Synthesis of azabicyclo[4.2.0]octa-1,3,5-trien-8-one analogues of 1H-imidazo[4,5-c]quinoline and evaluation of their antimicrobial and anticancer activities

Article abstract of DOI:10.1007/s00044-013-0885-9

In search of new and efficient antimicrobial and anticancer agents based on the imidazoquinoline structural framework, a series of novel 7-(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)-7-Azabicyclo[4.2.0]octa-1,3, 5-trien-8-ones (8a-f) were synthesized from the corresponding 2,4-dihydroxoquinoline derivative through multistep reactions. The structures of these compounds were established by IR, ¹H NMR, ¹³C NMR and mass spectral studies. The 7-(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)-7- Azabicyclo[4.2.0]octa-1,3,5-trien-8-one (8a-f) analogues were evaluated for their in vitro antimicrobial activity by serial dilution method minimum inhibitory concentration (MIC). The derivatives 8c, 8e and 8f exhibited excellent antibacterial activity comparable to the parent drug ampicillin with MIC value. Compounds 7a-f and 8a-f were also assessed for their cytotoxic activity (IC₅₀) against HeLa cells using the Trypan blue exclusion assay method. The compounds 7c and 8b displayed potential anticancer activity. In a molecular docking study, these compounds showed minimum binding energy and good affinity towards the active pocket. They are believed to be good inhibitors of β-tubulin. The results of these studies provided evidence that 7-(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)-7-Azabicyclo[4.2.0]octa-1,3, 5-trien-8-one (8a-f) derivatives are a promising class of antibacterial and anticancer agents.

Full text of DOI:10.1007/s00044-013-0885-9

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-013-0885-9
ORIGINAL RESEARCH
Synthesis of azabicyclo[4.2.0]octa-1,3,5-trien-8-one analogues
of 1H-imidazo[4,5-c]quinoline and evaluation of their
antimicrobial and anticancer activities
•
•
•
Reshma Kayarmar G. K. Nagaraja Manjunath Bhat Prashantha Naik
•
•
K. P. Rajesh Suchetha Shetty T. Arulmoli
•
Received: 5 April 2013 / Accepted: 18 November 2013
Ó Springer Science+Business Media New York 2013
Abstract In search of new and efficient antimicrobial and
anticancer agents based on the imidazoquinoline structural
(IC50) against HeLa cells using the Trypan blue exclusion
assay method. The compounds 7c and 8b displayed
potential anticancer activity. In a molecular docking study,
these compounds showed minimum binding energy and
good affinity towards the active pocket. They are believed
to be good inhibitors of b-tubulin. The results of these
studies provided evidence that 7-(1-isobutyl-1H-imi-
dazo[4,5-c]quinolin-4-yl)-7-azabicyclo[4.2.0]octa-1,3,5-trien-
8-one (8a–f) derivatives are a promising class of antibacterial
and anticancer agents.
framework,
a series of novel 7-(1-isobutyl-1H-imi-
dazo[4,5-c]quinolin-4-yl)-7-azabicyclo[4.2.0]octa-1,3,5-
trien-8-ones (8a–f) were synthesized from the corre-
sponding 2,4-dihydroxoquinoline derivative through mul-
tistep reactions. The structures of these compounds were
1
established by IR, H NMR, 13C NMR and mass spectral
studies. The 7-(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-
yl)-7-azabicyclo[4.2.0]octa-1,3,5-trien-8-one (8a–f) ana-
logues were evaluated for their in vitro antimicrobial
activity by serial dilution method minimum inhibitory
concentration (MIC). The derivatives 8c, 8e and 8f
exhibited excellent antibacterial activity comparable to the
parent drug ampicillin with MIC value. Compounds 7a–f
and 8a–f were also assessed for their cytotoxic activity
Keywords Imidazoquinoline Á Antimicrobial activity Á
Anticancer activity Á Docking study Á b-Tubulin
Introduction
1H-Imidazo[4,5-c]quinolines are an important class of N-
tricyclic compounds. These compounds are also known as
imidazoquinolines. 1H-Imidazo[4,5-c]quinoline deriva-
tives have been the focus of attention for the chemists for
long a time owing to their wide array of biological activ-
ities, such as antimalarial (Backman et al., 1950), anti-
convulsant and cardiovascular agent (Jain et al., 1968).
Certain imidazoquinoline and tetraimidazoquinoline
compounds containing urea, thiourea, acylurea, sulfonylurea,
amide, sulphonamide, oxime or N-oxide functionalities at the
1-position are said to be useful immunomodulators (Griesgr-
aber, 2004; Coleman et al., 2003, 2000; Krepski et al., 2005).
These compounds act as immune modifiers (in vitro and
in vivo) and demonstrate antiviral and antitumor activities
through endogenous cytokine production (Gilchrist, 1985).
The search for different interferon-inducing compounds led to
the discovery of a series of 1H-imidazo[4,5-c]quinolines that
R. Kayarmar Á G. K. Nagaraja (&) Á M. Bhat
Department of Studies in Chemistry, Mangalore University,
Mangalagangothri 574199, Karnataka, India
e-mail: nagarajagk@gmail.com
R. Kayarmar Á G. K. Nagaraja Á M. Bhat Á T. Arulmoli
SeQuent Scientific Limited, No. 120 A & B, Industrial Area,
Baikampady, New Mangalore 575011, Karnataka, India
P. Naik
Department of Bioscience, Mangalore University,
Mangalagangotri 574199, Karnataka, India
K. P. Rajesh
Department of P.G. Studies and Research in Biotechnology and
Bioinformatics, Kuvempu University, Shankaraghatta 577 451,
Karnataka, India
S. Shetty
B.C. Road Clinical Laboratory, Kaikamba, B.C. Road 574219,
Karnataka, India
123

Med Chem Res
Fig. 1 Structure of imiquimod
(a), BEZ235 (b) and resiquimod
(c)
N
HO
O
NH
O
N
N
N
N
N
N
N
N
NH
2
NH
CN
2
(a)
(b)
(c)
induced interferon and other cytokines (Miller et al., 1999).
1H-Imidazo[4,5-c]quinoline derivatives are frequently used
in antiviral and anti-allergic creams. Drugs with an imidazo-
quinoline moiety include Imiquimod (a), BEZ235 (b) and
Resiquimod (c) Fig. 1.
in DMF (Ramahan, 1999). We carried out the condensation
of 4-chloro-1-isobutyl-1H-imidazo[4,5-c]quinoline (6) with
substituted anthranilic acids in DMF. We observed the
formation of an undesired product that was confirmed by
single crystal study (Loh et al., 2011). The reaction was not
initiated in the absence of DMF. The reaction with methanol
using 1.1 equivalent of DMF gave 2-[(1-isobutyl-1H-imi-
dazo[4,5-c]quinolin-4-yl)amino]benzoic acids (7a–f). The
yield details and reaction conditions are as given in Table 1.
The above-reported literature indicated that a variety of
pharmacological activities of imidazoquinoline are attributable
to variations of substituents at the 1-position of imidazoquin-
oline, which prompted us to develop new imidazoquinoline
condensed azabicyclo[4.2.0]octa-1,3,5-trien-8-ones (8a–f)
having derivatives at the 4-position of 1-isobutyl-1H-imi-
dazo[4,5-c]quinoline and to study their antimicrobial and
anticancer activities.
1
The structures of 7a–f were confirmed by IR, H NMR,
1
13C NMR and mass spectral studies. The H NMR spectra
showed one singlet in the range of d 7.60–8.09 ppm cor-
responding to an NH proton. The carboxylate proton
appeared as a singlet in the range d 12.9–11.9 ppm. The IR
spectra of 7a–f showed a broad absorption band in the range
of 3,500–2,500 cm-1 that was assigned to –OH of acid
groups. The presence of an absorption band at 1,599 cm-1
was due to a C=O group. The molecular ion of the com-
pounds 7a–f was consistent with the molecular formula.
The final compounds 8a–f were prepared by the cycli-
sation of 7a–f using POCl3. The absence of -OH stretching
bands in the range of 3,500–2,500 cm-1 in the IR spectra
of compounds 8a–f confirmed the cyclised structure. In 1H
NMR spectra, the absence of two singlets due to COOH
and NH protons (d 12.9–11.9 and d 8.09–7.56, respec-
tively) confirmed the cyclised structure. The yields of
compounds 8a–f are tabulated in Table 2. The molecular
ions of compounds 8a–f were accordance with their
molecular formula.
In silico molecular docking techniques play an important
role in drug design and discovery to predict the conforma-
tions of each ligand molecule at the active site. Therefore,
the in silico molecular docking studies of newly synthesized
compounds were carried out to predict b-tubulin inhibitory
activity and the results are reported in Fig. 2.
Results and discussions
Chemistry
Compounds 7-[1-(2-methylpropyl)-1H-imidazo[4,5-c]quino-
lin-4-yl]-7-azabicyclo octa-1,3,5-trien-8-one (8a–f) were pre-
pared starting from substituted 2-[(1-isobutyl-1H-imidazo
[4,5-c]quinolin-4-yl)amino]benzoic acids (7a–f). Compounds
7a–f were synthesized from the corresponding 4-chloro-1-
isobutyl-1H-imidazo[4,5-c]quinoline (6). Compound (6) was
prepared from 2,4-dihydroxoquinoline as described in the
literature. The structure of 4-chloro-1-isobutyl-1H-imidazo
[4,5-c]quinoline (6) was confirmed by spectral studies and
elemental analyses. The 1H NMR of 4-chloro-1-isobutyl-1H-
imidazo [4,5-c]quinoline (6) showed a signal at d 7.9 ppm
corresponding to the imidazole ring proton. In the IR spectrum,
the NH2 absorption band (3,350 cm-1) was absent, confirming
the structure. A mass spectrum of 4-chloro-1-isobutyl-1H-im-
idazo [4,5-c]quinoline (6) exhibited the molecular ion peak at
m/z 260.7, confirming the molecular weight.
The cyclisation of compounds 7a–f was also carried out
using fused sodium acetate and polyphosporic acid. The
results showed that the yields were not significantly
improved even by increasing the reaction time and
increasing the mole ratio of cyclising agents (Table 3).
Biological evaluations
Antibacterial activity
The antibacterial activity of all the newly synthesized
compounds 8a–f were evaluated against the Gram-positive
bacteria: Staphylococcus aureus (ATCC25923) and Bacil-
lus subtilis (ATCC 1633), and the Gram-negative bacteria:
According to the literature, the condensation of primary
amines with 4-chloro quinoline derivatives was carried out
123

Med Chem Res
Fig. 2 Sequential steps in the synthesis of 7-(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)-7-azabicyclo[4.2.0]octa-1,3,5-trien-8-ones (8a–f)
123

Med Chem Res
Table 1 The reaction of 4-chloro-1-isobutyl-1H-imidazo[4,5-c]quin-
oline with substituted anthranilic acid
Table 4 In vitro antibacterial activity of analogues 7a–f and 8a–f
Compounds
no.
S. aureus
(ATTC-
25923)
B. subtills
(ATTC-
1633)
E. coli
(ATTC-
5922)
P. aeruginosa
(ATTC-
27853)
Entry
R
DMF
Time (h)
Yield (%)
7a
7b
7c
7d
7e
7f
H
1.1
1.1
1.1
1.1
1.1
1.1
72
72
72
72
72
72
94
80
70
76
73
73
7a
7b
7c
50
50
50
50
3-Br
5-Br
4-Cl
5-Cl
5-I
25
25
25
25
25
50
50
50
7d
7e
25
50
50
50
25
50
50
50
7f
25
50
50
50
8a
8b
8c
25
50
50
50
Table 2 The cyclisation of compounds 7a–f using POCl3
25
50
50
50
Entry
R
mol
Yield (%)
6.25
25
12.5
25
6.25
25
12.5
25
8d
8e
8a
8b
8c
8d
8e
8f
H
3
3
3
3
3
3
90
90
75
90
79
70
6.25
6.25
0
12.5
12.5
0
6.25
6.25
0
12.5
12.5
0
3-Br
5-Br
4-Cl
5-Cl
5-I
8f
DMF
Ampicillin
(standard)
6.25
12.5
12.5
3.125
MIC minimum inhibition concentration was evaluated in lg/ml
mol of POCl3 used for cyclisation
phenyl ring, respectively, showed improved biological activity
against various pathogens when compared to the uncyclised
derivatives 7c, 7e and 7f. The results are tabulated in Table 4.
Table 3 Cyclisation of 7a–f using fused sodium acetate and poly-
phosphoric acid
Entry
Cyclising agents
mol
Time (h)
Yield (%)
Antifungal activity
1
2
3
4
Fused sodiumacetate
Fused sodiumacetate
PPA
3
6
3
6
8
8
6
6
10
35
10
45
Newly synthesized compounds were also tested for their
antifungal activity against Penicillium marneffei (recul-
tured), Trichophyton mentagrophytes (recultured), Asper-
gilus flavus (NICM No.524) and Aspergilus fumigates
(NCIM No.902) by the serial dilution method (Khan, 1997;
Varma, 1998). Sabourauds agar media [prepared by dis-
solving peptone (1 g), D-glucose (4 g) and agar (2 g) in
distilled water (100 ml) and adjusting the pH to 5.7] was
used as the medium for fungal growth. Normal saline was
used to make the spore suspension of fungal strains. The
test compounds were dissolved in DMF. Itraconozole was
taken as the standard drug for antifungal screening.
PPA
mol of sodium acetate, polyphosphoric acid used for cyclisation
Escherichia coli (ATTC-25922) and Pseudomonas aeru-
ginosa (ATTC-27853). The antibacterial activity was
measured by minimum inhibitory concentration (MIC) using
the serial dilution method (Mackie and McCartney, 1989).
The test compounds were dissolved in serially diluted DMF,
then a standard drop of culture prepared for assay was added
to each of the dilutions and incubated for 16–18 h at 37 °C.
Ampicillin was used as the standard drug.
The results of antifungal activity clearly indicated that
8c, 8e and 8f have a similar efficacy against P. marneffei
and Trichophyton mentagrophytes with an MIC value of
6.25 lg/ml. The other derivatives showed moderate anti-
microbial activity against all the tested microbial strains. It
was noted that the activity of uncyclised products 7c, 7e
and 7f were increased significantly after cyclisation.
Compound 7b showed similar activity after cyclisation to
8b with MIC values of 12.5–25 lg/ml. It may be gen-
eralized from the antifungal activity that uncyclised acids
showed high efficacy after the formation of a four-member
ring that resembled the lactam ring. The ortho-substituted
uncyclised acid 7b and its cyclised derivative 8b showed
From the results of the antibacterial screening, it was
clear that the compounds 8c, 8e and 8f showed significant
activity against different bacterial strains. The compounds
8c, 8e and 8f showed equipotent activity against S. aureus
and B. subtilis with MIC values 6.25 and 12.5 lg/ml, which
is comparable to the standard drug Ampicillin. Compounds
8c, 8e and 8f also exhibited excellent activity against E. coli
with an MIC value of 6.25 lg/ml. Compounds 7a–f, 8a, 8b
and 8d were less active against all the tested bacterial strains
when compared to the Ampicillin.
The antibacterial evaluation clearly indicated that the deriv-
atives 8c, 8e and 8f with Br, Cl and I in the 3-position of the
123

Med Chem Res
Table 5 In vitro antifungal
activity of analogues 7a–f and
8a–f compounds
Compounds no.
P. marneffei
(recultred)
T. mentagrophytes
(recultured)
A. flavus
(NICM No. 524)
A. fumigates
(NCIM No. 902)
7a
7b
7c
50
50
50
50
12.5
25
12.5
25
25
25
25
25
7d
7e
50
50
12.5
25
12.5
25
25
25
7f
25
25
12.5
12.5
25
12.5
12.5
25
8a
8b
8c
25
25
12.5
6.25
50
12.5
6.25
50
6.25
50
6.25
50
8d
8e
6.25
6.25
0
6.25
6.25
0
25
50
8f
50
50
DMF
0
0
MIC minimum inhibition
concentration was evaluated in
lg/ml
Itraconozole
(standard)
6.25
6.25
3.125
1.56
equipotent activity when compared to para- and meta-
substituted acids. The results are summarized in Table 5.
was mixed with 50 ll of 0.4 % trypan blue dye and left for
1–2 min at room temperature. The stained and unstained
cells were counted using a haemocytometer and the per-
centage of dead cells was determined (Freshney, 2006).
Among the screened compounds, 7c and 8b were found to
show high anticancer activity towards HeLa cells. Com-
pounds 7b, 7d, 8c, 8d and 8e exhibited moderate cytotox-
icity. The position of bromo and chloro derivatives had
greatly affected the cytotoxicity after cyclisation, which
could be clearly seen from the result. The 4-chloro uncyc-
lised product showed better activity compared to cyclised
moiety 8d. The current cytotoxic evaluation suggested that
the presence of the chloro and bromo groups in 4-chloro-2-
[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)amino]benzoic
acid 7d and 3-bromo-7-[1-(2-methylpropyl)-1H-imidazo
[4,5-c]quinolin-4-yl]-7-azabicyclo[4.2.0]octa-1,3,5-trien-8-
one 8b, respectively, at particular positions enhance the
cytotoxicity against human cervical cancer cells (HeLa). In
comparison, the IC50 values obtained from the recommended
drug candidates 7c and 8b were approximately fourfold less
potent to the cyclophosphamide. Nevertheless, the efficacy
of any compound cannot compare directly to the conven-
tional drug as it depends on other factors, especially the lethal
toxicity (Trevor et al., 2010). Further studies on the deter-
mination of a therapeutic index based on the comparison
between the amount of the drug candidates for the thera-
peutic effect and median lethal dose in animals can give an
insight into the efficacy of the compounds. In addition,
the mechanism of action is also an important criterion for
the efficacy of the agents as understood by the anti-
cancer drug-screening programme (Boyd and Paull,
1995). Cyclophosphamide metabolizes to phosphoramide
mustard that irreversibly forms DNA crosslinks between
and within DNA strands at guanine N-7 positions, leading
Anticancer activity
All the newly synthesized compounds were evaluated for
their cytotoxic activity using HeLa cells. The anticancer
activity of derivatives 7a–f and 8a–f were measured with
respect to control and compared to the standard drug
Cyclophosphamide. All the pharmacological data were
expressed as IC50 ( SD).
Cell culture
A stock solution of each test compound was prepared in
DMSO at a concentration of 1,000 lg/ml. Initially, a wide
concentration range (1–1,000 lg/ml) of each test compound
was taken. Based on the results from the first range, concen-
trations in a narrower range, i.e. 10–100 lg/ml were used in
the subsequent trial. The selected concentration of each test
compound was dissolved in DMSO. The conventional anti-
cancerdrugCP (0.5–10.0 lg/ml)was usedaspositive control.
Trypan blue exclusion assay
HeLa cells in the exponential growth phase were washed
with phosphate buffered saline solution, trypsinized, and
re-suspended in Dulbecco’s modified Eagle Medium. Cells
were plated at a concentration of 30,000 cells/well in 6
wells. All the plates were incubated at 37 °C in a humidified
incubator with 5 % CO2 for a period of 24 h during which a
partial monolayer was formed. After incubation, the cells
were exposed to the selected concentrations of the test
compounds. At the end of 24 h, 50 ll of the cell suspension
123

Med Chem Res
anticancer activity. Structures of newly synthesized mole-
cules were drawn and analysed using ChemDraw Ultra V
6.0. 3D coordinates were prepared using the Dundee
Table 6 Anticancer activity of test compounds 7a–f and 8a–f against
HeLa cancer cells using trypan blue exclusion assay
Compound no.
IC50 value
31 1.63
PRODRG2
(http://davapc1.bioch.dundee.ac.uk/prodrg/)
7a
server. The protein structural file (PDB ID: 1OJ0) was
retrieved from the PDB (www.rcsb.org/pdb). Protein–ligand
interactive visualization and analysis was carried out in Py-
mol viewer 1.5.4. ADMET property of molecules was
achieved through the Organic chemistry portal (http://www.
organic-chemistry.org/prog), a web-based application for
predicting in silico ADMET property. Molecular docking
was performed using AutoDock V 4.2 on Windows 7 (64-bit)
with Sony VAIO (Intel Core i5-560 M Processor 2.66 GHz,
4 GB memory).
7b
19 1.6
16.4 1.4
7c
7d
17.33 1.25
23.65 2.03
30.33 2.5
46 2.45
7e
7f
8a
8b
16.3 0.45
17.6 0.37
18.1 0.98
18.33 1.27
35.7 1.79
4.2 0.21
8c
8d
8e
8f
Preparation of ligand and macromolecule
Cyclophosphamide
The ligands were drawn in ChemDraw Ultra 6.0 assigned
with proper 2D orientation (ChemOffice package) and the
structure of each ligand was analysed using Chem-3D Ultra
6.0 (ChemOffice package). Energy minimization was per-
formed by employing Dundee PRODRG2. The protein
structure file (PDB ID: 1OJ0) was retrieved from PDB
(www.rcsb.org/pdb) and edited by removing the heteroat-
oms, adding C-terminal oxygen, polar hydrogen and
Gasteiger charges.
Molecular docking
Automated docking was used to determine the orientation
of inhibitors bound in the active site of b-tubulin.
A Lamarckian genetic algorithm method implemented in
the programme AutoDock 4.2 was employed to identify
appropriate binding modes and conformations of the
ligands. For docking calculations, Gasteigere–Marsili par-
tial charges were allotted to the ligands and non-polar
hydrogen were merged. All torsions of the ligands were
allowed to rotate during docking. The grid map was cen-
tred on the active pocket, predicted from the ligplot and
was generated by AutoGrid. The Lamarckian genetic
algorithm, the pseudo-Solis and Wets methods were
applied for energy minimization using default parameters.
Fig. 3 Bar diagram of anticancer activity of test compounds 7a–f and
8a–f
to cell death (Siddik, 2002). The probable mechanism of
7c and 8b for their cytotoxicity is by binding to b-tubulin,
as revealed by our in silico molecular docking study. It
could be concluded from the above data that chloro at
para-position interacted with acid group before cyclisation
and bromo- and chloro-derivatives on the ortho- or meta-
position interacted with the carbonyl group of four-
membered ring after cyclisation. The results are tabulated
in Table 6 and represented by the graph in Fig. 3 shows
anticancer activity (IC50 values) of compounds 7a–f and
8a–f against the HeLa cell line.
Molecular docking results and discussions
In drug discovery, the important task is the characterization
of pharmacokinetics and toxicological evaluation of new
chemical agents. By using the in silico approach, it is easy
to predict ADMET property of chemical agents. None of
the synthesized molecules showed toxicity (Table 7).
The molecular docking of ligand molecules 7c and 8b
with b-tubulin revealed that these compounds exhibit an
interaction with amino acids in the active pocket. Figure 4
In silico molecular docking
Tools and servers
In relation to in vitro anticancer activity, it is considered
worthwhile to carry out in silico studies to support the
123

Med Chem Res
Table 7 In silico ADMET property of newly synthesized molecules
7c and 8b
Table 8 Molecular docking studies of 7c and 8b based on binding
energy, ligand efficiency, internal energy, torsional energy, RMS, no.
of H bonds and bond length
Sl. no.
1
2
Sl. no:
1
2
Molecules
7c
8b
Molecules
7c
8b
Mutagenic
Tumerogenic
Irritation
N
N
Binding energy
Ligand efficiency
Internal energy
Torsional energy
RMS
-1.76
-0.06
-3.25
1.49
0.0
1.92
-0.06
-3.71
1.79
0.0
N
N
N
N
Reproductive effect
Clog P
N
N
5.5
-5.58
-4.5
0.2
7.6
-6.77
0.85
0.22
Solubility
No. of H bonds
Bond length ()
0
1
Drug likeness
Drug score
–
1.981
binding energy were -1.76 and -1.92 kJ mol-1, respec-
tively, and that they were considered to be good inhibitors
of b-tubulin. It could be predicted that the anticancer
activity of the synthesized molecules may be due to inhi-
bition of b-tubulin and interfering with microtubule
dynamics and consequently disturbing microtubule-based
processes.
Conclusions
In summary, we describe the synthesis of 7-(1-isobutyl-1H-
imidazo[4,5-c]quinolin-4-yl)-7-azabicyclo[4.2.0]octa-1,3,
5-trien-8-ones (8a–f) in moderate to good yield by the
cyclisation of substituted-2-[(1-isobutyl-1H-imidazo[4,5-
c]quinolin-4-yl)amino]benzoic acids (7a–f) using POCl3.
The antimicrobial evaluation of these synthesized com-
pounds indicated that among the synthesized compounds
8c, 8e and 8f exhibited potent and well-balanced antibac-
terial and antifungal activities.
Fig. 4 The interaction of 7c with b-tubulin
An anticancer screening revealed that compounds 7c
and 8b are potentially attractive anticancer agents.
Materials and methods
All melting points were determined by open capillary
method and were uncorrected. The purity of compounds
was checked by thin-layer chromatography (TLC) on a
silica plate. The IR spectra were obtained in KBr disc on a
Shimadzu FT-IR 4100 Type. 1H NMR and 13C NMR
spectra were recorded either on Brucker WH-200 or on a
Perkin-Elmer EM-390 (100, 400 and 300 MHz) in DMSO-
d6 and CDCl3 as solvent and using TMS as an internal
standard. Chemical shift values were recorded in d ppm.
The mass spectra were recorded in a MDSSCIEX, API
4000 spectrometer. The elemental analyses (CHN) were
performed on CHNS-O analyser Flash EA 1112 series.
Fig. 5 The interaction of 8b with b-tubulin
shows the interaction of 7c with b-tubulin and Fig. 5 shows
the interaction of 8b with b-tubulin. The binding energy of
ligand molecules 7c and 8b are depicted in Table 8. The
docking of b-tubulin with 7c and 8b revealed that their
123

Med Chem Res
Materials
J = 7.2 Hz), 6.22 (br, 1H, NH), 7.68 (t, 2H, Quinoline-H6
and H7), 8.18 (d, 2H, Quinoline-H5 and H8, J = 8 Hz).
13C NMR: (100 MHz, DMSO-d6): d 20.40 (isopropyl-
2CH3), 28.79 (isopropyl-CH), 51.09 (isopropyl-CH2),
120.45, 123.62, 126.66, 127.19, 128.93, 132.00, 141.50,
144.89, 145.69 (Quinoline carbons); MS: (m/z) = 280.72
(M?1); Anal. calcd for: C13H14ClN3O2: C, 55.82; H, 5.04;
N, 15.02; Found: C, 55.80; H, 5.02; N, 15.00 %.
All the reagents and solvents were purchased from Spect-
rochem and Aldrich. They were used without purification.
Experimental
Synthesis of 2,4-dihydroxy-3-nitroquinoline (2)
Synthesis of 2-chloro-4-isobutylquinoline-3,4-diamine
Fuming nitric acid (6.29 g, 0.099 mol) was added dropwise
to a cooled mixture of 2,4-dihydroxy quinoline (10 g,
0.062 mol) and acetic acid (7.6 ml) for 30 min. The reac-
tion mixture was heated for 5 h at 65 °C. The mixture was
cooled. The product was separated by filtration and re-
crystallized from methanol. Yield 92 %; M.p: 198–200 °C;
1H NMR: (300 MHz, DMSO-d6) d 7.65 (t, 2H, Quinoline-
H6 and H7), 8.16 (d, 2H, Quinoline-H5 and H8,
J = 7.8 Hz), 11.98 (s, 2H, OH); 13C NMR: (100 MHz,
DMSO-d6): d 120.20, 123.67, 124.65, 127.24, 128.98,
132.99, 141.55, 144.94, 145.74 (Quinoline carbons); MS:
(m/z) = 207.16 (M?1); Anal. calcd. for: C9H6N2O4: C,
52.43; H, 2.93; N, 13.59; Found: C, 52.41; H, 2.91; N,
3.57 %.
(5)
To a solution of 2-chloro-N-isobutyl-3-nitroquinoline (4)
(2.5 g, 0.009 mol) in ethanol (25 ml), 5 % Raney nickel was
added and 2 kg/cm2 H2 pressure was applied in an autoclave.
The reaction mixture was heated at 60 °C for 17 h. The
product was obtained by filtering the catalyst, concentrating
the filtrate and recrystallizing from methanol. Yield 85 %;
M.p: 145–148 °C; 1H NMR: (400 MHz, CDCl3): d 1.00 (d,
6H, isopropyl-2CH3, J = 6.8 Hz), 2.00 (m, 1H, isopropyl-
CH), 3.91 (b, 2H, NH2), 4.05 (d, 2H, isopropyl-CH2,
J = 7.2 Hz), 7.65 (t, 2H, Quinoline-H6 and H7), 8.02 (d, 2H,
Quinoline-H5 and H8, J = 8 Hz). 13C NMR: (100 MHz,
DMSO-d6): d 20.40 (isopropyl-2CH3), 29.81 (isopropyl-
CH), 54.35 (isopropyl-CH2), 120.05, 123.24, 125.95,
126.56, 128.11, 129.05, 137.73, 142.39 (Quinoline carbons);
MS: (m/z) = 250.74 (M?1); Anal. calcd. for: C13H16N3: C,
62.52; H, 6.46; N, 16.83; Found: C,62.50; H, 6.44; N,
16.81 %.
Synthesis of 2,4-dichloro-3-nitroquinoline (3)
2,4-Hydroxy-3-nitroquinoline (2) (2 g, 0.009 mol) was
added to POCl3 (10 ml) at 65 °C and further heated to
85–90 °C for 4 h. The contents were poured onto crushed
ice and neutralized with 50 % sodium hydroxide (10 ml).
The solid obtained was filtered and recrystallized from
ethanol. Yield 84 %; M.p: 264–266 °C; 1H NMR:
(400 MHz, CDCl3): d 7.98 (t, 2H, Quinoline-H6 and H7),
8.21 (d, 2H, Quinoline-H5 and H8, J = 8 Hz); 13C NMR:
(100 MHz, CDCl3): d 120.24, 123.68, 126.69, 127.28,
129.00, 133.00, 141.59, 145.79, 144.99 (Quinoline car-
bons); MS: (m/z) = 244.05 (M?1); Anal. calcd. for
C9H4Cl2N2O2: C, 44.48; H, 1.66; N, 11.53; Found: C,
44.46; H,1.64; N, 11.53 %.
Synthesis of 4-chloro-1-isobutyl-1H-imidazo [4,5-c]
quinoline (6)
A mixture of 2-chloro-4-isobutylquinoline-3,4-diamine (5)
(2 g, 0.008 mol) and triethyl orthoformate (8 ml) was
heated at 80 °C for 3 h. The product was isolated by dis-
tilling triethyl orthoformate under vacuum at 60–65 °C.
The obtained solid was dissolved in CHCl3, washed with
water, dried over Na2SO4 and distilled. Yield 75 %; M.p:
139–140 °C; IR (KBr, tmax/cm-1), 3,038 (Ar–H), 2,960
1
(C–H), 1,576 (C=N), 1,542 (C=C), 877 (C–Cl); H NMR:
Synthesis of 2-chloro-N-isobutyl-3-nitroquinoline (4)
(400 MHz, CDCl3): d 1.04 (d, 6H, isopropyl-2CH3,
J = 6.8 Hz), 2.44 (m, 1H, isopropyl-CH), 4.34 (d, 2H,
isopropyl-CH2, J = 7.2 Hz), 7.68 (t, 2H, Quinoline-H7 and
H8), 8.50 (s, 1H, Imidazole-H2), 8.36 (d, 2H, Quinoline-
H6 and H9). 13C NMR: (100 MHz, CDCl3): d 19.77 (iso-
propyl-2CH3), 28.81 (isopropyl-CH2), 55.28 (isopropyl-
CH), 117.69, 120.08, 126.88, 127.97, 130.08, 133.96,
135.18, 144.04, 144.24 (Quinoline carbons), 144.17
(Imidazole carbon); MS: (m/z) = 260.73 (M?1); Anal.
calcd. for: C14H14ClN3: C, 64.74; H, 5.43; N, 16.18;
Found: C, 64.72; H, 5.41; N, 16.16 %.
To stirred solution of 2,4-dichloro-3-nitro quinoline (3)
(2 g, 0.0082 mol) in ethanol (20 ml) K2CO3 (2.3 g,
0.0096 mol) was added, followed by the addition of iso-
butyl amine (0.5 g, 0.008 mol) for 30 min and continued
stirring for 2 h. The solution was diluted with water and
stirring was continued for 1 h. The precipitated product
was washed with water and recrystallized with ethanol.
Yield 82 %; M.p: 85–88 °C; 1H NMR: (400 MHz, DMSO-
d6): d 1.05 (d, 6H, isopropyl-2CH3, J = 6.8 Hz), 2.17
(m, 1H, isopropyl-CH), 4.12 (d, 2H, isopropyl-CH2,
123

Med Chem Res
General procedure for the synthesis of substituted-2-
[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-
yl)amino]benzoic acid (7a–f)
(M?1); Anal. calcd. for:C21H19BrN4O2: C, 57.42; H, 4.36; N,
12.75; Found: C, 57.4; H, 4.34; N, 12.73 %.
5-Bromo-2-[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-
yl)amino]benzoicacid (7c)
A mixture of 4-chloro-1-(2-methylpropyl)-1H-imidazo[4,
5-c]quinoline (6) (0.01 mol) and different anthranilic acids
(0.01 mol) in methanol (30 ml) containing a catalytic
amount of DMF (3.3 ml) was refluxed for 72 h. The mix-
ture was cooled. The product was separated by filtration
and re-crystallized from methanol.
Yield 96 %; M.p: 140–142 °C; IR (KBr, tmax/cm-1),
3,500–2,500 (–OH), 1,599 (C=O), 1,577 (C=N), 1,487 (C=C),
1,294 (C–N); 1H NMR: (400 MHz, DMSO-d6): d 0.92 (d, 6H,
isopropyl-2CH3, J = 6.8 Hz), 2.22–2.15 (m, 1H, isopropyl-
CH), 4.46 (d, 2H, isopropyl-CH2, J = 7.2 Hz), 7.20 (d, 1H,
Ar–H4, J = 4 Hz), 7.29 (t, 2H, Quinoline-H7 and H8), 7.82
(d, 1H, Ar–H2, J = 2 Hz), 7.89 (s, 1H, Ar–H6), 8.00 (s, 1H,
NH), 8.05 (d, 1H, Quinoline-H9, J = 8 Hz), 8.19 (s, 1H,
Imidazole-H2), 8.34 (d, 1H, Quinoline- H6, J = 8.0 Hz), 11.7
(s, 1H, acid proton); 13C NMR: (100 MHz, CDCl3): d 19.61
(isopropyl-2CH3), 28.69 (isopropyl-CH), 53.26 (isopropyl-
CH2), 112.25, 117.34, 120.40, 121.90, 123.45, 126.58, (Aro-
matic carbons), 127.90, 128.33, 129.38, 131.94, 132.88,
133.25, 136.80, 143.64, 143.98 (Quinoline carbons), 142.80
(Imidazole carbon), 158.68 (C=O); MS (m/z) = 440.31
(M?1); Anal. calcd. for: C21H19BrN4O2: C, 57.42; H, 4.36; N,
12.75; Found: C, 57.4; H; 4.34; N; 12.73 %.
2-[(1-Isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)amino]
benzoic acid (7a)
Yield 96 %; M.p: 216–218 °C; IR (KB, tmax/cm-1),
3,500–2,500 (–OH), 1,599 (C=O), 1,579 (C=N), 1,487 (C=C),
1,293 (C–N); 1H NMR: (400 MHz, DMSO-d6): d 0.92 (d, 6H,
isopropyl-2CH3, J = 6.8 Hz), 2.22–2.16 (m, 1H, isopropyl-
CH), 4.45 (d, 2H, isopropyl-CH2, J = 7.2 Hz), 6.97 (t, 1H,
Ar–H4), 7.42 (t, 1H, Ar–H5), 7.53 (t, 2H, Quinoline-H7 and
H8),7.56(s, 1H, NH),7.89(d, 1H, Ar–H3,J = 8 Hz), 8.04(d,
1H, Ar–H6, J = 7.2 Hz), 8.09 (d, 1H, Quinoline-H9,
J = 8 Hz), 8.27 (s, 1H, Imidazole-H2), 9.57 (d, 1H, Quino-
line-H6, J = 8 Hz), 12.9 (s, 1H, acid proton); 13C NMR:
(100 MHz, CDCl3): d 19.77 (isopropyl-2CH3), 28.92 (iso-
propyl-CH), 53.97 (isopropyl-CH2), 116.08, 119.21, 119.98,
120.96, 123.42 (Aromatic carbons), 127.48, 128.25, 129.83,
131.75, 132.13, 132.33, 148.12 (Quinoline carbons),
143.44.(Imidazole carbon), 170.7 (C=O); MS: (m/z) =
361.41 (M?1); Anal. calcd. for: C21H20N4O2: C, 69.98; H,
5.59; N, 15.55; Found: C, 69.96; H, 5.57; N, 15.53 %.
4-Chloro-2-[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)
amino]benzoic acid (7d)
Yield 96 %; M.p. 186–190 °C; IR (KBr, tmax/cm-1),
3,500–2,500 (OH), 1,599 (C=O), 1,578 (C=N), 1,487
(C=C), 1,295(C–N); 1HNMR: (400 MHz, DMSO-d6): d
0.92 (d, 6H, isopropyl-2CH3, J = 6.8 Hz), 2.22–2.15 (m,
1H, isopropyl-CH), 4.46 (d, 2H, isopropyl-CH2,
J = 7.2 Hz), 7.44 (s, 1H, Ar–H3), 7.59 (t, 2H, Quinoline-
H7 and H8), 7.92 (d, 1H, Ar–H6, J = 8 Hz), 7.93 (d, 1H,
Ar–H5, J = 4 Hz), 8.09 (s, 1H, NH), 8.15 (d, 1H, Quino-
line-H9, J = 8 Hz), 8.34 (s, 1H, imidazole-H2), 8.55 (d,
1H, Quinoline-H6, J = 8 Hz), 11.8 (s, 1H, acid proton);
13C NMR: (100 MHz, CDCl3): d 19.76 (isopropyl-2CH3),
28.92 (isopropyl-CH), 54.01 (isopropyl-CH2), 112.45,
117.50, 118.12, 120.30, 123.45, 126.65, (Aromatic car-
bons), 127.22, 128.36, 129.35, 131.00, 133.60, 133.90,
135.02, 136.72, 144.15 (Quinoline carbons), 143.78
(Imidazole carbon), 169.64 (C=O); MS (m/z) = 395.85
(M?1); Anal. calcd. For: C21H19Cl1N4O2: C, 63.88; H,
4.85; N, 14.19; Found: C, 63.86; H, 4.83; N, 14.17 %.
3-Bromo-2-[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)
amino]benzoic acid (7b)
Yield 96 %; M.p:134–136 °C; IR (KBr,
t
max/cm-1),
3,500–2,500 (–OH), 1,599 (C=O), 1,577 (C=N), 1,487 (C=C),
1,294 (C–N); 1H NMR: (400 MHz, DMSO-d6): d 0.92 (d, 6H,
isopropyl-2CH3, J = 6.8 Hz), 2.22–2.15 (m, 1H, isopropyl-
CH), 4.30 (d, 2H, isopropyl-CH2, J = 7.2 Hz), 6.99 (t, 1H,
Ar–H5), 7.27 (t, 2H, Quinoline-H7 and H8), 7.80 (d, 1H, Ar–
H4, J = 2 Hz), 7.88 (d, 1H, Ar–H6, J = 8 Hz), 7.89 (s, 1H,
NH), 8.10 (d, 1H, Quinoline-H9, J = 8 Hz), 8.15 (s, 1H,
imidazole-H2), 8.27 (d, 1H, Quinoline-H6, J = 8.0 Hz), 11.4
(s, 1H, acid proton); 13C NMR: (100 MHz, CDCl3): d 19.62
(isopropyl-2CH3), 28.70 (isopropyl-CH), 53.27 (isopropyl-
CH2), 112.29, 117.28, 120.43, 121.95, 123.48, 126.60, (Aro-
matic carbons), 127.97, 128.35, 129.40, 131.96, 132.90,
133.32, 136.85, 143.67, 144.10 (Quinoline carbons), 142.80
(Imidazole carbon), 158.68 (C=O); MS: (m/z) = 440.31
5-Chloro-2-[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)
amino]benzoic acid (7e)
Yield 96 %; M.p: 200–202 °C; IR (KBr, tmax/cm-1),
3,500–2,500 (–OH), 1,599 (C=O), 1,578 (C=N), 1,487
123

Med Chem Res
1
7-[1-(2-Methylpropyl)-1H-imidazo[4,5-c]quinolin-4-yl]-
(C=C), 1,295 (C–N); HNMR: (400 MHz, DMSO-d6): d
7-azabicyclo[4.2.0]octa-1,3,5-trien-8-one (8a)
0.92 (d, 6H, isopropyl-2CH3, J = 6.8 Hz), 2.22–2.15 (m,
1H, isopropyl-CH), 4.46 (d, 2H, isopropyl-CH2,
J = 7.2 Hz), 7.45 (d, 1H, Ar–H3, J = 4 Hz), 7.61 (t, 2H,
Quinoline-H7 and H8), 7.94 (d, 1H, Ar–H4, J = 2 Hz),
7.98 (s, 1H, Ar–H6), 8.05 (s, 1H, NH), 8.18 (d, 1H,
Quinoline-H9, J = 8 Hz), 8.38 (s, 1H, imidazole-H2), 8.79
(d, 1H, Quinoline-H6, J = 8 Hz), 11.9 (s, 1H, acid proton);
13C NMR: (100 MHz, CDCl3): d 19.74 (isopropyl-2CH3),
28.90 (isopropyl-CH), 53.94 (isopropyl-CH2), 112.47,
117.46, 118.10, 120.29, 123.44, 126.58, (Aromatic car-
bons), 127.19, 128.32, 129.38, 130.97, 133.58, 133.85,
134.95, 136.68, 144.49 (Quinoline carbons), 143.70
(Imidazole carbon), 169.62 (C=O); MS: (m/z) = 395.85
(M?1); Anal. calcd. for: C21H19Cl1N4O2: C, 63.88; H,
4.85; N, 14.19; Found: C, 63.86; H, 4.83; N, 14.17 %.
Yield 96 %; M.p: 236–38 °C; IR (KBr, tmax/cm-1), 3,038
(Ar–H), 2,956 (C–H), 1,590 (C=O); H NMR: (400 MHz,
1
CDCl3): d 1.04 (d, 6H, isopropyl-2CH3, J = 6.8 Hz),
2.36–2.29 (m, 1H, CH), 4.27 (d, 2H, isopropyl-CH2,
J = 7.2 Hz), 7.48 (t, 1H, Azabicyclo-H4), 7.54 (t, 2H,
Quinoline-H6 and H7), 7.84 (t, 1H, Azabicyclo-H3), 7.88
(s, 1H, Imidazole-H2), 7.89 (d, 1H, Azabicyclo-H5,
J = 7.2 Hz), 7.97 (d, 1H, Azabicyclo-H2, J = 8 Hz), 8.43
(d, 1H, Quinoline-H9, J = 8 Hz), 9.35 (d, 1H, Quinoline-
H6, J = 8 Hz); 13C NMR: (100 MHz, CDCl3): d ppm,
19.75 (isopropyl-2CH3), 28.9 (isopropyl-CH), 55.43 (iso-
popyl-CH2), 117.55, 120.05, 120.38, 123.55, 125.69,
126.42 (Aromatic carbons), 127.08, 127.10, 129.21, 133.80,
134.13, 134.63, 143.65, 146.74 (Quinoline carbons), 143.99
(Imidazole ring), 163.37 (C=O); MS (m/z) = 343.39
(M?1); Anal. calcd. for: C21H18N4O: C, 73.67; H, 5.29; N,
16.36; Found: C, 73.65; H, 5.27; N, 16.36 %.
5-Iodo-2-[(1-isobutyl-1H-imidazo[4,5-c]quinolin-4-yl)
amino]benzoic acid (7f)
Yield 96 %; M.p: 168–170 °C; IR (KBr, tmax/cm-1),
3,500–2,500 (–OH), 1,599 (C=O), 1,576 (C=N), 1,487
(C=C), 1,293 (C–N); 1H NMR: (400 MHz, CDCl3): d 0.91
(d, 6H, isopropyl-2CH3, J = 6.8 Hz), 2.21–2.10 (m, 1H,
isopropyl-CH), 4.39 (d, 2H, isopropyl-CH2, J = 7.2 Hz),
7.59 (d, 1H, Ar–H3, J = 4 Hz), 7.50 (t, 2H, Quinoline-H7
and H8), 7.82 (d, 1H, Ar–H4, J = 2 Hz), 7.90 (s, 1H, Ar–
H6), 7.93 (s, 1H, NH), 8.16 (d, 1H, Quinoline-H9,
J = 8 Hz), 8.29 (s, 1H, imidazole-H2), 8.39 (d, 1H,
Quinoline-H6, J = 8 Hz), 11.7 (s, 1H, acid proton); 13C
NMR: (100 MHz, CDCl3): d 19.70 (isopropyl-2CH3),
28.90 (isopropyl-CH), 54.01 (isopropyl-CH2), 117.45,
120.35, 121.60, 123.48, 126.68, (Aromatic carbons),
127.25, 128.92, 129.55 133.65, 133.94, 136.12, 144.00,
144.10 (Quinoline carbons), 143.24.(Imidazole carbon),
169.84 (C=O); MS: m/z = 487.31 (M?1); Anal. calcd. for:
C21H19IN4O2: C, 51.87; H, 3.94; N, 11.52; Found: C,
51.85; H, 3.92; N, 11.50 %.
5-Bromo-7-[1-(2-methylpropyl)-1H-imidazo[4,5-
c]quinolin-4-yl]-7-azabicyclo[4.2.0]octa-
1,3,5-trien-8-one (8b)
Yield 60 %; M.p: 272–276 °C; IR (KBr, tmax/ cm-1), 3,038
(Ar–H), 2,958 (C-H), 1,590 (C=O); 1HNMR (400 MHz,
CDCl3) d 1.04 (d, 6H, isopropyl-2CH3, J = 6.8 Hz),
2.38–2.25 (m, 1H, isopropyl-CH), 4.29 (d, 2H, isopropyl-
CH2, J = 7.2 Hz), 7.05 (t, 1H, Azabicyclo-H3), 7.31 (t, 2H,
Quinoline-H7 and H8), 7.80 (s, 1H, Imidazole-H2), 7.84 (d,
1H, Azabicyclo-H4, J = 8HZ), 7.85 (d, 1H, Azabicyclo-H2,
J = 2 Hz), 8.38 (d, 1H, Quinoline-H9, J = 8 Hz), 8.90 (d,
1H, Quinoline-H6, J = 8 Hz); 13C NMR: (100 MHz,
CDCl3) d 19.59 (isopropyl-2CH3), 28.68 (isopropyl-CH),
54.72 (isopropyl-CH2), 112.30, 117.32, 120.44, 122.01,
123.50, 126.62, (Aromatic carbons), 127.99, 128.38, 129.43,
131.98, 132.93, 133.37, 136.89, 143.69, 144.18 (Quinoline
carbons), 142.86 (Imidazole carbon), 158.73 (C=O); MS (m/
z) = 422.29 (M?1). Anal.calcd.for: C21H17BrN4O: C,
59.87; H, 4.07; N, 13.29; Found: C, 59.85; H, 4.05; N,
13.27 %.
General procedure for the synthesis of substituted 7-
[1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-yl]-
7-azabicyclo[4.2.0]octa-1,3,5-trien-8-one (8a–f)
3-Bromo-7-[1-(2-methylpropyl)-1H-imidazo
[4,5-c]quinolin-4-yl]-7-azabicyclo[4.2.0]octa-
1,3,5-trien-8-one (8c)
POCl3 (0.03 mol) was added dropwise to pre-cooled
solutions of substituted 2-[(1-isobutyl-1H-imidazo[4,5-
c]quinolin-4-yl)amino]benzoic acids (7a–f) (0.01 mol) in
acetonitrile (15 ml). The reaction mixture was refluxed for
4 h. The mixture was cooled and poured in to ice-cold
water and basified using 20 % NaOH solution. The pre-
cipitated product was washed with water and recrystallized
from ethyl acetate/methanol.
Yield 90 %; M.p: 280–282 °C; IR (KBr, tmax/cm-1), 3,038
(Ar–H), 2,958 (C–H), 1,590 (C=O); H NMR:(400 MHz,
1
CDCl3): d 1.04 (d, 6H, isopropyl-2CH3, J = 6.8 Hz),
2.39–2.26 (m, 1H, isopropyl-CH), 4.30 (d, 2H, isopropyl-
CH2, J = 7.2 Hz), 7.33 (t, 2H, Quinoline-H7 and H8), 7.50
123

Med Chem Res
(d, 1H, Azabicyclo-H5, J = 4 Hz), 7.85 (s, 1H, Imidazole-
H2), 7.82 (d, 1H, Azabicyclo-H4, J = 8 Hz), 7.89 (s, 1H,
Azabicyclo-H2), 8.39 (d, 1H, Quinoline-H9, J = 8 Hz),
8.97 (d, 1H, Quinoline-H6, J = 8 Hz); 13C NMR:
(100 MHz, CDCl3) d 19.58 (isopropyl-2CH3), 28.65 (iso-
propyl-CH), 54.70 (isopropyl-CH2), 112.27, 117.38,
120.43, 121.99 (Aromatic carbons), 127.97, 128.00,
129.40, 131.95, 132.90, 133.30, 136.85, 143.65, 143.95
(Quinoline carbons), 142.80 (Imidazole carbon), 158.69
(C=O); MS (m/z) = 422.29 (M?1). Anal. calcd. for
:C21H17BrN4O: C, 59.87; H, 4.07; N, 13.29; Found: C,
59.85; H, 4.05; N, 13.27 %.
(m/z) = 377.84 (M?1); Anal. calcd. for: C21H17Cl1N4O:
C, 66.93; H, 4.55; N, 14.87; Found: C, 66.91; H, 4.53; N,
14.85 %.
3-Iodo-7-[1-(2-methylpropyl)-1H-imidazo
[4,5-c]quinolin-4-yl]-7-azabicyclo[4.2.0]octa-
1,3,5-trien-8-one (8f)
Yield 83 %; M.p: 238–290 °C; IR (KBr, tmax/cm-1), 3,038
(Ar–H), 2,953 (C–H), 1,590 (C=O); H NMR (400 MHz,
1
CDCl3): d ppm, 1.04 (d, 6H, isopropyl-2CH3, J = 6.8 Hz),
2.36–2.29 (m, 1H, isopropyl-CH), 4.27 (d, 2H, isopropyl-
CH2, J = 7.2 Hz), 7.54 (t, 2H, Quinoline-H7 and H8), 7.65
(d, 1H, Azabicyclo-H5, J = 4 Hz), 7.80 (s, 1H, Imidazole-
H2), 7.84 (d, 1H, Azabicyclo-H4, J = 8 Hz), 7.87 (s, 1H,
Azabicyclo-H2), 8.25 (d, 1H, Quinoline-H9, J = 8 Hz),
8.34 (d, 1H, Quinoline-H6, J = 8 Hz); 13C NMR:
(100 MHz, CDCl3): d ppm, 19.75 (isopropyl-2CH3), 28.92
(isopropyl-CH), 55.46 (isopropyl-CH2), 117.50, 120.37,
121.62, 123.50, 126.70, (Aromatic carbons), 127.29,
128.95, 129.56, 133.56, 133.67, 136.16, 144.07, 144.17,
146.03 (Quinoline carbons), 144.27 (Imidazole carbon),
161.91 (C=O); MS (m/z) = 469.29 (M?1); Anal. calcd.
for: C21H17I1N4O: C, 53.86; H, 3.66; N, 11.96; Found: C,
53.86; H, 3.64; N, 11.94 %.
4-Chloro-7-[1-(2-methylpropyl)-1H-imidazo[4,5-c]
quinolin-4-yl]-7-azabicyclo[4.2.0]octa- 1,3,5-trien-8-
one (8d)
Yield 85 %; M.p: 192–194 °C; IR (KBr, tmax/cm-1), 3,038
(Ar–H), 2,957 (C–H), 1,590 (C=O). HNMR: (400 MHz,
1
CDCl3): d 1.04 (d, 6H, isopropyl-2CH3, J = 6.8 Hz),
2.34–2.27 (m, 1H, CH), 4.27 (d, 2H, isopropyl-CH2,
J = 7.2 Hz), 7.44 (s, 1H, Azabicyclo-H5), 7.55 (t, 2H,
Quinoline-H7 and H8), 7.90 (s, 1H, Imidazole-H2), 7.94 (d,
1H, Azabicyclo-H2, J = 4 Hz), 7.95 (d, 1H, Azabicyclo-
H3, J = 8 Hz), 8.36 (d, 1H, Quinoline-H9, J = 8 Hz),
9.35 (d, 1H, Quinoline-H6, J = 8 Hz); 13C NMR:
(100 MHz, CDCl3): d 19.70 (isopropyl-2CH3), 28.89
(isopropyl-CH), 55.44 (isopropyl-CH2), 112.50, 117.52,
118.14, 120.36, 123.50, 126.69, (Aromatic carbons),
127.25, 128.74, 129.44, 133.63, 133.92, 135.08, 134.99,
136.75, 144.17 (Quinoline carbons), 143.89 (Imidazole
carbon), 162.32 (C=O); MS (m/z) = 377.84 (M?1). Anal.
calcd. for: C21H17Cl1N4O: C, 66.93; H, 4.55; N, 14.87;
Found: C, 66.91; H, 4.53; N, 14.85 %.
Acknowledgments Authors are grateful to the management of
SeQuent Scientific LTD, New Mangalore, India for their invaluable
support and allocation of resources for this work. Authors are also
thankful to late Prof. A. Srikrishna IISc Bangalore, India for pro-
viding spectral analysis. We are also thankful Prof. H-Kun Fun for the
single crystal study of the compound.
References
3-Chloro-7-[1-(2-methylpropyl)-1Himidazo
[4,5-c]quinolin-4-yl]-7-azabicyclo[4.2.0]octa-
1,3,5-trien-8-one (8e)
Backman GB, Bennett GE, Barker RS (1950) Synthesis of substituted
quinolylamines Derivatives of 4-amino-7-chloroquinoline. J Org
Chem 15:1278–1284
Boyd MR, Paull KD (1995) Some practical considerations and
applications of the national cancer institute in vitro anticancer
drug discovery screen. Drug Dev Res 34:91–109
Coleman PL, Crooks SL, Griesgraber GW, Lindstrom KJ, Merrill BA,
Rice MJ (2000) Amide substituted imidazoquinolines WO-A-
765057
Coleman PL, Crooks SL, Griesgraber GW, Lindstrom KJ, Merrill BA,
Rice MJ (2003) Amide substituted imidazoquinolines US Patent-
A 0144283
Freshney RI (2006) Culture of animals cells: (eds) A manual of basic
technique. Wiley, Singapore
Gilchrist TL (1985) Heterocyclic chemistry the bath press ISBN
0-582-01421-2
Griesgraber GW (2004) Sulfonamide and sulfamide substituted
imidazoquinolines US Patent 6,677,349
Jain PC, Kapoor V, Anand Nitya, Patnaik GK, Ahmad Allauddin,
Vohra MC (1968) Chemical and pharmacological investigations
Yield 75 %; M.p: 218–220 °C; IR (KBr, tmax/cm-1), 3,038
(Ar–H), 2,957 (C–H), 1,590 (C=O); H NMR: (400 MHz,
1
CDCl3): d 1.04 (d, 6H, isopropyl-2CH3, J = 6.8 Hz),
2.39–2.25 (m, 1H, isopropyl-CH), 4.22 (d, 2H, isopropyl-
CH2, J = 7.6 Hz), 7.54 (d, 1H, Azabicyclo-H5, J = 4 Hz),
7.56 (t, 2H, Quinoline-H7 and H8), 7.91 (s, 1H, Imidazole-
H2), 7.96 (s, 1H, Azabicyclo-H2), 7.97 (d, 1H, Azabicyclo-
H4, J = 8 Hz), 8.35 (d, 1H Quinoline-H9, J = 8 Hz), 9.35
(d, 1H, Quinoline-H6, J = 8 Hz); 13C NMR: (100 MHz,
CDCl3): d 19.70 (isopropyl-2CH3), 28.89 (isopropyl-CH),
55.44 (isopropyl-CH2), 112.48, 117.48, 120.30,, 123.48,
126.60, (Aromatic carbons), 127.20, 128.35, 129.40,
130.99, 133.60, 133.90, 134.99, 136.70,144.00 (Quinoline
carbons), 143.75 (Imidazole carbon), 162.30 (C=O); MS
of some.omega.-substituted
J Med Chem 11:87–92
alkylamino-3-aminopyridines.
123

Med Chem Res
Khan ZK (1997) In vitro and vivo screening techniques for bioactivity
screening and evaluation. In: Proceeding International Workshop
UNIDO-CDRI
Krepski LR, Dellaria JF, Duffy DE, Amos DT, Zimmermann BM,
Squire DJ, Marszalek GJ, Heppner PD, Kshirsagar TA (2005)
Hydroxylamine and oxime substituted imidazoquinolines imi-
dazopyridines and imidazonapthyridines WO-A-051324
Loh WS, Fun HK, Reshma K, Viveka S, Nagaraja GK (2011)
1-isobutyl-N, N-1H-imidazo[4,5-c] quinolin-4-amine. Acta Crys-
tallor E67:o406
Mackie, McCartney (1989) In: Collee JC, Duguid JP, Fraser AG,
Marmion BP (eds) Practical medicinal microbiology, 13th edn.
Churchil Livingstone, London
Miller RL, Gerster JF, Owens ML, Slade HB, Tomai MO (1999)
Review article imiquimod applied topically: a novel immune
response modifier and new class of drug Int. J Immunopharmacol
21:1–14
Ramahan AM (1999) Fused quinoline heterocycles 1. First example
of the 2,4-diazidoquinoline-3-carbonitrile and 1-aryl-1,2,3,4,5,6–
hexaazaacephenanthrylenes ring system. J Chem Soc Perkin
Tran 1:2183–2188
Siddik ZH (2002) Mechanisms of action of cancer chemotherapeutic
agents: DNA-interactive alkylating agents and antitumour plat-
inum-based drugs. doi:10.1002/0470025077
Trevor AJ, Katzung BG, Masters SB (2010) Katzung and Trevor’s
Pharmacology Examination and Board Review, 9th edn.
McGraw Hill, New York, p 15
Varma RS (1998) Antifungal agents. Past, present and future
prospects. National academy of chemistry and biology India,
Lucknow, pp 55–128
123