Synthesis and molecular modeling studies of 3-chloro-4-substituted-1-(8- hydroxy-quinolin-5-yl)-azetidin-2-ones as novel anti-filarial agents

Article abstract of DOI:10.1016/j.bmcl.2010.04.106

A series of 3-chloro-4-substituted-1-(8-hydroxy-quinolin-5-yl)-azetidin-2- ones were synthesized and evaluated for their in vitro anti-filarial activity. To pre-assess the anti-filarial behavior of synthesized compounds (V _a-f) on a structural basis, automated docking studies were carried out with Molecular Design Suite (MDS v 3.5) into the active site of glutathione-S-transferase (GST) enzyme; scoring functions of these compounds at the active site of the GST enzyme were used for correlation with observed activity. Compounds V_e and V_f have shown good affinity for receptor GST, as well as in vitro anti-filarial potency.

Full text of DOI:10.1016/j.bmcl.2010.04.106

Bioorganic & Medicinal Chemistry Letters 20 (2010) 3640–3644
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and molecular modeling studies of 3-chloro-4-substituted-1-(8-hyd-
roxy-quinolin-5-yl)-azetidin-2-ones as novel anti-filarial agents
b
c
d
d
Santosh S. Chhajed a, , Puranik Manisha , Virupaksha A. Bastikar , Haldar Animeshchandra , V. N. Ingle ,
*
Chandrashekhar D. Upasani e, Sachin S. Wazalwar f
a Department of Pharmaceutical Chemistry, S.M.B.T. College of Pharmacy, Dhamangaon, Dist – Nasik, MS, India
b Institute of Pharmaceutical Education and Research, Borgaon (Meghe), Wardha, MS, India
c Dr. D.Y. Patil Institute of Biotechnology and Bioinformatics, Belapur, Navi – Mumbai, India
d Department of Chemistry, R.T.M. Nagpur University, Nagpur, MS, India
e S.S.D.J. College of Pharmacy, Chandwad, Dist – Nashik, MS, India
f Rajiv Gandhi College of Engineering, Research & Technology, Chandrapur, MS, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 3-chloro-4-substituted-1-(8-hydroxy-quinolin-5-yl)-azetidin-2-ones were synthesized and
evaluated for their in vitro anti-filarial activity. To pre-assess the anti-filarial behavior of synthesized
compounds (Va–f) on a structural basis, automated docking studies were carried out with Molecular
Design Suite (MDS v 3.5) into the active site of glutathione-S-transferase (GST) enzyme; scoring func-
tions of these compounds at the active site of the GST enzyme were used for correlation with
observed activity. Compounds Ve and Vf have shown good affinity for receptor GST, as well as
in vitro anti-filarial potency.
Received 6 December 2009
Revised 22 April 2010
Accepted 23 April 2010
Available online 17 May 2010
Keywords:
Synthesis
Azetidin-2-ones
In vitro anti-filarial
Molecular docking, MDS
Ó 2010 Elsevier Ltd. All rights reserved.
Filariasis comprises a group of diseases produced by the inva-
sion of the lymphatic system or connective tissues by the nema-
todes Filarioidea. The most formidable pathogens of man include
Wuchereria bancrofti, Brugia (Wuchereria) malayi, Loa loa, and
Onchocerca volvulus. Current global estimates suggest that around
80 countries are endemic for lymphatic filariasis (LF).1 An esti-
mated population of 22 million is known to be the host for circu-
lating microfilaria and 16 million people suffer from filarial
manifestations like elephantiasis of limbs, genitals, and hydrocele.2
Low priority was given to this disease, although it is responsible for
significant morbidity and consequently the World Health Assem-
bly has adopted a resolution on the global elimination of lymphatic
filariasis as a public health problem.3,4 The available control strat-
egies have significant limitations as current drugs are principally
macrofilaricidal and require annual repeated treatment for a num-
ber of years, thus there is still a need for the development of a mac-
rofilaricidal agent or drug combination for the curative treatment
or sustained suppression of the microfilariae.5–8 Drug resistance
to ivermectin appears to be another issue of concern, especially
in areas where diethylcarbamazine (DEC) cannot be given. The can-
didate drug Diethylcarbamazine (DEC) which kills microfilaria has
no effect on most of the adult filarial species and causes side ef-
fects.9 Therefore, R&D activities are directed to the search of a
new molecular structure as macrofilaricidal or at least a sterilizing
agent.
A number of molecules from heterocycles are known as good
anti-filarials agent.10 Benzimidazoles11 and triazines12,13 have re-
cently been shown to possess anti-filarial activity. Extensive
work has been done on 4-aminoquinolines as anti-filarials. It is
evident that bulky substituent at fourth position of quinolines
are found to be good anti-filarial activity.14 But no sincere efforts
have been carried out in exploring 5th position of quinoline nu-
cleus. In the present work, we have explored 8-hydroxyl-5-ami-
noquinoline derivatives as a new lead compounds in anti-filarial
chemotherapy. Present work is an attempt to observe the com-
bined effect of quinoline nucleus along with another equally po-
tent b-lactam nucleus for the anti-filarial activity. Effect of a new
series which incorporates the combination of two biologically ac-
tive nuclei, that is, quinoline and b-lactam was studied for its
anti-filarial properties. In the present work, we synthesized six
new 3-chloro-4-substituted-1-(quinolin-5-yl) azetidin-2-ones,
and tested for in vitro anti-filarial activity.
* Corresponding author. Tel.: +91 9850081911.
E-mail address: santosh_chhajed@rediffmail.com (S.S. Chhajed).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.04.106

S. S. Chhajed et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3640–3644
3641
Table 1
NO
In vitro anti-filarial screening of compounds on B. malayi
NaNO2/H2SO4
Sr. No.
Compound
Percent loss of motility after 48 h
Concentration (ng/mL)
N
N
20
40
60
80
100
OH
OH
(I)
(II)
1
2
3
4
5
6
7
Va
Vb
Vc
Vd
Ve
Vf
DMSO
Nil
Nil
Nil
Nil
67
Nil
10
Nil
Nil
76
61
Nil
Nil
19
12
3
91
67
Nil
2
02
59
37
23
91
81
Nil
36
26
16
91
76
Nil
SnCl2/HCl
R
53
Nil
NH
OH
NH2
Aldehydes
Note. Nil indicates no motility observed.
Methanol/ H2SO4
N
N
OH
(IV )
(III)
Cl
R
ClCH2COCl
Table 2
Molecular docking showing binding score of synthesized compounds in the active site
of GST
Triethylamine/DMSO
HN
O
Sr. No.
Ligand
Binding score using GA dock
1
2
3
4
5
6
7
Va
Vb
Vc
Vd
Ve
17,623
12,021
14,092
15,923
10,112
10,876
10,943
N
OH
(V)
H
H
O
H
Vf
DEC
O
H
H
O
O
O
R = CH CHO
,
3
,
,
,
,
Br
OMe
Cl
F
model of the catalytic site of GST enzyme, and to well correlate
the obtained binding score with inhibitory activities of compounds.
Obtained results were evaluated in terms of binding score into the
catalytic site of GST, low binding scores represent high affinity for
the receptor (Fig. 1).
Scheme 1. Synthetic protocol of compounds.
In summary, synthesis of 5-amino-8-hydroxyquinoline we se-
lected a two step method consisting of nitrosation of 8-hydroxy-
quinoline, followed by reduction with tin and hydrochloric acid.
When nitrosation is carried out at the 15–18 °C, the nitroso group
was directed selectively to para position to the hydroxyl group. The
target compounds Va–f were prepared by cyclization of IVa–f Schiff
bases with chloroacetyl chloride. Triethylamine was used as base
in this reaction to absorb released hydrochloric acid. Spectral data
and elemental analysis by CHN of the target compounds (Va–f) are
in accordance with their structures Tables 3 and 4. The synthesized
scaffold was screened for in vitro anti-filarial activity against B. ma-
layi. Results are summarized in Table 1. Compounds Ve and Vf
showed promising activity against brugia. Compound Ve resulted
in 91% loss of motility at concentration of 60 ng/mL and compound
Vf shows 76% loss of motility at 80 ng/mL where as Vb shows mod-
erate activity with 53% loss of motility at 100 ng/mL. Molecular
docking analysis shows that compounds Vb, Ve, and Vf show min-
imum binding scores 10,112, 10,876, and 12,021, respectively, in
the series. Results are summarized in Table 2. This shows that com-
pounds Vb, Ve, and Vf possess more binding affinity for receptor
glutathione-S-transferase than other compounds in the series. Fur-
ther binding score of known anti-filarial agent, DEC is 10,943. It is
evident from docking analysis that, binding affinity of compound
Ve and Vf, for enzyme GST is better than that of DEC. Good correla-
tion was found in molecular docking analysis and in vitro anti-
filarial screening for all the compounds. Compounds that showed
good binding affinity for receptor were found to possess promising
biological activity.
The synthesis of our target compounds Va–f is outlined in
Scheme 1. Structures of compounds (IVa–f) and (Va–f) are confirmed
by spectral data and elemental analysis by CHN. Key intermediate
5-amino-8-hydroxyquinoline (III) was synthesized by nitrosation
of 8-hydroxyquinoline (I),15 followed by reduction of 5-nitroso-8-
hydroxy quinoline (II) with tin metal in hydrochloric acid.16 Com-
pounds (IVa–f) were prepared by Schiff’s base formation17 between
5-amino-8-hydroxyquinoline (III) and 4-substituted/unsubstituted
aliphatic/aromatic aldehydes. Target compounds (Va–f), ware pre-
pared by cyclization of 5-(4-substituted/unsubstituted benzylide-
neamino)-quinoline-8-ol (IVa–f) with chloroacetyl chloride.18 The
synthesized scaffold was screened for in vitro anti-filarial activity
against B. malayi by method of Chatterjee and co-workers.19 Re-
sults are summarized in Table 1.
Glutathione-S-transferase (GST) (E.C. 2.5.1.18)20 is one of the
major detoxification system ubiquitous among eukaryotes and
have been found in a wide range of parasitic helminthes. The inhi-
bition of parasite GST(s) thus deprives the parasite of its major de-
fense against oxidative stress and impairs its ability to survive.
Filarial GST is therefore important target for anti-filarial drug de-
sign.21 To pre-assess the anti-filarial behavior of synthesized com-
pounds (Va–f) on a structural basis, automated docking studies
were carried out and scoring functions, their binding affinities
and orientation of these compounds at the active site of the GST
enzyme were found out. Results are summarized in Table 2. The
protein–ligand complex was constructed on the basis of the
X-ray structure of GST (PDB deposition – 5GSS).22 Docking was
performed using Molecular Design Suite (MDS) v 3.5, into the 3D

3642
S. S. Chhajed et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3640–3644
Fig.1b.DEC in active site of GST it has binding
Molecule Vb in the active site of enzyme GST showing
Van der Wals interactions
score 10943
Binding mode of compound V into the binding site of
Binding mode of compound Vd into the
binding site of GST, it has binding score 15923 and form
hydrogen bond shown as white dotted line, showing one
hydrogen bond between O of 2-oxo of azetidinone
and Methionine -522 of distances of 1.1 A.U.
e
GST, it form hydrogen bond shown as white dotted lines
showing one hydrogen bond between O of 2-oxo of azetidinone
and Tyrosine -385 of distances of 2.1 A.U. it has binding score
of 10112.
Fig. 1. Best poses, orientations, hydrogen bond formed, and Van der Waals interactions of synthesized compounds with GST.
Table 3
Physicochemical and spectral data for compounds IVa–f
Sr. No.
1
Compound
–R
Mp (°C)
1H NMR (dppm), IR (cmÀ1, KBr), mass (m/e)
1H NMR: d 9.52 (s, 1H, Ar–OH), d 7.02 (s, N@CH–), d 6.8–8.9 (m, Ar–H). IR (cmÀ1):
3382.75 (O–H str), 1642.19 (C@N str of imines), 1250 (phenolic C–O str), m/z = 249
IVa
122–124
1H NMR: d 7.44 (s, 1H, N@CH–), 6.96–9.45 (m, Ar–H), 10.41 (s, 1H, Ar–OH). IR (cmÀ1):
2931.78 (C–H str), 1647.69 (C@N str of imines), 1261.13 (aromatic C@C str),
1238.12 (C–O str of phenols), m/z = 282
2
3
4
IVb
IVc
IVd
187–189
244–246
68–70
Cl
1H NMR: d 7.24 (s, 1H, N@CH–), 6.96–8.9 (m, Ar–H), 9.74 (s, 1H, Ar–OH). IR (cmÀ1):
2939.04 (C–H str), 1648.62 (C@N str of imines), 1267.35 (aromatic C@C str),
1249.54 (C–O str of phenols), m/z = 269
F
1H NMR: d 7.21 (s, 1H, N@CH–), 6.61–8.6 (m, Ar–H), 9.53 (s, 1H, Ar–OH). IR (cmÀ1):
2932.24 (C–H str), 1647.62 (C@N str of imines), 1277.28 (aromatic C@C str),
1249.87 (C–O str of phenols), m/z = 326
Br
1H NMR: d 3.8 (s, 3H, Ar–OCH3), d 6.96 (s, 1H, N@CH–), 6.9–8.9 (m, Ar–H), 9.75
(s, 1H, Ar–OH). IR (cmÀ1): 3310.35 (O–H str), 3134.37 (aromatic C–H str), 1653.07
(C@N str of imines), 1255 and 1043.54 (C–O str of phenyl alkyl ether), m/z = 278
5
6
IVe
IVf
134–136
112–114
OMe
–CH3
1H NMR: d 8.1 (s, 1H, N@CH–), 9.74 (s, 1H, Ar–OH). IR (cmÀ1): 2939.04 (C–H str),
1648.62 (C@N str of imines), 1267.35 (aromatic C@C str), 1249.54 (C–O str of phenols), m/z = 186

S. S. Chhajed et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3640–3644
3643
Table 4
Spectral and analytical data for target compounds (Va–f
)
Cl
R
HN
O
N
OH
Compound
–R
Mp (°C)
CHN calculated % found %
1H NMR (ppm), IR (cmÀ1, KBr), mass (m/e)
C
H
N
66.57
66.49
4.03
3.92
8.63
8.55
d 9.6 (s, 1H, Ar–OH), 5.0 (s, 1H, C4–H), d 5.4 (s, 1H, C3–H), 6.9–8.9 (m, Ar–H),
3294.66 (O–H str), 1747.34 (C@O str), 3119.37, (C–H str) 2889.02 (asym.
and sym. C–H str). m/e – 325
Va
166–168
60.19
60.09
3.37
3.28
7.80
7.70
d 9.5 (s, 1H, Ar–OH), d 5.1 (s, 1H, C4–H), d 5.6 (s, 1H, C3–H), d 6.8–8.9 (m, Ar–H),
3305.12 (O–H str), 3157 (aromatic C–H str), 2937.43, 2900.65 (asym. and sym.
C–H str) 1749.32 (C@O str). m/e – 345
Vb
134–136
Cl
63.08
63.01
3.53
3.43
8.17
8.11
d 9.5 (s, 1H, Ar–OH), d 5.2 (s, 1H, C4–H), d 5.4 (s, 1H, C3–H), d 6.7–8.6 (m, Ar–H),
3315.12 (O–H str), 3152 (aromatic C–H str), 2929.87, 2904.65 (asym. and sym.
C–H str) 1747.43 (C@O str). m/e – 342
Vc
220–222
182–184
F
56.67
56.56
3.25
3.18
3.48
3.41
d 9.4 (s, 1H, Ar–OH), d 5.2 (s, 1H, C4–H), d 5.8 (s, 1H, C3–H), d 6.8–9.3 (m, Ar–H),
3305.12 (O–H str), 3157 (C–H str), 2937.33, 2896.00 (asym. and sym. C–H str)
1749.46 (C@O str). m/e – 402
Vd
Br
64.32
64.21
4.26
4.19
7.90
7.80
d 3.8 (s, 3H, Ar–OCH3), 6.96 (s, 1H, N@CH–), 6.9–8.8 (m, Ar–H), 9.75 (s, 1H, Ar–OH),
3353.98 (O–H str), 3151 (C–H str), 2956.82 and 2937.35 (asym. and sym. C–H str),
1747.32 (C@O str), 1248.67 and 1035.56 (C–O str). m/e – 342
Ve
Vf
117–119
92–94
OMe
–CH3
59.44
59.49
4.22
4.16
10.66
10.57
d 10.1 (s, 1H, Ar–OH), d 5.4 (s, 1H, C4–H), d 6.1 (s, 1H, C3–H), d 2.3 (s, 3H –CH3),
3335.01 (O–H str), 2928.12, 2909.18 (asym. and sym. C–H str) 1739.09 (C@O str). m/e – 262
13. Srivastava, S.; Chauhan, P. M.; Bhaduri, A. P.; Murthy, P. K.; Chatterjee, R. K.
Bioorg. Med. Chem. Lett. 2000, 10, 313.
Acknowledgments
14. Tewari, S.; Chauhan, P. M. S.; Bhaduri, A. P.; Chatterjee, R. K. Bioorg. Med. Chem.
Our sincere thanks go to Dr. M.V.R. Reddy and Dr. Kalyan Gos-
ami, Department of Biochemistry, J.B. Tropical Disease Research
Centre, MGIMS, Sevagram, MS, India, for in vitro anti-filarial
screening. Professor Dr. Anjali Rahatgaonkar, Department of Chem-
istry, Institute of Science, Nagpur, SAIF Chandigarh, Punjab Univer-
sity for spectral studies.
Lett. 2000, 10, 1409.
15. Synthesis of 5-nitroso-8-hydroxyquinoline (I): 8-Hydroxyquinoline (7.34 g,
0.05 mol) was dissolved in
a continuously stirred solution of 66.7 mL of
distilled water and 3 mL of concentrated sulfuric acid at 15–18 °C. Sodium
nitrite (3.67 g) in distilled water (6.78 mL), was added drop wise to the
reaction mixture over
a period of 30–40 min at 15–18 °C, mixture was
maintained at this temperature for 3 h. The reaction mixture was neutralized
with 40% sodium hydroxide solution. It was then acidified with glacial acetic
acid to pH 3.0–4.0. Yellow precipitate obtained was filtered, washed with
distilled water, and dried. Yield: 6.7 g (89.5%) mp: 234–236 °C.
References and notes
16. Synthesis of 5-amino-8-hydroxyquinoline (III). 0.174 g (0.01 mol) of 5-nitroso-8-
hydroxyquinoline in 25 mL of concentrated hydrochloric acid was allowed to
warm. To this was added slowly, in small portions tin (Sn) metal (0.236 g,
0.02 mol). The reaction mixture was heated at reflux for 6 h in boiling water
bath. The reaction mixture was allowed to cool to room temperature. To the
reaction mixture was slowly added 20% solution of sodium hydroxide to get
the precipitate. 5-Amino-8-hydroxyquinoline was extracted with ether. Yield:
0.154 g (79.87%), mp: 137–140 °C, IR (cmÀ1): 3360.41–3270.26 (asymmetric
and symmetric N–H str, respectively), 1609.02 (N–H def) 1250 (C–N str), 1H
NMR: d 9.9 (s, 1H, Ar–OH), d 6.6–8.9 (M, Ar–H) d 3.97 (s, @N–H, Ar–NH2).
17. General procedure for synthesis of Schiff bases (IVa–f): Equimolar quantities of
substituted aromatic/aliphatic aldehydes and 5-amino-8-hydroxy quinoline
were dissolved in 20 mL of warm dry ethanol. To it 1–2 drops of concentrated
sulfuric acid were added and heated at reflux for 2–3 h. After standing for
approximately 24 h at room temperature, the crystalline product was
separated by filtration and dried. Physicochemical and spectral data is
summarized in Table 3.
1. Fischer, P.; Manoempil, T.; Supali, G. S.; Rucker, P. Trans. R. Soc. Trop. Med. Hyg.
2006, 11, 464.
2. Thomas, P. A. Parasitology 2001, 122, S65.
3. Ottesen, E. A. Trop. Med. Int. Health 2000, 5, 591.
4. Ottesen, E. A. Am. J. Trop. Med. Hyg. 1989, 41, S9.
5. Michael, E. D.; Bundy, A. P. Parasitol. Today 1997, 13, 472.
6. Khan, A. M.; Mahanta, J. Curr. Sci. 2005, 88, 1718.
7. Das, P. K.; Pani, S. P. Int. Med. Sci. Acad. 2000, 13, 18.
8. Hoerauf, A.; Volkmann, L.; Hamelmann, C.; Adjei, O.; Buttner, D. W. Lancet
2000, 35, 1242.
9. Chauhan, P. M. S.; Singh, S. N.; Chatterjee, R. K. Indian J. Chem., Sect B 1993, 32,
858.
10. Tripathi, R. P.; Katiyar, D.; Dwivedi, N.; Singh, B. K.; Pandey, J. Curr. Med. Chem.
2006, 13, 3319.
11. Collier, L.; Balows, A.; Sussman, M. Parasitology 1998, 5, 349.
12. Bose, C.; Agarwal, S. K.; Chatterjee, R. K.; Srivastava, V. M. Indian J. Chem., Sect B
1994, 33, 32.
18. General procedure for synthesis of 3-chloro-1-(8-hydroxyquinolin-5-yl)-4-
substituted-azetidin-2-one(Va–f): To 0.01 M substituted 5-(benzylideneamino)-

3644
S. S. Chhajed et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3640–3644
quinoline-8-ols (IVa–f), 20 mL of 1,4 dioxane was added. The mixture was
19. Mukherjee, M.; Misra, S.; Chatterjee, R. K. Acta Trop. 1998, 70, 251.
20. Gupta, S.; Srivastava, A. K. Acta Parasitol. 2005, 50, 1230.
21. Ahmad, R.; Srivastava, A. K. Helminthologia 2008, 45, 114.
22. Oakley, A. J.; Bello, M. L.; Battistoni, A.; Ricci, G.; Rossjohn, J.; Villar, H. O.;
Parker, M. W. J. Mol. Biol. 1997, 274, 84.
warmed to dissolve. The resultant solution was allowed to cool, and to it was
added 0.01 M triethylamine and 0.01 M chloroacetyl chloride with stirring.
Mixture was refluxed on the boiling water bath for 3–4 h. It was allowed to
cool and filtered at pump, air dried. Physicochemical and spectral data for
synthesized scaffold (Va–f) is summarized in the Table 4.