Synthesis and photophysical properties of chiral dendrimers with quinoline surface group via click chemistry

Article abstract of DOI:10.1016/j.tetlet.2010.06.059

Synthesis of some novel chiral dendrimers containing quinoline as surface group and 1,2,3-triazole as branching unit is described. The chiroptical property exhibits the widening of the torsional angle in the BINOL core as the generation increases. The photophysical properties indicate an increase in the molar extinction coefficient and fluorescence intensity and a decrease in quantum yield and lifetime as the generation of the dendrimer increases.

Full text of DOI:10.1016/j.tetlet.2010.06.059

Tetrahedron Letters 51 (2010) 4365–4370
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and photophysical properties of chiral dendrimers with quinoline
surface group via click chemistry
*
Perumal Rajakumar , Rathinam Raja
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis of some novel chiral dendrimers containing quinoline as surface group and 1,2,3-triazole as
branching unit is described. The chiroptical property exhibits the widening of the torsional angle in
the BINOL core as the generation increases. The photophysical properties indicate an increase in the
molar extinction coefficient and fluorescence intensity and a decrease in quantum yield and lifetime as
the generation of the dendrimer increases.
Received 28 April 2010
Revised 8 June 2010
Accepted 11 June 2010
Available online 16 June 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Click chemistry
Quinoline
Chiral S-(ꢀ)-BINOL
Alkynes
Azide
1
,2,3-Triazole
Dendrimers are monodisperse macromolecular architectures
with a high degree of surface functionality. Dendrimers find appli-
no protection-deprotection protocol in addition to air and moisture
tolerant reaction conditions. Studies of synthesis, DNA binding, and
photonuclease activity of 1,2,3-triazole-fused quinoline-peptidom-
1
cations in light harvesting systems,2 catalysis,3 drug delivery,
4
5
18
multivalent diagnostics for magnetic resonance imaging (MRI),
imetics have been reported. Synthesis of dendrimers using click
molecular encapsulation,6 and bioconjugate chemistry. Dendri-
mers are also used in organo electronic devices such as organic
light-emitting diodes (OLEDs).8 Quinoline is a bioactive residue
present in various natural products and drugs and also used for
the synthesis of electronics and optoelectronic devices due to its
excellent mechanical properties.9 Quinoline-based fluorophoric
systems find applications in sensor,10 OLEDs , and exhibit bacteri-
cidal, antitumor, antimalarial, anti-inflammatory, pro-apoptotic,
7
chemistry has received much attention during recent times. Syn-
19
thesis of water-soluble glycodendrimers and chalchone dendri-
mers through click chemistry has been reported from our
2
0
laboratory. Dendrimers with chiral S-(ꢀ)-BINOL core exhibit
2
1
chiroptical, photophysical properties , and also used as enantiose-
22
lective lewis acid catalysts. Moreover, in the current context
11
though optically inactive and cheap core molecules can be em-
ployed for the synthesis of dendrimer with quinoline surface
group, we prefer to use S-(ꢀ)-BINOL core for many reasons. The
chiral BINOL core-based dendrimer could be used as a chiral base
1
2
and antiproliferative and also other biological activities. Quino-
line-based conjugated dendrimers exhibit photophysical, electro-
luminescence properties and function as electron transport
2
2,23
and chiral auxiliary in organic synthesis,
further by increasing
13
materials for light-emitting diodes. Further quinoline-based den-
the dendrimer generation, the dendritic wedges would go farther
apart which could increase the dihedral angle in the naphthyl unit,
thereby making them chiral auxiliary with higher degree of molar
rotation values. We report herein the versatile and highly efficient
synthesis as well as chiroptical and photophysical properties of a
new family of S-(ꢀ)-BINOL-based quinoline dendrimers 1–3
(Fig. 1) with 1,2,3-triazole as building unit through click chemistry
by convergent approach.
1
4
drimers have also been used in ‘on–off’ switchable luminescence
15
and for metal complexation.
1
6
Click chemistry refers to Cu(I)-catalyzed Huisgen 1,3-dipolar
cycloaddition of an azide to a terminal alkyne to yield triazole
which can function as a possible ligand for metal ions and as a pro-
ton transport facilitator.17 In the present study click chemistry ap-
proach is chosen as the best process for the synthesis of triazoles.
The advantages of employing click chemistry are the excellent che-
moselectivity, extraordinary reliability, high yield, atom-economy,
The synthesis of 3-(azidomethyl)-2-methoxyquinoline 8 is out-
lined in Scheme 1. 2-Chloro-3-formylquinoline 4 was synthesized
2
4
from acetanilide via Vilsmeier–Haack reaction. The reaction of
2
-chloro-3-formylquinoline 4 with methanol in the presence of
*
Corresponding author. Tel.: +91 044 22202810; fax: +91 44 22300488.
E-mail address: perumalrajakumar@gmail.com (P. Rajakumar).
2
5
KOH afforded 2-methoxy-3-formylquinoline 5,
which was
0
040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.06.059

4
366
P. Rajakumar, R. Raja / Tetrahedron Letters 51 (2010) 4365–4370
N
N
N
N
N
MeO
N
N
N
N
OMe
N
N
N
N
O O
N
N
O
O
O
O
N
N
O
O
N
N
N
N
N
N
N
N
N
OMe
1
MeO
N
OMe
N
MeO
N
N
2
N
N
MeO
OMe
N
N
N
N
N
N
OMe
O
MeO
O
N
N
N
N
N
N
N
O
O
N
N
N
N
N
N
N
N
N
N
N
N
O
O
O
O
O
N
N
N
N
N
N
O
N
N
N
N
N
N
O
O
N
N
N
O
O
MeO
OMe
N
N
N
N
N
N
MeO
OMe
N
3
N
Figure 1. Molecular structure of dendrimers 1–3.
CH
2
Cl
2
gave 2-methoxy-3-(iodomethyl)quinoline 7 in 64% yield.
in DMF at 60 °C afforded
CHO
Cl
X
i
v
1
The reaction of the iodide 7 with NaN
3-(azidomethyl)-2-methoxyquinoline 8 in 81% yield. The structure
3
N
4
N
OMe
of the azide 8 has been confirmed from spectral and analytical
data.
5
X = CHO
2
7
ii
6
X = CH2OH
X = CH2I
The core unit bis(propargyloxy)-S-(ꢀ)-BINOL 9 was obtained by
iii
the reaction of S-(ꢀ)-BINOL with propargyl bromide in the pres-
7
8
2
0a
26
iv
ence of K
CO
3
in DMF as reported earlier.
The reaction of
2
X = CH N
2
3
0
.5 equiv of bis(propargyloxy)-S-(ꢀ)-BINOL 9 with 1 equiv of quin-
oline azide 8 in the presence of CuSO O (5 mol %) and sodium
4
ꢁ5H
2
Scheme 1. Synthesis of dendrimer 1. Reagents and conditions: (i) MeOH, KOH,
reflux, 3 h, 5, 85%; (ii) NaBH , MeOH, 0 °C to rt, 6 h, 6, 87%; (iii) PPh , I , imidazole,
°C, 5 h, 7, 72%; (iv) NaN , DMF, 60 °C, 6 h, 8, 81%; (v) 0.5 equiv bis(propargyloxy)-
O (5 mol %), sodium ascorbate (10 mol %), H O/THF (1:3),
4
3
2
ascorbate (10 mol %) in a mixture of water and THF (1:3) at room
0
3
temperature gave the bis-triazole chiral dendrimer 1 in 84% yield
S-(ꢀ)-BINOL 9, CuSO
4
ꢁ5H
2
2
1
(
Scheme 1). In H NMR spectrum of dendrimer 1 showed a singlet
rt, 10 h, 1, 84%.
at d 3.99 for methoxy protons and two set of doublets at d 5.06 and
5.15 for methylene protons attached to the S-(ꢀ)-BINOL and a sin-
glet at d 5.34 for the methylene protons attached to the triazole
reduced with NaBH
4
in MeOH to give the alcohol 6 which on fur-
and I in the presence of imidazole in dry
ther reaction with PPh
3
2

P. Rajakumar, R. Raja / Tetrahedron Letters 51 (2010) 4365–4370
4367
ring in addition to aromatic protons. The 13C NMR spectrum of
dendrimer 1 displayed methoxy carbons at d 49.4 and methylene
carbons at d 51.1, 63.9 respectively, in addition to the aromatic car-
bons. The structure of the dendrimer 1 was further confirmed from
spectral and analytical data.30
Chiroptical studies of enantiopure chiral dendrimers 1–3: The mo-
lar specific rotation values were determined for the chiral dendri-
2
D
5
mers 1–3 in CHCl
rotation data are given in Table 1. The specific rotation value de-
creases with an increase in the dendrimer generation G to G
3
at 589 nm. The specific rotation ½
a
ꢂ
and molar
0
2
.
In order to synthesize the first generation dendrimer 2, the
building unit viz. 3,5-bis(propargyloxy)benzyl chloride 10 was ob-
tained as follows: the bis-propargyl derivative obtained by the
reaction of methyl 3,5-dihydroxybenzoate with propargyl bromide
The molar rotation values are due to the presence of chiral S-(ꢀ)-
BINOL unit which makes the dendrimer as an auxiliary chiral mol-
ecule with dendritic wedges. The dihedral angle between the naph-
thyl units in the BINOL core increases as the generation of the
dendrimer increases, which leads to a greater steric repulsion be-
tween the dendritic wedges and hence increases to negative values
of specific rotation. In our earlier observation with respect to chiral
in DMF in the presence of K
2 3
CO was treated with LAH followed by
the reaction of SOCl /Py in DCM to give the chloride 10. The reac-
2
tion of 3,5-bis(propargyloxy)benzyl chloride 10 with 2 equiv of
quinoline azide 8 under the Cu(I)-catalyzed Huisgen ‘click reaction’
2
0
glycodendrimers, the specific rotation of the dendrimer was due
to the presence of both the glucose unit and binaphthyl unit and
hence the overall rotation values could switch over from negative
to positive values as the generation increases. However, in the
present study the molar rotation changes to large negative values
on passing over from zero to second generation, because of the in-
crease in the dihedral angle at the naphthyl moiety and the den-
dritic wedges broaden out to a maximum value due to steric
hindrance. Similar observation has also been reported by Meijer
conditions gave the first generation chloride G
AB -type). The dendritic chloride 11 with NaN
afforded the first generation azide G -N 12 in 83% yield. The
reaction of 0.5 equiv bis(propargyloxy)-S-(ꢀ)-BINOL core unit 9
with 1 equiv of dendritic azide G -N 12 in the presence of the
Cu(I)-catalyzed Huisgen ‘click reaction’ conditions generated the
1
-Cl 11 in 91% yield
(
2
3
in DMF at 60 °C
2
8
1
3
1
3
(
2
AB
).
2
1
-type) first generation dendrimer (G ) 2 in 78% yield (Scheme
1
33
34
35
The H NMR spectrum of dendrimer 2 showed a singlet at d 3.98
and co-workers, Chen et al. and Gibson and Rendell in various
chiral dendrimer with binaphthyl core unit. However the molar
rotation values do not switch over to the positive side, which indi-
cate that broadening of the dihedral angle occurs without exceed-
ing the critical angle of 110°. The enhancement of molar rotation
value of the dendrimers, which have the same molar content of
the element, upon the addition of large dendritic fragments turns
out to be the most interesting result.
for methoxy proton and two sets of doublets at d 4.93 and 5.01 for
–
CH
2
– protons attached to S-(ꢀ)-BINOL unit and three singlets at d
5
.03, 5.04, and 5.59 for –N–CH
2
– and –O–CH – protons, in addition
2
13
to aromatic protons. The C NMR spectrum of dendrimer 2 dis-
played methoxy carbons at d 49.2 and –N–CH – carbons at d
3.6, 53.8, and 61.9 and –O–CH – carbon at d 63.8 in addition to
2
5
2
aromatic carbons. In the MALDI-TOF mass spectrum, the molecular
+
ion peak appeared at m/z 1723.31 (M+Na) and the structure of the
Photophysical properties of chiral dendrimers 1–3: The photo-
physical data for chiral dendrimers 1–3 are listed in Table 2. Figure
2 shows the absorption spectra of compounds 1–3 in DMSO. There
are three major absorption bands at 272, 312, and 324 nm and
three shoulder peaks at 282, 298, and 339 nm due to the BINOL
and quinoline units, respectively. Molar extinction coefficients of
the absorption bands increase significantly as the generation of
the dendrimer increases. Also, it should be noted that there is no
spectral broadening or spectral shift with increase in generation
(Fig. 2) which reflects the perfection of the synthesized quinoline
dendrimers. The absorbance in UV spectrum increases relatively
to a small extent while passing from zero to first generation due
to slight increase in the number of quinoline units from 2 to 4.
However, on passing from first to second generation the absor-
bance probably increases enormously due to the presence of a
large number of quinoline units viz. 8.
dendrimer 2 was further confirmed from spectral and analytical
3
1
data.
A similar synthetic strategy was adopted for the synthesis of
second generation dendrimer 3 from the building block viz. 3,5-
bis(propargyloxy)benzyl chloride 10 and dendritic azide G
under Cu(I)-catalyzed Huisgen click reaction conditions to give
second generation chloride (G -Cl) 13 in 75% yield. The use of
NaN in DMF at 60 °C allowed the conversion of the desired den-
dritic chloride 13 to the dendritic azide G
The reaction of the bis(propargyloxy)-S-(ꢀ)-BINOL core unit 9 with
equiv of dendritic azide G -N 14 in the presence of Cu(I)-cata-
lyzed Huisgen click reaction conditions gave dendrimer 3 (AB
1 3
-N 12
2
3
2
9
2 3
-N 14 in 79% yield.
2
2
3
2
-
type) in 68% yield (Scheme 3). In the MALDI-TOF mass spectrum,
+
the molecular ion peak appeared at m/z 3541.41 (M+Na) and the
structure of the dendrimer 3 was further confirmed from spectral
3
2
and analytical data.
Figure 3 shows fluorescence spectra of dendrimers 1–3 in DMSO
and the fluorescence parameters for these compounds are col-
lected in Table 2. As shown in Figure 3, on excitation at 324 nm,
the dendrimers 1–3 give emission bands at 374 nm due to the
quinoline units. It is clear from Figure 3, the fluorescence intensity
of the chiral dendrimers increases as the generation grows, which
is consistent with the increased number of fluorophoric quinoline
X
Cl
O
O
3
6
units, otherwise known as multivalency effect in dendrimer
chemistry. The fluorescence quantum yields U of dendrimers 1–
N
N
i
N
N
f
iii
2
N
N
3 have been measured in DMSO using anthracene as the standard.
The quantum yields of dendrimers 1–3 are listed in Table 2. As the
generation increases, the quantum yield decreases consistently.
To further prove the observed decrease in the quantum yield we
have carried out fluorescence lifetime measurement by exciting the
sample at 295 nm using time correlation single photon counting
method. Lifetime of all the three dendrimers shows biexponential
decay as shown in Figure 4. Lifetime values with their relative ampli-
tudes are given in Table 3. The average lifetime of the dendrimers is
found to be lower with increasing length of the dendritic arm, which
is in good agreement with the observed decrease in fluorescence
quantum yield of dendrimers 1–3. The observed biexponential
O
O
1
0
N
OMe
ii
MeO
1 X = Cl
2 X = N3
N
1
1
Scheme 2. Synthesis of dendrimer 2. Reagents and conditions: (i) 2 equiv 2-
methoxy-3-azidomethylquinoline 8, CuSO (5 mol %), sodium ascorbate
ꢁ5H
10 mol %), H O/THF (1:3), rt, 10 h, 11, 80%; (ii) 1.5 equiv NaN , DMF, 60 °C, 6 h,
2, 83%; (iii) 0.5 equiv bis(propargyloxy)-S-(ꢀ)-BINOL 9, CuSO ꢁ5H O (5 mol %),
sodium ascorbate (10 mol %), H O/THF (1:3), rt, 10 h, 2, 78%.
4
2
O
(
2
3
1
4
2
2

4
368
P. Rajakumar, R. Raja / Tetrahedron Letters 51 (2010) 4365–4370
X
O
O
N
N
i
N
N
iii
12
+
10
3
N
N
N
O
N
N
O
N
N
N
O
N
O
N
N
OMe
MeO
N
N
N
N
N
MeO
OMe
N
N
1
3 X = Cl
ii
1
4 X = N3
Scheme 3. Syntheis of dendrimer 3. Reagents and conditions: (i) CuSO
4
ꢁ5H
2
O (5 mol %), sodium ascorbate (10 mol %), H
O/THF (1:3), rt, 10 h, 3, 72%.
2 3
O/THF (1:3), rt, 10 h, 13, 75%; (ii) 1.5 equiv NaN ,
DMF, 60 °C, 6 h, 14, 79%; (iii) 9, CuSO
4
ꢁ5H
2
O (5 mol %), sodium ascorbate (10 mol %), H
2
Table 1
Specific rotation of chiral quinoline dendrimers 1–3
3000000
3
Compound
Mass calculated
25
D
Molar rotation
½aꢂ
2
2
1
500000
000000
500000
2
1
2
3
790.03
1700.64
3521.33
ꢀ41.40
ꢀ24.97
ꢀ16.65
ꢀ327.07
ꢀ424.64
ꢀ586.30
1
Table 2
1000000
500000
0
ꢀ
5
Photophysical properties data for chiral dendrimers 1–3 in DMSO (1 ꢃ 10 mol/L)
4
Compound
k
abs max (nm)
e
(mol/L) (ꢃ10 )
k
em max (nm)
U
F
1
272
3
3
272
3
3
272
3
3
1.74
1.12
1.33
2.64
1.62
1.85
4.94
3.02
3.39
374
374
374
0.65
0.60
0.49
12
24
2
3
350
400
450
500
550
600
12
24
Wavelength, nm
Figure 3. Fluorescence spectra of the chiral dendrimers 1–3 in DMSO
(1 ꢃ 10ꢀ5 mol/L).
12
24
0
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
.0
1
0000
1
3
1
000
3
100
2
10
1
1
3
13
23
33
43
Time, ns
53
63
73
83
93
2
75
300
325
350
375
400
Wavelength (nm)
Figure 4. Fluorescence decay curve for the dendrimers 1–3 in DMSO. The excitation
wavelength is 295 nm.
Figure 2. Absorption spectra of chiral dendrimers 1–3 in DMSO (1 ꢃ 10ꢀ5 mol/L).

P. Rajakumar, R. Raja / Tetrahedron Letters 51 (2010) 4365–4370
4369
Table 3
2007, 15, 1280; (b) Moret, V.; Laras, Y.; Cresteil, T.; Aubert, G.; Ping, D. Q.; Di, C.;
Barthelemy-Requin, M.; Beclin, C.; Peyrot, V.; Allegro, D.; Rolland, A.; Angelis, F.
D.; Gatti, E.; Pierre, P.; Pasquini, L.; Petrucci, E.; Testa, U.; Kraus, J. Eur. J. Med.
Chem. 2009, 44, 558.
Fit parameters for fluorescence decay curves shows in Figure
4
in DMSO
avg (ns)
1 ꢃ 10ꢀ mol/L)
5
(
2
Compound
s
1
(ns)
B
1
s
2
(ns)
B
2
v
s
13. Kwon, T. W.; Alam, M. M.; Jenekhe, S. A. Chem. Mater. 2004, 16, 4657.
1
1
1
1
4. Tsukube, H.; Suzuki, Y.; Paul, D.; Kataoka, Y.; Shinoda, S. Chem. Commun. 2007,
533.
5. (a) Shen, L.; Li, F.; Sha, Y.; Hong, X.; Huaung, C. Tetrahedron Lett. 2004, 45, 3961;
b) Kikkeri, R.; Hossain, L. H.; Seeberger, P. H. Chem. Commun. 2008, 2127.
6. (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004;
b) Tornoe, C. M.; Christensen, C.; Maldal, M. J. J. Org. Chem. 2002, 67, 3057.
7. (a) Subbaraman, R.; Ghassemi, H.; Zawodzinski, T. A., Jr. J. Am. Chem. Soc. 2007,
129, 2238; (b) Martwiseta, S.; Woudenberga, R. C.; Granados-Focila, S.;
Yavuzcetinb, O.; Yuominenb, M. T.; Coughlin, E. B. Solid State Ionics 2007,
1
2
3
1.48
3.24
3.82
29.27
67.78
79.45
26.27
21.27
16.32
70.73
32.22
20.55
1.09
1.18
1.11
19.01
9.05
6.39
2
(
(
fluorescence decay is probably due to the presence of two fluoro-
phoric units viz. BINOL and quinoline and decay time is due to
the quinoline moiety, which increases together with their relative
s
1
1
78, 1398.
18. Aravinda, T.; Bhojya Naik, H. S.; Prakash Naik, H. R. Int. J. Pept. Res. Ther. 2009,
15, 273.
amplitude as the number of quinoline unit increases from zero to
19. (a) Lee, J. W.; Kim, B. K.; Hen, S. C.; Kim, J. H. Bull. Korean Chem. Soc. 2009, 30,
second generation. The
and the decay time and its amplitude has decreased because of ex-
cess crowding in G generation. The number of BINOL unit remains
the same in all the dendrimers. Only when the generation increases
the crowding increases from G to G and hence biexponential decay
2
s decay time could be due to BINOL unit
1
3
57; (b) Li, Z.; Yu, G.; Wu, W.; Liu, Y.; Ye, C.; Qin, L. Z. Macromolecules 2009, 42,
864; (c) Shen, X.; Liu, H.; Li, Y.; Liu, S. Macromolecules 2008, 41, 2421; (d)
2
Elmer, S. L.; Man, S.; Zimmerman, S. C. Eur. J. Org. Chem. 2008, 3845.
0. (a) Rajakumar, P.; Ananthan, R.; Kalpana, V. Synlett 2009, 1417; (b) Rajakumar,
P.; Raja, S. Synth. Commun. 2009, 39, 3888.
2
2
0
2
1. Ma, L.; Lee, S. J.; Lin, W. Macromolecules 2002, 35, 6178.
is observed. Therefore, the decreased quantum yield and lifetime are
attributed to self-quenching effect and the enhancement of nonradi-
ative transition in the higher generation dendrimers compared to
the lower generations.
22. Liu, G.-H.; Fan, Q.-H.; Yang, X.-Q.; Chen, X.-M. ARKIVOC 2003, ii, 123.
23. (a) Bandyopadhyaya, A. K.; Sangeetha, N. M.; Maitra, U. J. Org. Chem. 2000, 65,
8239; (b) Pu, L. Chem. Rev. 1998, 98, 2405.
2
2
4. Meth-Cohn, O.; Narine, B.; Tarnowski, B. Tetrahedron Lett. 1979, 33, 3111.
5. Kuethe, J. T.; Wong, A.; Qu, C.; Smitrovich, J.; Davies, I. W.; Hughes, D. L. J. Org.
Chem. 2005, 70, 2555.
In conclusion, synthesis of 1,2,3-triazole-linked chiral quinoline
dendrimers has been achieved by click reaction. Though, UV absorp-
tion and emission spectra did not show the changes in absorptionand
emission bands, the molar extinction coefficients and fluorescence
intensity increased with increase in dendrimer generation due to in-
crease in the number of quinoline surface group. Fluorescence quan-
tum yield and lifetime were found to be lower for the higher
generations due to self-quenching effect and the enhancement of
nonradiative transitions. The detailed biological activities and the
use of such dendrimers for the cleavage of DNA are underway.
2
6. General procedure for the Cu-catalyzed Huisgen click reaction: acetylenic
derivative (1.0 mmol) was added to dendritic azide (2.0 mmol) in a mixture
of THF and water (3:1) solution. Solid sodium ascorbate (10 mol %) was added
to the reaction mixture, followed by the addition of CuSO
reaction mixture was stirred overnight at rt. The solvent was evaporated under
reduced pressure and the crude product was dissolved in EtOAc (100 mL),
4
ꢁ5H
2
O (5 mol %). The
washed with NH
4 2
Cl solution (50 mL), brine solution (50 mL), H O (100 mL),
dried (Na SO ), and concentrated. Evaporation of the solvent afforded the
2
4
residue which was purified by column chromatography (silica gel) with CHCl
MeOH (99.7:0.3) as eluent to give the corresponding triazole.
3
/
)
8: pale yellow liquid; yield: 81%; 1H NMR: (300 MHz, CDCl
0 2 3
7. Azide [G ]–CH –N
2
3
d 4.05 (s, 3H); 4.14 (s, 2H); 7.33 (t, 1H, J = 7.5 Hz); 7.56 (t, 1H, J = 7.7 Hz); 7.66
d, 1H, J = 7.8 Hz); 7.79 (t, 1H, J = 8.1 Hz); 7.88 (s, 1H). 13C NMR: (75 MHz,
CDCl ) d 50.1, 53.6, 120.1, 124.3, 124.9, 127.0, 127.4, 129.7, 137.2, 146.2, 160.1.
MS (ESI): m/z = 215.1 [M+1]. Anal. Calcd for C11 O: C, 61.67; H, 4.71; N,
6.15. Found: C, 61.56; H, 4.79; N, 26.24.
28. First generation dendritic azide [G ]–CH –N
) d 4.11 (s, 6H); 4.23 (s, 2H); 5.18 (s, 4H); 5.64
s, 4H), 6.56 (s, 2H); 6.60 (s, 1H); 7.39 (t, 2H, J = 7.5 Hz); 7.61–7.68 (m, 4H); 7.71
(
3
Acknowledgments
10 4
H N
2
The authors thank DST and CSIR, New Delhi, India, for financial
assistance and DST-FIST for providing NMR facilities to the depart-
ment. R.R. thanks DST, New Delhi for fellowship and National center
for ultra fast process, University of Madras, for fluorescence studies.
1
2
3
12: white solid; yield: 83%; mp:
1
1
58 °C; H NMR: (300 MHz, CDCl
3
(
(
13
3
s, 2H), 7.81 (s, 2H); 7.85 (d, 2H). C NMR: (75 MHz, CDCl ) d 49.2, 53.8, 54.6,
62.1, 101.7, 107.5, 119.1, 123.3, 124.6, 124.8, 127.1, 127.6, 130.2, 137.8, 138.3,
1
C
43.9, 146.6, 159.5, 159.6. MS (ESI): m/z = 670.3 [M+1]. Anal. Calcd for
: C, 62.77; H, 4.67; N, 23.01. Found: C, 62.86; H, 4.61; N, 23.13.
]–CH –N 14: white solid; yield: 79%; mp:
3
18 °C; H NMR: (300 MHz, CDCl ) d 4.10 (s, 12H); 4.17 (s, 2H); 5.09 (s, 12H);
35
31 11 4
H N O
References and notes
2
9. Second generation dendritic azide [G
2
2
3
1
1
1
2
3
.
.
.
(a) Frechet, J. M. J. Science 1994, 263, 1710; (b) Tomalia, D. A. Adv. Mater. 1994,
, 529.
(a) Adronov, A.; Frechet, J. M. J. Chem. Commun. 2000, 1701; (b) Gilat, S. L.;
Adronov, A.; Frechet, J. M. J. Angew. Chem., Int. Ed. 1999, 38, 1422.
(a) Kleiji, A. W.; Gossage, R. A.; Gebbink, R. J. M. K.; Brinkmann, N.; Reijerse, E. J.;
Kragl, U.; Lutz, M.; Speck, A. L.; Koten, V. G. J. Am. Chem. Soc. 2000, 122, 12112;
5.53 (s, 4H), 6.60 (s, 8H); 6.48 (s, 6H); 6.55 (s, 1H); 6.59 (s, 2H); 7.36 (t, 4H,
6
J = 7.1 Hz); 7.58 (d, 2H, J = 6.6 Hz); 7.63 (d, 8H, J = 7.5 Hz); 7.71 (s, 4H); 7.78 (s,
4H); 7.87 (d, 4H, J = 8.4 Hz). 13C NMR: (125 MHz, CDCl
3
) d 49.3, 53.9, 54.1, 54.6,
61.9, 70.0, 101.6, 102.0, 107.4, 107.5, 119.1, 123.1, 123.6, 124.6, 124.8, 126.9,
127.6, 130.2, 136.8, 137.7, 138.3, 143.6, 144.1, 146.5, 159.4, 159.5, 159.8. MS
(ESI): m/z = 1580.5 [M+1]. Anal. Calcd for C83
22.15. Found: C, 62.93; H, 4.59; N, 22.27.
H
73
N
25
O
10: C, 63.07; H, 4.66; N,
30. Dendrimer 1: white solid; yield: 84%; mp: 88 °C; 1H NMR: (300 MHz, CDCl
) d
3
(
2
b) Mager, M.; Becke, S.; Windisch, H.; Denninger, U. Angew. Chem., Int. Ed.
001, 40, 1898.
4
.
(a) Svenson, S.; Tomalia, D. A. Adv. Drug Delivery Rev. 2005, 57, 2106; (b)
Majoros, I. J.; Myc, A.; Thomas, T.; Mehta, C. B.; Baker, J. R., Jr. Biomacromolecules
3.99 (s, 6H); 5.06 (d, 2H, J = 12.6 Hz); 5.15 (d, 2H, J = 12.6 Hz); 5.34 (s, 4H); 6.58
(s, 2H); 7.05 (d, 4H, J = 3.6 Hz); 7.14–7.19 (m, 2H); 7.35–7.40 (m, 4H); 7.45 (s,
2H); 7.53 (d, 2H, J = 8.1 Hz); 7.62–7.67 (m, 4H); 7.71 (s, 2H); 7.87 (d, 2H,
2
006, 7, 572.
J = 8.4). 13C NMR: (125 MHz, CDCl
5
.
.
Wiener, E. C.; Brechbiel, M. W.; Brothers, H.; Magin, R. L.; Tomalia, D. A.;
Lauterbur, P. C. Magn. Reson. Med. 1994, 3, 1.
Kleiji, A. W.; Gossage, R. A.; Gebbink, R. J. M. K.; Brinkmann, N.; Reijerse, E.;
Vogtle, F.; Vicinelli, V.; Ceroni, P.; Maestri, M.; Balzani, V. Angew. Chem., Int. Ed.
3
) d 48.9, 53.7, 63.9, 115.8, 119.1, 120.6,
122.9, 123.9, 124.6, 124.8, 125.3, 126.3, 127.1, 127.6, 127.8, 129.4, 129.4, 130.2,
133.8, 137.8, 144.8, 146.5, 153.5, 159.4.. MS (ESI): m/z = 791.2 [M+1]. Anal.
6
Calcd for C48
14.24.
H
38
N
8
O
4
: C, 72.90; H, 4.84; N, 14.17. Found: C, 72.75; H, 4.90; N,
2
002, 41, 3595.
31. Dendrimer 2: white solid; yield 78%; mp: 106 °C; 1H NMR: (300 MHz, CDCl
7
.
(a) Wang, Q.; Chan, T. R.; Hilgraf, R.; Fokin, V. V.; Sharpless, K. B.; Finn, M. G. J.
Am. Chem. Soc. 2003, 125, 3192; (b) Burley, G. A.; Gierlich, J.; Mofid, M. R.; Nir,
H.; Tal, S.; Eichen, Y.; Carell, T. J. Am. Chem. Soc. 2006, 128, 1398.
(a) Jiuyan, Li.; Liu, Di. J. Mater. Chem. 2009, 19, 7584; (b) Shih-Chen, Lo.; Burn, P.
L. Chem. Rev. 2007, 107, 1097.
3
) d
3.99 (s, 12H); 4.93 (d, 2H, J = 12.6 Hz); 5.01 (d, 2H, J = 11.4); 5.03 (s, 4H); 5.04
(s, 8H); 5.59 (s, 8H); 6.34 (s, 4H); 6.51 (s, 2H); 6.59 (s, 2H); 7.07–7.12 (m, 4H);
7.18–7.23 (m, 2H); 7.31–7.36 (m, 6H); 7.57–7.61 (m, 8H), 7.73 (s, 10H,
8
.
.
J = 9.9 Hz); 7.80 (d, 6H, J = 8.7 Hz). 13C NMR: (75 MHz,CDCl
3
) d 49.2, 53.6, 53.8,
9
(a) Chaudhuri, M. K.; Hussain, S. J. Chem. Sci. 2006, 118, 199; (b) Michael, J. P.
Nat. Prod. Rep. 1997, 14, 605; (c) Jegou, G.; Jenekhe, S. A. Macromolecules 2001,
61.9, 63.8, 101.7, 107.4, 115.9, 119.1, 120.6, 122.5, 123.6, 123.9, 124.6, 124.8,
125.3, 126.4, 127.1, 127.6, 127.9, 129.5, 130.2, 133.9, 136.9, 138.3, 143.6, 145.1,
+
34, 7926.
146.5, 153.6, 159.4, 159.7. MS (MALDI-TOF): m/z = 1723.31 [M+Na] . Anal.
1
0. (a) Hu, H.-Y.; Chen, C.-F. Tetrahedron Lett. 2006, 47, 175; (b) Ghosh, K.; Adhikari,
S. Tetrahedron Lett. 2008, 49, 658.
1. (a) Liang, F.; Xie, Z.; Wang, L.; Jing, X.; Wang, F. Tetrahedron Lett. 2002, 43, 3427;
Calcd For C96
18.13.
80 22
H N O10: C, 67.75; H, 4.74; N, 18.11. Found: C, 67.87; H, 4.83; N,
32. Dendrimer 3: white solid; yield 72%; mp: 106 °C; 1H NMR: (300 MHz, CDCl
)
3
1
(
2
b) Jiang, P.; Zhu, W.; Gan, Z.; Huang, W.; Li, J.; Zeng, H.; Shi, J. J. Mater. Chem.
009, 19, 4551.
d 4.04 (s, 24H); 4.81 (d, 4H, J = 12.9 Hz); 4.90 (d, 4H, J = 7.9 Hz); 4.94 (s, 8H);
5.01 (s, 16H); 5.30 (s, 8H); 5.53 (s, 16H), 6.17 (s, 4H); 6.45 (s, 10H); 6.48 (s,
2H); 6.52 (s, 4H); 7.02 (s, 4H); 7.13–7.21 (m, 2H); 7.32 (t, 8H, J = 7.3 Hz);
7.55–7.60 (m, 20H); 7.64 (s, 8H); 7.67–7.73 (m, 14H); 7.79 (d, 8H,
1
2. (a) Musiol, R.; Jampilek, J.; Kralova, K.; Richardson, D. R.; Kalinowski, D.;
Podeszwa, B.; Finster, J.; Niedbala, H.; Palka, A.; Polanski, J. Bioorg. Med. Chem.

4
370
P. Rajakumar, R. Raja / Tetrahedron Letters 51 (2010) 4365–4370
J = 8.7 Hz). 13C NMR: (125 MHz, CDCl
1.9, 63.7, 101.6, 101.9, 107.3, 107.4, 115.8, 119.1, 120.5, 122.7, 123.4, 123.6,
) d 49.2, 53.5, 53.8, 53.9, 61.7, 61.7,
33. (a) Peerling, H. W. I.; Meijer, E. W. Eur. J. Org. Chem. 1998, 573; (b) Rosini, C.;
Superchi, S.; Peerlings, H. W. I.; Meijer, E. W. Eur. J. Org. Chem. 2000, 61.
34. Chen, Y.-M.; Chen, C.-F.; Xi, F. Chirality 1998, 10, 661.
3
6
1
1
23.9, 124.6, 124.6, 127.9, 129.4, 130.2, 133.8, 136.9, 138.2, 143.5, 143.7,
46.5, 153.5, 159.4, 159.6, 159.7. MS (MALDI-TOF): m/z = 3541.41 [M+Na] .
+
35. Gibson, S. E.; Rendell, J. T. Chem. Commun. 2008, 922.
Anal. Calcd for C192
H, 4.75; N, 20.01.
H
164
N
50
O
22: C, 65.44; H, 4.69; N, 19.88. Found: C, 65.56;
36. Galeazzi, S.; Hermans, T. M.; Paolino, M.; Anzini, M.; Mennuni, L.; Giordani, A.;
Caselli, G.; Makovee, F. Biomacromolecules 2010, 11, 182.