Synthesis and antiviral activity of an imidazo[1,2-a]pyrrolo[2,3-c]pyridine series against the bovine viral diarrhea virus

Article abstract of DOI:10.1016/j.ejmech.2010.01.023

A series of imidazo[1,2-a]pyrrolo[2,3-c]pyridines has been prepared and evaluated for their anti-BVDV activities in MDBK cells. From the synthesized analogues bearing modifications of the substituents at positions 2, 3, 7 and 8, compounds 10a, b, 16, 24, 25 and 26 exhibited significant anti-BVDV activities.

Full text of DOI:10.1016/j.ejmech.2010.01.023

European Journal of Medicinal Chemistry 45 (2010) 2044–2047
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
Synthesis and antiviral activity of an imidazo[1,2-a]pyrrolo[2,3-c]pyridine series
against the bovine viral diarrhea virus
,
b
,
c
a
,
,
b
a,b
Jean-Michel Chezal a , Jan Paeshuyse , Vincent Gaumet b, Damien Canitrot a , Aurelie Maisonial
,
*
´
Claire Lartigue a b, Alain Gueiffier a b, Emmanuel Moreau a b, Jean-Claude Teulade a
,
,
,
,
,b
Olivier Chavignon a b, Johan Neyts c
,
,d
a
´
Clermont Universite, Univ Clermont 1, EA 4231, Clermont-Ferrand F-63001, France
b Centre Jean Perrin, Clermont-Ferrand F-63011, France
c Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium
d Univ François Rabelais, EA 3857, Tours F-37200, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of imidazo[1,2-a]pyrrolo[2,3-c]pyridines has been prepared and evaluated for their anti-BVDV
activities in MDBK cells. From the synthesized analogues bearing modifications of the substituents at
positions 2, 3, 7 and 8, compounds 10a, b, 16, 24, 25 and 26 exhibited significant anti-BVDV activities.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Received 30 September 2009
Received in revised form
7 January 2010
Accepted 11 January 2010
Available online 20 January 2010
Keywords:
Imidazo[1,2-a]pyridine
Imidazo[1,2-a]pyrrolo[3,2-c]pyridine
BVDV activity
Antiviral
1. Introduction
hepatitis C virus (HCV) [11] although robust HCV replicon and HCV
cell culture systems are now available [12–14].
The bovine viral diarrhea virus (BVDV) belongs together with
viruses such as the classical swine fever virus (CSFV) and the border
disease virus (BDV) to the genus Pestivirus that is classified along
with the genus Hepacivirus and Flavivirus in the family of the Fla-
viviridae [1].
Pestiviruses cause important diseases of livestock such as bovine
viral diarrhea in cattle [2], classical swine fever in pigs [3] and border
disease in sheep. BVDV remains an agronomical burden regardless of
the availability of vaccines against BVDV and the implementation of
elaborate eradication or control programs [4,5]. An alternative
approach to combat pestiviral infections could be the use of antiviral
agents that specifically inhibit the replication of these viruses [6–8].
We recently reported proof of concept studies, in which it was
demonstrated that an anti-pestivirus agent (an imidazopyridine
derivative) has a marked effect on the replication of CSFV in infected
pigs and on the transmission of the virus to uninfected sentinels
[9,10]. BVDV has also been considered to be a surrogate virus for
We demonstrated earlier that the imidazo[1,2-a]pyrrolo[3,2-
c]pyridines 1a, b [15] (Fig. 1) selective inhibit the replication of pes-
tiviruses by targeting a region of the finger domain of the RdRp [16].
Furthermore we showed that resistant virus to imidazo[1,2-a]pyr-
rolo[3,2-c]pyridineanalogue10a (AG110)iscross-resistantwiththree
other inhibitors of pestivirus replication i.e. compound 1453[17], BPIP
[8] and VP32947 [18]. Obviously, this region of the polymerase, that is
only 7 Å across, is (i) crucial for the functioning of the polymerase and
the viral replication complex and (ii) is apparently a hot spot binding
site for selective inhibitors of pestivirus replication [16].
We report here the synthesis and the antiviral activity of imi-
dazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives, which led to the
identification of the lead compound 10a. Starting from compounds
1a, b, modifications were introduced in positions 2, 3, 7 and 8 of the
imidazo[1,2-a]pyrrolo[3,2-c]pyridine ring system and the struc-
ture–activity relationship (SAR) studies were discussed.
2. Chemistry
The first step of our synthetic approach required the synthesis of
imidazo[1,2-a]pyridine-8-carbaldehyde precursors according to
* Corresponding author. Tel.: þ33 4 73 15 08 00; fax: þ33 4 73 15 08 01.
E-mail address: j-michel.chezal@u-clermont1.fr (J.-M. Chezal).
0223-5234/$ – see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.01.023

J.-M. Chezal et al. / European Journal of Medicinal Chemistry 45 (2010) 2044–2047
2045
CO2Et
EtO2C
8
CO2Et
CO2Et
R
N3
i
N
iii
v
N
N
N
CHCl2
CH(OEt)2
13 R = CH2OH
2
+
CH(OEt)2
CH(OEt)2
HN
N
11
N
N
N
12
N
2R
7
15
ii
N
iv
3
14
R = CHO
C
EtO2
EtO2C
HN
1a R = H
1b R = Br
viii
ix
HN
N
N
CH2OH
CH2Cl
N
N
19
EtO2C
HN
EtO2C
HN
18
vi
vii
Fig. 1. Structures of compounds studied in the text.
N
N
CH(OEt)2
CHO
EtO2
C
N
16
N
17
HN
N
x
N
CO2Et
NH2
CO2Et
N
N
3a-f
N
CH2OH
N
N
20
ii
i
R
R
N
Scheme 4. Reagents and conditions: (i) (a) 1,1,3-trichloracetone, DME, rt; (b) EtOH,
reflux; (ii) DMAP, EtOH, reflux; (iii) LiAlH4, THF, 0 ꢀC; (iv) MnO2, CHCl3, reflux; (v) ethyl
azidoacetate, EtONa, EtOH, ꢁ30 ꢀC; (vi) chlorobenzene, reflux; (vii) (a) HCl, CH3CN,
H2O, rt; (b) aq Na2CO3; (viii) NaBH4, EtOH, rt; (ix) SOCl2, NEt3, CH2Cl2, 0 ꢀC. (x) (a)
(CH3)2NH, HCl, NEt3, MeOH, rt; (b) NaBH3CN, rt.
2
4a-f
R
CHO
a
Me
Ph
m-MeOPh
CF3
i-Pr
t-Bu
5a–f. Substituents on 3-position can be easily introduced at this
stage by using electrophilic substitution reactions that occur in
imidazo[1,2-a]pyridine series mostly at this position [20].
Following standard procedures, selective bromination of aldehydes
6 [15] and 5a afforded respectively 3-bromo derivatives 7a and 7b,
while 3-nitro compound 8 was obtained by classical nitration of 5a.
iii
N
b
c
d
e
f
R
N
5a-f
Substituted
ethyl
imidazo[1,2-a]pyrrolo[2,3-c]pyridine-8-
carboxylates in positions 2 and 3 of the imidazole ring were easily
obtained in two steps from the corresponding imidazo[1,2-a]pyri-
dine-8-carbaldehydes according to the Chezal’s procedure [15,21]
(Scheme 3). Briefly, aldehydes 5a–f, 7a–b and 8 were converted
into the corresponding ethyl azidopropenoate compounds 9a–i, by
the addition of ethyl azidoacetate in the presence of an ethanolic
sodium ethoxide solution [22], which can subsequently be cyclised
in refluxing chlorobenzene to yield compounds 10a–i.
Further chemical modifications were introduced at the 2-posi-
tion as outlined in Scheme 4. Condensation of the 2-aminopyridine
2 with 1,1,3-trichloracetone afforded a mixture of dichloro deriva-
tive 11 and ketal 12 in 70 and 4% yields respectively. Compound 11
was converted into 12 in the presence of 4-dimethylaminopyridine
in refluxing anhydrous ethanol. According to the synthesis devel-
oped for compound 10, aldehyde 14, which was obtained in two
steps from ester 12 via the hydroxymethyl intermediate 13, was
treated with ethyl azidopropenoate to give after thermal ring
closure 2-ketal substituted derivative 16. Deprotection of the ketal
group was accomplished in presence of catalytic hydrochloric acid
to give aldehyde 17. Reduction of 17 with sodium borohydride
afforded alcohol 18, which was treated in the presence of thionyl
chloride to give 2-chloromethyl 19. Reductive amination of alde-
hydes 17 yielded dimethylamino compound 20.
Scheme 1. Reagents and conditions: (i) XCH2COR (X ¼ Cl, Br), EtOH or BuOH, reflux;
(ii) LiAlH4, THF, 0 ꢀC; (iii) MnO2, CHCl3, reflux.
CHO
CHO
N
N
i
R
R
N
N
Br
6
R = H
7a R = H
5a
R = Me
ii
7b
R = Me
CHO
N
5a
Me
NO2
N
8
Scheme 2. Reagents and conditions: (i) Br2, AcOH, rt; (ii) HNO3, H2SO4, 0 ꢀC then rt.
Schemes 1 and 2. Condensation of ethyl 2-aminopyridine-3-
carboxylate (2) [19] with the corresponding
a-halo carbonyl
compounds in refluxing ethanol or butanol provided 2-substituted
ethyl esters 3a–f in moderate to good yields (43–73%). Reduction of
esters 3a–f in presence of lithium aluminium hydride yielded
alcohols 4a–f which were oxidized with MnO2 to afford aldehydes
CO2Et
EtO2C
HN
CHO
N3
N
i
ii
N
R1
R1
N
R1
N
N
N
R2
R2
R2
R1 = Me, R2 = H
R1 = Me, R2 = H
R1 = Me, R2 = H
10a
10b
10c
10d
10e
10f
5a
5b
5c
5d
5e
9a
9b
9c
9d
9e
R
R
1 = Ph, R2 = H
1 = m-MeOPh, R2 = H
R
R
1 = Ph, R2 = H
1 = m-MeOPh, R2 = H
R1 = Ph, R2 = H
R1 = m-MeOPh, R2 = H
R1 = CF3, R2 = H
R1 = i-Pr, R2 = H
R1 = t-Bu, R2 = H
R1 = H, R2 = Br
R1 = CF3, R2 = H
R1 = CF3, R2 = H
R
1 = i-Pr, R2 = H
R
1 = i-Pr, R2 = H
5f R1 = t-Bu, R2 = H
7a
9f R1 = t-Bu, R2 = H
9g
R1 = H, R2 = Br
R1 = H, R2 = Br
10g
10h
10i
R1 = Me, R2 = Br
R1 = Me, R2 = Br
R1 = Me, R2 = Br
R1 = Me, R2 = NO2
7b
9h
8
R
1 = Me, R2 = NO2
9i
R
1 = Me, R2 = NO2
Scheme 3. Reagents and conditions: (i) ethyl azidoacetate, EtONa, EtOH, ꢁ30 ꢀC; (ii) chlorobenzene, reflux.

2046
J.-M. Chezal et al. / European Journal of Medicinal Chemistry 45 (2010) 2044–2047
HOH2C
EtO2C
HN
i
HN
100
80
60
40
20
0
100
80
60
40
20
0
N
N
Me
Me
N
N
21
10a
ii
iii
HO2C
HN
RO2C
Me N
N
N
Me
Me
Me
N
N
22
23
R = Et
0.05
0.1
0.4
1
4
11
33
100
+
compound 10c (µM)
iv
24 R = Me
RO2C
HN
Fig. 2. Effect of compound 10c on BVDV (NADL)-induced CPE formation in MDBK cells
(open bars) and on the proliferation of exponentially growing MDBK cells (diamonds).
Data are mean values ꢂ standard deviations from three independent experiments.
N
N
of compound 10a with methyl iodide in the presence of sodium
hydride in various solvents such as DMF or DMSO failed to afford N-
methyl compound 23. Access to the latter compound was achieved
on the basis of Guillonneau’s [24] protocol. Briefly, methylation of
10a with dimethyl carbonate in the presence of potassium
carbonate and adogenÒ 464 produced 23 and the unexpected
methyl ester 24 in 31 and 17% yields respectively. Finally,
compound 10a was converted in two steps into the corresponding
methyl and butyl esters 25 and 26 via the acid 22.
25 R = Me
26
R = Bu
Scheme 5. Reagents and conditions: (i) LAH, THF, 0 ꢀC; (ii) (a) THF, EtOH, aq KOH 2N,
rt; (b) HCl, 0 ꢀC; (iii) (MeO)2CO, K2CO3, Adogen 464, DMF, 110 ꢀC; (iv) ROH, HCl gas,
H2SO4, reflux.
Substituted derivatives at the 7 and 8 positions were prepared
as shown in Scheme 5. Hydroxymethyl 21 was obtained by
reduction of ester 10a with LAH. Methylation [23] at the 7-position
Table 1
3. Results and discussion
Structure, anti-BVDV activity and cytotoxic/cytostatic activity of compounds 1a,b,
10a–i and 16–26.
Anti-BVDV activity, toxicity data and selective index values of all
title compounds are listed in Table 1. Some of these derivatives
exhibited moderated activity against BVDV effects in bovine MDBK
cells. As show in Table 1, most of compounds had little or not
R4
N
R3
N
R1
cytotoxic effect on the uninfected host cell [a CC50 > 100 mM except
N
for 10c, 16 and 26]. Starting from the lead compounds 1a, b,
analogues 10a–i and 16–20 were first synthesized to investigate the
structure–activity relationship (SAR) of the C-2 and C-3 positions.
The most potent of these compounds was the 2-m-methoxyphenyl
R2
Compounds R1
R2
R3 R4
BVDV
compound 10c (Fig. 2), which had an EC50 of about 0.4
also the most cytotoxic (CC50 ¼ 31 M). The 2-methyl and
2-diethyloxymethyl derivatives 10a and 16 displayed however
a significant antiviral activity (EC50 2.1 M) with favourable selec-
mM but was
EC50
(
mM) CC50
(
m
M) SIb
>20
>7.6
a
a
m
1a
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CO2Et 5.0 ꢂ 1.1
>100
m
1b
Br
CO2Et 13.1 ꢂ 2.8 >100
10a
10b
10c
10d
10e
10f
10g
10h
10i
16
Me
Ph
m-MeOPh
CF3
i-Pr
t-Bu
H
Me
CO2Et 2.1 ꢂ 0.5
CO2Et 3.7 ꢂ 0.5
>100
>100
>47.6
>27.1
71
>7.8
>4.3
>2
>7.1
>1.3
>1.5
46.6
>4.6
>1.9
>2.1
>2.2
>2.3
>19.6
>17.9
>60.6
>87.2
41.8
tive indexes (>45). Introduction of a substituent in position 3
resulted in reduced activity as seen for 3-bromo or 3-nitro deriv-
atives 10g–i comparatively to the 3-unsubstitued parent
compounds 1a and 10a.
To further investigate SAR of the pyrrole ring moiety, we
designed and synthesized analogues bearing the 2-methyl
substituent of compound 10a and different substituent groups on
N-7 and C-8 positions. These structural modifications had not much
CO2Et 0.4 ꢂ 0.02 31.1 ꢂ 0.2
CO2Et 12.8 ꢂ 1.7 >100
CO2Et 23.1 ꢂ 3.4 >100
CO2Et 50.3 ꢂ 22.0 >100
Br
Br
NO2
H
CO2Et 14.1
>100
CO2Et 78.9 ꢂ 9.3 >100
Me
CO2Et 64.8
>100
99.2 ꢂ 1.2
CH(OEt)2
CHO
CH2OH
CH2Cl
CH2N(Me)2
Me
CO2Et 2.1 ꢂ 1.1
impact on the antiviral activity (EC50 values of about 1.1–5.6 mM for
compounds 22–26).
17
18
19
20
H
H
H
H
H
H
H
H
CO2Et 21.8 ꢂ 5.6 >100
CO2Et 53.8 ꢂ 37.5 >100
CO2Et 47.6 ꢂ 10.5 >100
CO2Et 46.5 ꢂ 2.2 >100
CH2OH 43.9 ꢂ 3.3 >100
21
4. Conclusion
22
Me
CO2H
5.1 ꢂ 0.7
>100
>100
>100
>100
23
Me
Me CO2Et 5.6 ꢂ 1.7
Me CO2Me 1.7 ꢂ 0.5
We prepared several imidazo[1,2-a]pyrrolo[3,2-c]pyridines
with modifications both at the C-2 and C-3 imidazole moiety at the
N-7 and C-8 pyrrole positions. Several analogues displayed
moderated to excellent anti-BVDV activity. Substitution at the C-3
position decreased the antiviral potency, modifications on the
pyrrole ring did not significantly influence the biological activities.
24
Me
25
Me
H
H
H
H
CO2Me 1.1 ꢂ 0.2
CO2Bu 2.1 ꢂ 0.6
26
Me
89.8 ꢂ 7.7
a
Data (for active compounds) are mean values ꢂ standard deviation for 4 inde-
pendent experiments.
b
In vitro selectivity index (CC50/EC50).

J.-M. Chezal et al. / European Journal of Medicinal Chemistry 45 (2010) 2044–2047
2047
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G. Puerstinger, J. Neyts, J. Virol. 80 (2006) 149–160.
Further synthesis of imidazo[1,2-a]pyrrolo[3,2-c]pyridine deriva-
tives will be carried out to elucidate the SAR of this original class of
compounds.
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Acknowledgments
We thank Carolien Dekeyzer for excellent technical assistance.
This study was supported by a grant of the Flemish Fund for
Scientific Research (Fonds voor Wetenschappelijk Onderzoek,
Vlaanderen) FWO, Jan Paeshuyse is a post-doctoral research fellow
from FWO.
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Appendix. Supplementary data
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.ejmech.2010.01.023.
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