Design, synthesis and in vitro antiprotozoal activity of benzimidazole-pentamidine hybrids

Article abstract of DOI:10.1016/j.bmcl.2008.05.009

A series of ten novel hybrids from benzimidazole and pentamidine were prepared using a short synthetic route. Each compound was tested in vitro against the protozoa Trichomonas vaginalis, Giardia lamblia, Entamoeba histolytica, Leishmania mexicana, and Pl

Full text of DOI:10.1016/j.bmcl.2008.05.009

Bioorganic & Medicinal Chemistry Letters 18 (2008) 3147–3151
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis and in vitro antiprotozoal activity of benzimidazole-
pentamidine hybrids
Héctor Torres-Gómez a, Emanuel Hernández-Núñez a, Ismael León-Rivera b, Jorge Guerrero-Alvarez b,
Roberto Cedillo-Rivera c, Rosa Moo-Puc c, Rocío Argotte-Ramos d, María del Carmen Rodríguez-Gutiérrez d,
Manuel Jesús Chan-Bacab e, Gabriel Navarrete-Vázquez a,
*
a Facultad de Farmacia, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos 62209, Mexico
b
´
Centro de Investigaciones Quımicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos 62209, Mexico
c Unidad Interinstitucional de Investigación Médica, IMSS-Facultad de Medicina, UADY, Mérida, Yucatán 97000, Mexico
d Centro de Investigación sobre Enfermedades Infecciosas, Instituto Nacional de Salud Pública, Cuernavaca, Morelos 62508, Mexico
e Departamento de Microbiolog´ıa Ambiental y Biotecnolog´ıa, Universidad Autónoma de Campeche, Campeche 24030, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of ten novel hybrids from benzimidazole and pentamidine were prepared using a short synthetic
route. Each compound was tested in vitro against the protozoa Trichomonas vaginalis, Giardia lamblia, Ent-
amoeba histolytica, Leishmania mexicana, and Plasmodium berghei, in comparison with pentamidine and
metronidazole. Some analogues showed high bioactivity in the low micromolar range (IC50 < 1 lM)
against the first four protozoa, which make them significantly more potent than either standard. 1,5-
bis[4-(5-methoxy-1H-benzimidazole-2-yl)phenoxy]pentane (2) was 3- and 9-fold more potent againstG.
lamblia than metronidazole and pentamidine, respectively. This compound was 23-, 108-, and 13-fold
more active than pentamidine against T. vaginalis, E. histolytica and L. mexicana, respectively. Studying
further structure–activity relationships through the use of bioisosteric substitution in these hybrids
should provide new leads against protozoal diseases.
Received 7 April 2008
Received 25 April 2008
Accepted 1 May 2008
Available online 4 May 2008
Keywords:
Antiprotozoal
Benzimidazole
Pentamidine
Giardia
Ó 2008 Elsevier Ltd. All rights reserved.
Trichomonas
Entamoeba
Bioisosteric replacement
Parasitic infections, such as helminthiasis and protozoosis, are
still major problem in developing countries, affecting mainly the
infant population.1–3
For the treatment of some kinds of protozoosis such as giardia-
sis, trichomoniasis, and amoebiasis, metronidazole is the drug of
choice.4 Recent studies have shown that this drug has several toxic
effects such as genotoxicity, gastric mucus irritation, and sperma-
tozoid damage.5–7 Although current drug therapy for the treatment
of these infections is effective, most available drugs have signifi-
cant side effects that restrict their use.8
Benzimidazole derivatives, such as mebendazole and albenda-
zole, are clinically anthelminthic useful drugs. More recently, anti-
protozoal activity of 2- and 5-substituted benzimidazoles has been
reported.9–14 Benzimidazole core is of a wide interest because of its
diverse biological activities, and it is a well-known privileged
structure in medicinal chemistry.15
Pentamidine, an aromatic diamidine, is used at primary stage in
African trypanosomiasis, antimony-resistant leishmaniasis, and
AIDS associated Pneumocystis jirovecii pneumonia.16–18 Pentami-
dine is not effective when given orally and several toxic effects
including hypotension, dysglycemia, renal, pancreatic, and hepatic
toxicity have been reported.18–22 The recent increase in life-threat-
ening P. jirovecii pneumonia in patients with AIDS has resulted in a
revived interest in pentamidine and related derivatives.23
As a part of our search for basic information about structural
requirements for antiprotozoal activity, we have synthesized a ser-
ies of hybrids between benzimidazole and pentamidine (Fig. 1).
The in vitro antiparasitic activity of these compounds on intes-
tinal protozoa (Giardia lamblia, Entamoeba histolytica), a urogenital
tract parasite (Trichomonas vaginalis), a red blood cell parasite
(Plasmodium berghei) and an intracellular kinetoplastid parasite
(Leishmania mexicana), is also reported in this letter.
Compounds 1–10 were prepared by alkylation of appropriate
4-hydroxybenzaldehyde, followed by conversion of the resulting
bis-aldehyde to the respective benzimidazole by treatment with
1,2-phenylenediamine adequately substituted, as shown in
Scheme 1. The required substituted bis-aldehydes 11 and 12 were
prepared in good yields, starting from 4-hydroxybenzaldehyde
(14) or 4-hydroxy-3-methoxybenzaldehyde (15) with 1,5-dibro-
mopentane (13) in presence of potassium carbonate under acetoni-
trile reflux.24 The cyclocondensation reaction of 11 and 12 with the
* Corresponding author. Tel./fax: +52 777 3297089.
E-mail address: gabriel_navarrete@uaem.mx (G. Navarrete-Vázquez).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.05.009

3148
H. Torres-Gómez et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3147–3151
HN
NH
O
O
H2N
NH2
Pentamidine
Hybridization with
benzimidazole
R1
R1
N
N
O
O
N
H
N
H
R2
R2
1-10
Figure 1. Drug design of hybrids 1–10.
CHO
O
H
a
O
2
+
Br
Br
CH2
R2
R2
OH
2
13
14: R2=H
11: R2=H
15: R2=OCH3
12: R2=OCH3
R1
R1
NH2
NH2
N
O
H
b
O
+
O
2
2
CH2
CH2
2
N
H
R2
R2
2
16: R1=H
11: R2=H
18: R1=CH3
20: R1=NO2
6: R1=H; R2=OCH3
8: R1=CH3; R2=OCH3
10: R1=NO2; R2=OCH3
1: R1=H; R2=H
12: R2=OCH3
3: R1=CH3; R2=H
5: R1=NO2; R2=H
R1
R1
NO2
NH2
N
O
H
c
O
O
+
CH2
CH2
2
N
H
R2
R2
2
17: R1=OCH3
19: R1=CF3
11: R2=H
2: R1=OCH3; R2=H,
4: R1=CF3; R2=H
12: R2=OCH3
7: R1=OCH3; R2=OCH3
9: R1=CF3; R2=OCH3
Scheme 1. Reagents and conditions: (a) MeCN, K2CO3, 78 °C, 17–19 h; (b) 2.1 equiv Na2S2O5, DMF, 90 °C, 20 h; (c) 10 equiv Na2S2O4, H2O:EtOH, 80 °C, 10–14 h.
corresponding 4-substituted-1,2-phenylendiamines 16, 18 and 20,
and sodium metabisulfite in DMF afforded the corresponding hy-
brids 1, 3, 5, 6, 8, and 10 (Scheme 1).25
Compounds 2, 4, 7 and 9 were prepared using a one-pot reduc-
tion–cyclization reaction according to the previous described
method,26,27 where bis-aldehydes 11 and 12 reacted with the cor-
responding 5-substituted-2-nitroaniline (17, 19) in the presence of
sodium dithionite (reducing reagent) and a mixture of tap water
and ethanol as solvent (Scheme 1).
spectra HH and CH COSY) have been carried, in order to assign
the signals of the 1H and 13C NMR spectra correctly.28
The aromatic region of the 1H NMR spectrum contained an ABX
pattern signals ranging from d 7.01 to 8.34 (dd, Jmeta = 1.2–2.2;
Jpara = 0.0–1.0 Hz), 6.84 to 8.06 (dd, Jortho = 8.4–8.9; Jmeta = 1.2–
2.2 Hz), and 7.11 to 7.69 (dd, Jmeta = 1.2–2.2; Jpara = 0.0–1.0 Hz)
attributable to H-4, H-6, and H-7, of the benzimidazole 5-substi-
tuted core, respectively. For compounds 1–5 the aromatic region
of the 1H NMR spectrum also contained an A2B2 pattern signals
ranging from d 7.15 to 8.12 (d, Jortho = 8.1–8.8 Hz) and 7.09 to 8.11
(d, Jortho = 8.1–8.9 Hz) attributable to the equivalents H-20, H-60
and H-30, H-50, respectively, of the benzene ring. For the com-
pounds 6–10, another ABX pattern signals ranging from d 7.11 to
7.83 (d, Jmeta = 0.0–1.6 Hz), 7.11 to 7.18 (d, Jortho= 8.4–8.8 Hz) and
7.69 to 7.77 (dd, Jortho = 8.4–8.8; Jmeta = 0.0–1.6 Hz) attributable to
H-20, H-50 and H-60, respectively, of the benzene ring.
The chemical structures of the synthesized compounds were
confirmed on the basis of their spectral data (NMR and mass spec-
tra), and their purity ascertained by microanalysis. The elemental
analysis was within 0.4% of the theoretical values. Physical con-
stants of the title compounds are shown in Table 1.
In the nuclear magnetic resonance spectra (1H NMR; d ppm),
the signals of the respective protons of the compounds were veri-
fied on the basis of their chemical shifts, multiplicities and cou-
pling constants. To elucidate the structures of the compounds,
one and two-dimensional (homo- and heteronuclear correlation
The new hybrids from benzimidazole and pentamidine (1–10)
were tested in vitro as antiprotozoal agents. Biological assays re-
sults against the five protozoa tested are summarized in Table 1.

H. Torres-Gómez et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3147–3151
3149
Table 1
Physicochemical data and antiprotozoal bioactivity of compounds 1–10
R1
R1
N
N
O
O
N
H
N
H
R2
R2
Compound
R1
R2
MW
Mp (°C)
Yield (%)
IC50 (lM)
T. vaginalis
G. lamblia
E. histolytica
P. berghei
L. mexicana
1
2
3
4
5
6
7
8
–H
–H
–H
–H
–H
488
548
516
624
578
548
608
576
685
638
180 (dec)
185 (dec)
215 (dec)
174.9 (dec)
174.3 (dec)
138.5 (dec)
187.3 (dec)
168 (dec)
125 (dec)
183 (dec)
90
68
90
90
92
90
64
68
76
98
3.176
0.164
4.161
4.96
3.583
6.153
6.293
1.017
NT
1.838
0.435
4.888
9.601
7.412
12.739
5.192
0.372
NT
0.436
0.109
0.153
7.288
10.223
5.186
0.284
4.503
NT
100(37%)a
34.641
100(43%)a
6.531
1.065
0.712
0.368
>50
>50
>50
>50
>50
>50
–OCH3
–CH3
–CF3
–NO2
–H
–OCH3
–CH3
–CF3
–NO2
–H
100(46%)a
165.951
23.981
NI
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
9
10
63.091
25.942
CDb
0.794
3.815
0.286
3.397
4.079
1.286
12.053
11.801
0.771
16.849
9.568
NT
Pentamidine
Metronidazole
NT
(dec), Compound melt with decomposition.
NI, no inhibition; NT, not tested.
a
% Inhibition presented at maximum tested concentration (100 lM).
CD: Cell damage, due to cytophatic effect caused by pentamidine.
b
Comparison was made among new compounds and the antiproto-
zoal drug of choice: metronidazol. In order to compare bioactivi-
ties, pentamidine was also tested. In vitro susceptibility assays
were performed using a method previously described.28,29 In gen-
eral, all the screened compounds showed high bioactivity
(<6.3 lM) against T. vaginalis. Compound 2, with a methoxy group
at position 5 of benzimidazole ring, was two times more active
than metronidazole and 23-fold more potent than pentamidine.
Compounds 8 (–CH3) and 10 (–NO2), with a methoxy group at-
tached at position 2 of benzene ring, were 4- and 5-fold more po-
tent than pentamidine, respectively. Compounds 1, 3–5 showed
the same activity than pentamidine.
Against G. lamblia, compounds 2 and 8 were three and four
times more active than metronidazole, respectively. Pentamidine
was nine and 11-fold less active in comparison with these
compounds.
Against E. histolytica, compounds 1–3 and 7 showed high bioac-
tivity in the low micromolar range (<0.5 lM). They were two, se-
ven, five, and three times more active than metronidazole,
respectively. Compound 2 was 108-fold more potent than pentam-
idine, whereas compounds 1, 3, and 7 were 27-, 77-, and 41-fold
more active than this drug.
Cultured schizonts of Plasmodium berghei were used to assess
antimalarial activity of all compounds synthesized and were pre-
pared following the protocol described previously.30 Biological as-
say results against P. berghei is also indicated in Table 1. Only
compound 4, with a –CF3 at position 5 of benzimidazole ring,
showed moderated antimalarial activity with IC50 of 6.53 lM. Fig-
ure 2 shows the optical microscopy studies from erythrocytes in-
fected with this protozoan. Pentamidine caused marked cell
damage, and the IC50 could not be calculated, due to the cytopathic
effect presented by this drug. On the other hand, we did not ob-
serve any damage produced by screened compounds to erythro-
cytes. However, they reduced the number of schizonts compared
with the negative control, without showing cytopathic effect.
In vitro antileishmanial assays were performed as described
previously.31 Compounds 1–3 exhibited high bioactivity. They
were 9-, 13-, and 26-fold more active than pentamidine, respec-
tively. This is a promising result since pentamidine is used in the
treatment of antimony-resistant leishmaniasis.
Figure 2. Optical microscopy studies: (A) Culture only with vehicle; erythrocyte
infected with P. berghei developed schizonts (S) after 16 h. (B) Treated culture with
compound 4, showing erythrocytes infected with P. berghei where development of
shcizont did not progress after 16 h culture. Parasite remain at the trophozoite
stage (T), and no cell damage is observed. (C) Culture with pentamidine, cell da-
mage is observed (cytopathic effect).
The bioactivity observed against these five protozoa suggests
that the introduction of benzimidazole core into the pentamidine
structure, and the inclusion of electron-donating moieties
(Fig. 3), enhances the antiprotozoal activity.
Electron donating
group
R1
N
O
CH2
N
H
R2
2
Pentamidine
spacer
Benzimidazole
ring
Figure 3. Proposed pharmacophoric group, based on the bioactivity pattern against
T. vaginalis, G. lamblia, E. histolytica and L. mexicana.

3150
H. Torres-Gómez et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3147–3151
21. Poola, N. R.; Kalis, M.; Plakogiannis, M. F.; Taft, D. R. J. Antimicrob. Chemother.
In conclusion, we have synthesized and screened the vitro
2003, 52, 397.
antiprotozoal activity of new hybrids of pentamidine, in which
the central pentyldioxyphenyl spacer was retained and the termi-
nal amidine groups were replaced with 5-substituted benzimid-
azole scaffold. The obtained results are very promising since
many of the compounds showed activity comparable with the
current used antiprotozoal drugs metronidazole and pentamidine,
whereas compounds 1–3 exhibited even higher bioactivity, espe-
cially toward E histolytica and L. mexicana. This study demon-
strated that the bioisosteric replacement of benzimidazole ring
instead of amidine moiety in pentamidine, results in an enhance-
ment of antiprotozoal bioactivity. Further optimization and phar-
macokinetic characterization of this series are in progress in our
laboratory.32
22. Assan, C.; Peroonne, C.; Assan, D.; Chotard, L.; Mayaud, C.; Matheron, S.;
Zucman, D. Diabetes Care 1995, 18, 47.
23. Tidwell, R. R.; Hall, J. E.; Fairley, T. A.; Cory, M.; Bell, C. A. Antimicrob. Agents
Chemother. 1991, 35, 1099.
24. General method of synthesis of bis-aldehydes 11 and 12. The corresponding 4-
hydroxybenzaldehyde 14 or 15 (0.041 mol) and potassium carbonate (6.7 g,
0.049 mol) were dissolved in acetonitrile (100 mL) and the mixture was heated
at 78 °C. After an hour, 1,5-dibromopentane (9.4 g, 5.6 mL, 0.041 mol) was
added dropwise. TLC was used to monitor the reaction. When almost all the
starting material was reacted (7–9 h),
a second charge (1.9 equiv) of the
corresponding 4-hydroxybenzaldehyde (0.0697 mol) and potassium carbonate
(10.8 g, 0.0779 mol) was added. After the completion of the reaction (10 h +),
the solvent was removed under reduced pressure and the resulting solid
washed with water to extract the formed KBr. The crude solid product was
then recrystallized from acetonitrile. 1,5-bis(4-carboxyaldehy dephenoxy)
pentane (11). Yield 13.56 g (78.63%) of a crystalline white solid. Mp 79–
81 °C. 1H NMR (200 MHz, DMSO-d6): d: 1.56 (m, 2H, OCH2CH2CH2), 1.80 (m,
4H, OCH2CH2CH2), 4.09 (t, 4H, OCH2), 7.11 (d, 4H, H-2, H-6, J = 8.5 Hz), 7.85 (d,
4H, H-3, H-5, J = 8.5 Hz), 9.85 (s, 2H, CHO) ppm. MS (IE) m/z (% rel. int.) 190
(70), 121 (100), 68 (49), 41 (76). 1,5-bis(2-methoxy-4-carboxyaldehy
Acknowledgments
dephenoxy)pentane (12) Yield 5.95 g (81%) of
a white solid. Mp 107.4–
This work was supported by grants from SEP-PROMEP UAE-
MOR-PTC 131. H. Torres-Gómez acknowledges the fellowship
109 °C. 1H NMR (200 MHz, DMSO-d6): d: 1.55 (m, 2H, OCH2CH2CH2), 1.81 (m,
4H, OCH2CH2CH2), 3.81 (s, 6H, 30-OCH3), 4.09 (t, 4H, OCH2), 7.16 (d, 2H, H-6,
J = 8.1 Hz), 7.36 (d, 2H, H-3, J = 1.5 Hz), 7.53 (dd, 2H, H-5, J = 1.47, J = 8.06 Hz),
9.82 (s, 2H, H-3) ppm. MS (IE) m/z (% rel. int.) 372 (M+, 20), 221 (80), 152 (70),
69 (47), 41 (47).
´
awarded by SEP-PROMEP. We are grateful with Marıa Medina Pin-
tor and Victoria Labastida Galván from the Centro de Investigaci-
´
ones Quımicas, UAEM, for the determination of all mass spectra.
25. General method of synthesis of 5-substituted bis(1H-benzimidazoles)1, 3, 5, 6,
8, and 10. The corresponding bis-aldehyde 11 or 12 (0.0006 mol) and sodium
metabisulfite (0.29 g, 0.0015 mol) were dissolved in 5 mL of DMF. The mixture
was stirred and heated under reflux during 1 h. After this time, the appropriate
4-substituted-1,2-phenylendiamine (0.0007 mol) in DMF (3 mL) was added.
The mixture was heated at 90 °C. When all starting materials were reacted (2–
8 h), a second charge of the corresponding 4-substituted-1,2-phenylendiamine
(0.0007 mol) was added, and the temperature maintained during 20 h. After
the completion of the reaction, the mixture was cooled to room temperature
and washed with tap water (20 mL). The crude solid product was filtered
and recrystallized from Ethanol-acetone. 1,5-bis[4-(1H-benzimidazole-2-
yl)phenoxy] pentane (1). Yield 0.723 g (90.1%) of a white solid. Mp 180 °C
(dec). 1H NMR (200 MHz, DMSO-d6): d: 1.58 (m, 2H, OCH2CH2CH2), 1.80 (m, 4H,
OCH2CH2CH2), 4.06 (t, 4H, OCH2), 7.10 (d, 4H, H-50, H-30, J = 8.79 Hz), 7.17 (dd,
4H, H-5, H-6, J = 3.3, J = 6.1), 7.55 (dd, 4H, H-4, H-7, J = 3.3, J = 6.1), 8.09 (d, 4H,
H-20, H-60, J = 8.8) ppm. 13C NMR (50 MHz, DMSO-d6) d: 22.25 (OCH2CH2CH2),
28.41 (OCH2CH2CH2), 67.72 (OCH2), 114.46 (C-30, C-50), 114.90 (C-4, C-7),
121.95 (C-10, C-50, C-60), 128.47 (C-20, C-60), 137.41 (C-3a, C-7a), 150.68 (C-2),
160.59 (C-40) ppm. MS (FAB+) m/z 489 (M+H)+; Anal. Calcd for C31H28N4O2: C,
76.21; H, 5.80; N, 10.21. Found: C, 76.45; H, 5.71; N, 9.85. 1,5-bis[4-(5-methyl-
1H-benzimidazole-2-yl) phenoxy]pentane (3) Yield 0.162 g (90%) of beige
solid. Mp 215 °C (dec). 1H NMR (400 MHz, DMSO-d6): d: 1.58 (m, 2H,
OCH2CH2CH2), 1.81 (m, 4H, OCH2CH2CH2), 2.41 (s, 6H, 5-CH3), 4.05 (t, 4H,
OCH2), 7.01 (dd, 2H, H-6, J = 1.1, J = 8.2 Hz), 7.09 (d, 4H, H-30, H-50, J = 8.7 Hz),
7.35 (s, 2H, H-4), 7.45 (d, 2H, H-7, J = 8.2 Hz), 8.08 (d, 4H, H-20, H-60, J = 8.7 Hz)
ppm. 13C NMR (100 MHz, DMSO-d6) d: 21.41 (5-CH3), 22.31 (OCH2CH2CH2),
28.48 (OCH2CH2CH2), 67.65(OCH2), 113.99 (C-4), 114.60 (C-6), 114.80 (C-30, C-
50), 121.98 (C-10), 124.48 (C-7), 127.97 (C-20, C-60), 131.24 (C-5), 137.25 (C-7a),
138.49 (C-3a), 150.76 (C-2), 160.02 (C-40) ppm. MS (FAB+) m/z 517 (M+H)+;
Anal. Calcd for C33H32F6N4O2: C, 76.72; H, 6.24; N, 10.84. Found: C, 76.41; H,
6.45; N, 10.11. 1,5-bis{4-[5-nitro-1H-benzimidazole-2-yl] phenoxy}pentane
(5). Yield 0.339 g (91.62%) of orange solid. Mp 174.3 °C (dec). 1H NMR
(200 MHz, DMSO-d6): d: 1.61 (m, 2H, OCH2CH2CH2), 1.81 (m, 4H,
OCH2CH2CH2), 4.09 (t, 4H, OCH2), 7.12 (d, 4H, H-30, H-50, J = 8.8 Hz), 7.69 (d,
2H, H-7, J = 9.2 Hz), 8.05 (d, 2H, H-4, J = 1.8 Hz), 8.12 (d, 4H, H-20, H-60,
J = 8.8 Hz), 8.36 (dd, 2H, H-6, J = 1.8, J = 9.2 Hz) ppm. 13C NMR (50 MHz, DMSO-
d6) d: 22.17 (OCH2CH2CH2), 28.29 (OCH2CH2CH2), 67.66 (OCH2), 114.13 (C-4),
114.9 (C-30, C-50), 115.28 (C-7), 117.65 (C-6), 121.13 (C-10), 128.59 (C-20, C-60),
128.96 (C-3a, C-7a), 142.29 (C-5), 155.78 (C-2), 160.75 (C-40) ppm. MS (FAB+)
m/z 579 (M+H)+; Anal. Calcd for C31H26N6O6: C, 64.35; H, 4.53; N, 14.53. Found:
C, 65.59; H, 5.02; N, 13.91. 1,5-bis[4-(1H-benzimidazole-2-yl)-2-methoxy-
phenoxy] pentane (6). Yield 0.358 g (90.1%) of a white solid. Mp 138.5 °C (dec).
1H NMR (200 MHz, DMSO-d6): d: 1.61 (m, 2H, OCH2CH2CH2), 1.83 (m, 4H,
OCH2CH2CH2), 3.89 (s, 6H, 30-OCH3), 4.08 (t, 4H, OCH2), 7.16 (dd, 2H, H-50,
J = 1.6, J = 8.4 Hz), 7.23 (dd, 4H, H-5, H-6, J = 2.8, J = 9.2 Hz), 7.61 (dd, 4H, H-4,
H-7, J = 2.8, J = 9.2 Hz), 7.75 (dd, 2H, H-60, J = 1.2, J = 8.8 Hz), 7.79 (d, 2H, H-20,
J = 1.6 Hz) ppm. 13C NMR (50 MHz, DMSO-d6) d: 22.29 (OCH2CH2CH2), 28.41
(OCH2CH2CH2), 55.72 (30-OCH3), 67.27 (OCH2), 110.12 (C-20), 112.88 (C-50),
114.39 (C-5, C-6), 119.72 (C-60). 121.05 (C-10), 122.392 (C-4, C-7), 137.75 (C-3a,
C-7a), 149.00 (C-40), 150.11 (C-30), 159.83 (C-2) ppm. MS (FAB+) m/z 549
(M+H)+; Anal. Calcd for C33H32N4O4: C, 72.24; H, 5.88; N, 10.21. Found: C,
71.99; H, 5.93; N, 10.29. 1,5-bis[2-methoxy-4-(5-methyl-1H-benzimidazole-2-
yl)phenoxy] pentane (8). Yield 0.31 g (68.4 %) of brown solid. Mp 168 °C (dec).
1H NMR (200 MHz, DMSO-d6): d: 1.59 (m, 2H, OCH2CH2CH2), 1.80 (m, 4H,
OCH2CH2CH2), 2.43 (s, 6H, 5-CH3), 3.89 (s, 6H, 30-OCH3), 4.05 (t, 4H, OCH2), 7.11
(d, 2H, H-7, J = 8.0 Hz), 7.17 (d, 2H, H-50, J = 8.4 Hz), 7.41 (s, 2H, H-4), 7.52 (d,
2H, H-6, J = 8.0 Hz), 7.77 (d, 2H, H-60, J = 10.2 Hz), 7.83 (s, 2H, H-20) ppm. 13C
NMR (50 MHz, DMSO-d6) d: 21.95 (OCH2CH2CH2), 22.98 (5-CH3), 29.04
We thank Marbella Ovilla-Muñoz from Instituto Nacional de Salud
Pública, for her technical support with the in vitro antimalarial as-
´
say. We are in debt to Andrés Uc Cachón and Nina Méndez-Domın-
guez from the UADY, for their technical assistance during
susceptibility assays against G. lambilia, T. vaginalis and E. histoly-
tica. Finally, the International Foundation of Science, Stockholm,
Sweden, and the Organization for the Prohibition of Chemical
Weapons, The Hague, The Netherlands, through a grant to M.J.
Chan-Bacab.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2008.05.009.
References and notes
1. Upcroft, J. A.; Upcroft, P. Parasitol. Today 1993, 9, 187.
2. Mammen-Tobin, A.; Wilson, J. D. Int. J. STD. AIDS 2005, 16, 488.
3. Pink, R.; Hudson, A.; Marie-Annick, M.; Bendig, M. Nat. Rev. Drug Disc. 2005, 4,
727.
4. Pylkkänen, L.; Lähdetie, J. Mutat. Res. 1984, 140, 137.
5. Kim, D. W.; Park; Baek, J. M.; Kim, J. E.; Kim, S. J. Neurol. Sci. 2004, 224, 107.
6. el-Nahas, A. F.; el-Ashmawy, I. M. Basic Clin. Pharmacol. Toxicol. 2004, 94,
226.
7. Purohit, V.; Basu, A. K. Chem. Res. Toxicol. 2000, 13, 673.
8. Valdez, J.; Cedillo, R.; Hernández-Campos, A.; Yépez, L.; Hernández-Luis, F.;
Navarrete-Vázquez, G.; Tapia, A.; Cortés, R.; Hernández, M.; Castillo, R. Bioorg.
Med. Chem. Lett. 2002, 12, 2221.
9. Kopanska, K.; Najda, A.; Justyna, Z.; Chomicz, L.; Piekarczyk, J.; Myjak, P.;
Bretner, M. Bioorg. Med. Chem. 2004, 12, 2617.
10. Navarrete-Vázquez, G.; Rojano-Vilchis, M. M.; Yépez-Mulia, L.; Meléndez, V.;
Gerena, L.; Hernández-Campos, A.; Castillo, R.; Hernández-Luis, F. Eur. J. Med.
Chem. 2006, 41, 135.
11. Navarrete-Vázquez, G.; Yépez, L.; Hernández-Campos, A.; Tapia, A.;
´
Hernández-Luis, F.; Cedillo, R.; González, J.; Martınez-Fernández, A.;
´
Martınez-Grueiro, M.; Castillo, R. Bioorg. Med. Chem. 2003, 11, 4615.
12. Kazimierczuk, Z.; Upcroft, J. A.; Upcroft, P.; Górska, A.; Starosciak, B.; Laudy, A.
Acta Biochim. Pol. 2002, 49, 185.
13. Navarrete-Vázquez, G.; Cedillo, R.; Hernández-Campos, A.; Yépez, L.;
Hernández-Luis, F.; Valdez, J.; Morales, R.; Cortés, R.; Hernández, M.; Castillo,
R. Bioorg. Med. Chem. Lett. 2001, 11, 187.
14. Katiyar, S. K.; Gordon, V. R.; McLaughlin, G. L.; Edlind, T. D. Antimicrob. Agents
Chemother. 1994, 38, 2086.
15. Horton, D. A.; Bourne, G. T.; Smythe, M. L. Chem. Rev. 2003, 103, 893.
´
16. Balaña-Fouce, R.; Redondo, M. C.; Pérez-Pertejo, Y.; Dıaz-González, R.; Reguera,
M. R. Drug Discov. Today 2006, 11, 733.
17. Sands, M.; Kron, M. A.; Brown, R. B. Rev. Infect. Dis. 1985, 7, 625.
18. Boykin, D. W. J. Braz. Chem. Soc. 2002, 13, 763.
19. Jones, H. E.; Blundell, G. K.; Tidwell, R. R.; Hall, J. E.; Farr, S. J.; Richards, R. J.
Toxicology 1993, 80, 1.
20. Johansson, A. M.; Grankist, K. G. AIDS 1996, 10, 684.

H. Torres-Gómez et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3147–3151
3151
(OCH2CH2CH2), 56.44 (30-OCH3), 68.90 (OCH2), 110.82 (C-20), 114.25 (C-4),
114.46 (C-7), 114.73 (C-50), 120.34 (C-60), 120.70 (C-10), 125.22 (C-6), 133.22
(C-5), 135.43 (C-7a), 136.95 (C-3a), 149.65 (C-40), 150.68 (C-30), 151.14 (C-2)
ppm. MS (FAB+) m/z 577 (M+H)+; Anal. Calcd for C35H36N4O4: C, 72.90; H, 6.29;
N, 9.72. Found: C, 73.61; H, 6.42; N, 9.55. 1,5-bis[2-methoxy-4-(5-nitro-1H-
benzimidazole-2-yl)phenoxy] pentane (10). Yield 0.343 g (97.9%) of orange
solid. Mp 183 °C (dec). 1H NMR (200 MHz, DMSO-d6) d: 1.59 (m, 2H,
OCH2CH2CH2), 1.81 (m, 4H, OCH2CH2CH2), 3.88 (s, 6H, 30-OCH3), 4.05 (t, 4H,
OCH2), 7.11 (m, 4H, H-20, H-50), 7.68 (d, 2H, H-7, J = 8.8 Hz), 7.69 (dd, 2H, H-60,
J = 2.2, J = 8.8 Hz) 8.06 (dd, 2H, H-6, J = 2.2, J = 8.8 Hz), 8.34 (d, 2H, H-4,
J = 1.8 Hz) ppm. 13C NMR (50 MHz, DMSO-d6) d: 22.98 (OCH2CH2CH2), 29.05
(OCH2CH2CH2), 56.41 (30-OCH3), 68.93 (OCH2), 110.85 (C-4), 111.73 (C-20),
113.37 (C-50), 11.91 (C-7), 118.89 (C-6), 120.49 (C-60), 121.19 (C-10), 138.53 (C-
3a), 142.74 (C-5), 143.38 (C-7a), 149.68 (C-40), 151.59 (C-30), 156.02 (C-2) ppm.
MS (FAB+) m/z 639 (M+H)+; Anal. Calcd. for C33H30N6O8: C, 62.06; H, 4.73; N,
13.16. Found: C, 63.60; H, 5.00; N, 13.03.
H-50, J = 9.3 Hz), 7.46 (dd, 2H, H-6, J = 8.2, J = 1.2 Hz), 7.70 (d, 2H, H-7,
J = 8.2 Hz), 7.86 (s, 2H, H-4), 8.11 (d, 4H, H-20, H-60, J = 8.8 Hz) ppm. 13C NMR
(50 MHz, DMSO-d6) d: 22.17 (OCH2CH2CH2), 28.32 (OCH2CH2CH2), 67.73
(OCH2), 96.86 (C-4), 112.34 (C-7), 115.01 (C-50), 119.05 (5-CF3), 120.5(C-6),
120.53 (C-10), 123.17 (C-5), 128.68 (C-20, C-60), 132.90, (C-7a), 139.90 (C-3a),
153.51 (C-2), 160.87 (C-40) ppm. MS (FAB+) m/z 625 (M+H)+; Anal. Calcd for
C
33H26F6N4O2: C, 63.46; H, 4.20; N, 8.97. Found: C, 64.60; H, 4.55; N, 8.23. 1,5-
bis[2-methoxy-4-(5-methoxy-1H-benzimidazole-2-yl)phenoxy] pentane (7).
Yield 0.209 g (63.9%) of
dark red solid. Mp 187.3 °C (dec). 1H NMR
a
(400 MHz, DMSO-d6) d: 1.58 (m, 2H, OCH2CH2CH2), 1.81 (m, 4H,
OCH2CH2CH2), 2.41 (s, 6H, 5-CH3), 4.05 (t, 4H, OCH2), 7.01 (dd, 2H, H-6,
J = 1.1, J = 8.2 Hz), 7.09 (d, 4H, H-30, H-50, J = 8.7 Hz), 7.35 (s, 2H, H-4), 7.45 (d,
2H, H-7, J = 8.2 Hz), 8.08 (d, 4H, H-20, H-60, J = 8.7 Hz) ppm. 13C NMR (100 MHz,
DMSO-d6) d: 21.41 (5-CH3), 22.31 (OCH2CH2CH2), 28.48 (OCH2CH2CH2), 67.65
(OCH2), 113.99 (C-4), 114.60 (C-6), 114.80 (C-30, C-50), 121.98 (C-10), 124.48 (C-
7), 127.97 (C-20, C-60), 131.24 (C-5), 137.25 (C-7a), 138.49 (C-3a), 150.76 (C-2),
160.02 (C-40) ppm. MS (FAB+) m/z 609 (M+H)+; Anal. Calcd for C35H36N4O6: C,
69.06; H, 5.96; N, 9.20. Found: C, 69.28; H, 5.95; N, 8.61. 1,5-bis{2-methoxy-4-
[5-(trifluoromethyl)-1H-benzimidazole-2-yl]phenoxy}pentane (9). Yield 0.35 g
(76%) of a light yellow solid. Mp 125 °C (dec). 1H NMR (400 MHz, DMSO-d6) d:
1.56 (m, 2H, OCH2CH2CH2), 1.80 (m, 4H, OCH2CH2CH2), 3.85 (s, 6H, 30-OCH3),
4.05 (t, 4H, OCH2), 7.15 (d, 2H, H-50, J = 8.4 Hz), 7.54 (dd, 2H, H-6, J = 1.6,
J = 8.8 Hz), 7.75 (d, 2H, H-7, J = 8.4 Hz), 7.76 (d, 2H, H-60, J = 8.4 Hz), 7.77 (d, 2H,
H-20, J = 1.6 Hz), 7.89 (s, 2H, H-4) ppm. 13C NMR (100 MHz, DMSO-d6) d: 22.52
(OCH2CH2CH2), 28.29 (OCH2CH2CH2), 55.85 (30-OCH3), 68.32 (OCH2), 110.47 (C-
20), 112.05 (C-4), 112.90 (C-50), 114.69 (C-7), 119.24 (C-5), 119.59 (C-6), 120.61
(C-60), 123.30 (5-CF3), 136.96 (C-3a), 138.64 (C-7a), 149.06 (C-40), 150.99 (C-30),
153.11 (C-2) ppm. MS (FAB+) m/z 686 (M+H)+; Anal. Calcd for C35H30F6N4O4: C,
61.40; H, 4.42; N, 8.18. Found: C, 62.41; H, 4.45; N, 8.11.
26. Yang, D.; Fokas, D.; Li, J.; Yu, L.; Baldino, M. C. Synthesis 2005, 1, 47.
27. General method of synthesis of 5-substituted bis(1H-benzimidazoles) 2, 4, 7
and9 via one-step reduction–cyclization reaction. A mixture of bis-aldehyde 11
or 12 (0.0006 mol), the corresponding 5-substituted-2-nitroaniline 17, 19
(0.0017 mol), and an excess of sodium dithionite (2.96 g, 0.017 mol, 10 equiv)
were dissolved in a mixture of ethanol–water 2:1 (30 mL). Then the mixture
was heated at 80 °C during 10–14 h. After the completion of the reaction, the
solvent was removed under reduced pressure and the resulting solid washed
with water. The crude solid product was then recrystallized from Ethanol–
acetone. 1,5-bis[4-(5-methoxy-1H-benzimidazole-2-yl) phenoxy]pentane (2).
Yield 0.12 g (68%) of yellow solid. Mp 185 °C (dec). 1H NMR (200 MHz, DMSO-
d6) d: 1.61 (m, 2H, OCH2CH2CH2), 1.83 (m, 4H, OCH2CH2CH2), 3.81 (s, 6H, 5-
OCH3), 4.11 (t, 4H, OCH2), 6.88 (dd, 2H, H-6, J = 2.2, J = 9.3 Hz), 7.08 (d, 2H, H-4,
J = 2.2 Hz), 7.15 (d, 4H, H-20, H-60, J = 8.8 Hz), 7.49 (d, 2H, H-7, J = 9.3 Hz), 8.07
(d, 4H, H-30, H-50, J = 8.8 Hz) ppm. 13C NMR (50 MHz, DMSO-d6) d: 22.31
(OCH2CH2CH2), 29.05 (OCH2CH2CH2), 56.23 (5-OCH3), 68.39 (OCH2), 97.67 (C-
4), 112.89 (C-6), 115.65 (C-30, C-50), 115.95 (C-7), 121.16 (C-10), 128.86 (C-20, C-
60), 132.62 (C-7a), 138.19 (C-3a), 150.84 (C-2), 156.81 (C-5), 161.11 (C-40) ppm.
MS (FAB+) m/z 549 (M+H)+; Anal. Calcd for C33H32N4O4: C, 72.24; H, 5.88; N,
10.21. Found: C, 72.63; H, 5.86; N, 9.35. 1,5-bis{4-[5-(trifluoromethyl)-1H-
benzimidazole-2-yl]phenoxy} pentane (4). Yield 0.35 g (87.6%) of a light yellow
solid. Mp 174.9 °C (dec). 1H NMR (200 MHz, DMSO-d6) d: 1.58 (m, 2H,
OCH2CH2CH2), 1.79 (m, 4H, OCH2CH2CH2), 4.06 (t, 4H, OCH2), 7.11 (d, 4H, H-30,
28. For more details, see supporting information.
29. Cedillo-Rivera, R.; Muñoz, O. J. Med. Microbiol. 1992, 37, 221.
30. Thathy, V.; Menard, R. Methods Mol. Med. 2002, 72, 317.
31. Encarnacion-Dimayuga, R.; Murillo-Álvarez, J. I.; Christophersen, C.; Chan-
Bacab, M.; Garc´ıa-Reiriz, M. L.; Zacchino, S. Nat. Prod. Commun. 2006, 1,
541.
32. At the same time that this manuscript was been written and submitted,
another group published one compound closely related to our work, see:
Mayence, A.; Pietka, A.; Collins, M. S.; Cushion, M. T.; Tekwani, B. L.; Huang, T.
L.; Vanden Eynde, J. J. Bioorg. Med. Chem. Lett. 2008, 18, 2658.