The P1 N-isopropyl motif bearing hydroxyethylene dipeptide isostere analogues of aliskiren are in vitro potent inhibitors of the human aspartyl protease renin

Article abstract of DOI:10.1016/j.bmcl.2009.05.128

Novel nonpeptide small molecule renin inhibitors bearing an N-isopropyl P₁ motif were designed based on initial lead structures 1 and aliskiren (2). (P₃-P₁)-Benzamide derivatives such as 9a and 34, as well as the corresponding P₁ basic tertiary amine derivatives 10 and 35 were found to display low nanomolar inhibition against human renin in vitro.

Full text of DOI:10.1016/j.bmcl.2009.05.128

Bioorganic & Medicinal Chemistry Letters 19 (2009) 4863–4867
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
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The P1 N-isopropyl motif bearing hydroxyethylene dipeptide isostere analogues
of aliskiren are in vitro potent inhibitors of the human aspartyl protease renin
Yasuchika Yamaguchi b, Keith Menear a, Nissim-Claude Cohen c, Robert Mah a, Frédéric Cumin a,
Christian Schnell a, Jeanette M. Wood a, Jürgen Maibaum a,
*
a Novartis Institutes for BioMedical Research, Novartis Campus, CH-4056 Basel, Switzerland
b Faculty of Pharmaceutical Sciences, Nagasaki International University, Sasebo, Nagasaki 859-3298, Japan
c Synergix Ltd, Technology Park Malha, Jerusalem 91487, Israel
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel nonpeptide small molecule renin inhibitors bearing an N-isopropyl P1 motif were designed based
on initial lead structures 1 and aliskiren (2). (P3–P1)-Benzamide derivatives such as 9a and 34, as well as
the corresponding P1 basic tertiary amine derivatives 10 and 35 were found to display low nanomolar
inhibition against human renin in vitro.
Received 25 March 2009
Revised 7 May 2009
Accepted 8 May 2009
Available online 26 June 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Renin–angiotensin–aldosterone system
RAAS, renin inhibitors
Aliskiren analogues
Hydroxyethylene dipeptide isosters
Hypertension is a major risk factor of high prevalence world-
wide for cardiovascular diseases.1 The pivotal functions of the re-
nin–angiotensin–aldosterone system (RAAS) in cardiovascular
(patho)physiology including the regulation of blood pressure, as
well as electrolyte and body fluid homeostasis have been well
established.2 The RAAS has emerged as an important target for
antihypertensive drug therapy, with angiotensin (Ang)-converting
enzyme inhibitors (ACEi) and AT1-receptor blockers (ARBs) having
proven effectiveness in preventing cardiovascular and renal
events.3 Direct blockade of highly substrate-specific renin activity
attenuates the formation of Ang I and Ang II, the principal mediator
of the RAAS, even at elevated circulating plasma renin levels due to
negative feedback mediated release from the kidney.4,5 The attrac-
tiveness of the aspartyl protease renin as an advantageous target6,7
with the potential to provide more effective suppression of the
RAAS has stimulated vast efforts to develop small molecule, orally
efficacious renin inhibitors.8
MeO
OH R1
H
H2N
N
R2
O
O
MeO
1 : R1 = Me; R2 = n-Bu
2 : R1 = iPr; R2 = CH2C(Me)2CONH2
N
'Approach A'
OH R3
H2N
NH
R1
R2
O
'Approach B'
N
We have discovered recently several series of potent, highly sol-
uble, and orally active non-peptide chemotype renin inhibitors,
such as 1 and 2 (Fig. 1).9 These transition-state mimetic (TSM)
inhibitors emerged from an unprecedented topological structure-
based design approach incorporating a direct spacer link of the
P1 and P3 moieties and concomitant removal of the P2–P4 backbone
Figure 1. Renin inhibitors 1 and 2, and ‘simplification’ strategies A and B by N
versus chiral CH* replacements at the P1 and/or P positions.
0
1
of classical peptide-like renin inhibitors.10–13 Aliskiren (2) is a
highly potent selective inhibitor of human renin demonstrating
sustained blood pressure lowering efficacy in vivo upon once-daily
oral dosing.12 It is the first direct renin inhibitor to be marketed as
a new therapy for hypertension,13 a hallmark of more than three
decades of intense research efforts worldwide.
* Corresponding author. Tel.: +41 61 6965560; fax: +41 61 6967155.
E-mail address: juergen_klaus.maibaum@novartis.com (J. Maibaum).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.05.128

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Y. Yamaguchi et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4863–4867
Our strategy during initial lead optimization of 1 and related
C2. The desired 4(S)-6 (mp 105 °C)17 was isolated in high diastereo-
meric purity (>17:1 by RP-HPLC) after single crystallization from n-
hexane–CHCl3 in 40% yield from aldehyde 4.
analogues was to reduce the chemical complexity of these novel
chemotype renin inhibitors by ‘simplifying’ structural elements
of the key TSM pharmacophore. Computational modeling based
on the X-ray structure of inhibitor 1 bound to the active site of re-
combinant human renin (rh-renin)9,10 suggested replacement of
the chirality center either at P10 (‘reversed carboxamides’, approach
A; Fig. 1),14 or at P1 and introduction of a functional spacer group to
tether the substituted phenyl moiety (approach B) to be viable
concepts.
Intermediate 6 was then subjected to N,O-acetal formation
(97%), followed by hydrogenolysis of the benzylether, mesylate for-
mation, and finally displacement with NaN3 in DMPU to afford
azide 7 in 83% (3 steps). Azide reduction and reductive amination
with acetone/NaBH3CN yielded the secondary amine 8 in good
overall yield. Inhibitors 9a–i bearing a tertiary N-isopropyl-benz-
amide group at the P1 position, as listed in Table 1, were prepared
via the activated esters from the corresponding benzoic acids18
using HBTU.19 Removal of the N,O-acetal protecting group with
cat. TsOH in MeOH proceeded uneventfully and in good isolated
yields (>80%). N-BOC deprotection with 4 N HCl–dioxane was con-
ducted at ꢀ20 °C in order to avoid formation of the dihydro-1,3-
imidazole 37 as a major side product (Fig. 2, vide infra) affording
the inhibitors as their mono-HCl salts after lyophilisation. Inhibitor
10 (di-HCl salt) bearing an N-isopropyl substituted tertiary amine
was obtained by reductive alkylation of 8 with 4-methoxy-3-(3-
methoxy-propoxy)-benzaldehyde20 in the presence of a Lewis acid
(NaBH3CN, Ti(OiPr)4; 40% yield), followed by two-step N,O-
deprotection.
We report herein our results on establishing a new series of
non-peptide renin inhibitors based on the N-isopropyl benzamide
P1–P3 motif and the corresponding N-isopropyl-N-benzylamine
analogues (approach B). A divergent chemistry strategy provided
ready access to a variety of analogues, starting from advanced ver-
satilely protected amine TSM intermediates. This tactic afforded
the opportunity for broad SAR investigation addressing structural
sp
modifications of the P3–P1 pharmacophore as well as the P3 side
chain.
The stereoselective synthesis of the key intermediate
0
(2R,4S,5S)-8 bearing a P1 Me at the hydroxyethylene TSM portion
is depicted in Scheme 1. Starting from commercial OBn-protected
N-BOC-serine 3, aldehyde 4 was obtained in >85% yield over 2
steps with >95% ee (by chiral HPLC of the corresponding alcohol,
obtained via LiBH4/THF reduction, on Chiralcel OJ with n-hexane-
isopropanol 96:4). Adaptation of the chiral homo-enolate addition
to amino acid derived aldehydes, as reported by DeCamp et al.,15
provided the hydroxyethylene moiety in an efficient and reliable
manner on a multi-gram scale. Thus, metallation of 3-iodo-2(R)-
methyl-propionic acid methyl ester with Zn(Cu)/Cl3Ti(OiPr) and
subsequent reaction (4 equiv of the homo-enolate species in ex-
The sulfonamide analogue 14 was prepared according to
Scheme 2. In brief, chlorosulfonylation of anisaldehyde 11 ren-
dered 12 in high yield, which then was coupled to secondary amine
8 in the presence of DIEA as base. Baeyer–Villiger oxidation with
m-chloro-perbenzoic acid and subsequent hydrolysis afforded
sp
intermediate 13, which was O-alkylated to introduce the P3
methoxypropoxy side chain. Final stepwise N,O-deprotection affor-
ded 14 in good overall yield. 15 was obtained in a similar fashion
via coupling of p-OMe-phenyl-sulfonylchloride to 8 (82% yield).
The synthesis of 3,4-disubstituted benzoic acids 18, 20, and 23–
25 with a modified P3 moiety was achieved according to standard
protocols from readily available starting materials (Scheme 3).18
The synthesis of the O-silyl protected TSM intermediate
cess) with 4 furnished the c-hydroxy esters 4S-5a/4R-5b (4:1 ratio)
in 50–60% overall yield.16 Further transformation to the respective
lactones under acidic conditions was followed by direct aminolysis
with n-butylamine at 80 °C without detectable epimerization at
0
(2S,4S,5S)-33 with isopropyl at the P1 position is described in
Scheme 4. Thus, Evans alkylation of the lithium enolate derived
from (S)-27 with (E)-4-bromo-but-2-enyloxymethyl)-benzene21
gave 28 in 77% yield with >95% de. Bromolactonization of 28 pro-
vided trans-29 in high yield as the only isolated isomer. Displace-
ment of the bromine in 29 under non-optimized reaction
conditions afforded azide 30 (>97% ee)22 in 30% isolated yield to-
gether with the elimination side product 31 (60%). The relative ste-
BocHN
BnO
CO2H
BocHN
BnO
CHO
c
a, b
3
4
OH
OH
d-f
BocHN
OMe
BocHN
BnO
OMe
reochemistry of lactones 29 and 30 was determined by 1H and 13
C
+
O
O
O
NMR as reported previously.23 Azide 30 was then converted to the
N-BOC protected lactone 32 by selective hydrogenation in the pres-
ence of (BOC)2O followed by O-debenzylation, mesylation, and fi-
nal azide substitution. Inhibitor 34 was prepared from 33 by the
reaction sequence analogous to the route described for 9a in
Scheme 1. Inhibitor 35 bearing a tertiary amine at P1 was obtained
as described in Scheme 4.
BnO
(4 : 1)
5a
5b
OH
O
BocN
N3
k, l
BocHN
BnO
NH-Bu
NH-Bu
OH
g-j
O
6
7
Structure–activity relationship (SAR) data based on IC50s for
inhibition of rh-renin, as well as of endogenous renin in human
plasma, is summarized for a set of representative inhibitors in Ta-
ble 1. We were gratified to find the in vitro potency of the P1 N-iso-
propyl benzamide 9a to be comparable to that of the
corresponding P1 carba-analogue 1 in the purified renin assay, al-
beit enzyme affinity of 9a dropped fivefold in the plasma assay
as compared to 1. Extending previous SAR10,24 by modification of
H2N
O
NH-Bu
X
BocN
HN
NH-Bu
m-o
R1
R2
O
N
O
9a-9i, 10
(see Table 1)
8
Scheme 1. Reagents and conditions: (a) MeI, K2CO3, DMF, 70 °C, 95%; (b) DIBAL,
toluene, ꢀ78 °C, >90%; (c) 3-iodo-2(R)-methyl-propionic acid methyl ester, Zn(Cu),
TiCl4–Ti(OiPr)4, N,N-dimethyl acetamide, toluene, ꢀ20 °C; (d) AcOH, toluene, reflux.
(e) n-BuNH2, 80 °C; (f) recrystallisation from n-hexane–CHCl3, 40% (4 steps from 3);
(g) 2-methoxypropene, cat. TsOH, CH2Cl2, rt, 97%. (h) H2, cat. Pd/C 10%, MeOH; (i)
MsCl, Et3N, CH2Cl2 0 °C; (j) NaN3, DMPU, 40 °C, 95% (3 steps); (k) H2, cat. Pd/C 10%,
MeOH; (l) acetone, NaBH3CN, rt, >90% (2 steps); (m) 4-methoxy-3-(3-methoxy-
propoxy)-benzaldehyde, Ti(OiPr)4, NaBH3CN, MeOH, 40%; or amide coupling to 3,4-
substituted benzoic acids using HBTU, Et3N, MeCN; (n) cat. TsOH, MeOH, rt; (o) 4 N
HCl, dioxane, ꢀ20 °C; followed by lyophilisation.
sp
the P3 side chain revealed that the phenol ether oxygen of 9a is
not important for binding interactions to purified renin (9b to
9d). The ether link in 9a was replaced by CH2 to afford an
in vitro highly potent inhibitor of rh-renin, 9b, which however
was 15-fold less active in the presence of plasma.25 A similar po-
tency loss in the plasma assay using angiotensinogen as the endog-
enous substrate has been observed in several other non-peptide

Y. Yamaguchi et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4863–4867
4865
Table 1
In vitro enzyme inhibition data for human renin
OH R3
OH R3
H
H
H2N
N
H2N
N
NH2
N
R1
R2
X
O
R1
R2
O
O
N
9a-9i, 10,
14, 15, 34
35
No.
X
R1
R2
R3
IC50 (nM), purifieda
IC50 (nM), plasmab
1
1
1
2
0.6
2
1
1
3
100
8
2
8
6
1
300
>100,000
13
7
0.6
5
15
4
9a
9b
9cd
9d
9e
9f
9g
9h
9i
34
14
15
10
35
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
SO2
SO2
CH2
O(CH2)3OMe
(CH2)4OMe
OMe
OMe
OMe
OMe
OMe
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
iPr
CH@CH(CH2)2OMe
CH2NHCO2Me
(CH2)2NHCO2Me
O(CH2)3OMe
O(CH2)3OMe
O(CH2)3OMe
O(CH2)3OMe
O(CH2)3OMe
O(CH2)3OMe
H
2
ndc
13
7
Et
Br
21
14
10
ndc
ndc
14
7
CCH
Et
OMe
OMe
OMe
OMe
Me
Me
Me
iPr
O(CH2)3OMe
O(CH2)3OMe
a
b
c
Purified rh-renin assay at pH 7.4.11
Inhibition of endogenous renin in plasma from human.11
Not determined.
d
Stereoisomer ratio Z:E = 10:1. All compounds showed similar IC50s against marmoset plasma renin, with high selectivity to bovine cathepsin D and porcine pepsin (IC50
>100
l
M). 9a, 9g, 9h, 10 had IC50 >20
lM for rat renin (for 35, IC50 = 1.4
lM). Calculated log P for 9a: 2.74; 9b: 3.60; 9g: 4.08; 34: 5.00; 35: 2.94.
OMe
NH
OHC
MeO
OHC
MeO
SO2Cl
c, d
a, b
Cl
O
CO2Et
CO2Et
CO2H
a
b-e
11
12
MeO
MeO
MeO
MeO
16
17
OH
O
18
H2N
O
BocN
O
NH-Bu
e-g
NH-Bu
f
O
O
NHCO Me
2
CN
HO
S
O
O
S
O
CO2H
N
N
HO
CO2H
CO2H
g, h, e
MeO
MeO
13
14
MeO
MeO
21
Scheme 2. Reagents and conditions: (a) HC(OEt)3, NH4Cl, EtOH, reflux, 90%. (b)
ClSO3H, 3 h at ꢀ5 °C, then 2 h at rt, 80%; (c) 8, DIEA, CH2Cl2, 0 °C, 16 h, 72%; (d)
MCPBA, CHCl3, 48 h, rt; then Et3N, MeOH, rt, 2 d, 55%. (e) MeO(CH2)3I, K2CO3, MeCN,
reflux, 18 h, 82%. (f) CSA, MeOH, rt, 89%; (g) 4 N HCl–dioxane, 0 °C, 2 h, 82%.
19
R1 = O(CH )3OMe
20
i-k
2
CO2R2
CO2H
R1O
Et
CO2H
R1O
R1O
l
n
, m
Br
e
22 (R2=Me)
23 (R2=H)
MeO
MeO
24
25
OH
H
O
NHBu
N
MeO
OH
NH
Scheme 3. Reagents and conditions: (a) (CHO)n, HCl, CHCl3, rt, 86%; (b) NaN3, KI,
DMPU, 100 °C, 81%; (c) Ph3P, THF; then H2O, 91%; (d) MeOCOCl, DIEA, dioxane, 60%;
(e) 1 N NaOH, MeOH; (f) NaCN, KI, MeCN, 100 °C, 76%; (g) H2, RaNi, 79%; (h)
MeOCOCl, CH2Cl2, 0 °C to rt, 4 h, 87%; (i) Br2, AcOH, rt, 12 h, 15%; (j) H2SO4, MeOH,
reflux, 18 h, 95%; (k) MeO(CH2)3I, K2CO3, reflux, 16 h, 98%; (l) trimethylsilylacet-
ylene, cat. Cl2Pd(PPh3)2, CuI, Et3N, rt, 15 h, 100%; (m) 1 N KOH, MeOH, 97%; (n) H2,
cat. Pd/C 10%, EtOH, 77%.
O
O
H
N
N
NHBu
MeO
37
O
O
36
Figure 2. Decomposition products of inhibitor 9a.
compound series upon minor structural modifications leading to a
subtle increase in overall hydrophobicity of the inhibitors.10,11,26
A methyl carbamate group tethered to the phenyl by a methy-
lene spacer provided highly active 9d with comparable enzyme
affinities in both in vitro assays. Both the NH and the MeO oxygen
of the carbamate were found in reasonable H-bonding distance to
the Ser219 side chain OH according to modeling. In contrast, the
homologous carbamate 9e with a two-carbon tether was only
weakly active against rh-renin.
Next, various small hydrophobic residues such as alkyl and hal-
ogen were investigated as replacements of the para-OMe group
which interacts with the S3 site of renin (Table 1, 9f–i). The P3 ethyl
derivative 9g was equipotent to 9a in both assays, whereas a three-
to four -fold increase in IC50s was observed for 9f, 9h, and 9i. Inhib-
0
itor 34 with a P1 isopropyl substituted hydroxyethylene isostere
0
showed similar in vitro activity as the P1 Me analogue 9g. The rel-
ative increase in IC50 of 9g in presence of plasma was surprisingly

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Y. Yamaguchi et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4863–4867
Ph
N
Ph
at the P1 position. This encouraging result prompted us, subse-
quent to the discovery of the highly potent development candidate
a
2 bearing an optimized P2 carboxamide moiety11, to explore its
Br
O
0
+
O
O
N
BnO
BnO
corresponding basic P1 analogue 35.28 We envisaged that the P1
0
O
c
O
O
27
O
isopropyl group of the dipeptide TSM, replacing the smaller Me
group in 10, would improve the in vitro enzyme inhibition, and
in particular oral in vivo potency, as demonstrated previously for
the lead series.11 Indeed inhibitor 35 showed strong inhibition in
both human renin in vitro assays with IC50s of 7 nM. However,
26
28
O
O
O
O
O
b
+
Br
BnO
N3
0
35 was only equipotent to the P1 Me analogue towards plasma re-
BnO
BnO
29
30
31
nin, and more than 10-fold less active as compared to 2 (Table 1).
The significant reduction in the potency of 35 limited its potential
attractiveness for more extensive investigations.
O
Si
O
O
d-g
h-j
We had established a primate in vivo pharmacology model in
telemetered sodium-depleted marmosets (Callthrix jacchus) for
non-invasive measurement of blood pressure (BP), heart rate,
and motor activity in freely moving animals to study oral effi-
cacy of renin inhibitors and other RAS blocking agents.29 Inhibi-
tor 9a, administered orally in saline solution at 3 mg/kg to
normotensive marmosets pre-treated with furosemide (N = 5;
6 mg/kg/d for 1 week), caused a significant change in mean arte-
rial pressure (MAP), compared to vehicle-treated animals, with a
rapid onset of action and paralleled by partial inhibition of plas-
H
NH2
BocHN
N3
BocHN
N
O
O
N3
32
33
MeO
OH
H
NH2
N
H2N
k-o
O
O
O
N
MeO
35
Scheme 4. Reagents and conditions: (a) LiN(TMS)2, THF, ꢀ78 °C, 77%; (b) NBS, 1:1
DME–H2O, 0 °C to rt, 15 h, 74%; (c) NaN3, DMPU, 40 °C, 18 h; 30 (30%) and 31 (60%);
(d) H2, cat. Pd/C 10%, BOC2O, EtOAc, 82%; (e) H2, cat. Pd/C 10%. (f) MsCl, Et3N,
CH2Cl2; (g) NaN3, DMPU, 60 °C, 20 h, 95% (3 steps from 30); (h) 1 M LiOH, 2:1 DME–
H2O, rt, 3 h; (i) TBDMSiCl, imidazole, DMF, >80% (2 steps); (j) HBTU, Et3N,
ma renin activity (PRA). The maximal depressor effect
D
MAP of
ꢀ18 mmHg observed 90 min post-dose was similar to
DMAPmax
of inhibitor 1 at the 3 mg/kg po dose in this model. However,
and in marked contrast to the sustained BP lowering potency
of 1 over up to 8 h,10 9a had only short-lasting effects, with com-
plete recovery to baseline after 4 h post-dose. Total peak plasma
H2NCH2C(CH3)2CONH2, DMF, 89%. (k) H2, cat. Pd/C 10%, EtOAc; (l) acetone,
0
NaBH3CN, 4 ÅA MS, MeOH, 74%. (2 steps); (m) 4-methoxy-3-(3-methoxy-propoxy)-
benzylbromide18, K2CO3, DMF, 50%; (n) Bu4NF, THF, rt, 63%; (o) 4 N HCl–dioxane, rt,
90%.
exposure was found to be low (0.07 lmol/L at 1.5 h post-dose).
The inferior potency of 9a in vivo suggested a poor pharmaco-
kinetics profile due to low oral absorption and/or rapid clearance
in marmosets.
more pronounced, in contrast to the SAR observed for the inhibitor
1 series.10
The sulfonamide P3–P1 spacer was explored with the aim to
identify potent inhibitors with improved physicochemical proper-
ties including crystallinity and chemical stability in plasma (vide
The chemical stability of inhibitors 9a and 9g in aqueous phos-
phate or Tris buffer solutions at pH 6.0, 7.4, and 8.0 was investi-
gated. Both compounds showed significant decomposition up to
30% and 12%, respectively, after 24 h at 37 °C. A trans-acylation
reaction to form the secondary amide 36 (Fig. 2) was found to be
the major decomposition pathway under weakly acidic conditions,
whereas in neutral or slightly basic solutions the formation of the
dihydro-1,3-imidazole derivative 3730 was observed in addition. In
DMSO at 100 °C, 9a was converted exclusively into 3631 within 1 h.
infra). Compound 14 with an IC50 of 0.3 lM towards rh-renin
was found to be greater than 100 times less potent compared to
the carboxamide analogue 9a (Table 1). Compound 15 lacking
sp
the P3 side chain did not show significant enzyme affinity up to
100 l
M. These results confirm previous findings,24,27 that binding
interactions to the contiguous S3–S1 hydrophobic pocket of renin
alone are not sufficient for strong enzyme affinity, and further sug-
gest the methoxypropoxy group of inhibitor 14 to interact with the
36 (rh-renin IC50 = 0.67 lM) was stable in aqueous buffers over a
broad pH range. Additional studies are required to demonstrate
whether the limited stability of 9a in physiological buffer may at
least partially contribute to the short duration of action in vivo in
marmosets.
sp
non-substrate P3 binding site. Computational docking of 14 into
the renin active site predicted a similar binding pose in an en-
ergy-minimized conformation as was observed by X-ray for inhib-
itor 1 complexed to rh-renin.9,10 The modeling pose suggested a H-
bond of a sulfonyl oxygen to the flap Thr77 NH, but also an unfavor-
able interaction of the sulfonyl with Gly217. This could explain at
least in part the marked drop in potency of 14 versus 9a.
Interestingly, the 3,4-dialkoxybenzyl substituted tertiary amine
10 showed high potency with similar affinities to recombinant and
plasma renin (Table 1).28 Compared to benzamide 9a, compound
10 was only threefold less active in vitro in the physiologically
more relevant plasma renin assay (IC50s of 14 vs 5 nM, respec-
tively). The increased potency of 9a over 10 was considered to be
due to a H-bond interaction of the spacer carbonyl to Thr77 of
the flap domain in its closed conformation. Other contributing fac-
tors could be a potential intramolecular H-bond favoring a solution
conformation of 9a similar to its enzyme-bound conformation, or
different desolvatation energies for 9a and 10 required for binding
into the solvent-shielded hydrophobic P3–P1 site of the catalytic
cleft. To the best of our knowledge, 10 is the first reported low
nanomolar inhibitor of renin, which incorporates a basic amine
In summary, the synthesis, the chemical stability and in vitro
SAR for inhibition of human renin has been explored for a novel
series of ‘symmetrized’ hydroxyethylene dipeptide mimetics. From
this work, the first low nanomolar renin inhibitors 10 and 35 with
a basic tertiary amine at the P1 position are described. The (P3–P1)-
benzamide analogue 9a showed potent but transient blood pres-
sure lowering effects in Na-depleted marmosets. In subsequent
studies as part of our continued renin inhibitor program, the N-iso-
propyl benzamide (P3–P1)-pharmacophore, as in 9a, has been com-
bined with a pyrrolidine-based center scaffold as TSM surrogate to
afford highly potent candidate inhibitors with promising in vivo
activity profiles.8,18 A full account of this more recent work will
be disclosed in due course.
Acknowledgments
The authors would like to thank Dr. E. Francotte and P. Richert
for chiral HPLC analysis. Y.Y. is indebted to Reto Wicki, Thomas Ste-
bler, and Patrick Duerst for excellent technical assistance.

Y. Yamaguchi et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4863–4867
4867
J = 12 Hz, 1H), 4.46 (s, 2H), 3.58–3.48 (m, 3H), 3.05–3.00 (m, 2H), 2.47–2.44 (m,
1H), 1.66–1.60 (m, 1H), 1.39 (s, 9H), 1.36–1.20 (m, 6H), 0.99 (d, J = 8 Hz, 3H),
0.85 (t, J = 8 Hz, 3H). HRMS [M+H]+ calcd 423.2854; found 423.2853.
18. For the preparation of other 3,4-disubstituted benzoic acid intermediates, see:
Ehrhardt, C.; Irie, O.; Lorthiois, E. L. J.; Maibaum, J. K.; Ostermann, N.; Sellner, H.
PCT Int. Appl. WO2006/100036(A1); Chem. Abstr. 2006, 145, 377192.
19. Knorr, R.; Trzeciak, A.; Bannwarth, W.; Gillessen, D. Tetrahedron Lett. 1989, 30,
1927.
References and notes
1. Rosamond, W.; Flegal, K.; Furie, K.; Go, A.; Greenlund, K.; Haase, N.; Hailpern, S.
M.; Ho, M.; Howard, V.; Kissela, B.; Kittner, S.; Lloyd-Jones, D.; McDermott, M.;
Meigs, J.; Moy, C.; Nichol, G.; O’Donnell, C.; Roger, V.; Sorlie, P.; Steinberger, J.;
Thom, T.; Wilson, M.; Hong, Y. Circulation 2008, 117, e25.
2. Nicholls, M. G.; Robertson, J. I. S. J. Hum. Hypertens. 2000, 14, 649.
3. Azizi, M.; Menard, J. Circulation 2004, 109, 2492.
4. Hershey, J. C.; Steiner, B.; Fischli, W.; Feuerstein, G. Drug Discovery Today:
Therap. Strateg. 2005, 2, 181.
5. Maibaum, J. K.; Feldman, D. L. Expert Opin. Ther. Patents 2003, 13, 589.
6. (a) Fisher, N. D. L.; Hollenberg, N. K. J. Am.Soc. Nephrol. 2005, 16, 592; (b) Fisher,
N. D. L.; Hollenberg, N. K. Exp. Opin. Invest. Drugs 2001, 10, 417.
20. Goeschke, R.; Stutz, S.; Heinzelmann, W.; Maibaum, J. Helv. Chim. Acta 2003, 86,
2848.
21. Bromide 26 was prepared from (E)-but-2-ene-1,4-diol by mono-benzylation
(NaH, BnBr, DMF, ꢀ20 °C, 35%) and bromination (NBS, Ph3P, CH2Cl2, ꢀ78 °C,
91%).
22. Enantiomeric purity of (3S,5S,10R)-30 was determined by chiral HPLC using its
(3R,5R,10S)-enantiomer prepared from (R)-configured 27 according to Scheme
4.
7. Danser, A. H. J. J. Cardiovasc. Pharmacol. 2007, 50, 105.
8. Yokokawa, F.; Maibaum, J. J. Expert Opin. Ther. Patents 2008, 18, 581.
9. Rahuel, J.; Rasetti, V.; Maibaum, J.; Rueeger, H.; Goeschke, R.; Cohen, N.-C.;
Stutz, S.; Cumin, F.; Fuhrer, W.; Wood, J. M.; Gruetter, M. G. Chem. Biol 2000, 7,
493.
10. Goeschke, R.; Stutz, S.; Rasetti, V.; Cohen, N.-C.; Rahuel, J.; Rigollier, P.; Baum,
H.-P.; Forgiarini, P.; Schnell, C. R.; Wagner, T.; Gruetter, M. G.; Fuhrer, W.;
Schilling, W.; Cumin, F.; Wood, J. M.; Maibaum, J. J. Med. Chem. 2007, 50, 4818.
11. Maibaum, J.; Stutz, S.; Goeschke, R.; Rigollier, P.; Yamaguchi, Y.; Cumin, F.;
Rahuel, J.; Baum, H.-P.; Cohen, N.-C.; Schnell, C. R.; Fuhrer, W.; Gruetter, M. G.;
Schilling, W.; Wood, J. M. J. Med. Chem. 2007, 50, 4832.
12. Wood, J. M.; Maibaum, J.; Rahuel, J.; Gruetter, M. G.; Cohen, N.-C.; Rasetti, V.;
Rueger, H.; Goeschke, R.; Stutz, S.; Fuhrer, W.; Schilling, W.; Rigollier, P.;
Yamaguchi, Y.; Cumin, F.; Baum, H.-P.; Schnell, C. R.; Herold, P.; Mah, R.; Jensen,
C.; O‘Brien, E.; Stanton, A.; Bedigian, M. P. Biochem. Biophys. Res. Commun. 2003,
308, 698.
23. Herold, P.; Duthaler, R.; Rihs, G.; Angst, C. J. Org. Chem. 1989, 54, 1178.
24. Goeschke, R.; Cohen, N.-C.; Wood, J. M.; Maibaum, J. Bioorg. Med. Chem. Lett.
1997, 7, 2735.
sp
25. The P3 methoxybutyl side chain substituted analogue of 2 was subsequently
identified as preclinical candidate with high oral potency in Na-depleted
marmosets.11
26. Plasma IC50 shifts in related series could be only in part rationalized by plasma
protein binding (PPB).11 Human %PPB for 9, 34, 35 were not determined.
27. Maibaum, J.; Rasetti, V.; Rueeger, H.; Cohen, N.-C.; Goeschke, R.; Mah, R.;
Rahuel, J.; Gruetter, M.; Cumin, F.; Wood, J. M. In Medicinal Chemistry: Today
and Tomorrow, Proceedings of the AFMC International Medicinal Chemistry
Symposium, Tokyo, Sept. 3–8, 1995, 1997, 155.
28. A recent patent application has disclosed related renin inhibitors including
compounds 10 and 35: Miyazaki, S.; Nakamura, Y.; Nagayama, T.; Tokui, T. PTC
Int. Appl. WO2007/148775(A1); Chem. Abstr. 2007, 148, 100512.
29. Schnell, C. R.; Wood, J. M. Am. J. Physiol. 1993, 264, H1509.
13. (a) Jensen, C.; Herold, P.; Brunner, H. R. Nat. Rev. Drug Disc. 2008, 7, 399; (b)
Cohen, N. C. Chem. Biol. Drug Des. 2007, 70, 557.
14. The N-acyl-(hydroxyethyl)amine TSM isostere approach has been recently
described for the inhibitor design targeting other aspartyl proteases. See for
example: Lee, C. E.; Kick, E. K.; Ellman, J. A. J. Am. Chem. Soc. 1998, 120, 9735.
15. (a) DeCamp, A. E.; Kawaguchi, A. T.; Volante, R. P.; Shinkai, I. Tetrahedron Lett.
1991, 32, 1867; (b) Nakamura, E.; Sekiya, K.; Kuwajima, I. Tetrahedron Lett.
1987, 28, 337; (c) Ochiai, H.; Nishihara, T.; Tamaru, Y.; Yoshida, Z. J. Org. Chem.
1988, 53, 1343; for related literature: Kano, S.; Yokomatsu, T.; Shibuya, S.
Tetrahedron Lett. 1991, 32, 233.
30. Derivative 37, isolated as major side product from N-BOC-9a deprotection with
4 N HCl–dioxane at rt showed weak affinity to rh-renin (IC50 = 1 lM).
31. The trans-acyl decomposition product 36 was synthesized according to the
following reaction scheme:
OH
H2N
NH-Bu
a-c
d-f
16. Typical procedure for the preparation of 5a/5b: To a suspension of Zn(Cu)
(43.3 g) in toluene (130 mL) was added a solution of 3-iodo-2(R)-methyl-
propionic acid methyl ester (92.5 g, 0.41 mol) in N,N-dimethyl acetamide
(69 mL) and toluene (560 mL) at rt over 10 min. The suspension was stirred at
rt for 1 h and then refluxed for 5 h. To a solution of Ti(OiPr)4 (30.1 mL) in
toluene (105 mL) and CH2Cl2 (530 mL) was added TiCl4 (33.3 mL) at <25 °C. The
solution was stirred at rt for 15 min, followed by addition of the Zn-
homoenolate solution while keeping the temperature below ꢀ20 °C. Then, a
solution of 4 (26.4 g, 0.09 mol) in CH2Cl2 (130 mL) was added below ꢀ35 °C,
and the mixture was stirred at ꢀ20 °C for 2 days. Standard workup afforded a
4:1 mixture of 5a/5b (27.7 g, 77%) as colorless oil.
8
36
O
CbzN
38
Reaction conditions: (a) Cbz–Cl, Et3N, CH2Cl2, 0 °C to rt, 18 h, (72%); (b) cat. p-
TsOH, MeOH, 58%; (c) TFA, CH2Cl2, 0 °C to rt, 3 h, 75%; (d) 4-methoxy-3-(3-
methoxy-propoxy)-benzoic acid, HOBT, EDC, N-methylmorpholine, DMF, rt,
16 h, 78%; (e) H2, cat. Pd/C, BOC2O, MeOH, rt, 7 h, 89%. (f) 4 N HCl–dioxane, rt,
69%.
17. Analytical data for 4(S)-6: TLC Rf 0.33 (hexane/EtOAc 1:1); mp 105 °C; 1H NMR
(400 MHz, DMSO-d6): d 7.65 (t, J = 8 Hz, 1H), 7.36–7.27 (m, 5H), 6.29 (d,