Poly(aryl ether) dendritic structures based on 1,4,8,11-tetraazacyclotetradecane core: Synthesis, characterization, photophysical properties and biological activity

Article abstract of DOI:10.14233/ajchem.2015.18414

This work describes the synthesis of two new dendrimers consisting of a 1,4,8,11-tetraazacyclotetradecane (cyclam) core appended with poly(aryl ether) dendritic structures carrying a donor (4-methyl-7-hydroxycoumarin) on the surface. Its structure was det

Full text of DOI:10.14233/ajchem.2015.18414

Asian Journal of Chemistry; Vol. 27, No. 7 (2015), 2587-2592
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.18414
Poly(aryl ether) Dendritic Structures Based on 1,4,8,11-Tetraazacyclotetradecane
Core: Synthesis, Characterization, Photophysical Properties and Biological activity
2
M. DILEK1,* and O. DILEK BAYINDIR
1Afyon Kocatepe University, Faculty of Engineering, Chemical Engineering Department, Afyonkarahisar, Turkey
2Department of Chemistry, Afyon Kocatepe University, Afyonkarahisar, Turkey
*Corresponding author: Fax: +90 272 2281422; Tel: +90 272 2281423/1112; E-mail: mdilek@aku.edu.tr
Received: 7 July 2014;
Accepted: 17 September 2014;
Published online: 30 March 2015;
AJC-17085
This work describes the synthesis of two new dendrimers consisting of a 1,4,8,11-tetraazacyclotetradecane (cyclam) core appended with
poly(aryl ether) dendritic structures carrying a donor (4-methyl-7-hydroxycoumarin) on the surface. Its structure was determined by 1H
NMR, 13C NMR and elemental analysis. The photophysical properties of the series of poly(aryl ether) dendrimers have been determined
and the effect of the generation number on the absorption and emission properties of the synthesized dendritic structures was investigated.
As the chromophore group number on the surface of the dendritic structure increased, molar absorptivity coefficients and emission
intensities of the structures were found to increase. The prepared dendritic structures were tested for their antimicrobial activity against,
Salmonella typhimurium NRRLB, Micrococcus luteus, Pseudomonas aeruginosa, Enterococcus fecalis ATCC-29212, Bacillus cereus
ATCC-117787, Klepsiella pneumonia, Bacillus subtilis NRS-744, Proteus vulgoris, Yersinia enterolitica and Saccharomyces cereviciae.
Synthesized dendritic structures showed moderate activity against different strains of bacteria.
Keywords: Dendrimers, Photophysics, Absorption spectra, 1,4,8,11-Tetraazacyclotetradecane, Biological activity.
prominent role of this structure within the dendrimer literature.
Indeed, poly(aryl ether) dendritic macromolecules have been
widely used by independent groups for a variety of appli-
cations15-18 and their chemistry19,20 and properties21 are now
well established.
INTRODUCTION
Dendrimers have received considerable attention over the
last 20 years due to the special properties by their unique physical
property and structure, such as highly branched structure,
monodispersed molecular weight, globular and symmetrical
conformation and high density of peripheral functionalities1-6.
These functional groups are reactive, thereby allowing modi-
fication of dendrimers. Their utility as molecular scaffolding
in many applications, e.g., liquid crystals, drug delivery systems,
catalytic nanoreactors and light-harvesting systems7-11.A great
deal of attention has been paid to this class of macromolecules
owing to their new forms of structure organization which
combines the properties of low and high molecular weight
compounds. This utilization arises from the fact that dend-
rimers have the ability to concentrate a high number of end
groups in high concentration in one molecule.
Macrocyclic structures are extremely favorable for metal
complexation and, thus, a large number of macrocyclic ligands
have been synthesized because of their importance in coordi-
nation chemistry. Among the various ligands, the 1,4,8,11-
tetraazacyclotetradecane (cyclam) is one of the most studied
azamacrocycles22-28. 1,4,8,11-Tetraazacyclotetradecane
fourteen membered tetraamine macrocycles show the ability
to complex various transition metal cations and their complexes
are often highly thermodynamically and kinetically stable with
respect to metal ion dissociation29. 1,4,8,11-Tetraazacyclo-
tetradecane and its derivatives have been studied as carriers
of metal ions in antitumor, imaging applications and as anti-
HIV agents30,31. In most cases, the cyclam derivatives contain
pendant functionalities to increase complex stabilities or to
allow attachment of other chemical species to the macrocyclic
structure31.
As the field of dendrimers rapidly grows12, a few key
architectures clearly stand out as the most attractive and best
documented ones within the highly diverse pool of branched
polymers described so far. Poly(aryl ether) dendrimers belong
to this class because the simplicity, reability and flexibility of
their convergent synthesis13,14, together with the commercial
availability of the monomer itself, strongly contribute to the
1,4,8,11-Tetraazacyclotetradecane is commercially avail-
able and its nitrogen atoms can be easily linked to functional
units, thus paving the way to a large variety of derivatives. For

2588 Dilek et al.
Asian J. Chem.
example, dendrons can be appended to the cyclam core. The
synthesis of cyclam-cored dendrimers proceeds via a conver-
gent approach, i.e., by coupling dendrons, containing appro-
priate functional units at the apical location, to the nitrogen
atoms of the cyclam core28.
δ (ppm) = 18.66, 23.99, 50.59, 51.51, 59.06, 70.43, 101.82,
112.01, 112.89, 113.72, 125.58, 127.43, 129.19, 134.11,
140.42, 152.56, 155.18, 161.23, 161.74. Anal. calcd. for
C82H80O12N4: C, 60.29; H, 4.94; N, 3.43; found: C, 61.09; H,
5.16; N, 3.80.
In continuation of our investigations on photoactive
dendritic structures we thought that cyclam could be a suitable
core for constructing dendrimers because they are less affected
by steric constraints. These kinds of structures are promising
candidates for variety of applications. Compounds derived
from cyclams by appending suitable subunits having signaling
functions have been devised to probe the important ionic guests
Synthesis of compound 5: 1,4,8,11-Tetraazacyclotetra-
decane (1 eq., 0.013 g, 0.065 mmol); K2CO3 (40 eq., 0.359 g,
2.600 mmol), compound 3 (4.4 eq., 0.222 g, 0.286 mmol) in
dry chloroform (40 mL) was refluxed under N2 for 72 h. After
cooling, the solution was filtered and filtrate was evaporated.
The residue was partitioned between H2O and CH2Cl2 and the
organic layer was washed with water. The separated organic
layer was evaporated and the product was purified by column
chromatography on silica gel (100: 3.5 CH2Cl2/MeOH) to yield
white solids. Yield, 43 %. mp.: 132 °C. IR (KBr, νmax, cm–1):
1722 (C=O), 1612 (C=C), 1388 (CH3), 1070 (C-N). 1H NMR
(400 MHz, CDCl3): δ (ppm) = 1.83 (s, 4H, CH2), 2.39 (s, 24H,
CH3), 2.54 (s, 8H, CH2N), 2.61 (s, 8H, CH2N), 3.39 (s, 8H,
ArCH2), 4.85 (s, 16H, ArCH2O), 5.07 (s, 16H, OCH2Ar, 6.12
(s, 8H, CH=C, coumarin), 6.42 (s, 4H, ArH, coumarin), 6.68
(d, J = 1.3 Hz, 8H, ArH), 6.82 (d, J = 2.36 Hz, 16H, ArH,
coumarin) 6.93-6.90 (m, 8H, ArH, coumarin), 7.50-7.36 (m,
32H, ArH). 13C NMR (100 MHz, CDCl3): δ (ppm) = 18.66,
44.93, 50.27, 51.69, 59.07, 69.38, 70.11, 100.70, 101.85,
107.65, 112.05, 112.79, 113.79, 125.63, 127.67, 127.75,
135.46, 137.23, 143.25, 152.53, 155.14, 159.70, 161.16,
161.56. Anal. calcd. for C182H160O32N4: C, 74.98; H, 5.53; N,
1.92; found: C, 74.19; H, 5.86; N, 1.71.
Antimicrobial screening: The biological activities of the
dendritic structures were tested against different microorganisms
with CH2Cl2 as the solvent. The sample concentration was 100
mg. In this study, Salmonella typhimurium NRRLB-4420,
Micrococcus luteus, Pseudomonas aeruginosa, Enterococcus
fecalis ATCC-29212, Bacillus cereus ATCC-117787, Klepsiella
pneumonia, Bacillus subtilis NRS-744, Proteus vulgaris, Yersinia
enterocolitica, Saccharomyces cereviciae were used as bacteria.
YEPD medium cell culture was prepared as described by
Connerton38. Ten milliliters of YEPD medium were inoculated
with each cell from plate cultures. Yeast extract 1 % (w/v),
bactopeptone 2 % (w/v) and glucose 2 % (w/v), was obtained
from Difco. Microorganisms were incubated at 35 °C for 24 h.
About 1.5 mL of these overnight stationary phase cultures were
inoculated onto 250 mL of YEPD and incubated at 35 °C until
OD600 reached 0.5. The antibiotic sensitivity of the polymers
was tested with the antibiotic disk assay as described39. Nutrient
agar (NA) was purchased from Merck. About 1.5 mL of each
prepared different cell culture were transferred into 20 mL of
nutrient agar and mixed gently. The mixture was inoculated into
the plate. The plates were rotated firmly and allowed to dry at
room temperature for 10 min. Prepared antibiotic discs (100 mg/
disc) were placed on the surface of the agar medium40. The plates
were kept at 5 °C for 30 min and then incubated at 35 °C for 2
days. If a toxic compound leached out from the disc, it means
that the microbial growth is inhibited around the sample. The
width of this area expressed the antibacterial or antifungal activity
by diffusion. The zones of inhibition of microorganism growth
of the dendritic structures were measured with a millimeter ruler
at the end of the incubation period.
and physical properties of system32-34
.
We have previously reported the synthesized poly(aryl
ether) dendritic structures 1 and 2 bearing chromophore
peripheral groups and via convergent methods and to determine
their photophysical properties and fluorescence quantum
yields35. Recently, we have synthesized two new dendrimers
consisting of a calix[4]arene and we have carried out photo-
physical investigations36,37. In this paper, we report the synthesis
of two new dendrimers consisting of a cyclam core and carried
out photophysical and biological activity of the dendrimers.
EXPERIMENTAL
All commercially available reagents were used without
further purification. K2CO3 was activated by heating at 150 °C
overnight under vacuum and stored in a desiccator. Column
chromatography was carried out with Merck silica gel 70-230
mesh. Preparative TLC plates were Merck aluminum sheets
covered with silica gel 60 F254. The FTIR spectra were recorded
via the KBr pellet method by using a Perkin-Elmer 1605 FTIR
1
spectrophotometer. H NMR and 13C NMR spectra were
recorded on a BRUKER DPX-400 High Performance Digital
FT NMR, with tetramethyl silane (TMS) as the standard. The
compounds were characterized by an ElementarVario CHNS-
932 (LECO) elemental analysis instrument. UV-visible
absorption spectra were measured using a Shimadzu UV-1700
Pharma spectrophotometer. The photoluminescence were
recorded on a VARIAN CARY ECLIPSE Fluorescence
spectrophotometer.
Synthesis of compound 4: 1,4,8,11-Tetraazacyclotetra-
decane (1 eq., 0.032 g, 0.160 mmol); K2CO3 (40 eq., 0.885 g,
6.400 mmol), 4-(4-methylcoumarin-7-yl-oxymethyl)benzyl-
bromide 1 (4.4 eq. , 0.253 g, 0.704 mmol) in dry chloroform
(50 mL) was refluxed under N2 for 72 h. After cooling, the
solution was filtered and filtrate was evaporated. The residue
was partitioned between H2O and CH2Cl2 and the organic layer
was washed with water. The separated organic layer was evapo-
rated and the product was purified by column chromatography
on silica gel (100:3.5 CH2Cl2/MeOH) to yield white solids.
Yield, 59 %. m.p.: 139 °C. IR (KBr, νmax, cm–1): 1733 (C=O),
1
1611 (C=C), 1390 (CH3), 1070 (C-N). H NMR (400 MHz,
CDCl3): δ (ppm) = 1.78 (t, 4H, J = 10 Hz, CH2), 2.4 (d, 12H,
J = 0.88 Hz, CH3), 2.55 (t, 8H, J = 6.4 Hz, CH2N), 2.62 (s, 8H,
CH2N), 3.47 (s, 8H, Ar-CH2), 5.09 (s, 8H, ArOCH2), 6.14 (s,
4H, CH=C), 6.86 (d, J = 2.43 Hz, 4H, ArH, coumarin), 6.95-
6.92 (m, 4H, ArH, coumarin), 7.31 (d, J = 17.72 Hz, 16H, Ar-
H). 7,5 (d, 4H ArH, coumarin). 13C NMR (100 MHz, CDCl3):

Vol. 27, No. 7 (2015)
Poly(aryl ether) Dendritic Structures Based on 1,4,8,11-Tetraazacyclotetradecane Core 2589
in the presence of excess NEt3 at -10 °C35. Following a standard
RESULTS AND DISCUSSION
convergent strategy, in the presence of K2CO3, cyclam was
The synthesis initially involves the preparation of 4-(4-
methylcoumarin-7-yl-oxymethyl)benzylbromide 1 and
compounds 2, 3 according to the literature procedures35
(Scheme-I). Under typical Williamson ether synthesis
conditions in the presence of K2CO3, 1,4-bis(bromomethyl)-
benzene was reacted with 4-methyl-7-hydroxycoumarin to
synthesize compound 1 in a yield35 of 41 %. Following a stan-
dard convergent strategy, the first generation of benzyl alcohol
(compound 2) was prepared in 68 % yield through a coupling
reaction of compound 1 and 3,5-dihydroxybenzyl alcohol
monomer (Scheme-I)35. Compound 2 was converted to the
compound 3 in 78 % yield using methane sulphonyl chloride
reacted compound 1 in chloroform at reflux temperature to
give compound 4 in 59 % yield (Scheme-II). The H NMR
1
spectrum of compound 4 reflects several characteristic features
of both cyclam and compound 1 systems: (i) the presence of
two triplets and one singlet due to methylene groups (1.78,
2.55, 2.62 ppm, respectively) of cyclam; (ii) the presence of
two singlet of ArCH2 and ArOCH2 groups at 3.47 and 5.09
ppm, respectively being clear evidence for a tetra-substituted
conformation of cyclam. All in accordance with proposed
structure of the whole system.
Following a standard convergent strategy, in the presence
of K2CO3, cyclam was reacted compound 3 in chloroform at
CH3
CH3
CH3
CH3
O
CH3
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Br
HO
OSO2CH3
3
1
2
Scheme-I
CH3
O
CH3
O
O
O
O
O
O
CH3
O
H
H
H
H
N
N
N
N
N
N
K2CO3
O
4.4
dry CHCl3
reflux, 72 h
N
N
CH3
CH3
O
Br
O
O
O
O
O
4
1
Scheme-II: Synthesis of dendrimer compound 4

2590 Dilek et al.
Asian J. Chem.
reflux temperature to give compound 5 in 43 % yield (Scheme-
III). The H NMR spectrum of compound 5 reflects several
Photophysical properties: The investigated dendritic
structures compounds 4 and 5 consist of four 4-methyl-7-
hydroxycoumarin units (compound 4), eight 4-methyl-7-
hydroxycoumarin units (compound 5), respectively. The absor-
ption and fluorescence emission spectra of these compounds
have been investigated35 in CH2Cl2. In these measurement
1 × 10-5 M solutions of each compound was used. Fig. 1 illus-
trates the absorption properties of the dendrimers consisting
of a cyclam core compounds 4 and 5.Accordingly, the spectra
1
characteristic features of both cyclam and compound 1 systems:
(i) the presence of three singlet due to methylene groups (1.83,
2.54, 2.61 ppm, respectively) of cyclam; (ii) the presence of
three singlet of ArCH2 and ArCH2O, OCH2Ar groups at 3.39,
4.85 and 5.07 ppm, respectively being clear evidence for a
tetra-substituted conformation of cyclam. All in accordance
with proposed structure of the whole system.
CH3
CH3
O
O
O
O
O
O
H
H
H
H
N
N
N
N
K2CO3, dry CHCl3
reflux, 72 h
+
O
O
4.4
OSO2CH3
CH3
H3C
3
OO
O
O
O
O
CH3
O
H3C
O
O
O
O
O
O
O
O
O
N
N
N
N
O
O
O
O
O
O
O
O
O
O
CH3
H3C
O
O
O
O
OO
5
CH3
H3C
Scheme-III: Synthesis of dendrimer compound 5

Vol. 27, No. 7 (2015)
Poly(aryl ether) Dendritic Structures Based on 1,4,8,11-Tetraazacyclotetradecane Core 2591
1.800
600
Compd.
5
1.500
1.000
0.500
400
200
0
Compound
5
Compd.
4
350
400
450
500
550
Wavelength (nm)
Compound
4
Fig. 2. Emission spectra of dendrimers having cyclano core compounds 4
and 5 in CH2Cl2
Ciprolfoxacin, Chloramphenicol, Eritromycin, Penicillin G and
Amikacin and under the same conditions. The data reported
in Table-1 and are the average data of three experiments. The
results show that the investigated dendritic structures have
moderate biological activity comparable with that of standard
drugs such as Ciprolfoxacin, Chloramphenicol, Eritromycin,
Penicillin G and Amikacin. These results may be traced to
nitrogene content of this dendritic structures. As expected
compound 4 is less effective to inhibit the growth of micro-
organisms. Although the nitrogen content of the dendritic
structures are the same compound 4 is less effective to inhibit
the growth of microorganisms.Although the lipophilic portion
of the substance is important to biological function in general,
the polar group contributes to biological activity. Thus, the
activity of these compounds may allow to design antimicrobial
systems specifically effective against certain microorganisms
and for probably certain health care a great deal of practical
applications.
0
257
300
Wavelength (nm)
350 360
Fig. 1. Adsorption spectra of dendrimers having cyclan core compounds 4
and 5 in CH2Cl2
of these compounds show absorption maximum in the 288,
320 nm. As expected, an increase in the generation number
leads an increase in the number of the peripheral chromophores
and doubles the absorption from one to the next. Hence, with
increasing generation number, the amount of light that the
peripheral antenna is capable of harvesting is dramatically
enhanced. Compound 4 contains 4-methyl-7-hydroxycoumarin
and benzene chromophoric groups. Compound 5 contains
dimethoxybenzene unit additionally. It is concluded that the
absorption spectra of the examined compounds are those
expected from the spectra of the component chromophoric
units. Fig. 2 illustrates the emission properties of the dend-
rimers consisting of a cyclam core (compounds 4 and 5). In
these measurement 1 × 10-5 M solutions of each compound
was used. Excitation of the dendrimers at λmax = 320 nm (maxi-
mum absorption wavelength for peripheral chromophore)
resulted in emissions at 381 nm (compound 4), 384 nm (com-
pound 5).
Conclusion
We have synthesized two new dendritic structures bearing
cyclam as a core through convergent synthetic strategy. It can
be seen from the absorption and emission spectra (Figs. 1, 2)
that as the number of peripheral chromophores double from
one generation to the next, the amount of absorbed and emitted
light also nearly doubles35. The synthesized dendritic structures
have good biological activity comparable with that of standard
drugs as Ciprolfoxacin, Chloramphenicol, Eritromycin,
Penicillin G and Amikacin.
Antimicrobial activity of the dendritic structures: The
dendritic structures thus obtained, were tested against different
microorganisms that are commonly employed in biodegra-
dability examinations. The results were standardized against
In conclusion, cyclam (1,4,8,11-tetraazacyclotetradecane)
can be easily functionalized with dendrons at each one of its
TABLE-1
ANTIMICROBIAL EFFECTS OF THE COMPOUNDS (mm OF ZONES)
Standards of antibiotic discs
Compound 4
Compound 5
CIPS
32
-
-
32
-
C30
28
-
-
0
E15
P10
4
-
-
8
-
AM10
100 µg
11
10
13
16
100 µg
14
16
17
22
Salmonella typhimurium
Micrococcus luteus
Pseudomonas aeruginosa
Enterococcus fecalis
Bacillus cereu
9
-
-
-
-
-
19
-
-
11
-
-
36
12
20
19
24
Klepsiella pneumonia
Bacillus subtilis
Proteus vulgoris
Yersinia enterocolitica
Saccharomyces cereviciae
39
-
-
20
-
18
12
19
11
24
14
23
15
36
-
31
32
-
34
6
-
-
0
-
-
-
CIPS (Ciprolfoxacin), C30 (Chloramphenicol), E15 (Eritromycin), P10 (Penicillin G.), AM10 (Amikacin)

2592 Dilek et al.
Asian J. Chem.
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ACKNOWLEDGEMENTS
The authors thank Afyon Kocatepe University Research
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