R. Hayashi et al. / Bioorg. Med. Chem. Lett. 26 (2016) 2886–2889
2887
Table 1
COOH
N
COOH
In vitro platelet inhibitory activity of 11–21a
O
CH3
O
Cl
COOH
O
N
N
N
CH3
O
O
N
N
O
R2
2
3
Figure 3. Our nonprostanoid IP agonists.
Inhibition of human platelet
aggregation IC50 (nM)
R2
Compound
b,c
11
220
970
COOtBu
HO
HO
a
b
c, d
O
12
N
O
F
NH
N
O
O
O
O
13
690
Cl
4
5
6
14
1200
OCH3
O
O
15
>10,000
>10,000
CF3
Wang
e
f
g, h
Wang
O
Wang
NH
O
O
16
N
O
O
N
Ph
OH
F
17
160
100
160
32
7
8
9
Cl
18
COOH
O
CH3
O
R1
19
i, j
Wang
R1
N
O
OCH3
N
20
N
O
R2
N
H
CF3
21
20,000
: R1 = Me
: R1 = Cl
10a
10b
11- 37
a
IC50 represents the concentration that inhibited induced platelet aggregation by
50%.
b
c
Scheme 1. Synthesis of compounds 11–37. Reagents and conditions: (a) allyl
chloroformate, NEt3, CH2Cl2, rt, 15 h, 74%; (b) BrCH2COOtBu, Bu4NBr, toluene, 10 M
NaOH aq, 50 °C, 14 h, 62%; (c) TFA, CH2Cl2, rt, 3 h; (d) Wang resin, DMP, DIC, DMF, rt,
15 h; (e) 1,3-dimethylbarbituric acid, Pd(PPh3)4, THF, rt, 15 h; (f) 2-bromoethanol,
K2CO3, DMF, rt, 12 h; (g) MsCl, NEt3, CH2Cl2, rt, 2 h; (h) substituted aniline, KI,
CH3CN, 70 °C, 12 h; (i) substituted BzCl, NEt3, THF, rt, 12 h; (j) TFA, CH2Cl2, rt, 1 h.
Platelet aggregation was induced by ADP (5
Values are means of two experiments.
lM) in human platelet rich plasma.
was immobilized on Wang resin. Compound 9 was obtained from
7 by nitrogen deprotection and then hydroxyethylation. The
hydroxyl group of 9 was mesylated, and an aniline moiety and a
benzoyl moiety were sequentially introduced. The final com-
pounds (11–37) were obtained by the cleaved from the Wang
resin. All compounds were purified by HPLC and identified by LC/
MS. Platelet aggregation inhibition activities of synthesized com-
pounds are shown in Tables 1 and 2.15
The type of substituent on the aniline moiety (4-methyl or 4-
chloro) did not influence the effect of substituents on the benzoyl
moiety, and introduction of a 4-methoxy or 4-chloro substituent
on the benzoyl moiety reduced the inhibitory activity. Introduction
of a CF3 or phenyl substituent on the benzoyl moiety resulted in an
especially strong reduction in the inhibitory activity
(Table 1, 15 and 16; Table 2, 26 and 27). On the other hand, substi-
tution at the 3-position of the benzoyl moiety, except introduction
of a CF3 substituent, increased the inhibitory activity. Since intro-
duction of a strongly electron-withdrawing CF3 group at any posi-
tion resulted in substantially decreased the inhibitory activity,
lower electron density in the benzoyl moiety possibly induced
the decreases in platelet aggregation inhibition activity
(Table 1, 15 and 21; Table 2, 26 and 32).
is unsatisfactory (IC50 = 130 nM). To obtain promising drug candi-
dates, the inhibitory activity of IP agonists needs to be improved.
In this letter, we report the design and synthesis of compounds
that maintained the favorable pharmacokinetic profile of 2 while
exhibiting higher platelet aggregation inhibitory activity
(IC50 <100 nM).
We previously showed that replacement of substituents on the
aniline moiety of 2 affected the level of platelet aggregation inhibi-
tory activity, but the same approach was not tested for the benzoyl
moiety, although a similar effect was expected. Accordingly, in this
study, we aimed to discover compounds with substituted benzoyl
moieties that increased platelet aggregation inhibitory activity.
Various substituents (e.g., halogen, electron-donating, electron-
withdrawing, and aromatic groups) at several positions on the ben-
zoyl moiety were tested. As in the case of 2 and 3, the 4-position of
the aniline moiety was substituted with a methyl or chloro. We
used the same solid-phase approach as in our previous study to
efficiently obtain a variety of compounds bearing the above-men-
tioned substituents (Scheme 1).
Also, an electron-donating methoxy group increased the inhibi-
tory activity of the compound when introduced at the 3-position,
but decreased it when introduced at the 4-position
(Table 1, 14 and 20; Table 2, 25 and 31). Tables 1 and 2 showed that
the 3-substituted benzoyl derivatives were more potent than the
After protecting the nitrogen atom of commercially purchased
4-hydroxypiperidine by treatment with allyl chloroformate, the
bromoacetic acid t-butyl ester structure was introduced by O-alky-
lation to produce 6. The ester moiety of 6 was hydrolyzed, and 7