Novel small molecule bradykinin B1 receptor antagonists. Part 2: 5-membered diaminoheterocycles

Article abstract of DOI:10.1016/j.bmcl.2009.11.120

Efforts to find new bradykinin B₁ receptor antagonists identified 2-aminobenzimidazole as a novel core. Subsequent transformation into five-membered diaminoheterocycle derivatives and their synthesis and SAR is described. This resulted in compounds with low nanomolar activity.

Full text of DOI:10.1016/j.bmcl.2009.11.120

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1229–1232
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel small molecule bradykinin B1 receptor antagonists. Part 2: 5-membered
diaminoheterocycles
Gunther Zischinsky, Roland Stragies, Marco Schaudt, Jochen R. Pfeifer, Christoph Gibson, Elsa Locardi,
*
Dirk Scharn, Uwe Richter, Holger Kalkhof, Klaus Dinkel, Karsten Schnatbaum
Jerini AG, Invalidenstraße 130, 10115 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Efforts to find new bradykinin B1 receptor antagonists identified 2-aminobenzimidazole as a novel core.
Subsequent transformation into five-membered diaminoheterocycle derivatives and their synthesis and
SAR is described. This resulted in compounds with low nanomolar activity.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 22 October 2009
Revised 23 November 2009
Accepted 24 November 2009
Available online 2 December 2009
Keywords:
Bradykinin B1
Antagonist
Oral bioavailability
Pharmacokinetic profile
Bradykinin(BK) and kallidin (KD)are peptidickinins which acton
the B2 receptor and mediate acute physiological actions of kinins on
the cardiovascular, renal, nervous and immune system.1 They are
metabolized by carboxypeptidase N and M, which remove the car-
boxy-terminal arginine residue to generate des-Arg-9-BK (DABK)
or des-Arg-10-kallidin (DAKD). DAKD is the only known natural ago-
nist for the human bradykinin B1 receptor and appears to be an
important mediator of inflammation and pain in man.2
Whereas the bradykinin B2 receptor is constitutively expressed
under normal conditions in most cell types, the bradykinin B1 recep-
tor is induced under pathophysiological conditions such as infec-
tions, inflammatory diseases and traumatic tissue injury.3 It has
been shown that the bradykinin B1 receptor is induced by various
pro-inflammatory stimuli (e.g., lipopolysaccharide, Interleukin-1b)
in several cell types including endothelial, smooth muscle, leuko-
cytes and neurons.4,5 Several studies have confirmed the presence
of kininogens, kallikreins and kinin receptors in immune cells sup-
porting an important role for kinins in immune response and
inflammation.6,7
target for the severe conditions associated with pathological
inflammation and pain, both acute and chronic.13
Recently, the discovery of semicarbazide-based B1 receptor
antagonists, similar to 1, has been reported.14 To identify addi-
tional new lead series, modification of the semicarbazide moiety
was investigated. The biaryl moiety was kept intact, as it repre-
sents a privileged scaffold in drug discovery.15 Previous studies16,17
have shown that a hydrogen bond acceptor in close proximity to
the biaryl, such as the carbonyl group of the semicarbazide of 1,
is essential for achieving high potency at the B1 receptor. These
findings prompted investigation of the structure–activity relation-
ship (SAR) of compounds represented by the general structure 2
(Fig. 1). The subsequent optimization to five-membered diamino-
heterocycles, as represented by 3, is reported herein.
R3
R2
O
R6
W
W = N, O
R7
X
Y
O
R1
N
Z
O
N
N
N
H
H
N
NH
NH
R8
Recent evidence strongly suggests an involvement of the brady-
kinin B1 receptor in various types of human disorders including
inflammatory and neuropathic pain,8 cardiovascular diseases9 as
well as inflammatory diseases such as rheumatoid arthritis,10
inflammatory bowel disease11 and psoriasis.12 Therefore the bra-
dykinin B1 receptor seems to be particularly useful as a therapeutic
X, Y = C, N, O, S
Z = C, N
F
F
F
O
O
F
O
F
R4
O
R5
F
* Corresponding author. Correspondence should be addressed to: Pericles Calias,
Shire HGT, 125 Spring Street, Lexington, MA 02421, USA. Tel.: +1 781 482 0701; fax:
+1 781 482 2961. E-mail: pcalias@shire.com.
1
2
3
Figure 1. Strategy for the development of new B1 receptor antagonists.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.11.120

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G. Zischinsky et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1229–1232
Different methods including reductive amination, alkylation,
NHBoc
N
H
N
NH2
nucleophilic substitution and ring closing reactions were applied
to install a hydrogen bond accepting functionality adjacent to the
biaryl fragment resulting in compounds 3a–q (Schemes 1–4).
Acetamide 3a was obtained by standard acetylation of amine
718 (Scheme 1). In addition, 7 was used to prepare the acetylated
1,2-diaminobenzimidazole 3e via isothiocyanate 8 which was
transformed with N0-(2-aminophenyl)acetohydrazide19 to the cor-
responding thiourea which underwent intramolecular cyclization
upon addition of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimid
(EDC).
The synthesis of derivatives 3b–d is shown in Scheme 2. The
aldehyde 5 was prepared via Suzuki reaction from iodide 4 and
3-fluoro-4-formylphenylboronic acid. Compound 5 was either
transformed to bromide 6 for alkylation reactions to yield 3b and
3c or directly used for reductive amination with 2-aminobenzimid-
azole to give 3d.
F
F
N
N
a, b
c, d
3f,l
O
O
N
N
N
Cl
F
Cl
F
9
10
Scheme 3. Reagents and conditions: (a) SCCl2, DCM/H2O, NaHCO3, 0 °C; (b) tert-
butyl 2-(2-aminophenyl)hydrazinecarboxylate, DMF, rt, then EDC, 80 °C; (c) HCl,
MeOH, rt; (d) 3-methoxyisoxazole-5-carbonyl chloride or Ac2O, DIPEA, DCM, rt.
R2
R2
O
R2
R2
Cl
O
O
a
R1
HN
NH2
R1
For the synthesis of 3f and 3l, amine 920 was converted to build-
ing block 10 utilizing the same reaction sequence as for the synthe-
sis of 3e (Scheme 3). The Boc protecting group of 10 was removed
and the intermediate amine acylated to give the desired
compounds.
A set of 1,2-diaminoheterocycles were used as starting materi-
als for the synthesis of compounds 3g–k and 3m–q (Scheme 4).
The building blocks 11–14 were obtained from a three-component
N
N
N
H
NH2
11, 12: R2 = H
13, 14: R2 = Me
11, 13: R1 = Me
12, 14: R1 = 3-methoxyisoxazole
b
ring synthesis of an
a-carbonyl chloride, a hydrazine amide and
Cl
O
cyanamide. Intermediate 15 was obtained by chlorination of 11
with NCS. Intermediates 16–19 were synthesized in a one step
acylation of commercially available starting materials (Scheme
4). Pyrazole 20 was prepared using standard transformation steps
from commercially available 4-nitro-1H-pyrazol-3-amine. Building
blocks 11–20 were obtained by reductive amination of aldehyde
22, in turn synthesized from oxadiazole 2121 via Suzuki reaction
(Scheme 4).
N
N
N
H
NH2
15
O
X
N
N
X
N
N
c
R1
NH2
N
H
NH2
NH2
16, 17: X = O
18, 19: X = S
NH2
NCS
16, 18: R1 = Me
17, 19-20: R1 = 3-methoxyisoxazole
F
F
a
c
b
3a
3e
O
O
F
O
F
HN
N
HN
N
HN
N
d,e
c,f
R1
NH2
O
O
NHBoc
O
N
H
NO2
NH2
NH2
20
7
8
Scheme 1. Reagents and conditions: (a) Ac2O; (b) SCCl2, DCM/H2O, NaHCO3, 0 °C;
(c) N0-(2-aminophenyl)acetohydrazide, DMF, rt, then EDC, 80 °C.
F
g
h
O
O
N
Br
N
3g-k,m-q
Br
N
N
O
F
F
Cl
F
Cl
F
21
22
a
b, c
d
I
O
F
O
F
O
F
3b,c
Scheme 4. Reagents and conditions: (a) H2N–CN, AcOH, 60 °C; (b) 11, N-chloro
succinimide, DMF, 50 °C; (c) 3-methoxyisoxazole-5-carbonyl chloride or AcCl, THF,
reflux; (d) Boc2O, NaHCO3, DMF, rt; (e) Raney-Ni, H2, MeOH/ethyl acetate; (f) HCl,
MeOH, rt; (g) 3-fluoro-4-formylphenylboronic acid, PdCl2(PPh3)2, Na2CO3, 1,4-
dioxane/H2O, 80 °C; (h) 11–20, Ti(OiPr)4, dichloroethane, 60 °C, then NaBH(OAc)3, rt.
O
O
O
4
5
6
e
Table 1 shows the initial efforts to identify acetamide analogues
of 1 endowed with reasonable activity. The in vitro functional
activity at the B1 receptor was assessed in a DAKD-mediated cal-
cium mobilization (CAM) assay using human lung fibroblasts
IMR-90 pretreated with IL-1 beta. Acetamide 3a revealed a three
orders of magnitude loss of potency when compared to semicarb-
3d
Scheme 2. Reagents and conditions: (a) 3-fluoro-4-formylphenylboronic acid,
PdCl2(PPh3)2, Na2CO3, 1,4-dioxane/H2O, 80 °C; (b) NaBH4, MeOH/DCM, rt; (c) PBr3,
DCM, 0 °C; (d) KHMDS, HNR0R00, NMP, rt or 60 °C; (e) 2-aminobenzimidazole,
Ti(OiPr)4, dichloroethane, 60 °C, then NaBH(OAc)3, rt.

G. Zischinsky et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1229–1232
1231
Table 1
Antagonistic activity of 3a–d
antagonists. This 6-ring scaffold suffered from unwanted bioactiva-
tion, which led to irreversible protein binding.24 It was proposed,
that a 6-ring benzoquinone was involved as a reactive intermediate.
In contrast, the five-membered heterocycles, disclosed herein,
should be less prone to such a bioactivation because enzymatic oxi-
dation is not facilitated by the formation of 6-ring benzoquinone-
like resonance structures.23 It will be a future task to verify this
experimentally by metabolic studies.
R
F
O
F
O
To increase the solubility, the benzimidazole core was opti-
mized. Incorporation of imidazoles 3g and 3h resulted in much
higher solubility in water (40 lM and 42 lM) than the benzimid-
Compound
R
CAM
IC50 (nM)a
azole 3f (Table 2, left column). While the dimethyl derivative suf-
fered from surprisingly poor activity, the removal of the methyl
groups led to a significant increase in activity to IC50 = 1.3 nM (3h).
Alternative five-membered heteroaromatic core structures
(3i–k) were also found to be highly potent. The most promising
compound in this series was the furazane derivative 3j which
O
3a
3b
35,000
42,000
NH
O
N
N
O
Table 2
Antagonistic activity of 3f–q
3c
6100
3500
R3
R2
O
X
Y
R1
N
Z
N
3d
N
NH
NH
Numerical average of at least two experiments .
H
NH
F
a
O
N
N
azide 1 (IC50 = 30 nM). Interestingly, the transformation of the
acetamide group of 3a to the hydrogen bond donor lacking pyrro-
lidinone 3b had no substantial effect on the activity at the B1 recep-
tor, whereas the introduction of an annulated phenyl group
increased the affinity by a factor of seven (3c). The most active
compound in this series was found to be the benzimidazole deriv-
ative 3d.
Cl
F
R3
X
R2
N
O
R1 = Me
O
R1
=
Y
N
Z
Compound CAM IC50 (nM)a Compound CAM IC50 (nM)a
As the benzimidazole group represents a privileged scaffold in
drug discovery, it was selected for further optimization. The trans-
formation of 3d to the optimized compound 3f is depicted in Scheme
5. Adding an acetamide moiety to 3d improved the IC50 value from
IC50 = 3500 nM to IC50 = 15 nM (3e). Further optimization of the
biaryl and the amide moieties led to compound 3f. This compound
exhibited excellent potency at the B1 receptor (IC50 = 0.7 nM) but
showed high P-gp efflux in a Caco-2 assay22 (efflux ratio 7.1) and
3f
0.7
3l
4.6
N
N
3g
3h
85
3m
3n
180
1.6
N
N
N
N
proved to be only moderately soluble (14
lM) in aqueous buffer. Re-
cently, a similar six-membered diaminoheterocycle, that is, diami-
nopyridine,23was described as
a
scaffold for B1 receptor
1.7
Cl
—
n.d.
3o
0.3
O
O
O
N
N
N
N
NH
NH
N
N
N
N
N
N
H
H
HN
N
O
NH
NH
3i
3.5
1.0
0.6
—
n.d.
7.7
1.7
F
F
F
O N
N
O
N
O
F
O
F
3j
3p
3q
N
O
O
S
N
N
Cl
F
3k
3d
3e
3f
Scheme 5. Transformation of lead 3d to the advanced lead 3e and optimization to
compound 3f.
a
Numerical average of at least two experiments.

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G. Zischinsky et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1229–1232
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revealed good human microsomal stability (61% remaining after
1 h25), high permeability (Papp, AꢀB = 48 ꢁ 10ꢀ6 cm/s) and no efflux
in a Caco-2 assay (efflux ratio 1.0). Unfortunately, 3j and 3k were
even less soluble than 3f. To improve solubility, the isoxazole
amide moiety was replaced by an acetamide (Table 2, right col-
umn). In the case of furazane (3p, IC50 = 7.7 nM) and thiofurazane
(3q, IC50 = 1.7 nM) this was accompanied with a loss in potency
although the expected increase in solubility was observed (e.g.,
3p, 21 lM vs 3j, 12 lM). To further increase solubility, we again
12. Pietrovski, E. F.; Otuki, M. F.; Regoli, D.; Bader, M.; Pesquero, J. B.; Cabrini, D. A.;
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investigated the imidazole derivatives (3l–o). As with the isoxazole
amide, the acetamide of the unsubstituted imidazole (3n,
IC50 = 1.6 nM) led to a highly active B1 receptor antagonist which
was intolerant of dimethyl substitution with regards to activity
(3m, IC50 = 180 nM). The most active compound was the chloroim-
idazole derivative 3l which showed an excellent IC50 of 0.3 nM as
14. Part
1 of this series on novel small molecule bradykinin B1 receptor
antagonists.
15. Bemis, G. W.; Murcko, M. A. J. Med. Chem. 1996, 39, 2887.
16. Wood, M. R.; Books, K. M.; Kim, J. J.; Wan, B.-L.; Murphy, K. L.; Ransom, R. W.;
Chang, R. S. L.; Tang, C.; Prueksaritanont, T.; Detwiler, T. J.; Hettrick, L. A.;
Landis, E. R.; Leonard, Y. M.; Krueger, J. A.; Lewis, S. D.; Pettibone, D. J.;
Freidinger, R. M.; Bock, M. G. J. Med. Chem. 2006, 49, 1231.
well as good solubility in water (40 lM).
17. Wood, M. R.; Schirripa, K. M.; Kim, J. J.; Kuduk, S. D.; Di Marco, C. N.; Chang, R.
K.; Wai, J. C.; DiPardo, R. M.; Wang, B. L.; Cook, J. L.; Holahan, M. A.; Lemaire,
W.; Mosser, S. D.; Bednar, R. A.; Wallace, A. A.; Mei, Q.; Yu, J.; Bohn, D. C.;
Clayton, F. D.; Adarayan, E. A.; Sitko, G. R.; Leonard, Y. M.; Murphy, K. L.;
Ransom, R. W.; Harrell, C. M.; Tang, C.; Prueksaritanont, T.; Pettibone, D. J.;
Bock, M. G. Bioorg. Med. Chem. Lett. 2008, 18, 716.
In summary, the discovery of a new series of B1 receptor antag-
onists with five-membered heteroaromatic scaffolds is reported.
Further optimization and pharmacological characterization of
these compounds is ongoing.
18. Kuduk, S. D.; Di Marco, C. N.; Chang, R. K.; Wood, M. R.; Kim, J. J.; Schirripa, K.
M.; Murphy, K. L.; Ransom, R. W.; Tang, C.; Torrent, M.; Ha, S.; Prueksaritanont,
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Acknowledgements
20. Kuduk, S. D.; Di Marco, C. N.; Chang, R. K.; Wood, M. R.; Schirripa, K. M.; Kim, J.
J.; Wai, J. C.; DiPardo, R. M.; Murphy, K. L.; Ransom, R. W.; Harrell, C. M.; Reiss,
D. R.; Holahan, M. A.; Cook, J. L.; Hess, J. F.; Sain, N.; Urban, M. O.; Tang, C.;
Prueksaritanont, T.; Pettibone, D. J.; Bock, M. G. J. Med. Chem. 2007, 50, 272.
21. Menzel, K.; Machrouhi, F.; Bodenstein, M.; Alorati, A.; Cowden, C.; Gibson, A.
W.; Bishop, B.; Ikemoto, N.; Nelson, T. D.; Kress, M. H.; Frantz, D. E. Org. Process
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22. Absorption systems express bidirectional permeability assay through Caco-2
cell monolayers: Artursson, P.; Palma, K.; Luthmanb, K. Adv. Drug Delivery Rev.
2001, 46, 27; Sambuy, Y.; De Angelis, I.; Ranaldi, G.; Scarino, M. L.; Stammati,
A.; Zucco, F. Cell Biol. Toxicol. 2005, 21, 1.
We thank Pericles Calias and Brigitte Hoch for proofreading the
manuscript and for their consent to handle any future correspon-
dence. We also thank Jessica Bald, Anja Borrmann, Antje Burian,
Anett Hauser, Birgit Hollmann, Bianka Knopp, Stephanie Köpke,
Ricarda Lange, Nicole Liebelt, Corinna Mewes, Daniel Ohlendorf,
Katy Pesta, Frank Polster, Dagmar Riexinger, Beatrice Rosskopp,
Jana Rother, Edith Weigt, Rocco Weise, Daniela Wulf and Ariane
Zwintscher for their skillful technical assistance.
23. Kuduk, S. D.; Ng, C.; Feng, D.-M.; Wai, J. M.-C.; Chang, R. S. L.; Harrell, C. M.;
Murphy, K. L.; Ransom, R. W.; Reiss, D.; Ivarsson, M.; Mason, G.; Boyce, S.; Tang,
C.; Prueksaritanont, T.; Freidinger, R. M.; Pettibone, D. J.; Bock, M. G. J. Med.
Chem. 2004, 47, 6439.
24. Tang, C.; Subramanian, R.; Kuo, Y.; Krymgold, S.; Lu, P.; Kuduk, S. D.; Ng, C.;
Feng, D. M.; Elmore, C.; Soli, E.; Ho, J.; Bock, M. G.; Baillie, T. A.; Prueksaritanont,
T. Chem. Res. Toxicol. 2005, 18, 934.
25. Determined as described in: Kunz, W.; Gieschen, H. Drug Metab. Dispos. 1998,
26, 1120. Microsomal preparations from different species were obtained from
Tebu-bio, Offenbach, Germany.
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