Synthesis, characterization and antiamoebic activity of benzimidazole derivatives and their vanadium and molybdenum complexes

Article abstract of DOI:10.1016/S0960-894X(02)00034-3

Reaction of [MoO₂(acac)₂] (where, acac=acetyl acetone) and KVO₃ with 2-(salicylidieneimine) benzimidazole lead to form new complexes [MoO₂(sal-BMZ)₂] and K [VO₂(sal-BMZ)₂] [where

Full text of DOI:10.1016/S0960-894X(02)00034-3

Bioorganic & Medicinal Chemistry Letters 12 (2002) 869–871
Synthesis, Characterization and Antiamoebic Activity of
Benzimidazole Derivatives and Their Vanadium and
Molybdenum Complexes
a
a
b
b
Neelam Bharti, Shailendra, M. T. Gonzalez Garza, Delia E. Cruz-Vega,
b
a
a
J. Castro-Garza, Kishwar Saleem, Fehmida Naqvi,
c
a,
Mannar R. Maurya and Amir Azam *
aDepartment of Chemistry, Jamia Millia Islamia, Jamia Nagar, New Delhi-110025, India
bDivision de Biologia Celular of Molecular, Centro de Investigacion, Biomedica sdel Noreste, IMSS, Monetary, NL, Mexico
cDepartment of Chemistry, University of Roorkee, Roorkee-247667, India
Received 13 September 2001; accepted 7 January 2002
Abstract—Reaction of [MoO
form newcomplexes [MoO (sal-BMZ) ] and K [VO (sal-BMZ) ] [where, sal-BMZ=2-(salicylidieneimine) benzimidazole], which
2 2 3
(acac) ] (where, acac=acetyl acetone) and KVO with 2-(salicylidieneimine) benzimidazole lead to
2
2
2
2
showed the monobasic bidentate nature of the ligand in which the phenolic oxygen and the imine nitrogen of the ligand are coor-
dinated to the metal ion. These complexes were characterized along with nine other complexes of oxoperoxovanadium (V),
molybdenum (Vl) and tungsten (Vl) with benzimidazole derivatives and screened in vitro by micro dilution technique for their
amoebicidal activity with a view to search for a more effective agent against Entamoeba histolytica suggests that compound 2 and 3
might be endowed with important antiamoebic properties since they showed IC50 values in a mM range. # 2002 Published by
Elsevier Science Ltd.
Amoebiasis is the infection of the human gastro-
intestinal tract by Entamoeba histolytica, a protozoan
parasite that is capable of invading the intestinal
mucosa and can infect almost every organ of the body,
the most frequent form of extra intestinal amoebiasis is
the amoebic liver abscess. Being responsible for
approximately 100,000 deaths annually, placing it sec-
ond only to malaria in mortality due to protozoan
an intramolecular electron transfer could occur which
reduces vanadium (V) to (IV) and oxidizes peroxo
group to the superoxide radical. This superoxide ion
generated in the process could trigger further biological
5
,6
events. Although metals have been used in medicine
for centuries, the success of cis-PtCl (NH ) (cisplatin)
2
3 2
7ꢀ9
as an anticancer drug
has stimulated a renewed
interest in metal based chemotherapy. It is desirable to
continue the search for new, more specific antiamoebic
drugs, which could provide a new dimension in therapy.
The significant potentials of transition metal complexes
as antiamoebic agents have so far been very little
1
parasite. The ideal treatment for amoebiasis does not
yet exist, mainly due to the toxicity of current anti-
2
amoebic drugs. Hydroxy substituted benzimidazoles
showed the most promising activity against enter-
oviruses, which have been attributed to their coordinat-
1
0ꢀ12
Approaches using vanadium, molybd-
explored.
enum and tungsten as antiparasitic agents has not yet
3
ing ability with metal ions. 2-Aminobenzimidazole
derivatives have been tested on some parasite models
6
,13ꢀ16
been reported. The biological importance
of these
4
and showed protozoicidal and antihelmintic activities.
Vanadium (V) complexes are of interest in biochemistry
because the heteroligand can shifts the redox potential
metals led us to study, the synthesis and characteriza-
tion of two new vanadium and molybdenum complexes
of 2-(salicylideneimine) benzimidazole (1) along with
nine previously reported compounds of vanadium,
0
of V(V)/V (IV) (E298 =1.00 v) towards the point where
3
molybdenum and tungsten with ligands (II) and (III)
(
1
Fig. 1) and they were tested in vitro against HM-1/
MSS strain of E. histolytica. To the best of our
knowledge this is the first report of screening using these
*
0
Corresponding author. Tel.: +91-11-683-1717-338; fax: +91-11-684-
229; e-mail: amir_jmi@rediff.com
0
960-894X/02/$ - see front matter # 2002 Published by Elsevier Science Ltd.
PII: S0960-894X(02)00034-3

870
N. Bharti et al. / Bioorg. Med. Chem. Lett. 12 (2002) 869–871
Figure 2. Proposed structure of dioxovanadium (V) (n=ꢀ1) and
dioxomolybdenum (VI) (n=0) complexes (M=V, Mo).
another at 389 nm (vanadium complex) or 337 nm
(molybdenum complex) in the visible region. These are
arising due to ligand and ligand to metal charge transfer
band (LMCT), respectively. On the basis of spectral
data an octahedral structure has been proposed for
these complexes (Fig. 2). Other complexes (5–7, 9, 10,
12) were synthesized and characterized by IR, electro-
3
Figure 1. Structure of benzimidazole derivatives (where R=H, CH ).
transition metal complexes with bezimidazole deriva-
tives against amoebiasis.
1
nic, H NMR spectra and thermogravimetric analysis.
Spectral and other physicochemical data compare well
6
,18
with the data reported in the literature.
Chemistry
2
-(Salicylideneimine) benzimidazole was prepared by
In vitro anti-amoebic activity
mixing salicyladehyde and 2-aminobenzimidazole in
equimolar ratio in methanol and refluxed for 4 h. 2-(a-
hydroxyalkyl) benzimidazoles and 2-(a-hydroxyphenyl)
benzimidazoles were prepared by literature meth-
ods.
ing their mp, spectral studies and elemental analysis.
Aqueous solution of KVO reacts with potassium salt of
3
Hsal–BMZ (prepared in-situ by the reaction of KOH) in
1
complex, K[VO (sal–BMZ) ]. The dioxomolybdenum
(VI) complex, [MoO2 (sal–BMZ)2].
according to eq. 1.
The anti-amoebic activity was assessed against HM-1/
1MSS strain of E. histolytica. The trophozoites were
2
1
maintained axenically in PEHPS medium by serial
culture. Trophozoites were used from 3-day axenic cul-
ture, grown in 16ꢁ125 mm screwcapped tubes with 11
mL of PEHPS medium. The medium was sterilized for
1
7,18
All these ligands were characterized by record-
ꢂ
15 min at 121 C. Culture tubes containing 11 mL of
1
ꢀ
:2 molar ratio at pH 7.5 to give dioxovanadium (V)
1
PEHPS were inoculated with 1000 trophozoites mL
ꢂ
9
and incubated at 36 C, the sub cultivation frequency
was every 4 days. The drug potency test was performed
2
2
2
0
was isolated
2
2
as described earlier. In brief, Borosilicate screwcap-
ped culture tubes containing 5.5 mL of fresh sterile
PEHPS medium were added with 50 mL of different
concentration of samples of metronidazole. In all deter-
minations the metronidazole and sample concentrations
were maintained in the ranges 0.0–3.0 and 0.0–50.0
mM/mL, respectively. Metronidazole was dissolved with
phosphate buffer saline (PBS). All the compounds were
dissolved in dimethyl sulphoxide (DMSO). The tubes
Â
Ã
MoO ðacacÞ þ 2 H salÀBMZ
2
2
!
MoO ðsalÀBMZÞ2 þ 2acacH
ð1Þ
2
All the complexes are soluble in DMF and DMSO,
sparingly soluble in methanol, ethanol and insoluble in
water. Analytical and spectral data (IR, electronic and
ꢂ
were incubated for 72 h at 36 C, cooled on ice water for
ꢀ1
1
19,20
H NMR spectra)
proposed structure. In IR spectra both complexes exhi-
are in good agreement with the
10 min and the number of trophozoites mL in each
tube determined with a haemocytometer. The results
were estimated as the percentage of growth inhibition
compared with the untreated controls and plotted as
probit values as a function of the drug concentration.
The IC50 and 95% confidence limits were interpolated in
the corresponding dose–response curve. At least three
experiments were performed for each compound tested.
ꢀ1
bit two IR active spectral bands in the 880–982 cm
region due to cis-MO structure arising due to antisym-
metric and symmetric stretching mode. A considerable
higher frequency shift of n(C=N) indicates the involve-
ment of azomethine nitrogen in coordination. The
2
ꢀ1
retention of broad feature at 2650–2800 cm and only
slight shift of n(C¼N) (ring) from free schiff base (1620
ꢀ1
cm ) in these complexes suggests the involvement of
ꢀ
The in vitro inhibitory effect of the compound (1–12)
screened against E. histolytica upon the growth of axe-
nic culture of HM1/1MSS strain are summarized in
Table 1. The antiamoebic effect was compared with the
most widely used antiamoebic medication metronid-
azole. Metronidazole had an 50% inhibition concentra-
tion (IC ) of 2.10 mM in our experiment, which lies
NH nitrogen in hydrogen bonding and non-involve-
ment of tertiary nitrogen (ring) in coordination. Coor-
dination of phenolic oxygen is authenticated by the
ꢀ1
absence of any band in the 3400 cm region. Thus, IR
data indicates the monobasic bidentate nature of the
ligand. Both complexes exhibit two bands in the elec-
tronic spectra, one in the UV region at ca. 285 nm and
5
0
within the range of IC50 value of metronidazole (2.92

N. Bharti et al. / Bioorg. Med. Chem. Lett. 12 (2002) 869–871
871
Table 1. In-vitro antiamoebic activity of benzimidazole derivatives,
metal complexes and metronidazole against HM-1/1MSS strain of
E. histolytica
6. Sawyer, D. T.; Valentine, J. S. Acc. Chem. Res. 1981, 14,
393.
7. Rosenberg, B. In Nucleic Acids–Metal Ion Interactions:
Spiro, T. G., Ed., Wiley: NewYork, 1980; p 1.
S.
No.
Compd
IC50
mM/mL
SD
8. Farrell, N. Transition Metal Complexes as Drugs and
Chemotherapeutic Agents. In Catalysis by Metal Complexes;
James, B. R, Ugo, R., Eds., Kluwer: Dordrecht, 1989.
. Sun, M. Science (Washington, DC) 1983, 222, 145.
10. Bharti, N.; Maurya, M. R.; Naqvi, F.; Bhattacharya, A.;
Bhattacharya, S.; Azam, A. Eur. J. Med. Chem. 2000, 35, 481.
11. Bharti, N.; Maurya, M. R.; Naqvi, F.; Azam, A. Bioorg.
Med. Chem. Lett. 2000, 10, 2243.
1
2
3
4
5
6
7
8
9
2-(Salicylideneimine) benzimidazole
{(salicylideneimine) benzimidazole}
{(salicylideneimine) benzimidazole}
9.20 1.45
2.35 0.72
2.99 0.87
9.59 1.81
4.19 0.54
5.14 1.12
9.13 1.75
10.12 1.63
5.16 0.94
9.60 1.69
11.52 1.97
8.55 1.37
2.10 0.34
9
K[VO
[MoO
2
2
]
]
2
2
2-(2-Hydroxymethyl) benzimidazole
[MoO (O ){(2-hydroxymethyl) benzimidazole}
K [VO (O ){(2-hydroxymethyl) benzimidazole}
[WO (O ){(2-hydroxymethyl) benzimidazole}
2-(2-Hydroxyethyl)benzimidazole
2
2
]
2
]
]
2
2
2
12. Shailendra; Bharti, N.; Gonzalez Garza, M. T.; Cruz-
Vega, D. E.; Garza, J. C.; Saleem, K.; Naqvi, F.; Azam, A.
[MoO(O
K[VO(O
2
){(2-hydroxyethyl)benzimidazole}
){(2-hydroxyethyl)benzimidazole}
2-(2-Hydroxyphenyl) benzimidazole
2
]
]
Bioorg. Med. Chem. Lett. 2001, 11, 2675.
10
11
12
13
2
2
1
1
3. Frieden, E. Adv. Exper. Med. Biol. 1973, 48, 4.
4. Postgate, J. R. The Fundamentals of Nitrogen Fixation;
[MoO (O
2
){(2-hydroxyphenyl) benzimidazole}
Metronidazole
2
]
Cambridge University Press: NewYork, 1982.
5. (a) Yamamoto, I.; Sasaki, T.; Ljungdahl, L. G. J. Bio.
1
SD, standard deviation.
Chem. 1983, 253, 1826. (b) White, H.; Strobl, G.; Feicht, R.;
Simon, H. Eur. J. Biochem. 1989, 184, 89.
16. Djordjevic, C.; Wampler, G. L. J. Inorg. Biochem. 1985,
25, 51.
17. Philips, M. A. J. Chem. Soc. 1928, 4, 2393.
2
3,24
mM) as reported previously.
Table 1 shows that all
the compounds screened for antiamoebic activity in
vitro, 10 compounds had IC50 of less than 10 mM and
two of these had IC50 less than 3 mM. As reported by
the other researcher, the compounds, which showed
IC , value less than 20 mM were considered as sig-
1
3
1
8. Maurya, M. R.; Bhakare, S. A. J. Chem. Res.(s) 1996,
90.
9. Synthesis of K[VO (sal–ABMZ) ]: V O (0.50 g, 5 mmol)
2 2 2 5
was dissolved in aqueous KOH (0.30 g, 5 mmol in 10 mL) and
stirred for 2 h. Hsal–ABMZ (2.37 g, 10 mmol) was also dis-
solved in aqueous KOH (0.6 g, 10 mmol in 20 mL) and added
after filtering to the above solution with stirring. The pH value
of the reaction mixture was adjusted to 7.5 with 4 M HCl.
After 2 h of stirring, the light yellowsolid wa s separated, fil-
tered, washed with water and dried in vacuo. Yield 45%
5
0
2
5
nificant amoebicidal agents. The activity of compound
2
and 3 showed that by introducing metal in organic
moiety enhances the activity of the compound as they
showthe IC 50 2.35 and 2.99 mM, respectively. All the
complexes are more active than their respective ligands,
this indicates that the complexation to metal enhances
the activity of the ligand. It is therapeutically more
relevant to test potential newdrugs on E. histolytica.
(found: C, 56.3; H, 3.6; N, 14.0. C28
H
20KN
O
V requires C,
] 285, 389;
asym), 927 (VO
)SO)/ppm 7.26 (16H, m, aryl); 11.32
2H, s, NH); 8.10 (2H, s, HC=N).
6
4
5
6.6; H, 3.4; N, 14.1%); l max/nm [HOCN(CH )
3 2
ꢀ1
nmax/cm
1686, 1628 (C¼N), 982 (VO
2
2
1
sym); H NMR((CD
3
(
2
2 2 2 2
0. Synthesis of [MoO (sal–BMZ) ]: [MoO (acac) ] (0.33 g, 1
Acknowledgements
mmol) was added to a hot solution of Hsal-BMZ (0.48 g; 2
mmol) in 20 mL MeOH while stirring and the resulting reac-
tion mixture was refluxed for 1 h. The light yellow solid, which
separated, was filtered, washed with methanol and dried in
vacuo. Yield 65% (found: C, 56.2; H, 3.2; N, 13.9.
C H MoN O requires C, 56.0; H, 3.3; N, 14.0%); lmax/nm
Neelam Bharti acknowledges Senior Research Fellow-
ship from Council of Scientific and Industrial Research,
NewDelhi, India.
2
8
20
6
4
ꢀ
1
[HOCN(CH
3
)
2
] 283, 337; nmax/cm 1688, 1628 (C¼N), 900
1
(
MoO
2
asym), 880 (MoO
2
sym); H NMR((CD
3
)SO)/ppm
7
2
.37 (16H, m, aryl); 11.59 (2H, s, NH); 8.27 (2H, s, HC¼N).
References and Notes
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2
1
3
3
4
. WHO Epidemiol. Record 1997, 14, 4.
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89.
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Dismutases; Academic: NewYork, 1977.
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5