Octahydrocyclopenta[c]pyridine and octahydrocyclopenta[c]pyran analogues as a protease activated receptor 1 (PAR1) antagonist

Article abstract of DOI:10.1007/s12272-015-0623-6

Protease activated receptor 1 (PAR1) has been considered as a promising antiplatelet target to prevent thrombotic cardiovascular events in patients with prior myocardial infarction or peripheral arterial diseases. Previously, we found a series of octahydroindene analogues to have high potency on PAR1 and no significant cytotoxicity but poor metabolic stability in human and rat liver microsomes. We have designed and synthesized fused 6/5 heterobicycle analogues with octahydrocyclopenta[c]pyridine or octahydrocyclopenta[c]pyran core scaffold by the insertion of heteroatom at C5 of octahydroindene ring aiming to improvement of metabolic stability. Both heterobicycle analogues showed much more improved metabolic stability compared with octahydroindenes without remarkable decrease in activity. Compounds 22 (IC₅₀ = 110 nM) and 33 (IC₅₀ = 50 nM) from this series showed good activity on PAR1 with moderate metabolic stability.

Full text of DOI:10.1007/s12272-015-0623-6

Arch. Pharm. Res.
DOI 10.1007/s12272-015-0623-6
RESEARCH ARTICLE
Octahydrocyclopenta[c]pyridine
and octahydrocyclopenta[c]pyran analogues as a protease
activated receptor 1 (PAR1) antagonist
Abdul Wadood1,2 Haejin Kim1,2 Chul Min Park1 Jong-Hwan Song1
Sunkyung Lee1,2
•
•
•
•
Received: 5 May 2015 / Accepted: 4 June 2015
Ó The Pharmaceutical Society of Korea 2015
Abstract Protease activated receptor 1 (PAR1) has been
considered as a promising antiplatelet target to prevent
thrombotic cardiovascular events in patients with prior
myocardial infarction or peripheral arterial diseases. Previ-
ously, we found a series of octahydroindene analogues to
have high potency on PAR1 and no significant cytotoxicity
but poor metabolic stability in human and rat liver micro-
somes. We have designed and synthesized fused 6/5 heter-
obicycle analogues with octahydrocyclopenta[c]pyridine or
octahydrocyclopenta[c]pyran core scaffold by the insertion
of heteroatom at C5 of octahydroindene ring aiming to
improvement of metabolic stability. Both heterobicycle
analogues showed much more improved metabolic stability
compared with octahydroindenes without remarkable
decrease in activity. Compounds 22 (IC50 = 110 nM) and
33 (IC50 = 50 nM) from this series showed good activity on
PAR1 with moderate metabolic stability.
Introduction
The beneficial effects of antiplatelet therapy on cardio-
vascular diseases have been proven (David and Patrono
2007). Thrombin regulates platelet aggregation mainly
through actions on protease activated receptor 1 (PAR1),
platelet surface G-protein coupled receptor (Coughlin
2000, 2005; Hein et al. 1994; Ishii et al. 1993; Trejo et al.
1998; Vu et al. 1991; Zhang et al. 2012). PAR1 has been
considered as a promising antiplatelet target to treat
patients with prior cardiovascular events, leading to the
reduction of the rate of cardiovascular death, myocardial
infarction (MI), stroke, and urgent coronary revascular-
ization (Chackalamannil et al. 2005; Chackalamannil and
Xia 2006; Chelliah et al. 2012, 2014; Clasby et al. 2006;
Dockendorff et al. 2012; Ramachandran et al. 2012).
Vorapaxar, a first-in-class PAR 1 antagonist, has been
approved by USFDA in 2014 as the indication for the
reduction of thrombotic cardiovascular events in patients
with a history of MI or with peripheral arterial disease
(PAD), which indicates the clinical validation on this
mechanism of action (Chackalamannil et al. 2008; Koso-
glou et al. 2012; Morrow et al. 2012; Xia et al. 2010).
Previously, we identified fused 6/5 bicycle, octahy-
droindene as a novel scaffold for PAR1 antagonists (Lee
2011; Lee et al. 2013). Although these series of compounds
showed high potency and no significant cytotoxicity, they
were metabolically unstable in both human and rat live
microsomes. We try to improve their metabolic stability by
the insertion of heteroatom at C5 which might be the site of
metabolism (Fig. 1). In this paper, we disclose the design,
synthesis, PAR1 inhibitory activity, and metabolic stability
of fused 6/5 heterobicycle compounds with octahydrocy-
clopenta[c]pyridine or octahydrocyclopenta[c]pyran core
scaffold.
Keywords Protease activated receptor 1 Á 6/5 Fused
heterobicycle Á Octahydrocyclopenta[c]pyridine Á
Octahydrocyclopenta[c]pyran Á Octahydroindene Á
Metabolic stability
& Sunkyung Lee
leesk@krict.re.kr
1
Division of Drug Discovery Research, Research Center for
Medicinal Chemistry, Korea Research Institute of Chemical
Technology, 141 Gajeong-ro, Yuseong, Daejeon 305-343,
Republic of Korea
2
Korea University of Science and Technology, 141 Gajeong-
ro, Yuseong, Daejeon 305-343, Republic of Korea
123

A. Wadood et al.
reaction NH4Cl solution was added, and the layers were
separated. An aqueous layer was extracted with CH2Cl2
twice. The combined organic layers were washed with
brine, dried over MgSO4, filtered, and concentrated under
reduced pressure. The residue was used for the next step
without purification.
Ethyl (E)-5-(t-butoxycarbonylamino)pent-2-enoate (4)
Fig. 1 Design of octahydrocyclopenta[c]pyrimidine and octahydro-
cyclopenta[c]pyran core
To the mixture of NaH (1.5 g, 64 mmol, 60 % in an oil) in
anhydrous THF (400 mL) was added ethyl 2-(di-
ethoxyphosphoryl)acetate (13.6 mL, 68.6 mmol) at 0 °C,
which was stirred for 10 min at 0 °C, and cooled to
-78 °C. The compound 3 dissolved in anhydrous THF
(30 mL) was added at -78 °C, and the mixture was stirred
for 1 h at rt. After the solvent was removed, the residue
was filtered through a silica gel pad using hexane/ethyl
acetate (3:1) solution. The filtrate was concentrated under
reduced pressure and the residue was purified by silica gel
column chromatography (hexane:ethyl acetate = 9:1) to
give a pale yellow oil (8 g, yield 74 % over 2steps).
1H NMR (300 MHz, CDCl3) d 1.27 (t, 3H, J = 7.1 Hz),
1.44 (s, 9H), 2.40 (q, 2H, J = 6.4 Hz), 3.26 (m, 2H), 4.18
(q, 2H, J = 7.1 Hz), 4.56 (s, 1H), 5.87 (m, 1H), 6.86 (m,
1H). MS 243 (M?).
Materials and methods
Chemistry
Anhydrous solvents were dried by conventional methods.
Reagents of commercial quality were used from freshly
opened containers unless otherwise stated. For purification
of products by column chromatography, Merck Silica gel
60 (230–400 mesh) was used. 1H NMR spectra were
recorded on a Varian Gemini 300 with TMS as an internal
standard. Chemical shifts are reported in d (ppm). Mass
spectra were obtained with a Bruker instrument by using
electron impact techniques.
tert-Butyl(3-hydroxypropyl)carbamate (2)
tert-Butyl (E)-5-(hydroxypent-3-enyl)carbamate (5)
To the solution of 3-amino-1-propanol (14 mL,
66.6 mmol) in CH2Cl2 (150 mL) were added Et3N (14 mL,
99.9 mmol) and di-tert-butyldicarbonate at 0°C. After
stirring for 1 h at rt, the reaction mixture was concentrated
under reduced pressure to remove all volatiles. The residue
was diluted with water, and extracted with ethyl acetate.
The organic layer was washed twice with brine, dried over
MgSO4, filtered, and concentrated under reduced pressure.
The residue was purified by silica gel column chromatog-
raphy (hexane:ethyl acetate = 1:1) to give an off-white oil
(1.1 g, yield 94 %).
To the solution of compound 4 (8 g, 32.9 mmol) in
anhydrous CH2Cl2 (300 mL), diisobutylaluminium hydride
(82.3 mL, 1 M in toluene) was added at -78°C, and the
reaction mixture was stirred for 1 h ar rt. Methanol was
added to the reaction and the mixture was filtered through a
silica gel pad. The filtrate was concentrated under reduced
pressure and the residue was purified by silica gel column
chromatography (hexane:ethyl acetate = 2:1) to give a
pale yellow oil (5.5 g, yield 83 %).
1H NMR (300 MHz, CDCl3) d 1.44 (s, 9H), 2.21–2.27
(m, 2H), 3.15–3.22 (m, 2H), 4.09–4.13 (m, 2H), 4.56 (1H,
s), 5.64–5.75 (m, 2H). MS 201 (M?).
1H NMR (300 MHz, CDCl3) d 1.45 (s, 9H), 1.65 (m
2H), 3.28 (t, 2H, J = 5.9 Hz), 3.68 (t, 2H, J = 5.4 Hz),
4.86 (s, 1H), MS 175 (M?).
tert-Butyl (E)-{5-[(tert-butyldimethylsilyl)oxy]pent-3-en-1-
tert-Butyl(3-oxopropyl)carbamate (3)
yl}carbamate (6)
The solution of DMSO (9.74 mL, 137.1 mmol) and oxalyl
chloride (5.8 mL, 68.6 mmol) in anhydrous CH2Cl2
(400 mL) was stirred for 15 min at -78 °C, and the
compound 2 (8 g, 45.7 mmol) dissolved in anhydrous
CH2Cl2 (30 mL) was added. The reaction mixture was
continuously stirred for an additional 1 h at -78 °C.
Subsequently, Et3N (31.8 mL, 228.5 mmol) was added,
and the reaction mixture was stirred for 1 h at rt. To the
To the solution of compound 5 (11 g, 54.7 mmol) in THF
(300 mL) were added imidazole (8.9 mg, 131.3 mmol) and
tert-butyldimethylsilyl chloride (9.9 g, 65.6 mmol). After
stirring for 1 h at rt, aqueous NH4Cl solution was added to
the reaction. The mixture was extracted with ethyl acetate.
The organic layer was washed twice with brine, dried over
MgSO4 and filtered. The filtrate was concentrated under
reduced pressure and the residue was purified by silica gel
123

Octahydrocyclopenta[c]pyridine and octahydrocyclopenta[c]pyran analogues as a protease…
column chromatography (hexane:ethyl acetate = 10:1) to
give a pale yellow (16 g, yield 93 %).
1H NMR (300 MHz, CDCl3) d 0.05 (s, 6H), 0.89 (s,
9H), 1.45 (s, 9H), 2.20 (m, 2H), 3.15 (m, 2H), 4.11 (m,
2H), 4.52 (s, 1H), 5.56–5.62 (m, 2H). MS 315 (M?).
The mixture was stirred under hydrogen atmosphere (60
psi) for 10 h, and was filtered through a silica gel pad. The
filtrate was concentrated under reduced pressure and the
residue was purified by silica gel column chromatography
(hexane:ethyl acetate = 5:1) to give a pale yellow oil
(1.7 g, yield 74 %).
tert-Butyl (E)-{5-[(t-butyldimethylsily)loxy]pent-3-en-1-
1H-NMR (300 MHz, CDCl3) d 0.02 (s, 6H), 0.85 (s,
9H), 1.46 (s, 9H), 1.57–1.63 (m, 1H), 1.82–1.90 (m, 1H),
2.14–2.25 (m, 3H), 2.45–2.61 (m, 2H), 3.30–3.36 (m, 1H),
3.60–3.88 (m, 4H), 3.90–3.95 (m, 1H). MS 383 (M?).
yl}(prop-2-yn-1-yl)carbamate (7)
To anhydrous THF (15 mL) were added NaH (1.35 g,
57.03 mmol, 60 % in oil) and 15-crown-5 (11.2 mL,
57.03 mmol) at -30 °C. The compound 6 (6 g, 19.1 mmol)
dissolved in anhydrous THF (180 mL) and propargyl bro-
mide (10.5 mL, 95.08 mmol) were added at -30 °C and the
mixture was stirred for 2 h at rt. Aqueous NH4Cl solution
was added to the reaction. The mixture was extracted with
ethyl acetate. The organic layer was washed twice with
brine, dried over MgSO4 and filtered. The filtrate was con-
centrated under reduced pressure and the residue was puri-
fied by silica gel column chromatography (hexane:ethyl
acetate = 5:1) to give a pale yellow oil (4.0 g, yield 60 %).
1H NMR (300 MHz, CDCl3) d 0.05 (s, 6H), 0.89 (s,
9H), 1.45 (s, 9H), 2.13 (m, 1H), 2.18–2.23 (m, 2H),
3.07–3.13 (m, 1H), 3.26–3.31 (m, 1H), 4.04–4.07 (m, 2H),
4.14 (m, 2H), 5.51–5.55 (m, 2H). MS 353 (M?).
tert-Butyl( )-(4aR,5R,7aR)-5-{[(t-
butyldimethylsilyl)oxy]methyl}-6-hydroxy-6-
methyloctahydro-2H-cyclopenta[c]pyridine-2-carboxylate
(10)
To the solution of ketone 9 (300 mg, 0.78 mmol) in
anhydrous THF (10 mL) was added CH3MgBr (1.0 M
solution, 1.6 mL) at -78 °C, which was stirred for 1 h at
rt, NH4Cl was added to the reaction mixture. After removal
of all volatiles under reduced pressure, the residue was
diluted with CH2Cl2. The organic layer was washed twice
with brine, dried over MgSO4 and filtered. The filtrate was
concentrated and purified by silica gel column chro-
matography (hexane:ethyl acetate = 10:1) to give a pale
yellow oil (130 mg, yield 42 %).
tert-Butyl( )-(4aS,5R)-5-{[(tert-
butyldimethylsilyl)oxy]methyl}-6-oxo-1,3,4,4a,5,6-
hexahydro-2H-cyclopenta[c]pyridine-2-carboxylate (8)
1H NMR (300 MHz, CDCl3) d 0.03 (s, 6H), 0.89 (s,
9H), 1.26 (s, 3H), 1.46 (s, 9H), 1.69–1.75 (m, 2H),
1.86–1.99 (m, 2H), 2.12–2.23 (m, 2H), 2.89–3.13 (m,
2H), 3.25–3.39 (m, 1H), 3.43–3.52 (m, 1H), 3.65 (m,
1H), 3.68–3.79 (m, 1H), 3.81–3.98 (m, 1H). MS 399
(M?).
To the solution of compound 7 (4.0 g, 11.3 mmol) in
anhydrous CH2Cl2 (150 mL) was added Co2(CO)8 (3.9 g,
11.3 mmol) at 0 °C, and the mixture was stirred at rt for
2 h to form a complex between the compound and Co. N-
Methylmorpholine-N-oxide (1.37 g, 11.77 mmol) was
added at 0 °C to the reaction mixture. After stirring for 2 h
at rt, the mixture was filtered through a silica gel pad and
the filtrate was concentrated. The residue was purified by
silica gel column chromatography (hexane:ethyl acet-
ate = 7:1) to give a pale yellow oil (2.3 g, yield 53 %).
1H NMR (300 MHz, CDCl3) d 0.04 (s, 6H), 0.08 (s,
9H), 1.58–1.64 (m, 1H), 2.09–2.18 (m, 2H), 2.83–2.88 (m,
1H), 3.56–3.64 (m, 1H), 3.80–3.89 (m, 2H), 4.02–4.13 (m,
1H), 4.15 (d, 1H, J = 13.4 Hz), 4.65 (d, 1H, J = 13.4 Hz),
5.88 (s, 1H). MS 381 (M?).
tert-Butyl( )-(4aR,5R,7aR)-6-hydroxy-5-(hydroxymethyl)-
6-methyloctahydro-2H-cyclopenta[c]pyridine-2-
carboxylate (11)
To the solution of compound 10 (130 mg, 0.325 mmol) in
anhydrous THF (4 mL) was added tetrabutylammonium
fluoride (1.0 M solution, 9 lL, 0.032 mmol) at 0 °C. The
mixture was stirred for 1 h at rt, and was diluted with
CH2Cl2. The organic layer was washed twice with brine,
dried over Na2SO4 and filtered. The filtrate was concen-
trated and purified by silica gel column chromatography
(hexane:ethyl acetate = 4:1) to give a pale yellow oil
(85 mg, yield 92 %).
1H NMR (300 MHz, CDCl3) d 1.23 (s, 3H), 1.46 (s,
9H), 1.63–1.85 (m, 2H), 2.03 (m, 2H), 2.31–2.43 (m, 3H),
3.06 (m, 1H), 3.35–3.36 (m, 2H), 3.36–3.38 (m, 1H),
3.73–3.77 (m, 2H). MS 285 (M?).
tert-Butyl( )-(4aR,5R,7aR)-5-{[(t-
butyldimethylsilyl)oxy]methyl}-6-octahydro-2H-
cyclopenta[c]pyridine-2-carboxylate (9)
To the solution of compound 8 (2.3 g, 6.03 mmol) in
ethanol (3 mL) was added Pd(OH)2 (0.23 g, 1.21 mmol).
123

A. Wadood et al.
tert-Butyl( )-(4aR,5S,7aR)-5-formyl-6-hydroxy-6-
methyloctahydro-2H-cyclopenta[c]pyridine-2-carboxylate
(12)
filtered. The filtrate was concentrated and purified by silica
gel column chromatography (hexane:ethyl acetate = 1:1)
to give a pale yellow solid (50 mg, yield 91 %).
1H NMR (300 MHz, CDCl3) d 1.24 (s, 3H), 1.50 (s,
9H), 1.85–1.87 (m, 2H), 2.01–2.02 (m, 2H), 2.41–2.44 (m,
1H), 2.47–2.51 (m, 1H), 2.90 (m, 2H), 3.36–3.45 (m, 2H),
3.53–3.55 (m, 1H), 4.52 (s, 2H), 6.60–6.64 (m, 1H),
6.73–6.82 (m, 1H), 7.08–7.11 (m, 1H), 7.25 (s, 1H), 7.38
(m, 2H), 7.43–7.54 (m, 1H), 7.83 (m, 1H), 8.81(d, 1H,
J = 1.3 Hz). MS 495 (M?).
To the solution of alcohol 11 (85 mg, 0.3 mmol) in CH2Cl2
was added o-iodoxybenzoic acid (180 mg, 0.642 mmol),
and the mixture was stirred for 2 h at rt. To the mixture was
added saturated NaHCO3 solution (1 mL). Layers were
separated, and the aqueous layer was extracted with CH2-
Cl2. The organic layers were combined, and dried over
MgSO4 and filtered. The filtrate was concentrated under
reduced pressure to give an aldehyde, which was used for
the next step without further purification.
( )-(4aR,5S,7aR)-5-(E)-2-{5-(3-fluorophenyl)pyridine-2-
yl]vinyl}-6-methyloctahydro-2H-cyclopenta[c]pyridine-6-
yl carbamate (15)
tert-Butyl( )-(4aR,5S,7aR)-5-(E)-2-{5-(3-
fluorophenyl)pyridine-2-yl]vinyl}-6-hydroxy-6-
methyloctahydro-2H-cyclopenta[c]pyridine-2-carboxylate
(13)
To the solution of compound 14 (50 mg, 0.101 mmol) in
CH2Cl2 (2 mL) was added CF3COOH (50 lL) at 0 °C. The
reaction mixture was stirred for 1 h at rt, neutralized by
1 N NaOH, and extracted with CH2Cl2. The organic layer
was washed twice with brine, dried over Na2SO4, filtered
and concentrated. The residue was purified by silica gel
column chromatography (CH2Cl2:MeOH = 10:1) to give a
pale yellow solid (36 mg, yield 90 %).
1H-NMR (300 MHz, CDCl3) d 0.21 (s, 3H), 2.01 (m,
1H), 2.41 (m, 1H), 2.48 (m, 1H), 2.53 (m, 1H), 2.71–2.86
(m, 3H), 2.96 (m, 1H), 4.58 (s, 2H), 6.57 (m, 1H), 6.77 (m,
1H), 7.11 (m, 1H), 7.28 (m, 1H), 7.32 (m, 2H), 7.43 (m,
1H), 7.83 (m, 1H), 8.77 (d, 1H, J = 0.9 Hz). MS 395
(M?).
In the solution of diethyl {[30-fluoro(1,10-biphenyl)4-
yl]vinyl}Phosphonate (150 mg, 0.45 mmol) in anhydrous
THF (2 mL) was slowly added n-BuLi (0.16 mL, 2.5 M
toluene solution) at 0 °C. After stirring for 30 min, the
aldehyde 12 dissolved in THF (1 mL) was slowly added.
After stirring for 2 h at rt, the mixture was extracted
with ethyl acetate. The organic layer was washed twice
with brine, dried over Na2SO4 and filtered. The filtrate was
concentrated and purified by silica gel column chro-
matography (hexane:ethyl acetate = 10:1) to give a pale
yellow oil (68 mg, yield 50 %).
1H NMR (300 MHz, CDCl3) d 1.22 (s, 3H), 1.48 (s,
9H), 1.65–1.83 (m, 2H), 2.01–2.03 (m, 2H), 2.35–2.42 (m,
2H), 3.08 (q, 1H, J = 6.02 Hz), 3.35–3.36 (m, 2H),
3.38–3.41 (m, 1H), 3.53–3.55 (m, 1H), 6.64–6.73 (m, 1H),
6.78–6.83 (m, 1H), 7.21–7.27 (m, 2H), 7.34–7.46 (m, 2H),
7.79–7.82 (m, 1H), 8.75 (s, 1H). MS 452 (M?).
( )-(4aR,5S,7aR)-2-carbamoyl-5-(E)-2-{5-(3-
fluorophenyl)pyridine-2-yl]vinyl}-6-methyloctahydro-2H-
cyclopenta[c]pyridine-6-yl carbamate (16)
To the solution of compound 15 (10 mg, 0.025 mmol) in
CH2Cl2 (1 mL) were added Et3N (5 lL, 0.038 mmol) and
triethylsilylisocyanate. The reaction mixture was stirred for
1 h at rt and diluted with CH2Cl2. The organic layer was
washed twice with brine, dried over Na2SO4, filtered and
concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (CH2Cl2:-
MeOH = 15:1) to give an off white solid (10 mg, yield
90 %) .
1H-NMR (300 MHz, CDCl3) d 1.19 (s, 3H), 1.94-2.02
(m, 2H), 2.21 (m, 1H), 2.27 (m, 1H), 2.42 (m, 1H), 2.98-
3.12 (m, 2H), 3.32 (m, 1H), 3.44 (m, 1H), 3.78 (m, 1H),
4.35 (s, 1H), 4.51–4.53 (m, 2H), 6.58 (m, 1H), 6.80 (m,
1H), 7.10 (m, 1H), 7.28 (m, 1H), 7.33–7.37 (m, 2H), 7.43
(m, 1H), 7.84 (m, 1H), 8.77(d, J = 1.1 Hz, 1H). MS 438
(M?).
tert-Butyl ( )-(4aR,5S,7aR)-6-(carbamoyloxy)-5-(E)-2-{5-
(3-fluorophenyl)pyridine-2-yl]vinyl}-6-methyloctahydro-
2H-cyclopenta[c]pyridine-2-carboxylate (14)
To the solution of compound 13 (48 mg, 0.106 mmol) in
anhydrous THF (2 mL) was added trichloroacetyl iso-
cyanate (0.025 mL, 0.212 mmol). The mixture was stirred
for 2 h at rt, and concentrated under reduced pressure to
remove all volatiles. Methanol (2 mL), H2O (0.1 mL) and
K2CO3 (0.038 g, 0.245 mmol) were added to the residue.
The mixture was stirred at rt until the starting material was
disappeared in TLC. After completion of the reaction, the
mixture was extracted with ethyl acetate The organic layer
was washed twice with brine, dried over MgSO4 and
123

Octahydrocyclopenta[c]pyridine and octahydrocyclopenta[c]pyran analogues as a protease…
( )-(4aR,5S,7aR)-5-(E)-2-{5-(3-fluorophenyl)pyridine-2-
stirring at 0 °C. After stirring for 10 min, the reaction
yl]vinyl}-2-formyl-6-methyloctahydro-2H-
mixture was warmed to rt and was stirred for 2 h. EtOH
(1 mL) was added to the reaction. To the mixture were
added 3 N NaOH (1 mL) and 30 % H2O2 (1 mL), which
was then heated at reflux with stirring for 2 h. The layers
were separated and the aqueous layer was extracted with
ethyl acetate (3 9 10 mL). The combined organic layers
were dried over anhydrous MgSO4 and filtered. The filtrate
was concentrated under reduced pressure and the residue
was purified by silica gel column chromatography (hex-
ane:ethyl acetate = 5:1) to give a pale yellow oil (85 mg,
yield 45 %).
cyclopenta[c]pyridine-6-yl carbamate (17)
(CH3CO)2O (3.6 lL, 0.038 mmol) and HCOOH (1.5 lL,
0.038 mmol) were stirred for 2 h at 50°C and added to the
solution of compound 16 (10 mg, 0.025 mmol) in THF
(1 mL). After stirring for 20 min at room temperature, the
mixture was diluted with CH2Cl2 and washed twice brine,
dried over Na2SO4, filtered and concentrated under reduced
pressure. The residue was purified by silica gel column
chromatography (CH2Cl2:MeOH = 12:1) to give a white
solid (10 mg, yield 90 %).
1H-NMR (300 MHz, CDCl3) d 1.19 (s, 3H), 2.00-2.09
(m, 2H), 2.27 (t, J = 1.4 Hz, 1H), 2.45–2.58 (m, 2H),
3.04–3.25 (m, 2H), 3.31–3.52 (m, 3H), 4.16 (m, 1H),
4.53–4.57 (m, 2H), 6.57 (m, 1H), 6.79 (m, 1H), 7.10 (m,
1H), 7.28 (m, 1H), 7.32 (d, J = 11.9 Hz, 1H), 7.45 (m,
1H), 7.84 (m, 1H), 8.09 (s, 1H), 8.79(s, 1H). MS 423 (M?).
1H-NMR (300 MHz, CDCl3) d 0.08 (s, 6H), 0.90 (s,
9H), 1.47 (s, 9H), 1.50–1.70 (m, 4H), 1.74–1.76 (m, 3H),
2.03–2.12 (m, 4H), 3.03–3.08 (m, 1H), 3.22 (s, 2H),
3.39–3.42 (m, 1H), 3.62–3.76 (m, 6H). MS 443 (M?).
tert-Butyl( )-(4aR,5R,7aR)-5-{[(tert-
butyldimethylsilyl)oxy]methyl}-50-oxooctahydro-30H-
spiro(cyclopenta [c]pyidine-6,20-furan)-2(1H)-carboxylate
(20)
tert-Butyl( )-(4aR,5R,7aR)-6-allyl-5-{[(tert-
butyldimethylsilyl)oxy]methyl}-6-hydroxyoctahydro-2H-
cyclopenta[c]pyidine-2-carboxylate (18)
To the solution of compound 19 (85 mg, 0.191 mmol) in
CH2Cl2 (2 mL) was added pyridium chlorochromate
(124 mg, 0.575 mmol) with stirring at rt, The resulting
dark brown suspension was stirred for 6 h at rt. A Celite
545 (100 mg) was added to the mixture, which was stirred
for 30 min. The reaction mixture was filtered through a
Celite 545 pad using CH2Cl2 (30 mL). The filtrate was
concentrated under reduced pressure and the residue was
purified by silica gel column chromatography (hex-
ane:ethyl acetate = 5:1) to give a pale yellow oil (62 mg,
yield 74 %).
1H-NMR (300 MHz, CDCl3) d 0.05 (s, 6H), 0.88 (s,
9H), 1.46 (s, 9H), 1.63–1.68 (m, 2H), 1.76–1.83 (m, 2H),
1.89–2.03 (m, 2H), 2.11–2.28 (m, 2H), 2.51–2.59 (m, 3H),
3.14 (m, 1H), 3.33 (m, 2H), 3.66–3.75 (m, 4H). MS 439
(M?).
To the solution of ketone 17 (200 mg, 0.521 mmol) in THF
(6 mL) was added allyl magnesium bromide (1.04 mL,
1.0 M in Et2O) with stirring at -78 °C. After stirring for
10 min, the reaction mixture was warmed to 0 °C and
stirred for 2 h at 0 °C. Saturated aqueous NH4Cl solution
(6 mL) was added to the mixture to stop the reaction. The
layers were separated and the aqueous layer was extracted
with ethyl acetate (3 9 10 mL). The combined organic
layers were dried over anhydrous MgSO4, filtered, and
concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (hex-
ane:ethyl acetate = 10:1) to give a pale yellow oil
(180 mg, yield 81 %).
1H-NMR (300 MHz, CDCl3) d 0.04 (s, 6H), 0.87 (s,
9H), 1.47 (s, 9H), 1.67–1.75 (m, 2H), 2.24–2.31 (m, 2H),
2.42–2.58 (m, 2H), 3.10–3.28 (m, 2H), 3.40–3.51 (m, 2H),
3.55–3.77 (m, 2H), 3.93 (m, 2H), 5.07 (d, 1H, J = 4.5 Hz),
5.85–5.94 (m, 2H). MS 425 (M?).
tert-Butyl( )-(4aR,5R,7aR)-5-(hydroxymethyl)-50-
oxooctahydro-30H-spiro(cyclopenta [c]pyidine-6,20-
carboxylate (21)
tert-Butyl( )-(4aR,5R,7aR)-5-{[(tert-
butyldimethylsilyl)oxy]methyl}-6-hydroxy-9-(3-
hydroxylpropyl)octahydro-2H-cyclopenta[c]pyidine-2-
carboxylate (19)
Using the compound 20 (62 mg, 0.141 mmol) as a starting
material, the same reaction to prepare compound 11 was
proceeded to give a pale yellow oil (36 mg, yield 78 %).
1H-NMR (300 MHz, CDCl3) d 1.49 (s, 9H), 1.60 (m,
1H), 1.83 (m, 1H), 1.97–2.05 (m, 4H), 2.29 (m, 1H),
2.38–2.45 (m, 1H), 2.55–2.64 (m, 2H), 3.15(m, 1H), 3.23
(m, 1H), 3.41 (m, 1H), 3.56 (m, 1H), 3.79 (m, 1H),
4.25–4.31(m, 2H). MS 325 (M?).
To the solution of compound 18 (180 mg, 0.423 mmol) in
THF (5 mL) was slowly added borane-methylsulfide
complex (0,63 mL, 2.0 M in THF, 1.27 mmol) with
123

A. Wadood et al.
tert-Butyl( )-(4aR,5S,7aR)-5-(E)-2-{5-(3-
fluorophenyl)pyridine-2-yl]vinyl}-50-oxooctahydro-30H-
spiro(cyclopenta [c]pyidine-6,20-furan)-2(1H)-carboxylate
(22)
washed twice with brine, dried over MgSO4, and filtered.
The filtrate was concentrated under reduced pressure and
the residue was purified by silica gel column chromatog-
raphy (hexane:ethyl acetate = 3:1) to give an of white oil
(14 g, yield 73 %).
1H-NMR (300 MHz, CDCl3) d 1.82 (m, 2H), 2.47 (s,
1H), 3.69 (t, 2H, J = 5.7 Hz), 3.74 (t, 2H, J = 5.4 Hz),
4.16 (s, 2H). MS 114 (M?).
Using the compound 21 (35 mg, 0.101 mmol) as a starting
material, the same reactions to prepare compound 12 and
13 were proceeded sequentially to give a pale yellow oil
(17 mg, yield 35 % over 2 steps).
1H-NMR (300 MHz, CDCl3)
d
1.47(s, 9H),
3-(Prop-2-yn-1-yloxy)propanal (26)
1.59–1.62(m, 1H), 1.82–1.83(m, 1H), 1.99–2.07(m, 4H),
2.17–2.25(m, 1H), 2.31–2.48(m, 1H), 2.50–2.54(m, 2H),
2.93–2.99(m, 1H), 3.11–3.19(t, J = 8.2 Hz, 1H),
3.31–3.33(m, 1H), 3.42–3.60(m, 1H), 3.73–3.81(m, 1H),
4.15(m, 1H), 6.65–6.74(m, 2H), 7.10(t, J = 1.5 Hz, 1H),
7.35–7.37(m, 2H), 7.44–7.46(m, 1H), 7.83(d, J = 4.5 Hz,
1H), 8.77(s, 1H). MS 492 (M?).
To the solution of compound 25 (14 g, 122.65 mmol) in
anhydrous CH2Cl2 (400 mL) were added molecular sieve,
sodium acetate (50.3 g, 613.25 mmol) and pyridinium
chlorochromate (65.8 g, 306.66 mmol) at 0 °C. The mix-
ture was stirred for 1 h at 0 °C, and filtered through a
Celite pad, and extracted with ether. The filtrate was con-
centrated and purified by silica gel column chromatogra-
phy (hexane:ethyl acetate = 3:1) to afford an off white oil
(6 g, yield 44 %).
( )-(4aR,5S,7aR)-5-(E)-2-{5-(3-fluorophenyl)pyridine-2-
yl]vinyl}decahydro-50H- spiro(cyclopenta [c]pyidine-6,20-
furan)-50-one (23)
1H-NMR (300 MHz, CDCl3) d 2.46 (s, 1H), 2.68 (t, 2H,
J = 6.06 Hz), 3.88 (t, 2H, J = 6.06 Hz), 4.16 (s, 2H), 9.79
(s, 1H). MS 112 (M?).
Using the compound 22 (16 mg, 0.032 mmol) as a starting
material, the same reaction to prepare compound 15 was
proceeded to give a pale yellow oil (10 mg, yield 78 %).
1H-NMR (300 MHz, CDCl3) d 1.72 (s, 4H), 2.01–2.07
(m, 2H), 2.19–2.22 (m, 2H), 2.45–2.53 (m, 2H), 2.75 (m,
2H), 2.88 (m, 1H), 2.94 (m, 1H), 3.16 (m, 1H), 6.62(m,
1H), 6.71 (m, 1H), 7.09 (m, 1H), 7.29 * 7.37 (m, 2H),
7.43 (m, 1H), 7.82 (m, 1H), 8.77 (d, 1H, J = 1.1 Hz). MS
392 (M?).
Ethyl (E)-5-(Prop-2-yn-1-yloxy)pent-2-enoatel (27)
Using the compound 26 (90 mg, 0.80 mmol) as a starting
material, the same reaction to prepare compound 4 was
proceeded to give a pale yellow oil (80 mg, yield 59 %).
1H-NMR (300 MHz, CDCl3) d 2.48 (s, 1H), 2.51(q, 2H,
J = 6.39 Hz, J = 13.0 Hz), 3.65 (t, 2H, J = 6.39 Hz),
3.73 (s, 3H), 4.15 (s, 2H), 5.94–5.88 (m, 1H), 6.99–6.94
(m, 1H). MS 182 (M?).
( )-(4aR,5S,7aR)-5-(E)-2-{5-(3-fluorophenyl)pyridine-2-
yl]vinyl}-50-oxooctahydro-30H-spiro(cyclopenta
[c]pyidine-6,20-furan)-2(1H)-carbaldhyde (24)
(E)-5-(Prop-2-yn-1-yloxy)pent-2-en-1-ol (28)
Using the compound 22 (10 mg, 0.025 mmol) as a starting
material, the same reaction to prepare compound 17 was
proceeded to give a pale yellow solid (9 mg, yield 84 %).
1H-NMR (300 MHz, CDCl3) d 1.97–2.11 (m, 4H),
2.23–2.38 (m, 2H), 2.43–2.52 (m, 2H), 2.96–3.11 (m, 2H),
3.20(m, 1H), 3.34 (m, 1H), 3.54 (m, 1H), 3.80 (m, 1H),
4.08 (m, 1H), 6.2 (m, 1H), 6.75 (m, 1H), 7.06 (m, 1H), 7.35
(m2H), 7.47(m, 1H), 7.83 (m, 1H), 8.08 (s, 1H), 8.77 (s,
1H). MS 420 (M?).
Using the compound 27 (150 mg, 0.89 mmol) as a starting
material, the same reaction to prepare compound 5 was
proceeded to give a pale yellow oil (100 mg, yield
quantitative).
1H-NMR (300 MHz, CDCl3) d 2.37 (q, 2H, J = 6.54,
12.7 Hz), 2.44 (t, 2H, J = 4.03 Hz), 3.58 (t, 2H,
J = 6.63 Hz), 4.14 (s, 2H), 5.74–5.70 (m, 2H). MS 140
(M?).
(E)-tert-Butyldimethyl{[5-(Prop-2-yn-1-yloxy)pent-2-en-1-
3-(Prop-2-yn-1-yloxy)propan-1-ol (25)
yl]oxy}silane (29)
To the solution of propargyl bromide (20 g, 168.12 mmol)
and 1,3-propandiol (25.5 g, 336.24 mmol) was added the
pulverized NaOH (8 g, 201.74 mmol) with stirring at 0°C.
After stirring for 24 h at rt, the mixture was diluted with
water, and extracted with CHCl3. The organic layer was
Using the compound 28 (150 mg, 0.89 mmol) as a starting
material, the same reaction to prepare compound 6 was
proceeded to give a pale yellow oil (42 mg, yield 45 %).
1H-NMR (300 MHz, CDCl3) d 0.03 (s, 6H), 0.84 (s,
9H), 2.29–2.34 (m, 2H), 2.35 (s, 1H), 3.49 (t, 2H,
123

Octahydrocyclopenta[c]pyridine and octahydrocyclopenta[c]pyran analogues as a protease…
Evaluation of inhibitory effect on PAR 1 using
radioligand binding assay
J = 6.87 Hz), 4.06–4.06 (m, 4H), 5.56–5.58 (m, 2H). MS
254 (M?).
Preparation of platelet membrane
( )-(4aR,5S)-5-(tert-butyldimethylsilyloxymethyl)-
3,4,4a,5-tetrahydrocyclopenta[c]pyran-6(1H)-one (30)
20 unit of platelet concentrate (Red Cross Blood Services,
Daejeon) was centrifuged for 20 min at 100 g to remove
red blood cells. The supernatant was collected and cen-
trifuged for 15 min (3000 g). The resulting precipitate was
mixed well with Buffer A (200 mL) (10 mM Tris Cl, pH
7.5, 5 mM EDTA, 150 mM NaCl) and centrifuged for
10 min at 4400 g. The resulting precipitate was mixed well
with Buffer A (200 mL) and centrifuged again for 10 min
at 4400 g. The resulting precipitate was mixed well with
Buffer B (30 mL) (10 mM Tris Cl, pH 7.5, 5 mM EDTA).
Then, the mixture was homogenized twenty times using a
Dounce homogenizer and centrifuged for 20 min at
41,0009g. The resulting precipitate was mixed well with
Buffer C (40 mL) (20 mM Tris Cl, pH 7.5, 1 mM EDTA,
(0.1 mM DTT)). This mixture was divided in 5 mL por-
tions, quickly cooled by liquid nitrogen and stored at
-80 °C. The portions stored at -80 °C were dissolved,
homogenized five times using a Dounce homogenizer and
centrifuged for 20 min at 41,0009g. The resulting pre-
cipitate was mixed well with Buffer D (20 mL) (10 mM
Tris ethanolamine HCl, pH 7.4, 5 mM EDTA) and cen-
trifuged for 20 min at 41,0009g. Then, the resulting pre-
cipitate was mixed well with Buffer E (20 mL) (50 mM
Tris Cl, pH 7.5, 10 mM MgCl2, 1 mM EGTA, (1 %
DMSO)). This mixture was divided in 250 lL portions,
quickly cooled by liquid nitrogen and stored at -80 °C.
Blood within 48 h after the blood collection must be used
and the blood should be kept at 4 °C after it is washed with
Buffer A.
Using the compound 29 (500 mg, 1.96 mmol) as a starting
material, the same reaction to prepare compound 8 was
proceeded to give a pale yellow oil (250 mg, yield 45 %).
1H-NMR (300 MHz, CDCl3) d 0.04 (s, 6H), 0.08 (s,
9H), 1.58 * 1.64 (m, 1H), 2.09–2.18 (m, 2H), 2.83–2.88
(m, 1H), 3.56–3.64 (m, 1H), 3.80–3.89 (m, 2H), 4.02–4.13
(m, 1H), 4.15 (d, 1H, J = 13.4 Hz), 4.65 (d, 1H,
J = 13.4 Hz), 5.88 (s, 1H). MS 282 (M?).
( )-(4aR,5R,7aS)-5-{[(tert-butyldimethylsilyl)oxy]methyl}
hexahydrocyclopenta[c]pyran-6(1H)-one (31)
Using the compound 30 (250 mg, 0.88 mmol) as a starting
material, the same reaction to prepare compound 9 was
proceeded to give a pale yellow oil (110 mg, yield 44 %).
1H-NMR (300 MHz, CDCl3) d 0.02 (s, 6H), 0.85 (s,
9H), 1.57–1.63 (m, 1H), 1.82–1.90 (m, 1H), 2.14–2.25 (m,
3H), 2.45–2.61 (m, 2H), 3.30–3.36 (m, 1H), 3.60–3.88 (m,
4H), 3.90–3.95 (m, 1H). MS 284 (M?).
( )(4aR,5S,7aR)-5-{(E)-2-[5-(3-Fluorophenyl)pyridin-2-
yl]vinyl}-6-methyloctahydrocyclopenta[c]pyran-6-ol (32)
Using the compound 31 as a starting material, the same
reactions to prepare compound 10, 11, 12, and 13 were
sequentially proceeded to give a pale yellow oil (yield 18,
82, 59, and 14 %, each).
1H-NMR (300 MHz, CDCl3) d 1.50 (s, 3H), 1.89–2.21
(m, 3H), 2.45–2.50 (m, 3H), 3.14 (t, 1H, J = 15 Hz),
3.48–3.80 (m, 4H), 6.65–6.81 (m, 2H), 7.08–7.84 (m, 6H),
8.77 (s, 1H). MS 353 (M?).
Evaluation of inhibitory effect on PAR1
First, the buffer for binding reaction (39 lL) was dis-
tributed into the reaction plate (Nunc 96 well plate #
269620). The human platelet membrane was diluted with
the buffer for binding reaction (50 mM Tris HCl, pH 7.5,
10 mM MgCl2, 1 mM EGTA, 0.1 % BSA) to prepare 29
concentration (the final 19 concentration: 0.15 mg/mL),
and 50 lL each was added to the reaction plate. The
compound was diluted with DMSO to prepare 109 solu-
tion, and 10 lL each was added to the reaction plate and
mixed by pipetting. To the positive control was added
DMSO (10 lL) and to the nonselective binding control was
added 109 unlabeled haTRAP (10 lL) (hexaamino acid
thrombin receptor antagonistic peptide; final concentration
100 lM). The radio-labeled ligand ([3H]-haTRAP, alanine-
p-fluorophenylalanine-arginine-cyclohexylalanine-ho-
moarginine-[3H]tyrosine-NH2) was diluted with DMSO to
( )(4aR,5S,7aR)-5-{(E)-2-[5-(3-Fluorophenyl)pyridin-2-
yl]vinyl}-6-methyloctahydrocyclopenta[c]pyran-6-yl
carbamate (33)
Using the compound 32 (3 mg, 0.0084 mmol) as a starting
material, the same reaction to prepare compound 14 was
proceeded to give a pale yellow oil (1.2 mg, yield 36 %).
1H-NMR (300 MHz, CDCl3) d 1.61 (s, 3H), 2.0 (brs,
2H), 2.38 (m, 3H), 2.77 (m, 1H), 3.20 (t, J = 5.0 Hz, 1H),
3.50 (t, J = 5.0 Hz, 1H), 3.73 (brs, 2H), 4.60 (brs, 2H),
6.61 (d, J = 17.6, 1H), 6.79 (m, 1H), 7.07 (t, J = 7.5 Hz,
1H), 7.23–7.47 (m, 4H), 7.83 (d, J = 2.5 Hz, 1H), 8.78 (s,
1H). MS 396 (M?).
123

A. Wadood et al.
prepare 1009 concentration, and 1 lL each was added to
the reaction plate and mixed by pipetting (the final con-
centration of the radio-labeled ligand was decided as the
concentration showing the binding of 60 % Bmax in the
saturation experiment). Then, reaction plate was treated in
a plate stirrer (Heidolph, Titramax 1000) for 15 s at
900 rpm to mix and incubated for 60 min at 30 °C. During
the incubation, the unifilter GF/C plate (Perkin Elmer, #
6005174) was wetted with 0.1 % polyethyleneimine
(100 lL). After completion of the reaction, the unifilter
GF/C plate was located in a Milipore Vacuum Manifold.
The reaction mixture was transferred and combined using a
pipette and washed six times with cooled washing buffer
(100 lL) (50 mM Tris HCl, pH 7.5, 10 mM MgCl2, 1 mM
EGTA). The unifilter GF/C plate was dried at rt. Micro-
scint-20 scintillation cocktail solution (Perkin Elmer, #
6013621) (40 lL) was added to each well and its
radioactivity was measured by Packard TOPCOUNT
scintillation counter to calculate the IC50 value.
Both cyclopentapyridine and cyclopentapyran rings
were manipulated using an intramolecular Pauson–Khand
reaction (PKR) (Jeong 1993; Kavanagh et al. 2009). The
acyclic enyne PKR precursor 7 was prepared in straight-
forward method (Scheme 1). The primary amine 1 was
protected with t-butylcarbamoyl group (Boc), and the pri-
mary alcohol group of 2 was oxidized to yield the aldehyde
3 by Swern reaction (Mancuso and Swern 1981), which
was converted to the allylic ester 4 using Hornor-Wads-
worth Emmons reaction (HWE) (Boutagy and Thomas
1974). The reduction of allylic ester to alcohol 5 was
performed using diisobutylaluminium hydride (DIBAL-H)
in CH2Cl2. Subsequent protection of primary alcohol
moiety with tert-butyldimethylsilyl (TBS), and then alky-
lation of carbamate 6 using propargyl bromide gave PKR
precursor 7. The standard PKR conditions gave cyclopen-
tenone 8, and following a stereoselective hydrogenation
from convex face afforded cis-fused bicyclic ring 9 (Ka-
vanagh et al. 2009). Racemic mixtures were used for the
next steps without separation. We decide to prepare the
racemic mixture for biological evaluation until we found a
compound with desirable activity and property.
Results and discussion
Chemistry
Starting from 9, we prepared 6-methy-6-hydroxy 13,
and 6-methyl-6-carbamate 14 compounds by published
procedures (Lee et al. 2013), which were found to be active
on PAR1 in our previous work (Scheme 2). N-Boc was
further derivatized to NH 15, N-carbamoyl 16 and N-for-
myl compound 17 in a straightforward method. N-Boc was
deprotected using TFA to give secondary amine 15, which
was carbamoylated using (CH3)3SiNCO (Mizuhara et al.
We have designed octahydrocyclopenta[c]pyridine and
octahydrocyclopenta[c]pyran analogues by the insertion of
heteroatom into C5 of octahydroindene ring, with the
expectation on improvement of metabolic stability (Fig. 1).
Scheme 1 Reagents and
conditions a Boc2O, Et3N,
CH2Cl2, rt, 94 %; b DMSO,
(COCl)2, Et3N, CH2Cl2,
-78 °C;
c P(O)(OEt)2CH2COOEt, NaH,
-78 °C to rt, THF, 74 % (2
steps from 2 to 4); d DIBAL-H,
CH2Cl2, -78 °C, 83 %;
e imidazole, TBDMSCl, THF,
rt, 93 %; f NaH, 15-crown-5,
propargyl bromide, -30 °C to
rt, 60 %; g Co2(CO)8, NMMO,
CH2Cl2, rt, 53 %; h Pd(OH)2,
EtOH, rt, 74 %
123

Octahydrocyclopenta[c]pyridine and octahydrocyclopenta[c]pyran analogues as a protease…
Scheme 2 Reagents and
conditions a CH3MgBr, THF,
-78 °C to rt, 2 h, 42 %;
b TBAF, THF, 0 °C to rt, 1 h,
92 %; c IBX, CH2Cl2, rt, 2 h;
d n-BuLi, THF, -78 °C to rt,
1 h, 50 % (2 steps from 11 to
13); e (i) CCl3CONCO, THF,
(ii) K2CO3, MeOH, rt, 91 %;
f TFA, CH2Cl2, 0 °C to rt, 1 h,
90 %; g (CH3)3SiNCO, Et3N,
CH2Cl2, rt, 1 h, 90 %; h Ac2O,
HCOOH, THF, 50 °C to rt, 1 h,
90 %
2012). The formylation of 15 was performed using acetic
anhydride and formic acid to give 17 (Scott et al. 1983).
We additionally prepared spironolactone compound 22–
24. 2-Ketone 9 was allylated with Grignard regent to pro-
vide 18, following hydroboration and oxidation using
borane-methylsulfide (BMS) and H2O2 provided 6-hy-
droxy-6-propanol 19 outlined in Scheme 3 (Makino et al.
2002). Oxidation of 19 using pyridium chlorochromate
(PCC) afforded spironolactone compound 20. The TBS of
20 was deprotected, following oxidation of alcohol to
aldehyde using 2-iodoxybenzoic acid (IBX), finally HWE
reaction gave the compound 22. N-Boc of 22 was further
derivatized to NH (23) and N-formyl (24) moiety.
alcohol functionality with TBS provided PKR precursor
29. Cis-fused 6/5 bicyclic compound 31 was prepared by
standard PKR, and subsequent hydrogenation from convex
face (Kavanagh et al. 2009). 6-Methyl-6-hydroxy 32 and
6-methyl-6-carbamate 33 compounds of this octahydrocy-
clopenta[c]pyrans were prepared using previous methods.
Evaluation of biological activity
We evaluated PAR1 inhibitory activity of octahydrocy-
clopenta[c]pyridine and octahydrocyclopenta[c]pyran
compounds using [3H]-labeled high affinity thrombin
receptor activation peptide ([3H]-haTRAP) as a radioligand
as described in our previous work (Ahn et al. 2000;
Andrade-Gordon et al. 1999). Additionally, we determined
metabolic stability of compounds in human and rat liver
microsomes, which was represented as R50, time when
50 % of the compound remains upon incubation with
human and rat liver microsomes.
Outlined in Scheme 4, we prepared octahydrocy-
clopenta[c]pyran compounds according to the similar
method to prepare octahydrocyclopenta[c]pyridines. The
monoalkylation of 1,3-propanediol with propargyl bromide
using NaOH gave 25, of which alcohol was oxidized to
aldehyde 26 using PCC. Hornor-Wadsworth Emmons
reaction with 26, following reduction of allylic ester 27 to
alcohol 28 using DIBAL-H, and protection of primary
Even though their activities were decreased compared
with those of octahydroindenes, both cyclopentapyridine
123

A. Wadood et al.
Scheme 3 Reagents and
conditions: a allylmagnesium
bromide, THF, -78 °C to rt,
2 h, 81 %; b (i) BH3ÁSMe2,
THF, (ii) 3 N NaOH, H2O2,
0 °C to rt, 45 %; c PCC,
CH2Cl2, rt, 6 h, 74 %; d TBAF,
THF, 0 °C to rt, 1 h, 78 %;
e IBX, DMSO, rt, 1 h; f n-BuLi,
THF, -78 °C to rt, 1 h, 35 % (2
step yields); g TFA, CH2Cl2,
0 °C to rt, 1 h, 78 %; h Ac2O,
HCOOH, THF, 50 °C to rt, 1 h,
84 %
and cyclopentapyran derivatives still represented the sig-
nificant inhibitory activity on PAR1 (Table 1).
Boc (14, IC50 = 0.36 lM), NH (15, IC50 = 0.62 lM), and
N-carbamoyl (16, IC50 = 1.2 lM). As our expectation, the
metabolic stability of cyclopentapyridines was generally
much more improved than that of octahydroindenes.
Especially, NH (15) and N-Boc (16) compounds showed an
excellent metabolically stability both in human and rat
liver microsomes. The most active compound 17 showed
marginal metabolic stability (R50 = 20.2 min in human,
16.2 min in rat, each) but much better than
The 6-methyl-6-carbamate compound (14, IC50 = 0.36
lM) showed better activity than 6-methyl-6-hydroxy
compound (13, IC50 = 2.8 lM) of N-Boc cyclopen-
tapyridine, which is the same trend with octahydroin-
dene’s. Among 6-methyl-6-carbamate compounds of
cyclopentapyridine (14–17), N-formyl compound (17,
IC50 = 0.065 lM) showed the best activity, following N-
Scheme 4 Reagents and
conditions a propargyl bromide,
NaOH, 0 °C to rt, 24 h, 73 %;
b PCC, CH2Cl2, 0 °C to rt,
44 %; c PO(OEt)2CH2COOEt,
NaH, THF, 1 h, 59 %;
d DIBAL-H, CH2Cl2, -78°,
1 h, 80 %; e TBSCl, imidazole,
DMF, rt, 30 min, 45 %;
f Co2(CO)8, NMO, 0 °C to rt,
2 h, 45 %; g H2, Pd(OH)2,
EtOAc, rt, 60 psi, 44 %;
h (i) CCl3CONCO, THF, (ii)
K2CO3, MeOH, rt, 36 %
123

Octahydrocyclopenta[c]pyridine and octahydrocyclopenta[c]pyran analogues as a protease…
Table 1 Inhibitory activity on PAR1 and metabolic stability data for compounds
Compound
C2 (Q)
C6 (R1, R2)
IC50 (lM)a
Metabolic stability (R50, min)c
Human
83.2
Rat
32.4
Vorapaxarb
0.015
2.8
13
NBoc
NBoc
NH
14
15
16
17
22
23
24
32
33
a
0.36
0.62
1.2
57.5
122.0
79.6
20.2
69.4
38.1
17.2
36.1
26.0
82.0
138.6
207.6
16.2
26.0
18.2
11.2
19.6
37.0
NC(O)NH2
NCOH
NBoc
NH
0.065
0.11
2.5
NCOH
O
0.61
1.0
O
0.05
PAR1 binding assay ligand [3H]haTRAP, 10 nM; The value is an average of three measurements
Vorapaxar was synthesized and evaluated by our laboratory as a reference standard
b
c
Time when 50 % of the compound remains upon incubation with human and rat liver microsomes
123

A. Wadood et al.
Chackalamannil, S., Y. Wang, W.J. Greenlee, J. Hu, H.S. Ahn, G.
Boykow, Y. Hsieh, J. Palamanda, J. Agans Fantuzzi, S.
Kurowski, M. Graziano, and M. Chintala. 2008. Discovery of
octahydroinden’s. 6-Spironolactone compounds (22–24)
were also active on PAR1 but a little weaker than
6-methyl-6-carbamates in general. In 6-spironolactone
series, N-Boc compound (22, IC50 = 0.11 lM) showed the
best activity, which is more potent than 6-methyl-6-car-
bamate with N-Boc (14, IC50 = 0.36 lM). The compound
22 showed reasonable metabolic stability (R50 = 69.4 min
in human, 36.0 min in rat, each), especially good in human
liver microsome.
a
novel, orally active himbacine-based thrombin receptor
antagonist (SCH 530348) with potent antiplatelet activity.
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Chelliah, M.V., S. Chackalamannil, Y. Xia, K. Eagen, W.J. Greenlee,
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Chelliah, M., K. Eagan, Z. Guo, S. Chackalamannil, Y. Xia, H. Tsai,
W.J. Greenlee, H.-S. Ahn, S. Kurowski, G. Boykow, Y. Hsieh,
and M. Chintala. 2014. Himbacine-Derived Thrombin Receptor
Antagonists: C7-Spirocyclic Analogues of Vorapaxar. ACS
Medicinal Chemistry Letters 5: 561–565.
Cyclopetapyran compound with 6-Methyl-6-carbamare
33 showed a good activity (IC50 = 50 nM) with moderate
metabolic stability (R50 = 26.0 min in human, 37.0 min in
rat, each).
Clasby, M.C., S. Chackalamannil, M. czarniecki, D. Doller, K. Eagen,
W. Greenlee, G. kao, Y. Lin, H. Tsai, Y. Xia, H.-S. Ahan, J.
Agans-Fantuzzi, G. Boykow, M. Chintala, C. Foster, A. Smith-
Torhan, K. Alton, M. Bryant, Y. Hsieh, J. Lau, and J. Palamanda.
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thrombosis and vascular biology. Journal of Thrombosis and
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Conclusions
From this studies, we found that the modification of
octahydroindene core to octahydrocyclopenta[c]pyridine
and octahydrocyclopenta[c]pyran generally improved
metabolic stability, while maintaining the significant
activity on PAR1. Compound 22 (IC50 = 110 nM) and 33
(IC50 = 50 nM) showed good activity on PAR1 with
moderate metabolic stability. We will keep trying to opti-
mize this series of compounds to improve both the activity
and druggable property.
Acknowledgments This work was supported by the Global Frontier
Project grants NRF-2013M3A6A4044802 and the center for Biolog-
ical Modulator of the 21st century Frontier R&D program by the
Ministry of Science, ICT and Future Planning of Korea.
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