Novel indole-based sigma-2 receptor ligands: synthesis, structure-affinity relationship and antiproliferative activity

Article abstract of DOI:10.1039/c5md00079c

We report the synthesis and biological evaluation of a series of indole-based σ₂ receptor ligands derived from siramesine. In vitro competition binding assays showed that these analogues possessed high to moderate affinity and selectivity for σ₂ receptors. Structure-affinity relationship analyses of these indole-based σ₂ receptor ligands were performed. In the 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, 1a and 1b displayed significant and comparable antiproliferative activity in DU145, MCF7 and C6 cells to siramesine. In cell cycle analyses, compounds 1a, 1b and siramesine were found to induce a G₁ phase cell cycle arrest in DU145 cells using flow cytometry. The combination of 5,6-dimethoxyisoindoline scaffold and N-(4-fluorophenyl)indole moiety was identified as a new σ₂ receptor ligand deserving further investigation as an antitumor agent.

Full text of DOI:10.1039/c5md00079c

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Novel indole-based sigma-2 receptor ligands:
synthesis, structure–affinity relationship and
antiproliferative activity†
Cite this: DOI: 10.1039/c5md00079c
Fang Xie,ab Torsten Kniess,b Christin Neuber,b Winnie Deuther-Conrad,b
Constantin Mamat,bc Brian P. Lieberman,d Boli Liu,a Robert H. Mach,d Peter Brust,b
a
Jörg Steinbach,bc Jens Pietzschbc and Hongmei Jia
*
We report the synthesis and biological evaluation of a series of indole-based σ2 receptor ligands derived
from siramesine. In vitro competition binding assays showed that these analogues possessed high to mod-
erate affinity and selectivity for σ2 receptors. Structure–affinity relationship analyses of these indole-based
σ2 receptor ligands were performed. In the 3-IJ4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide
(MTT) assay, 1a and 1b displayed significant and comparable antiproliferative activity in DU145, MCF7 and
C6 cells to siramesine. In cell cycle analyses, compounds 1a, 1b and siramesine were found to induce a
G1 phase cell cycle arrest in DU145 cells using flow cytometry. The combination of 5,6-dimethoxy-
isoindoline scaffold and N-IJ4-fluorophenyl)indole moiety was identified as a new σ2 receptor ligand deserv-
ing further investigation as an antitumor agent.
Received 23rd February 2015,
Accepted 14th April 2015
DOI: 10.1039/c5md00079c
www.rsc.org/medchemcomm
that in quiescent tumor cells.9–11 Moreover, σ2 receptor
ligands can rapidly internalize into tumor cells and activate
1. Introduction
Two subtypes of sigma (σ) receptors, termed σ1 and σ2, have
been identified.1 Both subtypes display different distributions
in the central nervous system and peripheral organs. The σ1
receptor contains 223 amino acids with two transmembrane
regions.2,3 It functions as “ligand-operated receptor chaper-
one” and regulates various ion channels, G protein-coupled
receptors, lipids, and other signaling proteins.4,5 In contrast,
the σ2 receptor has not been cloned so far, and its molecular
weight was estimated to be 21.5 kD. Recently, progesterone
receptor membrane component 1 (PGRMC1) was reported as
the putative σ2 receptor binding site.6
It is interesting that both subtypes are expressed in a vari-
ety of human and rodent tumor cell lines.7,8 However, the
expression of the σ2 receptor was found to be higher than
that of the σ1 receptor. In proliferating tumor cells, the den-
sity of the σ2 receptor was about 8- to 10-fold higher than
apoptosis via multiple pathways.12–15 Thus, the σ2 receptor
may both serve as a receptor-based biomarker to distinguish
different proliferative states of solid tumors and as a promis-
ing target for the treatment of cancer.16
In the past decades, morphans, indoles (siramesine analogues),
granatanes, flexible benzamides and N-cyclohexylpiperazines
have been reported to serve as selective σ2 receptor ligands.17
Among these ligands, siramesine (also known as Lu-28-179) and
its analogues, conformationally flexible amines such as RHM-1,
and PB28 analogues were more extensively investigated.17 Their
structures are presented in Fig. 1. Although clinical trials of
siramesine for the treatment of depression and anxiety were
paused in 2002, it proved to be non-toxic and well tolerated
in humans. Most importantly, siramesine was demonstrated to
induce cell death in many tumorigenic and immortalized cells
via different apoptotic pathways.12–14,18 To obtain selective σ2
receptor ligands with antiproliferative activity, we used
siramesine as the lead compound to design a series of novel
indole-based compounds. It was reported that the indole resi-
due and the butyl chain between the indole and the spirocyclic
piperidine moieties were important to maintain the σ2 receptor
selectivity for siramesine derivatives.17 We introduced different
functional groups to develop new σ2 receptor ligands. Moreover,
we also introduced the substituents with fluorine atom to find
PET radiotracers for σ2 receptor tumor imaging. The design
concept is shown in Fig. 2. First, by keeping the 4-fluorophenyl
ring at the indole N-atom and the butyl chain constant,
a Key Laboratory of Radiopharmaceuticals (Beijing Normal University), Ministry of
Education, College of Chemistry, Beijing Normal University, Beijing 100875,
China. E-mail: hmjia@bnu.edu.cn; Fax: +86 10 58808891; Tel: +86 10 58808891
b Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical
Cancer Research, POB 510119, D-01314 Dresden, Germany
c Technische Universität Dresden, Department of Chemistry and Food Chemistry,
D-01062 Dresden, Germany
d Department of Radiology, Perelman School of Medicine, University of
Pennsylvania, 231 S. 34th Street, Philadelphia, PA 19104, USA
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5md00079c
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Fig. 1 The structures of siramesine, RHM-1 and PB28.
Fig. 2 Design concept of the indole-based compounds.
3H-spiroIJ2-benzofuran-1,4′-piperidinyl) moiety was replaced by
different pharmacophores including σ1 preferred group C and
σ2 preferred group A, B, or D (1). Secondly, the 4-fluorophenyl
ring at the indole N-atom was replaced by a 2-fluoroalkyl group
(2). As a third approach, both the 4-fluorophenyl ring at the
indole N-atom and the 3H-spiroIJ2-benzofuran-1,4′-piperidinyl)
moiety were modified (3). Fourth, 4-fluorophenyl was replaced
by the 4-iodophenyl group, while the 3H-spiroIJ2-benzofuran-1,4′-
piperidinyl) moiety was replaced by C (4). Finally, the indole
core was replaced by 4-fluoro-benzophenone (5). Moreover, the
structure–affinity relationships (SAR) of these analogues for σ2
receptors were analyzed. The 3-IJ4,5-dimethythiazol-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) assay was performed to
investigate the antiproliferative activity of the most potent
ligands. In order to further support this, cell cycle analysis was
carried out to examine the effects of these potent compounds on
the cell cycle progression using flow cytometry in DU145 cells.
2. Results and discussion
2.1 Chemistry
The synthetic routes of fluorophenylindole derivatives 1a–1g
are depicted in Scheme 1. All compounds in this series were
prepared from the key bromobutyl derivative 6. Compounds 6,19
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Scheme 1 Synthesis of fluorophenylindole derivatives 1a–1g. Reagents and conditions: (a) K2CO3, NaI, DMF, 105 °C, overnight, 64–92%; (b) TFA,
CH2Cl2, °C, h; (c) K2CO3, NaI, CH3CN, 80 °C, h, for 1a, 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (16), 52%; for 1b, 5,6-
dimethoxyisoindoline (17), 52%; for 1c, 4-phenylpiperidine-4-carbonitrile (18), 42%; for 1d–1g, 12–15, 16–83%.
0
2
4
12,20 15 20 and 19 21 were synthesized according to the
method reported in the literature. Compound 7 or 8 reacted
with intermediates 9–11 under basic conditions, followed by
deprotection to obtain compounds 12–15 with yields of 56–95%.
N-Alkylation of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (16),
5,6-dimethoxyisoindoline (17), 4-phenylpiperidine-4-carbonitrile
(18) or 12–15 with compound 6 provided compounds 1a, 1b,
1c, or 1d–1g, respectively, with yields of 29–84%.
The synthetic route of compound 2 is presented in
Scheme 2. Protection of compound 19 with TBDMS chloride,
followed by N-alkylation of compound 20 with 2-bromo-
ethanol and tosylation of compound 21 with p-TsCl provided
compound 22. Deprotection of TBDMS and fluorination of
compound 22 with TBAF by a one-pot reaction afforded com-
pound 23 with yield of 56%. Tosylation of compound 23 led
to compound 24, which reacted with 3H-spiroij2-benzofuran-
1,4′-piperidine] (25) to obtain target compound 2.
alcohols 28 and 29 in 86% and 79% yield, respectively.
Alkylation with 1,4-dibromobutane yielded 30 and 31, followed
by fluorination with DAST to obtain 32 and 33. Finally, com-
pound 32 or 33 reacted with intermediate 16 to provide 3a and
3b, respectively. Compound 32 reacted with 25 to obtain 3c.
The synthetic routes of compounds 4 and 5 are depicted
in Scheme 4. Synthesis of compound 4 was similar to that of
compound 1c. Ullmann reaction between compound 19 and
1,4-diiodobenzene22 instead of the 4-fluorophenyl residue
provided 34 which was subsequently treated with PBr3 to
yield 35. Finally, reaction between 35 and intermediate 18
provided target compound 4. N-Alkylation of intermediate 16
with 5-bromo-1-IJ4-fluorophenyl)pentan-1-one (36) gave com-
pound 5 with yield of 62%.
2.2 In vitro radioligand competition studies and structure–
affinity relationship analyses
The synthetic routes of compounds 3a–3c are depicted in
Scheme 3. Reduction of indole-3-acetic acid (26) and indole-3-
propanoic acid (27) with LiAlH4 gave the corresponding
The affinities of the indole-based analogues for the σ1 and σ2
receptors were determined by radioligand competition binding
Scheme 2 Synthetic route of compound 2. Reagents and conditions: (a) TBDMSCl, imidazole, CH2Cl2, r.t., 2 h, 84%; (b) Ar atmosphere, 110 °C,
2-bromoethanol, NaH, DMF, overnight, 37%; (c) p-TsCl, DIPEA, DMAP, THF, r.t., 2 h, 18%; (d) TBAF, THF, r.t., overnight, 56%; (e) p-TsCl, DIPEA,
DMAP, THF, r.t., 2 h, 44%; (f) K2CO3, NaI, CH3CN, 3H-spiroij2-benzofuran-1,4′-piperidine] (25), 80 °C, 4 h, 38%.
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Scheme 3 Synthetic routes of compounds 3a–3c. Reagents and conditions: (a) Ar atmosphere, 0 °C, LiAlH4, anhydrous THF, 4 h, 86% for 28, 79%
for 29; (b) Ar atmosphere, 110 °C, 1,4-dibromobutane, NaH, DMF, overnight, 19% for 30, 34% for 31; (c) Ar atmosphere, −78 °C, DAST, anhydrous
CH2Cl2, 2 h, 58% for 32, 87% for 33; (d) K2CO3, NaI, CH3CN, 80 °C, 4 h, for 3a, 32, 16, 43%; for 3b, 33, 16, 36%; for 3c, 32, 25, 41%.
Scheme 4 Synthetic routes of compounds 4 and 5. Reagents and conditions: (a) 1,4-diiodobenzene, K2CO3, copper powder, DMF, 120 °C, 5 h,
23%; (b) PBr3, anhydrous CH2Cl2, 0 °C, 2 h, 58%; (c) K2CO3, NaI, CH3CN, 18, 80 °C, 4 h, 49%. (d) K2CO3, NaI, CH3CN, 16, 80 °C, 4 h, 62%.
assays as reported previously.23 (+)-[3H]Pentazocine and ij3H]1,3-
di-o-tolyl-guanidine (in the presence of 10 μM dextrallorphan)
were used as radioligands for the σ1 and σ2 receptors, respec-
tively. The results are listed in Table 1.
It was reported that siramesine possessed a subnanomolar
affinity IJIC50IJσ2) = 0.12 nM) and high subtype selectivity
IJIC50IJσ1) = 17 nM, IC50IJσ1)/IC50IJσ2) = 140) for σ2 receptors.24
More recently, Niso et al. revealed its high affinity IJKiIJσ2) =
12.6 nM) and low subtype selectivity IJKiIJσ1)/KiIJσ2) = 0.83).25
For comparison, we also synthesized this compound and our
sample showed nanomolar affinity IJKiIJσ2) = 3.08 nM) and low
subtype selectivity IJKiIJσ1)/KiIJσ2) = 1.52), which is in good
agreement with that reported by Niso et al.
but increased the subtype selectivity. Compounds 1a, 1b, 1d
and 1g showed moderate affinity IJKiIJσ2) = 48.4–68 nM) and
increased selectivity IJKiIJσ1)/KiIJσ2) = 4.8–10.7) compared to
siramesine. Compound 1d with substitution at the para-position
of the phenyl ring in group D showed comparable affinity to
compound 1g with substitution at the meta-position but
had a somewhat higher subtype selectivity. Substitution
at the para-position with an increased length of the
fluorooligoethoxylated chain (n = 2, 3) dramatically decreased
the affinities for σ1 and σ2 receptors (1e and 1f). In the litera-
ture, compound 1a was reported to possess nanomolar
affinity IJKiIJσ2) = 5.34 nM) and high subtype selectivity
IJKiIJσ1)/KiIJσ2)
=
260) for σ2 receptors.25 However, our
Keeping the 4-fluorophenyl ring at the indole N-atom and the
butyl chain constant, replacement of 3H-spiroIJ2-benzofuran-
1,4′-piperidinyl) moiety with σ1 preferred group C retained the
low nanomolar affinity and non-selectivity for σ2 receptors
(1c vs. siramesine). On the other hand, replacement with σ2
preferred group A, B, or D decreased the affinity for σ2 receptors
sample displayed only moderate affinity IJKiIJσ2) = 49.2 nM)
and selectivity IJKiIJσ1)/KiIJσ2) = 10.8). The above discrepancy
may result from the different experimental conditions
employed by different groups. It is interesting to note that
compound 1b with the 5,6-dimethoxyisoindoline moiety
displayed comparable affinity and selectivity to compound
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MCF7/adr cells.25 In order to find new scaffolds and new σ2
receptor ligands as potent antitumor agents, antiproliferative
activity of compounds 1a and 1b was evaluated in MCF7
(breast cancer), DU145 (androgen-independent human pros-
tate cancer) and C6 (rat glioma) cells using the MTT assay.
Antiproliferative activity of siramesine was also determined
in these cells as comparison. The effects of these compounds
on cellular viability were analyzed using different concentra-
tions between 100 nM and 100 μM. The results expressed as
EC50 values are shown in Table 2. All EC50 values were found
to be in the micromolar range. Compound 1a and siramesine
showed notable antiproliferative effects in MCF7 cells with
EC50 values of 20.9 and 23.6 μM, respectively, which are con-
sistent with that reported in the literature (with EC50 values
of 17.8 and 12.3 μM, respectively).25 It is interesting to note
that the new compound 1b exhibited the highest activity in
MCF7 cells. Moreover, compound 1b displayed notable and
comparable antiproliferative effects to compound 1a and
siramesine in DU145 cells. However, all of the three com-
pounds displayed a higher EC50 value in C6 cells than those
in the human DU145 and MCF7 tumor cells. Besides com-
pound 1a and siramesine, the indole-based compound 1b
with the 5,6-dimethoxyisoindoline moiety seems to be prom-
ising as an anti-tumor agent and warrants further evaluation.
Table
1 Binding affinities of indole-based analogues for σ1 and σ2
receptorsa
Compound
KiIJσ1) (nM)
KiIJσ2) (nM)
KiIJσ1)/KiIJσ2)
1a
530.8 181.1
1390 20
255.6 14.8
2.58 0.82
614 137
1110 252
2158 404
257 62.8
246 59.4
493.5 84.1
262.5 62.9
11.0 0.5
386 94
16.6 1.1
4.69 2.36
10.5 2.6
17
102.3 15.1
330 25
49.2 11.7
5.34 1.22
53.8 1.4
3.03 0.75
68.0 0.04
458 51
1879 11
48.4 2.65
44.0 28.1
27.5 0.7
28.5 4.9
29.8 1.6
18.5 5.7
12.4 0.6
3.08 0.68
12.6 0.1
0.12
10.8
260
4.8
0.9
9.0
2.4
1.1
5.3
5.6
17.9
9.2
0.4
20.9
1.3
1.5
0.8
140
3.6
1ab
1b
1c
1d
1e
1f
1g
2
3a
3b
3c
4
5
Siramesine
Siramesineb
Siramesinec
ISO-1
28.2 0.9
6.95 1.63
ISO-1d
47.5
a
Values are means standard deviation (SD) of three experiments
b
c
performed in triplicate. From ref. 25. IC50 value, from ref. 24.
d
From ref. 27.
1a. In the literature, 5-bromo-N-ij4-IJ5,6-dimethoxyisoindolin-2-
yl)butyl]-2,3-dimethoxybenzamide IJKiIJσ2) = 0.82 nM) was
found to possess ten-fold higher affinity for σ2 receptors com-
pared to 5-bromo-N-{4-ij6,7-dimethoxy-3,4-dihydroisoquinolin-
2IJ1H)-yl]butyl}-2,3-dimethoxybenzamide IJKiIJσ2) = 8.2 1.4 nM).26
These data indicate that the 5,6-dimethoxyisoindoline moiety
is a promising σ2 preferred group with less lipophilicity.
To evaluate a suitable approach for future fluorine-18
radiotracer development for imaging of σ2 receptors by posi-
tron emission tomography, a fluoroalkyl group was intro-
duced. Replacement of the 4-fluorophenyl ring at the indole
N-atom with a 2-fluoroethyl residue decreased the affinity for
σ2 receptors but slightly increased the subtype selectivity
(2 vs. siramesine). Compounds 3a and 3b with the σ2 pre-
ferred group A displayed comparable affinity for σ2 receptors
to ISO-1.27 However, compound 3b with a 3-fluoropropyl
group showed decreased selectivity in comparison to com-
pound 3a with a 2-fluoroethyl group. Replacement of σ2 pre-
ferred group A with 3H-spiroIJ2-benzofuran-1,4′-piperidinyl)
moiety increased the σ1 affinity significantly and thus
decreased the selectivity (3c vs. 3a). Moreover, replacement of
1-IJ4-fluorophenyl) moiety with 1-IJ4-iodophenyl) group slightly
decreased the affinity for σ2 receptors but increased the selec-
tivity (4 vs. 1c). Replacement of the whole indole moiety with
1-IJ4-fluorophenyl)carbonyl group dramatically increased the
affinity for σ1 receptors (5 vs. 1a, 5 vs. 3a, 5 vs. 3b), indicating
the high importance of the indole moiety to retain the selec-
tivity for σ2 receptors.
2.4 Cell cycle analysis
To further examine the antitumor activity of compounds 1a
and 1b, their effects on the cell cycle progression were ana-
lyzed by flow cytometry in DU145 cells. Cell cycle phase dis-
tribution in control DU145 cells and cells treated with differ-
ent concentrations of 1a, 1b and siramesine at 24 h time
point is presented in Fig. 3. The percentages of G1, S and G2
phases of the untreated DU145 cells (control) are 58.2%,
38.6% and 3.25%, respectively. Treatment with compound 1a
or 1b or siramesine increased the percentage of G1 cells in a
dose-dependent manner. After treatment with 40 μM 1a or
30 μM 1b, the percentages of G1 cells increased to 84.1% and
80.5%, respectively. At the same time, the percentages of S
cells decreased to 15.9% and 19.3%, respectively. The per-
centage of G1 phase cells was maintained at 75.7–77.2% after
treatment with 15 to 25 μM siramesine. These data suggest
that compounds 1a and 1b and siramesine could induce cell
cycle delay and arrest the cell cycle progression predomi-
nantly at the G1 phase in DU145 cells. It was reported that σ2
Table 2 EC50 values of compounds 1a and 1b in different tumor cellsa
EC50 (μM)
Cell lines
1a
1b
Siramesine
MCF7
MCF7b
DU145
C6
20.9 6.3
17.8 0.4
28.8 3.9
76.5 4.6
17.0 6.5
—
26.9 6.9
44.1 9.9
23.6 7.8
12.3 0.6
13.9 0.7
43.1 6.2
2.3 Antiproliferative activity
a
Recently, a series of compounds with the indole moiety were
reported to display antiproliferative activity in MCF7 and
Values are means
standard deviation (SD) of two to three
b
experiments performed in triplicate. From ref. 25.
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highest activity in MCF7 cells. Cell cycle analysis by flow
cytometry demonstrated that compounds 1a, 1b and
siramesine impaired the cell cycle progression predominantly
at the G1 phase in DU145 cells. The indole-based compound
1b with the 5,6-dimethoxyisoindoline moiety shows potential
as an antitumor agent and warrants further evaluation.
4. Experiments
4.1. Chemistry
All the chemicals or reagents were purchased from chemical
suppliers and used without further purification unless other-
wise noted. NMR spectra were recorded on a Varian Inova-
400 spectrometer or on a Bruker Avance III NMR spectrome-
ter at 400 (1H), 376 (19F), and 100 MHz (13C), respectively.
The chemical shifts of the spectra were reported in parts per
million (ppm) with tetramethylsilane (TMS) as an internal
standard, and coupling constants are reported in Hertz (Hz).
MS spectra were obtained using a Xevo TQ-S spectrometer
(Waters) with electrospray (ESI) as the ionization method.
High-resolution mass spectrometry (HRMS) was performed
on a LCT Premier XE ESI-TOF mass spectrometry instrument
(Waters, USA). Chromatographic separations were carried out
using Merck Silica Gel 60 (63–200 μm). TLC detections were
carried out using Merck Silica Gel 60 F254 sheets and TLCs
were developed by visualization under UV light (λ = 254 nm).
Microanalyses were carried out using a Hekatech CHNS ele-
mental analyser EuroEA 3000 or an Elementar 240C device
(PerkinElmer). The HPLC analyses were performed using an
AGILENT 1100 HPLC (Agilent Technologies, USA) equipped with
a DAD detector. Analyses were carried out using a Nucleodur
C18 ISIS column (250 × 4 mm, 5 μm, Macherey-Nagel, Germany)
with an eluent of acetonitrile/H2O (0.1% TFA) (30 : 70) at a flow
rate of 0.5 mL min−1. Cell cycle analysis was performed using
a BD FACSCalibur flow cytometer (BD Biosciences, California,
USA), and DNA distributions were analyzed using Modfit LT
MacIntel (Verity Software House, Topsham, ME, USA).
4.1.1. tert-Butyl 4-{4-ij2-IJ2-fluoroethoxy)ethoxy]phenyl}piperazine-
1-carboxylate (Boc-13). Compounds 7 (168 mg, 0.60 mmol) and
10 (190 mg, 0.72 mmol) were dissolved in CH3CN (25 mL),
followed by addition of K2CO3 (124 mg, 0.90 mmol) and NaI
(27 mg, 0.18 mmol). The mixture was heated under reflux
and stirred overnight. After cooling and filtration, the solvent
was removed under reduced pressure. The residue was puri-
fied by silica gel chromatography (PE (petroleum ether) : EE
(ethyl acetate) = 1 : 1) to afford Boc-13 (203 mg, 92%). 1H
NMR (400 MHz, CDCl3): δ 6.92–6.80 (m, 4H), 4.59 (dt, J = 47.7,
4.2 Hz, 2H), 4.10 (t, J = 5.8 Hz, 2H), 3.86 (t, J = 5.0 Hz, 2H), 3.82
(dt, J = 29.8, 4.2 Hz, 2H), 3.57 (t, J = 5.0 Hz, 4H), 3.00 (t, J = 4.8
Hz, 4H), 1.48 (s, 9H).
Fig. 3 Cell cycle phase distribution in control DU145 cells and cells
treated with different concentrations of 1a (A), 1b (B) and siramesine
(C) at 24 h time point.
ligands can induce the tumor cell death by multiple signaling
pathways.15 10 μM siramesine decreased the expression levels
of cyclin D1, which are responsible for progression through
the G1 phase in MDA-MB-435 cells in a time-dependent man-
ner. Thus, siramesine may block G1-phase progression by
decreasing cyclin D1 expression. In addition, siramesine also
mainly decreased cyclin B1 and pRb in MDA-MB-435 cells.
The investigation of the detailed mechanism in which com-
pounds 1a and 1b impair the G1 phase of the cell cycle pro-
gression in DU145 cells is in progress.
3. Conclusion
We have developed a series of indole-based σ2 receptor
ligands derived from siramesine. Structure–affinity relation-
ship analyses indicated the high importance of the indole
moiety and σ2 preferred group to improve the selectivity for
σ2 receptors. In the MTT experiments, compound 1b displayed
notable and comparable antiproliferative effects to com-
pound 1a and siramesine in DU145 cells and exhibited the
4.1.2. tert-Butyl 4-IJ4-{2-ij2-IJ2-fluoroethoxy)ethoxy]ethoxy}-
phenyl)piperazine-1-carboxylate (Boc-14). The procedure
described for the synthesis of Boc-13 was applied to com-
pounds 7 (152 mg, 0.55 mmol) and 11 (188 mg, 0.61 mmol)
1
to afford Boc-14 (171 mg, 75%). H NMR (400 MHz, CDCl3): δ
6.91–6.80 (m, 4H), 4.57 (dt, J = 47.7, 4.2 Hz, 2H), 4.09 (t, J =
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4.8 Hz, 2H), 3.84 (t, J = 4.8Hz, 2H), 3.81–3.70 (m, 6H), 3.57
(t, J = 5.0 Hz, 4H), 3.00 (t, J = 4.8Hz, 4H), 1.48 (s, 9H).
(2C), 24.9; 19F NMR (376 MHz, CDCl3): δ –116.0; MS (ESI+):
m/z = calcd. for C28H29FN2O2 [M + H]+ 445.2, found 445.2;
HRMS (EI): m/z calcd. for C28H29FN2O2 [M + H]+ 445.2291,
found 445.2296. Anal. calcd. for C28H29FN2O2 (444.54): C
75.65, H 6.58, N 6.30; found: C 75.14, H 6.62, N 6.30.
4.1.3. tert-Butyl 4-ij3-IJ2-fluoroethoxy)phenyl]piperazine-1-
carboxylate (Boc-15). The procedure described for the synthe-
sis of Boc-13 was applied to compounds 8 (414 mg, 1.49
mmol) and 9 (188 mg, 2.90 mmol) to afford Boc-15 (311 mg,
64%). 1H NMR (400 MHz, CDCl3): δ 7.18 (t, J = 8.2 Hz, 1H),
6.57 (d, J = 8.2 Hz, 1H), 6.51 (s, 1H), 6.44 (d, J = 8.1 Hz, 1H),
4.74 (dt, J = 47.4, 4.1 Hz, 2H), 4.20 (dt, J = 27.9, 4.1 Hz, 2H),
3.57 (t, J = 4.7 Hz, 4H), 3.14 (t, J = 4.4 Hz, 4H), 1.48 (s, 9H).
4.1.4. General procedure for the syntheses of compounds
12, 13, 14, and 15. The Boc-protected group of compound
Boc-12, Boc-13, Boc-14, or Boc-15 was cleaved using TFA in
dichloromethane solution at 0 °C for 1 h. Compounds 12–15
were obtained in nearly quantitative yields and used for the
next step without further purification.
4.2.3.
1-{4-ij1-IJ4-Fluorophenyl)-1H-indol-3-yl]butyl}-4-
phenylpiperdine-4-carbonitrile (1c). Compounds 6 (121 mg,
0.35 mmol) and 18 (89 mg, 0.48 mmol) and K2CO3 (483 mg,
3.5 mmol) in CH3CN (25 mL) afforded 1c as light-yellow oil
(66 mg, 42%). 1H NMR (400 MHz, MeOD) δ 7.52 (d, J = 7.7
Hz, 1H), 7.44–7.36 (m, 4H), 7.36–7.27 (m 3H), 7.25–7.20 (m,
1H), 7.19–7.10 (m, 3H), 7.09–7.04 (m, 1H), 7.03–6.98 (m, 1H),
2.94 (d, J = 12.1 Hz, 2H), 2.75 (t, J = 7.3 Hz, 2H), 2.39 (t, J = 7.7 Hz,
2H), 2.36–2.26 (m, 2H), 1.98 (t, J = 7.7 Hz, 4H), 1.75–1.65 (m, 2H),
1.61–1.51 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 137.0, 136.4,
135.8, 129.5, 129.1, 128.5 (2C), 126.0, 125.9, 125.6 (2C), 122.7,
120.4 (2C), 120.1, 119.1. 116.6, 116.3 (2C), 110.4, 57.7, 50.4 (2C),
41.9, 33.5 (2C), 27.3, 24.5, 23.6; MS (ESI+): m/z = calcd. for
C30H30FN3 [M + H]+ 452.3, found 452.7; HRMS (EI): m/z calcd.
for C30H30FN3 [M + H]+ 452.2502, found 452.2505. Anal. calcd.
for C30H30FN3·HCl·1/4H2O: C 73.16, N 8.53, H 6.45; found:
C 73.19, N 8.48, H 6.69.
4.2.4. 3-IJ4-{4-ij4-IJ2-Fluoroethoxy)phenyl]piperazin-1-yl}butyl)-
1-IJ4-fluorophenyl)-1H-indole (1d). Compounds 6 (180 mg,
0.52 mmol) and 12 (132 mg, 0.59 mmol) and K2CO3 (680 mg,
4.92 mmol) in CH3CN (25 mL) afforded 1d as white solid
(210 mg, 83%). 1H NMR (400 MHz, CDCl3): δ 7.65 (d, J =
7.6 Hz, 1H), 7.48–7.40 (m, 3H), 7.24–7.12 (m, 4H), 7.08 (s, 1H),
6.93–6.83 (m, 4H), 4.71 (dt, J = 47.4, 4.1 Hz, 2H), 4.16 (dt, J =
27.9, 4.2 Hz, 2H), 3.10 (t, J = 4.8 Hz, 4H), 2.84 (t, J = 7.4 Hz, 2H),
2.61 (t, J = 4.7 Hz, 4H), 2.46 (t, J = 7.6 Hz, 2H), 1.86–1.75
(m, 2H), 1.72–1.61 (m, 2H); 13C NMR (100 MHz, CDCl3): δ
160.8, 152.5, 146.3, 136.4, 136.1, 128.9, 125.9 (2C), 125.1, 122.5,
119.8, 119.4, 118.0 (2C), 117.8, 116.4 (2C), 115.5 (2C), 110.2,
82.1, 67.7, 58.6 (2C), 53.4, 50.4 (2C), 28.0, 26.9, 25.0; MS (ESI+):
m/z = calcd. for C30H33F2N3O [M + H]+ 490.3, found 490.6. Anal.
calcd. for C30H33F2N3O (489.60): C 73.60, H 6.79, N 8.58; found:
C 73.99, H 7.12, N 8.26.
4.2. General procedure for the syntheses of 1a–1g
3-IJ4-Bromobutyl)-1-IJ4-fluorophenyl)-1H-indole (6) and the
respective amine (12–18) were dissolved in CH3CN, followed by
addition of K2CO3. The mixture was heated under reflux and
stirred overnight. After cooling and filtration, the solvent was
removed under reduced pressure. The residue was purified by
silica gel chromatography (PE: EE = 1 : 1) to afford 1a–1g.
4.2.1.
2-{4-ij1-IJ4-Fluorophenyl)-1H-indol-3-yl]butyl}-6,7-
dimethoxy-1,2,3,4-tetrahydroisoquinoline (1a). The synthesis
of 1a was similar to that reported in the literature.25
3-IJ4-Bromobutyl)-1-IJ4-fluorophenyl)-1H-indole (18) (321 mg,
0.92 mmol), 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline
hydrochloride (5) (176 mg, 0.77 mmol) and K2CO3 (233 mg,
1.69 mmol) dissolved in CH3CN (25 mL) afforded 1a (185 mg,
44%) as light-yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.88–
7.66 (m, 1H), 7.50–7.40 (m, 3H), 7.28–7.13 (m, 4H), 7.10
(s, 1H), 6.60 (s, 1H), 6.52 (s, 1H), 3.85 (s, 3H), 3.84 (s, 3H), 3.57
(s, 2H), 2.90–2.80 (m, 4H), 2.72 (t, J = 5.9 Hz, 2H), 2.62–2.54
(m, 2H), 1.89–1.82 (m, 2H), 1.82–1.70 (m, 2H); 13C NMR (100
MHz, CDCl3): δ 160.7, 147.5, 147.2, 136.3, 136.0, 128.9, 126.1,
125.8, 125.7, 125.1, 122.4 (2C), 119.7, 119.3, 117.7, 116.3 (2C),
111.3, 110.1, 109.5, 58.1, 55.9 (2C), 55.7, 51.0, 28.5, 27.9, 27.1,
24.9; 19F NMR (376 MHz, CDCl3): δ –116.0; MS (ESI+): m/z =
calcd. for C29H31FN2O2 [M + H]+ 459.2, found 459.0; HRMS
(EI): m/z calcd. for C29H31FN2O2 [M + H]+ 459.2448, found
459.2441. Anal. calcd. for C29H31FN2O2·3/4H2O (472.08): C
73.78, H 6.94, N 5.93; found: C 73.52, H 6.83, N 5.74.
4.2.5 3-ij4-IJ4-{4-ij2-IJ2-Fluoroethoxy)ethoxy]phenyl}piperazin-
1-yl)butyl]-1-IJ4-fluorophenyl)-1H-indole (1e). Compounds
6
(488 mg, 1.41 mmol) and 13 (138 mg, 0.51 mmol) and K2CO3
(84 mg, 0.61 mmol) in CH3CN (25 mL) afforded 1e as light-
yellow oil (43 mg, 16%). 1H NMR (400 MHz, CDCl3): δ 7.65
(t, J = 7.6 Hz, 1H), 7.50–7.40 (m, 3H), 7.24–7.13 (m, 4H), 7.08
(s, 1H), 6.91–6.82 (m, 4H), 4.58 (dt, J = 47.7, 4.1 Hz, 2H), 4.09
(t, J = 4.8 Hz, 2H), 3.89–3.75 (m, 4H), 3.10 (t, J = 4.7 Hz, 4H),
2.84 (t, J = 7.4 Hz, 2H), 2.62 (t, J = 4.5 Hz, 4H), 2.46 (t, J =
7.6 Hz, 2H), 1.85–1.74 (m, 2H), 1.72–1.62 (m, 2H); 13C NMR
(100 MHz, CDCl3): δ 160.8, 152.8, 146.0, 136.3, 136.0, 128.9,
125.8, 125.8 (2C), 125.1, 122.5, 119.6 (2C), 118.0 (2C), 117.8,
116.4, 115.4 (2C), 110.2, 83.2, 70.6, 70.1, 68.0, 58.6 (2C), 53.4,
50.5 (2C), 28.0, 26.8, 25.0. HRMS (EI): m/z calcd. for
C32H37F2N3O2 [M + H]+ 534.2932, found 534.2916.
4.2.2.
3-ij4-IJ5,6-Dimethoxyisoindolin-2-yl)butyl]-1-IJ4-
fluorophenyl)-1H-indole (1b). Compounds 6 (233 mg, 0.67
mmol) and 17 (119 mg, 0.67 mmol) and K2CO3 (144 mg, 1.04
mmol) in CH3CN (25 mL) afforded 1b as brown solid (156
mg, 52%). 1H NMR (400 MHz, CDCl3): δ 7.65–7.69 (m, 1H),
7.49–7.41 (m, 3H), 7.25–7.15 (m, 4H), 7.11 (s, 1H), 6.74
(s, 2H), 3.91 (s, 4H), 3.86 (s, 6H), 2.87 (t, J = 7.4 Hz, 2H), 2.79
(t, J = 7.4 Hz, 2H), 1.92–1.83 (m, 2H), 1.78–1.67 (m, 2H); 13C
NMR (100 MHz, CDCl3): δ 160.7, 148.4 (2C), 136.3, 136.0,
131.6 (2C), 128.9, 125.8, 125.1, 122.4 (2C), 119.7, 119.3, 117.8,
116.3 (2C), 110.1, 106.8 (2C), 59.2 (2C), 56.1 (2C), 28.9, 27.8
4.2.6.
3-{4-ij4-IJ4-{2-ij2-IJ2-Fluoroethoxy)ethoxy]ethoxy}-
phenyl)piperazin-1-yl]butyl}-1-IJ4-fluorophenyl)-1H-indole (1f).
Compounds 6 (142 mg, 0.41 mmol) and 14 (129 mg, 0.41
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mmol) and K2CO3 (70 mg, 0.51 mmol) in CH3CN (25 mL)
afforded 1f (68 mg, 29%). H NMR (400 MHz, CDCl3): δ 7.65
2H), 2.73 (t, J = 7.5 Hz, 2H), 1.79–1.65 (m, 2H), 1.65–1.53
(m, 2H), 0.87 (s, 9H).
1
(d, J = 7.6 Hz, 1H), 7.48–7.40 (m, 3H), 7.24–7.14 (m, 4H), 7.08
(s, 1H), 6.91–6.82 (m, 4H), 4.56 (dt, J = 47.7, 4.1 Hz, 2H), 4.08
(t, J = 4.8 Hz, 2H), 3.83 (t, J = 4.8 Hz, 2H), 3.80–3.68 (m, 6H),
3.10 (t, J = 4.7 Hz, 4H), 2.84 (t, J = 7.4 Hz, 2H), 2.61 (t, J = 4.8
Hz, 4H), 2.46 (t, J = 7.6 Hz, 2H), 1.85–1.75 (m, 2H), 1.74–1.63
(m, 2H); 13C NMR (100 MHz, CDCl3): δ 160.7, 152.9, 145.9,
136.3, 136.0, 128.9, 125.8, 125.7, 125.1, 122.4, 119.5 (2C),
118.0 (2C), 117.7, 116.3 (2C), 115.3 (2C), 110.1, 83.1, 70.8,
70.5, 70.3, 69.9, 67.8, 58.6, 53.4 (2C), 50.5 (2C), 27.9, 26.8,
24.9; MS (ESI+): m/z = calcd. for C34H41F2N3O3 [M + H]+ 577.3,
found 577.4. Anal. calcd. for C34H41F2N3O3·2HCl·H2O
(668.64): C 61.07, H 6.78, N 6.28; found: C 61.47, H 6.80, N
6.38.
4.2.7. 3-IJ4-{4-ij3-IJ2-Fluoroethoxy)phenyl]piperazin-1-yl}butyl)-
1-IJ4-fluorophenyl)-1H-indole (1g). Compounds 6 (259 mg,
0.75 mmol) and 15 (168 mg, 0.75 mmol) and K2CO3 (132 mg,
0.97 mmol) in CH3CN (25 mL) afforded 1g as light-yellow oil
(130 mg, 35%). 1H NMR (400 MHz, CDCl3): δ 7.68–7.61
(m, 1H), 7.47–7.39 (m, 3H), 7.22–7.11 (m, 5H), 7.07 (s, 1H),
6.59–6.53 (m, 1H), 6.49 (t, J = 2.3 Hz, 1H), 6.44–6.36 (m, 1H),
4.71 (dt, J = 47.1, 4.2 Hz, 2H), 4.17 (dt, J = 27.8, 4.2 Hz, 2H),
3.18 (t, J = 5.2 Hz, 4H), 2.83 (t, J = 7.4 Hz, 2H), 2.57 (t, J =
5.0 Hz, 4H), 2.43 (t, J = 7.6 Hz, 2H), 1.87–1.71 (m, 2H), 1.73–
1.60 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 160.7, 159.4, 152.7,
136.3, 136.0, 129.7, 128.8, 125.8 (2C), 125.1, 122.4, 119.8, 119.3,
117.7, 116.3 (2C), 110.1, 109.3, 104.6, 103.2, 82.0, 67.0, 58.6,
53.2 (2C), 48.9 (2C), 27.9, 26.8, 24.9; 19F NMR (376 MHz,
4.2.10. 2-IJ3-{4-ij(tert-Butyldimethylsilyl)oxy]butyl}-1H-indol-
1-yl)ethyl 4-methylbenzenesulfonate (22). Compound 21 (805
mg, 2.32 mmol), TsCl (661 mg, 3.48 mmol), DIPEA (450 mg,
3.48 mmol), and DMAP (425 mg, 3.48 mmol) were dissolved
in 30 mL of THF. The mixture was stirred at room tempera-
ture for 2 h. After the solvent was removed under reduced
pressure, the crude product was extracted with CH2Cl2. The
organic layer was dried over MgSO4, filtered, and concen-
trated under vacuum. The residue was purified by silica gel
chromatography (PE : EE = 10 : 1) to afford 22 (208 mg, 18%).
1H NMR (400 MHz, CDCl3): δ 7.63–7.56 (m, 1H), 7.49 (d, J =
8.3 Hz, 2H), 7.17–7.04 (m, 5H), 6.80 (s, 1H), 4.36–4.24
(m, 4H), 3.72 (t, J = 6.3 Hz, 2H), 2.75 (t, J = 7.5 Hz, 2H), 2.36
(s, 3H), 1.86–1.73 (m, 2H), 1.73–1.64 (m, 2H), 0.97 (s, 9H).
4.2.11. 4-ij1-IJ2-Fluoroethyl)-1H-indol-3-yl]butan-1-ol (23).
TBAF (345 mg, 1.32mmol) and 22 (265 mg, 0.53 mmol) were
added into THF (20 mL). The mixture was stirred at room
temperature overnight. After the solvent was removed under
reduced pressure, the crude product was extracted with
CH2Cl2. The organic layer was dried over MgSO4, filtered, and
concentrated under vacuum. The residue was purified by sil-
ica gel chromatography (PE : EE = 3 : 1) to afford 23 (69 mg,
1
56%). H NMR (400 MHz, CDCl3): δ 7.63 (d, J = 7.9 Hz, 1H),
7.30 (d, J = 8.1 Hz, 1H), 7.43–7.21 (m, 2H), 7.17–7.10 (m, 1H),
6.95 (s, 1H), 4.69 (dt, J = 47.0, 5.0 Hz, 2H), 4.35 (dt, J = 25.7,
4.9 Hz, 2H), 3.68 (t, J = 6.5 Hz, 2H), 2.80 (t, J = 7.4 Hz, 2H),
1.87–1.75 (m, 2H), 1.75–1.63 (m, 2H).
CDCl3):
δ
–120.7, −228.6; MS (ESI+): m/z
=
calcd. for
4.2.12. 4-ij1-IJ2-Fluoroethyl)-1H-indol-3-yl]butyl 4-methyl-
benzenesulfonate (24). To a solution of 23 (120 mg, 0.51
mmol) in THF (20 mL), TsCl (116 mg, 0.61 mmol), DIPEA
(129 mg, 1.00 mmol), and DMAP (122 mg, 1.00 mmol) were
added. The mixture was stirred at room temperature for 2 h.
After the solvent was removed under reduced pressure, the
crude product was extracted with CH2Cl2. The organic layer
was dried over MgSO4, filtered, and concentrated under vac-
uum. The residue was purified by silica gel chromatography
C30H33F2N3O [M + H]+ 490.3, found 490.5; HRMS (EI): m/z
calcd. for C30H33F2N3O [M + H]+ 490.2670, found 490.2673.
Anal. calcd. for C30H33F2N3O·H2O (507.61): C 70.98, H 6.95, N
8.28; found: C 71.18, H 6.87, N 8.01.
4.2.8.
3-{4-ij(tert-Butyldimethylsilyl)oxy]butyl}-1H-indole
(20). To a solution of 19 (2.10 g, 11.1 mmol) in CH2Cl2 (40
mL), TBDMSCl (2.06 g, 13.7 mmol) and imidazole (1.43 g,
21.0 mmol) were added. The mixture was stirred at room
temperature for 2 h. After filtration, the solvent was removed
under reduced pressure. The residue was purified by silica
gel chromatography (PE : EE = 1 : 5) to afford 20 (2.80 g, 84%).
1H NMR (400 MHz, CDCl3): δ 7.87 (s, 1H), 7.58 (d, J = 7.9 Hz,
1H), 7.32 (d, J = 8.1 Hz, 1H), 7.20–7.13 (m, 1H), 7.12–7.04 (m, 1H),
6.95 (s, 1H), 3.63 (t, J = 6.5 Hz, 2H), 2.75 (t, J = 7.5 Hz, 2H),
1.80–1.68 (m, 2H), 1.65–1.58 (m, 2H), 0.87 (s, 9H).
4.2.9. 2-IJ3-{4-ij(tert-Butyldimethylsilyl)oxy]butyl}-1H-indol-1-
yl)ethanol (21). To a solution of compound 20 (1.88 g, 6.19
mmol) in DMF, 2-bromoethanol (1.23 g, 9.92 mmol) and
NaH (240 mg, 10.0 mmol) were added. The mixture was
stirred at 110 °C overnight. After cooling, the crude product
was extracted with ethyl acetate, dried with anhydrous
MgSO4, and purified by silica gel column chromatography
(PE : EE = 5 : 1) to afford 21 (805 mg, 37%). 1H NMR (400
MHz, CDCl3): δ 7.57 (d, J = 7.9 Hz, 1H), 7.30 (d, J = 8.2 Hz,
1H), 7.20–7.15 (m, 1H), 7.10–7.05 (m, 1H), 6.91 (s, 1H), 4.21
(t, J = 5.3 Hz, 2H), 3.92 (t, J = 5.3 Hz, 2H), 3.62 (t, J = 6.4 Hz,
1
(PE : EE = 5 : 1) to afford 24 (88 mg, 44%). H NMR (400 MHz,
CDCl3): δ 7.76 (d, J = 8.3 Hz, 2H), 7.50 (d, J = 7.9 Hz, 1H),
7.32–7.16 (m, 4H), 7.11–7.05 (m, 1H), 6.86 (s, 1H), 4.66 (dt, J =
47.0, 5.0 Hz, 2H), 4.32 (dt, J = 25.8, 5.0 Hz, 2H), 4.07–3.99
(m, 2H), 2.68 (t, J = 6.7 Hz, 2H), 2.40 (s, 3H), 1.75–1.68 (m, 4H).
4.2.13.
1′-{4-ij1-IJ2-Fluoroethyl)-1H-indol-3-yl]butyl}-3H-
spiroijisobenzofuran-1,4′-piperidine] (2). To a solution of 24
(88 mg, 0.23 mmol) in 20 mL of CH3CN, 3H-spiroijisobenzo-
furan-1,4′-piperidine] (25) (32 mg, 0.17 mmol) and K2CO3 (32
mg, 0.23 mmol) were added. The mixture was stirred at 80 °C
for 4 h. After the solvent was removed under reduced pres-
sure, the residue was purified by silica gel chromatography
1
(PE : EE = 1 : 1) to afford 2 (26 mg, 38%). H NMR (400 MHz,
CDCl3): δ 7.62 (d, J = 7.8 Hz, 1H), 7.31–7.25 (m, 3H), 7.24–
7.20 (m, 2H), 7.18–7.09 (m, 2H), 6.96 (s, 1H), 5.08 (s, 2H),
4.70 (dt, J = 47.0, 5.0 Hz, 2H), 4.36 (dt, J = 25.5, 5.0 Hz, 2H),
2.90 (d, J = 11.2 Hz, 2H), 2.80 (t, J = 7.3 Hz, 2H), 2.49 (t, J =
10.0 Hz, 2H), 2.41 (t, J = 11.1 Hz, 2H), 2.07–1.97 (m, 2H),
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1.84–1.63 (m, 6H); 13C NMR (100 MHz, CDCl3): δ 145.9,
139.1, 136.6, 128.5, 127.8, 127.6, 125.4, 121.9, 121.2, 121.1,
119.5, 119.1, 116.3, 109.1, 84.2, 81.8, 71.0, 59.1, 50.5 (2C),
46.5, 36.8 (2C), 28.5, 27.2, 25.2; 19F NMR (376 MHz, CDCl3):
δ –219.8; MS (ESI+): m/z = calcd. for C26H31FN2O [M + H]+
407.2, found 407.2; HRMS (EI): m/z calcd. for C26H31FN2O
[M + H]+ 407.2499, found 407.2492; purity (HPLC): 95%.
4.2.14. 2-IJ1H-Indol-3-yl)ethanol (28). Under ice bath and
argon atmosphere, a solution of 26 (1.00 g, 5.71 mmol) in
THF (60 mL) was added to a solution of LiAlH4 (642 mg, 17.1
mmol) in THF (40 mL). The mixture was stirred for 4 h at
room temperature, followed by addition of ethanol until no
H2 was formed. Then 4 M hydrochloric acid was added to
adjust the pH to 5. After filtration, the solution was concen-
trated under reduced pressure. The crude product was
extracted with ethyl acetate, dried with anhydrous MgSO4,
and purified by silica gel column chromatography (PE : EE =
extracted with ethyl acetate, dried with anhydrous MgSO4,
and purified by silica gel column chromatography (PE :EE =
10 : 1) to afford 32 (315 mg, 58%). H NMR (400 MHz, CDCl3):
1
δ 7.58 (d, J = 7.9 Hz, 1H), 7.30 (d, J = 8.2 Hz, 1H), 7.23–7.18
(m, 1H), 7.14–7.08 (m, 1H), 6.96 (s, 1H), 4.67 (dt, J = 47.2, 6.7 Hz,
2H), 4.11 (t, J = 6.9 Hz, 2H), 3.36 (t, J = 6.5 Hz, 2H), 3.15 (dt, J =
22.2, 6.5 Hz, 2H), 2.03–1.95 (m, 2H), 1.90–1.79 (m, 2H).
4.2.19. 1-IJ4-Bromobutyl)-3-IJ3-fluoropropyl)-1H-indole (33).
The procedure described for the synthesis of 32 was applied
to DAST (205 mg, 1.28 mmol) and 31 (360 mg, 1.16 mmol) to
afford 33 (315 mg, 87%). 1H NMR (400 MHz, CDCl3): δ 7.63
(d, J = 7.9 Hz, 1H), 7.33 (d, J = 8.2 Hz, 1H), 7.28–7.22 (m, 1H),
7.17–7.11 (m, 1H), 6.92 (s, 1H), 4.53 (dt, J = 47.3, 5.9 Hz, 2H),
4.12 (t, J = 6.8 Hz, 2H), 3.38 (t, J = 6.5 Hz, 2H), 2.92 (t, J = 7.5 Hz,
2H), 2.19–2.05 (m, 2H), 2.04–1.96 (m, 2H), 1.90–1.81 (m, 2H).
4.2.20.
2-{4-ij3-IJ2-Fluoroethyl)-1H-indol-1-yl]butyl}-6,7-
dimethoxy-1,2,3,4-tetrahydroisoquinoline (3a). The procedure
described for the synthesis of 3a was applied to 32 (78 mg,
0.26 mmol), 16 (76 mg, 0.39 mmol), and K2CO3 (54 mg, 0.39
1
5 : 1) to afford alcohol 28 (795 mg, 86%). H NMR (400 MHz,
CDCl3): δ 8.02 (s, 1H), 7.60 (d, J = 7.8 Hz, 1H), 7.35 (d, J = 8.1
Hz, 1H), 7.21–7.16 (m, 1H), 7.13–7.09 (m, 1H), 7.06 (d, J = 2.1
Hz, 1H), 3.89 (t, J = 6.3 Hz, 2H), 3.02 (t, J = 6.3 Hz, 2H).
4.2.15. 3-IJ1H-Indol-3-yl)propan-1-ol (29). The procedure
described for the synthesis of 28 was applied to 27 (3.00 g,
15.8 mmol) and LiAlH4 (2.93 g, 77.2 mmol) to afford alcohol
29 (2.18 g, 79%). 1H NMR (400 MHz, CDCl3): δ 7.93 (s, 1H),
7.65–7.55 (m, 1H), 7.37–7.30 (m, 1H), 7.23 (s, 1H), 7.19–7.14
(m, 1H), 7.12–7.07 (m, J = 8.0, 1H), 6.97 (s, 1H), 3.71 (t, J = 6.4
Hz, 2H), 2.90–2.78 (m, 2H), 2.04–1.93 (m, 2H).
1
mmol) to afford 3a (46 mg, 43%). H NMR (400 MHz, CDCl3):
δ 7.57 (d, J = 7.9 Hz, 1H), 7.31 (d, J = 8.2 Hz, 1H), 7.21–7.16
(m, 1H), 7.12–7.07 (m, 1H), 6.98 (s, 1H), 6.57 (s, 1H), 6.48
(s, 1H), 4.66 (dt, J = 47.2, 6.7 Hz, 2H), 4.11 (t, J = 7.0 Hz, 2H), 3.82
(s, 3H), 3.81 (s, 3H), 3.48 (s, 2H), 3.15 (dt, J = 22.1, 6.7 Hz, 2H),
2.78 (t, J = 5.7 Hz, 2H), 2.64 (t, J = 5.8 Hz, 2H), 2.48 (t, J = 5.8 Hz,
2H), 1.94–1.84 (m, 2H), 1.66–1.54 (m, 2H); 13C NMR (100 MHz,
CDCl3): δ 147.7, 147.4, 136.4, 128.1, 126.7, 126.4, 126.3, 121.7,
119.1, 119.0, 111.6, 109.8, 109.8, 109.7, 84.1, 57.9, 56.1, 56.0,
51.3, 46.3, 28.9, 28.4, 26.9, 26.6, 24.9; 19F NMR (376 MHz, CDCl3):
δ –213.3. MS (ESI+): m/z = calcd. for C25H31FN2O2 [M + H]+ 411.2,
found 411.1; HRMS (EI): m/z calcd. for C25H31FN2O2 [M + H]+
411.2448, found 411.2443; purity (HPLC): 95%.
4.2.16.
2-ij1-IJ4-Bromobutyl)-1H-indol-3-yl]ethanol
(30).
Under ice bath and argon atmosphere, alcohol 28 (220 mg,
1.37 mmol), 1,4-dibromobutane (875 mg, 4.11 mmol), and
NaH (98 mg, 4.11 mmol) were added into DMF (30 mL). The
mixture was stirred at 110 °C overnight. After cooling and fil-
tration, the crude product was extracted with ethyl acetate,
dried with anhydrous MgSO4, and purified by silica gel col-
umn chromatography (PE : EE = 3 : 1) to afford 30 (78 mg,
4.2.21.
2-{4-ij3-IJ3-Fluoropropyl)-1H-indol-1-yl]butyl}-6,7-
dimethoxy-1,2,3,4-tetrahydroisoquinoline (3b). The procedure
described for the synthesis of 3a was applied to 33 (113 mg,
0.36 mmol), 16 (73 mg, 0.38 mmol), and K2CO3 (60 mg, 0.43
mmol) to afford 3b (55 mg, 36%). 1H NMR (400 MHz, CDCl3):
δ 7.60 (d, J = 7.8 Hz, 1H), 7.33 (d, J = 8.2 Hz, 1H), 7.20 (t, J =
7.6 Hz, 1H), 7.11 (t, J = 7.4 Hz, 1H), 6.93 (s, 1H), 6.60 (s, 1H),
6.51 (s, 1H), 4.51 (dt, J = 47.4, 5.9 Hz, 2H), 4.13 (t, J = 7.0 Hz,
2H), 3.85 (s, 3H), 3.84 (s, 3H), 3.51 (s, 2H), 2.90 (t, J = 7.4 Hz,
2H), 2.81 (t, J = 5.6 Hz, 2H), 2.67 (t, J = 5.8 Hz, 2H), 2.51 (t, J =
7.3 Hz, 2H), 2.18–2.02 (m, 2H), 1.97–1.88 (m, 2H), 1.67–1.57
(m, 2H); 13C NMR (100 MHz, CDCl3): δ 147.7, 147.4, 136.6,
128.1, 126.8, 126.4, 125.6, 121.6, 119.2, 118.8, 113.9, 111.6,
109.7, 109.6, 83.7, 57.9, 56.1, 56.0, 51.3, 46.2, 31.3, 31.2, 28.9,
28.4, 24.9, 20.8; 19F NMR (376 MHz, CDCl3): δ –220.5; MS
(ESI+): m/z = calcd. for C26H33FN2O2 [M + H]+ 425.3, found
425.0; HRMS (EI): m/z calcd. for C26H33FN2O2 [M + H]+
425.2604, found 425.2601. Anal. calcd. for C26H33FN2O2 ·3/4H2O
(438.06): C 71.29, N 6.39, H 7.94; found: C 71.24, N 6.57, H 7.63.
1
19%). H NMR (400 MHz, CDCl3): δ 7.59 (d, J = 7.9 Hz, 1H),
7.30 (d, J = 8.2 Hz, 1H), 7.24–7.18 (m, 1H), 7.14–7.04 (m, 1H),
6.96 (s, 1H), 4.10 (t, J = 6.9 Hz, 2H), 3.87 (t, J = 6.4 Hz, 2H),
3.35 (t, J = 6.5 Hz, 2H), 3.00 (t, J = 6.4 Hz, 2H), 2.05–1.94
(m, 2H), 1.89–1.78 (m, 2H).
4.2.17. 3-ij1-IJ4-Bromobutyl)-1H-indol-3-yl]propan-1-ol (31).
The procedure described for the synthesis of 30 was applied
to alcohol 29 (1.20 g, 6.86 mmol), 1,4-dibromobutane (4.38 g,
20.6 mmol), and NaH (329 mg, 13.7 mmol) to afford 31 (728
mg, 34%). 1H NMR (400 MHz, CDCl3): δ 7.60 (d, J = 7.9 Hz,
1H), 7.29 (d, J = 8.2 Hz, 1H), 7.25–7.14 (m, 1H), 7.12–7.07 (m, 1H),
6.87 (s, 1H), 4.08 (t, J = 6.8 Hz, 2H), 3.70 (t, J = 6.4 Hz, 2H),
3.35 (t, J = 6.5 Hz, 2H), 2.84 (t, J = 7.5 Hz, 2H), 2.03–1.90 (m, 4H),
1.86–1.77 (m, 2H).
4.2.18. 1-IJ4-Bromobutyl)-3-IJ2-fluoroethyl)-1H-indole (32).
Under argon atmosphere (−78 °C), a solution of DAST (352
mg, 2.18 mmol) in CH2Cl2 (20 mL) was added into a solution
of 30 (538 mg, 1.82 mmol) in CH2Cl2 (20 mL). The mixture
was stirred for 2 h, followed by addition of saturated sodium
hyposulfite to quench the reaction. The crude product was
4.2.22.
1′-{4-ij3-IJ2-Fluoroethyl)-1H-indol-1-yl]butyl}-3H-
spiroijisobenzofuran-1,4′-piperidine] (3c). To a solution of 32
(70 mg, 0.24 mmol) in CH3CN (20 mL), 25 (45 mg, 0.24 mmol)
and K2CO3 (40 mg, 0.29 mmol) were added. The mixture was
stirred at 80 °C for 4 h. After cooling and filtration, the solvent
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1
was removed under reduced pressure. The residue was purified
by silica gel column chromatography (PE : EE = 1 : 5) to afford
3c (40 mg, 41%). H NMR (400 MHz, CDCl3): δ 7.58 (d, J = 7.9
to afford 4 (99 mg, 49%). H NMR (400 MHz, CDCl3): δ 7.74–
7.71 (m, 2H), 7.57 (d, J = 3.8 Hz, 1H), 7.46–7.41 (m, 3H), 7.34
(t, J = 7.2 Hz, 2H), 7.30–7.23 (m, 2H), 7.19–7.17 (m, 2H) 7.12–
7.08 (m, 1H), 7.03 (s, 1H), 2.98 (d, J = 11.96 Hz, 2H), 2.76 (t, J =
7.36 Hz, 2H), 2.47–2.38 (m, 4H), 2.04 (s, 4H), 1.74–1.68 (m, 2H),
1.61–1.58 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 139.2, 138.6
(2C), 137.6, 134.8, 128.2 (2C), 128.0, 127.1, 124.7 (2C), 124.6,
123.5, 121.7 (2C), 120.8, 119.1, 118.4, 117.3, 109.3, 88.9, 57.3,
49.8 (2C), 41.8, 35.4 (2C), 26.8, 25.7, 23.9; MS (ESI+): m/z = calcd.
for C30H30IN3 [M + H]+ 560.1, found 560.1. Anal. calcd. for
C30H30IN3·HCl·1/2H2O (604.95): C 59.56, N 6.95, H 5.33; found:
C 59.76, N 6.82, H 5.17.
1
Hz, 1H), 7.33 (d, J = 8.2 Hz, 1H), 7.29–7.16 (m, 4H), 7.15–7.07
(m, 2H), 6.99 (s, 1H), 5.06 (s, 2H), 4.66 (dt, J = 47.2, 6.7 Hz, 2H),
4.10 (t, J = 7.1 Hz, 2H), 3.16 (dt, J = 21.9, 6.7 Hz, 2H), 2.81 (d, J =
11.0 Hz, 2H), 2.47–2.29 (m, 4H), 2.03–1.81 (m, 4H), 1.75 (d, J =
12.5 Hz, 2H), 1.62–1.52 (m, 2H); 13C NMR (100 MHz, CDCl3): δ
145.8, 139.1, 136.4, 128.1, 127.8, 127.6, 126.3, 121.8, 121.3,
121.0, 119.1, 109.8, 109.8, 109.7, 84.9, 83.3, 71.0, 58.6, 50.4 (2C),
46.4, 36.8 (2C), 28.6, 26.8, 24.8; 19F NMR (376 MHz, CDCl3): δ –
213.2; MS (ESI+): m/z = calcd. for C26H31FN2O [M + H]+ 407.2,
found 407.1; HRMS (EI): m/z calcd. for C26H31FN2O [M + H]+
407.2499, found 407.2501; purity (HPLC): 96%.
4.2.26.
dimethoxy-1,2,3,4-tetrahydroisoquinoline (5). Compound 36
(279 mg, 1.08 mmol), 6,7-dimethoxy-1,2,3,4-tetra-
2-{4-ij1-IJ4-Fluorophenyl)-1H-indol-3-yl]butyl}-6,7-
4.2.23. 4-ij1-IJ4-Iodophenyl)-1H-indol-3-yl]butan-1-ol (34).
Compound 19 (595 mg, 3.14 mmol), 1,4-diiodobenzene (780
mg, 2.36 mmol), K2CO3 (3.12 g, 23.6 mmol), a catalytic
amount of copper powder, and 18-crown-6 were added into
25 mL of DMF. The mixture was stirred at 120 °C for 5 h.
After cooling and filtration, the crude product was extracted
with ethyl acetate and washed with 1 M HCl and saturated
NaCl solution. The organic layer was dried over MgSO4, and
the solvent was removed under reduced pressure. The residue
was purified by silica gel column chromatography (PE : EE =
hydroisoquinoline hydrochloride (153 mg, 0.67 mmol), and
K2CO3 (220 mg, 1.59 mmol) were added into 25 mL of
CH3CN. The mixture was stirred at 80 °C for 4 h. After the
solvent was removed under reduced pressure, the residue
was purified by silica gel column chromatography IJCH2Cl2 :
1
MeOH = 20 : 1) to afford 5 (153 mg, 62%). H NMR (400 MHz,
CDCl3): δ 7.98–7.90 (m, 2H), 7.09–7.02 (m, 2H), 6.54 (s, 1H),
6.47 (s, 1H), 3.80 (s, 3H), 3.79 (s, 3H), 3.52 (s, 2H), 2.96 (t, J =
7.2 Hz, 2H), 2.77 (t, J = 5.8 Hz, 2H), 2.67 (t, J = 5.9 Hz, 2H),
2.52 (t, J =7.3 Hz, 2H), 1.82–1.71 (m, 2H), 1.71–1.61 (m, 2H);
13C NMR (101 MHz, CDCl3): δ 198.6, 165.5, 147.5, 147.2,
133.3, 130.6 (2C), 126.5, 126.1, 115.6 (2C), 111.3, 109.4, 57.8,
55.9, 55.9, 55.7, 50.9, 38.2, 28.6, 26.6, 22.3; 19F NMR (376
1
4 : 1) to afford 34 (208 mg, 23%). H NMR (400 MHz, CDCl3):
δ 7.76–7.72 (m, 2H), 7.57 (t, J = 7.6 Hz, 1H), 7.46 (t, J = 8.2 Hz,
1H), 7.18–7.08 (m, 4H), 7.03 (s, 1H), 3.64 (t, J = 6.5 Hz, 2H),
2.76 (t, J = 7.4 Hz, 2H), 1.80–1.73 (m, 2H), 1.67–1.60 (m, 2H);
13C NMR (100 MHz, CDCl3): δ 139.6, 138.6 (2C), 135.8, 129.2,
125.7, 124.6, 122.7 (2C), 120.1, 119.4, 118.3, 110.3, 90.0, 62.9,
32.6, 26.1, 24.8; MS (ESI+): m/z = calcd. for C18H18INO [M + H]+
392.0, found 392.2.
4.2.24. 3-IJ4-Bromobutyl)-1-IJ4-iodophenyl)-1H-indole (35).
Under argon atmosphere and ice bath, PBr3 (192 mg, 0.71
mmol) was added to a solution of 34 (550 mg, 1.41 mmol) in
CH2Cl2. The mixture was stirred at room temperature for 2 h,
followed by addition of saturated NaHCO3 solution to quench
the reaction. The crude product was extracted with ethyl ace-
tate, dried with anhydrous MgSO4, and purified by silica gel
column chromatography (PE : EE = 4 : 1) to afford 35 (187 mg,
58%). 1H NMR (400 MHz, CDCl3): δ 7.81 (t, J = 8.2 Hz, 2H),
7.64 (t, J = 7.0 Hz, 1H), 7.52 (t, J = 8.1 Hz, 1H), 7.26–7.16 (m,
4H), 7.10 (s, 1H), 3.47 (t, J = 6.5 Hz, 2H), 2.83 (t, J = 7.24 Hz,
2H), 2.03–1.98 (m, 2H), 1.96–1.91 (m, 2H); 13C NMR (100
MHz, CDCl3): δ 139.6, 138.6 (2C), 135.8, 129.1, 125.7, 124.6,
122.7 (2C), 120.2, 119.4, 117.8, 110.4, 90.0, 33.8, 32.5, 28.4,
24.2; MS (ESI+): m/z = calcd. for C18H17BrIN [M + H]+ 454.0,
found 453.9.
MHz, CDCl3):
δ = calcd. for
–106.7; MS (ESI+): m/z
C22H26FNO3 [M + H]+ 372.2, found 372.2; HRMS (EI): m/z
calcd. for C22H26FNO3 [M + H]+ 372.1975, found 372.1972.
Anal. calcd. for C22H26FNO3·3/4H2O (384.96): C 68.64, N 3.64,
H 7.20; found: C 68.74, N 3.92, H 6.82.
4.3 In vitro radioligand competition studies
Competition assays of σ1 and σ2 receptors were performed as
previous reported in the literature.28,29 The detailed proce-
dures are provided in the ESI.†
4.4 Cell culture and antiproliferative assay
The cancer cell lines MCF7 (human mammary carcinoma),
DU145 (human prostate carcinoma) and C6 (rat glioma) were
routinely cultured in Beijing Normal University. The MTT
assay was used to determine the antiproliferative activity of
compounds 1a and 1b and siramesine in these cell lines as
described previously.30,31 The procedures are shown in the
ESI.†
4.2.25.
1-{4-ij1-IJ4-Iodophenyl)-1H-indol-3-yl]butyl}-4-
phenylpiperidine-4-carbonitrile (4). Compound 35 (163 mg,
0.36 mmol), 4-phenylpiperidine-4-carbonitrile (18) (147 mg,
0.72 mmol), K2CO3 (496 g, 3.60 mmol), and KI (64 mg, 0.39
mmol) were added into CH3CN solution. The mixture was
stirred at 80 °C for 4 h. After cooling and filtration, the sol-
vent was removed under reduced pressure. The residue was
purified by silica gel column chromatography (PE : EE = 2 : 1)
4.5 Flow cytometry cell cycle analysis
1a, 1b and siramesine were cultured in DU145 cell line for
24 h to examine cell cycle arrest as described previously.32
The detailed procedures are shown in the ESI.†
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Acknowledgements
14 M. J. Parry, J.-M. I. Alakoskela, H. Khandelia, S. A. Kumar,
M. Jäättelä, A. K. Mahalka and P. K. J. Kinnunen, J. Am.
Chem. Soc., 2008, 130, 12953–12960.
15 C. Zeng, J. Rothfuss, J. Zhang, W. Chu, S. Vangveravong, Z.
Tu, F. Pan, K. C. Chang, R. Hotchkiss and R. H. Mach, Br. J.
Cancer, 2012, 106, 693–701.
16 R. H. Mach, C. Zeng and W. G. Hawkins, J. Med. Chem.,
2013, 56, 7137–7160.
17 C. Abate, R. Perrone and F. Berardi, Curr. Pharm. Des.,
2012, 18, 938–949.
The excellent technical assistance of Aline Morgenegg,
Catharina Heinig, Tina Spalholz and Peggy Wecke is greatly
acknowledged. This work was supported by the National Nat-
ural Science Foundation of China (No. 21471019) and
supported in part (C.N., J.P., T.K., and J.S.) by the Helmholtz
Association within Helmholtz-Portfolio Topic “Technologie
und Medizin – Multimodale Bildgebung zur Aufklärung des
In-vivo-Verhaltens von polymeren Biomaterialien”. Fang Xie
acknowledges the financial support from China Scholarship
Council (CSC) for his study in HZDR.
18 M. H. Cesen, U. Repnik, V. Turk and B. Turk, Cell Death
Dis., 2013, 4, e818.
19 Y. Li, H. Jia, W. Deuther-Conrad, P. Brust, J. Steinbach and
B. Liu, He Huaxue Yu Fangshe Huaxue, 2010, 32, 99–105.
20 M. H. Herth, V. Kramer and F. Rösch, J. Labelled Compd.
Radiopharm., 2009, 52, 201–207.
21 H. Kubota, M. Fujii, K. Ikeda, M. Takeuchi, T. Shibanuma
and Y. Isomura, Chem. Pharm. Bull., 1998, 46, 351–354.
22 H. Shao, X. Chen, Z. Wang and P. Lu, J. Lumin., 2007, 127,
349–354.
23 C. Fan, H. Jia, W. Deuther-Conrad, P. Brust, J. Steinbach and
B. Liu, Sci. China, Ser. B: Chem., 2006, 49, 169–176.
24 J. Perregaard, E. K. Moltzen, E. Meier and C. Sanchez,
J. Med. Chem., 1995, 38, 1998–2008.
25 M. Niso, C. Abate, M. Contino, S. Ferorelli, A. Azzariti, R.
Perrone, N. A. Colabufo and F. Berardi, ChemMedChem,
2013, 8, 2026–2035.
Notes and references
1 R. Quirion, W. D. Bowen, Y. Itzhak, J. L. Junien, J. M.
Musacchio, R. B. Rothman, T. P. Su, S. W. Tam and D. P.
Taylor, Trends Pharmacol. Sci., 1992, 13, 85–86.
2 M. Hanner, F. F. Moebius, A. Flandorfer, H. G. Knaus, J.
Striessnig, E. Kempner and H. Glossmann, Proc. Natl. Acad.
Sci. U. S. A., 1996, 93, 8072–8077.
3 E. Aydar, C. P. Palmer, V. A. Klyachko and M. B. Jackson,
Neuron, 2002, 34, 399–410.
4 T. Hayashi and T. P. Su, Cell, 2007, 131, 596–610.
5 T. P. Su, T. Hayashi, T. Maurice, S. Buch and A. E. Ruoho,
Trends Pharmacol. Sci., 2010, 31, 557–566.
6 J. Xu, C. Zeng, W. Chu, F. Pan, J. M. Rothfuss, F. Zhang, Z.
Tu, D. Zhou, D. Zeng, S. Vangveravong, F. Johnston, D.
Spitzer, K. C. Chang, R. S. Hotchkiss, W. G. Hawkins, K. T.
Wheeler and R. H. Mach, Nat. Commun., 2011, 2, 380.
7 B. J. Vilner, C. S. John and W. D. Bowen, Cancer Res.,
1995, 55, 408–413.
8 A. Van Waarde, A. A. Rybczynska, N. K. Ramakrishnan, K.
Ishiwata, P. H. Elsinga and R. A. J. O. Dierckx, Curr. Pharm.
Des., 2010, 16, 3519–3537.
26 K.-H. Fan, J. R. Lever and S. Z. Lever, Bioorg. Med. Chem.,
2011, 19, 1852–1859.
27 Z. Tu, J. Xu, L. A. Jones, S. Li, C. Dumstorff, S.
Vangveravong, D. L. Chen, K. T. Wheeler, M. J. Welch and
R. H. Mach, J. Med. Chem., 2007, 50, 3194–3204.
28 Y. Li, X. Wang, J. Zhang, W. Deuther-Conrad, F. Xie, X.
Zhang, J. Liu, J. Qiao, M. Cui, J. Steinbach, P. Brust, B. Liu
and H. Jia, J. Med. Chem., 2013, 56, 3478–3491.
29 X. Wang, Y. Li, W. Deuther-Conrad, F. Xie, X. Chen, M.-C.
Cui, X.-J. Zhang, J.-M. Zhang, J. Steinbach, P. Brust, B.-L. Liu
and H.-M. Jia, Bioorg. Med. Chem., 2013, 21, 215–222.
30 C. Mamat, B. Mosch, C. Neuber, M. Köckerling, R.
Bergmann and J. Pietzsch, ChemMedChem, 2012, 7,
1991–2003.
31 B. Mosch, K. Mueller, J. Steinbach and J. Pietzsch, Int. J.
Radiat. Biol., 2009, 85, 1002–1012.
32 S. Li, X. Wang, Y. He, M. Zhao, Y. Chen, J. Xu, M. Feng, J.
Chang, H. Ning and C. Qi, Eur. J. Med. Chem., 2013, 67,
293–301.
9 I. Al-Nabulsi, R. H. Mach, L. M. Wang, C. A. Wallen, P. C.
Keng, K. Sten, S. R. Childers and K. T. Wheeler, Br. J.
Cancer, 1999, 81, 925–933.
10 K. T. Wheeler, L. M. Wang, C. A. Wallen, S. R. Childers, J. M. Cline,
P. C. Keng and R. H. Mach, Br. J. Cancer, 2009, 82, 1223–1232.
11 R. H. Mach, C. R. Smith, I. Al-Nabulsi, B. R. Whirrett, S. R.
Childers and K. T. Wheeler, Cancer Res., 1997, 57, 156–161.
12 M. S. Ostenfeld, N. Fehrenbacher, M. Høyer-Hansen, C. Thomsen,
T. Farkas and M. Jäättelä, Cancer Res., 2005, 65, 8975–8983.
13 L. Groth-Pedersen, M. S. Ostenfeld, M. Høyer-Hansen, J.
Nylandsted and M. Jäättelä, Cancer Res., 2007, 67, 2217–2225.
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