New classes of potent and bioavailable human renin inhibitors

Article abstract of DOI:10.1016/j.bmcl.2009.09.104

New classes of de novo designed renin inhibitors are reported. Some of these compounds display excellent in vitro and in vivo activities toward human renin in a TGR model. The synthesis of these new types of mono- and bicyclic scaffolds are reported, and properties of selected compounds discussed.

Full text of DOI:10.1016/j.bmcl.2009.09.104

Bioorganic & Medicinal Chemistry Letters 19 (2009) 6762–6765
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
New classes of potent and bioavailable human renin inhibitors
*
*
ˇ
L’uboš Remen , Olivier Bezençon , Sylvia Richard-Bildstein, Daniel Bur, Lars Prade, Olivier Corminboeuf,
Christoph Boss, Corinna Grisostomi, Thierry Sifferlen, Panja Strickner, Patrick Hess, Stéphane Delahaye,
Alexander Treiber, Thomas Weller, Christoph Binkert, Beat Steiner, Walter Fischli
Drug Discovery and Preclinical Research, Actelion Pharmaceuticals Ltd, Gewerbestrasse 16, CH-4123 Allschwil, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
New classes of de novo designed renin inhibitors are reported. Some of these compounds display excel-
lent in vitro and in vivo activities toward human renin in a TGR model. The synthesis of these new types
of mono- and bicyclic scaffolds are reported, and properties of selected compounds discussed.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 19 August 2009
Revised 24 September 2009
Accepted 24 September 2009
Available online 1 October 2009
Keywords:
Renin inhibitor
Rational design
Double transgenic rat (TGR) model
The Renin–Angiotensin–Aldosterone system (RAAS) is known to
be a major regulator of the cardiovascular, renal, and adrenal func-
tions, playing a major role in water and salt homeostasis, as well as
blood pressure control. From the point of view of medicinal chem-
ist, renin proved to be a challenging target as already summarized
in our previous publication1a and summarized recently by Tice.1b
As a part of our renin inhibitors program, we developed 3,9-
diazabicyclononene1a derivatives with subnanomolar IC50 values
for renin (in buffer), and showed in vivo efficacy after oral admin-
istration of 10 mg/kg in the double transgenic rat (TGR) model.2
Compounds 1a and 1b are representatives of such bicyclic renin
inhibitors3 (Fig. 1). We could show that substituents attached at
the N3-position of this diazabicyclic scaffold had only a minor
influence on binding affinity, but allowed significant modulation
of other compound properties.1a Here, we describe bicyclic com-
pounds (2a–6b, Fig. 1) with a newly designed central template
exploring the role of the introduced C2–N3–C4 bridge of the 3,9-
diazabicyclononene moiety.
Vinyl triflates 11–14 (Scheme 1) were prepared from the corre-
sponding known 9-methyl-3-oxa-9-aza-bicyclo[3.3.1]nonan-7-one
and 9-methyl-3-thia-9-aza-bicyclo[3.3.1]-nonan-7-one,4 and from
the commercially available 9-methyl-9-aza-bicyclo[3.3.1]nonan-
3-one and tropinone. These educts were first converted into their
corresponding b-ketoesters (LDA,5 then MeOCOCN, THF, ꢀ78 °C),
which were deprotonated with NaH in THF, and triflated using
Tf2NPh. Negishi or Suzuki couplings yielded compounds 16 and
19–21 in 58–82% yields. Compound 15a was prepared from the
corresponding aryl bromide,1a with pinacolborane, PdCl2(PPh3)2,
and Et3N in dioxane at 100 °C overnight. Removal of the N-methyl
group with 1-chloroethyl chloroformate, followed by hydrolysis of
the respective 1-chloroethyl carbamate with methanol,6 and reac-
tion with Boc2O yielded the N-Boc-protected compounds 17 and
22–26 in 55–93% yields. Oxidation of compound 17 to the corre-
sponding sulfoxide 18a and sulfone 18b, respectively, followed
by Mitsunobu couplings with 2-chloro-3,6-difluorophenol, led to
compounds 24 and 25. Ester hydrolysis of 22–26, subsequent
amide couplings, and deprotections delivered compounds 2a–6a
and 2b–6b.
In order to judge the importance of the C2–X3–C4 bridge, we
prepared tetrahydropyridine analogs 7a and 7b (Fig. 1) as reference
compounds. Since the double bond of these tetrahydropyridines
isomerized easily from the 3,4-position to the 4,5-position, and
back (vide infra), we also prepared the monocyclic analogs 8a,
8b, 9a, 9b, 10a, and 10b with a fully blocked C5-position with
two methyl groups, a cyclopropyl group, or two fluorine atoms,
respectively. Compound 27 (Scheme 2) was prepared from com-
mercially available 4-oxo-piperidine-3-carboxylic acid methyl es-
ter, which was Boc-protected, and triflated (NaH, Tf2NPh, THF).
Commercially available N-Boc-piperidone, was alkylated with (2-
chloroethyl)dimethylsulfonium iodide7 in tert-butanol using
potassium tert-butylate as base, to give Boc-protected 5-aza-spir-
o[2.5]octan-8-one which was carboxymethylated (LDA, then MeO-
COCN, THF, ꢀ78 °C), and triflated (NaH, Tf2NPh, THF) to yield
compound 28. Double methylation of N-Boc-piperidone, with
NaH and methyl iodide in THF, followed by carboxymethylation
(LDA, then MeOCOCN, THF, ꢀ78 °C) and triflation (NaH, Tf2NPh,
THF) gave compound 29. Suzuki couplings of 27–29 with 15a
* Corresponding authors.
E-mail address: olivier.bezencon@actelion.com (O. Bezençon).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.09.104

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L. Remen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6762–6765
6763
F
Cl
F
F
F
Br
Cl
Cl
O
O
O
O
O
O
O
O
F
Cl
R
O
R
R1
6
Cl
Cl
R1
X
4
3
7
4
N
N
8
Cl
Y
5
6
X
N
N
5
3
2
N
H
HN
1
2
1
N
H
N
H
9
7: X = Y = H
: X-Y = CH2CH2
9: X = Y = Me
10: X = Y = F
1; X = NH
2: X = O
5: X = SO
6: X = bond
7c
7d
: R = R1 =Cl
8
a
b: R = Me, R1 = OMe
: X = CH2
: R = R1 = Cl
3
a
4: X = SO2
b: R = Me, R1 = OMe
Figure 1. Described compounds with their corresponding numbering systems.
Cl
F
F
F
O
F
F
O
O
O
O
OTf
R
O
F
F
Cl
Cl
F
Cl
15a
N
(e)
(g)
R1
(f)
11: R = O
O
O
B
+
12: R = CH2
13: R = S
R
O
O
O
O
O
14: R = bond
N
R
R
R
N
BocN
OTBDMS
HN
22: R = O
19: R = O
23: R = CH2
24: R = SO
25: R = SO2
26: R = bond
20: R = CH2
21: R = bond
2: X = O
3: X = CH2
4: X = SO2
5: X = SO
15b
(a)
(d)
6: X = bond
a: R = R1 = Cl
b: R = Me, R1 = OMe
Br
TBDMSO
HO
HO
18a: n = 1
18b: n = 2
17
16
(b)
(c)
O
O
O
O
O
O
SOn
S
S
BocN
BocN
N
Scheme 1. Reagents and conditions: (a) (i) 15b,1a n-BuLi, THF, ꢀ78 °C, 30 min, (ii) ZnCl2, ꢀ78 °C to 0 °C, 15 min, (iii) Pd(PPh3)4, 13, 0 °C to reflux, 1.5 h, 80%; (b) (i)
CH3CClHOCOCl, ClCH2CH2Cl, reflux, 4 h, (ii) MeOH, rt, 4 h, (iii) Boc2O, DIPEA, CH2Cl2, 0 °C to rt, 2 h, 55%; (c) 18a: mCPBA, CH2Cl2, 0 °C, 30 min, 93%. 18b: mCPBA, CH2Cl2, 0 °C to
rt, overnight, 92%; (d) 2-chloro-3,6-difluorophenol, ADDP, PBu3, toluene, reflux, 1 h, 88–98%; (e) 15a, PdCl2(PPh3)2, Na2CO3, H2O, propanol, DMF, 80 °C, 1 h, 58–82%; (f)
CH3CClHOCOCl, NaHCO3, ClCH2CH2Cl, reflux, 2 h, (ii) MeOH, 50 °C, 1 h, (iii) Boc2O, DIPEA, CH2Cl2, 0 °C to rt, 2 h, 82–93%; (g) (i) NaOH, H2O, EtOH, 70 °C, 8 h, (ii) amine,1a
EDCꢁHCl, HOBt, DMAP, DIPEA, CH2Cl2, rt, 4–5 days, (iii) HCl, dioxane, CH2Cl2, 0 °C to rt, 1–2 h, 20–67%.
Cl
Cl
O
F
F
O
F
F
OTf
O
X
Y
(b)
(a)
O
N
R
O
O
Boc
R1
X
Y
X
Y
O
N
27:
X = Y = H
28: X-Y = CH2CH2
29: X = Y = Me
N
N
Boc
Boc
30:
31:
32:
X = Y = H
X-Y = CH2CH2
X = Y = Me
7:
X = Y = H
8: X-Y = CH2CH2
9
: X = Y = Me
(R = R1 = Cl) or
b: (R = Me, R1 = OMe)
a:
Scheme 2. Reagents and conditions: (a) 15a, PdCl2(PPh3)2, Na2CO3, H2O, propanol, DMF, 80 °C, 1 h, 48–84%; (b) (i) LiOH, H2O, THF, 60 °C, 3 days, (ii) amine,1a EDCꢁHCl, HOBt,
DMAP, DIPEA, CH2Cl2, rt, 3–10 days, (iii) HCl, dioxane, CH2Cl2, 0 °C to rt, 1–2 h, 20–38%.

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L. Remen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6762–6765
6764
OH
O
O
O
O
O
F
F
(b)
OEt
(a)
(c)
EtO
N
Bn
O
EtO
N
Bn
N
N
O
NHBn
F
F
N
Bn
35
N
34
33
(d)
F
TBDMSO
HO
10a: R = R1 = Cl
10b: R = Me, R1 = OMe
F
Cl
OTf
O
O
(e)
F
F
(f)
OEt
(g)
38
O
36
N
O
F
F
O
Bn
F
F
O
O
R
N
Bn
37
R1
N
Boc
F
F
N
N
H
Scheme 3. Reagents and conditions: (a) benzotriazole, formaldehyde, MeOH, rt, 94%; (b) BrF2CCO2Et, Zn, Me3SiCl, THF, 93%; (c) LDA, ꢀ78 °C, THF, 18 h, 81%; (d) (i) NaH, THF,
0 °C, 30 min, (ii) Tf2NPh, THF, 55 °C, 72 h, quant.; (e) (i) 15b, n-BuLi, THF, ꢀ78 °C, 30 min, (ii) ZnCl2, ꢀ78 °C to 0 °C, 30 min, (iii) 36, Pd(PPh3)4, THF, 0 °C to 45 °C, 18 h, 59%; (f)
H2, Pd/C,Boc2O, AcOH, EtOH, rt, 4 h; (g) (i) 2-chloro-3,6-difluorophenol, ADDP, PBu3, toluene, reflux, 2 h, 90%, (ii) NaOH, EtOH, H2O, 5 h, (iii) amine,1a EDCꢁHCl, HOBt, DMAP,
DIPEA, CH2Cl2, rt, 3 days, (iv) HCl, dioxane, CH2Cl2, 0 °C to rt, 2 h, 38%.
Table 1
Measured IC50 values in nM
Compound
1a
2a
3a
4a
5a
6a
7a
8a
9a
10a
IC50 (buffer)
IC50 (plasma)
0.40
36
0.68
55
1.1
113
6.4
ND
NP
NP
0.55
47
1.2
53
34
4000
31
2000
800
ND
1b
2b
3b
4b
5b
6b
7b
8b
9b
10b
IC50 (buffer)
IC50 (plasma)
1.37
54
0.49
42
0.92
101
NP
NP
64
ND
0.74
43
2.0
87
210
7400
170
7400
330
ND
ND = not determined, NP = not prepared.
yielded compounds 30–32, respectively. Ester hydrolysis followed
by amide couplings and final removal of the Boc-groups led to the
desired piperidine derivatives 7a–9b.
Saponification of compound 30 led to
a mixture of two
isomers—the desired ,b-unsaturated carboxylic acid and the b,c-
a
unsaturated acid. Such a partial displacement of the double bond
has actually already been observed with our diazabicyclononene
derivatives described earlier.1a The amide coupling with this mix-
ture delivered the corresponding amide products, which could only
be separated after extensive chromatographic purification.
Compound 34 (Scheme 3) was prepared starting from the
known N-benzyl-b-alanine ethyl ester via the benzotriazol
derivative 33, using a Reformatsky reaction.8 A Dieckmann cycliza-
tion led to tetrahydropyridine 35, which was converted into its
corresponding vinylic triflate 36. A Negishi coupling led to com-
pound 37, and the desired tetrahydropyridine 10 was obtained fol-
lowing standard chemistry.
The IC50 values of these compounds for renin were determinat-
ed as described previously1a and are presented in Table 1. As ex-
pected, optimal substituents from the diazabicyclononene
scaffold (compounds 1a and 1b) led to compounds with high affin-
ities on other scaffolds as well, as long as this scaffold fit in the ac-
tive site. The IC50 values in buffer for compounds 1a, 2a, 3a, 6a, and
7a on one hand, and for compounds 1b, 2b, 3b, 6b, and 7b on the
other hand, were almost identical. All these scaffolds could be con-
sidered as being very effective in terms of binding. This confirmed
our hypothesis that the C2–N3–C4 bridge of diazabicyclononene
scaffold does not influence the binding of these molecules to renin
Figure 2. X-ray structure analysis of compound 7c in renin; Gly40 and Ser41 are
pictured with their carbonyl groups and side-chain. PDB Code: 3k1w.
in an essential manner. Even the absence of any bridge (com-
pounds 7a and 7b) led to excellent renin inhibitors. As a matter
of fact, the tetrahydropyridine moiety differs only by an endocyclic
double bond from the chiral piperidine template that served as ba-
sis to the development of our renin inhibitors.9 Thus, the tetrahy-
dropyridine renin inhibitors of type 7 represent the first achiral,
potent renin inhibitors known in the literature.

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L. Remen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6762–6765
6765
200
180
160
140
120
200
200
180
160
140
120
J
180
J
J
J
J
J
J
J
J
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J
J
J
J
J
J
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J
J
160
140
120
J
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J
Vehicle,
Compound 2b
J
Vehicle
Vehicle,
Compound 7d
J
J
J
J
J
J
J
J
J
J J
J
J
J
J
J
J
J
J
Compound 6a
J
J
0
6
12
18
24
0
12
24
36
0
12
24
36
48
60
72
Time (hour)
Time (hour)
Time (hour)
Figure 3. Oral hypotensive activity of compounds 2b (10 mg/kg), 6a (10 mg/kg), and 7d (30 mg/kg) in the TGR model.
On the other hand, compounds 4a and 5b, as well as compounds
8a, 8b, 9a, 9b, 10a, and 10b turned out to be much less potent. A
possible explanation for the lack of affinity of compounds of type
4, 5, and 10 resides in the decreased pKa values of the secondary
amines in the various templates. Diazabicyclononene compounds
(e.g., 1) displayed pKa values around 8.2 and 3.6, while oxazobicy-
clononanes (e.g., 2b) displayed a pKa value around 6.5. The absence
of an electronwithdrawing heteroatom in the bridge led to slightly
enhanced pKa values around 8.4 for the tropane scaffold (e.g., 6),
and 8.0 for a tetrahydropyridine scaffold (e.g., 7). The pKa value
for the sulfone 4a was measured at 3.5, while the corresponding
sulfoxide 5b displayed a pKa value of 3.9. The two fluorine atoms
in compounds 10a and 10b had a strong pKa lowering effect. Since
these compounds were not well soluble in aqueous medium in
their neutral forms, the pKa values had to be determined in solvent
mixtures and could not be determined accurately. From these
experiments, they were estimated to be between 3 and 4, resulting
in a difference of 4–5 pKa units compared with the nonfluorinated
compounds. Models predict10 a difference of 3.7 log-units. With
pKa values in this range, compounds of type 4, 5, and 10 are only
partially protonated at the optimal pH for renin to cleave its sub-
strate (pH 5.5–6). A protonated nitrogen of the piperidine hetero-
cycles forms a tight salt bridge with the catalytically active
aspartyl residues, and is therefore indispensable for high binding
affinity.1a,9
Inhibition of the cytochrome P450 3A4 by these compounds
emerged as a selection criteria. While compound 1a inhibited
CYP3A4 only weakly (IC50 >10
2b proved to be a rather potent CYP3A4 inhibitor (IC50 = 1
Compound 6a (IC50 = 1.9 M), and compound 7a (IC50 = 1.3
l
M), the pure, active enantiomer
M).
M)
l
l
l
were potent CYP3A4 inhibitors as well. Clearly, the absence of a
second polar group beside the charged secondary amine, leads to
compounds significantly inhibiting the CYP3A4 enzyme.
In conclusion, we identified new scaffolds leading to highly po-
tent, orally active renin inhibitors. We also identified some achiral,
low-nanomolar inhibitors for human renin. Modulation of an exist-
ing bridge in these bicyclic scaffolds1a influences neither the bind-
ing affinity for renin nor the pharmacological efficacy, as long as
the basic properties of the essential secondary amine are
conserved.
Acknowledgments
We thank Patrick Eckert, Martin Faes, Sven Glutz, Luke Harris,
Pascal Occhiuto, Bela Humer, Daniel Marchal, Sophie Moujon, Pas-
cal Rebmann, Siefke Siefken, Daniel Trachsel, Gabrielle Vorburger,
Alain Chambovey, Antoinette Amrein, Geoffroy Bourquin, Fabienne
Drouet, Aude Weigel, Markus Rey and Daniel Wanner for their help
and engagement on this program.
Compounds of type 7, 8, or 9 do not comprise electronwith-
drawing substituents attached to the piperidine ring and display
pKa values in the range of 8.0. Modeling studies based on X-ray
structure analysis of compound 7c ( Figs. 1 and 2), led to the
hypothesis that a double substitution at the 5-position of the tetra-
hydropyridine scaffold should not be favorable due to potential
clashes of the equatorial substituent with Gly40 and/or Ser41.
The IC50 values of compounds 1a–9b in plasma (Table 1) were
higher by a factor of 50–100 independently of the scaffold. These
values indicate a strong plasma protein binding for these com-
pounds. The more polar 3-methoxy-2-methyl benzyl amides (b-
series) tended to show slightly less shifted plasma values if com-
pared with the corresponding, less polar, 2,3-dichlorobenzyl
amides (a-series).
The pharmacological efficacy of selected compounds was evalu-
ated in the TGR model2 at 10 and 30 mg/kg (Fig. 3). Compound 2b
showed a slightly inferior profile to analogous diazabicyclononene
derivatives.1a Obviously the exchange of the N3-nitrogen with an
oxygen exerts only minor effects on compound properties. The
hydrophobic compound 6a stands out by its exceptionally long
duration of action. Tetrahydropyridine 7d (Fig. 1; IC50 = 0.30 nM
in buffer, 35 nM in plasma, prepared in analogy to other com-
pounds of type 7) also displayed a pronounced pharmacological ef-
fect at 30 mg/kg, validating this achiral series as potent renin
inhibitors. Pharmacokinetic experiments (wistar rats, 10 mg/kg,
po) on similar tetrahydropyridines of type 7 showed bioavailabili-
ties varying between 10% and 70%.
References and notes
ˇ
1. (a) 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.;
Strickner, P.; Binkert, C.; Hess, P.; Steiner, B.; Fischli, W. J. Med. Chem. 2009, 52,
3689; (b) Tice, C. M. Ann. Rep. Med. Chem. 2006, 41, 155.
2. (a) Brockway, B. P.; Mills, P. A.; Azar, S. H. Clin. Exp. Hypertens., Part A 1991, 13,
885; (b) Guiol, C.; Ledoussal, C.; Surgé, J.-M. J. Pharmcol. Toxicol. Methods 1992,
28, 99; (c) Hess, P.; Clozel, M.; Clozel, J.-P. J. Appl. Physiol. 1996, 81, 1027.
3. Compond 1a is a pure enantiomer. All other compounds containing chiral
centers are racemates.
4. Jerchel, D.; Weidmann, H. Liebigs Ann. Chem. 1957, 607, 126.
5. List of abbreviations: ADDP, 1,10-(azodicarbonyl)-dipiperidine; Boc, tert-
butoxycarbonyl; n-BuLi, n-butyl lithium; DIPEA, diisopropylethylamine;
DMAP, 4-(N,N-dimethylamino)pyridine; EDCꢁHCl, N-(dimethylaminoproyl)-
N0-ethylcarbodiimide hydrochloride; HOBt, 3-hydroxybenzotriazol; LDA,
lithium diisopropilamide; mCPBA, meta-chloro peroxobenzoic acid; Tf,
CF3SO2ꢀ
.
6. Olofson, R. A.; Martz, J. T.; Senet, J. P.; Piteau, M.; Malfroot, T. J. Org. Chem. 1984,
49, 2081.
7. Ruder, S. M.; Ronald, C. R. Tetrahedron Lett. 1984, 25, 5501.
8. Katritzky, A. R.; Nichols, D. A.; Qi, M. Tetrahedron Lett. 1998, 39, 7063.
9. (a) Vieira, E.; Binggeli, A.; Breu, V.; Bur, D.; Fischli, W.; Güller, R.; Hirth, G.;
Märki, H. P.; Müller, M.; Oefner, C.; Scalone, M.; Stadler, H.; Wilhelm, M.; Wostl,
W. Bioorg. Med. Chem. Lett. 1999, 9, 1397; (c) Oefner, C.; Binggeli, A.; Breu, V.;
Bur, D.; Clozel, J.-P.; D’Arcy, A.; Dorn, A.; Fischli, W.; Grüinger, F.; Güller, R.;
Hirth, G.; Märki, H. P.; Mathews, S.; Müller, M.; Ridley, R. G.; Stadler, H.; Vieira,
E.; Wilhelm, M.; Winkler, F. K.; Wostl, W. Chem. Biol. 1999, 6, 127.
10. (a) Morgenthaler, M.; Schweizer, E.; Hoffmann-Röder, A.; Benini, F.; Martin, R.
E.; Jaeschke, G.; Wagner, B.; Fischer, H.; Bendels, S.; Zimmerli, D.; Schneider, J.;
Diederich, F.; Kansy, M.; Müller, K. ChemMedChem 2007, 2, 1100; (b) Hagmann,
W. K. J. Med. Chem. 2008, 51, 4359.