Synthesis of N-Alkyl-Carbazole Derivatives as 5-HT7R Antagonists

Article abstract of DOI:10.1002/bkcs.11555

We designed and synthesized a series of N-alkyl-carbazoles with different alkyl chains and amine moieties, and biological evaluation was performed to discover novel 5-HT₇R antagonists. Among 27 synthesized compounds, 20, 21, 23, and 24 showed excellent binding affinities to 5-HT₇R (K_i = 65, 64, 55, and 31 nM, respectively), and good selectivity profiles over other serotonin receptors. In functional assays, those compounds showed weak antagonistic activities against 5-HT₇R. In particular, the compound 24, 2-(4-(5-(9H-carbazol-9-yl)pentyl)piperazin-1-yl)phenol, could be considered as a potent and selective 5-HT₇R ligand with weak antagonistic effect. From the molecular docking study, the aromatic hydroxyl group in 24 was shown to play an important role in binding to 5-HT₇R through a hydrogen bonding interaction with Asp142 in the ligand binding pocket of 5-HT₇R.

Full text of DOI:10.1002/bkcs.11555

Article
DOI: 10.1002/bkcs.11555
BULLETIN OF THE
Y. Kim et al.
KOREAN CHEMICAL SOCIETY
Synthesis of N-Alkyl-Carbazole Derivatives as 5-HT R Antagonists
7
†
,‡
†
†,§
‡
§
Youngjae Kim, Miyoung Yeom, Soyeon Lee, Jinsung Tae, Hak Joong Kim,
Hyewhon Rhim,¶ Jihye Seong,
,k
†,**,††
Kyung Il Choi, Sun-Joon Min, and Hyunah Choo
‡‡
§§
†,k,
*
†Center for Neuro-Medicine, Brain Research Institute, Korea Institute of Science and Technology,
Seoul 02792, Korea
‡
Department of Chemistry, Yonsei University, Seoul 03722, Korea
Department of Chemistry, Korea University, Seoul 02841, Korea
§
¶
Center for Neuroscience, Brain Research Institute, Korea Institute of Science and Technology,
Seoul 02792, Korea
k
Division of Bio-Medical Science and Technology, KIST School, Korea University of Science
and Technology, Seoul 02792, Korea. *E-mail: hchoo@kist.re.kr
Convergence Research Center for Diagnosis Treatment Care of Dementia, Korea Institute of Science
and Technology, Seoul 02792, Korea
**
††
Department of Biological Chemistry, Korea University of Science and Technology,
Daejeon 34113, Korea
Small & Medium Enterprises Support Center, Korea Institute of Science and Technology,
Seoul 02792, Korea
Department of Chemical & Molecular Engineering/Applied Chemistry, Hanyang University,
Ansan 15588, Korea
‡
‡
§
§
Received May 25, 2018, Accepted July 17, 2018
We designed and synthesized a series of N-alkyl-carbazoles with different alkyl chains and amine moie-
ties, and biological evaluation was performed to discover novel 5-HT R antagonists. Among 27 synthe-
7
sized compounds, 20, 21, 23, and 24 showed excellent binding affinities to 5-HT R (K = 65, 64, 55, and
7
i
3
1 nM, respectively), and good selectivity profiles over other serotonin receptors. In functional assays,
those compounds showed weak antagonistic activities against 5-HT R. In particular, the compound 24,
7
2
5
-(4-(5-(9H-carbazol-9-yl)pentyl)piperazin-1-yl)phenol, could be considered as a potent and selective
-HT R ligand with weak antagonistic effect. From the molecular docking study, the aromatic hydroxyl
7
group in 24 was shown to play an important role in binding to 5-HT R through a hydrogen bonding inter-
7
action with Asp142 in the ligand binding pocket of 5-HT R.
7
Keywords: 5-HT receptor, Antagonist, N-alkyl-carbazole, Serotonin, GPCR
7
Introduction
production of cAMP and stimulation of G -mediated small
12
GTPases (e.g., Rho, Rac, and Cdc42) in living cell.
12–18
Serotonin receptors (5-HTRs) have been identified and
divided into seven subfamilies (5-HT R–5-HT R). Except
Recently, it was also verified that the recruitment of
β-arrestin is stimulated when serotonin activates the
1
7
19
5
-HT R, a ligand-gated ion channel, all other 5-HTRs are
5-HT R.
3
7
G protein-coupled receptors that activate an intracellular
second messenger. The 5-HTRs are activated by an endoge-
nous ligand, serotonin (5-hydroxytryptamine, 5-HT). Sero-
There has been much attention to discover selective
5-HT R antagonists over the past few decades. Up to now,
7
1
SB-258719
1-yl)butan-2-yl)benzenesulfonamide],
[(R)-N,3-dimethyl-N-(4-(4-methylpiperidin-
20,21
tonin is mainly distributed in the central nervous system
SB-269970
2
–7
(
5
CNS) and acts as a neurotransmitter. Serotonin activates
-HTRs to regulate psychological and physiological
changes such as mood, anxiety, aggression, pain, and sleep
[(R)-3-((2-(2-(4-methylpiperidin-1-yl)ethyl)pyrrolidin-1-yl)
2
2–26
sulfonyl)phenol]
and JNJ-18038683 [1-benzyl-3-(4-
27
chlorophenyl)-1,4,5,6,7,8-hexahydropyrazolo[3,4-d]azepine]
8–10
pattern.
Among 5-HTRs, 5-HT R is the most recently
have been found as selective and potent 5-HT R antago-
7
7
1
1
identified receptor. It is distributed in the several regions
of brain such as hypothalamus, thalamus, cortex, and hip-
pocampus, where it is involved in circadian rhythm, ther-
moregulation, endocrine regulation, sleep, mood regulation,
nists (Figure 1). SB-269970 and JNJ-18038683 exhibited
antidepressant-like effect in the forced swimming test and
2
5,26
the tail suspension test.
REM sleep pattern in the electroencephalogram test.
Especially, JNJ-18038683 is currently in Phase II clinical
Both compounds also changed
26,27
1
2–14
epilepsy, learning, memory, and depression.
The
28
5
-HT R activates G and G proteins that engage in the
development for major depressive and bipolar disorder.
7
s
12
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1

Article
BULLETIN OF THE
ISSN (Print) 0253-2964 | (Online) 1229-5949
KOREAN CHEMICAL SOCIETY
alkylamino groups were introduced to provide a series of
novel N-alkyl-carbazole derivatives 1–27 to obtain more
proper CNS drugs. The title compounds were then biologi-
cally evaluated for their 5-HT R binding affinities, func-
7
tional activities and selectivity profiles over other serotonin
receptors. In addition, in order to analyze the SAR, a
molecular docking study was performed.
Experimental
Chemistry. 9-(5-bromopentyl)-9H-carbazole (29, n = 3):
To a mixture of 9H-carbazole (2 g, 11.96 mmol) and t-
BuOK (1.3 g, 11.96 mmol) in THF (15 mL),
1
,5-dibromopentane (2.4 mL, 17.94 mmol) was added. The
ꢀ
reaction mixture was stirred at 40 C for 10 h. The mixture
was concentrated and the residue diluted with DCM. The
solution was washed with water, dried over MgSO , fil-
4
tered, concentrated and purified by column chromatography
(
SiO , Hex:DCM = 10:1) to give product 29 (n = 3) in
2
1
Figure 1. Representative 5-HT
7
R antagonists.
44% yield; H NMR (400 MHz, CDCl ) δ 8.07–8.02 (m,
3
2
7
H), 7.44–7.38 (m, 2H), 7.30 (d, J = 8.2 Hz, 2H),
.22–7.16 (m, 2H), 4.19 (t, J = 7.1 Hz, 2H), 3.23 (t,
Nevertheless, novel 5-HT R antagonists are still required to
understand the therapeutic potential of targeting the
7
J = 6.8 Hz, 2H), 1.82–1.70 (m, 4H), 1.45–1.36 (m, 2H).
-(4-(5-(9H-Carbazol-9-yl)pentyl)piperazin-1-yl)phenol
2
5
-HT R.
7
(24): To a solution of 9-(5-bromopentyl)-9H-carbazole
Previously, our research group has reported N-acyl-
(29, n = 3) (200 mg, 0.63 mmol) in ACN (5 mL),
carbazole compounds as well as biaryl derivatives as selec-
2
9–34
1-(2-hydroxyphenyl)piperazine (169 mg, 0.95 mmol) was
added. The reaction mixture was stirred under reflux condi-
tions for overnight. The mixture was diluted with DCM,
washed with H O. The organic phase was dried over
Na
tive 5-HT R ligands.
As a continuation of our previous
7
study, N-alkyl-carbazole derivatives were investigated to
study structure–activity relationship (SAR) of the carbazole
derivatives (Figure 2). Generally, CNS drugs are more
2
3
5
SO , concentrated, and purified by column chromatogra-
2 4
hydrophobic than non-CNS drugs. Lipophilicity of the N-
alkyl-carbazole compounds was increased by removing the
carbonyl group in N-acyl-carbazoles. Various terminal
phy (SiO , DCM:MeOH = 20:1) to give product 24
2
1
(
(
(
172 mg, 0.42 mmol) as a sticky oil in 66% yield; H NMR
400 MHz, CDCl ) δ 8.04 (d, J = 7.7 Hz, 2H), 7.42–7.38
m, 2H), 7.31 (d, J = 8.2 Hz, 2H), 7.19–7.15 (m, 2H),
3
7
.09–7.06 (m, 1H), 7.03–6.99 (m, 1H), 6.92 (dd, J = 6.0 Hz,
J = 1.5 Hz, 1H), 6.80 (td, J = 7.6 Hz, J = 1.5 Hz, 1H), 4.16
t, J = 7.1 Hz, 2H), 2.79 (t, J = 4.7 Hz, 4H), 2.41 (brs, 4H),
.20 (t, J = 7.6 Hz, 2H), 1.79 (quint, J = 7.4 Hz, 2H), 1.41
(
2
13
(
(
quint, J = 7.5 Hz, 2H), 1.32–1.24 (m, 2H); C NMR
100 MHz, CDCl ) δ 151.16, 140.06, 138.80, 125.96,
3
1
1
25.30, 122.51, 121.02, 120.06, 119.73, 118.48, 113.81,
08.33, 57.98, 53.47, 52.06, 42.52, 28.48, 26.26, 24.82;
+
LC/MS (ESI ): m/z: calcd for C H N O: 413.25,
27 31 3
+
[M + H] ; found: 414.15.
Serotonin Receptor Binding Affinity Assays. Eleven dif-
ferent concentrations (5X final concentration) of the test
and reference compounds were prepared by serial dilution
(0.05 nM, 0.5 nM, 1.5 nM, 5 nM, 15 nM, 50 nM, 150 nM,
5
00 nM, 1.5 μM, 5 μM, and 50 μM) in Standard Binding
Buffer (50 mM Tris–HCl, 10 mM MgCl , 1 mM EDTA,
2
pH 7.4). Radioligand appropriately selected for each seroto-
nin subtype receptor was diluted to five times of the assay
concentration in the buffer. The selected radioligand
(
50 μL) was added into the wells of a 96-well plate con-
Figure 2. Newly designed N-alkyl-carbazoles 1–27.
taining 100 μL of the buffer. Then, prepared 50 μL of the
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N-Alkyl-Carbazole Derivatives as 5-HT R Antagonists
KOREAN CHEMICAL SOCIETY
7
test and reference compound were treated in triplicate.
Lastly, crude membrane 50 μL fractions of cells expressing
recombinant receptor are dispensed into each well. The
Results and Discussion
The N-alkyl-carbazoles containing a variety of the terminal
alkylamino groups were synthesized straightforwardly in
two steps (Scheme 1). Carbazole 28 underwent nucleophilic
250 μL solution is protected from light and incubated at
room temperature for 1.5 h. Then it is harvested by rapid
filtration onto Whatman GF/B glass fiber filters pre-soaked
with 0.3% polyethylenimine using a 96-well Brandel har-
vester. In order to reduce non-specific binding, four rapid
washes with chilled buffer (500 μL) are performed. Filters
are kept in 6 mL of scintillation tubes and allowed to dry
for overnight. The following day, 4 mL of EcoScint scintil-
lation cocktail (National Diagnostics) are treated to each
tube. The tubes are capped, labeled, and counted by liquid
scintillation counting. The filter mats are dried, then scintil-
lant is melted onto the filters and the radioactivity preserved
on the filters is counted in a Microbeta scintillation counter.
The IC50 values were calculated using Prism 4.0 (GraphPad
Software, San Diego, California, US) and converted to Ki
values.
substitution with several dibromoalkanes (BrCH
(CH
)
2
2
n
ꢀ
CH
Br, n = 1–4) in the presence of t-BuOK at 40 C to
2
give N-bromoalkyl-carbazoles 29 in 17–53% yields. The N-
bromoalkyl-carbazoles 29, thus obtained, were treated with
various secondary amines under reflux conditions to afford
the title compounds 1–27 in 40–99% yields. The structures
1
13
of final compounds 1–27 were verified by H and
C
nuclear magnetic resonance (NMR) and liquid chromatog-
raphy-mass spectrometry (LC-MS), which can be found in
Appendix S1 (Supporting information).
The synthesized N-alkyl-carbazoles 1–27 were assessed
[
3H]
for their binding affinities to 5-HT R through
LSD
7
radioligand binding assays in transfected HEK293 cells
including SB-269970 as a positive control. According to
the previous results of N-acyl carbazoles, we first fixed
the carbon tether with n = 4. In order to investigate the role
of the terminal amine functionalities, the title compounds
with n = 4 and 15 different alkylamino groups (1–15) were
evaluated for their binding affinities to 5-HT R, and the
results are summarized in Table 1. Compounds with a ter-
minal acyclic amino (1 and 2) or pyrrolidine (3) group
failed to show potent binding affinity to 5-HT R with Ki
34
cAMP Accumulation Assay.
HEK293T cells co-
expressing the cAMP biosensor GloSensor-22F (Promega)
and human 5-HT R were seeded (30 000–40 000 cells/20
7
μL/well) into white, clear-bottom, tissue culture 384 well
plate in DMEM with 10% dialyzed FBS, 100 U/mL peni-
cillin and 100 μg/mL streptomycin. After 5–6 h recovery,
medium are removed from the wells and cells were treated
with 3% Glosensor cAMP reagent, luciferin (Promega)
7
7
values of 511, 1980, and 1546 nM, respectively. The piper-
idinyl carbozoles (4–8), however, showed substituent-
dependent binding affinities: the alkylpiperidine derivatives
2
2
1
0 μL in filter-sterilized assay buffer including 1X HBSS,
0 mM HEPES and third distilled water, pH 7.4. Then,
0 μL of ×4 of compounds 20, 21, 23, 24, SB-269970
(
4–6) were found to bind to the target with only moderate
(
10 μM), and serotonin (100 nM) were prepared in assay
buffer with 0.1% bovine serum albumin (BSA). After
0 min, cells were treated with 10 μL of compounds pre-
to marginal binding affinities (K = 597–1598 nM) while
i
the piperidines with an aromatic substituent, 7 and 8,
showed good 5-HT R binding affinities with K values of
3
7
i
pared above. The plates were incubated at room tempera-
ture for 15 min. The luminescence produced by
accumulation of cAMP level was quantified by using Flex-
station3 microplate reader (Molecular Devices, Downing-
town, PA, USA). For conforming antagonism, the plate
used above was treated with 10 μL of serotonin (100 nM).
After 10 min, the luminescence was measured again. The
results were analyzed by using Prism 6.0 program
(Graphpad Software).
Molecular Docking Studies. For molecular docking
study, the homology model protein structure of the 5-HT R
7
was constructed by the SwissModel server using the co-
crystal structure of 5-HT R with ergotamine (PDB:
1
B
36
4
IAR). The Prepare Protein module (CHARMm force
field) was used to prepare the homology model structure of
-HT R. The binding site was determined by the center of
5
7
co-crystal ligand, ergotamine. Ligands were prepared with
protonation at pH 7.4 and energy minimization. The dock-
ing modes of ligands were procured using CDOCKER of
Discovery Studio 2016 (v16.1.0.15350) program (Accelrys,
Inc., San Diego, California, US) based on the CHARMm
docking algorithm. For analysis, the docking poses of
ligands were obtained up to 10 poses.
Scheme 1. Synthesis of the N-alkyl-carbazoles 1–27: (a)
,3-dibromopropane (n 1), 1,4-dibromobutane (n 2),
1
=
=
1,5-dibromopentane (n = 3), or 1,6-dibromohexane (n = 4), t-BuOK,
ꢀ
THF, 40 C, 17–53%; (b) amines, CH
3
CN, reflux, 40–99%.
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N-Alkyl-Carbazole Derivatives as 5-HT R Antagonists
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2
12 and 232 nM, respectively. Other amino functionalities
such as azepane (9), morpholine (10), N-methylpieprazine
11) and N-acetylpiperazine (12) did not provide significant
Table 1 (continued)
Compd −NR R
1
2
a
b
pK
i
K
i
in nM
89
(
1
4
7.00 ꢁ 0.10
target binding affinities to the corresponding carbazole
derivatives. However, N-arylpiperazine group made com-
pounds 13 and 14 potent with Ki values of 145 and 89 nM,
respectively. In contrast, compound 15 with an N-
1
5
6.22 ꢁ 0.08
9.47 ꢁ 0.05
602
Table 1. Binding affinities (K
-HT R.
i
) of the compounds 1–15 against
SB-269970
0.34
5
7
a
Values are the mean ꢁ SEM of triplicate binding experiments.
b
c
d
Values are calculated from pK
-Inhibitions of the compound at 10 μM.
Not determined.
i
.
%
benzylpiperazine group showed only moderate binding
affinity with a K value of 602 nM.
Next, we selected the most active compounds 7, 13, and
14, and a moderately active compound 15 for further SARs
i
1
2
pKia
Kib in nM
Compd
−NR R
1
6.29 ꢁ 0.09
511
study, and the effect of alkyl chain length on 5-HT R bind-
7
32,34
ing affinity was examined.
Thus, the chain length was
2
5.7 ꢁ 0.08
1980
sequentially reduced from n = 4 to n = 1, and the 5-HT R
7
binding affinities of the corresponding compounds (16–27)
were evaluated (Table 2). All of the compounds 16–27
3
4
5.81 ꢁ 0.08
6.22 ꢁ 0.08
1546
597
showed good to potent binding affinities with K values
i
Table 2. Binding affinities (K ) of the compounds 16–27 against
i
5
-HT R.
5
6
7
6.04 ꢁ 0.09
5.80 ꢁ 0.08
6.67 ꢁ 0.08
909
1598
212
7
b
i
K in
nM
1
2
a
i
Compd
n
−NR R
pK
1
1
1
7
6
7
8
1
6.45 ꢁ 0.09
6.69 ꢁ 0.08
6.75 ꢁ 0.08
6.67 ꢁ 0.08
6.81 ꢁ 0.09
7.19 ꢁ 0.09
7.19 ꢁ 0.09
6.84 ꢁ 0.08
7.02 ꢁ 0.09
7.26 ꢁ 0.09
7.51 ꢁ 0.09
7.00 ꢁ 0.10
6.39 ꢁ 0.09
6.66 ꢁ 0.08
6.63 ꢁ 0.09
6.22 ꢁ 0.08
9.47 ꢁ 0.05
353
205
178
212
155
64
65
145
96
55
31
89
404
218
233
602
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
8
9
6.63 ꢁ 0.09
6.02 ꢁ 0.08
232
952
19
2
2
1
2
0
1
3
2
c
d
1
1
1
0
1
2
45.3%
—
c
d
49.4%
—
23
2
1
2
2
2
4
4
5
6
7
5.83 ꢁ 0.09
6.84 ꢁ 0.08
1485
145
1
3
15
SB-269970
a
0.34
Values are the mean ꢁ SEM of triplicate binding experiments.
b
i
Values are calculated from pK .
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N-Alkyl-Carbazole Derivatives as 5-HT R Antagonists
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between 31 and 404 nM. Overall, the binding affinities of
compounds with n = 2 or n = 3 were better than those with
n = 1 or n = 4 and, among the series, compounds 20, 21,
% Inhibition
1
1
50
00
23, and 24 with n = 2 or n = 3 showed the most potent
binding affinities to 5-HT R (K = 31–65 nM).
7
i
The most active compounds 20, 21, 23, and 24 were then
tested for their binding affinities to other 5-HTR subtypes,
and the selectivity to 5-HT R were evaluated as selectivity
7
indexes (SIs) (Table 3). The 5-HTR subtypes investigated
in this study include 5-HT R, 5-HT R, 5-HT R,
5
0
0
1
A
1B
1D
5
-HT R, 5-HT R, 5-HT R, 5-HT R, 5-HT R, 5-HT R,
1E 2A 2B 2C 3 5
and 5-HT R. All of the selected compounds 20, 21, 23, and
6
2
4 showed 5-HT R-selective binding affinities. In particu-
7
lar, they were very selective over 5-HT R, 5-HT R, and
1
B
1E
2
0
21
23
24
SB-269970
5
-HT R, while moderate (5-HT R, 5-HT R, 5-HT R,
3 1D 2C 5
Figure 3. Percentage inhibitions of 20, 21, 23, and 24 against
-HT7R at 10 μM. The results are the mean of triplicate binding
and 5-HT R) and relatively low (5-HT R, 5-HT R and
6
1A
2A
5
5-HT R) SI values were observed for other 5-HTR sub-
2B
experiments.
types. Among the selected four compounds, 24 demon-
strated the most potent (K = 31 nM) and selective 5-HT R
i
7
binding affinity (Tables 2 and 3).
We also carried out functional assays to identify whether
the N-alkyl-carbazoles discovered in this study act as weak
the four compounds 20, 21, 23, and 24 act as agonist or
antagonists against 5-HT R.
7
antagonist against 5-HT R (Figure 3). The functional
In order to elaborate the difference in binding affinities
7
assays were performed by using HEK293T cells co-
of the N-alkyl-carbazoles against 5-HT R, we performed
7
expressing the cAMP biosensor and human 5-HT R, and
molecular docking study on 21 and 24. We constructed a
7
intracellular accumulation of cAMP was monitored. Upon
treatment with the carbazole derivatives, no appreciable
increase in cAMP level was observed, which demonstrates
homology model of 5-HT R through the SwissModel
7
server using the co-crystal structure of 5-HT with ergota-
1B
36
mine (PDB: 4IAR) as a template. Structures of 21 and 24
were prepared by protonation of their amino groups and
energy-minimization. Both compounds docked to the
their lack of agonistic activity to 5-HT R. In contrast,
7
serotonin-induced increase in cAMP in the HEK293T cells
was attenuated upon co-treatment with 20, 21, 23, or 24.
The inhibitory activity of the title carbazoles (10 μM)
ligand-binding site of the 5-HT R homology model struc-
7
ture by using the CDOCKER docking module in Discovery
Studio. We have already found that there is a large and
against 5-HT R was estimated to be between 46% and
7
5
6%. Under the same conditions, the well-known 5-HT R
extended hydrophobic binding pocket in 5-HT R and the
7
7
29–34
antagonist SB-269970 showed complete inhibition of
serotonin-induced increase in cAMP. Thus, it indicates that
antagonists fully occupy the hydrophobic binding site.
Both of 21 and 24 were smoothly bound to the 5-HT R
7
Table 3. Selectivity of 20, 21, 23, and 24 over other 5-HTR subtypes.
2
0
21
23
24
a
b
a
b
a
b
a
b
5
-HTR subtypes
-HT
Ki (nM)
SI
Ki (nM)
SI
Ki (nM)
SI
Ki (nM)
SI
5
5
5
5
5
5
5
5
5
5
7
R
64
1.0
1.6
65
1.0
2.7
55
1.0
2.0
31
1.0
5.8
-HT1A
-HT1B
-HT1D
R
R
R
104
>10,000
545
>10,000
172
>10,000
671
>10,000
121
93
490
>10,000
588
863
111
>10,000
1125
>10,000
138
175
739
>10,000
608
683
180
>10,000
1342
>10,000
168
131
531
>10,000
335
161
c
d
c
d
c
d
c
d
—
—
—
—
8.5
10.3
20.5
43.3
c
d
c
d
c
d
c
d
-HT1E
R
—
—
—
—
-HT2A
-HT2B
-HT2C
R
R
R
78
73
1.2
1.1
7.0
1.9
1.4
7.5
2.5
3.2
5.4
4.2
449
>10,000
596
1512
13.4
17.1
c
d
c
d
c
d
c
d
-HT R
—
—
—
—
3
-HT
-HT
5
R
R
9.3
23.6
9.1
13.3
11.1
12.4
10.8
5.2
5
a
b
c
6
Values are the mean of triplicate binding experiments.
Selectivity Index (SI) = K for other 5-HTR subtype/K
values against 5-HT R were set as >10 000 nM due to lower than 50%-inhibition at 10 μM.
Not calculated.
i
i 7
for 5-HT R.
K
i
7
d
Bull. Korean Chem. Soc. 2018
© 2018 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
5

BULLETIN OF THE
Article
N-Alkyl-Carbazole Derivatives as 5-HT R Antagonists
KOREAN CHEMICAL SOCIETY
7
binding site sufficiently covering the hydrophobic pocket,
with others. In the functional assays, selected four com-
and the docking poses of the two compounds were similar
pounds 20, 21, 23, and 24 showed weak antagonistic activi-
(Figure 4(a) and (b)). From the molecular docking study,
ties against 5-HT R. Overall, the compounds discovered in
7
2D schematic molecule–protein interactions were deduced
this study could be considered as potent and selective
and shown in Figure 4(c) and (d). Like previously reported
molecular docking studies, the key interaction was an ionic
interaction between the protonated amino group of each
5-HT R ligand with weak antagonistic effect. Among
7
those, 24 showed the best properties. From the molecular
docking study, it was shown that the aromatic hydroxyl
group in 24 might play an important role to show potent
31,37–41
compound and Asp162 in the 5-HT R binding site.
7
Besides, both 21 and 24 showed additional interactions
such as ionic interactions with ASP142, π–sulfur interac-
tions with Cys166, carbon hydrogen bond interactions with
Cys231, π–π interactions with Phe343, and π–alkyl interac-
tions with Val 163, Leu232, Ile233 and Arg367. However,
5-HT R-binding affinity by hydrogen bonding interaction
7
with Asp142 in the ligand binding pocket. Based on these
results, further modifications and evaluations such as phar-
macokinetics and in vivo test for depression and sleep dis-
order will be done in due course.
comparison of the binding modes of 21 and 24 to 5-HT R
7
reveals a significant difference. While 24 forms additional
hydrogen bond with ASP142 by using its aromatic
hydroxyl group as a hydrogen bonding donor (shown as an
ionic interaction in Figure 4(d)), the methoxy substituent of
Acknowledgments. We are grateful to the US National
Institute of Mental Health (NIMH) Psychoactive Drug
Screening Program (contract: HHSN-271-2008-00025-C)
for providing binding affinity data. This research is sup-
ported by the Original Technology Research Program
21 is not capable of forming this hydrogen bond. Thus, it
could be presumed that 24 with an aromatic hydroxy group
(NRF-2016M3C7A1904344) funded by the National
is more potent 5-HT R binder than 21 with a methoxy
7
Research Foundation of Korea (NRF). And this work is
additionally funded by the Korea Institute of Science and
Technology (KIST) (2E27870 and 2E28412).
group due to the additional hydrogen bonding interaction
between the hydroxy group and Asp 142.
Supporting Information. Additional supporting informa-
tion may be found online in the Appendix S1 (Supporting
Information) section at the end of the article.
Conclusion
We designed and synthesized a series of N-alkyl-carbazole
derivatives. All of compounds 1–27 were biologically eval-
uated to obtain binding affinities, selectivity profiles, and
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© 2018 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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