Synthesis of Novel 3-N-substituted Carbazole Derivatives and Evaluation of their Abilities to Inhibit Platelet Aggregation

Article abstract of DOI:10.1002/bkcs.11462

The carbazole moiety exhibits various biological activities, including anticancer, antiviral, anti-inflammatory, and antimicrobial activities; some compounds containing the moiety also inhibit platelet aggregation. In the present study, we synthesized a series of 3-N-substituted carbazole derivatives and evaluated their abilities to inhibit in vitro platelet aggregation induced by collagen (5 μg/mL). Of the synthesized compounds, compound 5q (JSCa15), with a urea linkage within the carbazole framework, exhibited the strongest inhibitory activity (98.25% at 30 μM). Interestingly, reduction of the nitro group of compound 5q to an amine exhibited significantly decreased activity (compound 5r, 5.18% at 30 μM). Also, substitution of the urea moiety of compound 5q with a carbamate moiety resulted in a considerable loss of activity (compound 8a, 5.91% at 30 μM). These results suggest that the urea moieties and nitro groups of 3-N-substituted carbazole derivatives may play key roles in inhibiting in vitro platelet aggregation induced by collagen.

Full text of DOI:10.1002/bkcs.11462

Article
DOI: 10.1002/bkcs.11462
BULLETIN OF THE
J. Kim et al.
KOREAN CHEMICAL SOCIETY
Synthesis of Novel 3-N-substituted Carbazole Derivatives and
Evaluation of their Abilities to Inhibit Platelet Aggregation
†
†
†
‡
†
†
Jiseon Kim, Sang-Hyuk Jung, Eunju Yun, Soo-Hyun Cho, O Yuseok, Ji-Eun Kim,
†
†,
†,
*
*
Young-Ho Kim, Chang-Seon Myung, and Gyu-Yong Song
†Department of Pharmacy, Chungnam National University, Daejeon 34134, Republic of Korea.
*
E-mail: cm8r@cnu.ac.kr; gysong@cnu.ac.kr
‡
PCPIA BIT CO., Ltd, Yuseong-gu, Daejeon 34196, Republic of Korea.
Received August 1, 2017, Accepted March 30, 2018
The carbazole moiety exhibits various biological activities, including anticancer, antiviral, anti-inflammatory,
and antimicrobial activities; some compounds containing the moiety also inhibit platelet aggregation. In the
present study, we synthesized a series of 3-N-substituted carbazole derivatives and evaluated their abilities to
inhibit in vitro platelet aggregation induced by collagen (5 μg/mL). Of the synthesized compounds, com-
pound 5q (JSCa15), with a urea linkage within the carbazole framework, exhibited the strongest inhibitory
activity (98.25% at 30 μM). Interestingly, reduction of the nitro group of compound 5q to an amine exhibited
significantly decreased activity (compound 5r, 5.18% at 30 μM). Also, substitution of the urea moiety of
compound 5q with a carbamate moiety resulted in a considerable loss of activity (compound 8a, 5.91% at
3
0 μM). These results suggest that the urea moieties and nitro groups of 3-N-substituted carbazole derivatives
may play key roles in inhibiting in vitro platelet aggregation induced by collagen.
Keywords: Antiplatelet aggregation activity, 3-N-substituted carbazole derivatives, Collagen
Introduction
The carbazole moiety is existent in a great deal of natu-
rally occurring compounds and exhibits a variety of pharma-
19
20
Although many cardiovascular drugs are available, cardiovas-
cular disease is the leading cause of death worldwide.
cological effects including anticancer, anti-viral, anti-
1,2
21
22
23
inflammatory, anti-oxidant, antimicrobial activities.
Examples include cerebrovascular disease, myocardial infarc-
tion, stroke, atherosclerosis, hypertension, and peripheral vas-
Especially, it was reported that murrayafoline A (1-meth-
oxy-3-methyl-9H-carbazole), isolated from the roots of
3,4
24
cular disease. Thrombus formation, associated with platelet
Murraya euchrestifolia, inhibits platelet aggregation.
5,6
aggregation, is a major cause of cardiovascular disease.
Platelets are formed in the cytoplasm of giant cells,
Based on this finding, we hypothesized that 3-N-substituted
carbazole derivatives might elicit potent inhibition of plate-
let aggregation. Moreover, to the best of our knowledge,
there have been no reports on the structure–activity rela-
tionships of 3-N-substituted carbazole derivatives as platelet
aggregation inhibitor. We therefore synthesized a series of
3-N-substituted carbazole derivatives and explored whether
they inhibited collagen-induced aggregation of rabbit plate-
lets. The present paper will describe the structure–activity
relationships and biological activities on these novel plate-
let aggregation inhibitors.
7,8
termed megakaryocytes, and play a hemostatic role. If a
blood vessel is damaged, the platelets become activated and
3
aggregate at the site of injury. A loose plug is formed at
the wound site; the plug contains a combination of collagen
9
,10
and platelets.
When the platelets are ultimately
0
destroyed, serotonin, adenosine 5 -diphosphate(ADP),
thromboxane A2 (TxA2), and platelet-activating factor
(
PAF) stored in granules contained within the platelets are
1
1–14
released and activate platelet aggregation.
Collagen
and other factors exert positive feedback on this process,
and thrombin and fibrin are produced. The fibrin binds to
erythrocytes and a thrombus is formed.
Experimental
1
,3,5,15
Hemostasis is a defense mechanism minimizing blood
loss from the wound; blood circulation continues
The reagents and solvents were general reagent grade and
were used without further purification. All reactions were
monitored by analytical TLC on silica gel GF254. Column
chromatography was performed on Silicycle silica gel,
250–400 mesh. Melting points were measured with an
Electrothermal 9100. H and C NMR spectra were per-
formed on AVANCE III 600 (Tokyo, Japan) and JEOL
JNM-AL 400 spectrometer (Akishima, Japan). Mass spectra
3,16
smoothly.
However, excessive hemostasis and platelet
aggregation create a pathological blood clot and obstruct the
blood flow; this is the principal cause of cardiovascular dis-
5
1
13
ease. Therefore, drugs inhibiting platelet aggregation are
1
3
essential. An example is aspirin ; however, this drug has
17,18
various side-effects such that alternatives are required.
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Article
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KOREAN CHEMICAL SOCIETY
were performed using a Shimadzu (Kyoto, Japan) LCMS-
IT-TOF.
Schemes 1–4 show, respectively, the syntheses of
3-amino-9H-carbazole
(3a),
3-urea-substituted
9H-
carbazole derivatives (5a-s), 3-urea-substituted 9-methyl-
9
9
H-carbazole derivatives (6a-q), 3-carbamate-substituted
H-carbazole derivatives (8a–g), and analogs of 5q (11a-
e). We utilized the intermediate 3-amino-9H-carbazole (3a)
prepared in two steps from 9H-carbazole (Scheme 1) to
synthesize compounds containing urea (5a–s). Treatment of
Scheme 3. Reagents and conditions: (a) triethylamine, THF anhy-
drous, chloroformate, 0 C, 3 h.
ꢀ
3-amino-9H-carbazole (3a) with appropriately substituted
isocyanates in anhydrous THF gave 3-urea-substituted 9H-
carbazole derivatives (5a–s) in good yield. Next, the nitro
group of compound 5q was reduced to the amino group by
Pd/C (10%, w/v) to get compound 5r in good yield. Treat-
ment of 3-amino-9H-carbazole (3a) with appropriately
substituted chloroformates in the presence of triethylamine
and anhydrous tetrahydrofuran(THF) gave 3-carbamate-
substituted 9H-carbazole derivatives (8a–g) in good yield
Scheme 4. Reagents and conditions: (a) THF anhydrous, rt., 18 h.
(
Scheme 3). Also, treatment of 3-amino-9-methyl-9H-
continuous stirring (1000 rpm). Either dimethyl sulfoxide
carbazole (3b) with appropriately substituted isocyanates in
anhydrous THF gave 3-urea-substituted 9-methyl-9H-
carbazole derivatives (6a–q) in good yield (Scheme 2).
Finally, the target compounds 11a-e were synthesized by
(DMSO) or a DMSO solution of a test compound was
added. After preincubation (3 min) collagen (10 μg/mL)
was added and the extent of platelet aggregation measured.
treatment
of
4-nitrophenyl
isocyanate
with
Results and Discussion
2-aminoanthracene, cyclopentylamine, cyclohexylamine,
aniline, and 3-aminodibenzofuran, respectively; all com-
pounds were obtained in good yield (Scheme 4).
Tables 1–2 summarize the in vitro antiplatelet activities. As
shown in Table 1, compounds 5a–d with the alkyl chain
Our biological model was the collagen-induced aggrega-
tion of washed rabbit platelets. We measured platelet aggre-
(propyl, hexyl, nonyl, or cyclohexyl) of urea at the C-3
2
5
position of the carbazole did not exhibit significant antipla-
telet activity (23.9, 9.8, 1.96, and 2.66%, respectively).
gation using the turbidimetric method of Born,
as
2
6
described previously. In brief, a suspension of washed
platelets was incubated in an aggregometer (37 C) with
ꢀ
Table 1. Inhibitory activity of compounds 5a–6p on washed
rabbit platelet aggregation.
a
a
Compd.
% of inhibition
Compd.
% of inhibition
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
23.90
9.80
1.96
2.66
27.88
6.66
89.97
98.00
96.44
10.09
11.11
−6.53
10.09
−0.65
19.60
98.25
5.18
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
16.67
2.16
0.00
5.70
2.16
0.72
12.28
0.00
14.47
1.32
0.00
0.00
5.04
6.47
0.00
17.99
58.27
Scheme 1. Reagents and conditions: (a) water, 70% nitric acid, 40
C, 1 h, 80–90 C for 5 h, and stirring at rt. for 2 days; (b) ethanol,
Pd activated on carbon(10%), hydrogen gas, 35 psi, rt., 3 h.
ꢀ
ꢀ
p(JSCa15)
q
r
11.55
Scheme 2. Reagents and conditions: (a) THF anhydrous, rt.,
Aspirin(evaluated at 100 μM)
a
58.30
1
3
8–24 h; (b) Pd on activated carbon(10%), hydrogen gas, ethanol,
5 psi, rt., 3 h; (c) HCl, acetone, rt., 3 h.
These compounds were tested in concentration of 30 μM.
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Synthesis of Novel 3-N-substituted Carbazole Derivatives
KOREAN CHEMICAL SOCIETY
Table 2. Inhibitory activity of compounds 8a–g, 11a–e on washed
rabbit platelet aggregation.
Acknowledgments. This work was supported by research
fund of Chungnam National University.
%
of
a
a
Supporting Information. Additional supporting informa-
Compd.
inhibition
Compd.
% of inhibition
tion is available in the online version of this article.
8
8
8
8
8
8
8
a
a
b
c
d
e
f
5.91
15.73
−3.31
9.38
41.70
24.39
45.17
11a
11b
11c
11d
64.35
1.89
3.78
15.77
70.34
58.30
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2
Conclusion
2
In summary, we synthesized a novel series of 3-N-
substituted carbazole derivatives. The most active com-
pound 5q may serve as a potential lead compound in future
work on the development of inhibitors of platelet aggrega-
tion. Further structural optimization and in vivo antiplatelet
activity of 5q investigation are underway, and the results
will be reported in due course.
2
2
2
2
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3