Discovery of diphenylcarbamate derivatives as highly potent and selective IP receptor agonists: Orally active prostacyclin mimetics. Part 3

Article abstract of DOI:10.1016/j.bmcl.2005.04.047

The new classes of diphenylcarbamate derivatives with a tetrahydronaphthalene skeleton as highly potent and selective IP agonists have been discovered. The optimized diphenylcarbamate type compound FK-788: (R)-4 exhibited potent antiaggregative potency wi

Full text of DOI:10.1016/j.bmcl.2005.04.047

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3091–3095
Discovery of diphenylcarbamate derivatives as highly potent
and selective IP receptor agonists: Orally active
prostacyclin mimetics. Part 3
Kouji Hattori,a,* Akira Tanaka,a Osamu Okitsu,a Seiichiro Tabuchi,a Kiyoshi Taniguchi,a
Mie Nishio,b Satoshi Koyama,b Masahide Higaki,b Jiro Sekib and Kazuo Sakanea
aMedicinal Chemistry Research Laboratories, Fujisawa Pharmaceutical Co., Ltd, 2-1-6 Kashima,
Yodogawa-ku, Osaka 532-8514, Japan
bMedicinal Biology Research Laboratories, Fujisawa Pharmaceutical Co., Ltd, 2-1-6 Kashima,
Yodogawa-ku, Osaka 532-8514, Japan
Received 18 February 2005; revised 11 April 2005; accepted 22 April 2005
Abstract—The new classes of diphenylcarbamate derivatives with a tetrahydronaphthalene skeleton as highly potent and selective IP
agonists have been discovered. The optimized diphenylcarbamate type compound FK-788: (R)-4 exhibited potent antiaggregative
potency with an IC50 of 18 nM and high binding affinity for the human recombinant IP receptor with Ki values of 20 nM and selec-
tivity for human IP over all other members of the human prostanoid receptor family. Compound (R)-4 was shown to exhibit good
pharmacokinetic properties in rats and dogs, and also good bioavailability in healthy volunteers.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
maintaining homeostatic circulation.3 Some groups
have already disclosed novel PGI2 analogs without a
PG skeleton, which led us to create a novel PGI2 mi-
metic with improved chemical and metabolic stability.4
Hamanaka and co-workers disclosed AP-227 (3), which
has a tetrahydronaphthalene scaffold with a benzhydr-
ylimine group instead of the natural PG structure.5
We have previously disclosed the new diphenyloxazole
derivatives FR181157 (1) and FR193262 (2) as potent
and orally active prostacyclin mimetics (Fig. 1). We ex-
plored a second structural series with improved potency
and selectivity over all the other human PG receptors,
and good pharmacokinetic profiles. Optimization of
the benzhydrylimine moiety of 3 rapidly led to the iden-
tification of the potent diphenylcarbamate compound 11
in Figure 2. Despite high potency for the human IP
receptor, compound 11 exhibited a lack of selectivity
for the EP3 receptor and poor PK properties, hindering
further pharmacological evaluation. After extensive re-
search, we selected FK-788: (R)-4 as a potential candi-
date, since it exhibited highly potent and selective IP
receptor activity and improved solubility and bioavail-
ability. In this paper, we report the SAR of a series of
diphenylcarbamate derivatives and the biological and
pharmacokinetic profile of (R)-4.
Prostanoid receptors are members of the G-protein cou-
pled receptor superfamily. Recently, eight prostanoid
receptors have been cloned and characterized.1 PGE2
will bind preferentially to the EP1, EP2, EP3, and EP4
receptors, PGD2 to the DP receptor, PGF2a to the FR
receptor, PGI2 to the IP receptor and TXA2 to the TP
receptor. The molecular characterization of these recep-
tors has resulted in renewed interest in the field because
the selectivity of compounds to human prostanoid
receptors can now be determined.2 However, success
has been limited by the problems of identifying suitably
selective ligands. Many of the problems encountered
have been due to the existence of multiple prostanoid
receptor subtypes and the lack of the selectivity of pros-
taglandin analogs.
Prostacyclin (PGI2) is primarily derived from the vascu-
lar endothelium and plays an extremely important inhibi-
tory role in platelet aggregation and as a vasodilator in
Keywords: Diphenylcarbamate; Prostacyclin mimetic; IP receptor.
*
Corresponding author. Tel.: +81 6 6390 1220; fax: +81 6 6304
5435; e-mail: kouji_hattori@po.fujisawa.co.jp
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.04.047

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K. Hattori et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3091–3095
2. Chemistry
Ph
Ph
O
Ph
Ph
N
O
N
The racemic diphenylcarbamate derivatives were synthe-
sized by the routes shown in Scheme 1. Commercially
available 5-hydroxytetralone 5 was converted in four
steps to a,b-unsaturated ester 8. Reduction of 8 with DI-
BAL in toluene, followed by acylation with diphenylcar-
bamoyl chloride in pyridine gave the desired carbamate
9. Deprotection of phenol with tetrabutylammonium
fluoride followed by O-alkylation with ethyl bromoace-
tate and hydrolysis afforded the phenoxyacetic acid 10.
Catalytic hydrogenation of 10 with Pd/C gave the corre-
sponding unsaturated carbamate 11. Similarly the a-
alcohol 7 was transformed into a-alcohol carbamate
derivatives, which were resolved into the two diastereo-
isomers (cis and trans at alcohol with a ratio 5:2)
through chromatographic separation and followed by
the same conditions to give cis-14 and trans-15 as
racemates.
N
NaO2C
O
NaO2C
O
(S)-1: FR181157
2: FR193262
Ph
Ph
O
OH
N
Ph
O
O
N
n-Pr
Ph
HO2C
O
HO2C
O
3: AP-227
(R)-4: FK788
Figure 1.
Figure 2.
O
O
O
OH
O
O
O
a, b
92%
c
d
OEt
OEt
OEt
54%
92%
OH
OR
OR
OR
O
7
5
6: R = TBDPS
8
O
O
Ph
Ph
O
N
O
N
e, f
g, h, i
j
Ph
O
N
Ph
Ph
Ph
68%
71%
HO2C
79%
O
OR
HO2C
9
10
11
OH
O
OH
OH
O
Ph
Ph
O
N
O
N
g, h, i
Ph
Ph
77%
HO2C
HO2C
O
O
OR
k, f
55%
12
14
15
7
OH
O
O
g, h, i
Ph
Ph
O
N
O
N
Ph
82%
Ph
OR
13
Scheme 1. Reagents: (a) TBDPSiCl, imidazole, DMF; (b) (EtO)2CO, NaH, Tol; (c) NaBH4, EtOH–THF; (d) KHSO4, Tol; (e) DIBAL-H, Tol; (f)
ClCON(Ph)2, Py; (g) t-BuNF, THF (h) ethyl bromoacetate, K2CO3, DMF; (i) NaOH, THF–EtOH; (j) Pd/C, AcOEt–EtOH; (k) LiAlH4, THF.

K. Hattori et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3091–3095
3093
O
OH
O
O
O
OH
OH
OH
OH
Ph
d, e, f, g
a
b, c
OH
O
N
OEt
OEt
+
8
Ph
94%
88%
72%
OR
18
O
OR
OR
HO2C
16
17
(R)-4
c
c,d,e,f,g
59%
75%
OH
OH
OH
OH
O
OH
O
OH
Ph
Ph
d,e,f,g
OH
O
N
O
N
Ph
Ph
65%
OR
O
O
HO2C
HO2C
19
20
21
Scheme 2. Reagents: (a) AD-mix-a, t-BuOH–H2O; (b) PPh3–CBr4, CH2Cl2; (c) LAlH4, THF; (d) ClCON(Ph)2, Py; (e) t-BuNF, THF; (f) ethyl
bromoacetate, K2CO3, DMF; (g) NaOH, THF–EtOH.
Table 1. SAR of the diphenylcarbamate derivativesa
Scheme 2 shows asymmetric synthesis of diphenylcarba-
mate derivatives. The required optically active hydroxyl
was obtained via the Sharpless AD reaction. Asymmet-
ric dihydroxylation of 8 by the standard procedure6 with
1 mol % of AD-mix-a provided the diol 16 in 82% yield
and 92% ee with the ketone derivative 17 in 12% yield
and 91% ee. The cis-diol 16 was converted to a-bromo
intermediate by CBr4 and PPh3, followed by reduction
with LiAH4 to give the diol 18. The diol 18 was
smoothly converted to the desired b-hydroxy carbamate
(R)-4 using the same procedure. The optical pure prod-
uct was obtained by crystallization of ethyl ester of 4
with ethanol–ether (>98% ee as determined by HPLC
analysis with a chiral column: Chiralcel AD).7,8 The
(S)-enantiomer was prepared by the same method using
AD-mix-b. The cis-diol derivative 19 was also prepared
from the optically active cis-diol 16. Reduction of the
optically active ketone 17 by LiAH4 stereoselectively
produced the triol 20, followed by the same condition
to give the optically active trans-diol 21.
Compound
Function assay: IC50 (nM)
Rat Dog
Human
(R)-4: FK788 18 0.6
Monkey
1400 600 480 41 13 0.3
(S)-4
10
270 54
91 29
53 6.3
170
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
7400
11
14
15
19
3200
1300
21
3: AP-227
Iloprost
5.8
150 17
2.5 0.14
5600 470
a Results are the average of two or three experiments.
by addition of trans-dihydroxy 21 at the a-and b-posi-
tion of the tetrahydronaphthalene, while the addition
of cis-dihydroxy 19 was 70-fold less active than (R)-4.
The species difference suggested that inhibition of
ADP-induced platelet aggregation using rat and dog
platelet rich plasma was less potent than human (rat:
3. Biological activity
IC50 = 1400 nM, dog: IC50 = 480 nM, monkey: IC50
=
Compound (R)-4 displayed potent PGI2 agonist activity
and especially excellent selectivity over all other human
PG receptors. Table 1 shows the in vitro SAR results for
the diphenylcarbamate derivatives. PGI2 receptor bind-
ing was examined by the conventional ligand binding as-
say based on the displacement of [3H]-Iloprost from the
cloned human IP receptor.9 IC50 values in the functional
assay were obtained by measuring inhibition of ADP-in-
duced platelet aggregation using human, rat, dog, and
monkey platelet rich plasma. Compound (R)-4 exhibited
high binding affinity for the IP receptor with a Ki of
20 nM and good antiaggregative potency with an IC50
of 18 nM. The enantiomer (S)-4 was 15-fold less potent,
and the trans a-hydroxy derivative 15 and the cis deriv-
ative 14 showed decreased potency, with IC50 values of
3200 and 170 nM, respectively, under the same condi-
tions. Twofold improvement in activity also occurred
13 nM). The newly designed (R)-4 showed good affinity
for the IP receptor and excellent selectivity over other
human prostanoid receptors (receptor selectivity > 400)
in Table 2.1 Recent findings indicated that prostaglandin
coupled with Gs may be responsible for the induction of
HGF.10 Figure 3 shows the effect of (R)-4 on HGF pro-
duction in cultured human dermal fibroblasts. Com-
pound (R)-4 increased HGF production in
a
concentration-dependent manner and apparent in-
creases were observed at concentration of 1 nM or more.
On the other hand, the launched Beraprost with PG
skeleton increased HGF at the concentration of 3 nM
(data not shown).11,12
Table 3 shows the pharmacokinetic profiles in rats and
dogs. Compound (R)-4 without a PG skeleton displayed
good oral bioavailability (rat: F = 38%, dog: F = 98%) in

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K. Hattori et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3091–3095
Table 2. Affinity of (R)-4 and derivatives to eight prostanoid receptors
Compound
Human Kia (nM)
TP EP1
9600
IP
DP
2300
FP
EP2
EP3
8200
EP4
(R)-4
(S)-1
2
8.9 0.53
54 0.36
12 0.25
140
>10,000
>1000
>1000
NT
>10,000
>1000
>1000
NT
>10,000
>1000
>1000
>1000
>1000
>10,000
1020
>1000
>1000
NT
>1000
>1000
>1000
>1000
6800
>10,000
1900
>10,000
>10,000
>10,000
11
21
110
NT
NT
NT
>10,000
a Ki determination are averages of two or three experiments. Competitive binding assay based on the displacement of [3H]-Iloprost for human IP
receptor, [3H]-PGD2 for human DP receptors, [3H]-PGF2 for human FP receptors, [3H]-SQ29548 for human TP receptor, and [3H]-PGE2 for
human EP1–4 receptors.
detailed pharmacological work of (R)-4 will be pub-
lished in the near future.
Acknowledgments
We express our thanks to Dr. David Barrett for his crit-
ical reading of the manuscript.
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We designed and synthesized a series of diphenylcarba-
mate derivatives with a tetrahyronaphthalene skeleton
as prostacyclin mimetics. The clinical candidate (R)-4
with an optically active b-hydroxy group exhibited
highly potent and selective IP receptor activity and good
pharmacokinetic properties, especially, in healthy volun-
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Table 3. Pharmacokinetic profiles of (R)-4a
po (fasted) n = 3
iv n = 3
CLtot (mL/min/kg)
Ba (%)
Dose (mg/kg)
Cmax (ng/mL)
AUC (ng/mL h)
t1/2b (h)
Rat
Dog
10
342.4 42.1
305.2 28.5
1594 579
2199 300
1.81 0.43
7.94 1.86
37.95 3.51
2.31 0.33
38
98
0.32
a Results are shown as the mean SE.

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