Quinolinyl- and phenantridinyl-acetamides as bradykinin B1 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2012.03.065

A new series of quinolinyl- and phenantridinyl-acetamides were synthesizer and evaluated against bradykinin B1 receptor. In vitro metabolic stability data were reported for the key compounds.The analgesic effect of compound 20 from the phenantridine series was proved in-vivo.

Full text of DOI:10.1016/j.bmcl.2012.03.065

Bioorganic & Medicinal Chemistry Letters 22 (2012) 3095–3099
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Quinolinyl- and phenantridinyl-acetamides as bradykinin B1
receptor antagonists
⇑
János Éles , Gyula Beke, István Vágó, Éva Bozó, József Huszár, Ákos Tarcsay, Sándor Kolok, Éva Schmidt,
}
Mónika Vastag, Katalin Hornok, Sándor Farkas, György Domány, György M. Keseru
Gedeon Richter Plc., Budapest 10. POB 27, H-1475, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of quinolinyl- and phenantridinyl-acetamides were synthesizer and evaluated against bra-
dykinin B1 receptor. In vitro metabolic stability data were reported for the key compounds.The analgesic
effect of compound 20 from the phenantridine series was proved in-vivo.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 16 January 2012
Revised 15 March 2012
Accepted 16 March 2012
Available online 21 March 2012
Keywords:
Bradykinin
B1 Antagonists
Quinoline
Phenantridine
The term ‘kinins’ denote endogenously released oligopeptide
autacoid substances: bradykinin (BK) (RPPGFSPFR) and kallidin
(Lys-BK) (KRPPGFSPFR) and their active metabolites. The most
important piaster effects of kinins are vasodilatation, increased
vascular permeability, vascular and bronchial smooth muscle con-
traction, stimulation of sensory neurons, alteration of ion secretion
of epithelial cells, renal homeostasis, production of nitric oxide,
release of prostaglandins and cytokines.1–3 Pathological overpro-
duction of kinins was observed in several disorders, such as hyper-
algesia, hypotension, sepsis, pancreatitis, brain edema and a wide
variety of immunologic and inflammatory diseases (e.g., asthma,
rheumatoid arthritis, and multiple sclerosis). The piaster effects
of kinins are mediated by two G protein-coupled receptors, the
bradykinin 1 (B1) and the bradykinin 2 (B2) receptor.1,4–6 bradyki-
nin and kallidin are selective natural agonists of the bradykinin 2
receptor (B2R), which is constitutively expressed in numerous cell
types under normal piaster conditions to induce acute pain imme-
diately after tissue injury.2,3 In contrast, C-terminally truncated
des-Arg carboxypeptidase metabolites of BK (des-Arg9-BK) and
Lys-BK (des-Arg10-kallidin) are selective B1R agonists. B1R is
expressed only in low levels under normal conditions but the
expression is considerably induced locally by inflammation, tissue
injury or trauma.7 Under inflammatory conditions, a shift of kinin
receptor expression from B2R to B1R has been reported in both
in vitro and in vivo models.8,9 Using in vivo animal models, brady-
kinin B1 receptor agonists produce hyperalgesia, which is blocked
by peptide-derived B1 antagonists.10,11 In addition, transgenic B1
receptor knockout mice exhibit reduced sensitivity to painful stim-
uli, while appearing normal in all other respects. Studies suggest
that B1 receptors are constitutively expressed in the central ner-
vous system of mice, rats, and primates, implicating an essential
function for these receptors in addition to the widely acknowl-
edged peripheral mode of action.12–14 Therefore, bradykinin B1
receptor antagonists could have potential as novel therapeutic
agents for the treatment of chronic pain and inflammation.15
In this Letter we describe our first efforts to develop effective
bradykinin B1 receptor antagonists with acceptable metabolic pro-
file. In an earlier report,16 Merck disclosed a series of dihidroqui-
noxalinones, demonstrating that the phenylsulfonamide moiety
plays a key role in substrate-receptor binding that was further im-
proved by incorporation an imidazolyl-phenyl-ethylamine basic
side-chain (Fig. 1).
Sejbal et al. studied the peptide antagonist, B-9340, by NMR and
NMR constraint-based molecular dynamics simulations that re-
vealed the importance of b-turn feature of antagonists, involving
residues 2–9.17 Alignment of the proposed B-9340 conformation
(PDB:1BDK) with that of the energy minimized conformation of
compound 2 suggests complete mimicking of the b-turn region
(Fig. 2). Aromatic rings of compound 2 overlap with the DIgl8
and Thi6 residues, polar atoms mimic the backbone peptide atoms
and the basic moiety of the imidazol side chain is positioned sim-
ilarly to the critical DArg0 residue. On the basis of the spatial and
hydrophilic–hydrophobic molecular surface complementarities
we concluded that (i) the aryl-sulfonamine moiety is crucial for
the b-turn conformation, (ii) the basic side chain is essential Arg
⇑
Corresponding author.
E-mail address: j.eles@richter.hu (J. Éles).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.03.065

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J. Éles et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3095–3099
Figure. 1. bradykinin B1 antagonists.
Figure. 2. Shape alignment of B-9340 and compound 2 (A). Blue, green, gray, red, yellow, and white coloring represents nitrogen, B-9340 carbon, compound 2 carbon, oxygen,
sulfurate, and polar hydrogen atoms, respectively. Hydrophobic (red color) and hydrophilic (blue color) surface of B-9340 (B) and compound 2 (C) (the b-turn mimicking
moiety is highlighted with red color).
mimetic and (iii) the dihydroquinoxalinone scaffold is positioned
in a hydrophobic region.
This assignment held out the prospect that the imidazolyl-phe-
nyl-ethylamine side-chain might be an exploitable platform upon
which to explore variations in the conformationally constrained
arylsulfonamino-propanamide b-turn isoster motif. The side-chain
was prepared through the sequence demonstrated in Scheme 1.
Scheme 2 illustrates the standard coupling reaction to access the
Scheme 2. Reagents:HBTU, H2N-R3, DIPEA, DMSO.
target compounds.
In order to identify different scaffolds the dihidroquinoxalinone
core was replaced with alternative ring systems. Replacement with
benzoxazin-3-ylacetic amide (3) resulted in a significant diminu-
tion of B1 receptor binding affinity (Fig. 3), while compound 4
bearing a 1,2,3,4-tetrahidroquinolin-2-ylacetamide proved to be
an effective replacement for the dihidroquinoxalinone-acetamide
(Table 1). Despite its impressive potency compound 4 exhibited
poor ADME properties, it underwent extensive metabolism after
incubation with human liver microsomes.18 Therefore we investi-
Figure. 3. Benzoxazin derivative of 2.
gated the influence of the phenyl ring on the central core to the
affinity and the metabolic stability. The installation of the
1,2,3,4-tetrahidroisoquinolin-3-ylacetamide afforded compound
(5) with low affinity, while it was found that the earlier reported
1,2,3,4-tetrahidroisoquinolin-1-ylacetamide19 (6) can also serve
as an effective surrogate for the central core. Disappointingly, com-
pound 6 similarly to 4, was rapidly cleared in human liver micro-
somal preparations.
In our next approach we focused on improving the metabolic
stability by introduction of different side-chains (Tables 2 and 3).
Scheme 1. Reagents and condition:(a) phtalimide, DEAD, P(Ph)3, DMF, rt; (b) HCl
(gas), EtOH; (c) H2NCH2CH2NH2, EtOH; (d) NH2NH2 ⁄ H2O, EtOH.

J. Éles et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3095–3099
3097
Table 1
Table 3
Quinoline derivatives
1,2,3,4-Tetrahidroisoquinolin-1-ylacetamide derivatives
N
N
H
O
O
Q
NH
N
R
Cl
SO2
Cl
Cl
SO2
Cl
R
hKi
(nM)
CLint
Hu
Q
hKi(nM)
CLint
Rat
(ml/
min g)
Rat (ml/min g)
2.6
Hu (ml/min g)
7.1
(ml/
min g)
4
6.3
N
N
HN
N
N
N
10
11
138
3.8
nd
nd
2.4
13.1
5
481
nd
nd
NH
N
N
HN
12
1.0
1.1
12.5
N
H
6
2.2
1.9
4.2
N
12 displayed high affinity and high in vitro stability in rat liver
microsomal preparations but the human microsomal clearance
was still unacceptable.
The hydrophobic site similarities between B-9340 and com-
pound 2 around the b–turn region (Fig. 2) prompted us to design
a novel scaffold by hybridization of the privileged isoquinoline
derivatives. Scheme 3 shows the route employed to synthesize
the novel 5,6-dihidrophenanthridine scaffold. Compound 13 dis-
played high potency, but disappointingly it was also rapidly
cleared.
SAR work in this series was also extended to the aryl-sulfonyl
moiety to explore its effect on both affinity and metabolic stability
(Table 4). The introduction of 2,4,6-triMe-, 4-Me- or 4-OCH3-
phenylsulfonyl moieties led to compounds (14, 15, 16) with similar
potency and poor metabolic stability.
Table 2
1,2,3,4-Tetrahidroquinolin-2-ylacetamide derivatives
O
N
R
Cl
Cl
SO2
R
hKi(nM)
CLint
Rat
(ml/
min g)
Hu
(ml/
min g)
N
HN
HN
N
7
8
628
166
nd
nd
7.4
16.8
N
N
N
HN
N
9
4.3
0.6
9.0
N
H
The incorporation of designed, less flexible side chains such as
4-(1,40-bipiperidin-1’-yl)aniline (7, 10) led to dramatic loss of po-
tency. Only some decrease in flexibility of the side chain (11)
was tolerated but without any significant change in the clearance.
Compound 8 with terminal pyridine moiety led to marked loss of
potency.
It was previously published by Ritchie et al. that decreasing aro-
matic ring count exerts an improving effect on bioavailability-re-
lated parameters.20 Therefore, we installed a cyclohexyl moiety
instead of the phenyl ring into the side chain. Compounds 9 and
Scheme 3. Reagents and condition:(a) Pd(PPh)4, boronic acid, DMF, 90 °C.; (b)
methylacrylate, Pd(OAc)2, DMF 80 °C; (c) 3,4-di-Cl-benzenesulfonyl-chloride, Py;
(d) LiOH ⁄ H2O, THF:H2O=1:1.

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J. Éles et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3095–3099
Table 4
5,6-Dihidrophenanthridine derivatives
14
12
N
Y
C
N
H
O
A
B
N
NH
SO2
X
X
Y
hB1 Ki Rat B1
CLint
(nM)
IC50 (nM)
Rat
Hu
(ml/min g) (ml/min g)
Figure. 5. Antihyperalgesic effects of compound 20 compared to those of
SSR240612 and diclofenac in the CFA-induced knee monoarthritis test in rats.
Change from baseline at maximum effect (mean SEM at 60 or 120 min post-dose)
is shown. ⁄P <0.05, ⁄⁄P <0.01, one-way ANOVA followed by Dunnett’s test cf. vehicle
group. The mean baseline incapacitance was 39–42% in all groups.
13 3,4-diCl
14 2,4,5-triMe
15 4-Me
16 4-OMe
17 3,4-diCl
18 3,4-diCl
19 3,4-diCl
H
H
H
H
3.1
2.9
4.7
15.5
1.2
9.1
28
21
52
81
45
42
21
2.5
2.7
1.5
4.8
1.6
3.9
2.6
9.8
16.4
12.9
14.5
5.5
14-F
12,14-diF
12-OMe
8.0
1.0
1.7
Table 5
Dose-dependent edema suppression by B1 antagonists and diclofenac in the DABK
induced paw edema test in rats
Compound
Dose (mg/kg, po)
Inhibition (%)
20
0.03
0.1
0.3
1
19
27a
54a
6
SSR240612
Diclofenac
3
16
10
0.3
1
30a
23a
24a
35a
3
a
Statistically significant cf. vehicle (p<0.05; ANOVA & Dunnett).
drug diclofenac (Table 5). Furthermore, analgesic efficacy of com-
pound 20 was characterized in a complete Freund’s adjuvant
(CFA) induced monoarthritis test in rats.24 Compound 20 also
dose-dependently alleviated the CFA-induced joint pain with com-
parable efficacy to those of SSR240612 and diclofenac but with
effectiveness in a lower dose range than the reference compounds
(Fig. 5).
In summary, having selected the imidazolyl-phenyl-ethylamine
basic side-chain, bradykinin B1 antagonists containing different
sulfonamido scaffolds were synthesized. Assessing the potential
of the b-turn mimetic core several candidates were prepared and
promising core structures were identified. To fully exploit their po-
tential, further side-chain modifications were carried out. As a re-
sult of this iteration, in the newly discovered phenantridine series
both the core structure and the side-chain were optimized. The
acceptable metabolic stability of the potent compound 20 provided
a useful pharmacological tool for studying the in vivo therapeutic
effects of a bradykinin B1 antagonist. High in vivo, B1 receptor
antagonist potency of compound 20 was confirmed in a B1 ago-
nist-induced paw edema test in rats. Furthermore, compound 20
exhibited significant oral analgesic effect in a CFA-induced mon-
oarthritic pain test at relatively low doses.
Figure. 4. Profile of compound 20.
During the course of optimizing compound 13, vulnerable sites
of metabolism were identified. Metabolite profiling indicated that
ring C of the phenantridine scaffold was oxidized. Consequently,
we installed fluorine atoms at the phenantridine core in an attempt
to block this metabolic pathway. These modifications yielded com-
pounds 17 and 18. Compound 17 displayed improved B1 receptor
binding affinity, but only slight improvement in metabolic stability
was observed. The difluoro compound (18) did not exhibit any
enhancement either in the binding potency or the metabolic stabil-
ity. The introduction of a methoxy group in position 12 (19) re-
sulted in the only notable improvement in terms of human liver
clearance. As it was previously demonstrated, decrease in the aro-
matic ring count had a positive effect on rat metabolic stability.
The most impressive advance was obtained by installation of the
newly discovered saturated basic side chain21 (20), which was
identified first in the phenantridine series and led to a good bal-
ance in affecting receptor binding and microsomal clearance at
both human and rat liver microsomes (Fig. 4).
The phenantridine series of bradykinin B1 receptor antagonists
proved to be potent at both human and rat B1 receptors enabling
in vivo characterization of these compounds in classic rodent mod-
els of pain and inflammation. The in vivo B1 antagonistic and anti-
phlogistic effect of compound 20 was confirmed in a B1 agonist-
(des-Arg9-bradkinin; DABK)-induced paw edema test in rats.22
Compound 20, administered orally at doses of 0.03, 0.1 and
0.3 mg/kg, dose-dependently inhibited the DABK-induced edema
with a higher maximum effect as compared to the non-peptide
B1 antagonist SSR24061223 or the non-steroidal anti-inflammatory
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Under Thiopental (50 ml/kg) anesthesia, the animals received an intra-plantar
injection of the B1 agonist DABK (140 nmol in 0.1 ml). The paw volume was
measured using a Plethysmometer (Ugo Basile; type 7150) 0, 10, 20, 30 min
post-DABK and the maximum volume of paw edema was evaluated.
Compounds (SSR2460612, diclofenac or 20) or vehicle (5% (v/v) Tween 80 in
Saline) were administered via oral route 30, 60 or 120 min, respectively, before
injection of DABK. Percent inhibition was calculated by comparing drug treated
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