A novel class of orally active non-peptide bradykinin B2 receptor antagonists. 1. Construction of the basic framework

Article abstract of DOI:10.1021/jm970591c

A novel class of potent, selective, and orally active non-peptide bradykinin (BK) B₂ receptor antagonists were designed and synthesized starting from 8-benzyloxyimidazo[1,2-α]pyridine derivative 2. The unique screening lead (2) was discovered b

Full text of DOI:10.1021/jm970591c

564
J . Med. Chem. 1998, 41, 564-578
A Novel Cla ss of Or a lly Active Non -P ep tid e Br a d yk in in B2 Recep tor
An ta gon ists. 1. Con str u ction of th e Ba sic F r a m ew or k
Yoshito Abe,† Hiroshi Kayakiri,*,† Shigeki Satoh,† Takayuki Inoue,† Yuki Sawada,† Keisuke Imai,†
Noriaki Inamura,‡ Masayuki Asano,§ Chie Hatori,§ Akira Katayama,§ Teruo Oku,† and Hirokazu Tanaka|
Exploratory Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., 5-2-3 Tokodai, Tsukuba, Ibaraki 300-26, J apan
Received September 4, 1997
A novel class of potent, selective, and orally active non-peptide bradykinin (BK) B2 receptor
antagonists were designed and synthesized starting from 8-benzyloxyimidazo[1,2-a]pyridine
derivative 2. The unique screening lead (2) was discovered by a two-step intentional random
screening process, involving recognition of the relationship between BK and angiotensin II
(Ang II) and the common structural features. Systematic chemical modification of 2 elucidated
the structural requirements essential for B2 binding affinity leading to the identification of
8-[[3-(N-acylglycyl-N-methylamino)-2,6-dichlorobenzyl]oxy]-3-halo-2-methylimidazo[1,2-a]py-
ridine skeleton as the basic framework of this new series of B2 antagonists. A molecular
modeling study suggested the key role of the N-methylanilide moiety at the 3-position of the
2,6-dichlorobenzene ring to allow these compounds to adopt the characteristic active conforma-
tion. The representative lead compounds inhibited the specific binding of [3H]BK to guinea
pig ileum membrane preparations expressing B2 receptors, with nanomolar IC50s and also
displayed in vivo functional antagonistic activities against BK-induced bronchoconstriction in
guinea pigs at an oral dose of 1 mg/kg. Pharmacokinetic studies of compounds 47c and 50b in
rats highlighted their excellent oral bioavailabilities, indicating that they represent the first
orally active non-peptide B2 antagonists reported to date.
In tr od u ction
because of their poor oral bioavailability. Recently some
non-peptide B2 antagonists have been reported,16,17 but
they are much less potent than peptide antagonists and
unsatisfactory with regard to selectivity and/or oral
bioavailability.
Bradykinin (BK) is an endogenous nonapeptide pro-
duced by tissue and plasma kallikreins from kininogens
in the course of inflammatory responses.1-5 It displays
potent and diverse biological activities, such as relax-
ation of venular smooth muscle, contraction of smooth
muscle of airway, plasma extravasation, stimulation of
sensory neurons, alteration of ion secretion of epithelial
cells and release of nitric oxide, prostaglandins, leuko-
trienes, and cytokines.1-7 On the basis of these strong
proinflammatory properties, BK is believed to play
important roles in a variety of inflammatory diseases
including asthma, rhinitis, pancreatitis, sepsis, rheu-
matoid arthritis, brain edema and angioneurotic edema.
BK has at least two subtypes of specific G-protein-
coupled cell surface receptors designated as B1 and
B2,1,4,8 both of which have been identified by molecular
cloning and pharmacological means. B2 receptors are
expressed constitutively in many tissues and are thought
to mediate most of the biological actions of BK.1,8
A number of peptide B2 antagonists have been syn-
thesized, and the representative “second-generation”
antagonists,9-13 icatibant (Hoel40)9,10 and bradycor
(CP0127),11 are in clinical trials. Although they have
very strong affinity for B2 receptors and longer duration
of action in vivo than the “first-generation” peptide
antagonists,14,15 their therapeutic use is still limited
To investigate the pathophysiological roles of BK and
to develop a new therapeutic drug for treatment of the
inflammatory diseases described above, we started a
research program to discover orally active non-peptide
B2 antagonists which could overcome the problems with
the peptide analogues. First of all we carried out a two-
step directed random screening of the Fujisawa chemi-
cal library and discovered the unique non-peptide
screening lead 2 (Chart 2). Extensive chemical modi-
fication of this simple screening lead, followed by
intensive optimization of the side chain, allowed us to
build up the basic structure of a novel class of potent
and selective non-peptide B2 antagonists. Herein we
describe the structure-activity relationships (SAR)
revealed on the way to the discovery of the first orally
active lead compounds (47c, 50b).
Ch em istr y
The compounds described in this study are shown in
Tables 1-8 and their synthetic methods are outlined
in Schemes 1-9. Condensation of 3-[(2,6-dichloroben-
zyl)oxy]-2-aminopyridine (4) with the corresponding
R-halo carbonyl compounds [XCH(R2)COR1]18,19 gave
substituted imidazo[1,2-a]pyridines 5a -e. Selective
halogenation at the 3-position of 5b was achieved by
means of N-chlorosuccinimide (NCS) or N-bromosuc-
cinimide (NBS) in EtOH20 to give 6a ,b. The 3-ester
derivative 5c was reduced with lithium aluminum
hydride to give alcohol 7 (Scheme 1).
† Department of Medicinal Chemistry.
‡ Present address: Exploratory Clinical Research, Development
Division, Fujisawa Pharmaceutical Co. Ltd., 2-1-6, Kashima, Yo-
dogawa-ku, Osaka 532, J apan.
§ Department of Pharmacology.
| Present address: New Drug Research Laboratories, Fujisawa
Pharmaceutical Co. Ltd., 2-1-6, Kashima, Yodogawa-ku, Osaka 532,
J apan.
S0022-2623(97)00591-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/22/1998

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 565
Sch em e 1a
a
(a) 2,6-Dichlorobenzyl bromide, NaH, DMF; (b) XCH(R2)COR1, EtOH; (c) NBS or NCS, EtOH; (d) LAH, THF.
Schemes 2-4 show the synthetic routes for the
compounds which have other types of linkers between
the imidazo[1,2-a]pyridine ring and the 2,6-dichloro-
phenyl moiety. The benzylamino derivative 10a was
synthesized by reductive alkylation of 8-aminoimidazo-
[1,2-a]pyridine 8 with 2,6-dichlorobenzaldehyde followed
by chlorination with NCS. Coupling of 8 with 2,6-
dichlorobenzoyl chloride and successive chlorination
gave the benzamido derivative 10b. The acetamide 11
was alkylated to give 9c, which was treated with NBS
to provide the benzylacetamido derivative 10c (Scheme
2). The phenoxycarbonyl 15a and the anilide 15b were
obtained from the acid 14 via its acid chloride. The
phenoxymethyl derivative 17 was synthesized by cou-
pling of 16 with 2,6-dichlorophenol via its methane-
sulfonate (Scheme 3). Wittig reaction of the aldehyde
1821 with (2,6-dichlorobenzyl)triphenylphosphonium bro-
mide was performed in DMSO in the presence of so-
dium hydride to give only the (E)-olefin 19, whose
stereochemistry was identified on the basis of the
observed coupling constant of 16 Hz between the olefinic
protons.21 Successive bromination at the 3-position
yielded 20 (Scheme 4).
and subsequent mesylation of the alcohol yielded the
mesylate 27a , which was coupled with 21 in the pres-
ence of sodium hydride to construct the basic skeleton
28a . Reduction of the nitro group of 29a with iron in
refluxing concentrated HCl and EtOH gave the highly
insoluble aniline 30a . Acetylation of 30a followed by
treatment with alkyl halides in the presence of sodium
hydride yielded the alkylamides 32a and 32c. Reduc-
tion of the amide 32a with borane-methyl sulfide
complex provided the amine 33. The 2,4,6-trichloroben-
zoic acid 34 was nitrated and was reduced with borane-
methyl sulfide complex to give the benzyl alcohol 26b.
Subsequent mesylation, coupling and bromination pro-
vided the nitro derivative 29b, which was reduced with
iron in refluxing acetic acid and EtOH to give the aniline
30b. Acetylation of 30b with acetic anhydride in
pyridine gave the diacetate 31b. Treatment of 31b with
methyl iodide and sodium hydride afforded the alkyl-
amide 32b.
Modifications of the amine at the 3-position of the
phenyl ring are shown in Scheme 7 and 8. Removal of
the acetyl group of 32a with sodium methoxide gave the
methylaniline 36 which was acylated or sulfonylated to
afford 37a -e. Treatment of 37c with methylamine in
methanol yielded the urea 38. The acetoxyacetamide
37e was hydrolyzed and alkylated to give the methyl
ether 40 (Scheme 7). The N-phthaloylglycinamides
42a -c were obtained from 30a by heating with the acid
chlorides (41a -c) and pyridine in N-methylpyrrolidone.
Alkylation of 42a -c with methyl iodide in the presence
of sodium hydride yielded 43a -c, which were depro-
tected with hydrazine monohydrate and successively
acetylated to give the acetamides 45a -c, respectively.
Methylation of 45a was performed with methyl iodide
and sodium hydride to give N-methylacetamide 45d .
Alkylation of 8-hydroxyimidazo[1,2-a]pyridine (21)19a
with appropriately substituted benzyl halides or benzyl
methanesulfonates followed by halogenation gave the
corresponding 8-(benzyloxy)-3-haloimidazo[1,2-a]py-
ridines 23a -e (Scheme 5).
Introduction of the nitrogen atom at the 3-position of
the phenyl ring is shown in Scheme 6. Treatment of
2,6-dichlorobenzaldehyde (24) with 70% nitric acid in
concentrated sulfuric acid provided the 3-nitro deriva-
tive 25 exclusively. Similar nitration of 2,6-dichlo-
robenzoic acid failed to proceed regioselectively (data
not shown). Reduction of 25 with sodium borohydride

566 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Abe et al.
Sch em e 2a
a
(a) 2,6-Cl2C6H3CHO, NaBH3CN, MeOH; (b) NCS, EtOH; (c) 2,6-Cl2C6H3COCl, Et3N, DMAP, CH2Cl2; (d) Ac2O, pyridine; (e) 2,6-
Cl2C6H3CH2Br, NaH, DMF; (f) NBS, EtOH.
Sch em e 3a
a
(a) NBS, EtOH; (b) 1 N NaOH, EtOH; (c) (COCl)2, DMF, CH2Cl2 then 2,6-Cl2C6H3OH or 2,6-Cl2C6H3NH2, Et3N, CH2Cl2; (d) LAH,
THF; (e) MsCl, Et3N, CH2Cl2; (f) NaH, 2,6-Cl2C6H3OH, DMF.
The hydrochloride 46 was obtained by treatment of 45a
with 10% hydrogen chloride in MeOH (Scheme 8).
ylamine yielded 49. Treatment of 44a with isocyanates
yielded the corresponding ureas 50a -c. 50a and 50c
were converted to the corresponding hydrochlorides 51a
and 51c, respectively.
Further chemical modifications of the amine 44a are
shown in Scheme 9. Reaction of 44a with sulfonyl
chloride or acid chlorides gave 47a -d in good yield.
47a ,b and 47d were treated with 10% hydrogen chloride
in MeOH to give the corresponding hydrochlorides 48a ,b
and 48d , respectively. Acylation of 44a with bromo-
acetyl chloride followed by the substitution with dimeth-
Biology
All compounds were tested for inhibiting the specific
binding of [3H]BK to B2 receptors in guinea pig ileum
membrane preparations as previously reported.22 Com-

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 567
Sch em e 4a
preparations with an IC50 value of 3.1 × 10-5 M.
Because of its low affinity and simple structure com-
pared to a nonapeptide BK, we supposed that 1 lacks
some important pharmacophores. So we carried out a
second screening of about 400 more structurally diverse
compounds incorporating a benzyloxy heteroaromatic
substructure and identified 8-benzyloxyimidazo[1,2-a]-
pyridine (2) with an IC50 value of 7.6 × 10-6 M as a
better screening lead compound (Chart 2). With this
unique lead in hand we started extensive chemical
modifications to investigate SAR for B2 binding activity.
a
(a) 2,6-Cl2C6H3CH2PPh3Br, NaH, DMSO; (b) NBS, EtOH.
At first we investigated the effect of 2- and 3-substit-
uents on the imidazo[1,2-a]pyridine ring (Table 1).
Removal of both substituents from the screening lead
2 gave 5a which was about 4 times less potent; however,
introduction of a 2-methyl group (5b) recovered the B2
binding affinity. Enlargement of the 2-substituent gave
slightly weaker 2-ethyl derivative 5d . Replacement of
the 2-methyl group with the electron-withdrawing tri-
fluoromethyl moiety (5e) resulted in significant loss of
activity. Concerning the 3-substituent, hydroxymethyl
derivative 7 was slightly weaker than 5b, and an ester
group (5c) caused severe loss of activity. On the other
hand, incorporation of halogen at the 3-position (6a ,b)
remarkably increased the affinity to submicromolar
levels. On the basis of this data we postulated that
2-methyl and 3-chloro or 3-bromo substituents contrib-
uted to B2 binding affinity by hydrophobic interactions
with the corresponding pockets of the B2 receptor and
that the pocket for the 2-methyl group was much
smaller than that for the 3-substituent. Since chemical
modifications at the 5-, 6-, and 7-positions of the
imidazo[1,2-a]pyridine ring failed to improve the bind-
ing affinity (data not shown), we decided to adopt
3-chloro- or 3-bromo-2-methylimidazo[1,2-a]pyridine as
the common substructure for further modifications.
Sch em e 5a
a
(a) NaH, benzyl halide or benzyl methanesulfonate, DMF; (b)
NCS or NBS, EtOH.
pounds having the potent binding affinities were then
tested for in vivo oral activity in inhibiting BK-induced
bronchoconstriction in guinea pigs. Pharmacokinetics
of the orally active BK antagonists were also studied.
The SAR of the linker group between the imidazo-
[1,2-a]pyridine ring and the dichlorophenyl moiety was
rather drastic (Table 2). Amino derivative 10a retained
about a 5-fold weaker binding affinity; however, N-
acetylation of the corresponding 3-bromo derivative gave
inactive compound 10c. Replacement of the oxymeth-
ylene group of 6a or 6b with two types of the amides
(10b, l5b), the ester (l5a ), and the ethenyl (20) group
resulted in complete loss of the activity. Even the
inverse methyleneoxy derivative (17) failed to show any
appreciable binding affinity, suggesting that the linker
group was important not only as a spacer but also as a
pharmacophore which had electrostatic interaction with
the B2 receptor via its oxygen atom.
Resu lts a n d Discu ssion
When we started our research program no selective
non-peptide BK antagonists had been reported. In
seeking a screening lead we took notice of the relation-
ship between BK and Ang II.17b Ang II is an octapeptide
which plays a key role in regulating cardiovascular
homeostasis and electrolyte/fluid balance through spe-
cific G-protein-coupled cell surface AT1 receptors as the
active component of the renin-angiotensin-aldosterone
system. It acts as a representative vasoconstrictor to
increase blood pressure whereas BK causes severe
systemic hypotension. Angiotensin-converting enzyme
(ACE), which generates Ang II from inactive Ang I, is
identical with kininase II which participates in the
degradation of BK (Chart 1). Furthermore, AT1 recep-
tors show the highest homology (29%) to B2 receptors
amongst G-protein-coupled receptors, with the exception
of the BK B1 receptor subtype which has 35% homology.
These suggestive relevance between Ang II and BK
prompted us to focus our initial screening efforts on AT1
antagonists and related compounds in the Fujisawa
chemical library. This directed random screening of
about 300 compounds revealed that a synthetic inter-
mediates for AT1 antagonists, i.e., compound 1, weakly
bound to B2 receptors in guinea pig ileum membrane
Table 3 shows that the dichloro group was the most
favorable among the examined dihalogen substituents
at the 2,6-position of the phenyl ring. We also investi-
gated substituents other than halogens in another series
of B2 antagonists and found that the 2,6-dichloro group
was superior to others. The data will be reported in
future publications.
As the next step, we introduced substituents into the
3- and 4-positions of the 2,6-dichlorophenyl ring to
improve the binding affinity (Table 4). Although the
3-chloro (23d ) and the 3-methoxy group (23e) weakened
the activity, the 3-nitro derivative (29a ) afforded an
approximately 5-fold increase in binding affinity. Re-
duction of the nitro group followed by N-acetylation

568 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Abe et al.
Sch em e 6a
a
(a) HNO3, H2SO4; (b) NaBH4, MeOH; (c) MsCl, Et3N, CH2Cl2; (d) NaH, DMF; (e) NBS, EtOH; (f) Fe, concentrated HCl (for 29a ) or
AcOH (for 29b), EtOH; (g) Ac2O, pyridine; (h) R2X, NaH, DMF; (i) BH3‚SMe2, THF.
resulted in a severe loss of activity; however, N-
methylacetamide derivative 32a was as potent as the
nitro derivative 29a . Additional introduction of chloro
to the 4-position of 32a gave a much less potent
compound (32b). These results suggest that steric
features around this position are much more important
for B2 binding affinity than electrostatic factors.
conformer compared to the trans-amide one of the model
compounds 3la ′, 32a ′, and 32b′ correlated to the in vitro
activities of the corresponding B2 ligands 31a , 32a , and
32b. These data might suggest that this class of B2
ligands bind to the receptor as the cis-amide conformer
and the 2,6-dichloro-3-N-methylanilide moiety plays a
key role in stabilizing the active conformation.
To investigate more detailed steric requirements for
B2 binding affinity, we carried out conformational
analysis of N-H and N-methyl acetamide model com-
pounds (31a ′, 32a ′,b′) by ab initio molecular orbital
calculations. For each model compound the most stable
structures of cis- and trans-amide conformers were
obtained by GAUSSIAN 94 using 6-31G** basis set.23
The energies and torsion angles for the cis- and trans-
amide conformers are shown in Table 5, and their
preferred conformations are drawn in Figure 1. Ener-
getic and conformational features of the most stable
structures were as follows. The N-H amide compound
(31a ′) adopted a trans-amide conformation with the
amide and phenyl plane coplanar whereas the N-methyl
compound (32a ′,b′) adopted a cis-amide conformation
with the amide and phenyl plane almost perpendicular.
Interestingly, the relative stabilities of the cis-amide
Thus we selected 32a as a lead compound for further
chemical modifications. Obviously 32a is much smaller
than the nonapeptide BK, so there should be many
binding sites on the B2 receptor remaining to be used
for interaction with non-peptide ligands. Seeking such
possibilities, we concentrated on chemical modifications
of the acetamide group of 32a (Table 6). N-Ethyl
derivative of 31a (32c) was 3-fold weaker than 32a ,
suggesting a strict steric restriction around the amide
group. Reduction of the carbonyl group (33) signifi-
cantly reduced the activity consistent with our hypoth-
esis discussed above. The carbamate (37a ), sulfonamide
(37b), and urea (38) congeners were remarkably less
potent and introduction of methyl (37d ), acetoxy (37e),
methoxy (40), or amino (44a ) groups gave compounds
that were only weakly active. However, acetylation of
the terminal amine of 44a afforded the new lead com-

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 569
Sch em e 7a
a
(a) NaOMe, MeOH; (b) RCl, Et3N or pyridine, CH2Cl2; (c) MeNH2, MeOH; (d) K2CO3, MeOH; (e) MeI, NaH, DMF.
Sch em e 8a
a
(a) pyridine, DMAP, N-methylpyrrolidone; (b) MeI, NaH, DMF; (c) H2NNH2‚H2O, EtOH; (d) Ac2O, pyridine, CH2Cl2; (e) MeI, NaH,
DMF; (f) HCl-MeOH.
pound 45a , with an IC50 of 16 nM. Since both extending
the methylene to ethylene (45c) and blocking the ter-
minal amide proton with a methyl group (45d ) reduced
the affinity, it was suggested that the terminal amide
group contributed to the interaction with the B2 receptor
as a hydrogen bond donor. Furthermore, introduction
of a methyl group at the methylene of the glycine moiety
(45b) reduced the affinity compared to 45a , indicating
that the methyl group sterically influences the interac-
tion with the receptor or the conformation of the side
chain.
Finally, further optimization of the terminal acyl
group led us to the discovery of a novel class of highly
potent non-peptide BK B2 antagonists as shown in Table
7. The n-butylamide (47c), (dimethylamino)acetamide
(49), and ethyl urea (50b) inhibited the specific binding

570 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Abe et al.
Sch em e 9a
a
(a) RCl, Et3N, CH2Cl2; (b) HCl-MeOH; (c) BrCH2COCl, Et3N, CH2Cl2 then HNMe2 in H2O; (d) RNCO, CH2Cl2.
Ch a r t 1
that hydrophobic contacts via 2-methyl and 3-chloro or
3-bromo groups on the imidazo[1,2-a]pyridine ring,
electrostatic interactions via linker oxygen, and hydro-
gen bonds via the terminal amide group significantly
contributed to the binding affinity to B2 receptors. It
is also noteworthy that the 2,6-dichloro-3-N-methyl-
anilide moiety was suggested to be the key feature to
allow these B2 antagonists to adopt the characteristic
active conformations. These speculations are sum-
marized in a pharmacophore model for the interactions
between the antagonists and B2 receptors (Figure 2).
The investigation of detailed SAR allowed us to identify
8-[[3-(N-acylglycyl-N-methylamino)-2,6-dichlorobenzyl]-
oxy]-3-halo-2-methylimidazo[1,2-a]pyridine skeleton as
the basic framework and led us to the discovery of the
first orally active non-peptide BK B2 antagonists whose
activities represent a 3 order of magnitude increase
relative to the screening lead 2. Further studies aiming
at clinical candidates are currently underway using the
representative antagonists obtained in this study as the
new lead compounds. The expanded SAR will be
presented in due course.25
of [3H]BK to B2 receptors with nanomolar IC50s and
their functional antagonistic properties were proven in
vivo at 1 mg/kg by oral administration in a guinea pig
BK-induced bronchoconstriction model. Furthermore,
the pharmacokinetic studies in rats revealed their good
to excellent oral bioavailabilities (Table 8). To our
knowledge these representative compounds are the first
non-peptide B2 antagonists which can inhibit the action
of BK in vivo by oral administration.
Exp er im en ta l Section
Con clu sion
Ch em istr y. Melting points were determined on Mel-Temp
(Mitamura Riken Kogyo, J apan) and are uncorrected. The 200
MHz proton NMR spectra were recorded on a Brucker AM200
spectrometer, and shifts were expressed in δ ppm with TMS
as internal standard. Mass spectra were recorded on VG
A unique screening lead (2) was found by a two-step
directed random screening process taking notice of the
relationship between BK and Ang II and structural
features. Extensive chemical modification of 2 revealed

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 571
Ch a r t 2
Ta ble 1. SAR at 2,3-Positions of the Imidazo[1,2-a]pyridine
compd
R1
R2
IC50, nMa
method
yield, %
mp, °C
formulab
2
Me
H
Me
Et
CF3
Me
Me
Me
Me
CH2OCH2CtCH
H
H
H
7600
31000
4500
5a
5b
5d
5e
5c
7
B
C
C
C
C
F
27.0
38.0
25.3
44.6
29.3
52.5
56.6
82.0
148-149
165-166
153-154
184-185
160-161
220-221
185-186
173-174
C
C
C
14H10Cl2N2O
15H12Cl2N2O
16H14Cl2N2O
10000
>100000
>100000
7500
H
C15H9Cl2F3N2O
C18H16Cl2N2O3
C16H14Cl2N2O2
C15H11Cl3N2O
CO2Et
CH2OH
Cl
6a
6b
200
230
D
E
Br
C15H11BrCl2N2O
a
IC50 for inhibition of specific binding of [3H]BK (0.06 nM) to B2 receptors in guinea pig ileum membrane preparations. For details, see
b
the Experimental Section. Analyses for C, H, and N are within (0.4% of the expected value for the formula.
(Fisons) ZAB-SE (FAB). IR spectra were taken with a Perkin-
Elmer FTIR 1600 spectrometer in Nujol or KBr and were
expressed in cm-1. Elemental analyses were performed on a
Perkin-Elmer 2400 CHN analyzer. Analytical results were
within (0.4% of the theoretical values unless otherwise noted.
Silica gel thin-layer chromatography was performed on pre-
coated plates Kieselgel 60F254 (E. Merck, AG, Darmstadt,
Germany). Silica gel flash chromatography was performed
with Kieselgel 60 (230-400 mesh) (E. Merck, AG, Darmstadt,
Germany). Extraction solvents were dried over magnesium
sulfate.
Meth od A. 3-[(2,6-Dich lor oben zyl)oxy]-2-a m in op yr i-
d in e (4). To a solution of 2-amino-3-hydroxypyridine (3) (11.0
g, 0.10 mol) in dry DMF (50 mL) was added 60% sodium
hydride in oil (4.4 g, 0.11 mol) portionwise in an ice-water
bath under nitrogen. The mixture was stirred at the same
temperature for 30 min, and 2,6-dichlorobenzyl chloride (25.2
g, 0.105 mol) was added portionwise therein. After 30 min of
stirring, the mixture was stirred at ambient temperature for
an additional 1 h. The reaction mixture was poured into
water, and the formed precipitate was collected by vacuum
filtration, washed with water, and dried in vacuo. The crude
product was recrystallized from hexane-AcOEt to give 4 (23.9
g, 88.8%) as pale gray crystals: mp 150-152 °C; 1H NMR
(CDCl3) δ 4.65 (2H, br s), 5.29 (2H, s), 6.65 (1H, dd, J ) 7, 5
Hz), 7.14 (1H, dd, J ) 7, 1 Hz), 7.21-7.43 (3H, m), 7.71 (1H,
dd, J ) 5, 1 Hz); IR (Nujol) 3455, 3270, 3125, 1620. Anal.
(C12H10Cl2N2O) C, H, N.
Compounds 9c and 22c were prepared following a procedure
similar to method A.
Meth od B. 8-[(2,6-Dich lor oben zyl)oxy]im id a zo[1,2-a ]-
p yr id in e (5a ). Compound 5a was prepared using the method
of Hand and Paudler.18 To a mixture of 2-(bromomethyl)-1,3-
dioxolane (372 mg, 2.23 mmol) and water (15 mL) was added
concentrated HCl (0.23 mL, 0.535 mmol) dropwise. The
mixture was stirred at ambient temperature for 2.5 h and then

572 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Abe et al.
Ta ble 2. SAR at the Linker Group between the Imidazo[1,2-a]pyridme and the 2,6-Dichlorobenzene
compd
R1
R2
IC50, nMa
method
yield, %
mp, °C
formulab
6a
6b
Cl
Br
Cl
Cl
Br
Br
Br
Br
Br
OCH2Arc
OCH2Ar
NHCH2Ar
NHCOAr
NAcCH2Ar
CH2OAr
200
230
1200
D
E
D
D
E
I
H
H
E
56.6
82.0
71.9
78.6
63.4
44.6
30.4
34.6
57.1
185-186
173-174
143-144
191-197
141-142
158-159
165-166
237-239
121-122
C15H11Cl3N2O
C15H11BrCl2N2O
C15H12Cl3N3
C15H10Cl3N3O
CI7H14BrCl2N2O
C15H11BrCl2N2O
C15H9BrCl2N2O2
C15H10BrCl2N3O
C16H11BrCl2N2
10a
10b
10c
17
15a
15b
20
>100000
>100000
>100000
>100000
>100000
>100000
CO2Ar
CONHAr
(E)-CHdCHArc
a
b
See Table 1. Analyses for C, H, and N are within (0.4% of the expected value for the formula. c Ar ) 2,6-dichlorophenyl.
Ta ble 3. SAR at the 2,6-Dihalobenzene
compd
R1
R2
IC50, nMa
method
yield, %
mp, °C
formulab
6b
Br
Cl
Cl
Br
2,6-Cl2PhCH2
2,6-Br2PhCH2
2,6-F2PhCH2
2-Cl-6-FPhCH2
230
1700
1800
1500
E
D
D
E
82.0
88.6
70.9
73.2
173-174
157-158
168-170
130-131
C15H11BrCl2N2O
C15H11Br2ClN2O
C15H11ClF2N2O
C15H11BrClFN2O
23a
23b
23c
a
b
See Table 1. Analyses for C, H, and N are within (0.4% of the expected value for the formula.
Ta ble 4. Introduction of the Substitutents on the 2,6-Dichlorophenyl Ring
compd
Rl
R2
n
IC50, nMa
method
yield, %
mp, °C
formulab
6b
H
Cl
OMe
NO2
H
H
H
H
H
H
H
Cl
0
0
0
0
1
0
0
0
230
490
540
42
1500
1800
54
E
E
E
E
82.0
70.9
26.6
95.1
77.2
93.6
58.9
29.7
173-174
168-170
175-176
217-219
186-187
210-212
201-204
oil
C15H11BrCl2N2O
23d
23e
29a
30a
31a
32a
32b
C
C
15H12ClF2N2O
16H13BrCl2N2O2
C15H10BrCl2N3O3
C15H12BrCl2N3O‚HCl
C17H14BrCl2N3O2
C18H16BrCl2N3O2
C18H15BrCl3N3O2
NH2
Exc
G
NHAc
NMeAc
NMeAc
M
M
420
a
b
See Table 1. Analyses for C, H, and N are within (0.4% of the expected value for the formula. c Ex ) experimental procedure
described.
at 80 °C for 30 min. After the mixture was cooled to ambient
(2H, s), 6.58-6.78 (2H, m), 7.19-7.40 (3H, m), 7.57 (2H, s),
7.82 (1H, d, J ) 7.5 Hz). Anal. (C14H10Cl2N2O) C, H, N.
Meth od C. 8-[(2,6-Dich lor oben zyl)oxy]-3-(eth oxyca r -
bon yl)-2-m eth ylim id a zo[1,2-a ]p yr id in e (5c). Substituted
imidazo[1,2-a]pyridines were prepared by using the method
reported by Kaminski et al.19 A mixture of 4 (15.0 g, 55.8
mmol) and ethyl 2-chloroacetoacetate (11.9 g, 72.5 mmol) in
EtOH (150 mL) was refluxed for 24 h. After cooling, the
reaction mixture was concentrated in vacuo, and the residue
was partitioned between AcOEt and saturated aqueous sodium
hydrogen carbonate. The organic layer was washed with water
and brine, dried, and evaporated in vacuo. The residue was
purified by flash silica gel column chromatography, eluting
temperature, sodium hydrogen carbonate (244 mg, 2.90 mmol)
and 4 (479 mg, 1.78 mmol) were added therein, and the
mixture was stirred at ambient temperature for 3 h. Dioxane
(10 mL) was added to this mixture, and the mixture was
heated under reflux for 10 h. The reaction mixture was
concentrated in vacuo to about half volume and extracted three
times with CH2Cl2. The organic extracts were combined,
washed with brine, dried, and evaporated in vacuo. The
residue was purified by flash silica gel column chromatogra-
phy, eluting with CHCl3-MeOH (20:1) followed by crystal-
lization from isopropyl ether to give 5a (140 mg, 27.0%) as
1
colorless crystals: mp 148-149 °C; H NMR (CDCl3) δ 5.49

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 573
Ta ble 5. Relative Energies and Torsion Angles for the cis- and
trans-Amide Conformers of Model Compoundsa
J ) 8 Hz), 7.19-7.41 (3H, m), 7.75 (1H, d, J ) 8 Hz). Anal.
(C15H11BrCl2N2O) C, H, N.
Compounds 10c, 13, 20, 23c-e, and 29a ,b were prepared
following a procedure similar to method E.
cis
trans
energy
torsion
(deg)
energy
torsion
(deg)
Met h od F . 8-[(2,6-Dich lor ob en zyl)oxy]-3-(h yd r oxy-
m eth yl)-2-m eth ylim id a zo[1,2-a ]p yr id in e (7). To a suspen-
sion of lithium aluminum hydride (716 mg, 18.8 mmol) in dry
THF (50 mL) was added 5c (3.00 g, 7.92 mmol) in portions
under nitrogen at 0 °C. The reaction mixture was stirred for
1 h in an ice-water bath. To the mixture was added a 3%
aqueous solution of NaOH (3.75 mL) dropwise below 10 °C.
The precipitate was removed by vacuum filtration and washed
with hot THF (150 mL) and hot CHCl3 (150 mL). The filtrate
and washings were combined and evaporated in vacuo. The
residue was recrystallized from MeCN to give 7 (1.40 g, 52.5%)
as colorless crystals: mp 220-221 °C; 1H NMR (CDCl3) δ 2.28
(3H, s), 4.72 (2H, br s), 5.08 (1H, br s), 5.38 (2H, s), 6.76-6.94
(2H, m), 7.45-7.68 (3H, m), 7.98 (1H, d, J ) 5 Hz); MS (FAB)
m/ z 337 (M + 1). Anal. (C16H14BrCl2N2O2) C, H, N.
Compound 16b was prepared following a procedure similar
to method F.
compd
(kcal/mol)
(kcal/mol)
31a ′
32a ′
32b′
3.99
0
0
100.6
94.0
91.9
0
2.41
1.73
180
101.3
94.4
a
Geometry optimizations and energy calculations were per-
formed by GAUSSIAN 94 using 6-31G** basis set. Full geometry
optimizations were performed to obtain most stable structure
starting from the amide and phenyl coplanar and perpendicular
structure.
8-[(2,6-Dich lor oben zyl)a m in o]-2-m eth ylim id a zo[1,2-a ]-
p yr id in e (9a ). To a solution of 8 (367 mg, 2.00 mmol) and
2,6-dichlorobenzaldehyde (350 mg, 2.00 mmol) in MeOH (6 mL)
was added sodium cyanoborohydride (138 mg, 2.20 mmol) at
ambient temperature under nitrogen. After 30 min, to the
mixture was added additional 2,6-dichlorobenzaldehyde (175
mg, 1.00 mmol) and sodium cyanoborohydride (69 mg, 1.10
mmol) at ambient temperature. The reaction mixture was
stirred for another 30 min and partitioned between AcOEt and
saturated aqueous sodium bicarbonate. The organic layer was
washed with water and brine, dried, and evaporated in vacuo.
The residue was purified by flash silica gel column chroma-
tography, eluting with hexane-AcOEt (1:1) followed by crys-
tallization from isopropyl ether to give 9a (110 mg, 18.0%) as
pale brown crystals: mp 119-121 °C; 1H NMR (CDCl3) δ 2.38
(3H, s), 4.69 (2H, d, J ) 4 Hz), 5.19 (1H, t, J ) 4 Hz), 6.29
(1H, d, J ) 8 Hz), 6.63 (1H, t, J ) 8 Hz), 7.15-7.36 (3H, m),
7.32 (1H, s), 7.47 (1H, d, J ) 8 Hz). Anal. (C15H13Cl2N3) C,
H, N.
F igu r e 1. Structures and preferred conformations of model
compounds 31a ′, 32a ′, and 32b′.
8-(2,6-Dich lor oben za m id o)-2-m eth ylim id a zo[1,2-a ]p y-
r id in e (9b). To a solution of 8 (410 mg, 2.79 mmol), triethyl-
amine (422 mg, 4.18 mmol), and 4-(dimethylamino)pyridine
(8 mg) in CH2Cl2 (8 mL) was added 2,6-dichlorobenzoyl
chloride (816 mg, 3.90 mmol) in portions, cooling with an ice-
water bath under nitrogen. The mixture was stirred at the
temperature for 30 min and after that stirred at ambient
temperature. After 2 h, the reaction mixture was washed with
water, saturated aqueous solution of sodium bicarbonate, and
brine, dried, and evaporated in vacuo. The residue was
purified by preparative thin-layer chromatography (hexane-
AcOEt, 1:2) followed by crystallization from ether to give 9b
(45 mg, 5.0%) as colorless crystals: mp 194-196 °C; 1H NMR
(CDCl3) δ 2.41 (3H, s), 6.79 (1H, t, J ) 8 Hz), 7.30-7.42 (4H,
m), 7.84 (1H, d, J ) 8 Hz), 8.32 (1H, d, J ) 8 Hz), 8.72 (1H, br
s). Anal. (C15H11Cl2N3O) C, H, N.
Meth od G. 8-Aceta m id o-2-m eth ylim id a zo[1,2-a ]p yr i-
d in e (11). A mixture of 8 (235 mg, 1.28 mmol), acetic
anhydride (261 mg, 2.56 mmol) and dry pyridine (2.3 mL) was
heated at 90 °C for 6 h. After cooling, the mixture was poured
into ice-water (10 mL). The precipitated solid was collected
by vacuum filtration, washed with water, and dried in vacuo.
The solid was crystallized from EtOH to give 11 (151 mg,
62.5%) as pale brown crystals: mp 169-170 °C; 1H NMR
(CDCl3) δ 2.30 (3H, s), 2.47 (3H, s), 6.79 (1H, t, J ) 8 Hz),
7.32 (1H, s), 7.77 (1H, d, J ) 8 Hz), 8.19 (1H, br d, J ) 8 Hz),
8.82 (1H, br s). Anal. (C10H11N3O) C, H, N.
with CH2Cl2-MeOH (100:1) followed by recrystallization from
AcOEt to give 5c (6.2 g, 29.3%) as colorless crystals: mp 160-
161 °C; 1H NMR (CDCl3) δ 1.43 (3H, t, J ) 8 Hz), 2.71 (3H, s),
4.42 (2H, q, J ) 8 Hz), 5.49 (2H, s), 6.83-6.98 (2H, m), 7.19-
7.41 (3H, m), 8.99 (1H, dd, J ) 5, 1 Hz). Anal. (C18H16Cl2N2O3)
C, H, N.
Compounds 5b,d ,e and 8 were prepared following a proce-
dure similar to method C.
Met h od D. 3-Ch lor o-8-[(2,6-d ich lor ob en zyl)oxy]-2-
m eth ylim id a zo[1,2-a ]p yr id in e (6a ). To a solution of 5b
(100 mg, 0.326 mmol) in EtOH (1 mL) was added N-chloro-
succinimide (65 mg, 0.489 mmol) at ambient temperature, and
the mixture was stirred the temperature for 1 h. To the
mixture was added water, and the resulting mixture was
extracted with CH2Cl2. The organic layer was washed with
brine, dried, and evaporated in vacuo. The residue was
purified by flash silica gel column chromatography, eluting
with CHCl3-MeOH (100:1) followed by recrystallization from
benzene-hexane to give 6a (63 mg, 56.6%) as colorless
crystals: mp 185-186 °C; 1H NMR (CDCl3) δ 2.43 (3H, s), 5.48
(2H, s), 6.69 (1H, d, J ) 8 Hz), 6.81 (1H, t, J ) 8 Hz), 7.19-
7.40 (3H, m), 7.69 (1H, d, J ) 8 Hz). Anal. (C15H11Cl3N2O)
C, H, N.
Compounds 10a ,b and 23a ,b were prepared following a
procedure similar to method D.
Compounds 31a ,b and 45a -c were prepared following a
procedure similar to method G.
Met h od E . 3-Br om o-8-[(2,6-d ich lor ob en zyl)oxy]-2-
m eth ylim id a zo[1,2-a ]p yr id in e (6b). The title compound
was prepared from 5b (80 mg, 0.260 mmol) and N-bromosuc-
cinimide (52 mg, 0.287 mmol) using a similar procedure for
6a and was crystallized from isopropyl ether to give colorless
crystals (82 mg, 82.0%): mp 173-174 °C; H NMR (CDCl3) δ
2.44 (3H, s), 5.48 (2H, s), 6.70 (1H, d, J ) 8 Hz), 6.82 (1H, t,
3-Br om o-2-m eth ylim id a zo[1,2-a ]p yr id in e-8-ca r boxyl-
ic Acid (14). A solution of 13 (1.00 g, 3.69 mmol) in EtOH
(10 mL) containing 1 N NaOH (4.06 mL) was heated at 60 °C
for 30 min. Upon cooling, the reaction mixture was diluted
with water (20 mL) and adjusted to pH 5 with 1 N HCl. The
1

574 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Ta ble 6. SAR at the 3-Position of the 2,6-Dichlorobenzene
Abe et al.
a
compd
R
IC50
,
nM
method
yield, %
mp, °C
formulab
31a
32a
32c
33
37a
37b
38
37d
37e
40
44a
45a
45c
45d
45b
NHAc
1800
54
G
93.6
58.9
63.5
62.7
94.0
37.3
56.0
74.1
71.6
19.4
95.8
67.4
80.5
93.5
98.0
210-212
201-204
161-162
oil
C17H14BrCl2N3O2
C18H16BrCl2N3O2
C19H18BrCl2N3O2
C18H18BrCl2N3O
C18H16BrCl2N3O3
C17H16BrCl2N3O3S
C18H17BrCl2N4O2
C19H18BrCl2N3O2
C20H18BrCl2N3O4
C19H18BrCl2N3O3
C18H17BrCl2N4O2
C20H19BrCl2N4O3
C21H21BrCl2N4O3
C21H21BrCl2N4O3
C21H21BrCl2N4O3
NMeAc
NEtAc
NMeEt
NMeCO2Me
NMeSO2Me
M
M
Exc
Exc
N
150
410
1400
2100
350
72
500
580
380
16
178-179
161-164
192-193
168-170
amorphous
145-146
175-178
187-189
amorphous
amorphous
amorphous
NMeCONHMe
NMeCOEt
Exc
N
NMeCOCH2OAc
NMeCOCH2OMe
NMeCOCH2NH2
NMeCOCH2NHAc
NMeCO(CH2)2NHAc
NMeCOCH2NMeAc
NMeCOCH(Me)NHAc
N
M
P
G
G
810
1600
770
M
G
a
b
See Table 1. Analyses for C, H, and N are within (0.4% of the expected value for the formula. c Ex ) experimental procedure
described.
Ta ble 7. Discovery of Orally Active B2 Antagonists
in vitro
in vivo
a
IC50
,
inhibn %b
compd
R
n
nM
1 mg/kg, po
method
yield, %
mp, °C
formulac
46
Ac
COEt
CO-n-Pr
CO-n-Bu
1
1
0
1
1
0
1
0
1
16
19
62.3**
48.4**d
52.7
Q
Q
R
Q
Q
Exe
Q
S
66.8
86.6
82.9
86.6
94.6
80.0
94.6
83.5
94.5
179-180
174-176
158-159
amorphous
174-176
175-177
153-155
171-173
168-171
C20H19BrCl2N4O3‚HCl
C21H21BrCl2N4O3‚HCl
48b
47c
48d
48a
49
51a
50b
51c
8.9
7.8
580
2.4
46
9.0
26
C22H23BrCl2N4O3
29.7
C23H25BrCl2N4O3‚HCl
C19H19BrCl2N4O4S‚HCl
C22H24BrCl2N5O3
C20H20BrCl2N5O3‚HCl
C21H22BrCl2N5O3
SO2Me
48.4**d
72.4
COCH2NMe2
CONHMe
CONHEt
CONH-n-Pr
41.5
57.2***
62.4**d
Q
C22H24BrCl2N5O3‚HCl
a
b
See Table 1. BK (5 µg/kg) was administered intravenously to anesthetized guinea pigs, and bronchoconstriction induced by the BK
administration was measured by the modified Konzett and Ro¨sseler method as previously reported. After 5 min, compounds were orally
administered. After 30 min, BK was administered again and bronchoconstriction was measured. Inhibition % was calculated from the
bronchoconstrictions measured before and after the drug administrations. **P < 0.01, ***P < 0.001 vs control (Student’s t-test). For
d
details, see the Experimental Section. c Analyses for C, H, and N are within (0.4% of the expected value for the formula. Inhibition %
at doses of 3.2 mg/kg. e Ex ) experimental procedure described.
mixture was extracted with CHCl3-MeOH (5:1) three times,
and the organic layer was dried and evaporated in vacuo. The
residue was crystallized from EtOH to give 14 (800 mg, 85.0%)
as colorless crystals: mp 191-195 °C; H NMR (DMSO-d6) δ
2.41 (3H, s), 7.20 (1H, t, J ) 8 Hz), 7.98 (1H, d, J ) 8 Hz),
8.52 (1H, d, J ) 8 Hz). Anal. (C9H7BrN2O2) C, H, N.
Meth od H. 2,6-Dich lor op h en yl 3-Br om o-2-m eth ylim i-
d a zo[1,2-a ]p yr id in e-8-ca r boxyla te (15a ). To a suspension
of 14 (100 mg, 0.392 mmol) in dry CH2Cl2 (2 mL) were added
oxalyl chloride (100 mg, 0.784 mmol) and DMF (1 drop) at
ambient temperature under nitrogen. After 1 h of stirring,
the reaction mixture was concentrated in vacuo, and the
residue was redissolved in CH2Cl2 (2 mL) and triethylamine
(79 mg, 0.784 mL). To the mixture was added 2,6-dichlo-
rophenol (70 mg, 0.431 mmol) with cooling in an ice water
bath. After 30 min, the reaction mixture was washed with
saturated aqueous sodium bicarbonate, water, and brine,
dried, and evaporated in vacuo. The residue was purified by
flash silica gel column chromatography, eluting with CHCl3-
MeOH (30:1) followed by crystallization from isopropyl ether
to give 15a (57 mg, 30.4%) as colorless crystals: mp 165-166
°C; 1H NMR (CDCl3) δ 2.56 (3H, s), 7.08 (1H, t, J ) 8 Hz),
7.21 (1H, m), 7.41 (2H, d, J ) 9 Hz), 8.35 (2H, d, J ) 8 Hz).
Anal. (C15H9BrCl2N2O2) C, H, N.
1

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 575
Ta ble 8. Oral Bioavailabilities of Representative B2
8 Hz), 8.05 (1H, d, J ) 16 Hz); MS (FAB) m/ z 303 (M + 1).
Anal. (C16H12Cl2N2) C, H, N.
Antagonistsa
Meth od J . 8-[(2,6-Dibr om oben zyl)oxy]-2-m eth ylim i-
d a zo[1,2-a ]p yr id in e (22a ). To a solution of 2,6-dibromo-
toluene (2.5 g, 10 mmol) in dry CH2Cl2 (25 mL) was added
N-bromosuccinimide (1.89 g, 10.5 mmol) and 2,2′-azobis(4-
methoxy-2,4-dimethylvaleronitrile) (Wako, V-70) (189 mg, 0.61
mmol) at ambient temperature. The reaction mixture was
refluxed for 2 h, cooled, and washed twice with water. The
organic layer was dried and evaporated in vacuo. The residue
was purified by flash silica gel column chromatography, eluting
with hexane followed by crystallization from isopropyl ether
to give 2,6-dibromobenzyl bromide (2.9 g, 88.4%) as a colorless
oil: 1H NMR (CDCl3) δ 4.82 (2H, s), 7.01 (1H, t, J )8 Hz),
7.55 (2H, d, J )8 Hz).
compd
AUC, µg‚h/mL
Cmax, µg/mL
T1/2, h
BA, %
46
47c
49
3.15
11.71
0.94
3.64
9.97
0.29
52.6
0.42
0.3
0.3
NTb
90.0
32.8
75.0
50b
58.9
0.5
a
Drug suspended in 0.5% methyl cellulose at a dose of 10 mg/
b
kg was orally administrered in rats. NT ) not tested.
To a solution of 8-hydroxy-2-methylimidazo[1,2-a]pyridine
(21)19a (100 mg, 0.676 mmol) and 2,6-dibromobenzyl bromide
(244 mg, 0.743 mmol) in dry DMF (1 mL) was added potassium
carbonate (130 mg, 2.03 mmol) at ambient temperature under
nitrogen. The mixture was stirred for 2 h. To the mixture
was added water, and the precipitate was collected by vacuum
filtration, washed with water, and dried. The solid was
crystallized from isopropyl ether to give 22a (227 mg, 84.8%)
as colorless crystals: mp 159-162 °C; 1H NMR (CDCl3) δ 2.43
(3H, s), 5.49 (2H, s), 6.59 (1H, d, J ) 8 Hz), 6.67 (1H, t, J ) 8
Hz), 7.08 (1H, t, J ) 8 Hz), 7.30 (1H, s), 7.58 (2H, d, J ) 8
Hz), 7.71 (1H, d, J ) 8 Hz). Anal. (C15H12Br2N2O) C, H, N.
Meth od K. 8-[(2,6-Dich lor o-3-m eth oxyben zyl)oxy]-2-
m eth ylim id a zo[1,2-a ]p yr id in e (22e). To a solution of 2,6-
dichloro-3-methoxybenzoic acid (1.3 g, 5.88 mmol) in dry THF
(26 mL) was added 10 M borane-methyl sulfide complex (1.18
mL, 11.76 mmol) under nitrogen at ambient temperature. The
reaction mixture was refluxed for 10 h and cooled. The
mixture was acidified with 1 N HCl and extracted three times
with AcOEt. The organic layer was washed with saturated
aqueous sodium bicarbonate and brine, dried, and evaporated
in vacuo. The residue was purified by flash silica gel column
chromatography, eluting with hexane-AcOEt (3:1) followed
by crystallization from hexane to give 2,6-dichloro-3-methoxy-
benzyl alcohol (973 mg, 79.6%) as colorless crystals: mp 99-
F igu r e 2. Suggested pharmacophore model for the interac-
tions between the antagonists and B2 receptors.
Compound 15b was prepared following a procedure similar
to method H.
Meth od I. 3-Br om o-8-[[(2,6-d ich lor op h en yl)oxy]m eth -
yl]-2-m eth ylim id a zo[1,2-a ]p yr id in e (17). To a solution of
16 (200 mg, 0.837 mmol) and triethylamine (118 mg, 1.17
mmol) in dry CH2Cl2 (4 mL) was added methanesulfonyl
chloride (105 mg, 0.921 mmol) cooled in an ice-water bath
under nitrogen. After 30 min of stirring, the reaction mixture
was washed with water, saturated aqueous sodium bicarbon-
ate, and brine, dried, and evaporated in vacuo. The residue
was crystallized from ether to give 3-bromo-8-[(methanesulfo-
nyloxy)methyl]-2-methylimidazo[1,2-a]pyridine (172 mg, 64.8%)
as colorless crystals: mp 104-106 °C; 1H NMR (CDCl3) δ 2.49
(3H, s), 3.16 (3H, s), 5.15 (2H, s), 6.98 (1H, t, J ) 8 Hz), 7.39
(1H, d, J ) 8 Hz), 8.09 (1H, d, J ) 8 Hz).
To a solution of the above methanesulfonate (100 mg, 0.313
mmol) and 2,6-dichlorophenol (57 mg, 0.347 mmol) in DMF (1
mL) was added potassium carbonate (130 mg, 0.942 mmol) at
ambient temperature. After 2 h of stirring, to the mixture was
added water and this mixture was extracted with CH2Cl2. The
organic layer was washed with brine, dried, and evaporated
in vacuo. The residue was crystallized from EtOH to give 17
(82 mg, 82.0%) as colorless crystals: mp 158-159 °C; 1H NMR
(CDCl3) δ 2.47 (3H, s), 5.51 (2H, s), 6.91-7.10 (2H, m), 7.32
(2H, d, J ) 9 Hz), 7.67 (1H, d, J ) 8 Hz), 8.03 (1H, d, J ) 8
Hz). Anal. (C15H11BrCl2N2O) C, H, N.
1
101 °C; H NMR (CDCl3) δ 2.12 (1H, br s), 3.90 (3H, s), 4.98
(2H, s), 6.86 (1H, d, J ) 9 Hz), 7.30 (1H, d, J ) 9 Hz).
Following a procedure similar to method I, the title compound
was obtained in 66.3% yield from 21 and the above alcohol as
colorless crystals after crystallization from ether: mp 179-
180 °C; 1H NMR (CDCl3) δ 2.43 (3H, s), 3.91 (3H, s), 5.48 (2H,
s), 6.70 (1H, d, J ) 8 Hz), 6.82 (1H, t, J ) 8 Hz), 6.92 (1H, d,
J ) 9 Hz), 7.31 (1H, d, J ) 9 Hz), 7.72 (1H, d, J ) 8 Hz).
Anal. (C16H17Cl2N2O2) C, H, N.
Compounds 22d and 28b were prepared following a proce-
dure similar to method K.
Meth od L. 2,6-Dich lor o-3-n itr oben zaldeh yde (25). Con-
centrated sulfuric acid (17.1 mL, 0.321 mol) was added
dropwise to 70% nitric acid (24.3 mL, 0.383 mol) for 40 min in
an ice-water bath kept below 10 °C. This mixture was added
to a solution of 2,6-dichlorobenzaldehyde (24) (50.4 g, 0.288
mol) in concentrated sulfuric acid (250 mL) dropwise for 1 h
and cooled in an ice-water bath. The mixture was stirred at
same temperature for 1.5 h and poured into ice-water (1.5 L)
slowly. This mixture was stirred at ambient temperature for
30 min. The precipitate was collected by vacuum filtration
and washed with water to give 25 (61.0 g, 96.2%) as yellow
crystals: mp 73-74 °C; 1H NMR (CDCl3) δ 7.57 (1H, d, J ) 9
Hz), 7.90 (1H, d, J ) 9 Hz), 10.44 (1H, s). Anal. (C7H3Cl2-
NO3) C, H, N.
Compounds 22b and 28a were prepared following a proce-
dure similar to method I.
(E)-8-[2-(2,6-Dich lor oph en yl)eth en yl]-2-m eth ylim idazo-
[1,2-a ]p yr id in e (19). A suspension of 60% sodium hydride
in oil (15 mg, 0.374 mmol) in dry DMSO (1 mL) was stirred at
60 °C for 1 h and cooled to ambient temperature under
nitrogen. To this mixture was added (2,6-dichlorobenzyl)-
triphenylphosphonium bromide (188 mg, 0.374 mmol), and the
mixture was stirred at ambient temperature for 30 min.
2-Methylimidazo[1,2-a]pyridine-8-carboxaldehyde (18)19a (50
mg, 0.310 mmol) was added therein, and the mixture was
stirred for 3 h. The mixture was poured into water and
extracted three times with AcOEt. The combined organic
layers were washed with water and brine, dried, and evapo-
rated in vacuo. The residue was purified by preparative thin
layer chromatography to give 19 (64 mg, 65.7%) as a colorless
oil: 1H NMR (CDCl3) δ 2.50 (3H, s), 6.78 (1H, t, J ) 8 Hz),
7.06-7.41 (4H, m), 7.55 (1H, d, J ) 16 Hz), 8.00 (1H, d, J )
Compound 35 was prepared following a procedure similar
to method L.
2,6-Dich lor o-3-n itr oben zyl Alcoh ol (26a ). To a solution
of 25 (50 g, 0.227 mol) in MeOH (250 mL) was added sodium
borohydride (3.43 g, 0.091 mol) portionwise below 10 °C in an
ice-water bath under nitrogen. The reaction mixture was
stirred at the temperature for 1 h. To the ice-cooled mixture
were added dropwise saturated aqueous solution ammonium
chloride (125 mL) and water (125 mL). After 30 min the

576 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Abe et al.
precipitate was collected by vacuum filtration and washed with
water to give 26a (46.8 g, 92.9%) as yellow crystals: mp 107-
108 °C; 1H NMR (CDCl3) δ 2.18 (1H, t, J ) 8 Hz), 5.07 (2H, d,
J ) 8 Hz), 7.50 (1H, d, J ) 9 Hz), 7.73 (1H, d, J ) 9 Hz).
Anal. (C7H5Cl2NO3) C, H, N.
crystals: mp 184-187 °C; 1H NMR (CDCl3) δ 2.44 (3H, s), 2.91
(3H, d, J ) 6 Hz), 4.46 (1H, m), 5.46 (2H, s), 6.63 (1H, d, J )
9 Hz), 6.71 (1H, d, J ) 7.5 Hz), 6.83 (1H, t, J ) 7.5 Hz), 7.24
(1H, d, J ) 9 Hz), 7.73 (1H, d, J ) 7.5 Hz). Anal. (C16H14
-
BrCl2N3O) C, H, N.
8-[(3-Am in o-2,6-d ich lor oben zyl)oxy]-3-br om o-2-m eth -
ylim id a zo[1,2-a ]p yr id in e Hyd r och lor id e (30a ). A suspen-
sion of 29a (2.22 g, 5.15 mmol) and iron (powder, 1.15 g, 20.6
mmol) in a mixture of concentrated HCl (9 mL) and MeOH (9
mL) was refluxed for 30 min. After cooling, the mixture was
poured into cooled 1 N HCl (9 mL). The precipitates were
collected and washed with water. The crystals were triturated
with MeCN to give 30a (1.74 g, 77.2%) as an off-white solid:
mp 186-187 °C; 1H NMR (DMSO-d6) δ 2.42 (3H, s), 5.48 (2H,
s), 6.95 (1H, d, J )8 Hz), 7.24 (1H, d, J ) 8 Hz), 7.42 (1H, t,
J ) 8 Hz), 7.62 (1H, d, J ) 8 Hz), 8.25 (1H, d, J ) 8 Hz).
Anal. (C15H12BrCl2N3O‚HCl) C, H, N.
Meth od M. 3-Br om o-8-[[2,6-d ich lor o-3-(N-m eth yla c-
e t a m id o)b e n zyl]oxy]-2-m e t h ylim id a zo[1,2-a ]p yr id in e
(32a ). To a solution of 31a (222 mg, 0.5 mmol) in dry DMF (2
mL) was added 60% sodium hydride in oil (24 mg, 0.6 mmol)
in one portion at ambient temperature. The mixture was
stirred at the same temperature for 30 min, and iodomethane
(142 mg, 1.0 mmol) was added therein. After 30 min of
stirring, the mixture was poured into water and extracted with
AcOEt. The extracts were washed with water and brine, dried,
and evaporated in vacuo. The residue was purified by flash
silica gel column chromatography, eluting with hexane-AcOEt
(3:1) followed by crystallization from isopropyl ether to give
32a (135 mg, 58.9%) as colorless crystals: mp 201-204 °C;
1H NMR (CDCl3) δ 1.88 (3H, s), 2.46 (3H, s), 3.19 (3H, s), 5.52
(2H, s), 6.72 (1H, d, J ) 8 Hz), 6.87 (1H, t, J ) 8 Hz), 7.31
(1H, d, J ) 8 Hz), 7.48 (1H, d, J ) 8 Hz), 7.80 (1H, d, J ) 8
Hz). Anal. (C18H16BrCl2N3O2) C, H, N.
3-Br om o-8-[[2,6-d ich lor o-3-[N-(m eth oxylca r bon yl)-N-
m et h yla m in o]b en zyl]oxy]-2-m et h ylim id a zo[1,2-a ]p yr i-
d in e (37a ). To a solution of 36 (100 mg, 0.24 mmol) and
4-(dimethylamino)pyridine (44 mg, 0.36 mmol) in dry CH2Cl2
(2 mL) was added methyl chlorocarbonate (45 mg, 0.48 mmol)
in portions at ambient temperature under nitrogen. The
mixture was stirred for 1 day, and the reaction mixture was
washed with water, saturated aqueous sodium bicarbonate,
and brine, dried, and evaporated in vacuo. The residue was
purified by flash silica gel column chromatography (CH2Cl2-
AcOEt, 10:1) followed by crystallization from ether to give 37a
(107 mg, 94.0%) as colorless crystals: mp 178-179 °C; 1H
NMR (CDCl3) δ 2.48 (3H, s), 3.22 (3H, s), 3.65 (3H, s), 5.49
(2H, s), 6.78 (1H, br d, J ) 7.5 Hz), 6.90 (1H, t, J ) 7.5 Hz),
7.25 (1H, d, J ) 9 Hz), 7.39 (1H, d, J ) 9 Hz), 7.79 (1H, d, J
) 7.5 Hz). Anal. (C18H16BrCl2N3O3) C, H, N.
Meth od N. 3-Br om o 8-[[2,6-d ich lor o-3-(N-m eth yl-N-
[[(4-n itr op h en yl)oxy]ca r bon yl]ben zyl]oxy]-2-m eth ylim i-
d a zo[1,2-a ]p yr id in e (37c). To a solution of 36 (100 mg, 0.16
mmol) in dry pyridine (0.5 mL) and dry CH2Cl2 (2 mL) was
added p-nitrophenyl chlorocarbonate (40 mg, 0.20 mmol) in
portions at ambient temperature under nitrogen. The mixture
was stirred for 1 h, washed with water, saturated aqueous
sodium bicarbonate, and brine, dried, and evaporated in vacuo.
The residue was crystallized from ether to give 37c (84 mg,
88.3%) as pale yellow crystals: mp 229-230 °C; 1H NMR
(CDCl3-CD3OD) δ 2.41 (3H, s), 3.32 (3H, s), 5.49 (1H, d, J )
10 Hz), 5.57 (1H, d, J ) 10 Hz), 6.73 (1H, d, J ) 7.5 Hz), 6.88
(1H, t, J ) 7.5 Hz), 7.19-7.57 (4H, m), 7.78 (1H, d, J ) 7.5
Hz), 8.20 (2H, d, J ) 10 Hz), 7.79 (1H, d, J ) 7.5 Hz). Anal.
(C23H17BrCl2N4O5) C, H, N.
Compounds 32b,c, 40, 43a -c, and 45d were prepared
following a procedure similar to method M.
Compounds 37b and 37d ,e were prepared following a
procedure similar to method N.
3-Br om o-8-[[2,6-d ich lor o-3-(N-eth yl-N-m eth yla m in o)-
ben zyl]oxy]-2-m eth ylim id a zo[1,2-a ]p yr id in e (33). To a
solution of 32a (100 mg, 0.242 mmol) in dry THF (2 mL) was
added 10 M borane-methyl sulfide complex (0.07 mL, 0.726
mmol) under nitrogen at ambient temperature. The reaction
mixture was refluxed for 1 h and cooled. The mixture was
acidified with 1 N HCl and refluxed for 15 min. The cooled
reaction mixture was neutralized with saturated aqueous
solution of sodium bicarbonate and extracted with CH2Cl2. The
organic layer was washed with water and brine, dried, and
evaporated in vacuo. The residue was purified by flash
silica gel column chromatography, eluting with hexane-AcOEt
(5:1) to give 33 (67 mg, 62.7%) as a colorless oil: 1H NMR
(CDCl3) δ 1.13 (3H, t, J ) 8 Hz), 2.43 (3H, s), 2.75 (3H, s),
3.00-3.11 (2H, m), 5.50 (2H, s), 6.71 (1H, br d, J ) 8 Hz),
6.86 (1H, br t, J ) 8 Hz), 7.09 (1H, br d, J ) 8 Hz), 7.23-7.31
(1H, m), 7.70 (1H, d, J ) 8 Hz). Anal. (C18H18BrCl2N3O) C,
H, N.
3-Br om o-8-[[2,6-dich lor o-3-(N-m eth yl-N′-m eth ylu r eido)-
ben zyl]oxy]-2-m eth ylim id a zo[1,2-a ]p yr id in e (38). A mix-
ture of 37c (63 mg, 0.109 mmol) and 30% solution of methyl-
amine in MeOH (2 mL) was heated under reflux for 3 h. After
addition of another 30% solution of methylamine in MeOH (1
mL), the mixture was heated under reflux for additional 1 h.
The reaction mixture was evaporated in vacuo, and the residue
was extracted with AcOEt. The extract was evaporated in
vacuo, and the residue was purified by preparative thin-layer
chromatography (CH2Cl2-MeOH, 20:l) followed by crystal-
lization from ether to give 38 (28 mg, 56.0%) as colorless
crystals: mp 192-193 °C; 1H NMR (CDCl3) δ 2.42 (3H, s), 2.79
(3H, d, J ) 5 Hz), 3.20 (3H, s), 4.20 (1H, br d, J ) 5 Hz), 5.49
(2H, s), 6.71 (1H, d, J ) 7.5 Hz), 6.85 (1H, t, J ) 7.5 Hz), 7.32
(1H, d, J ) 9 Hz), 7.42 (1H, d, J ) 9 Hz), 7.78 (1H, d, J ) 7.5
Hz). Anal. (C18H17BrCl2N4O2) C, H, N.
8-[(3-Am in o-2,4,6-t r ich lor ob e n zyl)oxy]-3-b r om o-2-
m eth ylim id a zo[1,2-a ]p yr id in e (30b). A suspension of 29b
(1.50 g, 3.22 mmol) and iron (powder, 899 mg, 16.1 mmol) in
a mixture of acetic acid (12 mL) and EtOH (6 mL) was refluxed
for 40 min. After cooling, the mixture was filtered and washed
with CH2Cl2-MeOH (4:1). The filtrate was evaporated in
vacuo. The residue was partitioned between CH2Cl2-MeOH
(10:1) and saturated aqueous sodium bicarbonate. The organic
layer was dried and evaporated in vacuo. The residue was
crystallized from EtOH to give 30b (1.33 g, 94.8%) as an off-
white powder: mp 217-219 °C; 1H NMR (DMSO-d6) δ 2.30
(3H, s), 5.35 (2H, s), 6.99 (1H, d, J ) 8 Hz), 7.58 (1H, s), 7.92
(1H, t, J ) 8 Hz). Anal. (C15H11BrCl3N3O) C, H, N.
3-Br om o-8-[[2,6-d ich lor o-3-(m eth yla m in o)ben zyl]oxy]-
2-m eth ylim id a zo[1,2-a ]p yr id in e (36). To a suspension of
32a (560 mg, 1.23 mmol) in dry MeOH (2 mL) was added 28%
sodium methoxide in MeOH (1.93 g, 10 mmol) at ambient
temperature under nitrogen. The mixture was refluxed for 3
days and cooled. The precipitated solid was filtered, washed
with MeOH, and dried to give 36 (350 mg, 77.0%) as colorless
3-Br om o-8-[[3-[N-(h yd r oxya cetyl)-N-m eth yla m in o]-2,6-
dich lor oben zyl]oxy]-2-m eth ylim idazo[1,2-a ]pyr idin e (39).
A mixture of 37e (1.42 g, 2.76 mmol), potassium carbonate
(761 mg, 5.51 mmol) in MeOH (7 mL), and THF (7 mL) was
stirred at ambient temperature for 1 h. The mixture was
partitioned between CH2Cl2 and water. The aqueous layer was
extracted with twice CH2Cl2. The combined organic layers
were washed with brine, dried, and evaporated in vacuo. The
residue was crystallized from EtOH to give 39 (1.16 g, 89.2%)
as colorless crystals: mp 217-218 °C; 1H NMR (CDCl3) δ 2.45
(3H, s), 3.19-3.32 (4H, m), 3.69 (1H, d, J ) 15 Hz), 3.82 (1H,
d, J ) 15 Hz), 5.50 (2H, s), 6.70 (1H, d, J ) 8 Hz), 6.83 (1H,
t, J ) 8 Hz), 7.29 (1H, d, J ) 9 Hz), 7.49 (1H, d, J ) 9 Hz),
7.78 (1H, d, J ) 8 Hz). Anal. (C18H16BrCl2N3O3) C, H, N.
Meth od O. 3-Br om o-8-[[2,6-d ich lor o-3-[N-(p h th a lim i-
d oa cetyl)a m in o]ben zyl]oxy]-2-m eth ylim id a zo[1,2-a ]p y-
r id in e (42a ). To a mixture of 30a (15.0 g, 34.2 mmol),
4-(dimethylamino)pyridine (418 mg, 3.42 mmol), dry pyridine
(40 mL), and N-methylpyrrolidone (120 mL) was added N-
phthaloylglycyl chloride (41a ) (11.5 g, 51.3 mmol) at ambient

Non-Peptide Bradykinin B2 Receptor Antagonists
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4 577
temperature under nitrogen. The reaction mixture was stirred
at 50 °C for 2 h. To the mixture was added water (160 mL)
dropwise in an ice-water bath. The precipitated solid was
collected by vacuum filtration, washed with water, and dried
in vacuo. To the solid was added MeOH (160 mL), and the
mixture was stirred for 2 h. The solid was collected by vacuum
filtration and washed with MeOH to give 42a (19.1 g, 95.0%)
as pale brown crystals: mp 245-246 °C; 1H NMR (CDCl3-
CD3OD) δ 2.41 (3H, s), 4.71 (2H, s), 5.39 (2H, s), 7.10-7.31
(3H, m), 7.77-7.88 (3H, m), 7.90-8.01 (2H, m), 8.10 (1H, d, J
) 9 Hz). Anal. (C25H17BrCl2N4O4) C, H, N.
at ambient temperature for 1 h. The reaction mixture was
washed with aqueous sodium bicarbonate solution, water, and
brine. The organic layer was dried and evaporated in vacuo.
The residue was purified by flash silica gel column chroma-
tography, eluting CH2Cl2-MeOH (50:l) and crystallized from
AcOEt. The crystals were recrystallized from MeCN to give
49 (472 mg, 80.0%) as colorless crystals: mp 175-177 °C; 1H
NMR (CDCl3) δ 2.32 (6H, s), 2.43 (3H, s), 2.96 (2H, s), 3.25
(3H, s), 3.55 (1H, dd, J ) 18, 4 Hz), 3.85 (1H, dd, J ) 18, 4
Hz), 5.50 (2H, s), 6.71 (1H, d, J ) 8 Hz), 6.86 (1H, t, J ) 8
Hz), 7.32 (1H, d, J ) 9 Hz),7.49 (1H, d, J ) 9 Hz), 7.78 (1H, d,
J ) 8 Hz), 7.89 (1H, br t, J ) 4 Hz); IR (KBr) 3356, 2944,
Compounds 42b,c were prepared following a procedure
similar to method O.
2856, 2828, 2774, 1684, 1666, 1546, 1512. Anal. (C22H24
BrCl2N5O3) C, H, N.
-
Meth od P . 8-[[3-(N-Am in oa cetyl-N-m eth yla m in o)-2,6-
d ich lor oben zyl]oxy]-3-br om o-2-m eth ylim id a zo[1,2-a ]p y-
r id in e (44a ). To a suspension of 43a (450 mg, 0.748 mmol)
in EtOH (4.5 mL) was added hydrazine monohydrate (56 mg,
1.12 mmol) at ambient temperature, and the mixture was
refluxed for 1 h. After the reaction mixture was cooled, the
precipitates formed were filtered off. The filtrate was evapo-
rated in vacuo, CH2Cl2 was added to the residue, and precipi-
tates were filtered off. The filtrate was evaporated in vacuo,
and the residue was crystallized from ether to give 44a (338
mg, 95.8%) as colorless crystals: mp 175-178 °C; 1H NMR
(CDCl3) δ 2.43 (3H, s), 2.92-3.20 (2H, m), 3.23 (3H, s), 5.49
(2H, s), 6.70 (1H, d, J ) 8 Hz), 6.83 (1H, t, J ) 8 Hz), 7.29
(1H, d, J ) 9 Hz), 7.47 (1H, d, J ) 9 Hz), 7.79 (1H, d, J ) 8
Met h od S. 3-Br om o-8-[[2,6-d ich lor o-3-[N-[(N′-et h yl-
u r eid o)a cetyl]-N-m eth yla m in o]ben zyl]oxy]-2-m eth ylim i-
d a zo[1,2-a ]p yr id in e (50b). To a solution of 44a (100 mg,
0.212 mmol) in dry CH2Cl2 (2 mL) was added ethyl isocyanate
(45 mg, 0.636 mmol) at ambient temperature under nitrogen.
The reaction mixture was stirred for 1 h and evaporated in
vacuo. The residue was crystallized from AcOEt and recrys-
tallized from MeCN to give 50b (94 mg, 83.5%) as colorless
crystals: mp 171-173 °C; 1H NMR (CDCl3) δ 1.20 (3H, t, J )
8 Hz), 2.42 (3H, s), 3.09-3.33 (5H, m), 3.56 (1H, dd, J ) 17, 5
Hz), 3.80 (1H, dd, J ) 17, 5 Hz), 4.71 (1H, br t, J ) 5 Hz), 5.49
(2H, s), 6.71 (1H, d, J ) 8 Hz), 6.88 (1H, t, J ) 8 Hz), 7.31
(1H, d, J ) 9 Hz), 7.46 (1H, d, J ) 9 Hz), 7.78 (1H, d, J ) 8
Hz); IR (KBr) 3328, 3043, 3003, 2970, 2930, 2872, 1667, 1642,
1566, 1547. Anal. (C21H22BrCl2N5O3) C, H, N.
Hz); MS (FAB) m/ z 471, 473 (M + 1). Anal. (C18H17
BrCl2N4O2) C, H, N.
-
Compounds 44b,c were prepared following a procedure
similar to method P.
Compounds 50a and 50c were prepared following a proce-
dure similar to method S.
Meth od Q. 8-[[3-[N-(Acetam idoacetyl)-N-m eth ylam in o]-
2,6-dich lor oben zyl]oxy]-3-br om o-2-m eth ylim idazo[1,2-a ]-
p yr id in e Hyd r och lor id e (46). To a suspension of 45a (190
mg, 0.37 mmol) in MeOH (1.9 mL) was added 10% hydrogen
chloride in MeOH (0.5 mL) at ambient temperature. After 5
min of stirring, the solution was evaporated in vacuo. The
residue was crystallized from MeCN-AcOEt, and the product
was recrystallized from acetone-water to give 46 (136 mg,
66.8%) as colorless crystals: mp 179-180 °C; 1H NMR (DMSO-
d6) δ 1.83 (3H, s), 2.40 (3H, s), 3.12 (3H, s), 3.37 (1H, dd, J )
16, 5 Hz), 3.67 (1H, dd, J ) 16, 5 Hz), 5.59 (2H, s), 7.31-7.78
(4H, m), 8.10 (1H, t, J ) 5 Hz), 8.25 (1H, d, J ) 8 Hz). Anal.
(C20H19BrCl2N4O3‚HCl) C, H, N.
Biologica l Meth od s. Recep tor bin d in g: Gu in ea P ig
Ileu m . The specific binding of [3H]BK (a high affinity B2
ligand) was assayed according to the method previously
described26 with minor modifications. Male Hartley guinea
pigs (from Charles River J apan, Inc.) were killed by exsan-
guination under anesthesia. The ilea were removed and
homogenized in ice-cold buffer (50 mM sodium (trimethylami-
no)ethanesulfonate (TES) and 1 mM 1,10-phenanthroline, pH
6.8) with a Polytron. The homogenate was centrifuged to
remove cellular debris (1000g, 20 min, 4 °C), and the super-
natant was centrifuged (100000g, 60 min, 4 °C). Then, the
pellet was resuspended in ice-cold assay buffer (50 mM TES,
1 mM 1,10-phenanthroline, 140, µg mL-1 bacitracin, 1 mM
dithiothreiol, 1 µM captopril, and 0.1% bovine serum albumin
(BSA), pH 6.8) and was stored at -80 °C until use.
Compounds 48a ,b, 48d , 51a , and 5lc were prepared follow-
ing a procedure similar to method Q.
In the binding assay, membranes (0.2 mg of protein mL-1
)
Meth od R. 3-Br om o-8-[[2,6-d ich lor o-3-[N-(m eth a n e-
su lfon a m id oa cetyl)-N-m eth yla m in o]ben zyl]oxy]-2-m eth -
ylim id a zo[1,2-a lp yr id in e (47a ). To a solution of 44a (100
mg, 0.212 mmol) and triethylamine (32 mg, 0.316 mmol) in
dry CH2Cl2 (2 mL) was added methanesulfonyl chloride (27
mg, 0.236 mmol) cooled in an ice-water bath under nitrogen.
The reaction mixture was stirred at the same temperature for
30 min and stirred at ambient temperature for 1 h. The
reaction mixture was washed with water, saturated aqueous
sodium bicarbonate, and brine, dried, and evaporated in vacuo.
The residue was purified by flash silica gel column chroma-
tography (CH2Cl2-MeOH, 30:1) to give 47a (103 mg, 88.3%)
as a colorless amorphous solid: 1H NMR (CDCl3) δ 2.45 (3H,
s), 2.97 (2.7H, s), 3.02 (0.3H, s), 3.27 (2.7H, s), 3.30 (0.3H, s),
3.50 (1H, dd, J ) 16, 5 Hz), 3.67 (1H, dd, J ) 16, 5 Hz), 5.18
(1H, m), 5.51 (2H, s), 6.71 (1H, d, J ) 8 Hz), 6.87 (1H, t, J )
8 Hz), 7.32 (1H, d, J ) 9 Hz), 7.51 (1H, d, J ) 9 Hz), 7.78 (1H,
d, J ) 8 Hz). Anal. (C19H19BrCl2N4O4S) C, H, N.
were incubated with [3H]BK (final concentration 0.06 nM) and
varying concentrations of test compounds or unlabeled BK at
room temperature for 60 min. Receptor-bound [3H]BK was
harvested by filtration through Whatman GF/B glass fiber
filters under reduced pressure, and the filter was washed five
times with 300 µL of ice-cold buffer (50 mM Tris-HCl). The
radioactivity retained on the washed filter was measured with
a liquid scintillation counter. Specific binding was calculated
by subtracting the nonspecific binding (determined in the
presence of 1 µM unlabeled BK) from total binding.
BK-In du ced Br on ch ocon str iction in Gu in ea P igs. Male
Hartley guinea pigs weighing 470-750 g (from Charles River
J apan, Inc.) were fasted overnight and anesthetized by intra-
peritoneal injection of sodium pentobarbital (30 mg kg-1), and
the trachea, jugular vein, and esophagus were cannulated. The
animals were ventilated at a tidal volume of 10 mL kg-1 with
a frequency of 60 breaths min-1 through the tracheal cannula.
To suppress spontaneous respiration, alcuronium chloride (0.5
mg kg-1) was administered intravenously through the jugular
vein cannula. Then, propranolol (10 mg kg-1) was also
Compounds 47b-d were prepared following a procedure
similar to method R.
3-Br om o-8-[[2,6-d ich lor o-3-[N-(N,N-d im et h ylglycyl)
glycyl-N-m eth yla m in o]ben zyl]oxy]-2-m eth ylim id a zo[1,2-
a ]p yr id in e (49). To a solution of 44a (500 mg, 1.06 mmol)
and triethylamine (160 mg, 1.59 mmol) in dry CH2Cl2 (5 mL)
was added dropwise bromoacetyl chloride (183 mg, 1.16 mmol)
at -60 °C in a dry ice-acetone bath under nitrogen. After 20
min, to the mixture was added 50% dimethylamine-H2O
solution (0.96 mL, 10.6 mmol), and this mixture was stirred
administered subcutaneously. After 10 min, BK (5 µg kg-1
,
dissolved in saline with 0.1% BSA) was administered intra-
venously through the jugular vein cannula. Bronchoconstric-
tion was measured by the modified Konzett and Rossler
method as the peak increase of pulmonary insufflation pres-
sure (PIP).27 Each dose of the compound suspended in 0.5%
methylcellulose solution or vehicle was administered through

578 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 4
Abe et al.
(11) Cheronis, J . C.; Whalley, E. T.; Nguyen, K. T.; Eubanks, S. R.;
Allen, L. G.; Duggan, M. J .; Loy, S. D.; Bonham, K. A.; Blodgett,
J . K. A New Class of Bradykinin Antagonists: Synthesis and
In Vitro Activity of Bissuccinimidoalkane Peptide Dimers. J .
Med. Chem. 1992, 35, 1563-1572.
(12) Kyle, D. J .; Martin, J . A.; Burch, R. M.; Carter, J . P.; Lu, S.;
Meeker, S.; Prosser, J . C.; Sullivan, J . P.; Togo, J .; Noronha-
Blob, L; Sinsko, J . A.; Walters, R. F.; Whaley, L. W.; Hiner, R.
N. Proving The Bradykinin Receptor: Mapping The Geometric
Topography Using Ethers of Hydroxyproline in Novel Peptides.
J . Med. Chem. 1991, 34, 2649-2653.
(13) Kyle, D. J . Structure-Based Drug Design: Progress Toward The
Discovery of The Elusive Bradykinin Receptor Antagonists. Curr.
Pharm. Des. 1995, 1, 233-254.
(14) Burch, R. M.; Farmer, S. G.; Steranka, L. R. Bradykinin Receptor
Antagonists. Med. Res. Rev. 1990, 10, 237-269.
the oesophageal cannula after the first BK-induced bronchoc-
onstriction. After 30 min, BK was administered again and
the bronchoconstriction was measured in the same manner.
A 0% response was determined as PIP before the administra-
tion of BK and the 100% response was determined as the first
BK-induced bronchoconstriction before drug administration.
The percent response was calculated from the following
formula: % response ) (∆PIPafter drug/∆PIPbefore drug) × 100.
Sta tistica l An a lysis. The results are expressed as the
mean ( SEM, and statistical significance of between groups
was analyzed by Student’s t test. IC50 or ED50 value was
obtained by using the nonlinear curve-fitting methods with a
specific computer program made by our company’s engineer.
Mea su r em en t of P la sm a Level a n d Bioa va ila bility.
Male Sprague-Dawley rats (3) were starved overnight and
dosed orally with the compound as a solution in 0.5% methocel
(0.5 mL/100 g). Blood was taken from the femoral artery at
0, 0.5, 1, 2, 4, and 6 h after dosing. In the intravenous studies,
compounds were dissolved in DMSO and injected intrave-
nously in the femoral vein (dose volume ) 0.05 mL). Blood
was taken from the femoral artery at 0, 5, 15, and 30 min and
1, 2, 4, and 6 h after dosing. Blood was centrifuged and plasma
collected. A 100 µL plasma sample was extracted by 4 mL of
CHCl3 for 5 min followed by centrifugation at 700g for 5 min.
The organic layer was removed and evaporated to dryness
under nitrogen at 30 °C. The residue was reconstituted with
100 µL of MeOH and a 20 µL aliquot injected onto the HPLC
system. The parent compound was quantitated from the area
of the corresponding peak, relative to the standard (plasma
sample at time 0 min, spiked with varying concentrations of
the compound).
(15) Stewart, J . M. Bradykinin Antagonists: Development and
Applications. Biopolymers 1995, 37, 143-155.
(16) Calixto, J . B.; Yunes, R. A.; Rae, G. A.; Medeiros, Y. S.
Nonpeptide Bradykinin Antagonists. In Bradykinin Antagonists,
Basic and Clinical Reset; Burch, R. M., Ed.; Marcel Dekker,
Inc.: New York, 1991; pp 97-129.
(17) (a) Salvino, J . M.; Seoane, P. R.; Douty, B. D.; Awad, M. M. A.;
Dolle, R. E.; Houck, W. T.; Faunce, D. M.; Sawurtz, D. G. Design
of Potent Non-Peptide Competitive Antagonists of the Human
Bradykinin B2 Receptor. J . Med. Chem. 1993, 36, 2583-2584.
(b) Hoyer, D.; Awad, M. M. A.; Salvino, J . M.; Seoane, P. R.;
Dolle, R. E.; Houck, W. T.; Sawurtz, D. G. ACE Inhibitors as a
Template for the Design of Bradykinin B2 Receptor Antagonists.
Bioorg. Med. Chem. Lett. 1995, 5, 367-370.
(18) Hand, E. S.; Paudler, W. W. Teleamination of the Imidazo[1,2-
a]pyridine System. J . Org. Chem. 1978, 43, 2900-2906.
(19) (a) Kaminski, J . J .; Bristol, J . A.; Puchalski, C.; Lovey, R. G.;
Elliott, A. J .; Guzik, H.; Solomon, D. M.; Conn, D. J .; Domalski,
M. S.; Wong, S.-C.; Gold, E. H.; Long, J . F.; Chiu, P. J . S.;
Steinberg, M.; McPhail, A. T. Antiulcer Agents. 1. Gastric
Antisecretory and Cytoprotective Properties of Substituted
Imidazo[1,2-a]pyridines. J . Med. Chem. 1985, 28, 876-892. (b)
Kaminski, J . J .; Hilbert, J . M.; Pramanik, B. N.; Solomon, D.
M.; Conn, D. J .; Rizvi, R. K.; Elliott, A. J .; Guzik, H.; Lovey, R.
G.; Domalski, M. S.; Wong, S.-C.; Puchalski, C.; Gold, E. H.;
Long, J . F.; Chiu, P. J . S.; McPhail, A. T. Antiulcer Agents. 2.
Gastric Antisecretory, Cytoprotective, and Metabolic Properties
of Substituted Imidazo[1,2-a]pyridines and Analogues. J . Med.
Chem. 1987, 30, 2031-2046.
(20) Virgil, S. C. N-Bromosuccinimide. In Encyclopedia of Reagents
for Organic Synthesis, Vol. 1; Paquette, L. A., Editor-in-Chief;
J ohn Wiley & Sons Ltd: Chichester, 1995; pp 768-773.
(21) Kaminski, J . J .; Puchalski, C.; Solomon, D. M.; Rizvi, R. K.; Conn,
D. J .; Elliott, A. J .; Lovey, R. G.; Guzik, H.; Chiu, P. J . S.; Long,
J . F.; McPhail, A. T. Antiulcer Agents. 4. Conformational
Considerations and the Antiulcer Activity of Substituted Imi-
dazo[1,2-a]pyridines and Related Analogues. J . Med. Chem.
1989, 32, 1686-1700.
(22) Asano, M.; Inamura, N.; Hatori, C.; Sawai, H.; Fujiwara, T.;
Katayama, A.; Kayakiri, H.; Satoh, S; Abe, Y.; Inoue, T.; Sawada,
Y.; Nakahara, K.; Oku, T.; Okuhara, M. The Identification of
an Orally Active, Non-peptide Bradykinin B2 Receptor Antago-
nist, FR173657. Br. J . Pharmacol. 1997, 120, 617-624.
(23) Gaussian 94, Revision E.1; Gaussian, Inc.: Carnegie Office Park,
Building 6, Pittsburgh, PA 15106.
Ack n ow led gm en t. We are grateful to Dr. I. Ar-
amori for his valuable suggestions.
Su p p or tin g In for m a tion Ava ila ble: The coordinates of
ab initio molecular orbital calculations of cis-/ trans-31a ′, cis-
/ trans-32a ′, and cis-/ trans-32b′ and physical data of 5b-e,
8, 9c, 10a -c, 13, 15b, 16, 20, 22b-d , 23a -e, 28a ,b, 29a ,b,
31a ,b, 32b,c, 35, 37b,d ,e, 40, 42b,c, 43a -c, 44b,c, 45a -d ,
47b,d , 48a -d , 50a ,c, and 51a ,c (20 pages). Ordering infor-
mation is given on any current masthead page.
Refer en ces
(1) Regoli, D.; Barabe´, J . Pharmacology of Bradykinin and Related
Kinins. Pharmacol. Rev. 1980, 32, 1-46.
(2) Marceau, F.; Lussier, A.; Regoli, D.; Giroud, J . P. Pharmacology
of Kinins: Their Relevance to Tissue Injury and Inflammation.
Gen. Pharmacol. 1983, 14, 209-229.
(3) Proud, D.; Kaplan, A. P. Kinin Formation: Mechanisms and Role
in Inflammatory Disorders. Annu. Rev. Immunol. 1988, 6,49-
83.
(4) Dray, A.; Parkins, M. Bradykinin and Inflammatory Pain.
Trends. Neurosci. 1993, 16, 99-104.
(5) Greaves, M. W. Inflammation and Mediators. Br. J . Dermatol.
1988, 119, 419-426.
(6) Bhoola, K. D.; Figueroa, C. D.; Worthy, K. Bioregulation of
Kinins: Kallikreins, Kininogens and Kininases. Pharmacol. Rev.
1992, 44, 1-80.
(24) J P patent 4-18091.
(25) Compound 50b was advanced for evaluation of binding activity
to human B2 receptors expressed on A-431 cells (human epider-
moid carcinoma), and showed an IC50 value of 3000 nM. It was
revealed that there was estrangement of binding affinity in
guinea pig ileum and human A-431 cell. Further optimization
to overcome this specific differences between human and guinea-
pigs will be reported in due course.
(26) Manning, D. C.; Vavrek, R.; Stewart, J . M.; Synder, S. H. Two
Bradykinin Binding Sites with Picomolar Affinities. J . Phar-
macol. Exp. Ther. 1986, 237, 504-512.
(27) Asano, M.; Inamura, N.; Nakahara, K.; Nagayoshi, A.; Isono,
T.; Hamada, K.; Oku, T.; Notsu, Y.; Kohsaka, M.; Ono, T. A
5-Lipoxygenase Inhibitor, FR110302, Suppresses Airway Hy-
perresponsiveness and Lung Eosinophilia Induced by Sephadex
Particles in Rats. Agents Actions 1992, 36, 215-221.
(7) Farmer, S. G.; Burch, R. M. The Pharmacology of Bradykinin
Receptors. In Bradykinin Antagonists: Basic and Clinical
Research; Burch, R. M., Ed.; Marcel Dekker, Inc.: New York,
1991; pp 1-31.
(8) McEachern, A. E.; Shelton, E. R.; Bhakta, S.; Obernolte, R.; Bach,
C.; Zuppan, P.; Fujisaki, J .; Aldrich, R. W.; J arnagin, K.
Expression Cloning of a Rat B2 Bradykinin Receptor. Proc. Natl.
Acad. Sci. U.S.A. 1991, 88, 7724-7728.
(9) Hock, F. J .; Wirth, K.; Albus, U.; Linz, W.; Gerhards, H. J .;
Wiemer, G.; Henke, S.; Breipohl, G.; Ko¨nig, W.; Knolle, J .;
Scho¨lkens, B. A. Hoe 140 A New Potent and Long Acting
Bradykinin-Antagonist: In Vitro Studies. Br. J . Pharmacol.
1991, 102, 769-773.
(10) Wirth, K.; Hock, F. J .; Albus, U.; Linz, W.; Alpermann, H. G.;
Anagnostopoulos, H.; Henke, St.; Breipohl, G.; Konig, W.; Knolle,
J .; Scho¨lkens, B. A. Hoe 140 A New Potent and Long Acting
Bradykinin-Antagonist: In Vivo Studies. Br. J . Pharmacol.
1991, 102, 774-777.
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