Synthesis and antiamoebic activity of new cyclooctadiene ruthenium(II) complexes with 2-acetylpyridine and benzimidazole derivatives

Article abstract of DOI:10.1016/S0960-894X(00)00446-7

Reaction of [Ru(η⁴-C₈H₁₂) (CH₃CN)₂ Cl₂] with 2-(2-pyridyl) benzimidazole or Schiff bases derived from 2-acetylpyridine and S-methyldithiocarbazate, S-benzyldithiocarbazate and thiosemicarba

Full text of DOI:10.1016/S0960-894X(00)00446-7

Bioorganic & Medicinal Chemistry Letters 10 (2000) 2243±2245
Synthesis and Antiamoebic Activity of New Cyclooctadiene
Ruthenium(II) Complexes with 2-Acetylpyridine and
Benzimidazole Derivatives
Neelam Bharti,a Mannar R. Maurya,b Fehmida Naqvia and Amir Azama,*
aDepartment of Chemistry, Jamia Millia Islamia, Jamia Nagar, New Delhi 110 025, India
bDepartment of Chemistry, University of Roorkee, Roorkee 246776, U.P., India
Received 15 May 2000; accepted 17 July 2000
AbstractÐReaction of [Ru(ꢀ4-C8H12) (CH3CN)2 Cl2] with 2-(2-pyridyl) benzimidazole or Schi€ bases derived from 2-acetylpyridine
and S-methyldithiocarbazate, S-benzyldithiocarbazate and thiosemicarbazide leads to form new complexes of the type [Ru(ꢀ4-
C8H12)(L)C12] (where L=ligand). In vitro, most of the compounds exhibited potent activity and the Ru derivatives 1a [Ru(ꢀ4-
C8H12)(2-Acpy-SMDT)Cl2], 2a [Ru(ꢀ4-C8H12)(2-Acpy-SBDT)Cl2] and 3a [Ru(ꢀ4-C8H12)(2-Acpy-TSC)Cl2] were found more active
than metronidazole against (HK-9) strain of Entamoeba histolytica. # 2000 Elsevier Science Ltd. All rights reserved.
Amoebiasis is a world-wide parasitic disease and a
public health problem in developing countries,1 which is
responsible for up to 100,000 deaths per annum.2
Metronidazole [1-(2-hydroxyethyl)-2-methyl-5-nitroimid-
azole], is one of the most e€ective antiamoebic medications.
However, it has mutagenic e€ect in bacteria, is carcinogenic
to rodents3 and is associated with transient myopia,
neuropathy and immunosuppression.4 There have been few
reports of resistance of E. histolytica to metronidazole.5
The drug is relatively ine€ective against asymptomatic
infection in the intestinal lumen.3 Therefore, the ideal
treatment for this disease does not exist and new agents
are required.6 There is rapidly growing interest in the use
of transition metal complexes in medicine and other bio-
logical areas, particularly in the ®eld of cancer.7 Hetero-
cyclic thiosemicarbazone and its metal complexes are
important due to their biological activity.8 Thiosemi-
carbazone derivatives are important due to their anti-
bacterial,9 antiprotozoal,10 antiviral11 and antineoplastic12
activities. The Ru complexes were also tested against
malaria13 and trypanosoma.14 The antitumor properties
of a number of transition metal complexes of methyl 3-
[1-(2-pyridyl) ethylidene] carbodithioate15 have been
reported. Earlier studies on Ru complexes, such as cis-
RuCl2(DMSO)4 as antineoplastic agents, have suggested
a DNA binding mechanism.16 [RuCl2(DMSO)2(4-nitro-
imidazole)2] has been used as radiosensitizer successfully.16
Additional advantages of Ru are the availability of
both the Ru(II) and Ru(III) oxidation states under
physiological conditions and the general substitution
inertness of these ions when coordinated to nitrogen
ligand.17
In a previous paper of this series we have described our
strategy for the development of alternative metal based
drugs against E. histolytica.18 Continuing our e€orts to
develop improved antiamoebic drugs, we now report
that coordination compounds of the following ligands
(Fig. 1) with 1,5-cyclooctadiene ruthenium(II) fragment
produce new compounds which are very active against
in vitro culture of E. histolytica.
Chemistry
The precursor [Ru(ꢀ4-C8H12)(CH3CN)2C12] was syn-
thesized as reported by Albers et al.19 S-Methyldithio-
carbazate,20 S-benzyldithiocarbazate21 and 2-(2-pyridyl)
benzimidazole22 were prepared using literature procedures.
The Schi€ bases, 2-Acpy-SMDT (1), 2-Acpy-SBDT (2)
and 2-Acpy-TSC (3) were prepared by re¯uxing equimolar
amounts of 2-acetylpyridine and the respective amine in
methanol. Their purities were checked by their melting
point determinations and structures were con®rmed by
IR, H NMR and electronic spectral studies. All (ꢀ4-
1
C8H12)Ru(II) complexes were prepared by mixing
an appropriate ligand (0.001 mol) and [Ru(ꢀ4-C8H12)
(CH3CN)2Cl2] (0.001 mol) in re¯uxing methanol. The
*Corresponding author. Tel.:+0091-11-6831717/338; fax: +0091-11-
6821232; e-mail: amir_ch@jmi.ernet.in
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00446-7

2244
N. Bharti et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2243±2245
Figure 1. 2-Acpy-SMDT=2-acetylpyridine-S-methyldithiocarbazate, 2-Acpy-SBDT=2-acetylpyridine-S-benzyldithiocarbazate, 2-Acpy-TSC=2-
acetylpyridine thiosemicarbazide, 2-(2-Py-BMZ)=2-(2-pyridyl)benzimidazole.
product thus separated was ®ltered after cooling the
solution at 0 ꢀC overnight and washed with methanol.
shift of v(CˆN) (azomethine) to higher frequency in
comparison to their respective free ligand, indicates the
coordination of azomethine nitrogen to ruthenium. A
1
strong band at 1050±1083 cm ascribed to v(CˆS) of
ligands is shifted to lower frequency (20±57 cm 1),
indicating the bonding of metal through thionic sul-
phur. The preferential coordination of sulphur over
pyridinic nitrogen is due to the more nucleophilic
character of the former. Thus, an octahedral structure
(Fig. 2) is suggested for these complexes. Spectral data
(IR as well as 1H NMR) of 4a are comparable
to [M0O2{2-(2-py-BMZ)}] where coordination through
both nitrogen atoms has been con®rmed.24
CH3OH
‰Ruꢀꢀ4-C8H12†ꢀCH3CN†2Cl2Š ‡ L
‰Ruꢀꢀ4-C8H12†ꢀL†Cl2Š ‡ 2CH3CN
(where L=ligands 1, 2, 3 and 4).
!
5 h; reflux
Recrystallizations were e€ected in methanol:DMF (9:1).
All these complexes are insoluble in water, sparingly
soluble in methanol and ethanol, and fairly soluble in
DMF and DMSO. These complexes are high melting
solids and decompose before their melting temperature.
Analytical and spectral data (IR, electronic and 1H
NMR)23 are in good agreement with the composition
[Ru(Z4-C8H12) (L)Cl2]. Analytical and other physico-
chemical data of the complexes are presented in Table 1.
The band due to v(CˆN) (ring) of the pyridine moiety
remains unaltered in 1a, 2a and 3a (Fig. 2) while the
Biological Properties
Preliminary experiments were carried out to determine
the antiamoebic activities of ligands (1±4) and their
complexes (1a±4a) using in vitro culture against HK-9
strain of E. histolytica as previously described25 using
a method in which amoeba were grown in a 96-well
Table 1. Analytical and physicochemical data of complexes
Found (Calcd)
S. No.
Compound/stoichiometrya
Colour
Yield (%)
53
Dec. temp (ꢀC)
300
C
H
N
Cl
1a
[Ru(ꢀ4-C8H12)(2-Acpy-SMDT)Cl2]
17H23N3S2Cl2Ru
Steel gray
40.28
(40.39)
4.59
(4.55)
8.09
(8.32)
14.30
(14.06)
C
2a
3a
4a
[Ru(ꢀ4-C8H12)(2-Acpy-SBDT)Cl2]
Dark brown
Yellow/cream
Dark brown
61
65
54
250
250
235
47.67
(47.50)
4.34
(4.65)
7.20
(7.23)
12.47
(12.22)
C23H27N3S2Cl2Ru
[Ru(ꢀ4-C8H12)(2-Acpy-TSC)Cl2]
C16H22N4SCl2Ru
40.21
(40.50)
4.46
(4.64)
11.59
(11.81)
15.22
(14.98)
[Ru(ꢀ4-C8H12){2-(2-Py-BMZ}Cl2]
C20H21N3Cl2Ru
50.31
(50.52)
4.80
(4.42)
9.01
(8.84)
14.62
(14.94)
aFor abbreviations see Fig. 1.

N. Bharti et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2243±2245
2245
Jawaharlal Nehru University, New Delhi for providing
laboratory facilities for biological studies.
References and Notes
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copeia, 28th ed., The Pharmaceutical Press: London, 1982;
pp 968±970.
Figure 2. Structure of ruthenium complexes (1a: R=S-CH3, 2a: R=
S-CH2C6H5, 3a: R=NH2).
4. Goodman, A.; Rall, T. W.; Nies, A. S.; Taylor, P. The
Pharmacological Basis of Therapeutics, 8th edn; Pergamon
Press: New York, 1991; pp 1002±1005.
5. Johnson, P. J. Parasitology Today 1993, 9, 183.
6. Wright, C. W.; Phillipson, J. D. Phytotherapy Res. 1990, 4, 127.
7. (a) Farrell, N.; Skov, K. A. J. Chem. Soc., Chem. Commun.
1987, 1043. (b) Keppler, B. K. New J. Chem. 1990, 14, 389.
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Chem. 1982, 25, 1261.
9. Oong, O. E.; Martelli, S. Farmaco 1994, 49, 513.
10. (a) Loiseau, P. M.; Nguyen, D. X. Trop. Med. Int. Health
1996, 1, 379. (b) Casero, R. A.; Klayman, D. L.; Childs, G. E.;
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11. Hadjipavlou-litina, D. Pharmazie 1996, 51, 468.
12. Quiroga, A. G.; Perez, J. M.; Lopez-Solera, I.; Masaguer,
J. R.; Luque, A.; Raman, P. et al. J. Med. Chem. 1998, 41,
1399.
Table 2. Antiamoebic activity of ligands and their ruthenium com-
plexes against HK-9 strain of E. histolytica
S. No. Compound
IC50 mg/mL S.D.aÂ10
1
1a
2
2a
3
3a
4
2-Acpy-SMDT
[Ru(ꢀ4-C8H12)(2-Acpy-SMDT)Cl2]
2-Acpy-SBDT
0.38
0.28
0.40
0.26
0.31
0.30
0.42
0.36
0.33
0.28
0.42
0.14
0.35
0.56
0.28
0.42
0.42
0.56
[Ru(ꢀ4-C8H12)(2-Acpy-SBDT)Cl2]
2-Acpy-TSC
[Ru(ꢀ4-C8H12)(2-Acpy-TSC)Cl2]
2-(2-Py-BMZ)
[Ru(ꢀ4-C8H12){2-(2-Py-BMZ)}Cl2]
Metronidazole
4a
5
aS.D.=Standard deviation.
microplate. After 72 h incubation in the presence of
serial dilutions of the compounds under test, inhibition
of growth was assessed by ®xing and then staining the
organism with eosin and measuring the optical density
with a microplate reader. Metronidazole was used as the
reference drug. The biological test was carried out using
DMSO as the solvent in which the complexes are stable.
The in vitro antiamoebic activity of new ruthenium
complexes and its ligands are listed in Table 2.
13. Sanchez-Delgado, R. A.; Navarro, M.; Perez, H.; Urbina,
J. A. J. Med. Chem. 1996, 39, 1095.
14. Sanchez-Delgado, R. A.; Lazardi, K.; Rincon, L.; Urbina,
J. A. J. Med. Chem. 1993, 36, 2041.
15. Das, M.; Livingstone, S. E. Br. J. Cancer 1978, 37, 466.
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Int. J. Radiation Oncology Biol. Phy. 1986, 12, 1059.
17. Clarke, M. J.; Lippard, S. J. ACS Symp. 1983, 209, 335.
18. Bharti, N.; Maurya, M. R.; Naqvi, F.; Bhattacharya, A.;
Bhattacharya, S.; Azam, A. Eur. J. Med. Chem. 2000, 35, 481.
19. Albers, M. O.; Ashworth, T. V.; Oosthuizen, H. E.;
Singleton, E. Inorg. Synth. 1989, 26, 68.
Metronidazole had a 50% inhibitory concentration
(IC50) of 0.33 mg/mL in our experiments which is close
to the previously reported IC50 of 0.32 mg/mL obtained
against E. histolytica.26 As shown in Table 2, complexes
1a and 2a cause a marked inhibition, while the parent
compounds are less active than metronidazole. Com-
pounds 3a and 4a showed slightly better activity as
compared to 3 and 4. These activities indicate that the
incorporation of the metal fragments generally pro-
duced an enhancement of the activity. Biological tests
on the e€ect of complexes are very encouraging. This
means that complexation to Ru increases the activity
of the parental drug. These results illustrate well
the potential of the novel metal-based approach for
the development of chemotherapeutic agents against
E. histolytica. Detailed in vivo studies, modi®cation of
these complexes and their mechanism of action are in
progress.
20. Das, M.; Livingstone, S. E. Inorg. Chim. Acta. 1979, 19, 5.
21. Ali, M. A.; Tarafder, M. T. H. J. Inorg. Nucl. Chem. 1977,
39, 1785.
22. Addison, A. W.; Burke, P. J. J. Heterocycl. Chem. 1981, 803.
23. 1a 1H NMR (DMSO-d6) d 3.34 (m, 4H, CH), 2.84 (m, 4H,
exo CH2), 2.08 (m, 4H, endo CH2), 2.54 (s, 3H, CH3), 2.61 (s,
3H, SCH3), 7.10±7.75 (m, 4H, aryl); IR v (cm 1) 3200 (NH),
1641 (CˆN), 1587 (CˆC), 1032 (CˆS), 510, 482, 450 (Ru±N,
Ru±S); l max (cm 1) (DMF) 30300, 26315, 18180. 2a 1H
NMR (DMSO-d6) d 3.50 (m, 4H, CH), 2.88 (m, 4H, exo CH2),
7.20±7.98 (m, 9H, aryl); IR v (cm 1) 3200 (NH), 1595 (CˆN),
1575 (CˆC), 1030 (CˆS), 509, 472 (Ru±N, Ru±S); l max
1
(cm 1) (DMF) 29410, 19010. 3a H NMR (DMSO-d6) d 2.50
(m, 4H, exo CH2), 2.08 (m, 4H, endo CH2), 2.87 (s, 3H, CH3),
7.83±8.85 (m, 4H, aryl); IR v (cm 1) 3250 (NH), 1613 (CˆN),
1
1577 (CˆC), 1026 (CˆS), 526, 457, 420 (Ru±N); l max (cm
)
(DMF) 31847, 27777. 4a 1H NMR (DMSO-d6) d 3.58 (m, 4H,
CH), 2.61 (m, 4H, exo CH2), 2.26 (m, 4H, endo CH2), 7.60±
8.30 (m, 4H, aryl); IR v (cm 1) 3050 (NH), 1613 (CˆN), 1585
(CˆC), 508, 454 (Ru±N); l max (cm 1) (DMF) 31950, 29410.
24. Maurya, M. R.; Jayaswal, M. N. J. Chem. Res. (S) 1998,
446.
Acknowledgements
25. Wright, C. W.; O'Neill, M. J.; Phillipson, J. D.; Warhurst,
D. C. Antimicrob. Agents Chemother. 1988, 1725.
26. Wright, C. W.; O'Neill, M. J.; Phillipson, J. D.; Warhurst,
D. C. J. Pharm. Pharmacol. 1987, 39, 105.
N. Bharti acknowledges the senior research fellowship
from CSIR, New Delhi, India. The authors thank Prof.
Alok Bhattacharya, and Dr. Sudha Bhattacharya,