Synthesis and antiproliferative activity of some benzimidazole-4,7-dione derivatives

Article abstract of DOI:10.1016/S0960-894X(00)00429-7

A series of benzimidazole-4,7-diones bearing at the 2-position the thiomethyl group or the 2-pyridyl moiety has been synthesized and tested in vitro on three tumor cell lines. Two of them show a very good antiproliferative effect. Compounds 1 and 2d are more active or equiactive, respectively, than MMC against human lymphoblastic leukemia. Both compounds exhibit high activity on human non-Hodgkin lymphoma. Compound 1 is non toxic at all the concentrations used in the antiproliferative assay and 2d is toxic only at high concentration. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00429-7

Bioorganic & Medicinal Chemistry Letters 10 (2000) 2193±2195
Synthesis and Antiproliferative Activity of Some Benzimidazole-
4,7-dione Derivatives
Laura Garuti,a,* Marinella Roberti,a Monica Malagoli,b Tiziana Rossic
and Mario Castellib
aDepartment of Pharmaceutical Science, University of Bologna, via Belmeloro 6, I-40126 Bologna, Italy
bDepartment of Biomedical Science, University of Modena, via Campi 287, I-41100 Modena, Italy
cDepartment of Pharmaceutical Science, University of Modena, via Campi 287, I-41100 Modena, Italy
Received 9 May 2000; revised 17 July 2000; accepted 25 July 2000
AbstractÐA series of benzimidazole-4,7-diones bearing at the 2-position the thiomethyl group or the 2-pyridyl moiety has been
synthesized and tested in vitro on three tumor cell lines. Two of them show a very good antiproliferative e€ect. Compounds 1 and
2d are more active or equiactive, respectively, than MMC against human lymphoblastic leukemia. Both compounds exhibit high
activity on human non-Hodgkin lymphoma. Compound 1 is non toxic at all the concentrations used in the antiproliferative assay
and 2d is toxic only at high concentration. # 2000 Elsevier Science Ltd. All rights reserved.
A great number of heterocyclic quinones display interest-
ing antitumour activities. Their mechanism of action is
very di€erent for the various types of compounds.
Many of them act as bioreductive alkylating agents.
Compounds of note include mitomycin C (MMC),1 4
mitosenes, such as EO95,6 and many indole analogues.7
Other quinones exert their action via inhibition of DNA
synthesis: these include streptonigrin,8,9 several quino-
line10 and quinoxaline diones.11 Signi®cant biological
properties appeared also in some benzimidazole-
diones.12 14 5-Amino-6-bromobenzimidazole-4,7-dione12
shows good antitumor activity in vivo on P388 leuke-
mia. Pyrrolo[1,2-a] benzimidazole and benzimidazole-
based aziridinyl quinones13 18 possess strong antitumor
activity by virtue of their ability to cleave DNA. More-
over, studies on simple heterocyclic quinones containing
nitrogen show that the number and position of nitro-
gens are important for the cytotoxicity.18 On the basis
of these considerations, a series of variously substituted
benzimidazole-4,7-diones has been synthesized and tes-
ted for antiproliferative activity. The aim is to investi-
gate the substituent e€ect at the 5(6) position of
simpli®ed quinone systems, related to general structure
1 and 2. The 5(6) substituents, by varying the quinone
reduction ease, in¯uence its single-strand DNA cleavage
capability and therefore its activity. Hence a range of
compounds containing the thiomethyl group (1, 1a±c,
1e±g) or the pyridyl moiety (2a, 2c±e) at C-2 is prepared.
The C-5 position is unsubstituted or substituted with an
amino function, with the methoxy group or with an
electron withdrawing group as the bromine atom.
Chemistry
4,7-Dimethoxybenzimidazol-2-(3H)-thione19 3 and 2,3-
diamino-1,4-dimethoxybenzene20 4 were reported in the
literature. The hydroquinone 5 (Scheme 1) was obtained
by heating 3 with 48% hydrobromic acid at 120 ꢀC for
6 h. The S-methylation occurred during this hydrolysis
and led to the 4,7-dihydroxy-2-methylthio benzimida-
zole as the main product in good yield. Oxidation of 5
with ferric chloride in aqueous solution at room tem-
perature gave the 2-methylthiobenzimidazole-4,7-dione
1. The 5(6)-substituted derivatives were obtained by
nucleophilic addition reaction on the quinone. The
reaction of 1 with primary and secondary amines in
methanol solution resulted in the formation of 5(6)-
amino-substituted-4,7-benzimidazolediones 1a and 1b.
*Corresponding author. Tel.: +39-051-2099715; fax: +39-051-2099734;
e-mail: mrobi@alma.unibo.it
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00429-7

2194
L. Garuti et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2193±2195
Scheme 1. (a) HBr, 120 ꢀC; (b) Aq. FeCl3; (c) dimethylamine or 2-chloroethylamine, MeOH; (d) Br2, 1,2-DME; (e) HBr; (f) NH4OH, MeOH.
Scheme 2. (a) 2-Pyridinecarboxaldehyde, nitrobenzene; (b) HBr, 120 ꢀC; (c) Aq. FeCl3; (d) dimethylamine, MeOH; (e) HBr; (f) NH4OH, MeOH.
The 5,6-dibromo derivative 1c was obtained by addition
Results and Discussion
of bromine to 1 in 1,2-dimethoxyethane. Treating of 1
with 48% hydrobromic acid gave 5(6)-bromo-4,7-ben-
zimidazolediol hydrobromide 1d which was oxidized to
quinone 1e in aqueous ferric chloride solution. The
reaction of 1e with ammonium hydroxide in methanol
at room temperature yielded a mixture of 1f (24.4%)
and 1g (15%), which was separated by column chroma-
tography. Re¯uxing 4 with 2-pyridinecarboxaldehyde in
nitrobenzene gave 2-(2-pyridyl)-4,7-dimethoxybenz-
imidazole 6, which was puri®ed by column chromato-
graphy. The remaining compounds in this series, namely
7, 2, 2a±e were prepared (Scheme 2) by methods similar
to those used for the 2-methylthio series.21
The series of benzimidazole-4,7-diones 1, 1a±c, 1e±g and
2a, 2c±e were screened for activity against Molt-3 cells,
from human lymphoblastic leukemia, SupT-1 cells,
from human non-Hodgkin lymphoma and MCF-7 cells
from human breast adenocarcinoma and comparison
was made with mitomycin C (MMC).22,23 The results,
reported in Table 1, show that compounds 1 and 2d
possess the best antiproliferative e€ect. Such activity is
strong against SUPT1 cells, although lower than that of
the MMC. Moreover, compound 1 is more active than
MMC on human lymphoblastic leukemia, whereas

L. Garuti et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2193±2195
2195
Table 1. The antiproliferative activities of benzimidazole-4,7-diones
and MMC
high antiproliferative activity of 1 and 2d on leukemia
and lymphoma cells, also at small doses, and the fact
that 1 is not toxic and 2d is toxic only at the higher
concentration (90 mM), we believe that these two com-
pounds could be interesting candidates for further in
vivo testing.
ID50 (mM)a
Compound
SupT1
Molt3
MCF7
1
2.87
38
15.31
6.26
5.03
1.32
18.32
30.6
11.99
32.14
20.82
60.4
22.45
7.52
2.63
39.67
2.66
62.65
>90
>90
40.3
62.8
36
>90
>90
>90
26.4
>90
42.92
1a
1b
1c
1e
1f
1g
2a
2c
2d
2e
Acknowledgements
This research was supported by Ministero della Ricerca
Scienti®ca e Tecnologica (MURST).
5.07
10.8
17.44
5.57
2.57
29.30
<0.7
References and Notes
MMC
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aID50 drug dosage required to inhibit the cancer cell growth by 50%.
Table 2. Cytotoxicity of 1 and 2d on VERO cells
Compound
Conc. mM
Dye testa
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100
100
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73.6
100.7
99.3
16.4
71.2
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68.9
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16.2
81.3
97.2
11.2
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compound 2d and MMC are equiactive. Compounds 1e
and 1f have a moderate inhibitor activity. In contrast,
all derivatives show no activity on breast adenocarci-
noma; the MMC standard also is not active in this
assay. Because of their interesting antiproliferative
activity, the in vitro toxicity of derivatives 1 and 2d on
VERO cells has been evaluated.24 As reported in Table
2 the data from the dye test and the Lowry's method for
protein content, show that compound 1 is well tolerated
at all the concentrations used in antiproliferative assay
(90±0.7 mM), while compound 2d is toxic only at high
concentration (90 mM). The results obtained do not
permit an analysis of structure±activity relationships,
however, it is evident that, in the ®rst series of com-
pounds (1, 1a±c, 1e±g) the substituents on the quinone
ring have a negative e€ect, perhaps due to steric hin-
drance: the most active derivative is unsubstituted.
Among the derivatives bearing the 2-pyridyl moiety at
C-2 (2a, 2c±e) 2d is the most active with an ID50 2.57
and 2.63 mM on SupT1 and Molt3, respectively. In this
case, the presence of the methoxy group is an important
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nones. All derivatives bearing amine substituents at C-
5(6) (1a, 1b, 1g, 2a, 2e) are not active. Considering the
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1
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upon request.
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