Synthesis and biological evaluation of 2,3-diarylimidazo[1,2-a]pyridines as antileishmanial agents

Article abstract of DOI:10.1016/j.ejmech.2012.10.048

A novel series of 2,3-diarylimidazo[1,2-a]pyridines was synthesized and evaluated for their antileishmanial activities. Four derivatives exhibited good activity against the promastigote and intracellular amastigote stages of Leishmania major, coupled with a low cytotoxicity against the HeLa human cell line. The impact of compound lipophilicity on antiparasitic activities was investigated by Log D comparison. Although LmCK1 could be the parasitic target for three compounds (13, 18, 21), the inhibition of another target is under study to explain the antileishmanial effect of the most promising compounds.

Full text of DOI:10.1016/j.ejmech.2012.10.048

European Journal of Medicinal Chemistry 58 (2012) 543e556
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and biological evaluation of 2,3-diarylimidazo[1,2-a]pyridines as
antileishmanial agents
,
b
,
a
a,b
Sophie Marhadour a, Pascal Marchand a , Fabrice Pagniez
, Marc-Antoine Bazin , Carine Picot
,
*
**
Olivier Lozach c, Sandrine Ruchaud c, Maud Antoine d, Laurent Meijer e, Najma Rachidi c f, Patrice Le Pape b
,
a Université de Nantes, Nantes Atlantique Universités, Laboratoire de Chimie Thérapeutique, Cibles et Médicaments des Infections et du Cancer, IICiMed UPRES EA 1155,
UFR des Sciences Pharmaceutiques et Biologiques, 1 rue Gaston Veil, 44035 Nantes, France
b Université de Nantes, Nantes Atlantique Universités, Laboratoire de Parasitologie et Mycologie Médicale, Cibles et Médicaments des Infections et du Cancer, IICiMed UPRES EA 1155,
UFR des Sciences Pharmaceutiques et Biologiques, 1 rue Gaston Veil, 44035 Nantes, France
c CNRS, ‘Protein Phosphorylation & Human Disease’ Group, Station Biologique, Place Georges Teissier, 29680 Roscoff, France
d AtlanChim Pharma, 44000 Nantes, France
e Manros Therapeutics, Centre de Perharidy, 29680 Roscoff, France
f G5 Virulence Parasitaire, Département de Parasitologie et Mycologie, Institut Pasteur, 28 rue du Dr Roux, 75015 Paris, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of 2,3-diarylimidazo[1,2-a]pyridines was synthesized and evaluated for their anti-
leishmanial activities. Four derivatives exhibited good activity against the promastigote and intracellular
amastigote stages of Leishmania major, coupled with a low cytotoxicity against the HeLa human cell line.
The impact of compound lipophilicity on antiparasitic activities was investigated by Log D comparison.
Although LmCK1 could be the parasitic target for three compounds (13, 18, 21), the inhibition of another
target is under study to explain the antileishmanial effect of the most promising compounds.
Ó 2012 Elsevier Masson SAS. All rights reserved.
Received 14 September 2012
Received in revised form
22 October 2012
Accepted 29 October 2012
Available online 2 November 2012
Keywords:
Antileishmanial activity
2,3-Diarylimidazo[1,2-a]pyridines
Direct arylation
Lipophilicity
Casein kinase 1
1. Introduction
that are called cutaneous leishmaniasis (CL), diffuse cutaneous
leishmaniasis (DCL), mucocutaneous leishmaniasis (MCL) and
Leishmaniasis remains a public health problem worldwide,
affecting approximately 12 million people in 88 countries; 50,000
die of it each year. The disease is caused by Leishmania, obligate
intracellular vector-borne parasites. In spite of its huge health
impact on the populations in vast areas, leishmaniasis is one of the
most neglected diseases [1e4]. The life cycle of Leishmania involves
the transmission of flagellated promastigotes by phlebotomine
sandfly bites that invade macrophages and rapidly transform into
the infective form of the parasite (amastigote stage) which actively
divides within the mononuclear phagocytes. In humans, the
disease occurs in at least four major forms, depending on the
parasite species and the cellular immune response of the patient,
visceral leishmaniasis (VL) [5].
Concerning therapy, pentavalent antimonials remain the first-
line leishmaniasis treatment although miltefosine, an orally active
hexadecylphosphocholine, is now widely used for VL in all regions
where antimonial resistance is widespread. Other drugs that may
be used include pentamidine and amphotericin B. However these
drugs display some limitations such as long-term parenteral
administration, toxicity, high cost in endemic countries, resistance
and a high rate of treatment failure in HIV co-infected patients [5].
Other drugs such as paromomycin, sitamaquine, azoles and azi-
thromycin have been reported with variable cure rates [1e5].
Moreover, there is no effective vaccine to prevent leishmaniasis.
Consequently there is still a real need for new active compounds
that can provide therapeutic benefits but with fewer side effects.
Recently, selenocyanates and diselenides were described as
a new class of potent antileishmanial agents [6]. 3,7-Disubstituted
pyrazolo[4,3-d]pyrimidines also displayed promising inhibition
* Corresponding author. Tel.: þ33 240 412 874; fax: þ33 240 412 876.
** Corresponding author. Tel.: þ33 240 412 866; fax: þ33 240 412 867.
E-mail
addresses:
pascal.marchand@univ-nantes.fr
(P.
Marchand),
fabrice.pagniez@univ-nantes.fr (F. Pagniez).
0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2012.10.048

544
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
Table 1
activity against Leishmania donovani axenic amastigotes [7]. In
addition, novel 5-(5-nitrofuran-2-yl)-1,3,4-thiadiazol-2-amines
exhibited good antileishmanial activity against the promastigote
and amastigote forms of Leishmania major [8].
Structures of 2-arylimidazo[1,2-a]pyridines 2e10 and 2,3-diarylimidazo[1,2-a]
pyridines 11e36.
Compd Ar
Time
7 h
Yielda Compd Ar0
(%)
Time Yielda
(%)
We previously discovered 3-imidazolylalkylindoles to be highly
active against Leishmania mexicana amastigotes [9e11] and mech-
anism of action study suggested that the compounds interfere with
the ergosterol synthesis leading to plasmatic membrane disruption
[12]. We also evidenced that imidazolidin-2-one derivatives
exhibited antileishmanial activity through inhibition of PKC activity
and the parasite host cell invasion process [13], highlighting that
Leishmania protein kinases could be relevant therapeutic target for
the design of new antileismanial candidates [14]. Indeed, several
other protein kinases namely cyclin-dependent kinases (CDKs)
[7,15], mitogen-activated protein kinases (MAPKs) [16,17], casein
kinase 1 (CK1) [18] or Aurora kinase [19], have been shown to be
involved in parasite growth and survival.
The pharmacological interest of the imidazo[1,2-a]pyridine ring
system has been well established [20]. In order to find new drugs
with antileishmanial activity, we have synthesized and evaluated
new 2,3-diarylimidazo[1,2-a]pyridine-based compounds against
promastigote and amastigote forms of L. major. In addition, to
explore putative mechanism of action of the most active
compounds, kinase activity assessments were performed on
L. major PKC (LmPKC) and L. major CK1.2 (LmCK1.2 (lmjF35.1010)).
2
C6H5
43
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
C6H5
16 h 95
48 h 45
24 h 81
12 h 53b
4-MeC6H4
4-MeOC6H4
4-HOC6H4
4-PivOC6H4
4-(NO2)C6H4
4-(CN)C6H4
12 h
6c
36 h 93
18 h 99
4-(CO2Et)C6H4 18 h 98
3,5-(Cl)2C6H3 12 h 68
3-Pyridyl
4-Pyridyl
5-Pyrimidyl
3-Thienyl
C6H5
3-(NO2)C6H4
3-Pyridyl
C6H5
48 h 90
16 h 85
12 h 73
48 h 14
15 h 60
16 h 92
15 h 56
31 h 64
14 h 85
21 h 83
13 h 27
18 h 15
10 h 81
21 h 67
21 h 84
18 h 83
15 h 69
3
4
4-FC6H4
1 h
41
97
2-FC6H4
1 h
6 h
3-Pyridyl
C6H5
C6H5
5
6
7
8
3-ClC6H4
45
9
4-(CO2Et)C6H4 45 min
4-(NO2)C6H4
4-MeOC6H4
4 h
45 min 78
26
C6H5
C6H5
3-(NO2)C6H4
C6H5
C6H5
3-Pyridyl
9
10
2-MeOC6H4
1 h 94
3,5-(Cl)2C6H3 45 min 35
2. Results and discussion
a
Isolated yields.
Ar0X ¼ 4-iodophenyl acetate.
Side reaction from 14.
b
c
2.1. Chemistry
We were interested in preparing 2-arylimidazo[1,2-a]pyridines
as intermediates for synthesizing target compounds. As recently
described [21], our initial approach involved the preparation of
imidazo[1,2-a]pyridin-2-yl triflate 1 from commercially available 2-
aminopyridine in a two-step reaction (Scheme 1). A subsequent
Suzuki cross-coupling reaction gave the desired products 2e10. The
results (Table 1) indicate that 1 can be effectively arylated with
various arylboronic acids, although the yield is dependent on the
nature of the arylboronic acid. Arylboronic acids with electron-
donating groups gave better yields (compounds 8 and 9) in
comparison with their electron-withdrawing counterparts
(compounds 6 and 7). Surprisingly arylation occurred in very good
yield in the presence of 2-fluoro derivative 4. Indeed, even if both
Suzuki couplings with 2-fluoro and 4-fluoro derivatives led to
completion of the reaction, the difference of the yield (41% vs 97%)
seems to result from a deficient extraction rate for compound 3.
The direct arylation reaction at the 3-position was examined
using 2-arylimidazo[1,2-a]pyridines 2e10 and aryl halides,
applying optimized reaction conditions [21,22]. In the presence of
Pd(OAc)2 (2 mol %), PCy3$HBF4 (4 mol %), PivOH (0.3 equiv), K2CO3
(1.5 equiv), the reaction proceeded smoothly (10e48 h) in N,N-
dimethylacetamide (DMA) at 100 ꢀC and in a sealed tube. A variety
of substituents are tolerated on aryl halide.
2-phenylimidazo[1,2-a]pyridine 2 (Table 1, compounds 11,13, 16e
22). 3-Bromothiophene was not able to undergo direct arylation
in reasonable yield due to degradation of the reaction mixture.
Using 4-bromotoluene and 4-iodophenyl acetate as reagents,
compounds 12 and 14 were respectively obtained, but in moderate
yields. For the last one, pivalic acid ester 15 was also isolated,
resulting from a side reaction between phenol derivative 14, ob-
tained by in situ hydrolysis of acetate function, and pivalic acid in
the reaction medium.
We thought that this methodology could be extended to the
synthesis of various diarylimidazo[1,2-a]pyridines bearing
substituted phenyl ring at the 2-position, thus providing diversity
for structureeactivity relationship study. As previously discussed in
the literature [21], the desired products 24e36 were prepared in
low to good yields, depending on electronic effects of substituted
phenyl in position 2 of imidazo[1,2-a]pyridine scaffold.
Finally, acetyl analogue 37 of compound 15 was synthesized by
reaction between phenol derivative 14 and acetic anhydride in
pyridine at room temperature (Scheme 2).
Hydrogenation of nitro derivative 16, using a Raney-Nickel
catalyst, led to the corresponding aromatic amine 38 in good
yield. Amide analogue 39 was isolated by hydration of cyano
precursor 17 in the presence of hydrogen peroxide and potassium
carbonate in dimethyl sulfoxide at room temperature.
Bromobenzene, nitro-, cyano-, ethoxycarbonyl-, methoxyphenyl
bromides, pyridyl and pyrimidyl bromides reacted efficiently with
. HBr
N
O
N
+
NH2
N
N
N
(c)
(d)
(a)
(b)
Ar
OTf
Ar
N
N
N
N
. HBr
COOEt
NH
Ar'
11-36
N
1
2-10
Scheme 1. Reagents and conditions: (a) BrCH2CO2Et, 0 ꢀC / rt, 15 min, then EtOH, reflux, 18 h; (b) PhNTf2, Et3N, toluene, reflux, 20 h, 67% (two steps); (c) ArB(OH)2, Pd(PPh3)4,
Na2CO3, 1,4-dioxane/H2O (2/1), sealed tube, 100 ꢀC; (d) Ar0X (X ¼ Br, I), Pd(OAc)2, PCy3$HBF4, PivOH, K2CO3, DMA, sealed tube, 100 ꢀC.

S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
545
N
N
afforded a 3.5-fold more potent compound 21 with an IC50 value of
6.5 mM.
N
N
2.2.2. Cytotoxicity
Cytotoxicity on HeLa cell line was evaluated for compounds that
exhibited good to moderate antileishmanial activity (i.e.
IC50 < 45 mM) against promastigotes (Table 2) in order to identify
R
R'
(a)
(b)
(c)
(d)
drugs which were less toxic to human cells and as a prelude to
selecting drugs for in vitro assay on relevant clinical Leishmania
amastigote stage.
R = OH, 14
R = NO2, 16
R = CN, 17
R = CO2Et, 18
R' = OAc, 37
R' = NH2, 38
R' = CONH2, 39
R' = CO2H, 40
IC50 values ranged from 4 to 554
mM and most of drugs had IC50
less than 100 M. The selectivity index (SI) was calculated as the
m
ratio of cytotoxicity (IC50 value on HeLa cells) to activity (IC50 value
on promastigotes). This in vitro therapeutic index showed that
compounds 30 and 31, belonging to the second series of 2,3-
diarylimidazo[1,2-a]pyridines possessed the better selectivity
profile (SI of 8.65 and 18.46, respectively). Concerning the first
series, among the most active compounds on L. major promastigote
stage, SI was better than that of pentamidine (3.13) for three
molecules: 15, 16 and 21 (SI ¼ 5.43, 5.51 and 3.85, respectively). In
contrast 12, 13, 18, 19 and 29 showed a very low SI (less or equal to
2.34) explaining that they were less suitable for further
investigation.
Scheme 2. Reagents and conditions: (a) Ac2O, pyridine, r.t., 12 h, 63%; (b) H-CubeÒ, H2
10 bar, Ni Raney, EtOH/THF (5/1), r.t., 81%; (c) H2O2, K2CO3, DMSO, r.t., 12 h, 66%; (d)
2 M NaOH, EtOH, reflux, 1.5 h, 19%.
Saponification of ester 18, using classical conditions, afforded the
desired carboxylic acid 40 but in a low yield.
2.2. Biological evaluation
2.2.1. In vitro antileishmanial activity against promastigotes
In this study, antileishmanial activity of thirty compounds was
evaluated. Inhibitory concentrations 50 (IC50) on L. major promas-
tigote stage are reported in Table 2. Pentamidine was used as
control drug. Eight compounds (12, 13, 15, 16, 18, 19, 21 and 29)
2.2.3. In vitro antileishmanial activity against amastigotes
In view to study antileishmanial activity against amastigotes,
compounds were selected according to its high level of activity
against promastigotes and/or its high selectivity index. For better
understanding of SAR study, the direct analogues, at the positions 2
and 3 of diarylimidazo[1,2-a]pyridine heterocycle, were also pref-
erably chosen for additional amastigote testing. Three biological
profiles were observed. First profile concerns the compounds 12,13,
15, 16, 19 and 29 that exhibit antileishmanial activity on both
promastigote and amastigote stages of L. major as shown in Table 2
and Fig. 1A.
displayed IC50 values less than 10
active as pentamidine.
mM and could be considered as
Generally, most active compounds were obtained from 2-
phenylimidazo[1,2-a]pyridine series (11e23, 37e40), except
compound 29. The basic molecular structure 2,3-diphenylimidazo
[1,2-a]pyridine 11 offered only moderate efficacy. Based on
a comparison of compounds 13, 16, 18, 19 (IC50 values of 7.2, 4.9, 5.2
and 7.7
mM, respectively) with analogues 32, 31, 30, 35 (IC50 values
of 26.6, 30.0, 40.0, 39.0
m
M), switching substituents between
Among them, derivatives 15 and 16 displayed low cytotoxicity as
noted above. Moreover, antileishmanial potency against promas-
tigotes was not conserved on intracellular amastigote form for
compounds 18 and 21. Finally, weakly active compounds 11, 30, 31,
32 and 35, on promastigote form, were found to be very active on
positions 2 and 3 of the imidazo[1,2-a]pyridine ring led to decrease
in activity. The presence of the atom of chlorine in meta position of
2-aryl seemed to influence markedly the antileishmanial activity
against promastigotes (compounds 29 and 35).
In the second series (24e36), consisting of imidazo[1,2-a]pyri-
dines bearing a substituted phenyl in position 2 and a substituted or
unsubstituted aryl ring in position 3, most of the compounds
remained weakly active or inactive on promastigote form of
infected macrophages when treated at 10
amastigote burden). Interestingly, compound 35 remained active at
only 1 M coupled with low cytotoxicity on HeLa cells (IC50 value of
67 M). Compounds 15, 30 and 31 were also able to reduce
mM (84e95% inhibition of
m
m
L. major exhibiting IC50 values superior to 10
mM.
percentage of infected macrophages (Fig. 1B).
Considering structureeactivity relationships (SARs) of 2-
phenylimidazo[1,2-a]pyridines (11e23, 37e40), 4-Me (12), 4-OMe
(13), 4-OPiv (15) but also 4-NO2 (16) or 4-CO2Et (18) substitution
pattern on the 3-phenyl ring was consistent with antileishmanial
potency. Therefore, both electron-donating and electron-
withdrawing groups could be tolerated. Hydrophilic groups
seemed to be deleterious for the activity since 4-OH (14), 4-NH2
(38) or 4-CO2H (40) substitution produced only inactive
compounds with the highest IC50 values. In addition, 4-CN deriv-
ative 17 and the corresponding amide 39 exhibited no activity.
2.2.4. Determination of compound lipophilicity
There are physical differences between the test systems on
promastigote and amastigote forms of L. major which could give
some explanations of the results obtained. Promastigote assay
uses extracellular axenic parasite, making it more accessible than
the intracellular amastigotes which are in mouse peritoneal
macrophage phagolysosomes. Indeed, during the process of inva-
sion, the parasite initiates the formation of a membrane, the so-
called parasitophorous vacuole membrane, which surrounds the
intracellular parasite. Penetration of the two membranes (i.e.
plasmatic and vacuole) is therefore an important criterion for
activity and can differ from a compound to the other, depending on
its hydrophobic character.
In addition, in the macrophage system, the L. major amastigotes
are in acidic phagolysosomal compartments (pH 4.7e5.2) [23],
whereas the promastigote assays are performed at pH 7. This factor
may also affect the biological results since physicochemical prop-
erties of the compound, associated with ionized molecule or not,
are linked to its pKa and pH value in culture medium.
Finally, acetylated compound 37 (IC50 value of 16.0 mM) was less
potent than its bulkier pivaloyl counterpart. One example of
disubstituted compound 19 (3,5-diCl) provided interesting results
with an IC50 value of 7.7
We also checked the influence, on biological activity, of the
introduction of heteroaryl moiety in position of 2-
mM.
a
3
phenylimidazo[1,2-a]pyridine scaffold. 5-Pyrimidyl analogue 22
was totally inactive, whereas 3-thiophenyl (23) and 3-pyridyl (20)
derivatives displayed only moderate to low potency. Shifting of the
nitrogen from meta to para position of the pyridyl appendage

546
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
Table 2
In vitro antileishmanial activities of 2,3-diarylimidazo[1,2-a]pyridines 11e40 against promastigotes and intracellular amastigotes of L. major, and cytotoxicity evaluation.
N
Ar
N
Ar'
Compd
Ar
Ar0
IC50 ꢁ SEM (
m
M)a
IC50 ꢁ SEM (
m
M)a
Selectivity index
cytotoxicity (IC50)/anti
promastigotes activity (IC50
% Inhibitiona (conc.
mM)
L. major intracellular
amastigotes
L. major promastigotes
cytotoxicity
on HeLa cells
)
Pentamidine
11
12
13
14
37
15
16
38
17
39
18
40
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
4.8 ꢁ 0.8
22.5 ꢁ 0.6
4.0 ꢁ 0.4
7.2 ꢁ 0.3
40.0 ꢁ 6.1
16.0 ꢁ 6.1
7.0 ꢁ 1.0
4.9 ꢁ 0.2
43.0 ꢁ 2.0
>100
27.0 ꢁ 3.2
5.2 ꢁ 1.0
>100
7.7 ꢁ 0.2
22.5 ꢁ 6.0
6.5 ꢁ 1.6
>100
15 ꢁ 0.2
31 ꢁ 3
4 ꢁ 2
3.13
1.38
1.00
1.92
0.40
2.50
5.43
5.51
0.65
99 (10)
84 (10)
96 (10)
71 (10)
n.d.
C6H5
C6H5
4-MeC6H4
4-MeOC6H4
4-HOC6H4
4-AcOC6H4
4-PivOC6H4
4-(NO2)C6H4
4-(NH2)C6H4
4-(CN)C6H4
4-(CONH2)C6H4
4-(CO2Et)C6H4
4-(CO2H)C6H4
3,5-(Cl)2C6H3
3-Pyridyl
4-Pyridyl
5-Pyrimidyl
3-Thienyl
C6H5
3-(NO2)C6H4
3-Pyridyl
C6H5
3-Pyridyl
C6H5
C6H5
C6H5
C6H5
3-(NO2)C6H4
C6H5
14 ꢁ 2
16 ꢁ 6
40 ꢁ 1
38 ꢁ 7
27 ꢁ 3
28.1 ꢁ 8.7
n.d.
n.d.
95 (10)
68 (10)
n.d.
n.d.
n.d.
18 (10)
n.d.
79 (10)
n.d.
32 (10)
n.d.
n.d.
27 ꢁ 2
1.00
0.96
5 ꢁ 1
n.d.
18 ꢁ 3
2.34
0.18
3.85
4 ꢁ 1
25 ꢁ 11
n.d.
14.3 ꢁ 2.2
35 ꢁ 2
72 ꢁ 2
n.d.
87 ꢁ 25
18 ꢁ 3
29 ꢁ 1
5 ꢁ 1
2.45
3.13
4-FC6H4
2-FC6H4
23 ꢁ 4
n.d.
n.d.
n.d.
n.d.
>100
38.3 ꢁ 7.4
39.0 ꢁ 1.0
34.8 ꢁ 1.9
4.4 ꢁ 1.9
40.0 ꢁ 1.1
30.0 ꢁ 2.0
26.6 ꢁ 1.5
14 ꢁ 2
2.27
0.46
0.83
1.14
8.65
18.46
1.80
2.14
1.32
1.71
0.89
n.d.
3-ClC6H4
94 (10)
86 (10)
84 (10)
85 (10)
n.d.
n.d.
71 (1)
n.d.
4-(CO2Et)C6H4
4-(NO2)C6H4
4-MeOC6H4
346 ꢁ 174
554 ꢁ 48
48 ꢁ 2
30 ꢁ 2
24 ꢁ 14
67 ꢁ 2
28 ꢁ 5
2-MeOC6H4
3,5-(Cl)2C6H3
18.2 ꢁ 3.4
39.0 ꢁ 1.0
31.4 ꢁ 2.8
C6H5
3-Pyridyl
SEM: standard error of the mean.
n.d.: not determined.
a
Mean from at least three determinations.
To discuss this point of view, a pKa value close to 5.30 was
calculated for the molecules depicted in Table 3, using pKa Plugin of
MarvinSketch software from ChemAxon.
compounds 11e13, 18 and 32 are not consistent with the previous
observations. Indeed, other parameters are to be taken into account
to explain more in depth the data, especially the variation of
metabolite profiles of the tested compounds.
Lipophilicity was also determined by experimental procedure.
In order to measure rapidly liquideliquid partition coefficients, we
used reversed-phase HPLC method, with standards and correla-
tions [24]. Indeed, the logarithms of the retention factor of the
solutes are linearly correlated with the logarithm of their partition
coefficients as described first by Collander [25]. Logarithm of the
distribution coefficient (Log D) of the compounds, between an
organic phase (methanol) and an aqueous phase (buffer), was ob-
tained at pH 4.5 and 7.5, near pH values of biological tests.
Variation of lipophilicity was observed between the two pH
values, indeed, taking into account the pKa of 5.30, the molecules are
not ionized at pH 7.5 and at pH 4.5 the protonated species are in
majority in the medium. In conclusion, the physicochemical prop-
erties of the molecules can differ from testing conditions to the
others. Considering Log D at pH 7.5, it seems that promastigote
activity is not linked to lipophilicityof tested compounds since active
and inactive molecules display the same Log D values (for example,
compounds 19: Log D7.5 ¼ 5.88 and 35: Log D7.5 ¼ 6.10, Table 3).
Interestingly, as reported previously [26], very promising
amastigote antileishmanial activities were correlated with a rise in
lipophilicity as shown for compounds 15, 16, 19, 29, 30, 31 and 35
(Log D4.5 from 3.91 to 5.58). However, results observed for
Finally, the target expression could differ between the two
stages of the parasite, providing other hypothesis of the variability
of the observed results.
2.2.5. Kinase inhibitory activities
To investigate mechanism of action, LmCK1.2 inhibition study
was performed for thirteen compounds as indicated in Table 4 [18].
Three compounds exhibited IC50 values inferior to 10 mM.
Taking into account the first results, antileishmanial activity
against promastigotes seems to be only correlated with the inhi-
bition of LmCK1.2 for compounds 13, 18 and 21. However, no
selectivity was observed against the Leishmania target since these
same compounds were also able to inhibit porcine brain CK1 in the
micromolar or submicromolar range. As noted for 4-pyridyl
derivative 21, the most active compound on CK1 kinases was one
of the less active against amastigote form of L. major, and displayed
the lowest lipophilicity (additional protonation of the pyridine
nitrogen which could result in low cell permeability and thereby
reduced biological effects). In a general approach, amastigote
activity of the 2,3-diarylimidazo[1,2-a]pyridines was not correlated
with LmCK1.2 inhibition.

S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
547
plates. Column chromatography was carried out on silica gel Merck
60 (70e230 mesh ASTM). Melting points were determined on an
Electrothermal IA 9000 melting point apparatus and are uncor-
rected. Infrared spectra (IR) were recorded on a Paragon 1000 PC
PerkineElmer spectrometer. 1H and 13C NMR spectra were per-
formed in DMSO-d6 using a Bruker AVANCE 400 MHz spectrometer.
A
100
80
60
40
20
0
Chemical shifts are reported as
d values in parts per million (ppm)
relative to tetramethylsilane as internal standard and coupling
constants (J) are given in hertz (Hz). The following abbreviations
are used to describe peak patterns when appropriate: s (singlet),
d (doublet), t (triplet), q (quartet), m (multiplet). Mass spectra were
recorded using an Electrospray Ionization Method with Waters ZQ
2000 spectrometer. Elemental analyses were performed on
a Thermo Scientific Elemental Analyser Flash EA 1112 and were
found within ꢁ0.4% of the theoretical values.
Pentamidine
15
16
19
Compounds
21
30
31
B
4.1.1. Imidazo[1,2-a]pyridin-2-yl trifluoromethanesulfonate (1)
Compound 1 was synthesized according to previously described
procedure [21].
100
80
80
60
60
4.1.2. Representative Suzuki coupling procedure for the synthesis of
2-arylimidazo[1,2-a]pyridines 2e10
To a 10 mL vial with a magnetic stir bar were added imidazo[1,2-
a]pyridin-2-yl trifluoromethanesulfonate 1 (400 mg, 1.5 mmol,
1 equiv), arylboronic acid (1.8 mmol, 1.2 equiv), sodium carbonate
(382 mg, 3.6 mmol, 2.4 equiv) and tetrakis(triphenylphosphine)
palladium(0) (87 mg, 5 mol %) in a mixture of 1,4-dioxaneewater
(13.5 mL, 2:1). The vial was sealed and purged with argon through
the septum inlet for 5 min. The suspension was heated at 100 ꢀC for
45 min to 7 h. After cooling, the resulting mixture was diluted with
ethyl acetate, filteredthroughCeliteÒ andwashedwithethyl acetate.
Water was added and the organic layer was extracted twice with
ethyl acetate. The combined organic layers were washed with water,
dried over sodium sulfate, filtered and concentrated under vacuum.
The crude product was purified by silica gel chromatography using
petroleum ether/ethyl acetate as eluent. Trituration with diisopro-
pylic ether afforded 2-arylimidazo[1,2-a]pyridine 2e10 (Fig. 2).
40
40
20
20
0
0
Pentamidine
Pentamidine
15
15
16
16
19
19
21
21
30
30
31
31
Compounds
Fig. 1. In vitro activity against intramacrophage amastigotes of L. major at 10 mM.
Furthermore, compounds 15, 30, 31 and 35 were also tested for
L. major PKC inhibition [13,14]. Nevertheless, none of them were
able to reduce PKC activity.
Finally, it clearly appears that a different target has to be
investigated to explain promising activities of these new anti-
leishmanial agents.
4.1.2.1. 2-Phenylimidazo[1,2-a]pyridine (2). Compound was ob-
tained following the representative procedure, using imidazo[1,2-
a]pyridin-2-yl trifluoromethanesulfonate 1 (400 mg, 1.5 mmol,
1 equiv), phenylboronic acid (368 mg, 3.0 mmol, 2 equiv), Na2CO3
(636 mg, 6.0 mmol, 4 equiv), Pd(PPh3)4 (87 mg, 5 mol %) and
heating for 7 h. The crude product was purified by silica gel chro-
matography using petroleum ether/ethyl acetate (8/2) as eluent
and to afford 2-phenylimidazo[1,2-a]pyridine 2 as a beige powder
(125 mg, 43% yield).
3. Conclusion
We have developed a very promising 2,3-diarylimidazo[1,2-a]
pyridine series, acting as antileishmanial agents. In addition, the
synthetic pathway to achieve title compounds was also proved to be
very easy and efficient. Among the thirty tested compounds against
the promastigote form of L. major, thirteen were selected for anti-
leishmanial testing against intracellular amastigotes. 2,3-
Diarylimidazo[1,2-a]pyridines 15, and especially, 30 and 31 exhibi-
ted very good antileishmanial activity against amastigotes and high
therapeutic index. Analogue 35 was also of interest since its activity
Rf ¼ 0.43 (petroleum ether/EtOAc: 6/4); Mp ¼ 132e133 ꢀC (lit.
[27]: 130e132 ꢀC). 1H NMR (400 MHz, DMSO-d6):
d 8.57 (d, 1H,
3J ¼ 6.6 Hz, H5), 8.44 (s, 1H, H3), 8.01 (d, 2H, 3J ¼ 7.2 Hz, Ha), 7.62 (d,
1H, 3J ¼ 8.4 Hz, H8), 7.48 (dd, 2H, 3J ¼ 3J0 ¼ 7.2 Hz, Hb), 7.36 (t, 1H,
3J ¼ 7.2 Hz, Hc), 7.28 (ddd,1H, 3J ¼ 8.4 Hz, 3J ¼ 7.0 Hz, 4J ¼ 0.8 Hz, H7),
6.93 (ddd, 1H, 3J ¼ 7.0 Hz, 3J ¼ 6.6 Hz, 4J ¼ 0.4 Hz, H6). 13C NMR
on intracellular amastigotes was conserved when testing at 1 mM-
dose and its cytotoxicity was low on HeLa cells. An analysis of phys-
icochemical properties demonstrated a link between lipophilicity
and antiparasitic activity for the most promising compounds.
Although LmCK1.2 could be the parasitic target for three compounds
(13, 18, 21), the inhibition of another target is under study to explain
the antileishmanial effect of the most promising compounds.
(100 MHz, DMSO-d6):
d 144.99 (C), 144.52 (C), 134.09 (C), 128.87
(2Cb), 127.86 (Cc), 127.04 (C5), 125.73 (2Ca), 125.10 (C7), 116.81 (C8),
112.43 (C6), 109.26 (C3). IR (KBr) cmꢂ1: 3043 (
nCeHar), 1505, 1474
(
n
C]C and
n
C]N). MS (ESI) m/z (%): 195.1 (100) [M þ H]þ. Anal.
Calcd for C13H10N2: C, 80.39; H, 5.19; N, 14.42. Found: C, 80.61; H,
5.28; N, 14.44.
4. Experimental protocols
4.1.2.2. 2-(4-Fluorophenyl)imidazo[1,2-a]pyridine
(3). Compound
4.1. Chemistry
was obtained following the representative procedure, using 4-
fluorophenylboronic acid (252 mg, 1.8 mmol, 1.2 equiv) and heat-
ing for 1 h. The crude product was purified by silica gel chroma-
tography using petroleum ether/ethyl acetate (8/2) as eluent to
All reactions were carried out under argon. All reactions were
monitored by TLC analysis using Merck silica gel 60F-254 thin-layer

548
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
Table 3
In vitro antileishmanial activities of 2,3-diarylimidazo[1,2-a]pyridines against promastigotes and intracellular amastigotes of L. major, and lipophilicity determination.
N
Ar
N
Ar'
Compd
Ar
Ar0
IC50 ꢁ SEM (
m
M)a
% Inhibitiona (conc.
L. major amastigotes
m
M)
Log Db pH 7.5
Log Db pH 4.5
L. major promastigotes
Pentamidine
4.8 ꢁ 0.8
22.5 ꢁ 0.6
4.0 ꢁ 0.4
7.2 ꢁ 0.3
7.0 ꢁ 1.0
4.9 ꢁ 0.2
5.2 ꢁ 1.0
7.7 ꢁ 0.2
6.5 ꢁ 1.6
4.4 ꢁ 1.9
40.0 ꢁ 1.1
30.0 ꢁ 2.0
26.6 ꢁ 1.5
39.0 ꢁ 1.0
99 (10)
84 (10)
96 (10)
71 (10)
95 (10)
68 (10)
18 (10)
79 (10)
32 (10)
94 (10)
86 (10)
84 (10)
85 (10)
71 (1)
11
12
13
15
16
18
19
21
29
30
31
32
35
C6H5
C6H5
4.50
5.13
4.58
5.90
4.35
5.19
5.88
2.87
5.25
5.46
4.65
4.59
6.10
2.15
2.61
2.31
4.04
3.29
3.59
4.53
2.03
3.91
4.26
4.20
2.04
5.58
4-MeC6H4
4-MeOC6H4
4-PivOC6H4
4-(NO2)C6H4
4-(CO2Et)C6H4
3,5-(Cl)2C6H3
4-Pyridyl
C6H5
C6H5
C6H5
C6H5
C6H5
3-ClC6H4
4-(CO2Et)C6H4
4-(NO2)C6H4
4-MeOC6H4
3,5-(Cl)2C6H3
SEM: standard error of the mean.
a
Mean from at least three determinations.
Lipophilicity determined by RP-HPLC method.
b
afford 2-(4-fluorophenyl)imidazo[1,2-a]pyridine
3
as
a
white
afford 2-(2-fluorophenyl)imidazo[1,2-a]pyridine 4 as a beige powder
(309 mg, 97% yield).
powder (131 mg, 41% yield).
Rf ¼ 0.24 (petroleum ether/EtOAc: 7/3); Mp ¼ 159e160 ꢀC (lit.
Rf ¼ 0.40 (petroleum ether/EtOAc: 7/3); Mp ¼ 112e113 ꢀC. 1H
[27]: 158e160 ꢀC). 1H NMR (400 MHz, DMSO-d6):
d
8.56 (d, 1H,
NMR (400 MHz, DMSO-d6):
d
8.65 (d, 1H, 3J ¼ 6.8 Hz, H5), 8.39 (s,
3J ¼ 6.8 Hz, H5), 8.42 (s, 1H, H3), 8.04 (dd, 2H, 3J ¼ 8.8 Hz, 4J ¼ 5.2 Hz,
Ha), 7.61 (d, 1H, 3J ¼ 8.4 Hz, H8), 7.34e7.26 (m, 3H, H7 and Hb), 6.94
(ddd, 1H, 3J ¼ 7.2 Hz, 3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR (100 MHz,
1H, H3), 8.32 (ddd, 1H, 3J ¼ 9.6 Hz, 3J ¼ 7.6 Hz, 4J ¼ 2 Hz, Hb), 7.65 (d,
1H, 3J ¼ 9.2 Hz, H8), 7.43e7.30 (m, 4H, H7, Ha, Hc and Hd), 6.96 (ddd,
1H, 3J ¼ 7.6 Hz, 3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR (100 MHz,
DMSO-d6):
d
162.01 (d, 1J ¼ 242 Hz, CeF), 145.02 (C), 143.64 (C),
DMSO-d6):
d
159.75 (d, 1J ¼ 247 Hz, CeF), 144.32 (C), 137.91 (C),
130.68 (d, 4J ¼ 3 Hz, C), 127.69 (d, 3J ¼ 9 Hz, 2Ca), 127.09 (C5), 125.22
(C7), 116.79 (C8), 115.77 (d, 2J ¼ 22 Hz, 2Cb), 112.51 (C6), 109.13 (C3).
129.36 (d, 3J ¼ 9 Hz, Cd), 128.62 (d, 3J ¼ 3 Hz, Cb), 127.28 (C5), 125.63
(C7), 124.94 (Cc), 121.60 (d, 2J ¼ 13 Hz, C), 116.78 (C8), 116.02 (d,
IR (KBr) cmꢂ1: 3069 (
n
CeHar), 1595, 1435 (
n
C]C and
n
C]N), 1217
2J ¼ 22 Hz, Ca), 112.60 (C6), 112.49 (C3). IR (KBr) cmꢂ1: 3051 (
nCe
(
C
n
CeF). MS (ESI) m/z (%): 213.2 (100) [M þ H]þ. Anal. Calcd for
Har), 1546, 1483 (nC]C and nC]N), 1210 (nCeF). MS (ESI) m/z
13H9FN2: C, 73.57; H, 4.27; N, 13.20. Found: C, 73.71; H, 4.43; N,
(%): 213.0 (100) [M þ H]þ. Anal. Calcd for C13H9FN2: C, 73.57; H,
13.29.
4.27; N, 13.20. Found: C, 73.51; H, 4.59; N, 13.56.
4.1.2.3. 2-(2-Fluorophenyl)imidazo[1,2-a]pyridine
(4). Compound
4.1.2.4. 2-(3-Chlorophenyl)imidazo[1,2-a]pyridine
(5). Compound
was obtained following the representative procedure, using 2-
fluorophenylboronic acid (252 mg, 1.8 mmol, 1.2 equiv) and heat-
ing for 1 h. The crude product was purified by silica gel chroma-
tography using petroleum ether/ethyl acetate (8/2) as eluent to
was obtained following the representative procedure, using 3-
chlorophenylboronic acid (282 mg, 1.8 mmol, 1.2 equiv) and heat-
ing for 6 h. The crude product was purified by silica gel chroma-
tography using petroleum ether/ethyl acetate (8/2) as eluent to
Table 4
Inhibition of L. major CK1 and porcine brain CK1 activities.
Compd
Ar
Ar0
IC50
L. major CK1.2
(
m
M)a
IC50
(
m
M)a native
IC50 ꢁ SEM (
m
M)a
% Inhibitiona (concentration
mM) L. major amastigotes
porcine brain CK1
d/ε
L. major promastigotes
11
12
13
15
16
18
19
21
29
30
31
32
35
C6H5
C6H5
>10
>10
1.20
>10
>10
4.00
>10
0.30
>10
>10
>10
>10
>10
>10
>10
0.63
>10
>10
7.10
>10
0.25
>10
>10
>10
>10
>10
22.5 ꢁ 0.6
4.0 ꢁ 0.4
7.2 ꢁ 0.3
7.0 ꢁ 1.0
4.9 ꢁ 0.2
5.2 ꢁ 1.0
7.7 ꢁ 0.2
6.5 ꢁ 1.6
4.4 ꢁ 1.9
40.0 ꢁ 1.1
30.0 ꢁ 2.0
26.6 ꢁ 1.5
39.0 ꢁ 1.0
84 (10)
96 (10)
71 (10)
95 (10)
68 (10)
18 (10)
79 (10)
32 (10)
94 (10)
86 (10)
84 (10)
85 (10)
71 (1)
4-MeC6H4
4-MeOC6H4
4-PivOC6H4
4-(NO2)C6H4
4-(CO2Et)C6H4
3,5-(Cl)2C6H3
4-Pyridyl
C6H5
C6H5
C6H5
C6H5
C6H5
3-ClC6H4
4-(CO2Et)C6H4
4-(NO2)C6H4
4-MeOC6H4
3,5-(Cl)2C6H3
SEM: standard error of the mean.
a
Mean from at least two or three determinations.

S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
549
8
5
a
methoxyphenylboronic acid (274 mg, 1.8 mmol, 1.2 equiv) and
heating for 45 min. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as eluent
to afford 2-(4-methoxyphenyl)imidazo[1,2-a]pyridine 8 as a beige
powder (263 mg, 78% yield).
b
N
7
c
N
6
3
Fig. 2. 2-Arylimidazo[1,2-a]pyridines numbering for 1H and 13C NMR assignments.
Rf ¼ 0.14 (petroleum ether/EtOAc: 7/3); Mp ¼ 135e136 ꢀC (lit.
[27]: 133e134 ꢀC). 1H NMR (400 MHz, DMSO-d6):
d 8.53 (d, 1H,
3J ¼ 6.8 Hz, H5), 8.32 (s, 1H, H3), 7.93 (d, 2H, 3J ¼ 8.8 Hz, Ha), 7.58 (d,
1H, 3J ¼ 8.6 Hz, H8), 7.25 (ddd,1H, 3J ¼ 8.6 Hz, 3J ¼ 7.4 Hz, 4J ¼ 1.2 Hz,
H7), 7.04 (d, 2H, 3J ¼ 8.8 Hz, Hb), 6.90 (ddd, 1H, 3J ¼ 7.4 Hz,
3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6), 3.83 (s, 3H, OMe). 13C NMR (100 MHz,
afford 2-(3-chlorophenyl)imidazo[1,2-a]pyridine 5 as a beige powder
(155 mg, 45% yield).
Rf ¼ 0.34 (petroleum ether/EtOAc: 7/3); Mp ¼ 109e110 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.57 (d,1H, 3J ¼ 6.8 Hz, H5), 8.54 (s,1H,
DMSO-d6): d 159.19 (CeO), 144.90 (C), 144.62 (C), 127.04 (2Ca),
H3), 8.05 (dd, 1H, 4J ¼ 4J0 ¼ 2.0 Hz, Ha), 7.97 (ddd, 1H, 3J ¼ 8.0 Hz,
4J ¼ 2.0 Hz, 4J ¼ 1.0 Hz, Hb), 7.63 (d, 1H, 3J ¼ 8.4 Hz, H8), 7.51 (dd, 1H,
3J ¼ 3J0 ¼ 8.0 Hz, Hc), 7.42 (ddd, 1H, 3J ¼ 8.0 Hz, 4J ¼ 2.0 Hz,
4J ¼ 1.0 Hz, Hd), 7.31 (ddd,1H, 3J ¼ 8.4 Hz, 3J ¼ 7.4 Hz, 4J ¼ 1.2 Hz, H7),
6.96 (ddd, 1H, 3J ¼ 7.4 Hz, 3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR
126.86 (C5), 126.71 (C), 124.78 (C7), 116.56 (C8), 114.30 (2Cb), 112.20
(C6), 108.18 (C3), 55.30 (OMe). IR (KBr) cmꢂ1: 3070 (
n
CeHar), 1612,
1482 (nC]C and nC]N),1248 (nCeO). MS (ESI) m/z (%): 225.0 (100)
[M þ H]þ. Anal. Calcd for C14H12N2O: C, 74.98; H, 5.39; N, 12.49.
Found: C, 74.69; H, 5.56; N, 12.79.
(100 MHz, DMSO-d6):
d 145.04 (C), 142.95 (C), 136.30 (C), 133.75
(CeCl), 130.84 (Cc), 127.58 (Cd), 127.21 (C5), 125.55 (C7), 125.29 (Ca),
4.1.2.8. 2-(2-Methoxyphenyl)imidazo[1,2-a]pyridine
(9). Compo-
124.26 (Cb), 116.94 (C8), 112.74 (C6), 110.16 (C3). IR (KBr) cmꢂ1: 3035
und was obtained following the representative procedure, using 2-
methoxyphenylboronic acid (274 mg, 1.8 mmol, 1.2 equiv) and
heating for 1 h. The crude product was purified by silica gel chro-
matography using petroleum ether/ethyl acetate (8/2) as eluent to
afford 2-(2-methoxyphenyl)imidazo[1,2-a]pyridine 9 as a beige
powder (317 mg, 94% yield).
(nCeHar), 1601, 1568 (nC]C and nC]N), 746 (nCeCl). MS (ESI) m/z
(%): 229.0 (100) [M þ H]þ, 231.0 (45) [M þ H þ 2]þ. Anal. Calcd for
C
13H9ClN2: C, 68.28; H, 3.97; N, 12.25. Found: C, 68.42; H, 4.13; N,
12.09.
4.1.2.5. Ethyl 4-(imidazo[1,2-a]pyridin-2-yl)benzoate (6). Comp-
ound was obtained following the representative procedure, using 4-
ethoxycarbonylphenylboronic acid (350 mg, 1.8 mmol,1.2 equiv) and
heating for 45 min. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (8/2) as eluent
to afford ethyl 4-(imidazo[1,2-a]pyridin-2-yl)benzoate 6 as a beige
powder (36 mg, 9% yield).
Rf ¼ 0.24 (petroleum ether/EtOAc: 7/3); Mp ¼ 89e90 ꢀC (lit.
[29]: 95e97 ꢀC). 1H NMR (400 MHz, DMSO-d6):
d 8.61 (d, 1H,
3J ¼ 6.4 Hz, H5), 8.44 (s, 1H, H3), 8.34 (d, 1H, 3J ¼ 7.6 Hz, Hd), 7.60 (d,
1H, 3J ¼ 8.2 Hz, H8), 7.35 (dd, 1H, 3J ¼ 8.0 Hz, 3J ¼ 7.6 Hz, Hb), 7.26
(dd, 1H, 3J ¼ 8.2 Hz, 3J ¼ 6.4 Hz, H7), 7.17 (d, 1H, 3J ¼ 8.0 Hz, Ha), 7.09
(dd, 1H, 3J ¼ 3J0 ¼ 7.6 Hz, Hc), 6.90 (dd, 1H, 3J ¼ 3J0 ¼ 6.4 Hz, H6), 4.01
(s, 3H, OMe). 13C NMR (100 MHz, DMSO-d6):
d 156.63 (CeO), 143.67
Rf¼ 0.24(petroleumether/EtOAc:7/3);Mp¼ 141e142 ꢀC.1H NMR
(C), 140.16 (C), 128.75 (Cb), 128.18 (Cd), 127.04 (C5), 124.99 (C7),
122.28 (C), 120.71 (Cc), 116.53 (C8), 112.86 (C3), 111.97 (C6), 111.61
(400 MHz, DMSO-d6):
d 8.60e8.59 (m, 2H, H3 and H5), 8.15 (d, 2H,
3J ¼ 8.4 Hz, Hb), 8.07 (d, 2H, 3J ¼ 8.4 Hz, Ha), 7.64 (d,1H, 3J ¼ 9.0 Hz, H8),
7.32 (dd,1H, 3J ¼ 9.0 Hz, 3J ¼ 6.8 Hz, H7), 6.97 (dd,1H, 3J ¼ 3J0 ¼ 6.8 Hz,
H6), 4.37 (q, 2H, 3J ¼ 7.0 Hz, CH2),1.38 (t, 3H, 3J ¼ 7.0 Hz, CH3).13C NMR
(Ca), 55.64 (OMe). IR (KBr) cmꢂ1: 3065 (
nCeHar), 1631, 1487 (nC]C
and
n
C]N), 1239 (
n
CeO). MS (ESI) m/z (%): 225.1 (100) [M þ H]þ.
Anal. Calcd for C14H12N2O: C, 74.98; H, 5.39; N, 12.49. Found: C,
75.13; H, 5.77; N, 12.80.
(100 MHz, DMSO-d6): d 165.74 (C]O), 145.23 (C), 143.22 (C), 138.66
(C), 129.86 (2Ca), 128.87 (C), 127.28 (C5), 125.77 (2Cb), 125.67 (C7),
117.03 (C8), 112.82 (C6), 110.81 (C3), 60.86 (CH2), 14.39 (CH3). IR (KBr)
4.1.2.9. 2-(3,5-Dichlorophenyl)imidazo[1,2-a]pyridine
(10). Com-
cmꢂ1: 3042 (
n
CeHar), 1708 (
n
C]O), 1270 (
n
CeO). MS (ESI) m/z (%):
pound was obtained following the representative procedure, using
3,5-dichlorophenylboronic acid (344 mg, 1.8 mmol, 1.2 equiv) and
heating for 45 min. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as eluent
to afford 2-(3,5-dichlorophenyl)imidazo[1,2-a]pyridine 10 as a white
powder (138 mg, 35% yield).
267.0 (100) [M þ H]þ. Anal. Calcd for C15H11N2O2: C, 71.70; H, 4.41; N,
11.15. Found: C, 71.61; H, 4.73; N, 11.45.
4.1.2.6. 2-(4-Nitrophenyl)imidazo[1,2-a]pyridine (7).
Compound was obtained following the representative procedure,
using 4-nitrophenylboronic acid (301 mg, 1.8 mmol, 1.2 equiv) and
heating for 4 h. The crude product was purified by silica gel chro-
matography using petroleum ether/ethyl acetate (9/1) as eluent to
Rf ¼ 0.64 (petroleum ether/EtOAc: 7/3); Mp ¼ 142e143 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.63 (s,1H, H3), 8.57 (d,1H, 3J ¼ 6.8 Hz,
H5), 8.04 (d, 2H, 4J ¼ 2.0 Hz, Ha), 7.64 (d, 1H, 3J ¼ 8.6 Hz, H8), 7.58 (t,
1H, 4J ¼ 2.0 Hz, Hb), 7.33 (ddd,1H, 3J ¼ 8.6 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.2 Hz,
H7), 6.97 (ddd, 1H, 3J ¼ 7.2 Hz, 3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR
afford 2-(4-nitrophenyl)imidazo[1,2-a]pyridine
7 as a yellow
powder (93 mg, 26% yield).
Rf ¼ 0.14 (petroleum ether/EtOAc: 7/3); Mp ¼ 265e266 ꢀC (lit.
(100 MHz, DMSO-d6): d 145.09 (C), 141.59 (C), 137.72 (C), 134.75
[28]: 266e267 ꢀC). 1H NMR (400 MHz, DMSO-d6):
d
8.69 (s, 1H, H3),
(2CeCl), 127.34 (C5), 127.00 (Cb), 125.89 (C7), 124.09 (2Ca), 117.04
(C8), 112.99 (C6), 111.02 (C3). IR (KBr) cmꢂ1: 3071 (
CeHar), 1600,
CeCl). MS (ESI) m/z (%): 263.0
8.61 (d, 1H, 3J ¼ 6.8 Hz, H5), 8.35 (d, 2H, 3J ¼ 8.6 Hz, Hb), 8.27 (d, 2H,
3J ¼ 8.6 Hz, Ha), 7.67 (d, 1H, 3J ¼ 8.6 Hz, H8), 7.35 (dd, 1H, 3J ¼ 8.6 Hz,
3J ¼ 6.8 Hz, H7), 6.99 (dd, 1H, 3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR
n
1574 (nC]C and nC]N), 800, 754 (n
(100) [M þ H]þ, 265.0 (88) [M þ H þ 2]þ, 267.0 (16) [M þ H þ 4]þ.
Anal. Calcd for C13H8Cl2N2: C, 59.34; H, 3.06; N, 10.65. Found: C,
58.96; H, 3.22; N, 11.02.
(100 MHz, DMSO-d6): d 146.67 (C), 145.44 (C), 142.17 (C), 140.70 (C),
127.45 (C5), 126.48 (2Ca), 126.11 (C7), 124.37 (2Cb), 117.18 (C8), 113.11
(C6), 111.88 (C3). IR (KBr) cmꢂ1: 3070 (
nCeHar), 1513 (nasNO2), 1336
(
nsyNO2); 854 (
n
CeN). MS (ESI) m/z (%): 240.0 (100) [M þ H]þ. Anal.
4.1.3. Representative direct arylation procedure for the synthesis of
2,3-diarylimidazo[1,2-a]pyridines 11e36
Calcd for C13H9N3O2: C, 65.27; H, 3.79; N, 17.56. Found: C, 65.02; H,
3.83; N, 17.64.
To a 10 mL vial with a magnetic stir bar was added 2-
arylimidazo[1,2-a]pyridine (1.5 mmol,
1 equiv), (hetero)aryl
4.1.2.7. 2-(4-Methoxyphenyl)imidazo[1,2-a]pyridine
(8). Compo-
halides (1.5 mmol, 1 equiv), palladium(II) acetate (7 mg, 2 mol %),
und was obtained following the representative procedure, using 4-
tricyclohexylphosphine tetrafluoroborate (22 mg, 4 mol %), pivalic

550
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
acid (46 mg, 0.45 mmol, 0.3 equiv) and potassium carbonate
(318 mg, 2.3 mmol, 1.5 equiv) in dimethylacetamide (6.0 mL). The
vial was sealed and purged with argon through the septum inlet for
10 min. The suspension was heated at 100 ꢀC for 10e48 h. After
cooling, the resulting mixture was diluted with ethyl acetate. Water
was added and the organic layer was extracted twice with ethyl
acetate. The combined organic layers were washed with brine and
water, dried over sodium sulfate, filtered and concentrated under
vacuum. The crude product was purified by silica gel chromatog-
raphy. Trituration with appropriate solvent afforded 2,3-
diarylimidazo[1,2-a]pyridine 11e36 (Fig. 3).
4.1.3.3. 3-(4-Methoxyphenyl)-2-phenylimidazo[1,2-a]pyridine (13).
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine 2 (300 mg,1.5 mmol,1 equiv),
1-bromo-4-methoxybenzene (194 mL, 1.5 mmol, 1 equiv) and heat-
ing for 24 h. The crude product was purified by silica gel chroma-
tography using cyclohexane/ethyl acetate (8/2) as eluent and
trituration with petroleum ether afforded 3-(4-methoxyphenyl)-2-
phenylimidazo[1,2-a]pyridine 13 as a beige powder (376 mg, 81%
yield).
Rf ¼ 0.36 (petroleum ether/EtOAc: 7/3); Mp ¼ 129e130 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
7.99 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.69e7.65
(m, 3H, H8 and Ha), 7.45 (d, 2H, 3J ¼ 8.6 Hz, Hd), 7.36e7.26 (m, 4H,
H7, Hb and Hc), 7.19 (d, 2H, 3J ¼ 8.6 Hz, He), 6.91 (ddd, 1H, 3J ¼ 7.6 Hz,
3J ¼ 6.8 Hz, 4J ¼ 0.8 Hz, H6), 3.89 (s, 3H, OMe). 13C NMR (100 MHz,
4.1.3.1. 2,3-Diphenylimidazo[1,2-a]pyridine (11). Compound was
obtained following the representative procedure, using 2-
phenylimidazo[1,2-a]pyridine 2 (300 mg, 1.5 mmol, 1 equiv), bro-
DMSO-d6):
d 159.86 (CeO), 143.96 (C), 141.13 (C), 134.53 (C), 132.31
mobenzene (158
m
L, 1.5 mmol, 1 equiv) and heating for 16 h. The
(2Cd), 128.43 (2Cb), 127.45 (2Ca), 127.43 (Cc), 125.15 (C7), 123.92 (C5),
121.37 (C), 120.73 (C), 117.01 (C8), 115.32 (2Ce), 112.72 (C6), 55.42
crude product was purified by silica gel chromatography using
petroleum ether/ethyl acetate (7/3) as eluent to afford 2,3-
diphenylimidazo[1,2-a]pyridine 11 as a beige powder (397 mg,
95% yield).
(OMe). IR (KBr) cmꢂ1: 3040 (
nCeHar), 1609, 1509 (nC]C and nC]
N), 1240 (
n
CeO). MS (ESI) m/z (%): 301.1 (100) [M þ H]þ. Anal. Calcd
for C20H16N2O: C, 79.98; H, 5.37; N, 9.33. Found: C, 80.23; H, 5.69; N,
9.34.
Rf ¼ 0.58 (petroleum ether/EtOAc: 7/3); Mp ¼ 149e150 ꢀC (lit.
[30]: 150 ꢀC). 1H NMR (400 MHz, DMSO-d6):
d 8.05 (d, 1H,
3J ¼ 6.8 Hz, H5), 7.71 (d, 1H, 3J ¼ 9.2 Hz, H8), 7.65e7.59 (m, 5H, Ha, He
and Hf), 7.54 (dd, 2H, 3J ¼ 6.4 Hz, 4J ¼ 1.6 Hz, Hd), 7.38e7.27 (m, 4H,
H7, Hb and Hc), 6.93 (ddd, 1H, 3J ¼ 7.6 Hz, 3J ¼ 6.8 Hz, 4J ¼ 0.8 Hz, H6).
4.1.3.4. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)phenol
(14). Comp
ound was obtained following the representative procedure, using 2-
phenylimidazo[1,2-a]pyridine 2 (300 mg, 1.5 mmol, 1 equiv), 4-
iodophenyl acetate (394 mg, 1.5 mmol, 1 equiv) and heating for
12 h. The crude product was purified by silica gel chromatography
using petroleum ether/dichloromethane (1/1) as eluent to afford 4-
(2-phenylimidazo[1,2-a]pyridin-3-yl)phenol 14 as a white powder
(228 mg, 53% yield).
13C NMR (100 MHz, DMSO-d6):
d 144.15 (C), 141.42 (C), 134.38 (C),
130.86 (2Cd), 129.84 (2Ce), 129.56 (C), 129.25 (Cf), 128.44 (2Cb),
127.62 (2Ca), 127.58 (Cc), 125.37 (C7), 123.88 (C5), 120.88 (C), 117.09
(C8), 112.89 (C6). IR (KBr) cmꢂ1: 3061 (
nCeHar), 1508, 1443 (nC]C
and
n
C]N). MS (ESI) m/z (%): 271.1 (100) [M þ H]þ. Anal. Calcd for
C
19H14N2: C, 84.42; H, 5.22; N, 10.36. Found: C, 84.21; H, 5.20; N,
Rf ¼ 0.21 (petroleum ether/EtOAc: 7/3); Mp ¼ 296e297 ꢀC. 1H
10.52.
NMR (400 MHz, DMSO-d6): d 9.97 (s, 1H, OH), 7.99 (d, 1H,
3J ¼ 6.2 Hz, H5), 7.68e7.66 (m, 3H, H8 and Ha), 7.34e7.27 (m, 6H, H7,
4.1.3.2. 3-(4-Methylphenyl)-2-phenylimidazo[1,2-a]pyridine
(12).
Hb, Hc and Hd), 7.01 (d, 2H, 3J ¼ 8.4 Hz, He), 6.91 (dd, 1H,
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine (300 mg, 1.5 mmol,
1 equiv), 4-bromotoluene (185 L, 1.5 mmol, 1 equiv) and heating
3J ¼ 3J0 ¼ 6.2 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d 158.31 (CeO),
2
143.90 (C), 140.94 (C), 134.64 (C), 132.29 (2Cd), 128.45 (2Cb), 127.45
(2Ca), 127.43 (Cc), 125.11 (C7), 123.98 (C5), 121.18 (C), 119.61 (C),
m
for 48 h. The crude product was purified by silica gel chromatog-
raphy using cyclohexane as eluent and trituration with petroleum
ether afforded 3-(4-methylphenyl)-2-phenylimidazo[1,2-a]pyri-
dine 12 as a beige powder (192 mg, 45% yield).
117.00 (C8),116.77 (2Ce),112.69 (C6). IR (KBr) cmꢂ1: 1607,1483 (
nC]
C and nC]N), 1275, 1234 (nCeO). MS (ESI) m/z (%): 287.0 (100)
[M þ H]þ. Anal. Calcd for C19H14N2O: C, 79.70; H, 4.93; N, 9.78.
Found: C, 79.99; H, 4.66; N, 9.59.
Rf ¼ 0.48 (petroleum ether/EtOAc: 7/3); Mp ¼ 136e137 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.03 (d, 1H, 3J ¼ 7.0 Hz, H5), 7.69 (d,
4.1.3.5. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)phenyl 2,2-dimethylpr-
opanoate (15). By-product 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)
phenyl 2,2-dimethylpropanoate 15 was obtained from the purifi-
cation of compound 14 by silica gel chromatography as a beige
powder (33 mg, 6% yield).
1H, 3J ¼ 9.2 Hz, H8), 7.65 (d, 2H, 3J ¼ 6.8 Hz, Ha), 7.46e7.40 (m, 4H,
Hd and He), 7.36e7.26 (m, 4H, H7, Hb and Hc), 6.92 (ddd, 1H,
3J ¼ 8.0 Hz, 3J ¼ 7.0 Hz, 4J ¼ 1.2 Hz, H6), 2.47 (s, 3H, CH3). 13C NMR
(100 MHz, DMSO-d6): d 144.14 (C), 141.29 (C), 138.78 (C), 134.49 (C),
130.74 (2Ce), 130.51 (2Cd), 128.48 (2Cb), 127.62 (2Ca), 127.58 (Cc),
126.56 (C), 125.32 (C7), 123.91 (C5), 120.92 (C), 117.08 (C8), 112.85
Rf ¼ 0.41 (petroleum ether/EtOAc: 7/3); Mp ¼ 184e185 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.08 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.71 (d,
(C6), 21.22 (CH3). IR (KBr) cmꢂ1: 3039 (
n
CeHar), 1513, 1478 (
n
C]C
1H, 3J ¼ 9.2 Hz, H8), 7.63 (d, 2H, 3J ¼ 7.2 Hz, Ha), 7.59 (d, 2H,
3J ¼ 8.4 Hz, Hd), 7.39e7.28 (m, 6H, H7, Hb, Hc and He), 6.95 (dd, 1H,
3J ¼ 3J0 ¼ 6.8 Hz, H6), 1.39 (s, 9H, 3 ꢃ CH3). 13C NMR (100 MHz,
and
n
C]N). MS (ESI) m/z (%): 285.1 (100) [M þ H]þ. Anal. Calcd for
C
20H16N2: C, 84.48; H, 5.67; N, 9.85. Found: C, 84.61; H, 5.78; N,
10.37.
DMSO-d6): d 176.47 (C]O), 151.34 (CeO), 144.30 (C), 141.67 (C),
135.84 (C), 134.32 (C), 132.20 (2Cd), 131.76 (C), 128.58 (2Cb), 127.73
(2Ca), 126.95 (Cc), 125.59 (C7), 123.98 (C5), 123.26 (2Ce), 120.14 (C),
117.14 (C8), 113.07 (C6), 26.98 (3 ꢃ CH3). IR (KBr) cmꢂ1: 3040 (
n
Ce
8
5
a
Har), 1750 (nC]O), 1509, 1478 (nC]C and nC]N), 1203 (nCeO).
b
N
7
MS (ESI) m/z (%): 371.1 (100) [M
24H22N2O2: C, 77.81; H, 5.99; N, 7.56. Found: C, 78.04; H, 6.11; N,
8.03.
þ
H]þ. Anal. Calcd for
c
C
N
6
d
e
4.1.3.6. 3-(4-Nitrophenyl)-2-phenylimidazo[1,2-a]pyridine
(16).
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine 2 (300 mg, 1.5 mmol,
1 equiv), 1-bromo-4-nitrobenzene (304 mg, 1.5 mmol, 1 equiv)
f
Fig. 3. 2,3-Diarylimidazo[1,2-a]pyridines numbering for 1H and 13C NMR assignments.

S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
551
and heating for 36 h. The crude product was purified by silica gel
chromatography using cyclohexane/ethyl acetate (8/2) as eluent
to afford 3-(4-nitrophenyl)-2-phenylimidazo[1,2-a]pyridine 16 as
an orange powder (441 mg, 93% yield).
and heating for 12 h. The crude product was purified by silica gel
chromatography using dichloromethane as eluent and trituration
with methanol afforded 3-(3,5-dichlorophenyl)-2-phenylimidazo
[1,2-a]pyridine 19 as a white powder (347 mg, 68% yield).
Rf ¼ 0.24 (petroleum ether/EtOAc: 7/3); Mp ¼ 141e142 ꢀC. 1H
Rf ¼ 0.60 (petroleum ether/EtOAc: 7/3); Mp ¼ 210e211 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.43 (d, 2H, 3J ¼ 9.0 Hz, He), 8.29 (d,
NMR (400 MHz, DMSO-d6):
d
8.19 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.84 (t, 1H,
1H, 3J ¼ 7.2 Hz, H5), 7.84 (d, 2H, 3J ¼ 9.0 Hz, Hd), 7.76 (d, 1H,
4J ¼ 1.6 Hz, He), 7.73 (d, 1H, 3J ¼ 9.2 Hz, H8), 7.65 (d, 2H, 4J ¼ 1.6 Hz,
Hd), 7.61 (d, 2H, 3J ¼ 7.2 Hz, Ha), 7.42e7.32 (m, 4H, H7, Hb and Hc),
6.98 (dd, 1H, 3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
3J ¼ 9.2 Hz, H8), 7.59 (d, 2H, 3J ¼ 6.4 Hz, Ha), 7.45e7.35 (m, 4H, H7, Hb
3
and Hc), 7.01 (ddd, 1H, J ¼ 8.0 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.2 Hz, H6). 13
C
NMR (100 MHz, DMSO-d6):
d
147.29 (C), 145.00 (C), 143.11 (C),
d 144.55 (C),142.40 (C),135.27 (2CeCl),133.86 (C),133.16 (C),129.61
136.45 (C), 133.86 (C), 131.89 (2Cd), 128.68 (2Cb), 128.16 (2Ca),
128.08 (Cc), 126.27 (C7), 124.79 (2Ce), 124.17 (C5), 118.96 (C), 117.27
(2Cd), 128.87 (Ce), 128.64 (2Cb), 127.96 (Cc), 127.85 (2Ca), 125.96 (C7),
124.43 (C5), 118.18 (C), 117.05 (C8), 113.16 (C6). IR (KBr) cmꢂ1: 3036
(C8), 113.41 (C6). IR (KBr) cmꢂ1: 3024 (
n
CeHar), 1516 (nasNO2), 1345
(nCeHar), 1590, 1560 (nC]C and nC]N), 776, 750 (nCeCl). MS (ESI)
(
nsyNO2), 854 (
n
CeN). MS (ESI) m/z (%): 316.1 (100) [M þ H]þ. Anal.
m/z (%): 339.0 (100) [M þ H]þ, 341.0 (80) [M þ H þ 2]þ, 343.0 (15)
[M þ H þ 4]þ. Anal. Calcd for C19H12Cl2N2: C, 67.27; H, 3.57; N, 8.26.
Found: C, 67.50; H, 3.23; N, 7.98.
Calcd for C19H13N3O2: C, 72.37; H, 4.16; N, 13.33. Found: C, 72.27; H,
4.25; N, 13.56.
4.1.3.7. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)benzonitrile
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine (300 mg, 1.5 mmol,
(17).
4.1.3.10. 2-Phenyl-3-(pyridin-3-yl)imidazo[1,2-a]pyridine
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine 2 (300 mg, 1.5 mmol,
(20).
2
1 equiv), 4-bromobenzonitrile (274 mg, 1.5 mmol, 1 equiv) and
heating for 18 h. The crude product was purified by silica gel
chromatography using cyclohexane/ethyl acetate (8/2) as eluent
and trituration with diisopropylic ether afforded 4-(2-
1 equiv), 3-bromopyridine (221 mL, 2.3 mmol, 1.5 equiv) and
heating for 48 h. The crude product was purified by silica gel
chromatography using cyclohexane/ethyl acetate (7/3) as eluent
to afford 2-phenyl-3-(pyridin-3-yl)imidazo[1,2-a]pyridine 20 as
an orange powder (367 mg, 90% yield).
phenylimidazo[1,2-a]pyridin-3-yl)benzonitrile 17 as
a
beige
powder (439 mg, 99% yield).
Rf ¼ 0.07 (petroleum ether/EtOAc: 7/3); Mp ¼ 128e129 ꢀC. 1H
Rf ¼ 0.26 (petroleum ether/EtOAc: 7/3); Mp ¼ 186e187 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.77 (d,1H, 3J ¼ 3.2 Hz, Hg), 8.69 (s,1H,
NMR (400 MHz, DMSO-d6):
d
8.22 (d, 1H, 3J ¼ 6.8 Hz, H5), 8.07 (d,
Hd), 8.14 (d, 1H, 3J ¼ 6.4 Hz, H5), 8.05 (d, 1H, 3J ¼ 7.2 Hz, He), 7.74 (d,
1H, 3J ¼ 8.8 Hz, H8), 7.68e7.58 (m, 3H, Ha and Hf), 7.41e7.32 (m, 4H,
H7, Hb and Hc), 6.96 (dd, 1H, 3J ¼ 3J0 ¼ 6.4 Hz, H6). 13C NMR
2H, 3J ¼ 8.4 Hz, He), 7.77e7.73 (m, 3H, H8 and Hd), 7.58 (d, 2H,
3J ¼ 6.8 Hz, Ha), 7.43e7.31 (m, 4H, H7, Hb and Hc), 6.98 (dd, 1H,
3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d
144.77 (C),
(100 MHz, DMSO-d6): d 151.31 (Cd), 150.02 (Cg), 144.68 (C), 142.62
142.63 (C), 134.48 (C), 133.86 (C), 133.59 (2Ce), 131.66 (2Cd), 128.67
(2Cb), 128.08 (2Ca), 128.04 (Cc), 126.20 (C7), 124.15 (C5), 119.36 (CN),
(C), 138.63 (Ce), 134.07 (C), 128.60 (2Cb), 127.83 (Cc), 127.78 (2Ca),
125.90 (C), 125.84 (C7),124.63 (Cf), 124.12 (C5),117.72 (C),117.13 (C8),
118.82 (C), 117.18 (C8), 113.37 (C6), 111.45 (CeCN). IR (KBr) cmꢂ1
:
113.13 (C6). IR (KBr) cmꢂ1: 3028 (
nCeHar), 1510, 1458 (nC]C and
3038 (
n
CeHar), 2226 (
n
C^N), 1604, 1508 (
n
C]C and
n
C]N). MS
n
C
C]N). MS (ESI) m/z (%): 272.1 (100) [M þ H]þ. Anal. Calcd for
(ESI) m/z (%): 296.1 (100) [M þ H]þ. Anal. Calcd for C20H13N3: C,
18H13N3: C, 79.68; H, 4.83; N, 15.49. Found: C, 79.83; H, 4.99; N,
81.34; H, 4.44; N, 14.23. Found: C, 81.51; H, 4.80; N, 14.48.
15.12.
4.1.3.8. Ethyl 4-(2-phenylimidazo[1,2-a]pyridin-3-yl)benzoate (18).
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine 2 (300 mg, 1.5 mmol,
4.1.3.11. 2-Phenyl-3-(pyridin-4-yl)imidazo[1,2-a]pyridine
(21).
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine 2 (300 mg, 1.5 mmol,
1 equiv), 4-bromopyridine hydrochloride (292 mg, 1.5 mmol,
1 equiv) and heating for 16 h. The crude product was purified by
silica gel chromatography using petroleum ether/ethyl acetate (6/
4) as eluent and trituration with diisopropylic ether afforded 2-
phenyl-3-(pyridin-4-yl)imidazo[1,2-a]pyridine 21 as a yellow
powder (347 mg, 85% yield).
1 equiv), ethyl 4-bromobenzoate (245 mL, 1.5 mmol, 1 equiv) and
heating for 18 h. The crude product was purified by silica gel
chromatography using dichloromethane as eluent and trituration
with diisopropylic ether afforded ethyl 4-(2-phenylimidazo[1,2-
a]pyridin-3-yl)benzoate 18 as a beige powder (504 mg, 98%
yield).
Rf ¼ 0.42 (petroleum ether/EtOAc: 7/3); Mp ¼ 140e141 ꢀC. 1H
Rf ¼ 0.08 (petroleum ether/EtOAc: 7/3); Mp ¼ 181e182 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.19 (d,1H, 3J ¼ 7.0 Hz, H5), 8.16 (d, 2H,
NMR (400 MHz, DMSO-d6):
d
8.78 (d, 2H, 3J ¼ 6.0 Hz, He), 8.30 (d,
3J ¼ 8.2 Hz, He), 7.74 (d, 1H, 3J ¼ 8.8 Hz, H8), 7.70 (d, 2H, 3J ¼ 8.2 Hz,
1H, 3J ¼ 7.0 Hz, H5), 7.75 (d,1H, 3J ¼ 9.2 Hz, H8), 7.60e7.56 (m, 4H, Ha
and Hd), 7.44e7.33 (m, 4H, H7, Hb and Hc), 6.99 (ddd, 1H, 3J ¼ 8.0 Hz,
3
Hd), 7.60 (d, 2H, J ¼ 6.8 Hz, Ha), 7.42e7.32 (m, 4H, H7, Hb and Hc),
6.97 (dd, 1H, 3J ¼ 3J0 ¼ 7.0 Hz, H6), 4.41 (q, 2H, 3J ¼ 7.2 Hz, CH2), 1.40
3J ¼ 7.0 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d 150.98
(t, 3H, 3J ¼ 7.2 Hz, CH3). 13C NMR (100 MHz, DMSO-d6):
d
165.58
(2Ce), 144.95 (C), 142.96 (C), 137.47 (C), 133.88 (C), 128.64 (2Cb),
128.12 (2Cd), 128.07 (Cc), 126.19 (C7), 125.05 (2Ca), 124.21 (C5),
(C]O), 144.68 (C), 142.32 (C), 134.36 (C), 134.09 (C), 131.07 (2Cd),
130.47 (2Ce), 130.14 (C), 128.63 (2Cb), 127.96 (2Ca), 127.92 (Cc),
125.93 (C7), 124.08 (C5), 119.86 (C), 117.23 (C8), 113.26 (C6), 61.20
118.36 (C), 117.25 (C8), 113.37 (C6). IR (KBr) cmꢂ1: 3043 (
nCeHar),
1594, 1507 (nC]C and nC]N). MS (ESI) m/z (%): 272.1 (100)
(CH2),14.40 (CH3). IR (KBr) cmꢂ1: 3035 (
n
CeHar),1714 (
n
C]O),1274
[M þ H]þ. Anal. Calcd for C18H13N3: C, 79.68; H, 4.83; N, 15.49.
(
C
n
CeO). MS (ESI) m/z (%): 343.1 (100) [M þ H]þ. Anal. Calcd for
Found: C, 79.66; H, 4.89; N, 15.76.
22H18N2O2: C, 77.17; H, 5.30; N, 8.18. Found: C, 77.12; H, 5.48; N,
8.04.
4.1.3.12. 2-Phenyl-3-(pyrimidin-5-yl)imidazo[1,2-a]pyridine
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine (300 mg, 1.5 mmol,
(22).
4.1.3.9. 3-(3,5-Dichlorophenyl)-2-phenylimidazo[1,2-a]pyridine (19).
2
Compound was obtained following the representative procedure,
1 equiv), 5-bromopyrimidine (239 mg, 1.5 mmol, 1 equiv) and
heating for 12 h. The crude product was purified by silica gel
chromatography using cyclohexane/ethyl acetate (8/2) as eluent to
using 2-phenylimidazo[1,2-a]pyridine
2 (300 mg, 1.5 mmol,
1 equiv), 1,3-dichloro-5-iodobenzene (410 mg, 1.5 mmol, 1 equiv)

552
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
afford 2-phenyl-3-(pyrimidin-5-yl)imidazo[1,2-a]pyridine 22 as
a beige powder (299 mg, 73% yield).
nitrophenyl)imidazo[1,2-a]pyridine 25 as
a
yellow powder
(461 mg, 92% yield).
Rf ¼ 0.07 (petroleum ether/EtOAc: 7/3); Mp ¼ 154e155 ꢀC. 1H
Rf ¼ 0.24 (petroleum ether/EtOAc: 7/3); Mp ¼ 213e214 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
9.37 (s, 1H, He), 9.02 (s, 2H, Hd), 8.32
NMR (400 MHz, DMSO-d6): d 8.42e8.40 (m, 2H, Hc and Hf), 8.23 (d,
(d, 1H, 3J ¼ 6.8 Hz, H5), 7.76 (d, 1H, 3J ¼ 8.8 Hz, H8), 7.58 (d, 2H,
3J ¼ 6.8 Hz, Ha), 7.44e7.32 (m, 4H, H7, Hb and Hc), 6.99 (ddd, 1H,
3J ¼ 7.2 Hz, 3J ¼ 6.8 Hz, 4J ¼ 0.4 Hz, H6). 13C NMR (100 MHz, DMSO-
1H, 3J ¼ 6.8 Hz, H5), 7.97 (d, 1H, 3J ¼ 7.6 Hz, Hd), 7.89 (dd, 1H,
3J ¼ 3J0 ¼ 7.6 Hz, He), 7.74 (d, 1H, 3J ¼ 8.6 Hz, H8), 7.63 (dd, 2H,
3J ¼ 8.8 Hz, 4J ¼ 5.6 Hz, Ha), 7.41 (dd, 1H, 3J ¼ 8.6 Hz, 3J ¼ 6.8 Hz, H7),
7.21 (dd, 2H, 3J ¼ 3J0 ¼ 8.8 Hz, Hb), 6.98 (dd, 1H, 3J ¼ 3J0 ¼ 6.8 Hz, H6).
d6):
d 158.74 (2Cd), 158.35 (Ce), 145.15 (C), 143.73 (C), 133.73 (C),
128.75 (2Cb), 128.08 (Cc), 128.00 (2Ca), 126.30 (C7), 124.73 (C),
13C NMR (100 MHz, DMSO-d6):
d
169.72 (C), 161.92 (d, 1J ¼ 244 Hz,
124.55 (C5), 117.12 (C8), 114.62 (C), 113.27 (C6). IR (KBr) cmꢂ1: 3040
CeF), 148.85 (C), 144.60 (C), 141.56 (C), 137.64 (Cd), 131.42 (Ce),
131.00 (C), 130.40 (d, 4J ¼ 3 Hz, C), 129.86 (d, 3J ¼ 8 Hz, 2Ca), 126.07
(C7), 125.59 (Cc or Cf), 124.24 (C5), 123.91 (Cc or Cf), 118.54 (C), 117.11
(C8), 115.60 (d, 2J ¼ 22 Hz, 2Cb), 113.22 (C6). IR (KBr) cmꢂ1: 3063
(nCeHar), 1560, 1498 (nC]C and nC]N). MS (ESI) m/z (%): 273.1
(100) [M þ H]þ. Anal. Calcd for C17H12N4: C, 74.98; H, 4.44; N, 20.58.
Found: C, 75.11; H, 4.17; N, 20.09.
(
n
CeHar), 1530 (nasNO2), 1346 (nsyNO2), 1222 (
n
CeF); 840 (
H]þ. Anal. Calcd for
19H12FN3O2: C, 68.46; H, 3.63; N, 12.61. Found: C, 68.57; H, 3.39; N,
12.71.
nCeN).
4.1.3.13. 2-Phenyl-3-(thiophen-3-yl)imidazo[1,2-a]pyridine
Compound was obtained following the representative procedure,
using 2-phenylimidazo[1,2-a]pyridine (300 mg, 1.5 mmol,
1 equiv), 3-bromothiophene (216 L, 2.3 mmol, 1.5 equiv) and
(23).
MS (ESI) m/z (%): 334.1 (100) [M
C
þ
2
m
heating for 48 h. The crude product was purified by silica gel
chromatography using cyclohexane as eluent and trituration with
diisopropylic ether afforded 2-phenyl-3-(thiophen-3-yl)imidazo
[1,2-a]pyridine 23 as a beige powder (58 mg, 14% yield).
4.1.3.16. 2-(4-Fluorophenyl)-3-(pyridin-3-yl)imidazo[1,2-a]pyridine
(26). Compound was obtained following the representative
procedure, using 2-(4-fluorophenyl)imidazo[1,2-a]pyridine
3
(319 mg, 1.5 mmol, 1 equiv), 3-bromopyridine (145 L, 1.5 mmol,
m
Rf ¼ 0.40 (petroleum ether/EtOAc: 7/3); Mp ¼ 130e131 ꢀC. 1H
1 equiv) and heating for 15 h. The crude product was purified by
silica gel chromatography using petroleum ether/ethyl acetate (9/1)
as eluent and trituration with diisopropylic ether afforded 2-(4-
NMR (400 MHz, DMSO-d6):
d
8.08 (d,1H, 3J ¼ 6.8 Hz, H5), 7.94 (s,1H,
Hd), 7.89 (d, 1H, 3J ¼ 4.4 Hz, He), 7.70e7.68 (m, 3H, H8 and Ha), 7.39e
7.29 (m, 4H, H7, Hb and Hc), 7.25 (d, 1H, 3J ¼ 4.4 Hz, Hf), 6.96 (dd, 1H,
fluorophenyl)-3-(pyridin-3-yl)imidazo[1,2-a]pyridine
26
as
3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d
144.25 (C),
a beige powder (244 mg, 56% yield).
141.89 (C), 134.42 (C), 129.15 (Cf), 129.08 (C), 128.45 (2Cb), 128.19
(Ce), 127.65 (Cc), 127.50 (2Ca), 127.49 (Cd), 125.33 (C7), 124.33 (C5),
Rf ¼ 0.11 (petroleum ether/EtOAc: 7/3); Mp ¼ 125e126 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.78 (dd, 1H, 3J ¼ 4.6 Hz, 4J ¼ 1.4 Hz,
116.99 (C8), 116.15 (C), 112.85 (C6). IR (KBr) cmꢂ1: 3066 (
n
CeHar),
Hf), 8.70 (d, 1H, 4J ¼ 1.6 Hz, Hc), 8.14 (d, 1H, 3J ¼ 6.8 Hz, H5), 8.05
(ddd, 1H, 3J ¼ 7.8 Hz, 4J ¼ 1.6 Hz, 4J ¼ 1.4 Hz, Hd), 7.73 (d, 1H,
3J ¼ 8.8 Hz, H8), 7.67 (dd, 1H, 3J ¼ 7.8 Hz, 3J ¼ 4.6 Hz, He), 7.61 (dd,
2H, 3J ¼ 8.8 Hz, 4J ¼ 5.6 Hz, Ha), 7.40 (dd, 1H, 3J ¼ 8.8 Hz, 3J ¼ 6.8 Hz,
H7), 7.22 (dd, 2H, 3J ¼ 3J0 ¼ 8.8 Hz, Hb), 6.97 (dd, 1H, 3J ¼ 3J0 ¼ 6.8 Hz,
696 (
n
CeS). MS (ESI) m/z (%): 277.0 (100) [M þ H]þ, 278.0 (25)
[M þ H þ 1]þ, 279.0 (7) [M þ H þ 2]þ. Anal. Calcd for C17H12N2S: C,
73.88; H, 4.38; N, 10.14. Found: C, 74.01; H, 4.56; N, 9.88.
4.1.3.14. 2-(4-Fluorophenyl)-3-phenylimidazo[1,2-a]pyridine
Compound was obtained following the representative procedure,
using 2-(4-fluorophenyl)imidazo[1,2-a]pyridine (319 mg,
1.5 mmol, 1 equiv), bromobenzene (158 L, 1.5 mmol, 1 equiv) and
(24).
H6). 13C NMR (100 MHz, DMSO-d6):
d
161.89 (d, 1J ¼ 244 Hz, CeF),
151.31 (Cc), 150.12 (Cf), 144.66 (C), 141.70 (C), 138.67 (Cd), 130.58
(d, 4J ¼ 3 Hz, C), 129.72 (d, 3J ¼ 9 Hz, 2Ca), 125.97 (C7), 125.73 (C),
124.70 (Ce), 124.18 (C5), 117.60 (C), 117.10 (C8), 115.60 (d, 2J ¼ 21 Hz,
3
m
heating for 15 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded 2-(4-
fluorophenyl)-3-phenylimidazo[1,2-a]pyridine 24 as a yellow oil
(260 mg, 60% yield).
2Cb),113.20 (C6). IR (KBr) cmꢂ1: 1508,1465 (
nC]C and nC]N),1225
(
C
n
CeF). MS (ESI) m/z (%): 290.0 (100) [M þ H]þ. Anal. Calcd for
18H12FN3: C, 74.73; H, 4.18; N, 14.52. Found: C, 74.79; H, 4.00; N,
14.80.
Rf ¼ 0.51 (petroleum ether/EtOAc: 7/3). 1H NMR (400 MHz,
4.1.3.17. 2-(2-Fluorophenyl)-3-phenylimidazo[1,2-a]pyridine
(27).
DMSO-d6):
d
8.05 (d, 1H, 3J ¼ 7.0 Hz, H5), 7.70 (d, 1H, 3J ¼ 8.4 Hz, H8),
Compound was obtained following the representative procedure,
using 2-(2-fluorophenyl)imidazo[1,2-a]pyridine (319 mg,
1.5 mmol, 1 equiv), bromobenzene (189 L, 1.8 mmol, 1.2 equiv) and
7.66e7.59 (m, 5H, Ha, Hd and He), 7.54 (dd, 2H, 3J ¼ 8.4 Hz,
4J ¼ 1.6 Hz, Hc), 7.36 (ddd,1H, 3J ¼ 8.4 Hz, 3J ¼ 7.2 Hz, 4J ¼ 0.8 Hz, H7),
7.19 (dd, 2H, 3J ¼ 3J0 ¼ 8.8 Hz, Hb), 6.94 (ddd, 1H, 3J ¼ 7.2 Hz,
4
m
heating for 31 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded 2-(2-
3J ¼ 7.0 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d 161.76
(d, 1J ¼ 243 Hz, CeF), 144.15 (C), 140.50 (C), 130.89 (2Cc), 130.84 (C),
129.91 (2Cd), 129.49 (d, 3J ¼ 8 Hz, 2Ca), 129.35 (d, 4J ¼ 2 Hz, C),
129.34 (Ce), 125.49 (C7), 123.93 (C5), 120.70 (C), 117.05 (C8), 115.41
fluorophenyl)-3-phenylimidazo[1,2-a]pyridine 27 as
a
beige
powder (277 mg, 64% yield).
(d, 2J ¼ 21 Hz, 2Cb), 112.96 (C6). IR (KBr) cmꢂ1: 3055 (
nCeHar), 1603,
Rf ¼ 0.40 (petroleum ether/EtOAc: 7/3); Mp ¼ 119e120 ꢀC. 1H
1477 (
nC]C and
n
C]N), 1221 (nCeF). MS (ESI) m/z (%): 289.1 (100)
NMR (400 MHz, DMSO-d6):
d
8.33 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.73 (d,
[M þ H]þ. Anal. Calcd for C19H13FN2: C, 79.15; H, 4.54; N, 9.72.
1H, 3J ¼ 9.2 Hz, H8), 7.64 (ddd,1H, 3J ¼ 8.8 Hz, 3J ¼ 7.8 Hz, 4J ¼ 1.6 Hz,
Hb), 7.55e7.38 (m, 7H, H7, Hd, He, Hf and Hg), 7.28 (ddd, 1H,
3J ¼ 7.8 Hz, 3J ¼ 7.2 Hz, 4J ¼ 0.8 Hz, Hc), 7.19 (ddd, 1H, 3J ¼ 9.2 Hz,
3J ¼ 8.8 Hz, 4J ¼ 0.8 Hz, Ha), 7.08 (ddd, 1H, 3J ¼ 8.0 Hz, 3J ¼ 6.8 Hz,
Found: C, 78.96; H, 4.37; N, 9.91.
4.1.3.15. 2-(4-Fluorophenyl)-3-(3-nitrophenyl)imidazo[1,2-a]pyri-
dine (25). Compound was obtained following the representative
4J ¼ 1.2 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d 159.40 (d,
procedure, using 2-(4-fluorophenyl)imidazo[1,2-a]pyridine
3
1J ¼ 247 Hz, CeF), 144.41 (C), 137.56 (C), 132.29 (d, 3J ¼ 3 Hz, Cb),
130.16 (d, 3J ¼ 8 Hz, Cd), 129.47 (2Ce), 129.33 (2Cf), 129.16 (Cg),
128.58 (C),125.50 (C7),124.49 (Cc),123.97 (C5),122.77 (C),122.56 (d,
2J ¼ 15 Hz, C), 117.33 (C8), 115.96 (d, 2J ¼ 22 Hz, Ca), 113.16 (C6). IR
(319 mg, 1.5 mmol, 1 equiv), 1-bromo-3-nitrobenzene (304 mg,
1.5 mmol, 1 equiv) and heating for 16 h. The crude product was
purified by silica gel chromatography using petroleum ether/ethyl
acetate (9/1) as eluent and trituration with a mixture diisopropylic
(KBr) cmꢂ1: 3035 (
nCeHar), 1507, 1478 (nC]C and nC]N), 1224
etherepetroleum
ether
afforded
2-(4-fluorophenyl)-3-(3-
(n
CeF). MS (ESI) m/z (%): 289.1 (100) [M þ H]þ. Anal. Calcd for

S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
553
C19H13FN2: C, 79.15; H, 4.54; N, 9.72. Found: C, 78.87; H, 4.87; N,
9.55.
3J ¼ 8.0 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.2 Hz, H7), 6.97 (ddd, 1H, 3J ¼ 7.2 Hz,
3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6), 4.33 (q, 2H, 3J ¼ 7.2 Hz, CH2), 1.34 (t, 3H,
3J ¼ 7.2 Hz, CH3). 13C NMR (100 MHz, DMSO-d6):
d 165.62 (C]O),
4.1.3.18. 2-(2-Fluorophenyl)-3-(pyridin-3-yl)imidazo[1,2-a]pyridine
(28). Compound was obtained following the representative proce-
dure, using 2-(2-fluorophenyl)imidazo[1,2-a]pyridine 4 (319 mg,
144.36 (C), 140.12 (C), 139.02 (C), 130.81 (2Ce), 129.94 (2Cf), 129.51
(Cg), 129.32 (2Cb), 129.10 (C), 128.66 (C), 127.57 (2Ca), 125.87 (C7),
124.09 (C5), 122.12 (C), 117.26 (C8), 113.23 (C6), 60.80 (CH2), 14.31
1.5 mmol,1 equiv), 3-bromopyridine (145
mL, 1.5 mmol,1 equiv) and
(CH3). IR (KBr) cmꢂ1: 3047 (
nCeHar),1702 (nC]O),1277 (nCeO). MS
heating for 14 h. The crude product was purified by silica gel chro-
matography using petroleum ether/ethyl acetate (6/4) as eluent and
trituration with diisopropylic ether afforded 2-(2-fluorophenyl)-3-
(pyridin-3-yl)imidazo[1,2-a]pyridine 28 as a beige powder (370 mg,
85% yield).
(ESI) m/z (%): 343.1 (100) [M þ H]þ. Anal. Calcd for C22H18N2O2: C,
77.17; H, 5.30; N, 8.18. Found: C, 77.42; H, 4.88; N, 8.39.
4.1.3.21. 2-(4-Nitrophenyl)-3-phenylimidazo[1,2-a]pyridine
Compound was obtained following the representative procedure,
using 2-(4-nitrophenyl)imidazo[1,2-a]pyridine (360 mg,
1.5 mmol, 1 equiv), bromobenzene (189 L, 1.8 mmol, 1.2 equiv)
(31).
Rf ¼ 0.07 (petroleum ether/EtOAc: 7/3); Mp ¼ 133e134 ꢀC. 1H
7
NMR (400 MHz, DMSO-d6):
d
8.66 (dd, 1H, 3J ¼ 5.0 Hz, 4J ¼ 1.8 Hz,
m
Hh), 8.57 (d, 1H, 4J ¼ 2.0 Hz, He), 8.37 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.96
and heating for 18 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded 2-(4-
(ddd, 1H, 3J ¼ 8.0 Hz, 4J ¼ 2.0 Hz, 4J ¼ 1.8 Hz, Hf), 7.77 (d, 1H,
3J ¼ 8.8 Hz, H8), 7.71 (ddd, 1H, J ¼ 8.6 Hz, 3J ¼ 8.0 Hz, 4J ¼ 1.6 Hz,
3
Hb), 7.57 (ddd, 1H, 3J ¼ 8.0 Hz, 3J ¼ 5.0 Hz, 4J ¼ 0.4 Hz, Hg), 7.46e7.41
(m, 2H, H7 and Hd), 7.32 (ddd, 1H, 3J ¼ 8.0 Hz, 3J ¼ 7.6 Hz, 4J ¼ 0.8 Hz,
Hc), 7.19 (ddd, 1H, 3J ¼ 9.2 Hz, 3J ¼ 8.6 Hz, 4J ¼ 0.8 Hz, Ha), 7.03 (ddd,
1H, 3J ¼ 7.6 Hz, 3J ¼ 6.8 Hz, 4J ¼ 0.8 Hz, H6). 13C NMR (100 MHz,
nitrophenyl)-3-phenylimidazo[1,2-a]pyridine 31 as a yellow
powder (71 mg, 15% yield).
Rf ¼ 0.40 (petroleum ether/EtOAc: 7/3); Mp ¼ 157e158 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.22 (d, 2H, 3J ¼ 8.8 Hz, Hb), 8.07 (d,
DMSO-d6):
d
159.15 (d, 1J ¼ 246 Hz, CeF), 149.99 (Ce), 149.44 (Ch),
1H, 3J ¼ 7.0 Hz, H5), 7.87 (d, 2H, 3J ¼ 8.8 Hz, Ha), 7.76 (d, 1H,
3J ¼ 8.6 Hz, H8), 7.70e7.63 (m, 3H, Hd and He), 7.59 (dd, 2H,
3J ¼ 8.0 Hz, 4J ¼ 2.0 Hz, Hc), 7.42 (ddd, 1H, 3J ¼ 8.6 Hz, 3J ¼ 7.2 Hz,
144.93 (C), 138.42 (C), 137.03 (Cf), 132.34 (d, 3J ¼ 6 Hz, Cb), 130.44 (d,
3J ¼ 7 Hz, Cd), 126.01 (C7), 125.68 (C), 124.75 (Cc), 124.25 (Cg), 124.20
(C5), 122.07 (d, 2J ¼ 12 Hz, C), 119.74 (C), 117.35 (C8), 116.06 (d,
4J ¼ 1.2 Hz, H7), 6.99 (ddd, 1H, 3J ¼ 7.2 Hz, 3J ¼ 7.0 Hz, J ¼ 0.8 Hz,
4
2J ¼ 19 Hz, Ca), 113.41 (C6). IR (KBr) cmꢂ1: 3032 (
nCeHar), 1562, 1491
H6). 13C NMR (100 MHz, DMSO-d6):
d 146.45 (C), 144.53 (C), 141.11
(
n
C]C and
n
C]N), 1224 (
n
CeF). MS (ESI) m/z (%): 290.0 (100)
(C), 139.03 (C), 130.87 (2Cc), 130.11 (2Cd), 129.81 (Ce), 128.77 (C),
128.19 (2Ca), 126.32 (C7), 124.28 (C5), 123.89 (2Cb), 123.01 (C), 117.39
[M þ H]þ. Anal. Calcd for C18H12FN3: C, 74.73; H, 4.18; N, 14.52.
Found: C, 74.84; H, 4.23; N, 14.80.
(C8), 113.54 (C6). IR (KBr) cmꢂ1: 3093 (
nCeHar), 1506 (nasNO2), 1337
(
nsyNO2), 856 (
n
CeN). MS (ESI) m/z (%): 316.1 (100) [M þ H]þ. Anal.
4.1.3.19. 2-(3-Chlorophenyl)-3-phenylimidazo[1,2-a]pyridine
Compound was obtained following the representative procedure,
using 2-(3-chlorophenyl)imidazo[1,2-a]pyridine (344 mg,
1.5 mmol, 1 equiv), bromobenzene (158 L, 1.5 mmol, 1 equiv) and
(29).
Calcd for C19H13N3O2: C, 72.37; H, 4.16; N, 13.33. Found: C, 72.31; H,
4.28; N, 13.15.
5
m
4.1.3.22. 2-(4-Methoxyphenyl)-3-phenylimidazo[1,2-a]pyridine (32).
heating for 21 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded 2-(3-
Compound was obtained following the representative procedure,
using 2-(4-methoxyphenyl)imidazo[1,2-a]pyridine
8 (337 mg,
1.5 mmol, 1 equiv), bromobenzene (158 L, 1.5 mmol, 1 equiv) and
m
chlorophenyl)-3-phenylimidazo[1,2-a]pyridine 29 as
a
beige
heating for 10 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded 2-(4-
methoxyphenyl)-3-phenylimidazo[1,2-a]pyridine 32 as a beige
powder (366 mg, 81% yield).
powder (380 mg, 83% yield).
Rf ¼ 0.66 (petroleum ether/EtOAc: 7/3); Mp ¼ 143e144 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.04 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.72 (d,
1H, 3J ¼ 9.2 Hz, H8), 7.68e7.60 (m, 4H, Ha, Hf and Hg), 7.55e7.51 (m,
3H, Hb and He), 7.40e7.35 (m, 3H, H7, Hc and Hd), 6.95 (dd, 1H,
Rf ¼ 0.31 (petroleum ether/EtOAc: 7/3); Mp ¼ 101e102 ꢀC. 1H
3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d
144.22 (C),
NMR (400 MHz, DMSO-d6):
d
8.03 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.67 (d,
139.70 (C), 136.55 (C), 133.28 (CeCl), 130.89 (2Ce), 130.40 (Cc),
129.98 (2Cf), 129.59 (Cg), 129.10 (C), 127.37 (Cd), 127.09 (Ca), 125.88
(C7), 125.82 (Cb), 124.08 (C5), 121.53 (C), 117.20 (C8), 113.20 (C6). IR
1H, 3J ¼ 8.4 Hz, H8), 7.66e7.52 (m, 7H, Ha, Hd, He and Hf), 7.33 (ddd,
1H, 3J ¼ 8.4 Hz, 3J ¼ 6.8 Hz, 4J ¼ 0.8 Hz, H7), 6.93e6.90 (m, 3H, H6
and Hb), 3.77 (s, 3H, OMe). 13C NMR (100 MHz, DMSO-d6):
d 158.90
(KBr) cmꢂ1: 3069 (
n
CeHar), 1598, 1506 (
n
C]C and
n
C]N), 742
(CeO), 144.06 (C), 141.43 (C), 130.87 (2Cd), 129.84 (2Ce), 129.76 (C),
129.15 (Cf), 128.84 (2Ca), 126.79 (C), 125.13 (C7), 123.73 (C5), 119.93
(C), 116.87 (C8), 113.94 (2Cb), 112.69 (C6), 55.23 (OMe). IR (KBr)
(n
CeCl). MS (ESI) m/z (%): 305.0 (100) [M þ H]þ, 307.0 (36)
[M þ H þ 2]þ. Anal. Calcd for C19H13ClN2: C, 74.88; H, 4.30; N, 9.19.
Found: C, 75.01; H, 4.39; N, 9.36.
cmꢂ1: 3047 (
nCeHar), 1608, 1476 (nC]C and nC]N), 1250 (nCeO).
MS (ESI) m/z (%): 301.0 (100) [M þ H]þ. Anal. Calcd for C20H16N2O:
4.1.3.20. Ethyl 4-(3-phenylimidazo[1,2-a]pyridin-2-yl)benzoate (30).
Compound was obtained following the representative procedure,
using ethyl 4-(imidazo[1,2-a]pyridin-2-yl)benzoate 6 (400 mg,
C, 79.98; H, 5.37; N, 9.33. Found: C, 80.22; H, 5.55; N, 9.26.
4.1.3.23. 2-(4-Methoxyphenyl)-3-(3-nitrophenyl)imidazo[1,2-a]pyri-
dine (33). Compound was obtained following the representative
procedure, using 2-(4-methoxyphenyl)imidazo[1,2-a]pyridine 8
(337 mg, 1.5 mmol, 1 equiv), 1-bromo-3-nitrobenzene (304 mg,
1.5 mmol, 1 equiv) and heating for 21 h. The crude product was
purified by silica gel chromatography using petroleum ether/ethyl
acetate (9/1) as eluent and trituration with methanol afforded 2-(4-
methoxyphenyl)-3-(3-nitrophenyl)imidazo[1,2-a]pyridine 33 as an
orange powder (348 mg, 67% yield).
1.5 mmol, 1 equiv), bromobenzene (158 mL, 1.5 mmol, 1 equiv) and
heating for 13 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded ethyl 4-(3-
phenylimidazo[1,2-a]pyridin-2-yl)benzoate 30 as an orange
powder (139 mg, 27% yield).
Rf ¼ 0.41 (petroleum ether/EtOAc: 7/3); Mp ¼ 138e139 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.07 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.91 (d,
2H, 3J ¼ 8.6 Hz, Hb), 7.77e7.72 (m, 3H, H8 and Ha), 7.66e7.62 (m, 3H,
Hf and Hg), 7.56 (dd, 2H, 3J ¼ 8.0 Hz, 4J ¼ 2.0 Hz, He), 7.39 (ddd, 1H,
Rf ¼ 0.15 (petroleum ether/EtOAc: 7/3); Mp ¼ 190e191 ꢀC. 1H
NMR (400 MHz, DMSO-d6): d 8.41e8.39 (m, 2H, Hd and Hg), 8.22 (d,

554
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
1H, 3J ¼ 6.8 Hz, H5), 7.96 (d, 1H, 3J ¼ 7.6 Hz, He), 7.88 (dd, 1H,
3J ¼ 3J0 ¼ 7.6 Hz, Hf), 7.71 (d, 1H, 3J ¼ 8.6 Hz, H8), 7.53 (d, 2H,
3J ¼ 8.8 Hz, Ha), 7.38 (ddd, 1H, 3J ¼ 8.6 Hz, 3J ¼ 6.8 Hz, 4J ¼ 0.8 Hz,
H7), 6.97e6.92 (m, 3H, H6 and Hb), 3.78 (s, 3H, OMe). 13C NMR
as eluent and trituration with diisopropylic ether afforded 2-(3,5-
dichlorophenyl)-3-(pyridin-3-yl)imidazo[1,2-a]pyridine 36 as
a beige powder (353 mg, 69% yield).
Rf ¼ 0.18 (petroleum ether/EtOAc: 7/3); Mp ¼ 161e162 ꢀC. 1H
(100 MHz, DMSO-d6):
d
159.13 (CeO), 148.84 (C), 144.56 (C), 142.50
NMR (400 MHz, DMSO-d6):
d
8.83 (dd, 1H, 3J ¼ 5.0 Hz, 4J ¼ 1.6 Hz,
(C), 137.69 (Ce), 131.42 (C), 131.37 (Cf), 129.15 (2Ca), 126.26 (C),
125.77 (C7), 125.54 (Cd or Cg), 124.03 (C5), 123.74 (Cd or Cg), 117.79
(C), 116.95 (C8), 114.13 (2Cb), 112.98 (C6), 55.26 (OMe). IR (KBr)
Hf), 8.76 (d, 1H, 4J ¼ 1.6 Hz, Hc), 8.15 (d, 1H, 3J ¼ 6.8 Hz, H5), 8.10
(ddd, 1H, 3J ¼ 8.0 Hz, 4J ¼ 1.6 Hz, 4J ¼ 1.6 Hz, Hd), 7.76 (d, 1H,
3J ¼ 8.6 Hz, H8), 7.71 (ddd, 1H, 3J ¼ 8.0 Hz, 3J ¼ 5.0 Hz, 4J ¼ 0.8 Hz,
He), 7.58 (t, 1H, 4J ¼ 2.0 Hz, Hb), 7.51 (d, 2H, 4J ¼ 2.0 Hz, Ha), 7.44
(ddd, 1H, 3J ¼ 8.6 Hz, 3J ¼ 7.4 Hz, 4J ¼ 1.2 Hz, H7), 7.00 (ddd, 1H,
3J ¼ 7.4 Hz, 3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR (100 MHz, DMSO-
cmꢂ1: 3052 (
nCeHar), 1528 (nasNO2), 1348 (nsyNO2), 1257 (nCeO);
834 (
n
CeN). MS (ESI) m/z (%): 346.1 (100) [M þ H]þ. Anal. Calcd
for C20H15N3O3: C, 69.56; H, 4.38; N, 12.17. Found: C, 69.62; H, 4.33;
N, 12.36.
d6):
d 151.35 (Cc), 150.61 (Cf), 144.74 (C), 139.38 (C), 138.84 (Cd),
137.61 (C), 134.38 (2CeCl), 127.15 (Cb), 126.60 (C7), 125.83 (2Ca),
4.1.3.24. 2-(2-Methoxyphenyl)-3-phenylimidazo[1,2-a]pyridine (34).
Compound was obtained following the representative procedure,
125.08 (C), 124.74 (Ce), 124.48 (C5), 118.96 (C), 117.31 (C8), 113.66
(C6). IR (KBr) cmꢂ1: 3020 (
nCeHar), 1589, 1561 (nC]C and nC]N),
using 2-(2-methoxyphenyl)imidazo[1,2-a]pyridine
9
(337 mg,
800, 739 (
n
CeCl). MS (ESI) m/z (%): 340.0 (100) [M þ H]þ, 342.0 (70)
1.5 mmol,1 equiv), bromobenzene (210 L, 2.0 mmol,1.3 equiv) and
m
[M þ H þ 2]þ, 344.0 (12) [M þ H þ 4]þ. Anal. Calcd for C18H11Cl2N3:
heating for 21 h. The crude product was purified by silica gel
chromatography using petroleum ether/ethyl acetate (9/1) as
eluent and trituration with diisopropylic ether afforded 2-(2-
methoxyphenyl)-3-phenylimidazo[1,2-a]pyridine 34 as a beige
powder (379 mg, 84% yield).
C, 63.55; H, 3.26; N, 12.35. Found: C, 63.69; H, 3.59; N, 12.54.
4.1.4. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)phenyl acetate (37)
At room temperature, acetic anhydride (118 mL, 1.3 mmol) was
added portionwise to a solution of 4-(2-phenylimidazo[1,2-a]pyr-
idin-3-yl)phenol 14 (300 mg, 1.0 mmol) in pyridine (1.0 mL). The
reaction mixture was stirred for 12 h at room temperature. Water
was added and the aqueous layer was extracted with dichloro-
methane. The combined organic layers were successively washed
with a saturated aqueous solution of sodium bicarbonate, dried
over sodium sulfate, filtered and concentrated under vacuum.
Trituration with methanol afforded 4-(2-phenylimidazo[1,2-a]pyr-
idin-3-yl)phenyl acetate 37 as a beige powder (218 mg, 63% yield).
Rf ¼ 0.21 (petroleum ether/EtOAc: 7/3); Mp ¼ 187e188 ꢀC. 1H
Rf ¼ 0.23 (petroleum ether/EtOAc: 7/3); Mp ¼ 124e125 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.35 (d,1H, 3J ¼ 7.2 Hz, H5), 7.69 (d,1H,
3J ¼ 8.8 Hz, H8), 7.53e7.47 (m, 3H, Hd and Hg), 7.43e7.33 (m, 5H, H7,
Hb, Hf and Hh), 7.03 (dd, 1H, 3J ¼ 3J0 ¼ 7.6 Hz, Hc), 6.98e6.96 (m, 2H,
H6 and Ha), 3.29 (s, 3H, OMe). 13C NMR (100 MHz, DMSO-d6):
d
156.58 (CeO), 144.01 (C), 140.33 (C), 131.78 (Cd), 130.27 (C), 129.55
(Cb), 129.00 (2Cf), 128.87 (2Cg), 127.99 (Ch), 124.75 (C7), 123.89 (C),
123.63 (C5), 122.30 (C), 120.42 (Cc), 117.17 (C8), 112.78 (C6), 111.61
(Ca), 54.62 (OMe). IR (KBr) cmꢂ1: 3070 (
nCeHar), 1606, 1481 (nC]C
and
n
C]N), 1246 (
n
CeO). MS (ESI) m/z (%): 301.0 (100) [M þ H]þ.
NMR (400 MHz, DMSO-d6):
d
8.08 (d,1H, 3J ¼ 7.0 Hz, H5), 7.71 (d,1H,
Anal. Calcd for C20H16N2O: C, 79.98; H, 5.37; N, 9.33. Found: C,
79.70; H, 5.02; N, 9.39.
3J ¼ 9.2 Hz, H8), 7.63 (d, 2H, 3J ¼ 7.2 Hz, Ha), 7.59 (d, 2H, 3J ¼ 8.4 Hz,
Hd), 7.40 (d, 2H, 3J ¼ 8.4 Hz, He), 7.37e7.28 (m, 4H, H7, Hb and Hc),
6.95 (dd, 1H, 3J ¼ 3J0 ¼ 7.0 Hz, H6), 2.37 (s, 3H, CH3). 13C NMR
4.1.3.25. 2-(3,5-Dichlorophenyl)-3-phenylimidazo[1,2-a]pyridine
(35). Compound was obtained following the representative
procedure, using 2-(3,5-dichlorophenyl)imidazo[1,2-a]pyridine 10
(100 MHz, DMSO-d6): d 169.21 (C]O), 151.01 (CeO), 149.79 (C),
144.21 (C), 141.66 (C), 134.32 (C), 132.11 (2Cd), 128.48 (2Cb), 127.67
(2Ca), 126.92 (Cc), 125.45 (C7), 123.96 (C5), 123.27 (2Ce), 120.08 (C),
(395 mg, 1.5 mmol, 1 equiv), bromobenzene (158
mL, 1.5 mmol,
117.09 (C8), 112.95 (C6), 21.12 (CH3). IR (KBr) cmꢂ1: 3039 (
nCeHar),
1 equiv) and heating for 18 h. The crude product was purified by
silica gel chromatography using petroleum ether/ethyl acetate (9/1)
as eluent and trituration with diisopropylic ether afforded 2-(3,5-
1752 (nC]O), 1200 (nCeO). MS (ESI) m/z (%): 329.1 (100)
[M þ H]þ. Anal. Calcd for C21H16N2O2: C, 76.81; H, 4.91; N, 8.53.
Found: C, 77.10; H, 4.77; N, 8.57.
dichlorophenyl)-3-phenylimidazo[1,2-a]pyridine 35 as
a beige
powder (423 mg, 83% yield).
4.1.5. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)aniline (38)
Rf ¼ 0.78 (petroleum ether/EtOAc: 7/3); Mp ¼ 155e156 ꢀC. 1H
Using the H-CubeÒ system in controlled mode, 3-(4-
nitrophenyl)-2-phenylimidazo[1,2-a]pyridine 16 (1.1 g, 3.5 mmol)
was dissolved in a mixture ethanoletetrahydrofuran (120 mL, 5:1)
and passed through a cartridge of Raney nickel at room tempera-
ture with a flow rate of 0.8 mL/min at 10 bar. Afterwards, the
solvent was removed under reduced pressure. The crude product
was purified by silica gel chromatography using petroleum ether/
ethyl acetate (9/1) as eluent to afford 4-(2-phenylimidazo[1,2-a]
pyridin-3-yl)aniline 38 as an orange powder (806 mg, 81% yield).
Rf ¼ 0.12 (petroleum ether/EtOAc: 7/3); Mp ¼ 216e217 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d
8.05 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.73 (d,
1H, 3J ¼ 8.6 Hz, H8), 7.69e7.65 (m, 3H, Hd and He), 7.59 (dd, 2H,
3J ¼ 8.0 Hz, 4J ¼ 2.0 Hz, Hc), 7.55 (d, 2H, 4J ¼ 2.0 Hz, Ha), 7.54 (t, 1H,
4J ¼ 2.0 Hz, Hb), 7.41 (ddd,1H, 3J ¼ 8.6 Hz, 3J ¼ 7.4 Hz, 4J ¼ 1.2 Hz, H7),
6.98 (ddd, 1H, 3J ¼ 7.4 Hz, 3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6). 13C NMR
(100 MHz, DMSO-d6):
d 144.26 (C), 138.17 (C), 137.89 (C), 134.27
(2CeCl), 130.90 (2Cc), 130.07 (2Cd), 129.87 (Ce), 128.64 (C), 126.86
(Cb), 126.20 (C7), 125.58 (2Ca), 124.27 (C5), 122.15 (C), 117.27 (C8),
113.45 (C6). IR (KBr) cmꢂ1: 3034 (
nCeHar), 1588, 1561 (nC]C and
n
C]N), 802, 753 (
n
CeCl). MS (ESI) m/z (%): 339.0 (100) [M þ H]þ,
NMR (400 MHz, DMSO-d6):
d
7.99 (d, 1H, 3J ¼ 6.8 Hz, H5), 7.72 (d,
341.0 (83) [M þ H þ 2]þ, 343.0 (15) [M þ H þ 4]þ. Anal. Calcd for
2H, 3J ¼ 7.2 Hz, Ha), 7.64 (d,1H, 3J ¼ 9.2 Hz, H8), 7.35e7.24 (m, 4H, H7,
Hb and Hc), 7.13 (d, 2H, 3J ¼ 8.4 Hz, Hd), 6.89 (ddd, 1H, 3J ¼ 8.0 Hz,
3J ¼ 6.8 Hz, 4J ¼ 1.2 Hz, H6), 6.78 (d, 2H, 3J ¼ 8.4 Hz, He), 5.53 (s, 2H,
C
19H12Cl2N2: C, 67.27; H, 3.57; N, 8.26. Found: C, 66.95; H, 3.68; N,
8.34.
NH2). 13C NMR (100 MHz, DMSO-d6):
d 149.67 (C), 143.68 (C),140.54
4.1.3.26. 2-(3,5-Dichlorophenyl)-3-(pyridin-3-yl)imidazo[1,2-a]pyri-
dine (36). Compound was obtained following the representative
procedure, using 2-(3,5-dichlorophenyl)imidazo[1,2-a]pyridine 10
(C), 134.86 (C), 131.53 (2Cd), 128.33 (2Cb), 127.33 (2Ca), 127.24 (Cc),
124.79 (C7), 123.93 (C5), 121.91 (C), 116.94 (C8), 115.49 (C), 114.82
(2Ce), 112.43 (C6). IR (KBr) cmꢂ1: 3321 and 3215 (
nNeH), 1607, 1481
(395 mg, 1.5 mmol, 1 equiv), 3-bromopyridine (145
mL, 1.5 mmol,
(nC]C and
n
C]N). MS (ESI) m/z (%): 286.1 (100) [M þ H]þ. Anal.
1 equiv) and heating for 15 h. The crude product was purified by
silica gel chromatography using petroleum ether/ethyl acetate (8/2)
Calcd for C19H15N3: C, 79.98; H, 5.30; N, 14.73. Found: C, 79.84; H,
5.56; N, 14.32.

S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
555
4.1.6. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)benzamide (39)
a 96-well microplate (NuncÒ). The cultures were exposed for 96 h
at 26 ꢀC to the drugs. Four hours before measurement, 10
L of
resazurin solution (700 M) were added. Then fluorescence was
measured at 590 nm with an excitation at 550 nm.
At room temperature, a solution of hydrogen peroxide in water
m
(35%, 360
mL) and potassium carbonate (154 mg, 1.1 mmol) were
m
added to a solution of 4-(2-phenylimidazo[1,2-a]pyridin-3-yl)
benzonitrile 17 (150 mg, 0.51 mmol) in dimethyl sulfoxide (2.0 mL).
The reaction mixture was stirred for 12 h at room temperature.
Water was added and the precipitate was collected by filtration to
give 4-(2-phenylimidazo[1,2-a]pyridin-3-yl)benzamide 39 as
a yellow powder (105 mg, 66% yield).
4.2.1.3. Antileishmanial
activity
against
amastigote
stage.
Cytotoxicity against the intracellular amastigote stage of the para-
site was determined after infection of Balb/c mice peritoneal
macrophages (CE Janvier, Le Genest, France). 100 mL of a peritoneal
macrophage suspension were placed into a 24-well plate (Nunc) on
glass slides (10 mm diameter) at 1.5 ꢃ 105 cell/mL in RPMI 1640
with 15% FBS at 37 ꢀC and 5% CO2. Following a 24 h-incubation to
Rf ¼ 0.14 (EtOAc/petroleum ether: 7/3); Mp ¼ 277e278 ꢀC. 1H
NMR (400 MHz, DMSO-d6):
d 8.18 (s, 1H, NH2), 8.14 (d, 1H,
3J ¼ 6.8 Hz, H5), 8.10 (d, 2H, 3J ¼ 8.0 Hz, He), 7.72 (d, 1H, 3J ¼ 8.8 Hz,
H8), 7.64e7.60 (m, 4H, Ha and Hd), 7.56 (s, 1H, NH2), 7.40e7.29 (m,
4H, H7, Hb and Hc), 6.96 (dd, 1H, 3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR
allow attachment, macrophages were infected with 100
mL of
a stationary phase promastigote suspension (1.5 ꢃ 105 promasti-
gotes/mL in RPMI 1640 medium plus 15% FBS) and then incubated
for a 24 h-period at 37 ꢀC and 5% CO2 for infection. Macrophage
culture was washed and exposed to drugs at a concentration of
(100 MHz, DMSO-d6): d 167.47 (C]O), 144.44 (C), 141.96 (C), 134.58
(C), 134.22 (C), 132.39 (C), 130.63 (2Cd), 128.86 (2Ce), 128.52 (2Cb),
127.81 (2Ca), 127.74 (Cc), 125.64 (C7), 124.02 (C5), 120.16 (C), 117.14
(C8), 113.06 (C6). IR (KBr) cmꢂ1: 3344 and 3150 (
nNeH), 1670 (
n
C]
10 mM. Medium plus drugs were replaced after 48 h. After 2 days,
O), 1390 (
n
CeN). MS (ESI) m/z (%): 314.1 (100) [M þ H]þ. Anal. Calcd
cultures were fixed with methanol, stained with May-Grunwalde
Giemsa and microscopically examined. The average number of
amastigotes per macrophage was determined by counting the
number of amastigotes in 100 randomly chosen macrophages in
for C20H15N3O: C, 76.66; H, 4.82; N, 13.41. Found: C, 76.87; H, 4.99;
N, 13.16.
4.1.7. 4-(2-Phenylimidazo[1,2-a]pyridin-3-yl)benzoic acid (40)
To a solution of ethyl 4-(2-phenylimidazo[1,2-a]pyridin-3-yl)
benzoate 18 (200 mg, 0.58 mmol) in ethanol (10 mL) was added
a 2 M sodium hydroxide aqueous solution (5 mL). After refluxing for
1.5 h, the solvent was removed under reduced pressure. After-
wards, the reaction mixture was neutralized by a saturated aqueous
ammonium chloride solution, poured into water, extracted with
ethyl acetate and washed with brine. The combined organic layers
were successively dried over sodium sulfate, filtered and concen-
trated under vacuum. The crude product was purified by silica gel
chromatography using dichloromethane/ethanol (98/2) as eluent
to give 4-(2-phenylimidazo[1,2-a]pyridin-3-yl)benzoic acid 40 as
a white powder (35 mg, 19% yield).
each duplicate well. Inhibitory percentages after a 10 mM treatment
were calculated by using the values of the number of amastigotes
per macrophage. Percentage of infected macrophages was also
calculated [12].
4.2.2. Cytotoxicity assay
HeLa cells were subcultured every 4 days in RPMI 1640 medium
supplemented with 10% SBF (SigmaeAldrich). Cells were harvested
after a 5 min incubation with trypsine solution (SigmaeAldrich).
Hela cells were seeded in a 96-well microplate, 100
mL suspension in each well. After a 24 h-incubation time at 37 ꢀC
and 5% CO2, 100 L of drugs concentrations were added in dupli-
cate. After 96 h, 10 L of resazurin solution (700 mM) were added.
m
L of a 105/
m
m
Rf ¼ 0.14 (EtOAc/petroleum ether: 7/3); Mp ¼ 341e342 ꢀC. 1H
After a 3 h-incubation time at 37 ꢀC, 5% CO2, fluorescence was
NMR (400 MHz, DMSO-d6):
d
8.11e8.09 (m, 3H, H5 and He), 7.70 (d,
measured at 590 nm with an excitation at 550 nm.
1H, 3J ¼ 9.2 Hz, H8), 7.63 (d, 2H, 3J ¼ 7.2 Hz, Hd), 7.47 (d, 2H,
3J ¼ 7.6 Hz, Ha), 7.37e7.28 (m, 4H, H7, Hb and Hc), 6.93 (dd, 1H,
4.2.3. Kinase inhibitory activities
3J ¼ 3J0 ¼ 6.8 Hz, H6). 13C NMR (100 MHz, DMSO-d6):
d
167.00 (C]
4.2.3.1. PKC inhibition. ThePKC activity was measured using the PKC
kinase activity kit (Enzo Life Sciences). L. major promastigotes were
cultured for 6 days at 26 ꢀC. Then proteins were extracted with the
following extraction buffer: Mammalian Protein Extraction Reagent
M-PER (Thermo Scientifics), phosphatase inhibitor cocktail (Sigmae
Aldrich), protease inhibitor cocktail (SigmaeAldrich), Phenyl-
methylsulfonyl Fluoride (SigmaeAldrich), leupeptin (Sigmae
Aldrich), and aprotinin (SigmaeAldrich) and conserved at ꢂ80 ꢀC.
O), 144.52 (C), 142.07 (C), 134.17 (C), 133.21 (C), 130.71 (2Ce), 130.56
(2Cd), 130.46 (C), 128.54 (2Cb), 127.85 (2Ca), 127.79 (Cc), 125.73 (C7),
124.06 (C5), 120.13 (C), 117.17 (C8), 113.12 (C6). IR (KBr) cmꢂ1: 3422
(nOeH), 1701 (nC]O), 1240 (nCeO). MS (ESI) m/z (%): 315.1 (100)
[M þ H]þ. Anal. Calcd for C20H14N2O2: C, 76.42; H, 4.49; N, 8.91.
Found: C, 76.69; H, 4.44; N, 8.76.
4.2. Biological evaluation
The extracted proteins were assayed at a concentration of 0.2 mg/mL
that was chosen after a preliminary study to demonstrate PKC
Compounds were diluted in dimethyl sulfoxide (DMSO) in view
to obtain stock solutions (10 mM). Dilutions of each compound
were realized in medium in accordance with cell line culture and at
a maximum final concentration of 1% DMSO.
activity in this species. A PKC inhibitor, RO32-04325 (Sigmae
Aldrich), was used at 0.2
mM as inhibitor control. The positive
control is achieved using active PKC supplied with the kit. Drugs
were tested according to the protocol recommended by Enzo Life
Sciences. Drugs concentrations (10
mM or 50 mM) were chosen
4.2.1. In vitro antileishmanial activity
according to their IC50 against L. major promastigotes.
4.2.1.1. Strains. L. major (MHOM/IL/81/BNI) promastigotes were
maintained in Schneider’s insect medium (Sigma chemical Co. St
Louis, Mo) supplemented with 13% heat-inactivated foetal bovine
serum (FBS, SigmaeAldrich), penicillin (100 UI/mL) and strepto-
mycin (100 mg/mL) at 26 ꢀC by passage every 7 days.
4.2.3.2. CK1 and LmCK1.2 (lmjF35.1010) inhibition
4.2.3.2.1. Buffers. Buffer A: 60 mM
p-nitrophenylphosphate, 25 mM Mops (pH 7.2), 5 mM EGTA,15 mM
MgCl2, mM DTT, 0.1 mM sodium vanadate, mM
phenylphosphate.
4.2.3.2.2. Kinase preparations and assays. Kinase activities were
assayed in Buffer A, at 30 ꢀC, at a final ATP concentration of 15
M.
b-glycerophosphate, 30 mM
1
1
4.2.1.2. Antileishmanial activity against promastigote stage.
Promastigote susceptibility testing was performed with a spectro-
m
fluorimetric micromethod previously described [31]. Briefly, 100
mL
Blank values were subtracted and activities expressed in % of the
maximal activity, i.e. in the absence of inhibitors. Controls were
of a 106 promastigotes/mL suspension were placed into wells of

556
S. Marhadour et al. / European Journal of Medicinal Chemistry 58 (2012) 543e556
performed with appropriate dilutions of DMSO. CK1 and LmCK1
peptide substrates were obtained from Proteogenix (Oberhaus-
bergen, France).
software. The LmCK1.2 work was supported by an EEC grant (FP7
HEALTH-2007-2.3.4-1: LEISHDRUG) to LM and NR.
CK1d/ε (porcine brain, native) was assayed in three-fold diluted
References
buffer A, as previously described [32,33] but using 25
peptide (RRKHAAIGpSAYSITA), a CK1-specific substrate [34]. Its
m
M CKS
[1] T. Kobets, I. Grekov, M. Lipoldová, Curr. Med. Chem. 19 (2012) 1443e1474.
[2] T.S. Tiuman, A.O. Santos, T. Ueda-Nakamura, B.P. Dias Filho, C.V. Nakamura,
Int. J. Infect. Dis. 15 (2011) e525ee532.
[3] S. Malik, S. Kumar, A. Choudhary, A. Kumar, A. Singh, G. Avasthi, J. Chem.
Pharm. Res. 2 (2010) 70e91.
[4] J.V. Richard, K.A. Werbovetz, Curr. Opin. Chem. Biol. 14 (2010) 447e455.
[5] P. Le Pape, J. Enzyme Inhib. Med. Chem. 23 (2008) 708e718.
[6] D. Plano, Y. Baquedano, D. Moreno-Mateos, M. Font, A. Jiménez-Ruiz,
J.A. Palop, C. Sanmartín, Eur. J. Med. Chem. 46 (2011) 3315e3323.
kinase activity was assayed in buffer A, with 1 mg histone H1/mL, in
the presence of 15
a final volume of 30
reaction was stopped by deposing 25
m
M [
L. After incubation for 30 min at 30 ꢀC, the
L onto P81 phosphocellulose
g-
33P] ATP (3000 Ci/mmol; 10 mCi/mL) in
m
m
papers (Whatman) using a FilterMate harvester (PerkineElmer)
and were washed in 1% phosphoric acid. Scintillation fluid was
added and the radioactivity measured in a PerkineElmer counter.
LmCK1.2 (LmjF35.1010, L. major, recombinant, His-fusion protein
in Escherichia coli) [18a] was purified by affinity chromatography on
cobalt beads and its kinase activity was assayed as described for CK1.
ꢀ
ꢀ
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the chromatographic runs were performed on a Dionex Ultimate
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Chromeleon 7 software. The stationary phase consisted of XBridge
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0.70 cm3/g). The mobile phase consisted of methanol and appro-
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and a solutionof acetic acid0.01 M for pH ¼ 4.5). Foreach compound,
the retention factor expressed as k ¼ (tR ꢂ t0)/t0 was determined at
different proportions of methanol (three points were used to plot
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organic substance). The dataset included 30 compounds of the 60
described as the reference substances in the guideline for testing
chemicals of the Organization for Economic Co-operation and
Development (OECD) [35]. For each reference substance, the loga-
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described above, and then Log kw was plotted as a function of Log D
(values obtained in the chemical properties section of substance
detail in SciFinder). We determined Log kw of the library of imidazo
[1,2-a]pyridines using the above described procedure. Finally, the
distribution coefficient (Log D) was obtained by interpolation of the
calculated Log kw on the calibration graph for each pH.
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We thank AtlanChim Pharma Company for lipophilicity deter-
mination and ChemAxon Ltd for providing the MarvinSketch