Design and optimization of new piperidines as renin inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.08.086

The discovery of a new series of piperidine-based renin inhibitors is described herein. SAR optimization upon the P3 renin sub-pocket is described, leading to the discovery of 9 and 41, two bioavailable renin inhibitors orally active at low doses in a tra

Full text of DOI:10.1016/j.bmcl.2010.08.086

Bioorganic & Medicinal Chemistry Letters 20 (2010) 6286–6290
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and optimization of new piperidines as renin inhibitors
⇑
ˇ
ˇ
Olivier Corminboeuf, Olivier Bezençon , Corinna Grisostomi, Luboš Remen, Sylvia Richard-Bildstein,
Daniel Bur, Lars Prade, Patrick Hess, Panja Strickner, Walter Fischli, Beat Steiner, Alexander Treiber
Drug Discovery Chemistry & Biochemistry, Actelion Pharmaceuticals Ltd, Gewerbestrasse 16, 4123 Allschwil, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
The discovery of a new series of piperidine-based renin inhibitors is described herein. SAR optimization
upon the P3 renin sub-pocket is described, leading to the discovery of 9 and 41, two bioavailable renin
inhibitors orally active at low doses in a transgenic rat model of hypertension.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 15 June 2010
Revised 17 August 2010
Accepted 17 August 2010
Available online 22 August 2010
Keywords:
Hypertension
Renin–angiotensin–aldosterone system
Renin inhibitors
Piperidines
The renin–angiotensin–aldosterone system (RAAS) represents
one of the major and most studied regulating systems of the arte-
rial blood pressure in humans, and plays a primordial role in car-
diovascular diseases, renal diseases, and other metabolic diseases.1
The development of a new class of piperidines as renin inhibi-
tors is reported here. Piperidine-based renin inhibitors were first
reported in the late nineties.2 Unfortunately, and despite extensive
optimization work, type 1 piperidine-based derivatives (Fig. 1)
showed unsuitable pharmacokinetic properties.3
By de novo design and lead optimization, we have recently re-
ported diazabicyclononene derivatives such as 24 and tetrahydro-
pyridine derivatives such as 35 as renin inhibitors. Based on the
knowledge accumulated during this work and from literature
data,2,6 we predicted that piperidines, comprising trans-arranged
substituents in 3- and 4-positions such as, for example, in 4 would
provide suitable exit vectors. Replacing the long methoxypropoxy
linker present in piperidine derivatives of type 1 (Fig. 1) by the
shorter 1,2-ethylenedioxy linker should improve the metabolic
stability, as observed for diazabicyclononene based renin inhibi-
tors.4 Additionally, modification of the amide side chains should
improve the potency of the corresponding inhibitors.7
hydrolysis and amide coupling using amine of type 7 where
X = CH, R1 = R2 = Me, and R3 = H afforded, after cleavage of the
Boc-group, racemic piperidine 8 (Scheme 1 and Table 1, entry 1).
Piperidine rac-8 was up to four times more potent toward renin
than tetrahydropyridine 3, measured either in buffer (IC50 = 0.31 nM
vs 1.1 nM) or in plasma (IC50 = 12.8 nM vs 55.6 nM)5 and as potent in
plasma as 2 (IC50 = 19 nM),4 establishing the proof of concept for the
double bond reduction strategy. A slightly more basic secondary
amine on the piperidine template compared to the tetrahydropyri-
dine template (pKa = 8.5 vs 8.0 on other, similar compounds), and
slightly improved exit vectors at the 3- and 4-positions are possible
explanations for this improved potency. Moreover, while the tetra-
hydropyridine series, for which compound 35 is a good representa-
tive, significantly inhibited the CYP3A4 enzyme (IC50 = 0.8
racemic piperidine 8 inhibited CYP3A4 only moderately (IC50
>7 M).
Potency of this new derivative in 100% human plasma was not
lM),
l
yet considered as sufficient. Earlier publications indicated that re-
nin possesses a P3 sub-pocket (P3sp).3,6,7 In order to determine if it
was possible to reach this P3sp with our 3,4-trans-substituted
piperidines, and thereby improve potency in plasma, the known
amine 77 (X = CH, R1 = Cl, R2 = H, R3 = –(CH2)3OMe, Scheme 1)
was first chosen with the following intentions: the cyclopropyl ring
should fill a renin sub-pocket identified earlier4 while the meta ali-
The general synthetic pathway leading to 3,4-disubstituted
piperidines of type 4 took advantage of the chemistry elaborated
earlier for the tetrahydropyridine 3.5 The double bond of the
known ester 5 was reduced using magnesium8 to yield a mixture
of the racemic cis and trans esters (Scheme 1). Isomerization to
the thermodynamically more stable racemic, trans ester 6 was per-
formed under basic conditions (MeONa/MeOH). Further ester
phatic chain should better anchor the inhibitor by filling the P3sp
.
Based on previous work, we predicted that the active enantio-
mer should possess the (3R,4S) absolute configuration. To experi-
mentally confirm this, the enantiomeric pair of trans racemic
ester 6 was separated by preparative HPLC using a chiral stationary
phase (Regis R,R Whelk 01 column) followed by ester hydrolysis,
⇑
Corresponding author. Tel.: +41 61 565 65 77; fax: +41 61 565 65 00.
E-mail address: olivier.bezencon@actelion.com (O. Bezençon).
amide coupling, and deprotection. The active enantiomer
9
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.08.086

O. Corminboeuf et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6286–6290
6287
O
Cl
Cl
Cl
O
Cl
Cl
O
O
O
O
O
O
Cl
O
O
O
Cl
O
R1
N
Cl
R2
O
N
N
NH
HN
X
R
N
H
N
H
N
H
R3
type 1 piperidines
3
4
2
Figure 1. Design leading to 3,4-disubstituted piperidines of type 4 from type 1 based piperidines, diazabicyclonene 2 and tetrahydropyridine 3.
Cl
Cl
O
Cl
Cl
O
Cl
Cl
O
O
O
O
R1
R3
R2
HN
X
7
O
O
O
R1
(b)
R2
(a)
O
O
N
N
N
X
N
H
Boc
Boc
R3
8-36
5
6
Scheme 1. Synthetic pathway leading to 3,4-disubstituted piperidines of type 8–36 from known ester 5. Reagents and conditions: (a) (i) 1.2 equiv Mg, MeOH, rt, 2 h, 89%; (ii)
2.0 equiv MeONa, MeOH, 70 °C, 16 h, 95%; (b) (i) 3.5 equiv NaOH, MeOH, rt, 48 h; (ii) 1.25 equiv HOBt, 4.0 equiv DIPEA, 0.25 equiv DMAP, 1.5 equiv amine 7; (iii) 15 equiv 4 M
HCl in dioxane, CH2Cl2, 0 °C, 1.5 h, 20–70%.
Table 1
SAR of selected renin compounds: amide side chain modification
Entry
Compds
X
R1
R2
R3
Renin IC50 (nM)
Buffer to plasma ratio
CYP3A4 IC50
(
lM)
CYP3A4 TDI30
Buffer
Plasma
Mid
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
rac-8
9
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
Me
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
0.31
0.22
0.18
3.90
1.39
2.17
0.40
0.56
0.05
0.31
0.15
0.28
0.18
0.11
0.41
0.26
0.11
0.16
0.11
0.13
0.24
0.31
0.38
0.62
0.57
0.27
0.09
0.28
0.04
12.8
12.3
8.1
91.3
35.6
16.1
19.1
8.2
3.1
7.5
7.4
14.5
1.4
1.9
9.5
3.7
2.5
4.1
3.4
4.6
3.4
41
56
45
23
26
7
48
15
62
24
49
41
8
17
23
14
23
26
31
35
14
9
7.4
4.8
3.2
14
15
14
11
8.1
7
18
–(CH2)3OMe
–(CH2)2OMe
–(CH2)2NHMe
–CH2NHMe
–CH2NHEt
–(CH2)2NHEt
–(CH2)2NHcylopropyl
–(CH2)2NHCH2CHF2
–CH2NHcylopropyl
–CH2NHCH2CH2F
–CH2NHCH2CHF2
–(CH2)2NHAc
–(CH2)2C(O)NHMe
–(CH2)2NHC(O)CH2CF3
–(CH2)2NHC(O)CH2OtBu
–CH2C(O)NHEt
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
rac-36
16
17
17
18
1
2.1
15
1.7
7.3
3.1
2.4
2.9
2.8
9.9
4.8
6
8.9
4.5
8.4
18
8.7
21
6.9
2.1
5.1
7.1
8.4
8.7
4.1
–CH2NHAc
–CH2C(O)NHMe
–CH2NHC(O)Et
–CH2C(O)NHcyclopropyl
–CH2NHC(O)cyclopropyl
–CH2NHC(O)CH2CF3
–CH2OC(O)NHMe
–(CH2)2NHC(O)OMe
–(CH2)2OC(O)NHMe
–CH2NHC(O)OMe
–(CH2)3OMe
2.8
6.9
4.4
10.5
7.3
2.0
3.5
0.5
18
7
4
7.9
6.5
4.5
14
27
22
13
13
3.5
5.9
12
13
NO
–(CH2)3OMe
Mid: midazolam as a marker. Test: testosterone as a marker. The CYP3A4 TDI30 value represents the ratio of the CYP3A4 IC50 at t0 to the CYP3A4 IC50 after 30 min of pre-
incubation in the presence of liver microsomes.

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O. Corminboeuf et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6286–6290
Figure 2. 9 soaked into renin crystals. Resolution of 2.4 Å. PDB code 3O9L.
(absolute configuration established as 3R,4S based on X-ray ob-
tained via soaking into renin crystals, see Fig. 2) was about 500
times more potent than its enantiomer (0.22 nM vs 92 nM in buffer
and 12.3 nM vs 2615 nM in plasma). While the introduction of the
methoxypropyl side chain provided an acceptable pharmacokinetic
profile in rat with a bioavailability of 20%, compound 9 inhibited
CYP3A4 more strongly than rac-8. Furthermore, inhibitor 9 showed
a more important time-dependant inhibition of CYP3A4 after
30 min of pre-incubation in the presence of liver microsomes
(TDI30,Table 1, entry 2 vs entry 1).
From the work toward the design and optimization of a substi-
tuted amino propanamide series as renin inhibitor,7 it was known
that a high degree of freedom for structural variations of the meta
position on the phenyl ring of the amide side chain was tolerated.
Accordingly, we considered this as an opportunity to improve the
compound’s overall profile (potency in plasma and CYPs inhibition)
by further modifying this side chain starting from enantiomerically
pure ester 6.
Compound 10 (Table 1, entry 3) displayed no substantial differ-
ences when compared with rac-8 or 9 (entries 1 and 2) with re-
spect to the inhibitory potency against purified recombinant
human renin in buffer. However, introduction of a small, secondary
amine led to a reduced potency (Table 1, entries 4–6). This is prob-
ably due to the polar functionality which needs to be desolvated in
order to fit into the small P3sp. The buried NH functionality does
not seem to find a suitable H-bonding partner which explains the
overall unfavorable energy balance. However, the buffer to plasma
shift is reduced, and both the competitive and the time-dependant
inhibition constants (TDI) of CYP3A4 are improved, showing that
introducing hydrophilic, potentially protonated residues allow to
tackle CYP3A4 related issues.
Extending the side chain length and introducing two terminal
fluorines greatly improved potency (entry 9 vs entry 4), but failed
to reduce the buffer to plasma ratio. Slight increase of steric bulk
(entries 7 and 8) also allowed regaining potency. Shorter secondary
amines yielded similar trends but less pronounced. Modulating the
steric hindrance and/or nitrogen basicity led to increased potency
(entries 10–12 vs entry 5) but at the same time CYP3A4-linked is-
sues reappeared.
the CYP3A4 profile. Compounds 20 and 30 (entries 13 and 23)
led to a moderate blood pressure decrease in our double transgenic
rat model (À9 mmHg for 20 and À19 mm Hg for 30, at 3 mg/kg,
po), presumably due to a modest bioavailability. The potency of
the N-oxide rac-36 in plasma is remarkable, with a value in the
subnanomolar range, at least 25 times more potent than diazabicy-
clonene 2.4
Interestingly, the X-ray structure analysis of compound 15a,
analogous to compound 15 (Table 1 entry 6), in renin delivered
unexpected results since the meta substituent intended to fill the
P3sp showed an unexpected, previously unreported interaction
through formation of an hydrogen bond with the OH group of
Ser230 (Fig. 3). This interaction offers new opportunities in the de-
sign of renin inhibitors.
The removal of the double bond from the tetrahydropyridine
scaffold gave us the opportunity to introduce small polar groups
at the 4-position of the piperidine (Scheme 2) to modulate the
CYP3A4 activity. Starting from the known b-keto ester 37,5 a con-
vergent synthesis was designed to take advantage of the already
known 4-substituent side chain chemistry.4 The b-keto ester 37
was condensed in refluxing toluene with the desired amine fol-
lowed by addition of the lithiated derivative of aryl 39 leading to
the desired rac-derivative in a 4:1 cis–trans ratio. Removal of the
Boc-group followed by HPLC separation using a chiral stationary
phase (Regis R,R Whelk 01 column) afforded the desired pure,
trans-[3S,4R] stereoisomer.
Piperidine rac-40 (Scheme 2 and Table 2) revealed a good toler-
ance for the newly introduced alcohol in terms of potency. Com-
pound 41, whose stereochemistry was determined to be (3S,4R)
by analogy to compound 41a, soaked into a renin crystal (Fig. 4),
was slightly more potent than piperidine 10, while its (3R,4S)
enantiomer 42 was about 150-fold less active in buffer. Unfortu-
nately, the introduction of the hydroxyl moiety at 4-position did
not improve the CYP3A4 profile as exemplified by compound 41
(CYP3A4 IC50mid = 1.4 lM, CYP3A4 IC50test = 4.6 lM).
To determine the effect of these modifications on the in vivo effi-
cacy, compounds 9 (Table 1 entry 2) and 41 (Table 2) were selected
for further profiling. 4-Hydroxypiperidine 41 displayed the same
potency in buffer (0.24 nM) as the tetrahydropyridine analogue
439 (Fig. 5, 0.28 nM) but with an improved potency in human plas-
ma (5.6 nM vs 26.6 nM). When administered at a dose of 3 mg/kg,
po to double transgenic rats harboring both the human angiotensin-
ogen and the human renin gene,10 4-hydroxypiperidine 41 was
superior to its closest analogue tetrahydropyridine 43 with a two-
fold improvement in the maximal mean arterial pressure (MAP)
reduction (À36 vs À18 mmHg) and a 3–4-fold increase for the area
between the curves (ABC) (À1411 vs À382 mmHg h). Compound 9
Amides or inverse amides (entries 13–23) were suitable regard-
ing potency, demonstrating the high tolerance of the P3sp for dif-
ferent functional groups and substituents. Carbamates (entries
24–27) also displayed a nice activity profile. Finally, as already
seen in the amino propanamide series,7 pyridine and N-oxide pyr-
idine derivatives were well tolerated as phenyl replacements (en-
tries 28 and 29). While these compounds could improve the
buffer to plasma shift, amides or carbamates failed to improve

O. Corminboeuf et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6286–6290
6289
Figure 3. Compound 15a soaked into renin crystals. PDB code 3OAG.
Cl
Cl
O
Cl
Cl
O
O
O
R1
R3
R2
HN
R1
R3
O
O
R1
R3
O
O
O
39
Br
R2
HO
R2
N
N
O
(a)
(b)
N
Boc
N
Boc
N
H
38
40-42
37
Scheme 2. Synthetic pathway leading to 4-hydroxy piperidines 40–42. Reagents and conditions: (a) 1.1 equiv of amine, 0.13 equiv p-TsOH, toluene, 110 °C, 16 h, 75–85%; (b)
(i) 2.5 equiv 39, THF, 2.75 equiv n-BuLi, À78 °C, 30 min; (ii) 5.5 equiv DMPU, amide 38, THF, À78 °C, 10 min, 10–15% of cis-rac and 42–50% of trans-rac product; (iii) 15 equiv
HCl 4 M in dioxane, CH2Cl2, 0 °C, 1 h, 60–75%; (iv) chiral HPLC (Regis R,R Whelk 01 column), 20–45%.
which displayed a similar in vitro profile as compound 43, led to an
Table 2
even better in vivo efficacy (Fig. 5), presumably due to a more favor-
able pharmacokinetic profile.
SAR of selected renin inhibitors: modifications at the 4-position
Entry
R1
R2
R3
Renin IC50 (nM)
Buffer Plasma
To conclude, a novel series of piperidine-based renin inhibitors
with an improved efficacy in a double transgenic rat model has
been discovered. Piperidine 9 showed high efficacy at low dose
(3 mg/kg), but, despite intense efforts, the unfavorable CYP interac-
tions could not be eradicated. To tackle this issue, further modified
rac-40
41 [3S,4R]
42 [3R,4S]
Me
Cl
Cl
Me
H
H
H
0.18
0.24
35.3
45
5.6
—
–(CH2)2OMe
–(CH2)2OMe
Figure 4. Compound 41a soaked into renin crystals. PDB code 3OAD.

6290
O. Corminboeuf et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6286–6290
Cl
Cl
O
9
43
O
0.22
12.3
IC50 buffer (nM)
IC50 plasma (nM)
0.28
26.6
O
Cl
ABC (mmHg.h)
Max* (mmHg)
-382
-18
-1959
-43
N
N
H
*maximal blood pressure reduction
43
O
180
160
140
120
100
180
160
140
120
100
43
9
Control, n=6
Control, n=5
ACT-174966, 3 mg/kg po n=6
ACT-175909, 3 mg/kg po n=5
0
12
24
36
48
0
24
48
72
96
Time (hour)
Time (hour)
Figure 5. Pharmacodynamic behavior of compounds 43 and 9 when administered po at a dose of 3 mg/kg.
Strickner, P.; Binkert, C.; Hess, P.; Steiner, B.; Fischli, W. J. Med. Chem. 2009, 52,
piperidines comprising hydrophilic groups at the 4-position are re-
ported in the following Letter.
3689.
ˇ
ˇ
5. Remen, L.; Bezençon, O.; Richard-Bildstein, S.; Bur, D.; Prade, L.; Corminboeuf,
O.; Boss, C.; Grisostomi, C.; Sifferlen, T.; Strickner, P.; Hess, P.; Delahaye, S.;
Treiber, A.; Weller, T.; Binkert, C.; Steiner, B.; Fischli, W. Bioorg. Med. Chem. Lett.
2009, 19, 6762.
References and notes
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MeOH, rt, 48 h; (ii) 1.25 equiv HOBt, 4.0 equiv DIPEA. 0.25 equiv DMAP,
1.5 equiv of amine 7 (X = CH, R1 = Cl, R2 = H, R3 = –(CH2)3OMe); (iii) 15 equiv
4 M HCl in dioxane, CH2Cl2, 1.5 h, 0 °C.
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ˇ
ˇ
4. Bezençon, O.; Bur, D.; Weller, T.; Richard-Bildstein, S.; Remen, L.; Sifferlen, T.;
Corminboeuf, O.; Grisostomi, C.; Boss, C.; Prade, L.; Delahaye, S.; Treiber, A.;