alternatively, a
suspension of 2 (1.0 g, 2.37 mmol) and Pd/C (10%, 0.1 g) in
EtOAc (25 mL) was attached with a H2 gas-filled balloon and
stirred for 5 days at room temperature. The suspension was
filtered and washed, and the filtrate was concentrated and
purified to afford 4 (0.2 g, 84.8% after recovery of 0.7 g of
starting material). FT-IR (neat) ν: 3429, 1729, 1459, 1368,
1158. EI-MS m/z: 331 [M]+. 1H NMR (CDCl3) δ: 1.42 (s, 18
H), 1.66 (q, 2 H, J ) 6.0 Hz), 2.37 (t, 4 H, J ) 7.2 Hz), 2.60 (t,
2 H, J ) 6.0 Hz), 2.72 (t, 4 H, J ) 7.2 Hz), 3.71 (t, 2 H, J ) 6.0
Hz). 13C NMR (CDCl3) δ: 28.1, 28.4, 33.3, 49.4, 53.0, 63.2, 80.7,
171.7. HRMS m/z: calcd for
C17H33O5N 332.2437, found
332.2440.
J . Org. Chem, Vol. 68, No. 25, 2003 9701

Krishna and J ayaraman
Com p ou n d 5. Acrylonitrile (0.60 mg, 11.0 mmol) was added
to a mixture of 3 (1.30 g, 4.70 mmol) and aqueous NaOH (40%)
(0.50 mL), and the mixture was stirred for 6 h and worked up
as described in the general procedure I to afford 5 as a colorless
liquid (1.8 g, 98%). FT-IR (neat) ν: 2251, 1456, 1365, 1114.
EI-MS m/z: 387 [M]+. 1H NMR (CDCl3) δ: 1.72 (m, 6 H), 2.48
(t, 2 H, J ) 6.3 Hz), 2.57 (t, 4 H, J ) 6.6 Hz), 2.65 (t, 4 H, J
) 6.0 Hz), 3.50 (t, 4 H, J ) 6.0 Hz), 3.61 (t, 2 H, J ) 6.3 Hz),
3.57 (t, 4 H, J ) 6.6 Hz) 4.49 (s, 2 H), 7.27-7.39 (m, 5 H). 13C
NMR (CDCl3) δ: 18.9, 27.4, 27.5, 50.5, 50.8, 65.3, 65.9, 68.6,
72.9, 117.4, 127.5, 127.6, 128.4, 138.5. HRMS m/z: calcd for
3.78 (s, 3 H), 4.03 (b, 2 H), 6.83 (s, 4 H). 13C NMR (CDCl3 +
DMSO-d6) δ: 28.5, 48.5, 49.6, 50.6, 55.4, 65.1, 114.5, 115.3,
152.1,153.9, 171.3.
Com p ou n d 10. A solution of 8 (0.96 g, 2.2 mmol) in THF
(25 mL) was added dropwise to a suspension of LAH (0.20 g,
5.28 mmol) in THF (10 mL), and the reaction was continued
further as described in the general procedure III to obtain 10
as a colorless liquid (0.65 g, 99%). FT-IR (neat) ν: 3383, 1508,
1
1467, 1231, 1039. ES-MS m/z: 298 [M]+. H NMR (CDCl3) δ:
1.73 (q, 4 H, J ) 6.0 Hz), 1.96 (q, 2 H, J ) 6.0 Hz), 2.60-2.67
(m, 6 H), 3.73 (t, 4 H, J ) 6.0 Hz), 3.76 (s, 3 H), 3.95 (t, 2 H,
J ) 6.0 Hz), 6.83 (s, 4 H). 13C NMR (CDCl3) δ: 26.6, 28.5, 50.8,
52.8, 55.7, 62.4, 66.5, 114.6, 115.4, 152.9, 153.8. HRMS m/z:
calcd for C16H27O4N 298.2018, found 298.2045.
C
22H33O3N3 388.2600, found 388.2589.
Com p ou n d 6. A solution of 5 (0.25 g, 0.65 mmol) in MeOH
(25 mL) was treated with CoCl2‚6H2O (0.31 g, 1.29 mmol) and
NaBH4 (0.98 g, 25.8 mmol), and the reaction continued as
described in the general procedure II. The amine (0.25 g),
resulting from this reaction, was then treated with tert-butyl
acrylate (0.87 g, 5.34 mmol) and processed further as described
in the general procedure II to afford, after putifications
(alumina) (hexane/EtOAc, 85:15), 6 as a colorless liquid (0.25
g, 54% combined yield for nitrile group reduction and Michael
addition reaction). FT-IR (neat) ν: 1728, 1455, 1367, 1151.
Com p ou n d 11. Acrylonitrile (0.25 g, 4.84 mmol) was added
to a mixture of 10 (0.65 g, 2.2 mmol) and aqueous NaOH (40%)
(22 µL), and the mixture was stirred 15 h and worked up as
described in the general procedure I to afford 11 as a colorless
liquid (0.80 g, 90%). FT-IR (neat) ν: 2251, 1508, 1232, 1116.
1
ES-MS m/z: 404 [M]+. H NMR (CDCl3) δ: 1.70 (q, 4 H, J )
6.3 Hz), 1.87 (q, 2 H, J ) 6.6 Hz), 2.49 (t, 4 H, J ) 6.9 Hz),
2.56 (t, 6 H, J ) 6.3 Hz), 3.49 (t, 4 H, J ) 6.3 Hz), 3.58 (t, 4 H,
J ) 6.3 Hz), 3.76 (s, 3 H), 3.95 (t, 2 H, J ) 6.3 Hz), 6.83 (s, 4
H). 13C NMR (CDCl3) δ: 18.8, 27.1, 27.3, 50.2, 50.4, 55.7, 65.2,
69.3, 66.3, 114.5, 115.2, 117.9, 153.1, 153.6. HRMS m/z: calcd
for C22H33O4N3 404.2549, found 404.2560.
1
MALDI-TOF-MS m/z: 908 [M]+. H NMR (CDCl3) δ: 1.44 (s,
36 H), 1.68 (b, 10 H), 2.34 (t, 8 H, J ) 7.2 Hz), 2.46 (t, 10 H,
J ) 6.9 Hz), 2.71 (t, 8 H, J ) 7.2 Hz), 3.39 (t, 8 H, J ) 6.3 Hz),
3.50 (t, 2 H, J ) 6.3 Hz), 4.49 (s, 2 H), 7.29-7.36 (m, 5 H). 13
C
NMR (CDCl3) δ: 27.5, 27.7, 28.1, 33.8, 49.4, 50.6, 50.9, 68.5,
68.9, 69.1, 72.9, 80.1, 127.5, 128.3, 129.2, 138.6, 172.1. HRMS
m/z: calcd for C50H89O11N3 908.6575, found 908.6580.
Com p ou n d 12. Bis-nitrile derivative 11 (0.80 g, 1.98 mmol)
in MeOH (0.5 mL) was added with Raney Co catalyst (40 mL),
and the reaction was continued further as given in the general
procedure V to afford the amine intermediate. A solution of
amine (0.81 g, 1.96 mmol) in MeOH (5 mL) was treated with
tert-butyl acrylate (4.37 g, 34.1 mmol), and the reaction was
followed as given in general procedure V to afford, after
purifications (hexane/EtOAc, 85:15), 12 as a colorless liquid
(1.62 g, 89% combined yield for nitrile reduction and Michael
addition). FT-IR (neat) ν: 1728, 1508, 1367, 1232, 1156. ES-
Com p ou n d 7. A solution of 12 (0.5 g, 0.55 mmol) in MeCN/
H2O (5:1) (25 mL) was admixed with CAN (0.45 g, 0.83 mmol),
stirred at room temperature for 15 min, filtered through a plug
of Celite, and washed with EtOAc. The filtrate was concen-
trated and purified (alumina) (hexane/EtOAc, 70:30) to afford
7 as a colorless liquid (0.14 g, 30%). Alternatively, 6 (50 mg,
0.055 mmol) in EtOAc (25 mL) was added with Pd/C (10%)
(24 mg), attached with a H2-filled balloon, stirred at room
temperature for 5 days, filtered, and washed, and the filtrate
was concentrated and purified to afford 7 as a colorless liquid
(4 mg, 44% after recovery of 40 mg of starting material). FT-
IR (neat) ν: 3440, 1729, 1461, 1367, 1157. MALDI-TOF-MS
1
MS m/z: 924 [M]+. H NMR (CDCl3) δ: 1.40 (s, 36 H), 1.60-
1.68 (m, 8 H), 1.84 (q, 2 H, J ) 6.6 Hz), 2.31 (t, 8 H, J ) 7.2
Hz), 2.40-2.48 (m, 8 H), 2.52 (m, 2 H), 2.68 (t, 8 H, J ) 7.2
Hz), 3.32-3.38 (app. q, 8 H, J ) 6.3 Hz), 3.73 (s, 3 H), 3.91 (t,
2 H, J ) 6.0 Hz), 6.82 (s, 4 H). 13C NMR (CDCl3) δ: 27.6, 28.0,
33.7, 49.4, 50.5, 50.8, 55.7, 66.7, 68.9, 69.1, 80.2, 114.5, 115.3,
153.2, 153.4, 172.0. HRMS m/z: calcd for C50H89O12N3 924.6524,
found 924.6549.
1
m/z: 818 [M]+. H NMR (CDCl3) δ: 1.43 (s, 36 H), 1.68 (b, 10
H), 2.34 (t, 8 H, J ) 7.2 Hz), 2.47 (m, 8H), 2.64 (t, 2 H, J ) 5.7
Hz), 2.68 (t, 8 H, J ) 7.2 Hz), 3.38 (b, 8 H), 3.77 (t, 2 H, J )
5.4 Hz). 13C NMR (CDCl3) δ: 27.1, 27.6, 28.1, 29.7, 33.8, 49.4,
50.5, 51.0, 54.9, 64.4, 69.0, 80.2, 172.1. HRMS m/z: calcd for
Com p ou n d 13. To a solution of 12 (0.60 g, 0.6 mmol) in
CH2Cl2 (15 mL) were added AcCl (1.1 mL) and H2O (0.24 mL),
and the deprotection reaction was continued and worked up
as given in the general procedure IV for hydrolysis of tert-butyl
esters to afford 13 as a white, foamy solid (0.45 g, 99%). FT-
IR (KBr) ν: 3414, 1717, 1509, 1229, 1025. ES-MS m/z: 700
C
43H83O11N3 818.6106, found 818.6103.
Com p ou n d 8. Diisopropyl azidodicarboxylate (DIAD) (6.36
g, 31.5 mmol) was added to a mixture of 4 (8.0 g, 24.2 mmol),
p-methoxyphenol (9.0 g, 73 mmol), and PPh3 (8.5 g, 32 mmol)
in THF (75 mL), and the mixture was refluxed for 15 min.
Solvents were then removed in vacuo, and the crude product
was diluted with EtOAc (300 mL), washed with saturated
aqueous NaOH (6 × 150 mL) solution and brine (2 × 150 mL),
dried, and concentrated. The resulting crude product was
purified (SiO2) (hexane/EtOAc, 90:10) to afford 8 as a colorless
liquid (9.63 g, 91%). FT-IR (neat) ν: 1729, 1509, 1367, 1232,
1155. EI-MS m/z: 437 [M]+. 1H NMR (CDCl3) δ: 1.42 (s, 18
H), 1.89 (q, 2 H, J ) 6.6 Hz), 2.36 (t, 4 H, J ) 7.2 Hz), 2.58 (t,
2 H, J ) 6.6 Hz), 2.74 (t, 4 H, J ) 7.2 Hz), 3.76 (s, 3 H), 3.93
(t, 2 H, J ) 6.3 Hz), 6.82 (s, 4 H). 13C NMR (CDCl3) δ: 27.3,
28.1, 33.8, 49.4, 50.2, 55.7, 66.5, 80.2, 114.6, 115.4, 153.2, 153.6,
1
[M + 1]+. H NMR (D2O) δ: 1.88 (b, 8 H), 2.00 (b, 2 H), 2.70
(b, 8 H), 3.10 (b, 10 H), 3.25 (b, 8 H), 3.40 (b, 8 H), 3.61 (s, 3
H), 3.98 (b, 2 H), 6.81 (s, 4 H). 13C NMR (D2O) δ: 29.1, 50.2,
51.8, 52.7, 53.5, 56.6, 66.7, 68.4, 68.7, 116.0, 116.9, 152.8, 154.4,
175.1. HRMS m/z: calcd for C34H57O12N3 700.4020, found
700.3992.
Com p ou n d 14. To a suspension of LAH (84 mg, 2.28 mmol)
in THF (10 mL) was added dropwise 12 (0.43 g, 0.463 mmol)
in THF (5 mL), and the reaction continued further as described
in the general procedure III to afford 14 as a colorless liquid
(0.29 g, 97%). FT-IR (neat) ν: 3383, 1508, 1467, 1231, 1111,
1
1060. ES-MS m/z: 644 [M]+. H NMR (CDCl3) δ: 1.71 (b, 16
172.0. HRMS m/z: calcd for
C24H39O6N 438.2855, found
H), 1.85 (b, 2 H), 2.51 (b, 10 H), 2.61 (t, 8 H, J ) 6.0 Hz), 3.41
(m, 8 H), 3.71 (t, 8 H, J ) 5.4 Hz), 3.76 (s, 3 H), 3.94 (t, 2 H,
J ) 6.0 Hz), 6.82 (s, 4 H). 13C NMR (CDCl3) δ: 25.5, 26.9, 27.1,
28.5, 50.4, 50.7, 50.8, 52.6, 55.7, 62.2, 66.5, 68.7, 69.0, 114.5,
115.3, 153.0, 153.6. HRMS m/z: calcd for C34H65O8N3 644.4850,
found 644.4830.
438.2854.
Com p ou n d 9. To a solution of 8 (1.57 g, 3.5 mmol) in CH2-
Cl2 (50 mL) were added AcCl (1.4 mL) and H2O (0.36 mL),
and the deprotection reaction was continued and worked up
as given in the general procedure IV for hydrolysis of tert-butyl
esters to afford 9 as white foamy solid (1.2 g, 97%). FT-IR (KBr)
Com p ou n d 15. Acrylonitrile (0.20 g, 3.84 mmol) was added
to a mixture of 14 (0.54 g, 0.82 mmol) and aqueous NaOH
(40%) (36 µL), and the reaction mixture was worked up as
described in the general procedure I. The resulting product
1
ν: 3414, 1717, 1509, 1229, 1025. ES-MS m/z: 325 [M+]+. H
NMR (CDCl3 + DMSO-d6) δ: 2.32 (b, 2 H), 2.98 (t, 4 H, J )
6.6 Hz), 3.31 (t, 2 H, J ) 6.6 Hz), 3.42 (t, 4 H, J ) 6.9 Hz),
9702 J . Org. Chem., Vol. 68, No. 25, 2003

Poly(propyl ether imine) Dendrimers
was purified (alumina) (hexane/EtOAc, 1:1) to afford 15 as a
colorless liquid (0.66 g, 92%). FT-IR (neat) ν: 2251, 1508, 1231,
and the deprotection reaction was continued and worked up
as given in the general procedure IV for hydrolysis of tert-butyl
esters to afford 21 a white, foamy solid (0.6 g, 99%). FT-IR
(neat) ν: 2618, 1729, 1462, 1244, 1106. ES-MS m/z: 1938 [M]+.
1H NMR (D2O) δ: 1.90 (b, 24 H), 2.14 (b, 6 H), 2.71 (t, 24 H,
J ) 6.3 Hz), 3.16 (t, 30 H, J ) 6.3 Hz), 3.29 (t, 24 H, J ) 6.3
1
1118. ES-MS m/z: 856 [M]+. H NMR (CDCl3) δ: 1.70 (b, 16
H), 1.87 (q, 2 H, J ) 6.6 Hz), 2.46 (b, 18 H), 2.59 (t, 8 H, J )
6.3 Hz), 3.39 (b, 8 H), 3.53 (t, 8 H, J ) 6.3 Hz), 3.63 (t, 8 H, J
) 6.3 Hz), 3.75 (s, 3 H), 3.94 (t, 2 H, J ) 6.0 Hz), 6.82 (s, 4 H).
13C NMR (CDCl3) δ: 18.8, 27.1, 27.2, 27.3, 50.4, 50.7, 55.6,
65.2, 65.8, 69.0, 69.3, 114.5, 115.2, 117.9, 153.1, 153.6. HRMS
m/z: calcd for C46H77O8N7 856.5912, found 856.5908.
Hz), 3.44 (m, 24 H), 4.35 (t, 6 H, J ) 5.7 Hz), 8.66 (s, 3 H). 13
C
NMR (D2O) δ: 23.6, 24.0, 24.2, 29.3, 49.9, 50.4, 51.7, 52.9, 53.6,
64.1, 68.4, 68.9, 131.5, 135.4, 167.0, 175.3.
Com p ou n d 16. Tetrakis-nitrile 15 (0.60 g, 0.7 mmol) in
MeOH (0.5 mL) was added with Raney Co catalyst in H2O (40
mL), and the reaction was continued further as given in the
general procedure V to afford the amine intermediate. A
solution of the amine (0.50 g, 0.28 mmol) in MeOH (5 mL) was
treated with tert-butyl acrylate (4.37 g, 34.1 mmol), and the
reaction was followed as given in general procedure V to afford,
after purifications (hexane/EtOAc, 85:15), 16 as a colorless
liquid (1.08 g, 83% combined yield for nitrile reduction and
Michael addition reaction). FT-IR (neat) ν: 1728, 1508, 1367,
1232, 1156. MALDI-TOF m/z: 1897 [M]+. 1H NMR (CDCl3) δ:
1.41 (s, 72 H), 1.67 (b, 24 H), 1.85 (b, 2 H), 2.31 (t, 16 H, J )
7.2 Hz), 2.44 (b, 24 H), 2.55 (b, 2 H), 2.68 (t, 16 H, J ) 7.2 Hz),
3.37 (b, 24 H), 3.74 (s, 3 H), 3.91 (t, 2 H, J ) 6.3 Hz), 6.79 (s,
4 H). 13C NMR (CDCl3) δ: 27.6, 28.1, 33.7, 49.4, 50.5, 50.8,
55.7, 69.0, 80.2, 114.6, 115.4, 153.2, 153.4, 172.0.
Com p ou n d 17. To a solution of 16 (0.60 g, 0.31 mmol) in
CH2Cl2 (15 mL) were added AcCl (1.0 mL) and H2O (0.22 mL),
and the deprotection reaction was continued and worked up
as given in the general procedure IV to afford 17 as a white,
foamy solid (0.45 g, 99%). FT-IR (KBr) ν: 3414, 1717, 1509,
1229, 1025. ES-MS m/z: 1450 [M]+. 1H NMR (D2O) δ: 1.88 (m,
26 H), 2.71 (t, 16 H, J ) 6 Hz), 3.05 (t, 16 H, J ) 6.9 Hz), 3.15
(t, 26 H, J ) 6.6 Hz), 3.30-3.40 (b, 24 H), 3.62 (s, 3 H), 4.00
(b, 2 H), 6.83 (s, 4 H). 13C NMR (D2O) δ: 27.5, 29.2, 50.3, 51.4,
51.7, 53.0, 56.6, 68.3, 68.8, 116.0, 116.9, 152.9, 159.9, 175.1.
Com p ou n d 22.17 Acrylonitrile (5.83 g, 0.11 mol) was added
with aqueous NaOH (40%) (1 mL), and the reaction was
conducted as given in the general procedure I to afford 22 as
a colorless liquid (12.0 g, 98%). FT-IR (neat) ν: 2251, 1455,
1363, 1104. 1H NMR (CDCl3) δ: 2.62 (t, 4 H, J ) 6.3 Hz), 3.68
(t, 4 H, J ) 6.3 Hz). 13C NMR (CDCl3) δ: 18.8, 65.7, 117.5.
Com p ou n d 23. Bis-nitrile 22 (0.80 g, 6.56 mmol) in MeOH
(0.5 mL) was added with Raney cobalt catalyst in H2O (40 mL),
and the reaction was continued further as given in the general
procedure V to afford the amine intermediate. A solution of
the amine (0.82 g, 6.55 mmol) in MeOH (5 mL) was treated
with tert-butyl acrylate (4.37 g, 34.1 mmol), and the reaction
was followed as given in general procedure V to afford, after
purifications (hexane/EtOAc, 85:15), 23 as a colorless liquid
(3.78 g, 90% combined yield for nitrile reduction and Michael
addition reaction). FT-IR (neat) ν: 1729, 1457, 1367, 1153. EI-
MS m/z: 644 [M]+. 1H NMR (CDCl3) δ: 1.44 (s, 36 H), 1.69 (q,
4 H, J ) 6.3, 6.9 Hz), 2.35 (t, 8 H, J ) 7.2 Hz), 2.47 (t, 4 H, J
) 6.9 Hz), 2.72 (t, 8 H, J ) 7.2 Hz), 3.40 (t, 4 H, J ) 6.3 Hz).
13C NMR (CDCl3) δ: 27.6, 28.1, 33.7, 49.4, 50.5, 68.9, 80.2,
172.0. HRMS m/z: calcd for
C34H64O9N2 645.4690, found
645.4666.
Com p ou n d 24. To a solution of 23 (0.64 g, 1 mmol) in CH2-
Cl2 (15 mL) were added AcCl (1.7 mL) and H2O (0.36 mL),
and the deprotection reaction was continued and worked up
as given in the general procedure IV for hydrolysis of tert-butyl
esters to afford 24 as a white, foamy solid (0.41 g, 97%). FT-
IR (neat) ν: 2568, 1729, 1416, 1186. ES-MS m/z: 421 [M]+. 1H
NMR (D2O) δ: 1.89 (b, 4 H), 2.74 (t, 8 H, J ) 6.3 Hz), 3.18 (b,
4 H), 3.32 (t, 8 H, J ) 6.3 Hz), 3.44 (b, 4 H). 13C NMR (D2O)
δ: 23.9, 29.1, 50.3, 52.7, 68.8, 175.4. HRMS m/z: calcd for
Com p ou n d 18. A mixture of 4 (1.0 g, 3.0 mmol) and DMAP
(1.1 g, 0.9 mmol) in PhMe (20 mL) was added with 1,3,5-
benzenetricarbonyl trichloride (0.2 g 0.8 mmol), and the
reaction was continued and worked up as described in the
general procedure VI to afford, after purification (SiO2) (hex-
ane/EtOAc, 85:15), 18 as a colorless oil (0.8 g, 83%). FT-IR
(neat) ν: 1728, 1457, 1367, 1241, 1157. MALDI-TOF m/z: 1151
C
18H32O9N2 421.2186, found 421.2227.
Com p ou n d 25. A solution of 23 (3.78 g, 5.87 mmol) in THF
1
[M]+. H NMR (CDCl3) δ: 1.43 (s, 54 H), 1.95 (q, 6 H, J ) 6.3
(10 mL) was added dropwise to a suspension of LAH (1.06 g,
28 mmol) in THF (15 mL), and the reaction was continued
further as described in the general procedure III to afford 25
as a colorless liquid (2.14 g, 99%). FT-IR (neat) ν: 3378, 1465,
Hz), 2.36 (t, 12 H, J ) 6.9 Hz), 2.57 (t, 6 H, J ) 6.3 Hz), 2.74
(t, 12 H, J ) 6.9 Hz), 4.40 (t, 6 H, J ) 6.3 Hz), 8.82 (s, 3 H).
13C NMR (CDCl3) δ: 26.8, 28.1, 33.8, 49.4, 50.1, 64.1, 80.3,
131.5, 134.4, 165.0, 171.7.
1
1243, 1061. ES-MS m/z: 365 [M]+. H NMR (CDCl3) δ: 1.74
Com p ou n d 19. To a solution of 18 (0.73 g, 0.63 mmol) in
CH2Cl2 (15 mL) were added AcCl (2.5 g, 31.7 mmol) and H2O
(0.5 g, 28.5 mmol), and the deprotection reaction was continued
and worked up as given in the general procedure IV for
hydrolysis of tert-butyl esters to afford 19 as a white, foamy
solid (0.5 g, 97%). FT-IR (neat) ν: 2568, 1731, 1440, 1244, 1107.
MALDI-TOF m/z: 897 [M + 2Na + K]+. 1H NMR (D2O) δ: 2.20
(b, 6 H), 2.76 (t, 12 H, J ) 6.3 Hz), 3.32 (t, 6 H, J ) 7.2 Hz),
3.39 (t, 12 H, J ) 6.3 Hz), 4.38 (t, 6 H, J ) 5.4 Hz), 8.67 (s, 3
H). 13C NMR (D2O) δ: 23.6, 29.1, 51.6, 53.6, 63.6, 131.5, 135.4,
167.0, 173.4.
Com p ou n d 20. A mixture of 7 (0.6 g 0.13 mmol) and DMAP
(0.25 mg, 2 mmol) in PhMe (10 mL) was added with 1,3,5-
benzenetricarbonyl chloride (54 mg, 0.2 mmol), and the reac-
tion was continued and worked up as described in the general
procedure VI to afford, after purification (SiO2) (hexane/EtOAc,
70:30), to afford 20 as a colorless liquid (0.25 g, 47%). FT-IR
(neat) ν: 1731, 1463, 1366, 1244, 1157. ES-MS m/z: 2610 [M]+.
1H NMR (CDCl3) δ: 1.43 (s, 108 H), 1.62-1.68 (m, 30 H), 2.34
(t, 24 H, J ) 7.2 Hz), 2.46 (b, 30 H), 2.71 (t, 24 H, J ) 7.2 Hz),
3.40 (m, 24 H), 4.42 (t, 6 H, J ) 6.3 Hz), 8.81 (s, 3 H). 13C
NMR (CDCl3) δ: 26.8, 27.4, 27.7, 33.8, 49.4, 50.5, 50.8, 64.3,
69.0, 80.2, 131.5, 135.4, 165.0, 172.0.
(m, 12 H), 2.53 (t, 4 H, J ) 6.9 Hz), 2.60 (t, 8 H, J ) 6.3 Hz),
3.45 (t, 4 H, J ) 6.3 Hz), 3.71 (t, 8 H, J ) 6.3 Hz). 13C NMR
(CDCl3) δ: 26.8, 28.6, 50.9, 52.8, 62.4, 68.8. HRMS m/z: calcd
for C18H40O5N2 365.3015, found 365.3016.
Com p ou n d 26. Acrylonitrile (1.06 g, 20 mmol) was added
to a mixture of 25 (1.53 g, 4.2 mmol) and aqueous NaOH (40%)
(0.17 mL), and the reaction was continued and worked up as
given in the general procedure I to afford, after purification
(alumina) (CHCl3/MeOH, 99:1), 26 as a colorless liquid (2.2 g,
92%). FT-IR (neat) ν: 2251, 1508, 1232, 1116. ES-MS m/z: 578
[M]+. 1H NMR (CDCl3) δ: 1.66 (b, 12 H), 2.44 (b-m, 12 H),
2.56 (t, 8 H, J ) 6.3 Hz), 3.36 (t, 4 H, J ) 6.3 Hz), 3.47 (t, 8 H,
J ) 6.3 Hz), 3.59 (t, 8 H, J ) 6.3 Hz). 13C NMR (CDCl3) δ:
18.8, 27.3, 50.4, 50.7, 65.7, 69.3, 117.5. HRMS m/z: calcd for
C
30H53O5N6 577.4077, found 577.4054.
Com p ou n d 27. Tetrakis-nitrile 26 (0.8 g, 1.38 mmol) in
MeOH (0.5 mL) was added with Raney cobalt catalyst in H2O
(40 mL), and the reaction was continued further as given in
the general procedure V to afford the amine intermediate. A
solution of the amine (0.81 g, 1.38 mmol) in MeOH (5 mL) was
treated with tert-butyl acrylate (4.37 g, 34.1 mmol), and the
reaction was followed as given in general procedure V to afford,
after purifications (hexane/EtOAc, 85:15), 27 as a colorless
liquid (1.81 g, 80% combined yield for nitrile reduction and
Michael addition reaction). FT-IR (neat) ν: 1728, 1458, 1367,
Com p ou n d 21. To a solution of 20 (0.8 g, 0.3 mmol) in CH2-
Cl2 (15 mL) were added AcCl (1.6 mL) and H2O (0.36 mL),
J . Org. Chem, Vol. 68, No. 25, 2003 9703

Krishna and J ayaraman
1
1255, 1156. MALDI-TOF m/z: 1618 [M]+. 1H NMR (CDCl3) δ:
1.45 (s, 72 H), 1.69 (b-m, 20 H), 2.34 (t, 16 H, J ) 7.2 Hz),
2.40-2.46 (m, 20 H), 2.71 (t, 16 H, J ) 7.2 Hz), 3.40 (m, 20
H). 13C NMR (CDCl3) δ: 27.6, 28.1, 33.8, 49.4, 50.5, 50.8, 68.9,
69.1, 80.2, 172.0.
1255, 1157. ES-MS m/z: 3601 [M + K]+. H NMR (CDCl3) δ:
1.39 (s, 144 H), 1.64 (q, 52 H, J ) 6.9 Hz), 2.34 (t, 32 H, J )
6.9 Hz), 2.46 (b-t, 52 H, J ) 7.2 Hz), 2.71 (t, 32 H, J ) 7.2 Hz),
3.39 (app. t, 52 H). 13C NMR (CDCl3) δ: 28.3, 28.5, 29.0, 34.6,
50.3, 51.4, 51.7, 69.8, 70.1, 70.3, 81.0, 172.9.
Com p ou n d 28. To a solution of 27 (0.34 g, 0.21 mmol) in
CH2Cl2 (15 mL) were added AcCl (0.70 mL) and H2O (0.16 mL),
and the deprotection reaction was continued and worked up
as given in the general procedure IV to afford 28 as a white,
foamy solid (0.23 g, 97%). FT-IR (neat) ν: 2568, 1729, 1416,
Com p ou n d 32. To a solution of 31 (0.52 g, 1 mmol) in CH2-
Cl2 (15 mL) were added AcCl (1.0 mL) and H2O (0.36 mL),
and the deprotection reaction was continued and worked up
as given in the general procedure IV to afford 32 as a white,
foamy solid (0.38 g, 97%). FT-IR (neat) ν: 2568, 1729, 1416,
1
1
1186. H NMR (D2O) δ: 1.88 (b, 20 H), 2.78 (b, 16 H), 3.15 (b,
1186. H NMR (D2O) δ: 1.90 (b, 52 H), 2.74 (b, 32 H), 3.15 (b,
20 H), 3.34 (b, 16 H), 3.45 (b, 20 H). 13C NMR (D2O) δ: 24.8,
24.9, 27.4, 29.0, 29.9, 50.4, 50.7, 51.0, 52.1, 53.4, 68.9, 69.2,
69.4, 175.1.
52 H), 3.34 (b, 32 H), 3.45 (b, 52 H). 13C NMR (D2O) δ: 24.0,
24.3, 28.0, 29.3, 30.3, 49.7, 50.1, 50.3, 50.4, 51.3, 51.4, 68.3,
68.4, 68.8, 175.1.
Com p ou n d 29. A solution of 27 (0.36 g, 0.22 mmol) in THF
(5 mL) was added dropwise to a suspension of LAH (84 mg,
2.28 mmol) in THF (5 mL), and the reaction was continued
further as described in the general procedure III to afford 29
as a colorless liquid (0.23 g, 97%). FT-IR (neat) ν: 3383, 1508,
1467, 1231, 1111, 1060. MALDI-TOF m/z: 1087 [M + Na]+.
1H NMR (CDCl3) δ: 1.75 (m, 20 H), 1.86 (m, 16 H), 2.45 (m,
20 H), 2.60 (t, 16 H, J ) 6.3 Hz), 3.43 (m, 16 H), 3.75 (t, 20 H,
J ) 6.3 Hz). 13C NMR (CDCl3) δ: 25.6, 26.9, 27.1, 50.7, 50.9,
52.7, 62.3, 67.9, 68.8, 69.1.
Com p ou n d 30. Acrylonitrile (0.12 g, 2.26 mmol) was added
to a mixture of 29 (0.27 g, 0.26 mmol) and aqueous NaOH
(40%) (23 µL), and the reaction was continued and worked up
as given in the general procedure I to afford, after purification
(alumina) (CHCl3/MeOH, 98:2), 30 as a colorless liquid (0.35
g, 92%). FT-IR (neat) ν: 2251, 1508, 1231, 1118. ES-MS m/z:
1484 [M + 1]+. 1H NMR (CDCl3) δ: 1.63-1.75 (m, 36 H), 2.36-
2.47 (m, 20 H), 2.58 (t, 32 H, J ) 6.3 Hz), 3.40 (t, 20 H, J )
7.2 Hz), 3.51 (t, 16 H, J ) 6.6 Hz), 3.63 (t, 16 H, J ) 6.3 Hz).
13C NMR (CDCl3) δ: 18.8, 27.2, 27.3, 50.4, 50.7, 65.8, 69.0,
69.4, 117.4.
Com p ou n d 31. Octakis-nitrile 30 (0.35 g, 0.24 mmol) was
added with Raney cobalt catalyst in H2O (40 mL), and the
reaction was continued further as given in the general
procedure V to afford the amine intermediate. A solution of
the amine (0.25 g, 0.16 mmol) in MeOH (5 mL) was treated
with tert-butyl acrylate (4.37 g, 34.1 mmol), and the reaction
was followed as given in general procedure V to afford, after
purifications (alumina) (hexane/EtOAc, 60:40), 31 as a colorless
liquid (0.8 g, 95% combined yield for nitrile reduction and
Michael addition reaction). FT-IR (neat) ν: 1729, 1458, 1367,
Cytotoxicity Stu d ies (MTT Assa y). Chinese hamster
ovarian cells or breast cancer T47D cells were seeded at a
density of 10 000 cells/well in a 96-well plate and grown in 95
µL of culture medium supplemented with 10% fetal bovine
serum for 24 h. Following exposure of the cells with 5 µL of
aqueous solutions of dendrons or dendrimers for 24 h, 25 µL
of 5 mg/mL stock solution of 3-[4,5-dimethylthiazol-2-yl]-2,5-
diphenyltetrazolium bromide (MTT) was added to each well.
After 2 h of incubation at 37 °C, 100 µL of extraction buffer
(containing 20% w/v SDS in a solution of 50% of DMF, pH
4.7) was added. Absorbance was measured at 570 nm after
an overnight incubation at 37 °C.
Ack n ow led gm en t. We thank the Department of
Science and Technology, New Delhi, for financial sup-
port. T.R.K. thanks University Grants Commission,
New Delhi, for a research fellowship. We thank Profes-
sor Utpal Tatu, Ms. Mukta Belwal, and Mr. S. Sunder
Rajan, Department of Biochemistry of this Institute, for
their help to conduct cytotoxicity analyses, and Professor
M. Giridhar, Chemical Engineering Department, for
generously allowing us to use the hydrogenation reac-
tors.
Su p p or tin g In for m a tion Ava ila ble: General methods of
experimental details, 1H NMR spectrum of 31, 13C NMR
spectra of dendrons and dendrimers 1-21 and 23-32. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O035072Y
9704 J . Org. Chem., Vol. 68, No. 25, 2003