Identification of a new biaryl scaffold generating potent renin inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.07.127

The discovery and SAR of a series of potent renin inhibitors possessing a novel biaryl scaffold are described herein. Molecular modeling revealed that the cyclopropylamide spacer present in 1 can be replaced by a simple, substituted aromatic ring such as

Full text of DOI:10.1016/j.bmcl.2010.07.127

Bioorganic & Medicinal Chemistry Letters 20 (2010) 5822–5826
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Identification of a new biaryl scaffold generating potent renin inhibitors
*
Patrick Lacombe , Renée Aspiotis, Christopher Bayly, Austin Chen, Daniel Dubé, Réjean Fortin,
Michel Gallant, Hélène Juteau, Suzanna Liu, Dan McKay, Patrick Roy, Tom Wu
Merck Frosst Center for Therapeutic Research, PO Box 1005, Pointe Claire-Dorval, Québec, Canada H9R 4P8
a r t i c l e i n f o
a b s t r a c t
Article history:
The discovery and SAR of a series of potent renin inhibitors possessing a novel biaryl scaffold are
described herein. Molecular modeling revealed that the cyclopropylamide spacer present in 1 can be
replaced by a simple, substituted aromatic ring such as a toluene in 2. The resulting compounds exhibit
subnanomolar renin IC50 and good oral bioavailability in rats.
Received 16 June 2010
Revised 27 July 2010
Accepted 28 July 2010
Available online 3 August 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Renin
Inhibitor
Anti-hypertensive
The treatment of hypertension, a major risk factor for cardiovas-
cular disease, has been an active area of research for many years.
Unfortunately, despite the numerous advances that have been
made, most hypertensive patients still can not achieve the targeted
140/90 mmHg recommended by the American Heart Association
(AHA) by using the currently available therapies (i.e., diuretics,
b-blockers, calcium channel blockers, ACE inhibitors, AT1R antago-
nist, etc.).1 However, since the perturbation of the renin–angioten-
sin–aldosterone system (RAAS) at its various points (Fig. 1) with
ACE inhibitors and/or AT1R antagonists have proven to be a viable
strategy for the lowering of blood pressure,2 it therefore serves to
reason that the inhibition of the enzyme responsible for the initial
and rate-limiting cleavage of angiotensinogen to angiotensin I,
should confer the maximum benefit possible with this pathway.3
Furthermore, it has been hypothesized that renin inhibition should
be associated with fewer side effects when compared with other
therapies that target downstream events of the RAAS pathway.4 In-
deed, significant time and resources have been invested towards
the identification of a renin inhibitor suitable for clinical develop-
ment. To date, only Aliskiren has received FDA approval (2007) for
the treatment of essential hypertension.5
warhead. Consequently, it was felt that the amide bridge could
be effectively replaced by an aryl linker thereby allowing further
structural diversification from known renin inhibitors. Further-
more, the resulting biaryl compounds could be accessed using well
Previously, we described the design and optimization of a novel
series of substituted amino propanamide renin inhibitors, with
compound 1 (Fig 2) as a representative compound.6 Subsequent
molecular modeling7 and structural biology studies confirmed that
the amide functionality is not implicated in any stabilizing hydro-
gen bond interactions with the renin enzyme but simply serves as
a spacer between the terminal P3 aromatic plate and the cationic
* Corresponding author.
E-mail address: patrick_lacombe@merck.com (P. Lacombe).
Figure 1. Renin–angiotensin–aldosterone system (RAAS).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.07.127

P. Lacombe et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5822–5826
5823
Cl
O
O
Cl
Cl
O
amide
replacement
Cl
O
O
Cl
N
H2N
1
2
O
H2N
O
Figure 2. Aryl spacer as amide replacement.
established metal-catalyzed cross-coupling chemistry that is ame-
nable for rapid analogue synthesis.
alcohol 15 by treatment with borane dimethyl sulfide complex.
Alcohol 15 can then be elaborated further to either methyl ether
16 or carbamate 17 using the same reaction conditions described
above. Starting from 2-bromophenol (19), alkylation with either
1-bromo-3-methoxypropane or 2-bromoethyl methyl ether deliver
compounds 20 and 21, respectively. Finally, acylation of commer-
cially available amine 22 affords the desired acetamide 23.
Our initial SAR efforts were focused on determining which aryl
substituent (i.e., X, Table 1) would best occupy the renin P1 sub-
pocket that was previously filled by the cyclopropyl residue in
our earlier amino-propanamide series. The respective ability of
these compounds to inhibit the renin enzyme in either buffer10
or human plasma11 is shown in Table 1.
When a simple benzene spacer was used (X = H, 24), only mod-
erate inhibition of the renin enzyme was observed. The introduc-
tion of a small and greasy substituent such as fluorine (26)
proved to be beneficial for activity whereas the introduction of a
larger and more polar methoxy group (25) was not. Further optimi-
zation revealed that the appendage of a chlorine atom (28) could
improve the intrinsic potency by another 10-fold but the resulting
compound was found to be highly plasma protein bound. A toluene
spacer (X = Me, 27) proved to offer the best compromise between
intrinsic potency and plasma shift.
To test this hypothesis, we prepared a series of biaryl analogs
using the synthetic route described in Scheme 1. Briefly, sodium
borohydride reduction of the known8 aldehyde 3 and subsequent
Arbusov iodination of the resulting alcohol afforded benzyl iodide
4. Iodide 4 could then be used to alkylate a variety of 2-substituted
4-bromophenyl acetonitriles. The latter compounds were either
commercially available or readily prepared from the corresponding
benzyl bromides via cyanide displacement. The resulting alkylated
nitriles 5 could then be reduced by cobalt borohydride; prepared
in situ from cobalt(II) chloride hexahydrate and sodium borohy-
dride, protected as the tert-butyl carbamates and converted to
the desired boron pinacolates 6 under typical Miyaura conditions.9
Finally Suzuki cross-coupling of 6 with a suitable 2-substituted
phenyl bromide afforded, following BOC-deprotection with hydro-
chloric acid, the desired amines 8.
The requisite 2-substituted phenyl bromide for the penultimate
cross-coupling step can be obtained using the synthetic route de-
scribed in Scheme 2. Starting from commercially available alcohol
9, it can either be converted to the methyl ether 10 by treatment
with iodomethane under basic conditions, to the carbamate 11
with sodium cyanate under acidic conditions, or to the nitrile 12
via the Mitsunobu reaction. Starting from known carboxylic acid
13, it can either be converted to the amide 14 via the acid chloride,
or to the ester 18 under Fisher’s esterification conditions, or to the
Having established the optimal substitution pattern for the cen-
tral aromatic ring, we then turned our attention to the optimiza-

5824
P. Lacombe et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5822–5826
Cl
I
Cl
Cl
O
a, b
O
O
O
O
Cl
Cl
3
4
Br
N
c
X
Cl
O
O
O
O
Cl
O
B
Cl
O
Br
d, e, f
O
X
X
6
5
O
N
H
N
Cl
g
Br
Cl
R
O
O
O
O
Cl
Cl
h
R
R
O
X
H2N
X
O
N
7
8
H
Scheme 1. Synthesis of 8. Reagents and conditions: (a) NaBH4, MeOH; (b) I2, PPh3, imidazole, CH2Cl2; (c) LiHMDS, HMPA/THF; (d) CoCl2ꢀ6H2O, NaBH4, THF/MeOH;
(e) (BOC)2O, Hunig’s base, CH2Cl2; (f) PdCl2(dppf), Bis(pinacolato)diboron, KOAc, DMF; (g) Pd(OAc)2, Ph3P, Na2CO3, n-PrOH; (h) HCl, dioxane/CH2Cl2.
Table 1
Table 2
In vitro data for compounds 24–28
In vitro data for compounds 29–40
Cl
O
Cl
O
O
O
Cl
Cl
Y
Cl
X
H2N
H2N
a,b
a,c
a,b
a,c
Compd
Y
Renin buffer IC50
(nM)
Renin plasma IC50
(nM)
Compd
X
Renin buffer IC50 (nM)
Renin plasma IC50 (nM)
24
25
26
27
28
H
OMe
F
Me
Cl
44.4
47.6
7.0
6.0
0.52
—
29
30
31
32
33
34
35
36
37
38
39
40
CH2CH2OMe
CH2CH2CH2OMe
OCH2CH2OMe
OCH2CH2CH2OMe 1.7
CH2CO2Me
CH2CH2CO2Me
CH2CH2CONMe2
CH2CH2OCONH2
CH2CH2CN
CH2NHAc
CH2CH2NHAc
CH2CH2CH2NHAc
19.7
0.44
7.41
1915
116
1495
1158
534
141
1111
103
3622
1151
796
764
12.9
a
b
c
Values are means of at least two experiments.
See Ref. 10 for assay protocol.
0.09
30.8
1.02
10.6
2.1
See Ref. 11 for assay protocol.
544
138
9.6
0.04
0.97
tion of the terminal aromatic ring (Table 2). As was already demon-
strated in previous publications,6,12 maximizing the interaction
with the renin P3 sub-pocket is extremely important for renin
activity. However, it should be stressed that the SAR established
previously in the amide series6 did not directly translate to the
biaryl series. For example, the 2-methoxyethyl S3sp substituent
that was found to significantly improve binding to the renin en-
zyme in the amide series actually led to a threefold loss in potency
in the biaryl series (i.e., 29) when compared to its simple 2-chloro
analogue (i.e., 27). However, further extension of this side chain by
one methylene unit to a 3-methoxypropyl group (i.e., 30) led to a
much more potent renin inhibitor. Incorporation of an oxygen linker
131
a
b
c
Values are means of at least two experiments.
See Ref. 10 for assay protocol.
See Ref. 11 for assay protocol.
into the chain (i.e., 31, 32) did not prove to be beneficial. On the other
hand, replacement of the methoxy capping group by a methyl ester
afforded one of our most intrinsically potent biaryl renin inhibitor
(i.e., 34). Unfortunately, the potency of compound 34 was highly
shifted in the presence of human plasma. This however, could be
readily addressed by switching to a more polar acetamide capping

P. Lacombe et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5822–5826
5825
Table 3
Table 4
Comparative profile for compounds 1 and 39
In vitro data for compounds 27, 41–43
Cl
O
Cl
O
O
O
Cl
Cl
Cl
O
Ar
Cl
O
O
Cl
N
H2N
H2N
Compd
X
Renin buffer
IC50 (nM)
Renin plasma
IC50 (nM)
HN
O
1
39
a,b
a,c
O
H2N
27
2-ClPh
6.0
796
Compd Renin buffer Renin plasma SD rat PK F (%), P.O. AUC (
l
M h),
N
a,b
a,c
IC50 (nM)
IC50 (nM)
Cl (mL/min/kg), T1/2 (h), Vdss (L/kg)
41
3.9
416
N
1
39
0.09
0.04
2.4
9.6
41, 8.3, 35, 6, 12
23, 5.5, 34, 7, 9
N
a
b
c
N
N
Values are means of at least two experiments.
See Ref. 10 for assay protocol.
See Ref. 11 for assay protocol.
42
43
1.7
4.9
228
614
NH2
N
group (compounds 38–40). With the judicious choice in tether chain
a
b
c
length (compound 39), a renin inhibitor with a low nanomolar IC50
even in the presence of human plasma, was obtained.
,
Values are means of at least two experiments.
See Ref. 10 for assay protocol.
See Ref. 11 for assay protocol.
Br
Br
Br
a
b
O
O
NH2
O
OH
10
9
11
c
Br
12
N
Br
Br
Br
Br
d
e, f
OH
N
OH
O
O
O
O
15
13
14
g
b
a
Br
Br
NH2
O
O
O
16
17
19
18
h
i
Br
Br
Br
O
O
OH
O
O
20
21
23
Br
Br
j
O
N
NH2
H
22
Scheme 2. Synthesis of aryl bromide intermediates. Reagents and conditions: (a) MeI, NaH, DMF; (b) NaOCN, TFA, Benzene; (c) 1,10-(azodicarbonyl)dipiperidine, n-Bu3P,
acetone cyanohydrin, benzene; (d) BH3ꢀDMS, THF; (e) oxalyl chloride, DMF (cat.), CH2Cl2; (f) Me2NH, CH2Cl2; (g) H2SO4, MeOH; (h) 1-bromo-3-methoxypropane, Cs2CO3,
DMF; (i) 2-bromoethyl methyl ether, Cs2CO3, DMF; (j) AcCl, Hunig’s base, DMAP, CH2Cl2.

5826
P. Lacombe et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5822–5826
Soc. Nephrol. 2006, 1, 221; (d) Azizi, M.; Gradman, A. H.; Sever, P. S. J. R. A. A.
The profile of biaryl renin inhibitor 39 is summarized and com-
System 2009, 10, 65.
pared with that of amide renin inhibitor 1 in Table 3. Compound 39
was found to be intrinsically ꢁtwofold more potent against renin
than 1, but was also more plasma shifted. When given orally to
Sprague–Dowly rats as the HCl salt at a dose of 30 mpk (0.5%
methocel solution, 5 ml/kg) and iv at a dose of 4 mpk (60% PEG
200/water solution, 1 ml/kg), both renin inhibitors exhibited com-
parable pharmacokinetics, with compound 1 being more orally
bioavailable.
Finally a structurally diverse 75-member library was generated
from pinacol boronate 6 (X = Me) using rapid parallel synthesis
with various aryl halides. The three most promising hits, shown
in Table 4, revealed that the terminal 2-chlorophenyl P3 plate in
compound 27 can be effectively replaced with hetero-aromatics
without loss in renin potency.
In conclusion, with input from molecular modeling and struc-
tural biology, we were able to identify a novel series of biaryl re-
nin inhibitors with good in vitro potency and rodent PK.
Furthermore with this scaffold, parallel synthesis technology
could be employed that allowed us to rapidly modify and tune
the physical and chemical characteristics of our renin inhibitors.
Other biaryl-based renin inhibitors with different nitrogen bear-
ing warheads, as well as their associated properties, will be dis-
closed in due course.
5. (a) Greenlee, W. J. Med. Res. Rev. 1990, 10, 173; (b) Rosenberg, S. H. Prog. Med.
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Gagné, S.; Gallant, M.; Gaudreault, M.; Grimm, E.; Houle, R.; Lacombe, P.;
Laliberté, S.; Lévesque, J.-F.; Liu, S.; MacDonald, D.; Mackay, B.; Martin, D.;
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molecular dynamics calculations at 300 K with explicit solvent (TIP3P) and
periodic boundary conditions. (Case et al. AMBER: AMBER8 D.A.; University of
California: San Francisco, 2004, with extensive in-house small molecule
parameters.)
8. Bayly, C. I.; Chen, A.C.; Dubé, D.; Dubé, L.; Gallant, M.; Lacombe, P.; MacDonald,
D.; McKay, D.; Powell, D.A.; Grimm, E.L. WO-2007009250. 2007.
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10. Recombinant human renin (3 pg/
BSA, pH 7.4), human tetradecapeptide(1–14) substrate (5
hydroxyquinoline sulfate (30 mM in water), and assay buffer were pre-mix at
4 °C at ratio of 100:30:10:145. 47.5 per well of this pre-mix was
transferred into polypropylene plates. Test compounds were dissolved and
diluted in DMSO and 25 l added to the pre-mix, then incubated at 37 °C for
3 h. At the end of the incubation period, 5 l of the renin reaction (or standards
l
M) in assay buffer (PBS1X, 1 mM EDTA, 0.1%
lM in 10 mM HCl),
a
ll
l
l
in the assay buffer) were measured for AngI accumulation. The percentage of
renin inhibition (AngI decrease) was calculated for each compound and an IC50
was determined by curve fitting software.
11. Citrate-plasma from human volunteers was pooled, aliquoted and stored
frozen at ꢂ20 °C. Renin activity in pooled plasma was supplemented with
recombinant human renin (150 pg/ml final concentration) in order to increase
the readout of the assay. Five microliters of renin inhibitors, at various
concentration in DMSO, was added to 80 ll of a mixture (7:1) of human plasma
References and notes
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1:10 in horse serum) diluted initially 1:26.5 in assay buffer (PBS1X, 1 mM
EDTA, 0.1% BSA, pH 7.4) and then diluted 1:3:3 in 3 M Tris, 200 mM EDTA, pH
7.2 (final anti-serum dilution 1:50,000) and was incubated at 37 °C for 2 h. As
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assay buffer) were measured for AngI accumulation by immunoassay.
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