A simple stereoselective synthesis and biological evaluation of FR181157: Orally active prostacyclin mimetic

Article abstract of DOI:10.1016/j.bmcl.2003.09.054

Synthetic method of novel prostaglandin (PG) mimetic: FR181175 without PG skeleton are described. The key to success is creation of a chiral epoxide using Sharpless AD reaction with high ee yield. FR181157 shows high potency and agonist efficacy at the IP receptor and has good bioavailability.

Full text of DOI:10.1016/j.bmcl.2003.09.054

Bioorganic & Medicinal Chemistry Letters 13 (2003) 4277–4279
A Simple Stereoselective Synthesis and Biological Evaluation of
FR181157: Orally Active Prostacyclin Mimetic
Kouji Hattori,* Seiichiro Tabuchi, Osamu Okitsu and Kiyoshi Taniguchi
Medicinal Chemistry Research Laboratories, Fujisawa Pharmaceutical Co. Ltd, 1-6, Kashima 2-Chome, Yodogawa-Ku, Osaka, Japan
Received 18 August 2003; accepted 29 September 2003
Abstract—Synthetic method of novel prostaglandin (PG) mimetic: FR181175 without PG skeleton are described. The key to suc-
cess is creation of a chiral epoxide using Sharpless AD reaction with high ee yield. FR181157 shows high potency and agonist
efficacy at the IP receptor and has good bioavailability.
# 2003 Elsevier Ltd. All rights reserved.
Introduction
the focus for construction of the desired stereochemistry
of 4 was a chiral epoxide. A ring opening of the epoxide
by a nucleophile creates a chiral center at the benzyl
position and hydroxyl function favorable arranged for
the control of an exo-olefin in the process of elimination.5
Prostacyclin (PGI2): 1 is primarily derived from vas-
cular endothelium and plays an extremely important
inhibitory role in platelet aggregation and as a vasodi-
lator in maintaining homeostatic circulation.1 Despite
fascinating pharmacological properties, the inherent
instability of 1 limits its therapeutic applicability. An
Edinburgh University group,2 a Bristol-Myers Squibb
group,3 and an Ono group4 has already disclosed novel
PGI2 analogues without a PG skeleton. These investi-
gation led us to create of novel PGI2 mimetic with
improved on both chemical and metabolic stability.
After extensive research, we found the non prostanoid
structure FR181157: (S)-4 having potent PGI2 activity
with improved pharmacokinetic property. In order to
generate multigram quantities of (S)-4 for continuing
biological evaluation and its toxicity, an efficient syn-
thetic route had to be developed. In this paper, we would
like to describe a practical and simple stereoselective
synthesis and biological activity of (S)-4 (Fig. 1).
The required optically active epoxide 8 was obtained via
the Sharpless AD reaction and epoxidation shown in
Scheme 2. Commercially available 1-cyclohex-
enylcarboxylic acid 5 was easily transformed into
1-cyclohexenyloxazole 6 by condensation with benzoin
followed by treatment with ammonium acetate in acetic
acid. Asymmetric dihydroxylation of 6 by the standard
procedure6 with 1 mol% of AD-mix-a provided the diol
Chemistry
Our synthetic strategy is illustrated in Scheme 1. We
address to make this compound by especially control-
ling stereochemistry at a benzyl center and a double
bond of a cyclohexene ring. The key substrate that was
*Corresponding author. Tel.: +81-6-6390-1220; fax: +81-6-6304-
5435; e-mail: kouji_hattori@po.fujisawa.co.jp
Figure 1.
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.09.054

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K. Hattori et al. / Bioorg. Med. Chem. Lett. 13 (2003) 4277–4279
Table 1. In vitro effect of FR181157 and the derivatives
7 in 98% ee. Treatment by crystallization with hexane-
ether gave the optically pure product in 80% yield and
>99% ee as determined by HPLC analysis with a chiral
column (Chiralcel AD). The diols 7 was smoothly con-
verted to the epoxide 8 using the method involving a
cyclic acetoxonium intermediate.7 The key chiral epox-
ide 8 was effectively produced on 100–300 g scale with-
out any purification by column chromatography.
Function assay
(IC50 nM)
Binding assay
(Ki nM)
(S)-4: FR181157
(R)-4
14
6054
110NT
530NT
3: BMY 42393
2: Iloprost
3400
2.5
NT
6.5
The completion of the synthesis of (S)-4 from 8 was
accomplished by the route outline in Scheme 3. Ring
opening of 8 with methoxybenzylmagnesium chloride (5
equiv) in the presence of a catalytic amount of CuBr
provided quantitatively the alcohol compound 9 after
purification of short column chromatography. Elimina-
tion of water successfully proceeded with the predicted
regioselectivity upon treatment with p-toluenesulfonic
acid (0.2 equiv) under toluene azeotrope. The crude pro-
duct was purified by crystallization from hexane–ether to
obtain the exo-olefin 10 as a single isomer in 64% yield
and >99% ee (as determined by HPLC). This reaction
gave the olefin compounds with a ratio of exo/
endo=90:10.8 The regioselectivity of the obtained olefin
compounds may be controlled under kinetic control.
When the exo-olefin was treated with p-toluenesulfonic
acid under toluene azeotrope, we could not observe
isomerization to the endo-olefin. On the other hand, the
treatment of the endo-olefin isolated by column chro-
matography with the same condition could not also
occur isomerization. These results suggest that olefin are
not prone to rapid equilibration. Enantiomerically pure
10 was subsequently treated with BBr3 followed by
alkylation with ethylbromoacetate gave the ethyl ester
13. Finally, hydrolysis of 13 furnished (S)-4 in 81%
yield and >99% ee from 10.9
Biological activity
FR181157 possesses potent PGI2 agonist activity and
especially good pharmacokinetic properties. Table 1
was shown the in vitro activity. PGI2 receptor binding
was examined by the conventional ligand binding assay
Scheme 1.
Scheme 2. (a) SOCl2, CH2Cl2; (b) benzoin, Et3N, CH2Cl2; (c) AcONH4, AcOH; (d) AD-mix-a, tBuOH–H2O; (e) Me(OMe)3, cat. p-TsOH, CH2Cl2;
(f) AcBr, CH2Cl2; (g) K2CO3, MeOH.
Scheme 3. (a) m-MeOBzMgBr, cat. CuBr, THF; (b) cat. p-TsOH, Tol; (c) BBr3, CH2Cl2; (d) BrCH2CO2Et, K2CO3; DMF; (e) NaOH, EtOH.

K. Hattori et al. / Bioorg. Med. Chem. Lett. 13 (2003) 4277–4279
4279
Table 2. Pharmacokinetics profiles of FR181157
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8. The ratio of the crude product was determined by 1H NMR.
endo-Olefin was completely removed by crystallization. 1H
NMR of benzyl proton in CDCl3, 10: d 2.53 (1H, dd, J=10.2,
12.8 Hz), 2.31 (1H, dd, J=3.2, 12.8 Hz), 12: d 4.09 (2H, s).
9. The assignment of the absolute configuration of FR181157
was determined by X-ray structural analysis. (S)-4 [a]2D4 +93.0
(c 0.20, MeOH); HPLC (chiralcel AGP, 10 cmÂ0.4 cm I.D.,
flow rate 0.8 mL/min, 20% acetonitrile/0.02 M phosphate
buffer) Rt=4.0min ( >99%). [(R)-4: Rt=6.0min]. This com-
pound should be handled with extreme caution because of
PGI2 agonist activity and high permeability of skin.
(po, fasted)
(iv)
F (%)
Dose
(mg/kg) (ng/mL) (h) (ng h/mL) (h) (mL/min/kg)
Cmax Tmax AUC0À24 t1/2
b
CLtot
Rat 0.32
Dog 0.032
16.4
38.7
0.3
2.3
147.0
391.7
6.6
26
17.7
1.09
50
72
based on the displacement of [3H]-Iloprost from the
cloned human IP receptor.10 IC50 values of the func-
tional assay was obtained by measuring inhibition of
ADP-induced platelet aggregation using human platelet
rich plasma. FR181157 exhibited high binding affinity
for the IP receptor with a Ki of 54 nM and anti-aggre-
gative potency with an IC50 of 60nM. The enatiomer
isomer (R)-4 was 2-fold less potent, and also the endo-
olefin 14 was 9-fold less potent under the same condi-
tion. It is well known that this class of PGI2 mimetic has
species difference.1 FR181157 was also observed the
same result, inhibition of ADP-induced platelet aggre-
gation using rat and dog platelet rich plasma was
20-fold less potent than human (rat: IC50=1.2 mM, dog:
IC50=1.3 mM). Table 2 was shown the pharmacokinetic
profiles of rat and dog. FR181157 without a PG skelton
displayed a good oral bioavailability (rat: F=50%, dog:
F=72%) and long duration time in the both species.
The detailed pharmacological and pharmacokinetic
properties of FR181157 will be published in future.
Conclusion
In this communication, we have reported an oper-
ationally simple method for the highly stereoselective
synthesis and a biological evaluation of FR181157, a
potent and orally active prostacylin mimetic. This is a 12-
step synthesis from commercially available starting
materials, and involves only simple purification to give a
100-g scale. This route should be suitable for industrial
order.
Acknowledgements
We express our thanks to Dr. Hirokazu Tanaka, Dr.
Kazuo Sakane, and Dr. Hisashi Takasugi for their
practical guidance and Dr. David Barrett for his critical
reading of the manuscript.
10. Katsuyama, M.; Sugimoto, Y.; Namba, T.; Irie, A.;
Negishi, M.; Narumiya, S.; Ichikawa, A. FEBS Lett. 1994,
344, 74. Boie, Y.; Ruchmore, T. H.; Darmon-Goodwin, A.;
Grygorczyk, R.; Slipetz, D. M.; Metters, K.; Abramovitz, M.
J. Biol. Chem. 1994, 269, 12173.
References and Notes
1. (a) Wise, H.; Jones, R. L. TiPS 1996, 17, 17. (b) Meanwell,
N. A.; Romine, J. L.; Seiler, S. M. Drugs Future 1994, 19, 361.