Synthesis of polysubstituted benzofuran derivatives as novel inhibitors of parasitic growth

Article abstract of DOI:10.1016/j.bmc.2013.07.002

A series of polysubstituted benzofuran derivatives was easily and rapidly prepared using a tandem Sonogashira coupling/cyclization reaction. Subsequent acylation afforded a small library of 39 new compounds that were assayed in cellulo on Plasmodium falci

Full text of DOI:10.1016/j.bmc.2013.07.002

Bioorganic & Medicinal Chemistry 21 (2013) 4885–4892
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of polysubstituted benzofuran derivatives
as novel inhibitors of parasitic growth
Marion Thévenin a, Sylviane Thoret a, Philippe Grellier b, Joëlle Dubois a,
⇑
a CNRS, Institut de Chimie des Substances Naturelles, UPR2301, Centre de Recherche de Gif, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
b Muséum National d’Histoire Naturelle, UMR 7245 CNRS, Département RDDM, CP52, 57 rue Cuvier, 75005 Paris, 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 polysubstituted benzofuran derivatives was easily and rapidly prepared using a tandem Sono-
gashira coupling/cyclization reaction. Subsequent acylation afforded a small library of 39 new com-
pounds that were assayed in cellulo on Plasmodium falciparum and Trypanosoma brucei parasites. Some
of them exhibited good inhibitory activity on T. brucei proliferation.
Received 25 April 2013
Revised 25 June 2013
Accepted 1 July 2013
Available online 12 July 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Benzofurans
Sonogashira coupling reaction
Antiparasitic
T. brucei
P. falciparum
1. Introduction
derivatives to evaluate their antiproliferative effects on P. falcipa-
rum and on T. brucei.
According to WHO reports, Plasmodium falciparum is the major
cause of malaria in humans, with 200–300 million individuals af-
fected annually, causing 200–250 thousand deaths,1 while Trypan-
osoma brucei, responsible for the African sleeping sickness,
concerns 30 thousand persons and is lethal in absence of any treat-
ment.2 Currently resistance phenomena to established therapeu-
tics against these diseases has dramatically developed. Hence
new efficient antiparasitic agents are deeply needed.
Thus we synthesized benzofuran derivatives substituted at po-
sition 2 by an aryl or cyclopropyl group. These compounds were
either C-acylated at position 3 (A and B, Fig. 1) or O-acylated at po-
sition 4 (C, Fig. 1), the acyl substituent R2 being an aryl moiety
bearing various substituents. In order to increase the molecular
diversity in the C-acylated series, R3 at position 4 is either a hydro-
gen atom (A series), a hydroxyl group or a methoxy substituent (B
series).
In the course of our search for new active molecules, we synthe-
sized intermediate benzofuran derivatives that displayed good
antiparasitic activity. Benzofuran containing molecules have al-
ready been described to possess many biological properties as
antiinflammatory,3,4 antivasoconstriction,5 antimicrobial6 or
antifungal.7,8 However, to the best of our knowledge, few authors
studied their potential antiparasitic activity.9–13 From the chemical
standpoint, many syntheses of molecules possessing a benzofuran
motif have been developed. Recently rapid metal-catalyzed meth-
ods yielding benzofurans from phenols were described.14–17 As
well, Singh and Wirth published an efficient metal-free cyclization
of o-hydroxystilbenes to benzofurans catalyzed by hypervalent
iodine.18 Nevertheless 2,3-, 2,4- and 2,3,4-trisubstituted benzofu-
rans herein reported have rarely been studied. For all these reasons
we decided to create a library of polysubstituted benzofuran
Herein, we describe an easy and rapid synthesis of polysubsti-
tuted benzofuran derivatives along with their biological evaluation
on P. falciparum and T. brucei proliferation.
R2
R2
R2
R3
O
O
O
O
O
4
4
3
3
R1
R1
R1
2
2
2
O
O
A
B
C
R1 = aryl, cyclopropyl
R2 = aryl
R3= OH, OMe
⇑
Corresponding author. Tel.: +33 1 69 82 30 58; fax: +33 1 69 07 72 47.
E-mail address: joelle.dubois@cnrs.fr (J. Dubois).
Figure 1. General structures of benzofuran derivatives.
0968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.07.002

4886
M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
displayed low antiparasitic activity (see Table 3). Acylation yields
2. Chemistry
for A series (Table 1) were low with p-nitro- and trisubstituted
benzoyl chlorides (compounds 5, 6 and 9) and the 2-cyclopropyl-
3-(p-nitrobenzoyl)benzofuran could not be obtained under these
conditions. However, moderate to excellent yields were reached
with benzoyl chloride (compounds 4, 7 and 8).
2.1. Tandem Sonogashira coupling/cyclization reaction
2-Substituted benzofurans 1–3 and 11–14 were synthesized via
a tandem Sonogashira coupling/cyclization reaction from the com-
mercially available 2-iodophenol (Scheme 1) and from the pre-
pared 2-iodoresorcinol (Scheme 2), respectively. The substituent
R1 (aryl or cyclopropyl) was brought about by acetylene deriva-
tives. Though this same Sonogashira coupling reaction has already
been reported with 2-iodoresorcinol,19 it was only obtained with
hexyl or phenyl R1 substituent in 50% and 60% yield, respectively.
Therefore we tried to optimize this coupling reaction. Our major
aim was to avoid the Glaser coupling affording the dimer products
from terminal alkynes.20–22 Thus we found that a perfectly de-
gassed solvent by using the freeze-pump-thaw method could min-
imize this homocoupling reaction.
These conditions combined with the use of 3 equiv of alkynes
allowed to significantly increase the reaction yield up to 77% for
benzofuran-4-ol 11 (Scheme 2). Afterwards they were applied for
the formation of all 2-substituted derivatives. Thus synthesis of
benzofurans 1–3 (Scheme 1) was performed with moderate to high
yield (50–88%) as well as benzofuran-4-ols 11–13 (Scheme 2) (70–
77%). Only compound 14 possessing a xylyl group (Scheme 2) was
obtained in low yield (12%). Formation of benzofurans required di-
luted conditions in order to minimize homocoupling reaction.
Therefore, faced with a scale-up issue for derivatives 1–3, we
decided to use conditions described by Alami’s group23 allowing
the cyclization into benzofurans from 2-iodoanisole in two steps
(Scheme 3). Thus through this method, multigram scale reactions
have been carried out giving 5- to 10-fold greater amounts of de-
sired product. Moreover, formation of benzofuran 1 substituted
by a 4-methoxyphenyl group was performed in quantitative yield,
whereas a 50% yield was obtained using Sonogashira coupling
reaction. On the contrary, much better yields were observed with
the tandem reaction for the synthesis of compounds 2 and 3 with
88% and 70% yields, respectively, compared to 65% and 16% ob-
tained in two steps, respectively.
In order to avoid esterification of the 4-OH group in the B series,
protection of benzofuran-4-ols 11–14 was first carried out
(Scheme 2). Hence introduction of a benzyl or a methyl group
was performed yielding derivatives 15–18 with excellent yields
(81–92%). Under acylation conditions, the benzyl protecting group
was hydrolyzed affording the direct formation of 2,3,4-trisubsti-
tuted analogues 19–25 (Scheme 2 and Table 1). It should be no-
ticed that only traces of 2-phenyl-3-acylbenzofurans were
obtained in B series. Indeed, acylation of 2-phenyl derivatives
was unsuccessful probably because many positions of the 2-phenyl
ring were also acylated underFriedel–Crafts conditions, leading to a
complex mixture where the expected derivative was generally
formed as a minor product. Likewise, all reactions performed with
p-nitrobenzoyl chloride failed leading to many side products. On
the other hand, acylation of compound 18 (R1 = p-methoxyphenyl,
R3 = Me) afforded benzofurans 26–31 (Table 1) in better yields (up
to 41%). Only acylation with disubstituted benzoyl chloride was
less efficient (27% yield). The p-methoxyphenyl group was the only
R1 substituent used in this series because of our preliminary bio-
logical results (see Table 4).
Though our first goal was to obtain rapidly a small library of poly-
substituted benzofurans, we tried to optimize the acylation reaction.
Thus we found that using titanium(IV) chloride or aluminium(III) chlo-
ride instead of tin(IV) chloride as Lewis acid significantly increased the
yield reaction. Indeed 82% yield was obtained instead of 67% for the
optimized acylation performed to get compound 26 (Table 1).
2.3. O-Acylation
Further O-acyl benzofuran derivatives 32–51 (C series) were
prepared from compounds 11–14 bearing a free hydroxyl group,
according to Scheme 2. Obtained yields (Table 2) were moderate
(39–54%) for 2-phenyl-benzofuran derivatives 45–50. Only acyla-
tion with p-chlorobenzoyl chloride afforded expected compound
49 in good yield (71%). This reaction proved to be more efficient
on 2-p-methoxyphenyl-benzofuran leading to compounds 32–38
in good yield but the best results were obtained on 2-cyclo-
propylbenzofuran leading to compounds 39–44 in good to excel-
lent yields (69–96%) except with 2-ethoxynaphthaloyl chloride.
This reaction led to a modest yield only with the trisubstituted
benzoyl chloride that was synthesized just before acylation (11%
for compound 34, Table 3).
2.2. Friedel–Crafts acylation
A standard Friedel–Crafts acylation using tin(IV) chloride was
then carried out to form compounds 4–9 (A series), 19–25 and
26–31 (B series) bearing a hydrogen atom, a hydroxyl group and
a methoxy substituent at position 4 of benzofuran motif, respec-
tively (Scheme 2 and Table 1). The acyl chlorides used in this reac-
tion were generally commercially available except di- and
trisubstituted derivatives that were prepared just before the acyl-
ation reaction from the corresponding acid and thionyl chloride.
Few derivatives of the A series were prepared because they early
3. Biology
R2
All these benzofuran derivatives were assayed on the intra-
erythrocytic stages of P. falciparum,24–26 responsible for malaria
and the bloodstream forms of T. brucei gambiense, the pathogenic
agent of African sleeping sickness.27–29 Results are summarized
in Tables 3–5.
None of the 2,3-disubstituted benzofurans of the A series (Table 3)
were active against P. falciparum. Their activity against T. brucei was
moderate when R2 was a phenyl group (compounds 4, 7 and 8) and
compounds bearing a p-nitrobenzoyl moiety at position 3 (com-
pounds 4 and 9) were inactive. Only compound 6 where R2 was a tri-
O
I
R1
R1
O
(a)
(b)
R1
HO
O
R1
Homocoupling product
1-3
A SERIES
4-9
2
R1
=
R2 =
1
2
3
OMe
HO
OMe
NO2
OMe
MeO
substituted phenyl (IC50 = 6.7 lM) displayed a better activity.
Like 2,3-disubstituted benzofurans, B series derivatives (Table 4)
displayed no activity against P. falciparum. On the other hand, better
results were obtained on T. brucei. Almost all derivatives displayed
Scheme 1. Reagents and conditions: (a) PdCl2(PPh3)2 (5 mol %), CuI (10 mol %), Et3N
(10 equiv), MeCN, 60 °C, overnight, 1: 50%, 2: 88%, 3: 70%; (b) R2–COCl (1.2 equiv),
SnCl4 (1.2 equiv), DCM, rt, 1–5 h, 13–86% (see Table 1).

M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
4887
OH
OH
OR3
R1
I
R1
R1
(a)
(b) or (c)
O
O
HO
10
11-14
15-17 (R3 = Bn)
18 (R1 = p-OMePh; R3 = Me)
(e)
R2
(d)
R2
OR3
O
O
O
O
R1
R1
O
C SERIES
32-51
B SERIES
19-25 (R3 = H)
26-31 (R3 = Me)
MeO
OMe
EtO
R1
=
R2 =
11
OMe
HO
12
13
OMe
Cl
NO2
MeO
MeO
OPiv
14
OMe
OMe
Scheme 2. Reagents and conditions: (a) PdCl2(PPh3)2 (5 mol %), CuI (10 mol %), Et3N (10 equiv), MeCN, 60 °C, overnight, 11: 77%, 12: 73%, 13: 76%, 14: 12%; (b) BnBr (2 equiv),
K2CO3 (2 equiv), acetone, reflux, 4–10 h, 81–86%; (c) MeI (2 equiv), K2CO3 (2 equiv), DMF, rt, 19 h, 92%; (d) R2-COCl (1.2 equiv), SnCl4 or TiCl4 (1.2 equiv), DCM, rt, 1–5 h, 6–83%
(see Table 1); (e) R2-COCl (1.2 equiv), Et3N (1.2 equiv), DCM, 0 °C to rt, 2–5 h, 27–96% (see Table 2).
IC50 value below 10 lM and only compound 31 was found inactive.
R1
I
The presence of a 2,4,6-trisubstituted phenyl group at position 3
seemed to be detrimental to the inhibitory activity contrary to what
was observed in the A series. 4-Hydroxybenzofuran derivatives (19–
21) were slightly more active than their corresponding methoxy
analogues (26–28). Replacement of the methoxyphenyl group at po-
sition 2 by a cyclopropyl ring did not modify much the inhibitory
activity (compare 20–22 to 23–25) suggesting that this position is
not crucial for activity. Finally compound 22 was found to be the
most active derivative of this series on T. brucei proliferation
R1
(b)
O
(a)
MeO
MeO
1-3
Scheme 3. Reagents and conditions: (a) PdCl2(PPh3)2 (2 mol %), CuI (1 mol %), Et3N,
rt, overnight; (b) PTSAÁH2O, EtOH, MW (130 °C, 1 h) or sealed tube, 130 °C, 24 h, 1:
100%, 2: 65%, 3: 16% (in two steps).
(IC50 = 1.5 lM). By comparison with the A series, 4-position substi-
tution seemed to be beneficial for trypanocidal activities.
Table 1
C-Acylation results in the A and B series
Contrary to A and B series derivatives, some 4-O-acylated ben-
zofurans in the C series (33, 34 and 51) (Table 5) demonstrated
some activity against P. falciparum. Two of them (33 and 34) bear-
ing a p-methoxyphenyl group at position 2 and at least one meth-
oxy substituent in para position of the aroyl group displayed IC50
Compd R1
R2
R3
Yields (%)
4
5
6
Phenyl
4-Nitro phenyl
2-Hydroxy-4,6-dimethoxyphenyl
/
/
/
86
27
17
OMe
7
Phenyl
/
53
values of 11.2 and 7.9
larial compound of the series was the benzofuran derivative 51
showing an IC50 of 6.0 M. Therefore the 2-xylyl group seemed
lM, respectively. The most potent antima-
8
9
Phenyl
4-Nitro phenyl
/
/
83
13
l
to significantly improve the antiplasmodial activity. Better inhibi-
tory activities against T. brucei were obtained in the C series
(1.4 < IC50 < 20 lM) except for compound 34 bearing a trisubsti-
19
20
21
22
Phenyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
H
H
H
H
17
26
25
12
OMe
tuted phenyl moiety at position 4. As observed in the B series, tri-
substituted R2 group seemed to abolish trypanocidal activity.
Generally the R1 substituent had little influence on the activity.
However, for the O-benzoylbenzofurans 32, 39, 45 and 51 (Table 5),
we observed that inhibition increased with the steric hindrance of
the 2-substituent, m-xylyl compound 51 being more active than
p-methoxyphenyl 32, phenyl 45 and cyclopropyl 39, successively.
Furthermore, when R2 was a 4-chlorophenyl or 4-nitrophenyl
group lower IC50 values were obtained with the cyclopropyl
derivatives.
23
24
25
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
H
H
H
6
35
28
26
27
28
29
30
31
Phenyl
4-Methoxyphenyl
1-Naphthyl
4-Chlorophenyl
3-Methoxy-4-O-pivaloyl- phenyl
2,4,6-Trimethoxyphenyl
Me 67 (82)a
Me 67
Me 55
Me 41
Me 27
Me 67
OMe
a
Yield obtained under optimized conditions (TiCl4 1.2 equiv, DCM, rt, 1 h).

4888
M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
Table 2
Finally, we have noticed that O-acylated benzofurans 32–51
O-Acylation results in the C series
mainly possessed a little higher activities than their C-acyl homo-
logues 19–30 (compounds 20 and 23 compared to derivatives 33
and 40, respectively), except when these latters bear a naphthoyl
group substituted or not. In that case, better inhibitory effects were
observed for C-acyl benzofurans (compounds 21, 22, 24, 25 in Ta-
ble 4 compared to benzofurans 35, 36, 41, 42 in Table 5 respec-
tively). It should be noted that the best inhibitory activity on T.
Compd
R1
R2
Yields (%)
32
33
Phenyl
4-Methoxyphenyl
2-Hydroxy-4,6-dimethoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-Chlorophenyl
77
68
OMe
34
35
36
37
38
11
60
54
70
62
brucei proliferation (IC50 <2 lM) was observed in the B series with
4-Nitrophenyl
the 2-ethoxynaphthoyl derivative 22 and in the C series with
p-substituted esters of the 2-aryl-4-hydroxybenzofuran (33, 37,
38, 46, 49 and 50).
39
40
41
42
43
44
Phenyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-Chlorophenyl
4-Nitrophenyl
96
88
69
19
86
78
4. Conclusion
45
46
47
48
49
50
Phenyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-Chlorophenyl
4-Nitrophenyl
49
45
48
39
71
48
To conclude, we have reported the easy and rapid synthesis of a
novel series of 39 polysubstituted benzofuran derivatives. Indeed 2
and 3 steps were only necessary to obtain 4-O-acyl and 3-C-acyl
benzofurans, respectively, via a tandem Sonogashira coupling/
cyclization reaction. All these compounds were then assayed for
their antiparasitic effects. Most of them displayed good inhibitory
activities on T. brucei proliferation possessing IC50 values below
51
Phenyl
56
10 lM. The most potent trypanocidal inhibitors of this novel class
with micromolar IC50 values include one 3-C-acyl-2-substituted
benzofuran-4-ol and six 4-O-acyl-2-substituted benzofurans. The
Table 3
Inhibitory activity of 3-acyl-2-substituted benzofuran derivatives 4–9 (A series)
R2
O
R1
O
Compd
R1
R2
IC50
(lM)
IC50 (lM)
P. f
T. b
4
5
6
7
8
9
4-Methoxy phenyl
4-Methoxy phenyl
4-Methoxy phenyl
Cyclopropyl
Phenyl
Phenyl
Phenyl
>50
>50
>25
>50
>50
>50
21.2 0.9
>50
6.7 0.5
20.9 2.0
15.5 1.9
>50
4-Nitro phenyl
2-Hydroxy-4,6-dimethoxyphenyl
Phenyl
Phenyl
4-Nitro phenyl
Table 4
Inhibitory activity of 2,3,4-trisubstituted benzofuran derivatives 19–31 (B series)
R2
OR3
O
R1
O
Compd
R1
R2
R3
IC50
(
l
M)
IC50
T. brucei
6.5 0.6
(lM)
P. falciparum
19
20
21
22
23
24
25
26
27
28
29
30
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
Cyclopropyl
Phenyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
Phenyl
4-Methoxyphenyl
1-Naphthyl
4-Chlorophenyl
3-Methoxy-4-O-pivaloyl-phenyl
2,4,6-Trimethoxyphenyl
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
>25
>25
>50
>25
>50
>50
>25
>50
>25
>50
>50
>50
7.7
4.2 0.5
1.5 0.2
3.7 0.7
4.6 0.1
2.0 0.2
11.8 2.6
8.3 1.3
12.4 1.8
5.5 1.2
8.4 1.2
>50
Cyclopropyl
Cyclopropyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
31
>50
Chloroquine
Pentamidine
0.072 0.0074
0.011 0.0017

M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
4889
Table 5
Inhibitory activity of 4-O-acyl benzofuran derivatives 32–51 (C series)
R2
O
O
O
R1
Compd
R1
R2
IC50
(lM)
IC50 (lM)
P. falciparum
T. brucei
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
m-Xylyl
Phenyl
4-Methoxyphenyl
2-Hydroxy-4,6-dimethoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-chlorophenyl
4-Nitrophenyl
Phenyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-Chlorophenyl
4-Nitrophenyl
Phenyl
4-Methoxyphenyl
1-Naphthyl
2-Ethoxy-1-naphthyl
4-Chlorophenyl
4-Nitrophenyl
Phenyl
>25
3.2 0.3
1.8 0.1
>50
11.2 0.1
7.9 0.3
>50
>50
>25
>50
>50
>50
>50
>25
>50
>50
>25
>25
>25
>50
>25
14.9 6.2
7.7 1.0
1.5 0.2
1.7 0.1
14.7 1.0
2.7 0.2
12.6 0.8
6.4 0.4
7.1 0.4
12.2 1.0
14.0
1.7 0.1
21.3 0.7
6.7 0.2
1.6 0.0
1.8 0.1
2.0 0.1
>25
6.0 0.9
highest activities were found when there is a 4-methoxyphenyl
group at position 2, though modification at this position is possible,
and with a p-substituted acyl group. On the other hand, benzofuran
derivative 51 substituted by a xylyl group was found to be the
100% B/A for 3.5 min followed by 0:100 isocratic for 1 min at a flow
rate of 0.6 mL/min, where solvent A was 0.1% formic acid in H2O
and solvent B was 0.1% formic acid in CH3CN. Purity was deter-
mined on TAC (total absorbance current from 200 to 400 nM).
most potent compound on P. falciparum with IC50 = 6.0 lM.
Accordingly these promising results are paving the way for further
investigations on neglected antiparasitic activity of polysubstitut-
ed benzofuran derivatives. For instance we envision to add amidine
or guanidine substituents that proved beneficial for antiparasitic
activities as reported by Tidwell’s group.10
5.2. Preparation of 2-substituted benzofurans 1–3 and 2-
substituted benzofuran-4-ols (11–14)
To a well-degazed MeCN (90 mL) via a 3 cycles of freeze-pump-
thaw, phenol derivative (1 mmol), PdCl2(PPh3)2 (5 mol %), degazed
Et3N (10 mmol), terminal alkyne (3 mmol) and CuI (10 mol %) were
successively added under argon. The reaction mixture was allowed
to stir overnight at 60 °C. The resulting solution was concentrated
under reduced pressure and the residue obtained was dissolved in
HCl 1 N solution and CH2Cl2. The aqueous layer was extracted with
CH2Cl2 (3 Â 10 mL). The combined organic layers were washed
with a saturated aq. NaCl solution, dried over anhydrous MgSO4
and concentrated under vacuum. The crude product was then puri-
fied by flash chromatography on silica gel.
5. Experimental section
5.1. General experimental procedures
All commercial reagents were used without any further purifi-
cation. Analytical thin-layer chromatography was carried out on
precoated silica gel aluminium plates (SDS TLC plates, silica gel
60F254). Column chromatography was performed prepacked Redi-
sep columns. Preparative TLC (PLC) was performed on Merck TLC
with silica gel 60F254. NMR spectra, including 1H, 13C (HMQC and
HMBC) experiments, were recorded on a Brucker Avance 300
(300 MHz) and Avance 500 (500 MHz) spectrometers. Chemical
shifts (d) are given in ppm relative to CDCl3 (7.26 ppm;
77.2 ppm), CD3OD (3.34 ppm; 49.9 ppm), acetone-d6 (2.05 ppm;
30.5 ppm) or DMSO-d6 (2.50 ppm; 39.5 ppm). Splitting patterns
are designed as: s, singlet; d, doublet; t, triplet; q, quartet; m, mul-
tiplet and combinations thereof. Coupling constants J are reported
in hertz (Hz). IR spectra were recorded on a Perkin–Elmer Spec-
trum BX. Mass spectra were recorded on Thermoquest AQA Navi-
gator with a TOF detection (ESI-HRMS) and on MALDI (matrix:
DCTB). UHPLC analyses were realized on Waters Acquity UPLC.
Melting points were measured on Büchi b-450 and are
uncorrected.
5.2.1. 2-(4-Methoxyphenyl)benzofuran (1)
Flash chromatography using as eluent: gradient heptane to hep-
tane/AcOEt 9:1 (v/v) in 25 min. The product was obtained as a
white amorphous solid (50%): 1H NMR (CDCl3) d 7.83 (d, 2H,
J = 9.0 Hz), 7.60–7.52 (m, 2H), 7.29–7.24 (m, 2H), 7.00 (d, 2H,
J = 8.7 Hz), 6.91 (s, 1H), 3.88 (s, 3H); 13C NMR (CDCl3) d 160.3,
156.4, 155.0, 129.8, 126.7, 124.7, 124.1, 123.2, 120.9, 114.6,
111.3, 100.0, 55.7; MS (ESI+, MeOH+CH2Cl2) m/z 224.8 [M+H]+.
5.2.2. 2-Cyclopropylbenzofuran (2)
Flash chromatography using as eluent: isocratic heptane. The
product was obtained as a colorless oil (88%): 1H NMR (Acetone-
d6) d 7.49–7.46 (m, 1H), 7.40–7.37 (m, 1H), 7.20 (td, 1H, J = 7.2,
1.8 Hz), 7.16 (td, 1H, J = 7.2, 1.8 Hz), 6.48 (s, 1H), 2.15–2.04 (m,
1H), 1.05–0.90 (m, 4H); 13C NMR (CDCl3) d 161.5, 155.2, 130.1,
123.8, 123.4, 120.9, 111.2, 101.0, 100.9, 9.81, 7.62; MS (MALDI)
m/z 158.06 [M]+; HRMS calcd for C11H10O+ [M]+ 158.0732, found
The purity of all target compounds was measured using re-
versed-phase UHPLC (HSS C-18, 2.1 Â 50 mm column): compounds
were eluted with 95:5 A/B for 0.5 min then with a gradient of 5–

4890
M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
158.0723; IR (neat, cmÀ1) 1604, 1455, 1176, 1043, 1025; UPLC
method (H2O/MeCN): rt, 4.62 min, 100%.
room temperature. The reaction mixture was then refluxed until
the reaction was complete. The cooled resulting solution was di-
luted with water and extracted three times with EtOAc. The com-
bined organic layers were washed two times with a saturated aq.
NaCl solution, dried over anhydrous MgSO4 and concentrated un-
der vacuum. The crude product was then purified by flash chroma-
tography on silica gel.
5.2.3. 2-Phenylbenzofuran (3)
Flash chromatography using as eluent: isocratic heptane. The
product was obtained as a white amorphous solid (70%): 1H NMR
(Acetone-d6)
d 7.94 (d, 2H, J = 7.5 Hz), 7.64 (dd, 1H, J = 7.5,
1.5 Hz), 7.57 (dd, 1H, J = 7.5, 1.5 Hz), 7.50 (td, 2H, J = 7.5 Hz), 7.40
(td, 1H, J = 8.1, 1.5 Hz), 7.31 (td, 1H, J = 7.5, 1.5 Hz), 7.29 (s, 1H),
7.25 (td, 1H, J = 7.5, 1.5 Hz); 13C NMR (Acetone-d6) d 156.7, 155.7,
131.3, 130.2, 129.8, 129.6, 125.6, 125.4, 124.0, 122.0, 111.9,
5.3.1. 4-(Benzyloxy)-2-(4-methoxyphenyl)benzofuran (15)
Flash chromatography using as eluent: gradient heptane to hep-
tane/EtOAc 9:1 (v/v) in 25 min. The product was obtained as a
white amorphous solid (93%). 1H NMR (CDCl3) d 7.79 (d, 2H, J = 9
0 Hz), 7.52–7.35 (m, 5H), 7.17 (d, 2H, J = 4,0 Hz), 7.05 (s, 1H),
6.98 (d, 2H, J = 9.0 Hz), 6.73 (t, 1H, J = 4.0 Hz), 5.23 (s, 2H), 3.86
(s, 3H); 13C NMR (CDCl3) d 159.8, 155.9, 154.8, 152.5, 137.2,
128.6, 128.0, 127.5, 126.3, 124.4, 123.4, 120.1, 114.3, 104.8,
104.6, 97.4, 70.3, 55.4; MS (ESI, MeOH+CH2Cl2) m/z 401.1
102.5; MS (MALDI) m/z 195.1 [M]+; HRMS calcd for C14H10O3
+
194.0732, found 194.0729; IR (neat, cmÀ1) 1456, 1259, 1170,
1020; mp: 120–121 °C; UPLC method (H2O/MeCN): rt, 5.16 min,
100%.
5.2.4. 2-(4-Methoxyphenyl)benzofuran-4-ol (11)
[M+H]+; HRMS calcd for C22H19O3 [M+H]+ 331.1334, found 331;
+
Flash chromatography using as eluent: gradient toluene to tol-
uene/EtOAc 95:5 (v/v) in 25 min. The product was obtained as a
brown amorphous solid (77%): 1H NMR (CDCl3) d 7.78 (d, 2H,
J = 9.0 Hz), 7.12–7.07 (m, 2H), 6.98 (d, 2H, J = 9.0 Hz), 6.95 (s, 1H),
6.62 (dd, 1H, J = 6.3, 2.1 Hz), 5.20 (s, 1H), 3.86 (s, 3H); 13C NMR
(CDCl3) d 160.0, 156.4, 155.2, 149.0, 126.4, 124.5, 123.4, 114.4,
112.1, 108.1, 104.4, 96.5, 55.5; MS (ESI, MeOH+CH2Cl2) m/z 241.1
1320; IR (neat, cmÀ1) 1610, 1244, 1072, 1021; mp: 113–114 °C;
UPLC method (H2O/MeCN): rt, 5.84 min, 100%.
5.3.2. 4-(Benzyloxy)-2-cyclopropylbenzofuran (16)
Flash chromatography using as eluent: isocratic heptane. The
product was obtained as a colorless oil (81%): 1H NMR (CDCl3) d
7.49–7.31 (m, 5H), 7.09 (t, 1H, J = 8.1 Hz), 7.03 (d, 1H, J = 8.1 Hz),
6.68 (d, 1H, J = 8.1 Hz), 6.49 (s, 1H), 5.18 (s, 2H), 2.06–1.97 (m,
1H), 1.01–0.90 (m, 4H); 13C NMR (CDCl3) d 159.4, 155.8, 152.0,
137.4, 128.7, 128.0, 127.5, 123.6, 119.6, 104.9, 104.5, 97.9, 70.4,
À
[M+H]+; HRMS calcd for C15H11O3 239.0708, found 239.0704; IR
(neat, cmÀ1) 3452, 1177, 1076 cmÀ1; mp: 159–160 °C; UPLC meth-
od (H2O/MeCN): rt, 4.13 min, 95%.
5.2.5. 2-Cyclopropylbenzofuran-4-ol (12)
9.36, 7.30; MS (ESI, MeOH+CH2Cl2) m/z 265.1 [M+H]+; HRMS calcd
for C18H17O2 [M+H]+ 265.1228, found 265.1211; IR (neat, cmÀ1
)
+
Flash chromatography using as eluent: gradient heptane to hep-
tane/EtOAc 8:2 (v/v) in 25 min. The product was obtained as a
brown oil (73%): 1H NMR (CDCl3) d 7.03 (t, 1H, J = 8.0 Hz), 6.99
(d, 1H, J = 8.0 Hz), 6.57 (d, 1H, J = 8.0 Hz), 6,40 (s, 1H), 4.93 (s,
1H), 2.03–1.99 (m, 1H), 1.00–0.92 (m, 4H); 13C NMR (CDCl3) d
159.6, 156.0, 148.3, 123.7, 118.1, 107.9, 104.1, 96.9, 9.39, 7.35;
1594, 1277, 1071, 1054; UPLC method (H2O/MeCN): rt, 5.49 min,
96%.
5.3.3. 4-(Benzyloxy)-2-phenylbenzofuran (17)
Flash chromatography using as eluent: gradient heptane to hep-
tane/EtOAc 95:5 (v/v) in 25 min. The product was obtained as a
white amorphous solid (86%): 1H NMR (CDCl3) d 7.89 (d, 2H,
J = 7.5 Hz), 7.54 (d, 2H, J = 7.2 Hz), 7.49–7.19 (m, 6H), 7.23–7.19
(m, 2H), 7.21 (s, 1H), 6.76 (dd, 1H, J = 8.7, 3.3 Hz), 5.25 (s, 2H);
13C NMR (CDCl3) d 156.2, 154.7, 152.6, 137.1, 130.6, 128.8, 128.6,
128.3, 128.0, 127.5, 125.0, 124.8, 120.0, 104.8, 104.8, 99.1, 70.3;
MS (MALDI) m/z 174.0 [M]+; HRMS calcd for C11H10O2 [M]+
+
174.0681, found 174.0681; IR (neat, cmÀ1) 2963, 1258, 1013,
794; UPLC method (H2O/MeCN): rt, 3.58 min, 100%.
5.2.6. 2-Phenylbenzofuran-4-ol (13)
Flash chromatography using as eluent: gradient heptane to hep-
tane/EtOAc 8:2 (v/v) in 25 min. The product was obtained as a beige
amorphous solid (76%): 1H NMR (CDCl3) d 7.86 (d, 2H, J = 7.5 Hz),
7.45 (t, 2H, J = 7.5 Hz), 7.35 (t, 1H, J = 7.5 Hz), 7.15 (d, 1H,
J = 7.0 Hz), 7.14 (t, 1H, J = 7.0 Hz), 7.10 (s, 1H), 6.64 (d, 1H,
J = 7.0 Hz), 5.06 (s, 1H); 13C NMR (CDCl3) d 157.0, 155.3, 149.2,
130.5, 128.9, 128.6, 125.1, 125.0, 118.6, 108.1, 104.6, 98.1; MS (MAL-
DI) m/z 210.05 [M]+ HRMS calcd for C14H10O2+ [M]+ 210.0680, found
210.0680; IR (neat, cmÀ1) 3272, 1603, 1251, 1028; mp: 163–164 °C;
UPLC method (H2O/MeCN): rt, 4.17 min, 100%.
MS (ESI, MeCN+CH2Cl2) m/z 301.1 [M+H]+; HRMS calcd for
C21H17O2 [M+H]+ 301.1228, found 301.1235; IR (neat, cmÀ1
)
+
1601, 1245, 1070, 1025; mp: 96–97 °C; UPLC method (H2O/MeCN):
rt, 5.92 min, 100%.
5.4. Methylation of benzofuran 11
To a solution of benzofuran 11 (1 mmol) in anhydrous DMF
(3 mL), K2CO3 (2 mmol) and methyl iodide (2 mmol) (stirring
20 min beforehand) at room temperature. The reaction mixture
was allowed to stir under argon at room temperature overnight.
The resulting solution was diluted with water and extracted three
times with EtOAc. The combined organic layers were washed three
times with a saturated aq. NaCl solution, dried over anhydrous
MgSO4 and concentrated under vacuum. The crude product was
then purified by flash chromatography on silica gel using an eluent
gradient heptane to heptane/EtOAc 9:1 (v/v) in 25 min.
5.2.7. 2-(3,5-Dimethylphenyl)benzofuran-4-ol (14)
Flash chromatography using as eluent: gradient heptane to hep-
tane/EtOAc 8:2 (v/v) in 25 min. The product was obtained as a
brown oil (12%): 1H NMR (CDCl3) d 7.49 (s, 2H), 7.15 (t, 1H,
J = 8.0 Hz), 7.12 (d, 1H, J = 8.0 Hz), 7.07 (s, 1H), 7.00 (s, 1H), 6.64
(dd, 1H, J = 8.0, 1.5 Hz), 5.22 (s, 1H), 2.39 (s, 6H); 13C NMR (CDCl3)
d 156.5, 155.4, 149.1, 138.5, 130.5, 130.3, 124.9, 122.8, 118.7,
108.1, 104.5, 97.9, 21.5; MS (MALDI) m/z 238.08 [M]+ HRMS calcd
for C16H14O2 [M]+. 238.0994, found 238.0980; IR (neat, cmÀ1
3260, 1605, 1254, 1084, 1031.
)
5.4.1. 4-Methoxy-2-(4-methoxyphenyl)benzofuran (18)
+
The product was obtained as a white amorphous solid (92%): 1H
(CDCl3) NMR d 7.78 (d, 2H, J = 8.5 Hz), 7.20–7.13 (m, 2H), 6.99 (s,
1H), 6.98 (d, 2H, J = 8.5 Hz), 6.66 (d, 1H, J = 7.5 Hz), 3.96 (s, 3H), 3.86
(s, 3H); 13C NMR (CDCl3) d 159.9, 156.0, 154.9, 153.4, 126.4, 124.5,
123.6, 119.9, 114.4, 104.5, 103.5, 97.3, 55.8, 55.5; MS(ESI, MeCN+CH2-
Cl2) m/z 255.1 [M+H]+; HRMS calcd for C16H15O3+ [M+H]+ 255.1021,
5.3. Benzylation of benzofuran-4-ol 11–14
To a solution of benzofuran-4-ol (1 mmol) in acetone (3 mmol),
K2CO3 (2 mmol) and BnBr (2 mmol) were successively added at

M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
4891
found 255,0947; IR (neat, cmÀ1) 1607, 1248, 1095, 1021; mp: 99–
100 °C; UPLC method (H2O/MeCN): rt, 5.08 min, 100%.
calcd for C21H15O2 [M+H]+ 299.1072, found 299,1062; IR (neat,
cmÀ1) 1650, 1578, 1243, 1060; mp: 94–96 °C; UPLC method
(H2O/MeCN): rt, 5.34 min, 100%.
+
5.5. Friedel–Crafts acylation of benzofurans 1–3, 15–17 and 18
5.5.5. (4-Nitrophenyl)(2-phenylbenzofuran-3-yl)methanone (8)
Flash chromatography using as eluent: heptane/EtOAc 95:5 (v/
v) in 25 min; second flash chromatography using as eluent: iso-
cratic toluene. The product was obtained as a yellow amorphous
solid (13%): 1H NMR (Acetone-d6) d 8.17 (d, 2H, J = 8.7 Hz), 8.00
(d, 2H, J = 8.7 Hz), 7.77 (d, 1H, J = 8.1 Hz), 7.72 (d, 1H, J = 8.1 Hz),
7.64 (dd, 2H, J = 9.0, 1.5 Hz), 7.49 (td, 1H, J = 8.1, 1.2 Hz), 7.39 (td,
1H, J = 8.1, 1.2 Hz), 7.34 (m, 3H); 13C NMR (Acetone-d6) d 190.9,
160.8, 155.0, 150.9, 144.2, 131.5, 131.2, 130.0, 129.8, 129.3,
128.7, 128.0, 126.8, 125.2, 124.2, 122.4, 112.2; MS (MALDI) m/z
To
a solution of benzofuran (1 mmol) and acyl chloride
(1.2 mmol) in anhydrous CH2Cl2 (2 mL), SnCl4 or AlCl3 (1.2 mmol)
was added under argon. The mixture was then stirred at room tem-
perature under argon until the reaction was complete (30 min–
3 h). The reaction was quenched by addition of crushed ice and
the mixture was stirred for one more hour. The resulting solution
was diluted with water and extracted three times with CH2Cl2.
The combined organic layers were dried over anhydrous MgSO4
and concentrated under vacuum. The crude product was then puri-
fied by flash chromatography on silica gel.
343.1 [M]+ HRMS calcd for C21H13NO4 [M]+ 343.0845, found
+
343.0845; IR (neat, cmÀ1) 1640, 1603, 1521, 1346, 1070; mp:
5.5.1. (2-(4-Methoxyphenyl)benzofuran-3-
134–135 °C; UPLC method (H2O/MeCN): rt, 5.26 min, 100%.
yl)(phenyl)methanone (4)
Flash chromatography using as eluent: heptane/EtOAc 95:5;
second flash chromatography using as eluent: toluene. The product
was obtained as a yellow oil (86%):1H NMR (Acetone-d6) d 7.83 (d,
2H, J = 8.7 Hz), 7.65 (d, 3H, J = 8.7 Hz), 7.55 (t, 1H, J = 8.7 Hz), 7.54
(d, 1H, J = 8.7 Hz), 7.43–7.37 (m, 3H), 7.29 (td, 1H, J = 8.7, 0.9 Hz),
6.90 (d, 2H, J = 8.7 Hz), 3.80 (s, 3H); 13C NMR (Acetone-d6) d
192.4, 162.0, 158.8, 154.5, 139.1, 133.9, 130.9, 130.4, 129.5,
129.4, 126.0, 124.7, 122.7, 121.9, 115.7, 114.8, 112.0, 55.8; MS
5.5.6. (2-hydroxy-4,6-dimethoxyphenyl)(2-(4-methoxyphenyl)
benzofuran-3-yl)methanone (9)
Flash chromatography using as eluent: heptane/EtOAc 8:2 (v/v)
in 25 min. The product was obtained as a yellow oil (17%): 1H NMR
(CDCl3) d 13.1 (s, 1H), 7.76 (d, 2H, J = 8.5 Hz), 7.52 (d, 1H,
J = 7.5 Hz), 7.40 (d, 1H, J = 7.5 Hz), 7.29 (t, 1H, J = 7.5 Hz), 7.21 (t,
1H, J = 7.5 Hz), 6.92 (d, 2H, J = 8.5 Hz), 6.19 (d, 1H, J = 2.5 Hz),
5.76 (d, 1H, J = 2.5 Hz), 3.87 (s, 3H), 3.85 (s, 3H), 3.18 (s, 3H);
13C NMR (CDCl3) d 193.2, 167.2, 162.7, 160.9, 155.7, 153.6, 129.4,
128.6, 124.6, 123.6, 122.9, 120.4, 118.6, 114.3, 111.3, 107.5, 93.8,
91.5, 56.0, 55.7; MS (ESI, MeOH+CH2Cl2) m/z 427.1 [M+Na]+; HRMS
calcd for C24H20O6Na+ [M+Na]+ 427.1158, found 427.1168; IR (neat,
cmÀ1) 1676, 1626, 1576, 1248, 1177, 1151, 1020, 827; UPLC meth-
od (H2O/MeCN): rt, 5.59 min, 94%.
(MALDI) m/z 328.1 [M]+ HRMS calcd for C22H16O3 [M]+
+
328.1099, found 328.1089; IR (neat, cmÀ1) 1724, 1608, 1253,
1176, 1027; UPLC method (H2O/MeCN): rt, 5.30 min, 100%.
5.5.2. (2-(4-Methoxyphenyl)benzofuran-3-yl)(4-nitrophenyl)
methanone (5)
Flash chromatography using as eluent: heptane/EtOAc 95:5 (v/
v) in 25 min. The product was obtained as a white amorphous solid
(27%): 1H NMR (Acetone-d6) d 8.18 (d, 2H, J = 9.0 Hz), 7.98 (d, 2H,
J = 9.0 Hz), 7.73 (d, 1H, J = 8.1 Hz), 7.67 (d, 1H, J = 8.1 Hz), 7.59 (d,
2H, J = 9.0 Hz), 7.44 (td, 1H, J = 8.1, 1.2 Hz), 7.35 (td, 1H, J = 8.1,
1.2 Hz), 6.88 (d, 2H, J = 9.0 Hz), 3.78 (s, 3H); 13C NMR (Acetone-
d6) d 190.9, 162.4, 161.2, 154.7, 150.8, 144.4, 131.7, 131.5, 128.9,
126.4, 125.1, 124.2, 122.3, 122.2, 115.4, 114.8, 112.1, 55.8; MS
5.5.7. (4-Hydroxy-2-(4-methoxyphenyl)benzofuran-3-yl)
(phenyl)methanone (19)
Flash chromatography using as eluent: isocratic toluene. The
product was obtained as a yellow oil (17%): 1H NMR (Acetone-d6)
d 9.56 (s, 1H), 7.70 (d, 2H, J = 8.0 Hz), 7.42 (t, 1H, J = 8.0 Hz), 7.41
(d, 2H, J = 8.5 Hz), 7.30 (t, 1H, J = 8.5 Hz), 7.25 (t, 1H, J = 8.0 Hz),
7.12 (d, 1H, J = 8.5 Hz), 6.79 (d, 2H, J = 8.5 Hz), 6.76 (d, 1H,
J = 8.5 Hz), 3.77 (s, 3H); 13C NMR (Acetone-d6) d 196.6, 162.1,
159.5, 156.2, 153.0, 139.0, 133.4, 132.1, 130.6, 128.9, 128.1,
122.7, 116.3, 114.6, 110.8, 103,1, 55.8; MS (ESI, MeCN+CH2Cl2)
(MALDI) m/z 373.1 [M]+ HRMS calcd for C22H15NO5 [M]+
+
373.0950, found 373.0945; IR (neat, cmÀ1) 1638, 1602, 1518,
1342, 1249, 1071, 1033; mp: 155–156 °C; UPLC method (H2O/
MeCN): rt, 5.23 min, 100%.
m/z 345.1 [M+H]+; HRMS calcd for C22H17O4 [M+H]+ 345.1127,
+
found 345.1141; IR (neat, cmÀ1) 3060, 1736, 1592, 1277, 1034;
UPLC method (H2O/MeCN): rt, 5.12 min, 92%.
5.5.3. (2-Cyclopropylbenzofuran-3-yl)(phenyl)methanone (6)
Flash chromatography using as eluent: heptane/EtOAc 95:5 (v/v)
in 25 min. The product was obtained as a white amorphous solid
(53%): 1H NMR (Acetone-d6) d 7.87 (d, 2H, J = 8.1 Hz), 7.67 (td, 1H,
J = 8.1, 1.2 Hz), 7.56 (td, 2H, J = 8.1, 1.2 Hz), 7.47 (dd, 2H, J = 7.5,
1.2 Hz), 7.29 (td, 1H, J = 7.5, 1.2 Hz), 7.23 (td, 1H, J = 7.5, 1.2 Hz),
2.27–2.18 (m, 1H), 1.27–1.21 (m, 2H), 1.12–1.05 (m, 2H); 13C NMR
(Acetone-d6) d 191.9, 166.5, 153.8, 140.8, 133.3, 129.8, 129.4, 128.4,
125.2, 124.5, 121.7, 117.1, 111.6, 11.0, 9.89; MS (ESI, MeOH+CH2Cl2)
m/z 263.1 [M+H]+; HRMS calcd for C18H15O2+ [M+H]+ 263.1072, found
263,1076; IR (neat, cmÀ1) 1630, 1567, 1270, 1049, 1027; mp: 111–
114 °C; UPLC method (H2O/MeCN): rt, 5.06 min, 93%.
5.5.8. (4-Methoxy-2-(4-methoxyphenyl)benzofuran-3-yl)
(phenyl)methanone (26)
Flash chromatography using as eluent: isocratic toluene. The
product was obtained as a pale yellow amorphous solid (82%):
1H NMR (Acetone-d6) d 7.89 (d, 2H, J = 7.5 Hz), 7.71 (d, 2H,
J = 9.0 Hz), 7.62 (t, 1H, J = 7.5 Hz), 7.49 (t, 2H, J = 7.5 Hz), 7.32 (t,
1H, J = 8.0 Hz), 7.25 (d, 1H, J = 8.0 Hz), 6.98 (d, 2H, J = 9.0 Hz),
6,76 (d, 1H, J = 8.0 Hz), 3.82 (s, 3H), 3.54 (s, 3H); 13C NMR (Ace-
tone-d6) d 193.5, 161.6, 155.3, 154.4, 139.4, 134.1, 132.1, 130.0,
129.4, 129.0, 128.1, 127.0, 123.0, 119.4, 115.1, 105.5, 105.0, 55.9,
55.7; MS (ESI, MeCN+CH2Cl2) m/z 359.1 [M+H]+; HRMS calcd for
5.5.4. Phenyl(2-phenylbenzofuran-3-yl)methanone (7)
C )
23H19O4+ [M+H]+ 359.1283, found 359,1308; IR (neat, cmÀ1
Flash chromatography using as eluent: heptane/EtOAc 95:5 (v/
v) in 25 min.The product was obtained as a white amorphous solid
(83%): 1H NMR (Acetone-d6) d 7.83 (d, 2H, J = 8.7 Hz), 7.70–7.67 (m,
3H), 7.55 (td, 2H, J = 8.7, 1.5 Hz), 7.44 (td, 1H, J = 8.7, 1.5 Hz), 7.42–
7.29 (m, 6H); 13C NMR (Acetone-d6) d 192.4, 158.2, 154.7, 138.9,
134.0, 130.7, 130.4, 129.4, 129.3, 129.2, 126.5, 124.8, 122.1,
117.0, 112.1; MS (ESI, MeOH+CH2Cl2) m/z 299.1 [M+H]+; HRMS
1669, 1598, 1246, 1090, 1020; mp: 161–164 °C; UPLC method
(H2O/MeCN): rt, 5.23 min, 100%.
5.6. Preparation of 4-O-acyl benzofurans 32–51
To a solution of 2-substituted benzofuran-4-ol (1 mmol) and
Et3N (1.2 mmol) in CH2Cl2 (2 mL), chloride acid (1.2 mmol) was

4892
M. Thévenin et al. / Bioorg. Med. Chem. 21 (2013) 4885–4892
added at 0 °C under argon. The mixture was allowed to stir 1-3 h
until the reaction was complete.
determined from the dose–response curves with drug concentra-
tions ranging from 100
the standard deviation of three independent experiments. Pentam-
l
M to 50 nM. IC50 value is the mean +/À
5.6.1. 2-(4-Methoxyphenyl)benzofuran-4-yl benzoate (32)
Flash chromatography using as eluent: gradient heptane to hep-
tane/EtOAc 8:2 (v/v) in 25 min. The product was obtained as a
white amorphous solid (77%): 1H NMR (Acetone-d6) d 8.27 (d,
2H, J = 8.1 Hz), 7.90 (d, 2H, J = 9.0 Hz), 7.78 (t, 1H, J = 8.1 Hz), 7.65
(t, 2H, J = 8.1 Hz), 7.52 (d, 1H, J = 8.1 Hz), 7.37 (t, 1H, J = 8.1 Hz),
7.52 (d, 1H, J = 8.1 Hz), 7.19 (s, 1H), 7.05 (d, 2H, J = 9.0 Hz), 3.86
(s, 3H); 13C NMR (Acetone-d6) d 165.1, 161.5, 157.2, 156.7, 144.7,
134.7, 130.9, 130.4, 129.7, 127.4, 125.0, 124.5, 123.4, 116.7,
115.3, 109.6, 98.0, 55.7; MS (ESI, MeCN+CH2Cl2) m/z 345.1
idine was used as antitrypanosomal drug control.
Acknowledgments
The authors thank O. Thoison and her co-workers for UHPLC
analyses, V. Guérineau for MALDI analyses, ICSN and CNRS for
financial support.
Supplementary data
[M+H]+; HRMS calcd for C22H16O4 [M+H]+ 345,1127, found
+
Supplementary data (procedures for the preparation of starting
materials, spectral and analysis results for the other compounds)
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.bmc.2013.07.002.
345,1134; IR (neat, cmÀ1) 1731, 1614, 1250, 1025; mp: 121–
123 °C; UPLC method (H2O/MeCN): rt, 5.59 min, 100%.
5.7. Biological assays
References and notes
5.7.1. Assay for in vitro inhibition of P. falciparum growth
The chloroquine-resistant strain FcB1/Colombia of P. falciparum
was maintained in vitro on human erythrocytes in RPMI 1640
medium supplemented by 8% (v/v) heat-inactivated human serum,
at 37 °C, under an atmosphere of 3% CO2, 6% O2, and 91% N2. In vi-
tro drug susceptibility assays was measured by [3H]-hypoxanthine
incorporation as described.24–26 Drugs were prepared in DMSO at a
10 mM concentration. Compounds were serially diluted two-fold
1. Murray, C. J. L.; Rosenfeld, L. C.; Lim, S. S.; Andrews, K. G.; Foreman, K. J.; Haring,
D.; Fullman, N.; Naghavi, M.; Lozano, R.; Lopez, A. D. Lancet 2012, 379, 413.
2. Simarro, P. P.; Jannin, J.; Cattand, P. PLoS Med 2008, 5, 174. e55.
3. El-Diwani, H.; Nakkady, S.; El-Shabrawy, O.; Gohar, A. K.; Hishmat, O. Arch.
Pharm. Res. 1988, 11, 41.
4. Ragab, F. A. E.-F.; Eid, N. M.; Hassan, G. S.; Nissan, Y. M. Chem. Pharm. Bull. 2012,
60, 110.
5. Kaltenbronn, J. S.; Quin Iii, J.; Reisdorph, B. R.; Klutchko, S.; Reynolds, E. E.;
Welch, K. M.; Flynn, M. A.; Doherty, A. M. Eur. J. Med. Chem. 1997, 32, 425.
6. Abdel-Wahab, B. F.; Abdel-Aziz, H. A.; Ahmed, E. M. Eur. J. Med. Chem. 2009, 44,
2632.
7. Masubuchi, M.; Ebiike, H.; Kawasaki, K.-i.; Sogabe, S.; Morikami, K.; Shiratori,
Y.; Tsujii, S.; Fujii, T.; Sakata, K.; Hayase, M.; Shindoh, H.; Aoki, Y.; Ohtsuka, T.;
Shimma, N. Bioorg. Med. Chem. 2003, 11, 4463.
8. Ryu, C.-K.; Song, A. L.; Lee, J. Y.; Hong, J. A.; Yoon, J. H.; Kim, A. Bioorg. Med.
Chem. Lett. 2010, 20, 6777.
9. Ismail, E.; Tawfik, A. A.; El-Ebrashi, N. M. Arzneim. -Forsch. 1977, 27, 1393.
10. (a) Bakunova, S. M.; Bakunov, S. A.; Wenzler, T.; Barszcz, T.; Werbovetz, K. A.;
Brun, R.; Hall, J. E.; Tidwell, R. R. J. Med. Chem. 2007, 50, 5807; (b) Bakunov, S.
A.; Bakunova, S. M.; Wenzler, T.; Barszcz, T.; Werbovetz, K. A.; Brun, R.; Tidwell,
R. R. J. Med. Chem. 2008, 51, 6927; (c) Bakunov, S. A.; Bakunova, S. M.; Bridges,
A. S.; Wenzler, T.; Barszcz, T.; Werbovetz, K. A.; Brun, R.; Tidwell, R. R. J. Med.
Chem. 2009, 52, 5763.
11. Gibson, P. S.; Lauret, C.; Patent WO 2008/102232 A1, 2008.
12. Benaim, G.; Hernandez-Rodriguez, V.; Mujica-Gonzalez, S.; Plaza-Rojas, L.;
Silva, M. L.; Parra-Gimenez, N.; Garcia-Marchan, Y.; Paniz-Mondolfi, A.;
Uzcanga, G. Antimicrob. Agents Chemother. 2012, 56, 3720.
13. Yu, Z.; Brannigan, J. A.; Moss, D. K.; Brzozowski, A. M.; Wilkinson, A. J.; Holder,
A. A.; Tate, E. W.; Leatherbarrow, R. J. J. Med. Chem. 2012, 55, 8879.
14. Wang, S.; Li, P.; Yu, L.; Wang, L. Org. Lett. 2011, 13, 5968.
15. Arcadi, A.; Blesi, F.; Cacchi, S.; Fabrizi, G.; Goggiamani, A. Tetrahedron Lett. 2011,
52, 5149.
16. Chen, W.; Li, P.; Miao, T.; Meng, L.-G.; Wang, L. Org. Biomol. Chem. 2013, 11, 420.
17. Arcadi, A.; Blesi, F.; Cacchi, S.; Fabrizi, G.; Goggiamani, A.; Marinelli, F.
Tetrahedron 2013, 69, 1857.
18. Singh, F. V.; Wirth, T. Synthesis 2012, 44, 1171.
19. Kitamura, T.; Otsubo, K. J. Org. Chem. 2012, 77, 2978.
20. Glaser, C. Ber. Dtsch. Chem. Ges. 1869, 2, 422.
21. Glaser, C. Ann. Chem. Pharm. 1870, 154, 137.
22. Johansson Seechurn, C. C. C.; Kitching, M. O.; Colacot, T. J.; Snieckus, V. Angew.
Chem., Int. Ed. 2012, 51, 5062.
23. Jacubert, M.; Hamze, A.; Provot, O.; Peyrat, J.-F.; Brion, J.-D.; Alami, M.
Tetrahedron Lett. 2009, 50, 3588.
24. Guillon, J.; Grellier, P.; Labaied, M.; Sonnet, P.; Léger, J.-M.; Déprez-Poulain, R.;
Forfar-Bares, I.; Dallemagne, P.; Lemaître, N.; Péhourcq, F.; Rochette, J.;
Sergheraert, C.; Jarry, C. J. Med. Chem. 2004, 47, 1997.
25. Desjardins, R. E.; Canfield, C. J.; Haynes, J. D.; Chulay, J. D. Antimicrob. Agents
Chemother. 1979, 16, 710.
26. Bosc, D.; Lethu, S.; Mouray, E.; Grellier, P.; Dubois, J. MedChemComm 2012, 3,
1512.
27. O’Brien, J.; Wilson, I.; Orton, T.; Pognan, F. Eur. J. Biochem. 2000, 267, 5421.
28. Hirumi, H.; Hirumi, K. Parasitol. Today 1994, 10, 80.
29. Bosc, D.; Mouray, E.; Grellier, P.; Cojean, S.; Loiseau, P. M.; Dubois, J.
MedChemComm 2013, 4, 1034.
30. Räz, B.; Iten, M.; Grether-Bühler, Y.; Kaminsky, R.; Brun, R. Acta Tropica 1997,
68, 139.
with 100
asite cultures (100
were then added to each well and incubated for 24 h at 37 °C prior
to the addition of 0.5
Ci of [3H]-hypoxanthine (GE Healthcare,
lL culture medium in 96-well plates. Asynchronous par-
lL, 1% parasitaemia and 1% final hematocrite)
l
France, 1–5 CiÁmmol/mL) per well. After a further incubation of
24 h, plates were frozen and thawed. Cell lysates were then col-
lected onto glass-fiber filters and counted in a liquid scintillation
spectrometer. The growth inhibition for each drug concentration
was determined by comparison of the radioactivity incorporated
in the treated culture with that in the control culture maintained
on the same plate. The concentration causing 50% growth inhibi-
tion (IC50) was obtained from the drug concentration–response
curve and the results were expressed as the mean values stan-
dard deviations determined from several independent experi-
ments. Chloroquine was used as antimalarial drug control.
5.7.2. Assay for in vitro inhibition of T. brucei gambiense growth
Bloodstream forms of T. brucei gambiense strain Feo were cul-
tured in HMI9 medium supplemented with 10% FCS at 37 °C under
an atmosphere of 5% CO2.28,29 In all experiments, log-phage cell
cultures were harvested by centrifugation at 3000g and immedi-
ately used. Drug assays were based on the conversion of a redox-
sensitive dye (resazurin) to a fluorescent product by viable cells.30
Drug stock solutions were prepared in pure DMSO. T. b. gambiense
bloodstream forms (3 Â 104 cells/ml) were cultured as described
above in 96-well plates (200
lL per well) either in the absence
or in the presence of different concentrations of inhibitors and with
a final DMSO concentration that did not exceeded 1%. After a 72-h
incubation, resazurin solution was added in each well at the final
concentration of 45 lM. Fluorescence was measured at 530 nm
excitation and 590 nm emission wavelengths after a further 4-h
incubation. Each inhibitor concentration was tested in triplicate
and the experiment repeated twice. The percentage of inhibition
of parasite growth rate was calculated by comparing the fluores-
cence of parasites maintained in the presence of drug to that of
in the absence of drug. DMSO was used as a control. IC50s were