Antiplasmodial and cytotoxicity evaluation of 3-functionalized 2-azetidinone derivatives

Article abstract of DOI:10.1016/j.bmcl.2011.05.119

3-Azido-, 3-amino- and 3-(1,2,3-triazol-1-yl)-β-lactams were synthesized and evaluated for their antiplasmodial activity against four strains of Plasmodium falciparum and KB cells for their cytotoxicity profiles. The presence of a cyclohexyl substituent at N-1 and a phenyl group on the triazole ring markedly improved the activity profiles of triazole-tethered β-lactam exhibiting IC₅₀ values of 1.13, 1.21 and 1.00 μM against 3D7, K1 and W2 strains respectively.

Full text of DOI:10.1016/j.bmcl.2011.05.119

Bioorganic & Medicinal Chemistry Letters 21 (2011) 4561–4563
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Antiplasmodial and cytotoxicity evaluation of 3-functionalized 2-azetidinone
derivatives
Pardeep Singh a, Shaveta Sachdeva a, Raghu Raj a, Vipan Kumar a, , Mohinder P. Mahajan a, Shereen Nasser b,
⇑
Livia Vivas b, Jiri Gut c, Phillip J. Rosenthal c, Tzu-Shean Feng d, Kelly Chibale d
a Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India
b London School of Hygiene and Tropical Medicine, Keppel Street, London, UK
c Department of Medicine, San Francisco General Hospital, CA 94143, USA
d Department of Chemistry and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Private Bag, Rondebosch 7701, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
3-Azido-, 3-amino- and 3-(1,2,3-triazol-1-yl)-b-lactams were synthesized and evaluated for their anti-
plasmodial activity against four strains of Plasmodium falciparum and KB cells for their cytotoxicity pro-
files. The presence of a cyclohexyl substituent at N-1 and a phenyl group on the triazole ring markedly
improved the activity profiles of triazole-tethered b-lactam exhibiting IC50 values of 1.13, 1.21 and
Received 8 February 2011
Revised 27 May 2011
Accepted 31 May 2011
Available online 12 June 2011
1.00 lM against 3D7, K1 and W2 strains respectively.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
c-3 Functionalized b-lactams
Triazoles
Click chemistry
Antiplasmodial evaluation
Malaria is the most common of the parasitic diseases in tropical
and subtropical regions, and it is estimated that about 40% of the
world’s population lives in malaria endemic areas. With 300–500
million clinical cases and nearly 1 million deaths each year, malaria
remains a major issue in health control, especially in developing
countries.1 Quinoline-containing compounds have long been used
for the treatment of malaria, and systematic modification has led
to a variety of antimalarial drugs with diverse substitutions around
the quinoline ring.2 The emergence of Plasmodium falciparum
strains resistant to chloroquine, the cheapest and most widely used
drug has caused global concern as the alternatives available are
expensive and mostly beyond the reach of the affected population.
Urgent efforts are therefore necessary to identify new classes of
antimalarials3 and develop them as drugs with varied modes of ac-
tion to overcome the problem of resistance.4
significance.6 Because of this general trend of b-lactam use, the
search for clinically useful b-lactams that are antibiotics or have
other medically importance properties will continue. However, to
the best of our knowledge, not many reports have appeared in lit-
erature concerning the exploration of b-lactams as potential anti-
malarial agents.7 In continuation with our pursuits for the
synthesis of functionalized monocyclic b-lactam-derived medici-
nally important scaffolds,8 we report herein the synthesis and eval-
uation of 3-azido-, 3-amino- and 3-(1,2,3-triazol-1-yl)-b-lactams
and their evaluation against chloroquine sensitive (CQ-S) and chlo-
roquine resistant (CQ-R) strains of P. falciparum along with their
cytotoxic profiles against KB cells. The styryl group has been intro-
duced at C-4 position of the b-lactam ring because of its well doc-
umented potential in enhancing the anticancer profiles against KB
cells.9
Since the advent of penicillin, b-lactam antibiotics have been
the subject of much discussion and investigation; within both
the scientific and public sectors.5 The need for potent and effective
The desired scaffolds were synthesized by Staudinger reaction
of appropriately functionalized 1-azadienes with azido-ketene
generated in situ from azido-acetic acid in the presence of p-tolu-
ene sulphonylchloride and triethylamine in dry dichloromethane.
The structure to 3-azido-2-azetidinones 2, thus formed is assigned
on the basis of analytical data and spectral evidences (Scheme 1).
The cis-stereochemistry to the products was assigned on the basis
of observed coupling constant J = 5.4 Hz between H1 and H2.10
The 3-azido-2-azetidinone was then reduced by following the
zinc-ammonium chloride reduction protocol11 to result in the iso-
lation of corresponding 3-amino-2-azetidinones which were again
b
-lactamase antibiotics as well as more effective b-lactamase
inhibitors has motivated medicinal chemists to design new func-
tionalized 2-azetidinones, apart from their clinical use as antibac-
terial agents. These compounds have also been used as synthons
in the preparation of various heterocyclic compounds of biological
⇑
Corresponding author.
E-mail address: vipan_org@yahoo.com (V. Kumar).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.05.119

4562
P. Singh et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4561–4563
R
N
R
O
R
O
N
N
Zn/NH4Cl
C2H5OH:H2O
p-TsCl, Et3N
dry dichloromethane
OH
+
N3
NH2
N3
O
Ph
3
2
Ph
1
Ph
Entry
R
% yield
Entry
R
% yield
74
3a p-C6H5Cl
3b C6H11
81
80
2a
2b
2c
2d
2e
C6H5
p-C6H4-CH3 76
p-C6H5Cl 77
C6H11 73
C6H5CH2 75
3c p-C6H4-CH3 83
3d
C6H5
79
Scheme 1.
R
O
R
O
CuSO4.5H2O
Sodium ascorbate
ethanol:H2O
N
N
R2
R1
R2
+
N3
N
N
R1
N
Ph
Ph
4
2
Entry
4a
R
R1
R2
% yield
p-C6H5-CH3 CO2CH3 CO2CH3
C6H11 CO2CH3 CO2CH3
p-C6H4-Cl CO2CH3 CO2CH3
88
87
90
83
85
86
88
4b
4c
4d
4e
4f
C6H5
C6H5
C6H5
H
H
H
H
C6H11
p-C6H4-Cl C6H5
p-C6H5-CH3 C6H5
4g
Scheme 2.
characterized on the basis of analytical and spectral data. The
3-azido-2-azetidinone was also explored in click chemistry ap-
proaches utilizing azide-alkyne cycloaddition in the presence of
CuSO4Á5H2O/sodium ascorbate in ethanol–water mixture at room
temperature. The reaction resulted in good to excellent yields of
triazole-tethered b-lactams which were assigned the structure on
the basis of spectral studies and analytical data (Scheme 2).12
The synthesized b-lactams 2a–e to 3a–d were tested for their
antimalarial potential against D10 (Chloroquine sensitive) strain
of P. falciparum. Although the compounds didn’t show any
considerable antiplamodial activity when compared to the stan-
dard agent Chloroquine, they displayed an interesting behaviour
with respect to the substituents on N-1 and C-3 of the lactam ring.
As evident from the activity data, compounds with azido substi-
tuent at C-3 (2a–2e) displayed much better antimalarial profiles as
compared to the amine scaffolds (3a–3d). The activity was further
enhanced with the introduction of N-alkyl substituent on N-1 with
2d and 2e having cyclohexyl and benzyl substituents displayed
IC50 values of 2.36 and 4.70
lM respectively. The C-3 triazole
tethered b-lactams were evaluated against 3D-7 (Chloroquine
Table 1
Antiplasmodial and cytotoxic profiles of the test compounds
c log Pb Compound
3D7(CQ-S)a
K1 (CQ-R)a
W2 (CQ-R)a
KB cells (% inhibition)a
c log Pb
a
Compound
IC50
(lM)
(D10) (CQ-S)
IC50
(
lM)
IC50
(
lM)
IC50 (lM)
(10
lM) (100
l
M) IC50
M)
(
l
2a
2b
2c
2d
2e
3a
3b
3c
10.35
5.83
4.47
2.36
4.70
38.06
18.59
59.85
29.28
0.002
4.27
4.77
5.13
4.24
3.96
4.38
3.63
4.03
3.53
4a
4b
4c
4d
4e
4f
ND
ND
>20
>20
>20
ND
ND
8.07
ND
4.00
>45.66
25.05
>51.02
1.13
7.86
11.99
0.002
>45.66
12.27
>51.02
1.21
7.09
3.42
À7.70
19.48
10.02
76.75
16.84
14.66
31.42
>228.31 3.45
56.48
58.26
99.70
79.30
80.79
96.95
145.29
91.25
8.36
84.17
89.15
35.95
4.35
5.80
5.93
6.65
6.30
11.725
1
1
1
4g
CQ
0.012
0.02366
3d
CQ (Chloroquine)
POD
81.49
84.70
0.0005
(Podophyllotoxin)
(0.50 lM)
a
CQ-S: chloroquine sensitive, CQ-R: chloroquine resistant.
Calculated using Chemdraw Ultra 10.0;14 ND = not determined.
b

P. Singh et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4561–4563
4563
4. (a) Vennerstrom, J. L.; Arbe-Barnes, S.; Brun, R.; Charman, S. A.; Chiu, C. K.;
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Chem. Res. 1995, 28, 383; (f) Ojima, I.; Delaloge, F. Chem. Soc. Rev. 1997, 26, 377;
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D’hooghe, M.; Dekeukeleire, S.; Leemans, E.; De Kimpe, N. Pure Appl. Chem.
2010, 82, 1749.
sensitive); K1 (Chloroquine resistant); W2 (Chloroquine resistant)
strains for their malarial efficacy and KB cells, a cell line derived
from a human carcinoma of the nasopharynx, typically used as
an assay for antineoplastic agents, for cytotoxic profiles. KB cells
are maintained as monolayers in RPMI1640 + 10% HIFCS. All cul-
tures and assays are conducted at 37 °C under an atmosphere of
5% CO2/95% air mixture with Podophyllotoxin (POD) as the control
drug.13
The test compounds showed comparatively much weaker cyto-
toxic profiles compared to the standard agent Podophyllotoxin
while a comparable activity was observed when compared with
chloroquine. The results clearly revealed that the compounds
showed concentration dependent cytotoxicity with significant in-
crease in growth inhibition as the concentration increases from
10 lM to 100 lM as shown by the compounds 4e, 4f and 4g. The
compounds 4d–4g viz phenyl substituted triazoles have shown
potentially better cytotoxic profile compared to the carbome-
thoxy-substituted triazoles (4a–4c). The enhancement in activity
has been observed in case of N-cyclohexyl derivative 4e exhibiting
7. Nivsarkar, M.; Thavaselvam, D.; Prasanna, S.; Sharma, M.; Kaushik, M. P. Bioorg.
Med. Chem. Lett. 2005, 15, 1371.
8. (a) D’hooghe, M.; Dekeukeleire, S.; Mollet, K.; Lategan, C.; Smith, P. J.; Chibale,
K.; De Kimpe, N. J. Med. Chem. 2009, 52, 4058; (b) Anand, A.; Bhargava, G.;
Kumar, V.; Mahajan, M. P. Tetrahedron Lett. 2010, 51, 2312; (c) Singh, P.;
Bhargava, G.; Kumar, V.; Mahajan, M. P. Tetrahedron Lett. 2010, 51, 4272.
9. Nam, D. H.; Lee, K. Y.; Moon, C. S.; Lee, Y. S. Eur. J. Med. Chem. 2010, 45, 4288.
10. 3-Azido-1-cyclohexyl-4-styryl-azetidin-2-one (2d). Yellow oil, yield: 72%; IR
>99% growth inhibition with IC50 value of 8.36 lM better than that
of CQ (Table 1). A similar trend was observed in anti-malarial eval-
uation. The compounds 4e, 4f and 4g showed better antimalarial
efficacy among the test compounds with 4e exhibiting an IC50 va-
(KBr) m ;
max: 2108, 1755, 1514, 1388 cmÀ1 1H NMR (300 MHz, CDCl3), d 1.0–1.9
lue of 1.13, 1.21 and 1.00 lM against 3D-7, K1 and W2 strains. This
(m, 10H, Cyclohexyl H), 3.46 (m, 1H, Cyclohexyl H) 4.42 (dd, J = 5.4 Hz, 9.0 Hz,
1H, H2), 4.7 (d, J = 5.4 Hz,1H, H1), 6.15 (dd, J = 9.0 Hz, 15.9 Hz,1H, H3), 6.68 (d,
J = 15.9 Hz 1H, H4), 7.26–7.45 (m, 5H, Ar-H), 13C (CDCl3, 75 Hz): 22.3, 27.1, 31.1,
47.3, 53.3, 63.4, 123.3, 126.1, 127.0, 127.1, 128.0, 134.3, 173.3; MS m/z 296
(M+); Anal. calcd for C17H20N4O: C, 68.89 H,6.80; N, 18.90. Found: C, 68.83; H,
6.72; N, 18.86.
further confirms the presence of alkyl substituent preferably cyclo-
hexyl at N-1 and phenyl ring on the triazole being critical for good
activity profiles.
In conclusion, the synthesis of 3-azido-, 3-amino- and 3-(1,2,
3-triazol-1-yl)-b-lactams and their evaluation for antiplasmodial
and cytotoxic activity has been described. The compounds with
an N-cyclohexyl substituent in the b-lactam ring and a phenyl
group on the triazole showed better cytotoxicity as well as anti-
plasmodial activity. The results described indicate that these com-
pounds could serve as the basis for the development of a new
group of non-cytotoxic antiplasmodial agents.
11. Lin, W.; Zhang, X.; He, Z.; Jin, Y.; Gong, L.; Mi, A. Synth. Commun. 2002, 32, 3279.
12. General Procedure for the synthesis of triazole-tethered b-lactams (4). To a stirred
solution of azide (1 mmol) in ethanol:water (10:1) was added in succession
phenyl acetylene (1.1 mmol), copper sulphate (0.055 mmol) and sodium
ascorbate (0.143 mmol) at room temperature. On completion, as monitored
by tlc, water (15 ml) was added to the reaction mixture and extracted with
chloroform (2 Â 50). Combined oragnic layers were dried over anhydrous
sodium sulphate and concentrated under reduce pressure to result in a crude
product which was recrystallized using chloroform: hexane (2:10) mixture.
1-Cyclohexyl-3-(4-phenyl-[1,2,3]triazol-1-yl)-4-styryl-azetidin-2-one (4e). White
solid, yield 70%; mp 195–197 °C; IR (KBr)
NMR (300 MHz, CDCl3), 1.0–1.9 (m,10H, Cyclohexyl ring), 3.46 (m,1H,
m ;
max: 1755, 1514, 1388 cmÀ1 1H
Acknowledgement
d
Cyclohexyl ring), 5.13 (dd,J = 5.4 Hz, 9.0 Hz, 1H, H2), 5.80 (dd, J = 9.0 Hz,
15.9 Hz, 1H, H3), 6.36 (d, J = 5.4 Hz, 1H, H1), 6.71 (d, J = 15.9 Hz, 1H, H4), 7.26–
7.78 (m, 10H, Ar-H), 7.94 (s, 1H, triazole ring), 13C (CDCl3, 75 Hz): 22.3, 27.1,
31.1, 47.3, 60.4, 67.6, 123.5, 126.4, 127.2, 127.6, 127.9, 128.8, 129.0, 129.4,
131.4, 134.5, 134.8, 136.4, 173.3.; MS m/z 398 (M+); Anal. calcd for C25H26N4O:
C, 75.35 H, 6.58; N, 14.06. Found: C, 75.30; H, 6.52; N, 13.99.
Financial assistance from DST New Delhi under Fast Track
Young Scientist Scheme (VK) is gratefully acknowledged
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