Synthesis and antiviral activity against Coxsackie virus B3 of some novel benzimidazole derivatives

Article abstract of DOI:10.1016/j.bmcl.2004.10.087

Some benzimidazole derivatives were synthesized and the antiviral evaluation against Coxsackie virus B₃ is reported. These compounds are proved to be excellent inhibitors of CVB₃. Some benzimidazole derivatives were synthesized and evaluated for their antiviral properties. Compounds 20 and 21 showed potent selective activity against Coxsackie virus B₃ in VERO cells. Some structure-activity relationships were discussed.

Full text of DOI:10.1016/j.bmcl.2004.10.087

Bioorganic & Medicinal Chemistry Letters 15 (2005) 267–269
Synthesis and antiviral activity against Coxsackie virus B3 of
some novel benzimidazole derivatives
Jun Cheng, Jiangtao Xie and Xianjin Luo*
School of Chemistry and Chemical Engineering, Shanghai Jiaotong University, Shanghai 200240, PR China
Received 9 September 2004; revised 29 October 2004; accepted 30 October 2004
Available online 24 November 2004
Abstract—Some benzimidazole derivatives were synthesized and evaluated for their antiviral properties. Compounds 20 and 21
showed potent selective activity against Coxsackie virus B3 in VEROcells. Some structure–activity relationships were discussed.
Ó 2004 Elsevier Ltd. All rights reserved.
Benzimidazoles are regarded as a promising class of
biologically active agents. For example, some others
served as PARP inhibitors1 and some benzimidazole
derivatives showed potent antiviral activity.2,3 A series
of 2-pyridyl-1H-benzimidazole-4-(N-R2-carboxamide)
derivatives (compounds 9–26, general structure shown
in Fig. 1) were synthesized in this work, and it was found
that they had excellent inhibitory activity against Cox-
sackie virus B3 (CVB3), a non-enveloped single posi-
tive-strand RNA virus belonging to the picornaviridea
family, which is the major cause of virus-induced human
myocarditis.4 The IC50 value of ribavirin (RVB), a
well-known nucleoside analogue virustatic drug,5 was
provided as comparable data. In these synthesized
compounds, compounds 20 and 21 had excellent IC50
values (1.43 and 0.54lg/mL, respectively), far more active
than RVB with IC50 value of more than 400lg/mL.
derivatives, and the introduction of phenyl group in
R2 moiety could enhance the biological activity and
selectivity. The synthesis of 2-pyridyl-1H-benzimid-
azole-4-(N-R2-carboxamide) derivatives and the results
of evaluation of their antiviral activity were reported
herein.
Synthetical route of the primary compound 5, 2,3-di-
aminobenzoic acid is shown in Scheme 1. The syntheses
of 3-nitrophthalamic acid 3 and 3-nitroanthranilic acid 4
starting from 3-nitrophthalic anhydride 2 were reported
by Chapman and Stephen,6 and the compound 5 was
obtained in good yield (95%) by the reduction of
compound 4 with hydrazine hydrate in the presence of
Ranney Ni.
Following Williamꢀs method,7 the cyclization of 2,3-
diaminobenzoic acid 5 with 2-pyridylaldehyde, 3-pyridyl-
aldehyde and 4-pyridylaldehyde, respectively, in the
presence of copper acetate gave the corresponding
2-pyridyl-1H-benzimidazole-4-carboxylic acids (6–8) in
about 50% yield. However, a large quantity of reagent
methanol had to be used to dissolve 2,3-diaminobenzoic
acid 5 because of its poor solubility in non-alkaline
medium, since an acidic medium was necessary for
the existence of copper acetate. In addition, the post-
treatment was very complicated. Therefore, potassium
ferricyanide was chosen as an oxidant to act in an alka-
line medium, and with that a yield similar to the
Williamꢀs method was obtained. The synthetic route is
shown in Scheme 2.
Biological activity data demonstrated that 2-pyridyl
derivatives were much better than 3- and 4-pyridyl
CONH R2
N
R1= 2-, 3- and 4-pyridyl
R1
NH
R2= H, hydroxyethyl and aryl
1
Figure 1. The general structure of synthesized compounds.
Keywords: Benzimidazole; Coxsackie virus B3; Antiviral.
*
As outlined in Scheme 3, at first 2-pyridyl-1H-benzimid-
azole-4-carboxylic acids (6–8) were transformed to the
Corresponding author. Tel.: +86 021 54745863; fax: +86 021 5474
1297; e-mail: luoxianjin@sjtu.edu.cn
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.10.087

268
J. Cheng et al. / Bioorg. Med. Chem. Lett. 15 (2005) 267–269
O
O
COOH
COOH
COOH
CONH2
NO2
NH2
NO2
NH2
NH2
O
i
ii
iii
NO2
5
2
3
4
Scheme 1. Reagents and conditions: (i) NH3 (aq), 70°C; (ii) KOH, Br2, H2O , 80°C; (iii) NaOH, CH3OH, Ranney Ni, N2H4ÆH2O, reflux.
N
COOH
COOH
Table 1. Activity of benzimidazole derivatives against Coxsackie virus
B3 in VEROcells
6 R1 =
7 R1 =
8 R1 =
NH2
NH2
N
N
iv or v
SIc
a
b
R1
+
Compd R1
R2
TC50
(lg/mL)
IC50
(lg/mL)
R1CHO
NH
N
5
6~8
N
N
N
9
15.64 3.85
4.06
Scheme 2. Reagents and conditions: (iv) CH3OH, Cu(Ac)2, reflux,
then Na2S; (v) CH3OH, K3Fe(CN)6, reflux.
Cl
10
11
20.45 8.72
2.35
–CH2CH2OH
140.6
12.3
NAd
NA
—
F
N
N
N
12
13
14
—
COOH
CONH R2
N
vi
vii
N
Br
R1
8.24 4.12
2.0
R1
viii
NH
NH
CH3
6~8
9~26
27.8
2.42
11.48
Scheme 3. Reagents and conditions: (vi) SOCl2, reflux; (vii) NH3 (aq)
or R2NH2, rt; (viii) DCC, DMAP, R2NH2, rt.
N
N
NO2
OH
15
16
55.5
5.9
18.52
NA
2.99
—
corresponding carboxylic chlorides by the treatment of
thionyl chloride. Then 2-pyridyl-1H-benzimidazole-4-
(N-R2-carboxamide)s (9–26) were obtained by the reac-
tion of the corresponding carboxylic chlorides with
aqueous ammonia or amines, respectively. The conden-
sation of carboxylic acids and amides could also be
carried out in one step in the presence of DCC (dicy-
clohexylcarbodiimide) and DMAP (para-dimethylami-
nopyridin). However, the yields were low because of
the occurrence of by-products.
HO
N
N
17
18
18.5
4.05
4.56
COOCH3
OCOPh
NTe
>1000
NT
—
RVB
—
—
447.8
>2.23
a Cytotoxic concentration required to inhibit VEROcell growth by
50%.
b Concentration required to inhibit Coxsackie virus B3 growth by 50%.
c Selective Index values equal to TC50/IC50
.
2-Pyridyl-1H-benzimidazole-4-carboxamide derivatives
were evaluated for their antiviral activity against Cox-
sackie virus B3 in VEROcells. Antiviral activities of 4-
pyridyl derivatives were tested at first (as shown in Table
1), and those of 2- and 3-pyridyl derivatives were char-
acterized later (as shown in Table 2). In order to make
biological data in Tables 1 and 2 comparable, com-
pound 14 and ribavirin (RVB) were also listed in the
table. It is found that most of the synthesized com-
pounds had excellent antiviral activity, far more active
than RVB with IC50 value of more than 400lg/mL.
The IC50 value of compounds (13, 14, 17, 20, 21, 24
and 25) were even less than 5lg/mL. Moreover, com-
pounds 20 and 21 had particularly excellent IC50 values
(1.43 and 0.54lg/mL, respectively), together with emi-
nent selective indexes (38.8 and 28.3, respectively).
d Not active in the largest concentration which were not toxic to VERO
cells.
e Not tested.
compound 26, generally the introduction of 2-pyridyl
group was better than that of 3-pyridyl group. More-
over, 2-pyridyl derivatives were more efficient than 4-
pyridyl derivatives from the biological data provided
in the two tables. With regard to R2 moiety, the presence
of phenyl group enhanced inhibitory activity greatly,
because compounds 20 and 21 in 2-pyridyl derivatives
and compounds 24 and 25 in 3-pyridyl derivatives were
obviously more active and selective than compounds 19
and 22 (R2 = H and hydroxyethyl, respectively) and
compounds 23 and 26. On the one hand, the introduc-
tion of hydroxyethyl group reduced inhibitory activity,
and on the other hand, its existence enhanced TC50
value; so hydroxyethyl analogues resulted in a modest
selective index.
These results led to some considerations. 2-Pyridyl
derivatives (19–21) had greater antiviral activity and
selectivity than 3-pyridyl derivatives (23–25). Although
compound 22 was slightly less active and selective than

J. Cheng et al. / Bioorg. Med. Chem. Lett. 15 (2005) 267–269
269
Table 2. Activity of benzimidazole derivatives against Coxsackie virus
B3 in VEROcells
selective index, it is not essential to enhance the antiviral
activity.
a
b
Compd R1
R2
TC50
(lg/mL)
IC50
(lg/mL)
SIc
Acknowledgements
CH3
N
14
10.74
2.23
4.81
1
We thank Ms Chen Yan for H NMR support.
N
N
N
19
20
21
H
53.4
55.6
15.33
7.29
1.43
0.54
7.32
References and notes
38.8
1. White, A. W.; Almassy, T.; Calvert, A. H.; Crutin, N. J.;
Griffin, R. J.; Hostomsky, Z.; Maegley, K.; Newell, D. R.;
Srinivasan, S.; Golding, B. T. J. Med. Chem. 2000, 43, 4084.
2. Garuti, L.; Roberti, M.; Cermelli, C. Bioorg. Med. Chem.
Lett. 1999, 9, 2525.
3. Garuti, L.; Roberti, M.; De Clercq, E. Bioorg. Med. Chem.
Lett. 2002, 12, 2707.
4. Sole, M. J.; Liu, P. J. Am. Coll. Cardiol. 1993, 22, 99.
5. Gilbert, B. E.; Knight, V. Antimicrob. Agents Chemother.
1986, 30, 201.
F
28.3
N
22
–CH2CH2OH
H
160.2
37.0
4.32
N
N
23
24
18.5
6.2
2.98
9.17
10.74
1.17
6. Chapman, E.; Stephen, H. J. Chem. Soc. 1925, 127, 1791.
7. William, A. D.; Gordon, W. R.; Bruce, C. B. J. Med. Chem.
1990, 33, 814.
F
N
N
25
26
37.0
3.23
11.4
8. Selected 1H NMR data. Compound 19: 1H NMR
(400MHz, DMSO) d: 7.34–7.38 (t, 1H), 7.55–7.59 (m,
1H), 7.71–7.73 (m, 1H), 7.81–7.82 (d, 1H), 7.87–7.89 (m,
1H), 8.00–8.05 (m, 1H), 8.43–8.45 (m, 1H), 8.75–8.78 (m,
1H), 9.27–9.28 (d, 1H), 13.59 (s, 1H). Compound 20: 1H
NMR (400MHz, CDCl3) d: 7.14–7.18 (t, 1H), 7.41–7.47 (m,
4H), 7.64–7.66 (d, 1H), 7.92–8.00 (m, 3H), 8.27–8.29 (d,
1H), 8.45–8.47 (d, 1H), 8.67–8.69 (m, 1H), 11.07 (s, 1H),
12.11 (s, 1H). Compound 21: 1H NMR (400MHz, DMSO)
d: 7.14–7.19 (m, 1H), 7.24–7.28 (m, 1H), 7.40–7.48 (m, 2H),
7.60–7.63 (m, 1H), 7.80–7.83 (d, 1H), 8.02–8.04 (d, 1H),
8.12–8.16 (t, 1H), 8.45–8.47 (d, 1H), 8.64–8.68 (t, 1H), 8.80–
8.81 (d, 1H), 12.52 (s, 1H), 13.84 (s, 1H). Compound 22: 1H
NMR (400MHz, DMSO) d: 3.52–3.57 (q, 2H), 3.63–3.67
(q, 2H), 4.98–5.00 (t, 1H), 7.34–7.38 (t, 1H), 7.56–7.59 (m,
1H), 7.69–7.72 (d, 1H), 7.87–7.90 (d, 1H), 8.02–8.06 (m,
1H), 8.45–8.47 (d, 1H), 8.76–8.77 (m, 1H), 10.14–10.16 (t,
1H), 13.62 (s, 1H).
–CH2CH2OH
—
192.4
25.59
411.7
7.51
RVB
—
>1000
>2.42
a Cytotoxic concentration required to inhibit VEROcell growth by
50%.
b Concentration required to inhibit Coxsackie virus B3 growth by 50%.
c Selective Index values equal to TC50/IC50
.
In conclusion, it is evident that 2-pyridyl-1H-benzimid-
azole-4-carboxamide derivatives8 have an excellent anti-
viral activity. Moreover, 2-pyridyl derivatives are much
better than 3- and 4-pyridyl derivatives, and the intro-
duction of phenyl group in R2 moiety improves biolog-
ical activity and selectivity. In addition, although
hydroxyethyl group in R2 moiety brings on a modest