Design, synthesis and cytotoxic activities of novel hybrid compounds between 2-phenylbenzofuran and imidazole

Article abstract of DOI:10.1016/j.bmcl.2012.02.094

A series of novel hybrid compounds between 2-phenylbenzofuran and imidazole have been prepared and evaluated in vitro against a panel of human tumor cell lines. The results suggest that substitution of the imidazolyl-3-position with a naphthylacyl or brom

Full text of DOI:10.1016/j.bmcl.2012.02.094

Bioorganic & Medicinal Chemistry Letters 22 (2012) 2726–2729
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis and cytotoxic activities of novel hybrid compounds between
2-phenylbenzofuran and imidazole
Xiao-Dong Yang a, , Wei-Chao Wan a, Xiao-Yan Deng a, Yan Li b, , Li-Juan Yang c, Liang Li a,
⇑
⇑
Hong-Bin Zhang a
a Key Laboratory of Medicinal Chemistry for Natural Resource (Yunnan University), Ministry of Education, School of Chemical Science and Technology, Yunnan University,
Kunming 650091, PR China
b State Key Laboratory for Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Science, Kunming 650204, PR China
c Key Laboratory of Ethnic Medicine Resource Chemistry, State Ethnic Affairs Commission & Ministry of Education, Yunnan University of Nationalities, Kunming 650031, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel hybrid compounds between 2-phenylbenzofuran and imidazole have been prepared and
evaluated in vitro against a panel of human tumor cell lines. The results suggest that substitution of the
imidazolyl-3-position with a naphthylacyl or bromophenacyl group, were vital for modulating cytotoxic
activity. In particular, hybrid compound 15 was found to be the most potent compound against 4 strains
human tumor cell lines and more active than cisplatin (DDP), and exhibited cytotoxic activity selectively
against liver carcinoma (SMMC-7721).
Received 16 January 2012
Revised 27 February 2012
Accepted 28 February 2012
Available online 5 March 2012
Keywords:
Hybrid compound
Benzofuran
Ó 2012 Elsevier Ltd. All rights reserved.
Imidazole
Cytotoxic activities
Structure–activity relationships
Cancer remains one of the most difficult diseases worldwide to
treat and is the leading cause of human mortality exceeded only by
cardiovascular diseases.1 Therefore, developing new anticancer
drugs and more effective treatment strategies for cancer is of
importance.2 Natural products represent a significant source of
inspiration for the design of structural analogues with improved
pharmacological profile in medicinal chemistry.3 Naturally occur-
ring substituted-benzofurans are an important class of biologically
active oxygen-containing heterocycles. Natural products possess-
ing the 2-phenylbenzofuran moiety exhibit a broad range of bio-
logical and pharmacological activities.4 Recently, naturally
occurring benzofurans have been identified to possess antitumor
activity. As exemplified in Scheme 1, ebenfuran III5 and moracins
O6 are also 2-phenylbenzofuran derived compounds exhibiting po-
tent cytotoxic activities against human breast cancer cells and
hepatocellular cancer cells.5,6
activity against the human cancer cell lines.9 Recently, we have re-
ported the synthesis of a series of novel hybrid compounds of dihy-
drobenzofurans and imidazols moieties such as NMIB (Scheme 1)
and their potential antitumor activity.10
Molecular hybridization as a drug discovery strategy involves
the rational design of new chemical entities by the fusion of two
drugs, both active compounds and/or pharmacophoric units recog-
nized and derived from known bioactive molecules.11 Considering
the anticancer activities of naturally occurring 2-phenylbenzofu-
rans as well as the potent cytotoxic activities of natural and syn-
thetic imidazole derivatives, we were interested in synthesizing a
number of new hybrid compounds bearing 2-phenylbenzofuran
and imidazole moieties (Scheme 1).
Although benzofuran-triazoles hybrid molecules through a
heptyloxybenzene chain were synthesized and found to exhibit
CYP26A1 inhibitory activity by Simons,12 to the best of our knowl-
edge, no reports concerning antitumor activity for hybrid com-
pounds between 2-phenylbenzofuran and imidazole have been
reported.
In the present research, we have designed and synthesized a
series of novel hybrid compounds of imidazole scaffold-based
2-phenylbenzofurans. The purpose of this study was to investigate
the antitumor activity of 2-phenylbenzofuran-imidazole hybrids,
with the ultimate aim of developing novel potent antitumor
agents.
Imidazole and its derivatives have attracted considerable inter-
ests in recent years for their versatile properties in chemistry and
pharmacology. Biological activities of imidazolium salts have been
reported,7 especially antitumor activity.8 For example, two new
imidazolium halides (Scheme 1), Lepidiline A and Lepidiline B, iso-
lated from the roots of Lepidium meyenii, showed potent cytotoxic
⇑
Corresponding authors. Tel.: +86 871 5031119; fax: +86 871 5035538.
E-mail addresses: xdyang@ynu.edu.cn (X.-D. Yang), liyanb@mail.kib.ac.cn (Y. Li).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.02.094

X.-D. Yang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2726–2729
2727
Imidazole derivatives
Natural benzofuran moieties
OH
CHO
N
N
Cl
OH
O
MeO
R
HO
lepidiline A R = H
ebenfuran III
lepidiline B R = CH3
OH
OH
O
N
N
Br
HO
O
O
moracins O
NMIB
Hybrid Compounds
N
N
R
O
X
Scheme 1. Design of novel hybrid compounds.
As shown in Scheme 2, the key step in the formation of the
phenylbenzofuran backbone was readily achieved by reacting sal-
icylaldehydes (1) with 4-nitrobenzyl bromide (2) to produce 2-(4-
nitrophenyl)benzofuran (3, 78% yield) in refluxing DMF.13 The cor-
responding amino derivative 4 was prepared from compound 3 by
reduction with SnCl2 in refluxing toluene in 65% yield. Base on our
The potential cytotoxicity of all newly synthesized hybrid com-
pounds was evaluated in vitro against a panel of human tumor cell
lines according to procedures described in the literature.17 The pa-
nel consisted of myeloid liver carcinoma (SMMC-7721), colon carci-
noma (SW480), breast carcinoma (MCF-7), lung carcinoma (A549)
and leukaemia (HL-60).18 Cisplatin (DDP) was used as the reference
drug. The results are summarized in Table 2 (IC50 value, defined as
the concentrations corresponding to 50% growth inhibition).
As shown in Table 2, the structures of the hybrid compounds
have an obvious influence on the cytotoxic activities. 2-Phen-
ylbenzofuran-imidazole hybrid 5 lacked activity against all tumor
previous synthesis14
, 1-(4-(benzofuran-2-yl)phenyl)-substituted
imidazole 5 were prepared by treatment of 4-(benzofuran-2-
yl)benzenamine 4 with ammonia, formaldehyde and glyoxal.15 Fi-
nally, eleven phenylbenzofuran-based imidazolium salts (6–16)
were prepared with excellent yields by reaction of 1-phen-
ylbenzofuran-substituted imidazoles 5 with the corresponding
phenacyl and alkyl halides in refluxing toluene.16 The structures
and yields of hybrid compounds are shown in Tables 1.
cell lines investigated at the concentration of 40 lM. Meanwhile,
its imidazolium salt 11 with a 4-hydroxyphenacyl substituent at
position-3 of imidazole ring was inactive.
O
C
Br
t BuOK, DMF
H
NO2
reflux, 24h
78%
O
OH
NO2
3
4
2
1
SnCl2
EtOH
reflux, 12h
65%
30% glyoxal
MeOH, 70 oC
N
N
NH2
35% formaldehyde
NH4Cl, 85% H3PO4
O
O
62%
5
R
X
reflux, 12-24h
75-93%
toluene
N
N
R
R = phenacyl, benzyl or butyl
X = Br, I
O
X
6-16
Scheme 2. Synthesis of hybrid compounds 5–16.

2728
X.-D. Yang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2726–2729
Table 1
Structures and yields of hybrid compounds 5–16
Compound
R
X
Molecular formula
Mp (°C)
Yields (%)
5
6
7
8
9
10
11
12
13
14
15
16
–
–
C
C
C
C
25H19BrN2O2
24H19BrN2O
24H18Br2N2O
20H17BrN2O
Oil
62
93
86
89
85
85
90
92
84
88
82
75
Benzyl
2-Bromobenzyl
Allyl
Butyl
Phenacyl
4-Hydroxyphenacyl
4-Methoxyphenacyl
4-Fluorophenacyl
4-Bromophenacyl
Naphthylacyl
20-Phenyl-phenacyl
Br
Br
Br
I
Br
Br
Br
Br
Br
Br
Br
159–161
220–222
Oil
C21H21IN2O
Oil
C25H19BrN2O2
C25H19BrN2O3
C26H21BrN2O3
C25H18BrFN2O2
C25H18Br2N2O2
C29H21BrN2O2
155–157
255–257
215–217
177–179
252–254
221–223
194–196
C31H23BrN2O2
Table 2
Cytotoxic activities of hybrid compounds 5–16 in vitrob (IC50
However, imidazolium salt hybrids 6–9 with alkyl substituent
at position-3 of imidazole ring exhibited some degree of cytotoxic
activities. Among them, compound 7, bearing a 2-bromobenzyl
substituent at position-3 of imidazole, was the most active
compound, which displayed similar cytotoxic activity in vitro com-
pared with DDP.
Compared with above alkyl substituent imidazolium salt deriv-
atives 6–9, hybrid compounds 10–16 with phenacyl substituent at
position-3 of imidazole ring exhibited higher cytotoxic activity.
Most of this kind of derivatives showed moderate or potent activity
(except compound 11. The loss of potency in imidazolium salt 11 is
possibly due to the presence of a phenolic hydroxyl group in
phenacyl substituent.). Especially, compounds 14, 15 and 16, bear-
ing a naphthylacyl, bromophenacyl or phenylphenacyl substituent
at position-3 of the imidazole ring, displayed similar cytotoxic
activity in vitro compared with DDP. Interestingly, hybrid com-
pound 15, a naphthylacyl substituent at position-3 of imidazole,
was found to be the most potent derivative against all of human
,
l
Ma)
Compound
SMMC-7721
SW480
MCF-7
A549
HL-60
5
6
7
8
9
10
11
12
13
14
15
16
DDP
>40
>40
>40
>40
25.35
9.77
33.49
21.71
12.94
>40
9.79
19.65
8.46
10.93
6.79
11.68
>40
15.10
4.38
27.04
12.73
3.71
>40
3.71
13.54
3.39
1.65
3.31
8.86
19.92
12.71
>40
>40
10.34
>40
6.93
16.77
2.85
3.38
6.93
15.92
26.94
14.29
13.65
31.39
11.90
>40
11.28
16.69
2.84
5.37
1.97
14.49
11.76
2.61
>40
2.26
12.33
3.15
2.49
2.70
1.81
5.87
6.90
16.65
a
Cytotoxicity as IC50 for each cell line, is the concentration of compound which
reduced by 50% the optical density of treated cells with respect to untreated cells
using the MTT assay.
b
Data represent the mean values of three independent determinations.
N
N
R
N
N
O
O
X
(B)
(A)
hybrids:
benzofuran-imidazolium salts (B) > benzofuran-imidazole hybrids (A)
Better
phenacyl
benzyl
alkyl
>
R =
>
O
O
O
>
phenacyl =
>
Br
15 Among the best
16
14
O
O
O
O
>
>
OMe
>>
F
OH
12
10
13
11
Best Potent Compound
O
N
N
O
Br
15
Scheme 3. Structure–activity relationship of hybrid compounds.

X.-D. Yang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2726–2729
2729
8. (a) Fortuna, C. G.; Barresi, V.; Berellini, G.; Musumarra, G. Bioorg. Med. Chem.
2008, 16, 4150; (b) Ballistreri, F. P.; Barresi, V.; Benedetti, P.; Caltabiano, G.;
Fortuna, C. G.; Longo, M. L.; Musumarraa, G. Bioorg. Med. Chem. 2004, 12, 1689.
9. Cui, B.; Zheng, B. L.; He, K.; Zheng, Q. Y. J. Nat. Prod. 2003, 66, 1101.
10. (a) Yang, X. D.; Zeng, X. H.; Zhang, Y. L.; Qing, C.; Song, W. J.; Li, L.; Zhang, H. B.
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Qing, C.; Zhang, H. B. Bioorg. Med. Chem. Lett. 2010, 20, 1844; (c) Chen, W.;
Yang, X. D.; Li, Y.; Yang, L. J.; Wang, X. Q.; Zhang, G. L.; Zhang, H. B. Org. Biomol.
Chem. 2011, 9, 4250.
11. (a) Guantai, E. M.; Ncokazi, K.; Egan, T. J.; Gut, J.; Rosenthal, P. J.; Smith, P. J.;
Chibale, K. Bioorg. Med. Chem. 2010, 18, 8243; (b) Viegas Jnr, C.; Danuello, A.;
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tumor cell lines investigated and more active than DDP (except
against HL-60). Notably, this compound exhibited cytotoxic activ-
ity selectively against liver carcinoma (SMMC-7721) with IC50
value 5.4-fold more sensitive to DDP.
The results suggest that substitution of the imidazolyl-3-
position with a naphthylacyl or bromophenacyl group were vital
for modulating cytotoxic activity. The structure-activity relation-
ship (SAR) results were summarized in Scheme 3.
In conclusion, a series of novel 2-phenylbenzofuran-imidazole
hybrid compounds prepared in this research proved to be potent
antitumor agents. The hybrids 14 and 15, bearing a bromophenacyl
or naphthylacyl substituent at position-3 of the imidazole ring,
were found to be the most potent compounds. Compound 15
was found to be the most potent derivative against 4 strains
human tumor cell lines investigated and more active than DDP,
and exhibited cytotoxic activity selectively against liver carcinoma
(SMMC-7721). The phenylbenzofuran-based imidazolium salts 15,
14 and 16 can be considered promising leads for further structural
modifications guided by the valuable information derivable from
our detailed SARs.
12. Pautus, S.; Yee, S. W.; Jayne, M.; Coogan, M. P.; Simons, C. Bioorg. Med. Chem.
2006, 14, 3643.
13. Ono, M.; Cheng, Y.; Kimura, H.; Cui, M.; Kagawa, S.; Nishii, R.; Saji, H. J. Med.
Chem. 2011, 54, 2971.
14. (a) Liu, J. P.; Chen, J. B.; Zhou, Y. Y.; Li, L.; Zhang, H. B. Synthesis 2003, 2661; (b)
Liu, J. P.; Ren, Z. Y.; Zhou, Y. Y.; Zhang, H. B. Chin. J. Org. Chem. 2004, 24, 1091.
15. General procedure for the preparation of 2-phenylbenzofuran-imidazole hybrid 5.
To a magnetically stirred solution of the 30% glyoxal (1.2 mmol) and 35%
formaldehyde (1.2 mmol) in methanol (30 ml) at 70 °C, 4-(benzofuran-2-yl)
benzenamine 6 (1.0 mmol) and 25% ammonia (1.2 mmol) was added and
reaction mixture was stirred for 8 h at the same temperature. Reaction
progress was monitored by TLC. After removed the solvent, the dark residue
was poured into ice water (20 ml) and extracted by ethylacetate; organic layer
was washed by water and brine, dried (anhyd Na2SO4). The solvent was
evaporated under reduced pressure and the residue was chromatographed on
silica gel (petroleum ether 60–90 °C: ethyl acetate = 3:1) to afford 5 in 62%
yield. Compound 5: yellow oil. 1H NMR (300 MHz, CDCl3) d 7.91–7.88 (3H, m),
7.62 (2H, dd, J = 7.2, 6.6 Hz), 7.40 (2H, d, J = 8.4 Hz), 7.28–7.22 (4H, m), 7.01
(1H, s); 13C NMR (75 MHz, CDCl3): d 154.98, 154.44, 136.98, 135.42, 130.54,
129.65, 129.01, 128.78, 126.27, 124.73, 123.20, 121.48, 121.09, 117.97, 111.22,
102.08. HR-ESI-MS m/z Calcd for C17H12N2O 260.0950, found 260.0944.
16. General procedure for the preparation of 2-phenylbenzofuran imidazolium
Acknowledgment
This work was supported by Grants (30960460, 21062026,
2010GA014 and 2009CB522300) from National Natural Science
Foundation of China, Yunnan Province and National Basic Research
Program of China (973 Program).
bromides 6–16.
A mixture of 2-phenylbenzofuran-imidazole hybrids 5
(1 mmol) and alkyl bromides (1.2 mmol) was stirred in toluene (10 ml) at
reflux for 12–24 h. A white solid was formed. After completion of the reaction
as indicated by TLC, the precipitate was filtered through a small pad of Celite,
and washed with toluene (3 ꢀ 10 ml), then dried to afford 6–16 in 75–93%
yields. Pure samples were obtained after recrystallization from appropriate
solvent (acetone or methanol). Compound 15: white powder, yield 82%, mp
221–223 °C. 1H NMR (300 MHz, CDCl3): d 10.03 (1H, s), 8.92 (1H, s), 8.53 (1H,
s), 8.25–8.07 (9H, m), 7.84 (1H, d, J = 7.5), 7.78–7.66 (4H, m), 7.44–7.30 (2H, m),
6.36 (2H, s); 13C NMR (75 MHz, CDCl3): d 190.81, 153.95, 150.81, 136.68,
135.58, 134.54, 132.03, 130.86, 130.68, 129.71, 128.84, 128.41, 127.87, 127.42,
126.21, 125.52, 125.15, 123.38, 123.16, 122.47, 120.82, 120.37, 114.46, 111.23,
63.44. HRMS (ESI-TOF) m/z Calcd for C29H21N2O2 [M-Br]+ 429.1598, found
429.1596. Compound 14: white powder, yield 88%, mp 252–254 °C. 1H NMR
(300 MHz, CDCl3): d 9.62 (1H, s), 8.20 (1H, s), 8.10 (2H, s), 8.09 (2H, s), 7.77–
7.71 (3H, m), 7.60 (1H, d, J = 7.2), 7.58 (2H, d, J = 7.8), 7.50 (1H, d, J = 7.8), 7.30–
7.19 (3H, m), 6.07 (2H, s); 13C NMR (75 MHz, CDCl3): d 191.33, 155.75, 153.98,
136.56, 134.34, 133.26, 131.88, 130.15, 129.04, 128.04, 127.82, 126.55, 124.32,
123.51, 122.95, 121.87, 115.32, 112.53, 103.45, 56.98. HRMS (ESI-TOF) m/z
Calcd for C25H18BrN2O2 [MꢁBr]+ 457.0546, found 457.0543.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2012.02.094.
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18. The assay was in five kinds of cell lines (SMMC-7721, SW480, MCF-7, A549 and
HL-60). Cells were cultured at 37 °C under a humidified atmosphere of 5% CO2
in RPMI 1640 medium supplemented with 10% fetal serum and dispersed in
replicate 96-well plates. Compounds were then added. After 48 h exposure to
the compounds, cells viability were determined by the [3-(4,5-
dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide] (MTT) cytotoxicity
assay by measuring the absorbance at 570 nm with
spectrophotometer. Each test was performed in triplicate.
a microplate