Synthesis and antibacterial activity evaluation of metronidazole-triazole conjugates

Article abstract of DOI:10.1016/j.bmcl.2009.01.037

Synthesis and antibacterial activity of metronidazole-triazole conjugates are reported. Total 21 hybrid compounds have been synthesized with different substitution pattern on the triazole ring in order to study their influence on the antibacterial activit

Full text of DOI:10.1016/j.bmcl.2009.01.037

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1396–1398
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antibacterial activity evaluation of metronidazole–triazole
conjugates
Beena a, Nitin Kumar a, Rajesh K. Rohilla b, N. Roy b, Diwan S. Rawat a,
*
a Department of Chemistry, University of Delhi, Delhi 110007, India
b Department of Biotechnology, National Institute of Pharmaceutical Education and Research, SAS Nagar, Punjab 160062, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis and antibacterial activity of metronidazole–triazole conjugates are reported. Total 21 hybrid
compounds have been synthesized with different substitution pattern on the triazole ring in order to
study their influence on the antibacterial activity. These compounds demonstrated potent to weak anti-
bacterial activity against Gram-positive, and Gram-negative bacteria. Six compounds have shown equal
or better antibacterial activity against Gram-negative strains than the reference compound.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 31 October 2008
Revised 12 January 2009
Accepted 14 January 2009
Available online 19 January 2009
Keywords:
Metronidazole
Triazole
Antbacterial activity
Metronidazole, (MTZ, 1-[2-hydroxyethyl]-2-methyl-5-nitroimi-
dazole) has been a drug of choice for the treatment of anti-infec-
tious diseases against protozoa such as Trichomonas vaginalis,
Entamoeba histolytica, Giardia intestinalis, and infections caused
by Gram-negative anaerobes such as bacteroides and Gram-posi-
tive anaerobes such as clostridia.1–5 MZT has extensively been used
for the treatment of anaerobic infections after bowel surgery, and
infections caused by Clostridium difficile.6,7 MZT in combination of
other drugs has been used for the treatment of infections caused
by Helicobacter pylori8 and has also been used for the radiosensiti-
zation of hypoxic tumors and Crohn‘s disease.9–11 Since its discov-
ery in 1959, metronidazole has been among the top 100 most
prescribed drugs in the US and one of the 10 most used drugs dur-
ing pregnancy.12,13 Even today, it remains one of the best drug for
the treatment of Trichomonas vaginalis infections, a common dis-
ease of the pregnant women with a cure rate of approximately
95%.14,15 However, resistance to these compounds have been dem-
onstrated in trichomonads and Bacteroides fragilis, in both natural
and in vitro under drug pressure-induced populations.16,17 We
anticipated that hybrid molecule that contains metronidazole
and triazoles, one of the most active and widely studied pharmaco-
phore,18–20 will lead to a molecule of biomedical importance. For
this we decided to functionalize hydroxyl functionality of MTZ in
such a way that MTZ can be covalently linked to triazoles. As part
of our ongoing efforts towards the synthesis of biologically active
compounds,21–23 we report herein synthesis and antibacterial
activity of metronidazole–triazole conjugates. Synthesis of metro-
nidazole–triazole conjugates started from the preparation of
substituted alkynes by the literature method (scheme 1).24–26 1-
(2-Azido-ethyl)-2-methyl-5-nitro-1H-imidazole (5)27 was pre-
pared by literature method (scheme 2). Subsequent reaction of
compound 5 with substituted terminal alkynes (2a–2k) in pres-
ence of sodium ascorbate, and CuSO4Á5H2O in t-BuOH/H2O (1:1),
lead to the formation of desired hybrid molecules in good yield
(6a–6o, and 7a–7f). All of the reported compounds were purified
over silica gel column and characterized spectroscopically.28
In vitro antibacterial activity. Antimicrobial susceptibility testing
was carried out using National Committee for Clinical Laboratory
Standards (NCCLS) microdilution assay. Briefly, the bacterial
strains were grown in standard media until exponential growth
was achieved. Tests were performed in a 96-well microtiter plate
in a final volume of 100 ll. Test compounds were dissolved in 5%
DMSO at an initial concentration of 500
l
g and serially diluted in
OH
(i)
O
R
R
1
2a, R = H; 2b, R = o-methyl;
2c, R = p-methyl; 2d, R = m-methyl;
2e, R = o-NO2; 2f, R = p-NO2;
2g, R = o-CHO; 2h, R = p-CHO;
2i, R = p-COCH3; 2j, R = o-Cl;
2k, R = p-Cl
* Corresponding author. Tel.: +91 11 27667465; fax: +91 11 27667501.
E-mail address: dsrawat@chemistry.du.ac.in (D.S. Rawat).
Scheme 1. Reagents and condition: (i) Propargyl bromide, K2CO3, DMF, rt.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.01.037

Beena et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1396–1398
OH
1397
N3
NO2
NO2
OTs
NO2
(ii)
(i)
N
N
N
N
N
N
Me
Me
Me
3
5
4
R
R
O
N3
NO2
N
N
NO2
N
N
NO2
N
N
(iii)
(iii)
N
N
N
R
N
OR
N
N
Me
Me
6a, R = H; 6b, R = Me
6c, R = COEt; 6d, R = THP
6e, R = Ph; 6f, R = o-Me-Ph;
6g, R = p-Me-Ph; 6h, R = m-Me-Ph;
6i, R = o-NO2-Ph; 6j, R = p-NO2-Ph;
Me
5
7a, R = CH2CH2OH; 7b, R = CH2Br
7c, R = Ph; 7d, R = 2-Pyridine
7e, R = 3-Pyridine; 7f, R = 1-Cyclohexanole
6k, R = o-CHO-Ph; 6l, R = p-CHO-Ph;
6m, R = p-CH3CO-Ph; 6n, R = o-Cl-Ph;
6o, R = p-Cl-Ph
Scheme 2. Reagents and conditions: (i) Pyridine, p-TsCl, rt, 12 h; (ii) NaN3, DMF, 0 °C, and 70–80 °C; 1 h; (iii) t-BuOH:H2O (1:1), Sodium ascorbate, CuSO4Á5H2O.
plate. Each well was then inoculated with ꢀ2–5 Â 105 bacterial
cells and incubated at 37 °C for 24 h with shaking at 200 rpm.
One well containing cells and 5% DMSO without any test com-
pound (growth control), and one well containing only growth med-
ium (sterility control) were used as controls. Growth of bacteria
was determined using Power wave200 microplate scanning spec-
trophotometer (Bio-Tek Instruments, Winooski, VT, USA). Percent
survival was calculated using growth without any compound as
100% survival. IC50 values are calculated using Grafit 4.0 software
(Erithacus Software Ltd., Horley, Surrey, UK).
The compounds were evaluated against Gram-positive and
Gram-negative bacterial strains. IC50 values of each compounds
are shown in Table 1.
Compound 6a has shown potent antibacterial activity against
Gram-positive as well as Gram-negative bacteria with IC50 value
of 0.091–0.35 lg/mL. Introduction of one more CH2 group between
OH and CH2 of compound 6a, results in total loss of antibacterial
activity of the compound (entry 7a). Similarly substitution of OH
by OCOEt, OMe, tetrahydropyran or Br functional group in com-
pound 6a leads devoid of antibacterial activity of the compounds
(entry 6b–6d, and 7b). Compound 6l having CHO group at the para
position of the phenyl ring exhibit potent antibacterial activity
against E. Coli, P. aerogenosa while it has been inactive against
Gram-positive bacteria. Substitution at para position of the phenyl
ring by methyl, CHO or chloro group have shown very good anti-
bacterial activity of these compounds (6g, 6l, and 6o). Presence
of NO2 group at any position of the phenyl ring results in the de-
void of antibacterial activity of the compounds (entry 6i, and 6j).
From structural subset of 21 compounds, it is clear from Table 1
that substitution at ortho position of the phenyl ring has negative
effect on the antibacterial activity (entry 6f, 6n) and unsubstituted
phenyl ring containing compound also shows good antibacterial
activity (entry 6e) Similarly, compounds having phenyl or pyridyl
groups directly attached with the triazole ring exhibit potent anti-
bacterial activity (entry 7c–7e). Six compounds (6a, 6f–6h, 6l, 6o)
have shown better or equal antibacterial activity against Gram-
negative strains than tetracycline, which has been used as a stan-
dard drug in this study. Further structural modification of the most
active compounds (6a, 6f–6h, 6l, 6o, 7c–7f) is under progress and
results will be published in due course of time. All of these com-
pounds have also been tested against G. candidum, C. galbrata and
C. albicans and found to be inactive.
Table 1
Antibacterial activity of metronidazole–triazole conjugates
Compound
IC50
P. aerogenosa
(
l
g/mL)
E. Coli
S. aeureus
E. epidermidis
6a
6b
6c
6d
6e
6f
6g
6h
6i
0.091
0.180
0.350
0.350
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
0.670
0.028
0.060
0.130
*
0.030
0.130
In conclusion, we have reported the synthesis of 21 new metro-
nidazole–triazole conjugates and evaluated their antibacterial
activity. Some of the compounds exhibit weak to potent anti-bac-
terial activity against Gram-positive bacteria, but have shown po-
tent activity against Gram-negative bacteria. In particular six of
the reported compounds shows better antibacterial activity against
Gram-negative strains than the tetracycline which has been used
as a reference compound.
0.067
0.068
0.260
*
*
*
*
*
*
*
*
*
*
*
*
6j
6k
6l
0.070
0.070
*
*
6m
6n
6o
7a
7b
7c
7d
7e
7f
*
*
0.003
0.020
0.130
*
*
*
*
*
*
*
0.130
0.130
Acknowledgments
0.120
0.130
0.130
*
*
0.310
*
*
0.180
0.060
D.S.R. thanks Department of Science and Technology (SR/S1/OC-
08/2008), New Delhi, India for financial support. Beena and N.K. are
thankful to CSIR, New Delhi for the award of junior research
fellowship.
Tet
0.090
0.120
0.080
TetTetracycline was used as a reference compound.
*
IC50 > 500 lg/ml.

1398
Beena et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1396–1398
12. Bendesky, A.; Menendez, D.; Wegman-Ostrosky, P. Mut. Res. 2002, 511, 133.
Supplementary data
13. Thapa, P. B.; Whitlock, J. A.; Brockman, K. G.; Gideon, P.; Mitchel, E. F.; Pais, R.;
Ray, W. A. Cancer 1998, 83, 1461.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.01.037.
14. Durel, P.; Roiron, V.; Siboulet, A.; Borel, L. J. Br. J. Vener. Dis. 1960, 36, 21.
15. Crowell, A. L.; Sanders-Lewis, K. A.; Secor, W. E. Antimicrob. Agents Chemother.
2003, 47, 1407.
16. Meingassner, J. G.; Mieth, H.; Czok, R.; Lindmark, D. G.; Muller, M. Antimicrob.
Agents Chemother. 1978, 13, 1.
References and notes
17. Britz, M. L.; Wilkinson, R. G. Antimicrob. Agents Chemother. 1979, 16, 19.
18. Como, J. A.; Dismukes, W. E. N. Engl. J. Med. 1994, 330, 2126.
19. Demaray, J. A.; Thuener, J. E.; Dawjon, M. N.; Sucheck, S. J. Bioorg. Med. Chem.
Lett. 2008, 18, 4868.
20. Lin, R.; Connolly, P. J.; Huang, S.; Wetter, S. K.; Lu, Y.; Murray, W. V.; Emanuel, S.
L.; Gruninger, R. H. J. Med. Chem. 2005, 48, 4208.
1. Celik, A.; Ates, N. A. Drug Chem. Toxicol. 2006, 29, 85.
2. Finegold, S. M. Ann. Intern. Med. 1980, 93, 585.
3. Samuelson, J. Antimicrob. Agents Chemother. 1999, 43, 1533.
4. Freeman, C. D.; Klutman, N. E.; Lamp, K. C. Drugs 1997, 54, 679.
5. Goldman, P.; Koch, R. L.; Yeung, T. C.; Chrystal, E. J.; Beaulieu, B. B. Jr.;
Maclafferty, M. A.; Sudlow, G. Biochem. Pharmacol. 1986, 35, 43.
6. Soltys, B. J.; Gupta, R. S. J. Parasitol. 1994, 80, 580.
21. Atheaya, H.; Khan, S. I.; Mamgai, R.; Rawat, D. S. Bioorg. Med. Chem. Lett. 2008,
18, 1446.
22. Joshi, M. C.; Bisht, G. S.; Rawat, D. S. Bioorg. Med. Chem. Lett. 2007, 17, 3226.
23. Sharma, M.; Agarwal, N.; Rawat, D. S. J. Heterocylic Chem. 2008, 45, 737.
24. Ishikawa, T.; Mizutani, A.; Miwa, C.; Oku, Y.; Komano, N.; Takami, A.;
Watanabe, T. Heterocycles 1997, 45, 2261.
25. Pal, M.; Parasuraman, K.; Yeleswarapu, K. R. Org. Lett. 2003, 5, 349.
26. Joshi, M. C.; Joshi, P.; Rawat, D. S. Arkivoc 2006, 16, 65.
27. Hay, M. P.; Wilson, W. R.; Moselen, J. W.; Palmer, B. D.; Denny, W. A. J. Med.
Chem. 1994, 37, 381.
7. Wilcox, M. H. J. Antimicrob. Chemther. 1998, 41C, 41.
8. Falagas, M. E.; Walker, A. M.; Jick, H.; Ruthazer, R.; Griffith, J.; Snydman, D. R.
Clin. Infect. Dis. 1998, 26, 384.
9. Breccia, A.; Cavalerri, B.; Adams, G. E. Nitroimidazoles: Chemistry, Pharmacology
and Clinical Application; Plenum Press: New York, 1982.
10. Nair, M. D.; Nagarajan, K. In Progress in Drug Research: Nitroimidazoles as
Chemotherapeutic Agents; Jucker, E., Ed.; Birkhauser Verlag: Basel, 1983; Vol.
27, pp 163–252.
28. Synthetic methods and analytical data of all of the compounds reported in this
paper can be found at supporting information section.
11. Cudmore, S. L.; Delgaty, K. L.; Hayward-McClelland, S. F.; Petrin, D. P.; Garber,
G. E. Clin. Microbiol. Rev. 2004, 17, 783.