Selective angiotensin II AT2 receptor agonists: Arylbenzylimidazole structure-activity relationships

Article abstract of DOI:10.1021/jm0606185

Structural alterations in the 2- and 5-positions of the first drug-like selective angiotensin II AT₂ receptor agonist (1) have been performed. The imidazole ring system was proven to be a strong determinant for the AT₂ selectivity, and with few exceptions all variations gave good AT₂ receptor affinities and with retained high AT ₂/AT₁ selectivities. On the contrary to the findings with AT₁ receptor agonists, the impact of structural modifications in the 5-position of the AT₂ selective compounds were less pronounced regarding activation of the AT₂ receptor. The butyloxyphenyl (56) and the propylthienyl (50) derivatives were found to exert a high agonistic effect as deduced from their capacity to induce neurite elongation in neuronal cells, as does angiotensin II.

Full text of DOI:10.1021/jm0606185

7160
J. Med. Chem. 2006, 49, 7160-7168
Selective Angiotensin II AT2 Receptor Agonists: Arylbenzylimidazole Structure-Activity
Relationships
Xiongyu Wu,† Yiqian Wan,† A. K. Mahalingam,† A. M. S. Murugaiah,† Bianca Plouffe,‡ Milad Botros,§ Anders Karle´n,†
Mathias Hallberg,§ Nicole Gallo-Payet,*,‡ and Mathias Alterman*,†
Department of Medicinal Chemistry, BMC, Uppsala UniVersity, P.O. Box 574, SE-751 23 Uppsala, Sweden, SerVice of Endocrinology and
Department of Physiology and Biophysics, Faculty of Medicine, UniVersity of Sherbrooke, Sherbrooke J1H 5N4 (Quebec), Canada, and
Department of Biological Research on Drug Dependence, BMC, Uppsala UniVersity, P.O. Box 591, SE-751 23 Uppsala, Sweden
ReceiVed May 24, 2006
Structural alterations in the 2- and 5-positions of the first drug-like selective angiotensin II AT2 receptor
agonist (1) have been performed. The imidazole ring system was proven to be a strong determinant for the
AT2 selectivity, and with few exceptions all variations gave good AT2 receptor affinities and with retained
high AT2/AT1 selectivities. On the contrary to the findings with AT1 receptor agonists, the impact of structural
modifications in the 5-position of the AT2 selective compounds were less pronounced regarding activation
of the AT2 receptor. The butyloxyphenyl (56) and the propylthienyl (50) derivatives were found to exert a
high agonistic effect as deduced from their capacity to induce neurite elongation in neuronal cells, as does
angiotensin II.
Introduction
p44mapk activity is found associated with neuronal differentiation.
The activation of the p42/p44mapk pathway is essential to
promote neurite outgrowth and the ability of AT2 receptor
ligands to induce neurite outgrowth and can serve as a robust
AT2 agonist assay.14,15 The first nonpeptidic selective AT2
receptor agonist (1), that we reported recently, activates p42/
p44mapk as does Ang II.16
The agonist 1 was derived from the nonselective agonist 58
(L-162,313)17-19 after the nitrogen-containing heterocycle of the
latter had been altered (Figure 1). It is known from literature
that removal of a methyl group from the isobutyl side-chain of
the biphenyl analogue of 58 converts this AT1/AT2 nonselective
agonist to an AT1 antagonist (59, L-162,389).20 Furthermore,
if the terminal part of the propyl side chain of the latter
antagonist is replaced by a 3-methoxybenzyl group, the com-
pound is transformed into an AT1 selective agonist (60,
L-163,491).21 We previously observed that minor alterations of
the sulfonyl carbamate side chain of 58 had a dramatic negative
impact on the binding affinity to the AT2 receptor.19 Thus, it
seems apparent that relatively small structural modifications of
58 affect the biological outcome significantly.
Angiotensin II (Ang II), recognized as the most important
bioactive peptide of the rennin-angiotensin system, is the
endogenous activator of the AT1 and the AT2 receptors. The
AT1 receptor is closely associated with the regulation of blood
pressure, fluid, and electrolyte balance, but the role of the AT2
receptor is less clear due to the low level of AT2 expression in
healthy adults.1 One notable feature of the AT2 receptor is the
high level of expression in most fetal tissues, including the brain.
The AT2/AT1 receptor ratio decreases dramatically after birth,2,3
which may support a significant involvement of the AT2 receptor
in fetal development. In cells of neuronal origin, AT2 receptor
activation induces neurite outgrowth and modulates cell excit-
ability. In adults, activation of the AT2 receptor lowers blood
pressure, inhibitits cell proliferation, and induces programmed
cell death, extracellular matrix remodeling, and axonal regener-
ation.4-9 In addition, it has recently been demonstrated that
activation of the AT2 receptor stimulates alkaline secretion by
the duodenal mucosa in rats.10 However, most remarkably, the
AT2 receptor expression is up-regulated in pathological condi-
tions such as heart failure, renal failure, myocardial infarction,
brain lesions, vascular injury, and wound healing.7,11-13
The signaling pathways activated after AT2 receptor stimula-
tion are still controversial. This seven-transmembrane domain
receptor is not coupled to any of the classical, well established,
second messengers, such as cAMP or inositol phosphates, and
its coupling to a GRi protein, reported by several authors, is not
viewed in consensus.4-9 However, various mediators, which
could individually exert opposite effects, such as cGMP,
tyrosine, or serine/threonine phosphatases, and the extracellular
signal-regulated kinases p42/p44mapk have been associated with
activation of the AT2 receptor, depending on the cell types and
experimental conditions used. A sustained increase in p42/
Our preliminary study suggested that the imidazole ring of
the AT2 agonist 1 constitutes an important determinant for AT2
receptor selectivity.16 Herein, we report an extended SAR study
where the alkoxysulfonylamide and isobutyl groups as well as
the thienylphenyl scaffold of 1 were subjected to alterations.
Selective AT2 receptor ligands with a high agonistic potency
were identified.
Results
Chemistry. The thiopheneboronic acid 2, used as the starting
material for compounds 5-14 (Scheme 1), was prepared
essentially as described by Kevin et al.22,23 Thus, thiophene-2-
sulfonyl chloride was first converted to the N-tert-butylsulfon-
amide. Subsequent alkylation followed by selective 3-lithiation/
boronation delivered the key-intermediate 2. The 1-(4-bromo-
benzyl)-1H-imidazole 3 was obtained by N-alkylation of
imidazole with 4-bromobenzyl bromide, utilizing KOH as
base.16 The aryl bromide 3 was thereafter reacted with the
boronic acid 2 under Suzuki coupling conditions with Pd(PPh3)4
* Corresponding authors. E-mail: mathias.alterman@orgfarm.uu.se, Tel:
+46-18-4714905, Fax: +46-18-4714474; E-mail: nicole.gallo-payet@
usherbrooke.ca, Tel: +1-819-5645243, Fax: +1-819-5645292.
† Department of Medicinal Chemistry, Uppsala University.
‡ University of Sherbrooke.
§ Department of Biological Research on Drug Dependence, Uppsala
University.
10.1021/jm0606185 CCC: $33.50 © 2006 American Chemical Society
Published on Web 11/09/2006

SelectiVe Angiotensin II AT2 Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24 7161
Figure 1.
Scheme 1a
a Reagents and conditions: (a) Pd(PPh3)4, NaOH (aq), ethanol/ toluene, thermal heating or microwave heating; (b) TFA, anisole or BCl3 in CH2Cl2; (c)
acyl chloride (5-9), di-tert-butyl carbonate (10), with pyrrolidinopyridine, pyridine; (d) 4,4,4-triflurobutanol, CDI, DBU, THF; (e) butoxyacetic acid, CDI,
THF; (f) butyl isocyanate, acetone, NaOH; (g) butanesulfonyl chloride, NaOH, THF.
as the source of palladium and with KOH as base to give
compound 4.16 Deprotection of 4 by TFA or alternatively by
BCl3, a milder deprotecting reagent,24 delivered the primary
sulfonamide that was subsequently reacted with acyl chlorides
or alkyl chloroformates, at ambient temperature, in pyridine with
a 4-pyrrolidin-1-ylpyridine nucleophilic catalyst, to afford the
target compounds 5-9.
In the case where isobutyl chloroformate and isopropyl
chloroformate were employed, a reaction temperature of 50 °C
was required to obtain the compounds 7 and 9 in good yields.
For the preparation of compound 10, di-tert-butyl carbonate was
applied as the electrophile. In order to synthesize 11 with the
4,4,4-trifluorobutyloxy side chain, 4,4,4-trifluorobutanol was
first reacted with CDI in THF at 50 °C for 3.5 h, whereafter
this mixture was added to the deprotected sulfonamide in THF
with DBU, as base. Compound 11 was afforded in 64% yield.
The combination of CDI and DBU was also used for the
acylation with butoxyacetic acid in the preparation of compound
12. The amide 13 and the sulfone 14 were obtained by treating
the deprotected sulfonamide with NaOH and subsequent addition
of butyl isocyanate or butanesulfonyl chloride, respectively. As
outlined in Scheme 2, the introduction of the N-methyl-N-butyl-
amino side chain in compound 15 was accomplished by reacting
compound 6 with N-methylbutylamine at 90 °C for 3 h.

7162 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24
Wu et al.
Scheme 2
For the preparation of the target compounds 49-57 (Scheme
7) a series of different sulfonamides were required as precursors.
The N-tert-butyl-5-alkylthiophene-2-sulfonamides (Scheme 4)
were prepared by deprotonation of N-tert-butylthiophene-
sulfonamide with n-butyllithium and thereafter adding the proper
alkyl halides, to yield the compounds 24-26 in 45-81% yield.
To provide compound 27, 2-thiophene-2-ylethanol was first
reacted with methyl iodide and with sodium hydride as base
(Scheme 5). Compound 27 was thereafter slowly added to a
mixture of chlorosulfonic acid, phosphorus pentachloride, and
tert-butylamine to obtain compound 28 in 35% yield. The alkyl-
and alkoxyphenylsulfonamides (Scheme 6) were synthesized
from their corresponding alkyl- or alkoxyphenylsulfonyl chloride
(the isobutylphenylsulfonyl chloride was synthesized form
isobutylbenzene with chlorosulfonic acid) by reacting them with
tert-butylamine.
To synthesize compound 21, a sulfonamide-carbonyl switched
version of compound 5, thiophene was used as starting material
(Scheme 3). The lithiation of thiophene was conducted with
n-butyllithium, and isobutyl iodide was used as alkylating agent.
The reaction was sluggish and yielded only 30% of the
2-isobutylthiophene 16. A second lithiation and subsequent
treatment with tert-butyl isocyanate resulted in the tert-butyl
protected amide 17 in 70% yield. Compound 17 was converted
to the boronic acid 18 via lithiation and treatment with
triisopropyl borate and was subsequently reacted with 3 under
Suzuki conditions to obtain compound 19 in high yield. To
remove the tert-butyl protection of the amide, rather harsh
conditions were required. After 17 h of heating at 70 °C in TFA,
the deprotected primary amide 20 could be isolated in 83% yield.
The primary amide 20 was deprotonated with NaH and reacted
with butanesulfonyl chloride to obtain the carbonylsulfonyl
target compound 21.
The N-tert-butyl-aryl-sulfonamides 24-26, 28-32 were
converted to their corresponding boronic acids and subsequently
reacted with 3 under Suzuki conditions to obtain the compounds
41-48, in 20-96% yields (Scheme 7). Deprotection of tert-
24
butylsulfonamide by TFA or BCl3 delivered the primary
sulfonamide that was subsequently treated with butyl chloro-
formate or ethyl chloroformate, at ambient temperature, in
pyridine with 4-pyrrolidin-1-ylpyridine, to afford the target
compounds 49-57.
Binding Assays. Compounds 5-15, 21, 23, 49-57 were
evaluated in radioligand-binding assays by displacement of
[
125I]Ang II from AT1 receptors in rat liver membranes and from
The tetrazole analogue was prepared by dehydration of the
primary amide 20 with trifluoroacetic anhydride followed by
treatment of the obtained nitrile 22 with sodium azide and
Et3NHCl. This procedure provided the tetrazole compound 23
in high yield (Scheme 3).
AT2 receptors in pig uterus membranes as described previ-
ously.25,26 The natural substrate Ang II and the selective AT1
receptor antagonist losartan27 were used as reference substances.
The results are summarized in Table 1 and 2.
Scheme 3a
a Reagents and conditions: (a) n-BuLi, THF, 2-methylpropyl Iodide; (b) n-BuLi, THF, tert-butyl isocyanate; (c) n-BuLi, THF, triisopropyl borate; (d)
Pd(PPh3)4, NaOH (aq), ethanol/ toluene, 3; (e) TFA, anisole; (f) NaH, THF, butanesulfonyl chloride; (g) THF, pyridine, trifluorideacetic anhydride; (h)
NaN3, Et3NHCl, toluene.

SelectiVe Angiotensin II AT2 Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24 7163
Table 1
Scheme 4a
a Reagents and conditions: (a) n-BuLi, THF, iodo-butane (24), iodo-
propane (25), 1-bromomethyl-3-methoxy-benzene (26).
Scheme 5a
a Reagents and conditions: (a) MeI, NaH, THF; (b) ClSO3H, PCl5,
t-BuNH2.
Scheme 6a
a Reagents and conditions: (a) tert-butylamine, CH2Cl2
In the first series, the effects of modifications of the
sulfonamide side chain of the lead structure 1 (Ki AT2: 0.4 nM,
AT1: >10000 nM)16 were examined. As seen in Table 1, none
of the side chain modifications gave any detectable increase in
the AT1 affinity for the tested compounds, but the affinities for
the AT2 receptor were affected by the structural modifications.
Removing the carbamate oxygen from the side chain gave a
compound (compound 5) with a 100-fold decrease in affinity
for the AT2 receptor as compared to 1. Shortening or branching
of the butyloxy group rendered a 25-190 times decrease of
the affinity for the AT2 receptor (compound 6-10), and
surprisingly, introduction of a terminal trifluoromethyl group
resulted in an inactive compound (compound 11). On the other
hand, extension of the chain as in the case with the ether 12
did not affect the binding to the AT2 receptor significantly as
compared to compound 1. Substitution of the sulfonyl carbamate
for sulfonyl ureas (13 and 15) also resulted in fairly potent
ligands while considerable reduction in affinity was observed
after replacement with either a sulfonyl sulfonamide group as
in 14, a reverse sulfonamide as in 21, or a tetrazole as in 23.
In the second series, the isobutyl side chain and the thionyl-
phenyl scaffold of 1 were altered (Table 2). While a butyl or a
propyl instead of an isobutyl group rendered compounds 49 and
50 approximately ten times less active than 1, replacement of
one methylene group of 49 by an oxygen atom as in 52 led to
an additional loss of the AT2 receptor affinity of more than 1
order of magnitude. Furthermore, a compound containing a
methoxybenzyl group (51) was completely devoid of activity.
Compound 53 exhibited the same binding profile as 1 (Ki AT2:
0.6 nM, AT1: >10000 nM). In the biphenyl series all side chain
a Ki values are an average from three determinations. Standard deviations
are less than 15% in all cases.
variations (54, 55, and 57), except in the case where the benzene
ring was substituted with a butyloxy side chain (56), led to
derivatives that were poorer AT2 ligands than the parent
compound 53.
In Vitro Morphological Effects Induced by 56 and 50 in
NG 108-15 Cells. To study the effects of compound 56 and 50
on AT2 induced differentiation, NG108-15 cells were used. In
their undifferentiated state, neuroblastoma × glioma hybrid
NG108-15 cells have a rounded shape and divide actively. We
have shown previously that these cells express only the AT2
receptor28,29 and that a 3-day treatment with Ang II or the
selective peptidic AT2 receptor agonist CGP-42112 induces
neurite outgrowth.29 The mechanisms involve a sustained
increase in p42/ p44mapk activity15 and activation of the nitric
oxide/guanylyl cyclase/cGMP pathway30 (for a review see ref
9).
The cells were plated at the same initial density (4 × 104
cells/35 mm Petri dish) and were treated in the absence or
presence of Ang II, 56, or 50. After 3 days of culture, cells
were examined under a phase contrast microscope, and micro-
graphs were taken. We first tested compounds 56 and 50 at
concentrations ranging from 1 pM to 1 µM. Except for the

7164 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24
Wu et al.
Scheme 7a
a Reagents and conditions: (a) n-BuLi, THF, triisopropyl borate; (b) Pd(PPh3)4, NaOH (aq), ethanol/toluene, 3; (c) TFA, anisole or BCl3 in CH2Cl2; (d)
butyl chloroformate or ethyl chloroformate (55), with pyrrolidinopyridine, pyridine.
higher concentration of 1 µM, none of the other doses induced
cell death. As shown in Figure 2, treatment for 3 days with
concentrations of 0.1 µM of compounds 56 and 50 induced
neurite outgrowth, comparable with that of Ang II. This effect
was mediated through the AT2 receptor, since co-incubation of
56 and 50 with the AT2 receptor antagonist, 61 (PD 123,319)22
(1 µM), virtually abolished neurite elongation (Figure 2), while
alone, 61 did not alter the morphology compared to the untreated
cells (data not shown).
case where one of the nitrogens in the urea portion of the
molecule was methylated (15, Ki ) 4 nM), were apparently well
accepted by the AT2 receptor.
Alteration of the isobutyl side chain is known to affect the
AT1 agonistic properties of AT1/AT2 balanced compounds20 and
also to change the AT1/AT2 selectivity in favor of the AT1
receptor.22 As could have been expected,22 the n-butyl analogue
49 was less potent (5 nM) than the isobutyl analogue 1 (0.4
nM). A similar attenuation of the affinity for the AT2 receptor
was also observed with the propyl analogue 50. The replacement
of the isobutyl with a m-methoxybenzyl moiety, a group found
in the first AT1 selective agonist disclosed (60)21 lead to a totally
inactive compound (51) at both the AT1 and the AT2 receptors.
Discussion
The benzylimidazole fragment seems not to be tolerated by
the AT1 receptor. Thus, neither of the sulfonyl carbamates nor
the sulfonyl ureas nor the tetrazole derivative 21 were binding
to the AT1 receptor. This is notable, since the tetrazole ring
structure, that serves as a carboxylic acid bioisostere, is a
commonly used structure in AT1 receptor selective antagonists,
as in the sartans in clinic (e.g., losartan, valsartan, and
candersartan).31 Furthermore, it has previously been reported
that with compounds structurally related to the sartans and with
bicyclic heterocycles or other larger groups rather than an
imidazole ring linked to the biaryl scaffold, strong AT1 receptor
binding can be achieved with a variety of modified alkoxy
sulfonamide groups.32 Considering AT2 receptor affinities, all
sulfonamide side chain modifications afforded derivatives that
were weaker AT2 receptor binders than 1 (Table 1). However,
all the compounds in the first series showed affinity for to the
AT2 receptor and exhibited Ki values in the nanomolar range.
Only one exception, the trifluoromethyl compound 11 lacked
all affinity, an observation that we find difficult to rationalize.
In contrast, less subtle modifications, such as replacement of
the sulfonyl carbamate for a sulfonyl urea, in particular in the
The exchange of the thiophene for a phenyl ring did not affect
the binding to the AT2 receptor significantly (cf. 1 and 53), a
finding that is corroborated by results from previous studies of
nonselective AT1/AT2 compounds.33 This was also true for the
n-butyl analogues (c.f 49 and 54). By shortening the sulfonamide
side chain, the affinity to the AT2 receptor could be increased
slightly (55, 2 nM). Surprisingly, the n-butyloxy side chain
analogue (56) was as potent as the lead structure 1, while the
oxygen analogue of the isobutyl was much less active (57, 15
nM). We concluded that the imidazole ring strongly discrimi-
nates between the two receptor subtypes, and ligands with this
ring system favor binding to the AT2 receptor.
The most potent AT2 binder, compound 56, and the propyl-
thiophene 50 were chosen for further in vitro studies to
determine if the compounds acted as AT2 selective agonists or
antagonists. Although the receptor subtypes only share 34%
homology, it is known from literature that removal of a methyl
group from the isobutyl side-chain rendered an AT1 antagonist
(59). Thus, was a deletion of a methyl group from the branched

SelectiVe Angiotensin II AT2 Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24 7165
Table 2
Figure 2. Effect of 50 and 56 on neurite outgrowth in NG108-15 cells.
NG108-15 cells were plated at a density of 4 × 104 cells per dish in
35 mm Petri dishes and were cultured for 3 days in the absence or in
the presence of 0.1 µM Ang II, compound 50 or compound 56, alone
or in the presence of 1 µM 61. Cells with at least one neurite longer
than a cell body were counted as positive for neurite outgrowth. The
number of cells with neurites represent the percentage of the total
number of cells in the micrographs (from 50 to 100 cells according to
the experiment).
Furthermore, we concluded that removal of a methyl group
from the side chain of 1 delivers a compound (50) that acts as
an AT2 agonist with still a high agonistic potency. This finding
is notable considering that the structurally related AT1 agonist
L-162,782 is transformed into the AT1 antagonist 59 after the
same alteration.33
Experimental Section
Chemistry. General Considerations. 1H and 13C NMR spectra
were recorded on a JEOL JNM-EX 270 spectrometer at 270.2 and
67.8 MHz, respectively. Chemical shifts are given as δ values (ppm)
downfield from tetramethylsilane. Elemental analyses were per-
formed by Mikro Kemi AB, Uppsala, Sweden, or Analytische
Laboratorien, Lindlar, Germany. Flash column chromatography was
performed on silica gel 60 (0.04-0.063 mm, E. Merck). Thin-layer
chromatography was performed on precoated silica gel F-254 plates
(0.25 mm, E. Merck) and was visualized with UV light. Analytical
RP-LC/MS was performed on a Gilson HPLC system with a Zorbax
SB-C8, 5 µm 4.6 × 50 mm (Agilent Technologies) column, with
a Finnigan AQA quadropole mass spectrometer at a flow rate of
4.0 mL/min (H2O/CH3CN/0.05% HCOOH). All the organic phases
were dried over MgSO4, unless otherwise is stated. All chemicals
were purchased from commercial suppliers and used directly
without further purification.
a Ki values are an average from three determinations. Standard deviations
are less than 15% in all cases.
side chain transforming these ligands from agonists to antago-
nists as was the case among the AT1 receptor ligands? (cf. Figure
1).
Our results demonstrate that the two compounds induce
neurite outgrowth (Figure 2), one of the first step of neuronal
differentiation, as does Ang II and CGP-42112.15,29,30 The
butyloxy compound 56 was found to act as an agonist at the
AT2 receptor with a high potency, and even more remarkable
the propylthiophene derivative 50 was also found to possess
agonistic properties.
General Procedure for Compound 5-9. Compound 416 (150
mg, 0.311 mmol) and anisole (150 µL) were dissolved in TFA (5
mL) and stirred overnight. The reaction mixture was evaporated
under vacuum and coevaporated with acetonitrile twice. The residue
was dissolved in pyridine (1.6 mL), and pyrrolidinopyridine (52.1
mg, 0.35 mmol) was added. The solution was cooled on an ice
bath, and acyl chloride (20 equiv) was added under N2 (g)
atmosphere. The reaction was stirred at ambient temperature
overnight. The solvent was removed under vacuum and coevapo-
rated with acetonitrile twice. The residue was dissolved in ethyl
acetate (50 mL) and washed with citric acid (10% aq) and water.
The organic phase was dried, evaporated, and purified by column
chromatography to give the pure compounds 5-9.
N-Butylcarbonyl-3-(4-imidazol-1-ylmethylphenyl)-5-isobutyl-
thiophene-2-sulfonamide (5). Compound 4 was used according
to the general procedure and reacted with valeryl chloride (738
µL, 6.22 mmol), which after purification (CH2Cl2:MeOH 20:1) gave
compound 5 in 50% yield (72 mg, 0.156 mmol). 1H NMR (CDCl3)
δ 7.80 (br s, 1H), 7.54 (d, J ) 8.1 Hz, 2H), 7.09 (d, J ) 8.1 Hz,
2H), 6.84 (br s, 2H), 6.73 (s, 1H), 5.10 (br s, 2H), 2.69 (d, J ) 7.1
Hz, 2H), 2.11 (t, J ) 7.3 Hz, 2H), 1.93 (m, 1H), 1.44 (m, 2H),
Conclusion
In summary, we have presented a structure-activity relation-
ship study where the 2- and 5-positions of 1, and its phenyl
analogue, were altered. With few exceptions, all variations gave
good AT2 receptor affinities and with retained high AT2/AT1
selectivities. The trifluoroalkyl compound 11 and the m-
methoxyphenyl compound 51 were inactive at both receptors.
The butyloxyphenyl derivative 56 was found to exert a high
agonistic potency as deduced from a neurite elongation assay.

7166 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24
Wu et al.
1.22 (m, 2H), 0.98 (d, J ) 6.6 Hz, 6H), 0.81(t, J ) 7.1 Hz, 3H).
Anal. (C23H29N3O3S2) C, H, N.
MeOH 10:1) to give compound 20 (117.0 mg, 0.344 mmol) in 83%
yield. H NMR (CD3OD) δ 9.05 (br s, 1H), 7.63 (br s, 1H), 7.55
1
(br s, 1H), 7.51 (d, J ) 8.4 Hz, 2H), 7.45 (d, J ) 8.4 Hz, 2H), 6.81
(s, 1H), 5.47 (s, 2H), 2.68 (d, J ) 7.1 Hz, 2H), 1.90 (m, 1H), 0.96
(d, J ) 6.6 Hz, 6H). Anal. (C19H21N3OS) C, H, N.
N-(N-Butyl-methylaminocarbonyl)-3-(4-imidazol-1-ylmethyl-
phenyl)-5-isobutylthiophene-2-sulfonamide (15). A solution of
6 (29 mg, 0.065 mmol) and methylbutyl amine (11.6 mg, 0.133
mmol) in toluene was stirred at 90 °C for 3 h. The reaction mixture
was concentrated and purified by prep-HPLC (AcCN in H2O 0.5%
HCOOH, 20 to 80%) to give compound 15 (19 mg, 0.039 mmol)
in 60% yield. 1H NMR (CDCl3) δ 8.18 (br s, 1H), 7.84 (br s, 1H),
7.46 (d, J ) 8.2 Hz, 2H), 7.16 (d, J ) 8.2 Hz, 2H), 7.06 (br s, 1H),
6.99 (br s, 1H), 6.68 (s, 1H), 5.16 (s, 2H), 3.07 (br t, 2H), 2.67 (d,
J ) 7.1 Hz, 2H), 2.56 (br s, 3H), 1.91 (m, 1H), 1.35 (m, 2H), 1.19
(m, 2H), 0.96 (d, J ) 6.6 Hz, 6H), 0.84 (t, J ) 7.2 Hz, 3H). Anal.
(C24H32N4O3S2 × 1/2 H2O) C, H, N.
N-Butylsulfonyl-3-(4-imidazol-1-ylmethylphenyl)-5-isobutyl-
thiophene-2-carboxamide (21). To NaH (12.0 mg, 55% washed
with isopentane) was added a solution of 20 (46.0 mg, 0.136 mmol)
in THF (1 mL). The mixture was stirred at 50 °C for 0.5 h. To the
reaction mixture was added butanesulfonyl chloride (35.0 mg, 0.223
mmol) slowly. The reaction was stirred at rt for 1 h and then
concentrated. The crude product was purified by prep-HPLC (AcCN
in H2O 0.5% HCOOH, 10 to 80%) to give compound 21 (31.0
1
mg, 0.0674 mmol) in 50% yield. H NMR (CDCl3) δ 7.82 (br s,
1H), 7.32 (br s, 2H), 7.06 (d, J ) 7.4 Hz, 2H), 6.95 (br s, 2H),
6.64 (s, 1H), 5.09 (br s, 2H), 4.79 (br s, 1H, NH), 2.97 (br s, 2H),
2.62 (d, J ) 6.9 Hz, 2H), 1.90 (m, 1H), 1.65 (br s, 2H), 1.29 (m,
2H), 0.95 (d, J ) 6.5 Hz, 6H), 0.81 (t, J ) 6.6 Hz, 3H). Anal.
(C23H29N3O3S2 × 1/2 HCOOH) C, H, N.
2-Isobutylthiophene (16). To a solution of thiophene (5.7 mL,
0.071 mol) in dry THF (80 mL), at -78 °C, was added slowly
n-BuLi (54 mL, 1.6 M in hexane, 0.086 mol), under a N2
atmosphere. The mixture was stirred at -40 °C for 2 h. The solution
was cooled to -78 °C, and 2-methylpropyl iodide (9.94 mL, 0.0864
mol) was added slowly. The reaction mixture was stirred at 0 °C
for 2 h and then at r.t. overnight. The reaction was quenched with
water (25 mL) and extracted with petroleum ether. The organic
phase was dried and concentrated. The residue was distilled under
vacuum (54-55 °C at 12 mmHg) to give compound 16 (3.0 g,
3-(4-Imidazol-1-ylmethylphenyl)-5-isobutylthiophene-2-car-
bonitrile (22). To a solution of 20 (133.3 mg. 0.3927 mmol) in
THF (5 mL) was added pyridine (1.0 mL), and the mixture was
stirred for 0.5 h at rt. Trifluoroacetic anhydride (66.6 µL, 0.471
mmol) was added at 0 °C. The reaction mixture was stirred at rt
for 2 h. Ice was added to the solution and extracted with EtOAc.
The organic phase was concentrated and purified on column
chromatography (CH2Cl2:MeOH 24:1) to give compound 22 (50.0
1
0.021 mol) in 30% yield. H NMR (CDCl3), δ 7.14 (dd, J ) 5.1,
1.2 Hz, 1H), 6.95 (dd, J ) 5.1, 3.3 Hz, 1H), 6.79 (dd, J ) 3.3, 1.2
Hz, 1H), 2.72 (d, J ) 7.1 Hz, 2H), 1.92 (m, 1H), 0.97 (d, J ) 6.7
Hz, 6H). Anal. (C8H12S) C, H.
1
mg, 0.156 mmol) in 40% yield. H NMR (CDCl3) δ 7.72-7.58
(m, 3H), 7.23 (d, J ) 8.4 Hz, 2H), 7.10 (s, 1H), 6.93 (s, 2H), 5.17
(s, 2H), 2.70 (d, J ) 6.6 Hz, 2H), 1.92 (m, 1H), 0.97 (d, J ) 6.6
Hz, 6H). Anal. (C19H19N3S) C, H, N.
N-tert-Butyl-5-isobutylthiophene-2-carboxamide (17). To a
solution of 16 (1.0 g, 7.1 mmol) in dry THF (15 mL), at -78 °C,
was added slowly n-BuLi (5.3 mL, 1.6M in hexane, 8.5 mmol),
under a N2 atmosphere. The mixture was stirred at 0 °C for 2 h.
The solution was cooled to -78 °C, and tert-butyl isocyanate (0.896
mL, 7.84 mmol) was added slowly. The reaction mixture was stirred
at 0 °C for 2 h. The reaction was quenched with water (15 mL)
and extracted with EtOAc. The organic phase was dried and
concentrated. The crude product was purified on column chroma-
tography (P-ether: EtOAc 9:1) to provide compound 17 (1.2 g,
5-[3-(4-Imidazol-1-ylmethylphenyl)-5-isobutylthiophen-2-yl]-
1H-tetrazole (23). A mixture of 22 (48.1 mg, 0.150 mmol), sodium
azide (156.0 mg, 2.40 mmol), and Et3NHCl (330 mg, 2.40 mmol)
in toluene (toluene 5 mL) was heated to 110 °C for 48 h. Water (8
mL) was added, and the reaction mixture was extracted with CHCl3.
The organic phase was dried and concentrated. The crude product
was purified by prep-HPLC (AcCN in H2O 0.5% HCOOH, 10 to
80%) to give compound 23 (50.8 mg, 0.139 mmol) in 93% yield.
1H NMR (CDCl3) δ 14.10 (br s, 1H), 8.18 (s, 1H), 6.97 (br d, 4H),
6.78 (d, J ) 7.6 Hz, 2H), 6.64 (s, 1H), 5.02 (s, 2H), 2.61 (d, J )
6.3 Hz, 2H), 1.86 (m, 1H), 0.93 (d, J ) 6.4 Hz, 6H). Anal.
(C19H20N6S × 1/2 HCOOH) C, H, N.
1
5.0 mmol) as white needles, in 70% yield. H NMR (CDCl3) δ
7.24 (d, J ) 3.6 Hz, 1H), 6.69 (d, J ) 3.6 Hz, 1H), 5.72 (br s, 1H),
2.65 (d, J ) 7.2 Hz, 2H), 1.88 (m, 1H), 1.44 (s, 9H), 0.93 (d, J )
6.6 Hz, 6H). Anal. (C13H21NOS) C, H, N.
3-(4-Imidazol-1-ylmethylphenyl)-5-isobutyl-N-tert-butylthio-
phene-2-carboxamide (19). To a solution of 17 (0.50 g, 2.1 mmol)
in dry THF (50 mL), at -78 °C, was added slowly n-BuLi (3.3
mL, 1.6 M in hexane, 5.3 mmol), under a N2 atmosphere. The
mixture was stirred at -20 °C for 4 h. The solution was cooled to
-78 °C, and triisopropyl borate (0.724 mL, 3.136 mmol) was added
slowly. The reaction mixture was stirred at rt overnight. The reaction
was quenched with HCl (2 mL, 2 M) and extracted with EtOAc.
The organic phase was dried and concentrated. The resulting boronic
acid 18 was used without further purification. A reaction tube was
charged with the boronic acid 18 (200 mg, 0.706 mmol), 316 (80.0
mg, 0.337 mmol), Pd(PPh3)4 (16.3 mg, 0.0141 mmol), NaOH (0.84
mL, 1.63M, 1.38 mmol), toluene (10 mL), and ethanol (2 mL).
The reaction tube was flushed with N2(g) and sealed with a screw
cap. The reaction mixture was heated at 100 °C for 3 h. The reaction
mixture was diluted with water (15 mL) and extracted with EtOAc.
The organic phase was dried and concentrated. The crude product
was purified on column chromatography (CH2Cl2:MeOH 20:1) to
N-tert-Butyl-5-propylthiophene-2-sulfonamide (25). To a solu-
tion of N-tert-butylthiophene-2-sulfonamide (2.29 g, 10.44 mmol)
in dry THF (20 mL), at -78 °C, was added slowly n-BuLi (12.7
mL, 1.6M in hexane, 20.3 mmol), under a N2 atmosphere. The
mixture was stirred at -40 °C for 2 h. The solution was cooled to
-78 °C and iodo-propane (1.12 mL, 11.5 mmol) was added slowly.
The reaction mixture was stirred at rt overnight. The reaction was
quenched with NH4Cl (aq) (10 mL) and extracted with EtOAc. The
organic phase was dried and concentrated. The crude product was
purified on column chromatography (P-ether; EtOAc 12:1) to give
compound 25 (2.21 g, 8.45 mmol) in 81% yield. 1H NMR (CDCl3)
δ 7.42 (d, J ) 3.8 Hz, 1H), 6.69 (d, J ) 3.8 Hz, 1H), 4.89 (br s,
1H), 2.79 (t, J ) 7.5 Hz, 2H), 1.70 (m, 2H), 1.26 (s, 9H), 0.96 (t,
J ) 7.3 Hz, 3H). Anal. (C11H19NO2S2) C, H, N.
N-tert-Butyl-4-butyloxybenzenesulfonamide (31). To the solu-
tion of 4-n-butoxybenzene sulfonyl chloride (206.6 mg, 0.8306
mmol) in dry CH2Cl2 (12 mL) was tert-butylamine (900 µL, 8.56
mmol) added. The reaction mixture was stirred at rt for 1 h. Water
(5 mL) was added, and the reaction mixture was extracted with
CH2Cl2. The combined organic phase was washed with brine and
water. The organic phase was dried and concentrated to give the
pure compound 31 (230.8 mg, 0.8087 mmol) in 97% yield. 1H NMR
(CDCl3) δ 7.80 (d, J ) 9.0 Hz, 2H), 6.93 (d, J ) 9.0 Hz, 2H),
4.54 (br s, 1H), 4.00 (t, J ) 6.5 Hz, 2H), 1.79 (m, 2H), 1.50 (m,
2H), 1.21 (s, 9H), 0.98 (t, J ) 7.4 Hz, 3H). Anal. (C14H23NO3S)
C, H, N.
1
provide compound 19 (129.0 mg, 0.327 mmol) in 97% yield. H
NMR (CDCl3) δ 7.55 (br s, 1H), 7.41 (d, J ) 8.1 Hz, 2H), 7.24 (d,
J ) 8.1 Hz, 2H), 7.09 (br s, 1H), 6.89 (br s, 1H), 6.63 (s, 1H),
5.25 (br s, 1H, NH), 5.16 (s, 2H), 2.63 (d, J ) 6.9 Hz, 2H), 1.89
(m, 1H), 1.13 (s, 9H), 0.95 (d, J ) 6.6 Hz, 6H). Anal. (C23H29N3OS
× H2O) C, H, N.
3-(4-Imidazol-1-ylmethylphenyl)-5-isobutylthiophene-2-car-
boxamide (20). To 19 (165.0 mg, 0.417 mmol) were added TFA
(2.5 mL) and anisole (150 µL). The reaction mixture was stirred at
70 °C for 17 h. The reaction mixture was concentrated, and the
crude product was purified on column chromatography (CH2Cl2,
N-tert-Butyl-3-(4-imidazol-1-ylmethylphenyl)-5-propylthio-
phene-2-sulfonamide (42). To a solution of 25 (2.00 g, 7.65 mmol)

SelectiVe Angiotensin II AT2 Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 24 7167
in dry THF (40 mL), at -78 °C, was added slowly n-BuLi (12.0
mL, 1.6M in hexane, 19.1 mmol), under a N2 atmosphere. The
mixture was stirred at -20 °C for 4 h. The solution was cooled to
-78 °C, and triisopropyl borate (9.72 mL, 42.1 mmol) was added
slowly. The reaction mixture was stirred at rt overnight. The reaction
was quenched with HCl (15 mL, 2 M) and extracted with EtOAc.
The organic phase was dried and concentrated. The resulting boronic
acid 34 was used without further purification. A reaction tube was
charged with the boronic acid 34 (420 mg, 1.38 mmol), 1-(4-bromo-
benzyl)-1H-imidazol(ref) (188 mg, 0.793 mmol), Pd(PPh3)4 (64 mg,
0.055 mmol), NaOH (1.64 mL, 1.54 M, 2.53 mmol), toluene (15
mL), and ethanol (2 mL). The reaction tube was flushed with N2(g)
and sealed with a screw cap. The reaction mixture was heated at
100 °C for 3 h. The reaction mixture was diluted with water (15
mL) and extracted with EtOAc. The organic phase was dried and
concentrated. The crude product was purified on column chroma-
tography (CH2Cl2:MeOH 40:1) to provide compound 42 (278.1 mg,
N-Butyloxycarbonyl-2-(4-imidazol-1-ylmethylphenyl)-4-butoxy-
benzenesulfonamide (56). Compound 47 (34.7 mg, 0.0785 mmol)
and anisole (50 µL) were dissolved in TFA (2.0 mL) and stirred
overnight. The reaction mixture was evaporated under vacuum and
coevaporated with acetonitrile twice. The residue was dissolved in
pyridine (3.0 mL) and pyrrolidinopyridine (23 mg, 0.16 mmol) was
added. The solution was cooled on an ice bath and butyl chloro-
formate (20.0 µL, 0.157 mmol) was added under N2 (g) atmosphere.
The reaction was stirred at ambient temperature overnight. The
solvent was removed under vacuum and coevaporated with aceto-
nitrile twice. The residue was dissolved in ethyl acetate (50 mL)
and washed with citric acid (10% aq) and water. The organic phase
was dried, evaporated and purified by column chromatography
(CH2Cl2:MeOH 15:1) to give the entitled compound in 53% yield
(20.2 mg, 0.0416 mmol). 1H NMR (CDCl3) δ 8.53 (br s, 1H), 8.18
(d, J ) 8.9 Hz, 1H), 7.36 (d, J ) 8.1 Hz, 2H), 7.25 (d, J ) 8.1 Hz,
2H), 7.17 (br s, 1H), 7.12 (br s, 1H), 6.98 (dd, J ) 8.9, 2.5 Hz,
1H), 6.74 (d, J ) 2.5 Hz, 1H), 6.53 (br s, 1H), 5.32 (s, 2H), 4.01
(t, J ) 6.5 Hz, 4H), 1.77 (m, 2H), 1.48 (m, 4H), 1.22 (m, 2H),
0.96 (t, J ) 7.1 Hz, 3H), 0.86 (t, J ) 7.3 Hz, 3H). Anal.
(C25H31N3O5S) C, H, N.
1
0.6660 mmol) in 84% yield. H NMR (CDCl3) δ 7.73 (br s, 1H),
7.59 (d, J ) 8.2 Hz, 2H), 7.25 (d, J ) 8.2 Hz, 2H), 7.11 (s, 1H),
6.93 (s, 1H), 6.75 (s, 1H), 5.18 (s, 2H), 4.33 (br s, 1H), 2.78 (t, J
) 7.4 Hz, 2H), 1.72 (m, 2H), 0.99 (m, 12H). Anal. (C21H27N3O2S2)
C, H, N.
Acknowledgment. We gratefully acknowledge support from
the Swedish Research Council (VR), the Swedish Foundation
for Strategic Research (SSF), Knut and Alice Wallenberg
Foundation (VRmedicine 8663), and the Canadian Institutes of
Health Research to N.G.P. and M.D.P. (MOP 37891), and
Vicore Pharma AB. N.G.P. is a holder of a Canada Research
Chair in Endocrinology of the Adrenal Gland.
N-tert-Butyl-2-(4-imidazol-1-ylmethylphenyl)-4-butoxybenzene-
sulfonamide (47). To a solution of 31 (230.8 mg, 0.8087 mmol)
in dry THF (20 mL), at -78 °C, was added slowly n-BuLi (1.26
mL, 1.6M in hexane, 2.02 mmol), under a N2 atmosphere. The
mixture was stirred at -20 °C for 4 h. The solution was cooled to
-78 °C, and triisopropyl borate (0.28 mL, 1.2 mmol) was added
slowly. The reaction mixture was stirred at rt overnight. The reaction
was quenched with HCl (5 mL, 2 M) and extracted with EtOAc.
The organic phase was dried and concentrated. The resulting boronic
acid 39 was flushed trough a silica column (CH2Cl2:MeOH 40:1)
before further use. A reaction tube was charged with the boronic
acid 39 (76.3 mg, 0.232 mol), 316 (39.3 mg, 0.166 mmol), Pd(PPh3)4
(10.0 mg, 0.00865 mmol), NaOH (0.602 mL, 1.54 M, 0.927 mmol),
toluene (12 mL), and ethanol (2.0 mL). The reaction tube was
flushed with N2(g) and sealed with a screw cap. The reaction mixture
was heated at 100 °C for 4.5 h. The reaction mixture was diluted
with water (5 mL) and extracted with EtOAc. The organic phase
was dried and concentrated. The crude product was purified on
column chromatography (CH2Cl2:MeOH 40:1) to provide com-
pound 47 (52.0 mg, 0.118 mmol) in 71% yield. 1H NMR (CDCl3)
δ 8.04 (d, J ) 8.9 Hz, 1H), 7.78 (br s,1H), 7.49 (d, J ) 8.1 Hz,
2H), 7.23 (d, J ) 8.1 Hz, 2H), 7.12 (br s, 1H), 6,96 (br s, 1H),
6.91 (dd, J ) 8.8, 2.6 Hz, 1H), 6.74 (d, J ) 2.6 Hz, 1H), 5.21 (s,
2H), 3.99 (t, J ) 6.4 Hz, 2H), 3.61 (s, 1H), 1.76 (m, 2H), 1.47 (m,
2H), 1.10-0.85 (m, 12H). Anal. (C24H31N3O3S × 1/2 H2O) C, H,
N.
Supporting Information Available: Experimental procedures
including the synthesis of compounds 6-14, 24, 26-30, 32-41,
43-46, 48, 49, 51-55, and 57 with characterization data, NMR
data for compounds presented in the experimental part, and
biological assays. This material is available free of charge via the
Internet at http://pubs.acs.org.
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1
(50.0 mg, 0.108 mmol). H NMR (30%CD3OD in CDCl3) δ 7.79
(br s, 1H), 7.49 (d, J ) 7.7 Hz, 2H), 7.17 (d, J ) 7.7 Hz, 2H), 7.01
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