Synthesis and cytotoxic activity of novel tetrahydrobenzodifuran–imidazolium salt derivatives

Article abstract of DOI:10.1016/j.bmcl.2017.02.053

The synthesis of a series of novel 4-substituted 2,3,6,7-tetrahydrobenzo [1,2-b;4,5-b′]difuran–1H-imidazolium salts is presented. The biological properties of the compounds were evaluated in vitro against a panel of human tumor cell lines. Results suggest that the 5,6-dimethyl-benzimidazole or 2-methyl-benzimidazole ring, and substitution of the imidazolyl-3-position with a 2-naphthylmethyl substituent or 2-naphthylacyl substituent, were important to the cytotoxic activity. Notably, 3-(2-Naphthylmethyl)-1-((2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b′]difuran-4-yl)methyl)-1H-5,6-dimethyl-benzimidazol-3-ium bromide (42) was found to be the most potent derivative against five human tumor cell lines with IC₅₀ values of 1.06–4.34?μM and more selective towards SMMC-7721, A549 and SW480 cell lines. 3-(2-Naphthylacyl)-1-((2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b′]difuran-4-yl)methyl)-1H-2-methyl-benzimidazol-3-ium bromide (37) showed higher selectivity to SMMC-7721 and MCF-7 cell lines with IC₅₀ values 2.7-fold and 8.4-fold lower than DDP. Study regarding to the antitumor mechanism of action showed that compound 37 could induce cell cycle G1 phase arrest and apoptosis in SMMC-7721 cells.

Full text of DOI:10.1016/j.bmcl.2017.02.053

Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and cytotoxic activity of novel tetrahydrobenzodifuran–
imidazolium salt derivatives
b,
Chao-Bo Zhang a, Yang Liu a, Zheng-Fen Liu a, Sheng-Zu Duan a, Min-Yan Li c, Wen Chen a, , Yan Li
⇑
⇑
,
Hong-Bin Zhang a, Xiao-Dong Yang a,
⇑
a Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, 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 Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, United States
a r t i c l e i n f o
a b s t r a c t
The synthesis of a series of novel 4-substituted 2,3,6,7-tetrahydrobenzo [1,2-b;4,5-b0]difuran–1H-imida-
zolium salts is presented. The biological properties of the compounds were evaluated in vitro against a
panel of human tumor cell lines. Results suggest that the 5,6-dimethyl-benzimidazole or 2-methyl-ben-
zimidazole ring, and substitution of the imidazolyl-3-position with a 2-naphthylmethyl substituent or
2-naphthylacyl substituent, were important to the cytotoxic activity. Notably, 3-(2-Naphthylmethyl)-
1-((2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b0]difuran-4-yl)methyl)-1H-5,6-dimethyl-benzimidazol-3-ium
bromide (42) was found to be the most potent derivative against five human tumor cell lines with IC50
Article history:
Received 25 October 2016
Revised 10 February 2017
Accepted 22 February 2017
Available online xxxx
Keywords:
Tetrahydrobenzodifurans
Imidazolium salts
Cytotoxic activity
Cell cycle
values of 1.06–4.34 lM and more selective towards SMMC-7721, A549 and SW480 cell lines. 3-(2-
Naphthylacyl)-1-((2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b0]difuran-4-yl)methyl)-1H-2-methyl-benzimidazol-
3-ium bromide (37) showed higher selectivity to SMMC-7721 and MCF-7 cell lines with IC50 values
2.7-fold and 8.4-fold lower than DDP. Study regarding to the antitumor mechanism of action showed that
compound 37 could induce cell cycle G1 phase arrest and apoptosis in SMMC-7721 cells.
Ó 2017 Elsevier Ltd. All rights reserved.
Apoptosis
Tetrahydrobenzodifurans and dihydrobenzofurans represent as
important classes of biologically active oxygen-containing hetero-
cycles. Naturally occurring compounds and biologically active
agents with dihydrobenzofuran and tetrahydrobenzodifuran
moieties exhibit a wide range of remarkable biological activities,
especially antitumor activity.1 As exemplified in Fig. 1, Megapodiol
with dihydrobenzofuran moiety is an anti-leukaemic agent,2
while Mesocyperusphenol A with tetrahydrobenzodifuran moiety
showed powerful cytotoxic activity against human T-cell leukemia
cells.3 Further study showed that Mesocyperusphenol A was a
potent 5-lipoxygenase inhibitor.4 On the other hand, imidazole
and their derivatives have attracted wide attention due to their
pharmaceutical potential resulting from their significant biological
activities,5 especially antitumor activity.6 For instance, natural imi-
dazolium chlorides Lepidiline A and B (Fig. 1) showed potent cyto-
toxic activity against four human cancer cell lines.7 However, to
the best of our knowledge, no scientific study on the exactly molec-
ular targets of Lepidilines was reported. Considering the value of
imidazolium salts, we have previously reported the synthesis of a
series of novel imidazolium salts, such as NMIB (Fig. 1), and their
potential antitumor activity.8 Further study of molecular mecha-
nisms showed that the imidazolium salt hybrids can induce the
cell cycle arrest and apoptosis in tumor cells.8c,g Studies on
molecular targets demonstrated that the imidazolium salt
hybrids may be the inhibitors of mTOR (mammalian target of
rapamycin) signaling.8i And the docking calculations also
supported this conclusion.8f,i
Molecular hybridization is a useful strategy in new drug design
and development during the past two decades.9 Considering the
anticancer activities of tetrahydrobenzodifuran, as well as the
potent cytotoxic activities of imidazole derivatives, we are inter-
ested in the preparation of the hybridizing compounds of 4-substi-
tuted 2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b0]difuran with imidazole
moieties. During the past several years, some anticancer agents
based on imidazolium salts were reported.8,10 To the best of
our knowledge, no reports concerning antitumor activity of
4-substituted 2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b0]difuran–imida-
zole hybrids could be found in the literature.
⇑
Corresponding authors.
E-mail addresses: chenwenchem@163.com (W. Chen), liyanb@mail.kib.ac.cn
Herein, a series of novel 4-substituted 2,3,6,7-tetrahydrobenzo
[1,2-b;4,5-b0] difuran imidazolium salts were synthesized to
(Y. Li), xdyang@ynu.edu.cn (X.-D. Yang).
http://dx.doi.org/10.1016/j.bmcl.2017.02.053
0960-894X/Ó 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Zhang C.-B., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.02.053

2
C.-B. Zhang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Fig. 1. Representative structures of dihydrobenzofuran, tetrahydrobenzodifuran and imidazolium salts.
Scheme 1. Synthesis of tetrahydrobenzodifuran–1H-imidazolium salts 12–46.
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C.-B. Zhang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
3
explore the cytotoxic activity of tetrahydrobenzodifuran–imida-
zole hybrids with the ultimate aim of developing potent antitumor
agents.
To prepare the tetrahydrobenzodifuran–1H-imidazolium salts,
hydroquinone 1 was selected as the starting material for the
synthese of a series of hybrid derivatives (12–46, Scheme 1).
Hydroquinone 1 was alkylated with 1-bromo-2-chloroethane in
acetone to afford 1,4-bis(2-chloroethoxy)benzene 2. Bromination
of bis(2-chloroethyl) ether 2 give the dibromo product 3. Cycliza-
tion of 3 by reacting with n-butyllithium in THF afforded tetrahy-
drobenzodifuran 4 in 80% yield.11 Formylation of key intermediate
4 with dichloro(methoxy)methane and SnCl4 to afford the 4-formyl
product 5. Reduction of 5 using NaCNBH3 afforded 4-methanol
tetrahydrobenzodifuran 6 in 96% yield. Then, 4-methanol com-
pound 6 was treated with the mesylate to afford the respective
tetrahydrobenzodifuran–imidazoles (8–11) bearing various imida-
zoles (imidazole, benzimidazole, 2-methyl-benzimidazole and
5,6-dimethyl-benzimidazole) by heating under DMF with 60–85%
yields (two steps).12 Finally, thirty-nine tetrahydrobenzodifuran–
1H-imidazolium salt derivatives (12–50) were synthesized with
good yields via treating tetrahydrobenzodifuran–imidazoles with
the various alkyl halides in refluxing toluene (58–95%).13 The
structures and yields of tetrahydrobenzodifuran–1H-imidazolium
salt derivatives are showed in Table 1.
Fig. 2. X-ray crystal structures of compound 30.
To confirm the structures of the tetrahydrobenzodifuran–1H-
imidazolium salts, compound 30 was selected as representative
compounds and characterized by X-ray crystallography (CCDC
1507586),14 as shown in Fig. 2.
The potential cytotoxicity of all above synthesized tetrahy-
drobenzodifuran–1H-imidazolium salts were evaluated in vitro
against a panel of human tumor cell lines, including leukaemia
(HL-60), myeloid liver carcinoma (SMMC-7721), lung carcinoma
Table 1
Structures and yields of compounds 8–50.
Entry
Compound
Imidazole ring
R2
X
Molecular formula
Yields (%)
1
2
3
4
5
6
7
8
8
9
Imidazole
Benzimidazole
2-Methyl-benzimidazole
5,6-Dimethyl-benzimidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Benzimidazole
Benzimidazole
Benzimidazole
Benzimidazole
Benzimidazole
–
–
–
–
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
14H14N2O2
18H16N2O2
19H18N2O2
20H20N2O2
65
76
73
80
90
87
75
81
78
73
64
76
79
58
74
82
64
65
71
63
71
71
73
80
66
67
78
64
86
62
64
72
93
95
68
74
84
70
67
76
62
80
78
10
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
37
38
39
40
41
42
43
44
45
46
47
48
49
50
4-Methylbenzyl
4-Bromobenzyl
2-Bromobenzyl
4-Nitrobenzyl
2-Naphthylmethyl
4-Methoxyphenacy
4-Bromophenacyl
Naphthylacyl
4-Methylbenzyl
4-Bromobenzyl
2-Bromobenzyl
4-Nitrobenzyl
2-Naphthylmethyl
Phenacyl
4-Methoxyphenacy
4-Bromophenacyl
Naphthylacyl
4-Methylbenzyl
4-Bromobenzyl
2-Bromobenzyl
4-Nitrobenzyl
2-Naphthylmethyl
Phenacyl
4-Methoxyphenacy
4-Bromophenacyl
Naphthylacyl
4-Methylbenzyl
4-Bromobenzyl
2-Bromobenzyl
4-Nitrobenzyl
2-Naphthylmethyl
Phenacyl
4-Methoxyphenacy
4-Bromophenacyl
Naphthylacyl
4-Methylbenzyl
4-Bromobenzyl
2-Naphthylmethyl
4-Bromophenacyl
22H23BrN2O2
21H20Br2N2O2
21H20Br2N2O2
21H20BrN3O4
25H23BrN2O2
23H23BrN2O4
22H20Br2N2O3
26H23BrN2O3
26H25BrN2O2
25H22Br2N2O2
25H22Br2N2O2
25H22BrN3O4
29H25BrN2O2
26H23BrN2O3
27H25BrN2O4
26H22Br2N2O3
30H25BrN2O3
27H27BrN2O2
26H24Br2N2O2
26H24Br2N2O2
26H24BrN3O4
30H27BrN2O2
27H25BrN2O3
28H27BrN2O4
27H24Br2N2O3
31H27BrN2O3
28H29BrN2O2
27H26Br2N2O2
27H26Br2N2O2
27H26BrN3O4
31H29BrN2O2
28H27BrN2O3
29H29BrN2O4
28H26Br2N2O3
32H29BrN2O3
28H29ClN2O2
27H26BrClN2O2
31H29ClN2O2
28H26BrClN2O3
9
10
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
37
38
39
40
62
42
43
Benzimidazole
Benzimidazole
Benzimidazole
Benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
2-Methyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
5,6-Dimethyl-benzimidazole
Cl
Cl
Cl
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4
C.-B. Zhang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Table 2
Cytotoxic activities of compounds 8–50 in vitrob (IC50
,
l
Ma).
Entry
Compound
HL-60
SMMC-7721
A-549
MCF-7
SW480
1
2
3
4
5
6
7
8
8
9
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
4.12
4.90
>20
2.30
>20
5.99
5.81
1.88
>20
3.63
>20
>20
1.76
>20
5.14
4.70
0.80
1.58
0.49
3.18
>20
1.06
5.68
2.71
4.04
1.95
0.38
0.57
0.29
2.38
2.06
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
17.81
>20
>20
5.66
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
10.67
>20
>20
16.12
7.73
>20
>20
>20
>20
9.14
>20
>20
>20
6.10
5.82
6.90
8.64
>20
4.34
>20
15.37
8.00
7.77
4.06
9.01
3.62
15.26
7.61
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
10
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
37
38
39
40
41
42
43
44
45
46
47
48
49
50
DDP
9
10
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
37
38
39
40
41
42
43
44
>20
>20
5.40
8.30
>20
2.62
>20
6.60
5.12
2.20
>20
4.86
>20
10.05
8.95
>20
4.11
>20
13.95
5.11
5.42
>20
7.22
>20
>20
5.95
5.25
>20
7.42
>20
>20
5.50
>20
>20
3.40
>20
>20
4.10
>20
>20
7.87
6.43
1.65
7.39
6.85
7.29
>20
3.94
7.80
9.87
12.66
8.67
7.98
8.05
8.34
17.97
13.93
10.12
8.29
4.49
6.15
10.13
7.87
>20
3.48
11.87
13.70
16.27
13.97
6.31
7.76
6.84
15.18
8.17
11.75
4.52
4.43
4.72
5.96
>20
2.99
17.43
6.87
6.23
5.64
6.49
6.61
2.98
12.98
12.36
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.
(A549), breast carcinoma (MCF-7) and colon carcinoma (SW480),
on the basis of the procedures in the literature.15 DDP (Cisplatin)
was chosen as positive control. The results were listed in Table 2.
As shown in Table 2, the structures of tetrahydrobenzodifuran–
imidazole derivatives have an evident influence on the inhibitory
activities. Tetrahydrobenzodifuran–imidazoles 8–11 and tetrahy-
drobenzodifuran–imidazolium salts 12–19 lacked activities against
higher inhibitory activity compared with DDP. However, com-
pounds 30–37 with 2-methyl-benzimidazole ring and 38–46 with
5,6-dimethyl-benzimidazole ring displayed powerful inhibitory
activities. Among them, compounds 33, 37 and 42, with a 2-naph-
thylmethyl or 2-naphthylacyl group at position-3 of the substi-
tuted benzimidazole ring, showed potent higher inhibitory
activity in vitro than DDP.
all tumor cell lines investigated at the concentration of 20
l
M.
For the substituents of imidazolium salts, a 4-nitrobenzyl sub-
stituent at position-3 of imidazole rings, such as 15, 23, 32 and
41, lacked activities against all tumor cell lines. A 2-bromobenzyl,
4-methylbenzyl, or phenacyl substituent at position-3 of imidazole
rings, such as 20, 22, 25, 29, 31 and 34, decreased the inhibitory
activities, while a 4-bromobenzyl, 4-bromophenacyl or 4-methox-
yphenacyl substituent, such as 21, 26, 27, 30, 35, 36 and 39, could
slightly improve the inhibitory activities. Especially, compound 39
However, their benzimidazolium salts 20–50 displayed some
degree or high cytotoxicity. This difference in inhibitory activities
between neutral molecules and their salts may be introduced by
the changes of molecular structure, charge distribution and water
solubility.16
For the imidazole rings (imidazole, benzimidazole, 2-methyl-
benzimidazole or 5,6-dimethyl-benzimidazole), imidazolium salts
12–19 with imidazole rings lacked activities against all tumor cell
lines. Meanwhile, compounds 20–28 with benzimidazole rings
showed medium inhibitory activities. Among them, only com-
pounds 24 and 28, bearing a 2-naphthylmethyl or 2-naphthylacyl
substituent at position-3 of the benzimidazole ring, exhibited
was more selective to HL-60 cell lines with IC50 values of 0.49 lM.
Interestingly, compared with above substituents, a 2-naphthyl-
methyl substituent in 24, 33 and 42 or 2-naphthylacyl substituent
in 28, 37 and 46 could cause obvious improvement of the
inhibitory activities against tumor cell lines. Most of these kinds
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C.-B. Zhang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
5
of slats exhibited strong cytotoxic activities and were more active
than DDP. Notably, compound 42, with a 2-naphthylmethyl sub-
stituent at position-3 of 5,6-dimethyl-benzimidazole, was found
to be the most potent derivative against five human tumor cell
38.30 0.03% and 91.23 2.26%, respectively, which were statisti-
cally significantly different from the control (4.61 0.52%).
The results of cell cycle analysis on SMMC-7721 cells treated
with compound 37 were presented in Fig. 3. Compared with the
control cells, the percentage of cells of G1 phase increased during
the cells incubated with compound 37 with a dose dependent
manner. Compound 37 treatment caused 79.59 0.75% cells in
G0/G1 phase as compared to control showing 70.12 0.18%. On
the contrary, the fraction of cells in S and G2/M phase decreased
slightly accordingly from 14.85 0.21% to 8.75 1.48% and
4.37 0.04% to 0.94 0.65%, respectively. The data showed that
compound 37 may induce G1 phase arrest in the cell cycle (Fig. 4).
In our previous work, we found that imidazolium salts which
were synthesized might be potential inhibitors of mTOR signal-
ing.8k In order to rationalize the observed SARs for this series of
compound, we attempted to dock compound 42 with some
crystal structure of proteins in this signaling pathway, e. g.
mTORC1, mTORC2, and PI3K, using Autodock 4.2. Although this
compound could not dock with mTORC1 or mTORC2, it could
lines investigated with IC50 values below 4.34 lM, and exhibited
inhibitory activity selectively against SMMC-7721, A549 and
SW480 cell lines compared with DDP. Meanwhile, compound 37
with a 2-naphthylacyl substituent was more selective to MCF-7
cell lines with IC50 value 8.4-fold lower than DDP.
For the different salts, imidazolium chlorides 47, 48, 49 and 50
displayed similar inhibitory activities to imidazolium bromides 38,
39, 42 and 45, respectively. Salt effect of different halides had little
effect on the cytotoxic activities of imidazolium salt derivatives.
This observation suggests that the existence of 5,6-dimethyl-
benzimidazole or 2-methyl-benzimidazole ring, and substitution
of the imidazolyl-3-position with
a
2-naphthylmethyl or
2-naphthylacyl group, were important for the antitumor activity.
In general, the structure-activity relationship (SAR) results were
summarized in Scheme 2.
SMMC-7721 cells were exposed to increasing concentrations of
compound 37 and cell apoptosis was determined with Annexin
V-FITC/PI double-labeled cell cytometry. As shown in Fig. 2, after
dock well with PI3Kc (PDB code 3PRZ). Fig. 5 shows that
compound 42 is predicted to engage a hydrogen bond with
ARG690 using furan oxygen, and it also shows that hybrid z1-c6
can foster van der Waals interactions with the gap bounded by
HIS295, ARG849, GLU846, TRP292, LEU657, ARG690, ARG277,
treatment of cells with compound 37 at 4, 8, 12, 16
lM for
48 h, the apoptotic cell rate was 4.96 0.49%, 5.83 0.47%,
Scheme 2. Structure analysis of tetrahydrobenzodifuran–1H-imidazolium salts.
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6
C.-B. Zhang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Fig. 3. Compound 37 caused significant apoptosis of SMMC-7721 cells. (A) Cells were treated with 4, 8, 12, 16
lM compound 37 for 48 h. Cell apoptosis was determined by
Annexin V-FITC/PI double-staining assay. (B) The quantification of cell apoptosis. Data represents the mean S.D. of three independent experiments.
Fig. 4. Compound 37 induces G1 phase arrest in SMMC-7721 cells. (A) Cells were treated with 2 and 4 lM of compound 37 for 24 h. Cell cycle was determined by PI staining
and cell cytometry. (B) The percentages of cells in different phases were quantified. At least three independent experiments were performed and data of one representative
experiment is shown.
ASP788, GLY868, TYR867, and PRO866. All these favorable
interactions contribute to achieve good docking score
Compound 42 was found to possess the most potent derivative
against five human tumor cell lines with IC50 values below
a
(AutoDock binding energy is ꢀ10.41 kcal/mol) and an excellent
inhibitory activity as it results from the experimental data. These
interesting findings would be helpful for our further research.
In summary, a series of novel 4-substituted 2,3,6,7-tetrahy-
drobenzo[1,2-b;4,5-b0] difuran–1H-imidazolium salts were syn-
thesized and proved to potent cytotoxic activity. Compounds 24,
28, 33, 37, 42 and 46, with a 5,6-dimethyl-benzimidazole or
2-methyl-benzimidazole ring, and 2-naphthylmethyl substituent
or 2-naphthylacyl substituent at position-3 of the benzimidazole
ring, were found to be the most potent derivatives. Notably,
4.34 lM and showed more selective towards SMMC-7721, A549
and SW480 cell lines. Compound 37 was more selective to
SMMC-7721 and MCF-7 cell lines with IC50 values 2.7-fold and
8.4-fold lower than DDP. Study on the antitumor mechanism of
action showed that compound 37 could induce cell cycle G1 phase
arrest and apoptosis in SMMC-7721 cells. The 4-substituted
2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b0]difuran–1H-imidazolium salts
24, 28, 33, 37, 42 and 46 are promising leads for further structural
modifications, guided by the valuable information obtained from
our SARs.
Please cite this article in press as: Zhang C.-B., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.02.053

C.-B. Zhang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
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Fig. 5. Model of compound 42 docked into PI3Kc.
12. General procedure for the preparation of tetrahydrobenzodifuran–imidazoles 8–11.
To a solution of compound 6 (1 mmol) in dichloromethane (30 mL) was added
methanesulfonyl chloride (1.5 mmol) and triethylamine (2 mmol) at 0 °C. The
resulting mixture was stirred at room temperature for 2 h. After quenching the
reaction with water (30 mL), the layers were separated. The organic phase was
dried over anhydrous Na2SO4 and concentrated, and carried over to the next
synthetic step. To the resulting, methanesulfonate was added imidazole, or
substituted imidazole (3 mmol), and the mixture was stirred in DMF (15 ml) at
reflux for 24–48 h (monitored by TLC). After cooling to room temperature, the
solvent was concentrated, and the residue was diluted with EtOAc (20 mL). The
organic layer was washed with water (20 mL) and brine (20 mL), dried over
anhydrous Na2SO4 and concentrated. The residue was purified using column
chromatography (silica gel, petroleum ether 60–90 °C: ethyl acetate = 2:1 to
1:1) to afford 8–11 in 65–80% yield (two steps). Compound 11: white powder,
yield 80%. IR mmax (cmꢀ1): 3435, 3072, 2963, 2887, 1629, 1452, 1329, 1223,
1160, 1010, 941, 860, 754. 1H NMR (400 MHz, DMSO) d: 8.11 (1H, s), 7.39 (1H,
s), 7.25 (1H, s), 6.62 (1H, s), 5.26 (2H, s), 4.58 (2H, t, J = 8.4 Hz), 4.39 (2H, t,
J = 8.4 Hz), 3.13 (2H, t, J = 8.4 Hz), 2.85 (2H, t, J = 8.4 Hz), 2.28 (3H, s), 2.27 (3H,
s). 13C NMR (100 MHz, DMSO) d: 154.42 (C), 152.26 (C), 143.88 (CH), 142.39 (C),
132.67 (C), 131.37 (C), 130.37 (CH), 126.96 (C), 125.49 (CH), 119.91(CH), 114.69
(C), 110.86 (CH), 106.30 (CH), 71.89 (CH2), 71.49 (CH2), 41.31 (CH2), 30.30
(CH2), 28.49 (CH2), 20.79 (CH3), 20.29 (CH3). HRMS (ESI-TOF) m/z Calcd for
Acknowledgments
This work was supported by grants from the Natural Science
Foundation of China (21662043, 21462049, 21332007 and
U1402227), Program for Changjiang Scholars and Innovative
Research Team in University (IRT13095) and Excellent Young
Talents of Yunnan University.
A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2017.02.
053.
References
C
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salts 12–46. A mixture of compound 8–11 (0.2 mmol), and phenacyl bromides
or alkyl bromides (0.24 mmol), was stirred in toluene (5 ml) at reflux for 12–
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m
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(CH), 126.76 (CH), 125.16 (C), 124.00(CH), 113.69 (CH), 113.52 (CH), 112.07 (C),
107.01 (CH), 72.32 (CH2), 71.66 (CH2), 52.39 (CH2), 43.53 (CH2), 30.02 (CH2),
28.76 (CH2), 11.34 (CH3). HRMS (ESI-TOF) m/z Calcd for C31H27N2O3 [MꢀBr]+
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Please cite this article in press as: Zhang C.-B., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.02.053