Heteroaryl β-tetralin ureas as novel antagonists of human TRPV1

Article abstract of DOI:10.1016/j.bmcl.2007.09.036

We report on a series of α-substituted-β-tetralin-derived and related phenethyl-based isoquinolinyl and hydroxynaphthyl ureas as potent antagonists of the human TRPV1 receptor. The synthesis and Structure-activity relationships (SAR) of the series are described.

Full text of DOI:10.1016/j.bmcl.2007.09.036

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 17 (2007) 6160–6163
Heteroaryl b-tetralin ureas as novel antagonists of human TRPV1
Michele C. Jetter,a,* Mark A. Youngman,a James J. McNally,a Mark E. McDonnell,a
Sui-Po Zhang,a Adrienne E. Dubin,b Nadia Nasser,b Ellen E. Codd,a
Christopher M. Floresa and Scott L. Daxa
aJohnson & Johnson Pharmaceutical Research and Development, Welsh and McKean Roads, Spring House, PA 19477, USA
bJohnson & Johnson Pharmaceutical Research and Development, 3210 Merryfield Row, San Diego, CA 92121, USA
Received 17 July 2007; revised 5 September 2007; accepted 7 September 2007
Available online 12 September 2007
Abstract—We report on a series of a-substituted-b-tetralin-derived and related phenethyl-based isoquinolinyl and hydroxynaphthyl
ureas as potent antagonists of the human TRPV1 receptor. The synthesis and Structure–activity relationships (SAR) of the series are
described.
ꢀ 2007 Elsevier Ltd. All rights reserved.
TRPV1 receptor, previously known as the capsaicin
receptor or VR1, is a non-selective cation channel which
is stimulated by a number of endogenous and exogenous
activators including capsaicin, the pungent component of
chili peppers, as well as acid (low pH) and heat.1 TRPV1 is
a member of the superfamily of transient receptor poten-
tial channels or TRP channels and is expressed primarily
on small-diameter, nociceptive sensory neurons. In light
of its role in the detection of noxious stimuli, human
TRPV1 receptor has emerged as a promising target for
the development of new agents for the treatment of
inflammatory pain and other painful disorders.2 Our
group3–6 and many others7 have reported on numerous
series of small molecule TRPV1 antagonists. We previ-
ously described a series of N-isoquinolin-5-yl-N0-ara-
lkylureas6 and 7-hydroxynaphthalen-1-ylureas4 that
were found to be potent functional antagonists of human
TRPV1 possessing exquisite binding affinity. We sought
to further investigate the requisite pharmacophore ele-
ments in order to design improved TRPV1 antagonists.
Through detailed SAR studies, we observed that substitu-
tion at the a-position of the phenethyl chain produced
compounds with enhanced in vitro functional potency.
Furthermore, constraint of the open chain analogs within
a b-tetralin scaffold resulted in compounds that exhibited
outstanding functional antagonist activities and binding
affinities.
Thus we describe here novel TRPV1 antagonist series
that incorporate either a b-phenethylamine or b-amino-
tetralin scaffold as a key structural element.
b-Phenethylamino ureas 1 were prepared starting from
substituted phenyl acetonitriles 3 (Scheme 1). Conden-
sation with an appropriately substituted aldehyde fol-
lowed by stepwise reduction of the resulting a-
substituted unsaturated nitrile 4 gave the amine inter-
mediate 6. The b-phenethyl amines 6 were then reacted
with the phenyl carbamate 7 derived from either 5-
aminoisoquinoline or 2-hydroxy-8-amino naphthalene
to give the target ureas as racemic mixtures (Scheme
2).
The aminotetralin scaffolds were synthesized from the
corresponding b-tetralones (Scheme 3). The tetralones
10 were obtained by Friedel–Crafts reaction of the
appropriate acid chloride 9 with ethylene gas. Conden-
sation of the tetralone 10 with various aldehydes gave
the a,b-unsaturated b-tetralone 11. Alternatively, initial
reaction of the b-tetralone 10 with pyrrolidine followed
by alkylation of the enamine 12 with the desired bro-
mide and hydrolysis yielded the a-substituted b-tetr-
alone 13. Reductive amination of either b-tetralone
intermediate gave the aminotetralin derivatives 14 in
moderate-good yield as a diastereomeric mixture, which
was predominantly, composed of the cis isomer.8 Sepa-
ration of the diastereomers was achieved by fractional
crystallization. The aminotetralins thus obtained were
then reacted with the aryl carbamates in a similar man-
Keywords: TRPV1; Antagonists; Tetralin ureas.
*
Corresponding author. Tel.: +1 215 540 4873; fax: +1 215 628
4985; e-mail: mjetter@prdus.jnj.com
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.09.036

M. C. Jetter et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6160–6163
6161
affinity at human TRPV1, measuring displacement of
radiolabeled resiniferatoxin (RTX).11
R2
a
CN
R1
CN
R1
Both the aryl phenethyl and the aryl tetralin ureas 1–2 be-
haved as functional antagonists of the TRPV1 channel
and also displayed potent binding affinity (Tables 1 and
2). From previous studies we learned that 5-isoquinolinyl
and 7-hydroxy-1-naphthyl groups afforded the most po-
tent analogs. In our work presented herein, substitution
at the a-position generally led to an increase in both bind-
ing affinity and functional potency relative to these earlier
series (Table 1, entry 1a). The nature of the phenyl substi-
tuent, R1, did not greatly influence the potency as both po-
lar groups such as OCH3 and lipophilic groups such as F
and CF3 were well tolerated. However, in contrast, substi-
tution at the a-position with a polar substituent such as a
3-pyridylmethyl group yielded compounds with only
moderate functional and binding potencies. However,
lipophilic substituents gave compounds with excellent
functional and binding potencies (Table 1). With few
exceptions, the functional and binding activities of the
analogs tested were in close agreement (within an order
of magnitude).
~70%
3
4
b
~85%
R2
R2
NH2
c
CN
R1
R1
~60%
5
6
Scheme 1. Reagents and condition: (a) R2CHO, K2CO3, MeOH, heat;
(b) NaBH4, MeOH; heat (c) BH3 THF, heat.
H
R2
O
N
a
b
H
N
H
N
Aryl
H2N
Aryl
O
Aryl
> 90 %
60-80 %
O
7
R1
1
Scheme 2. Reagents: (a) PhOC(O)Cl, aq NaHCO3,CH2Cl2 (92%); (b)
amine 6, DMSO (60–80%).
In the tetralin urea series, heteroaryl substitution was al-
lowed, as evidenced by compounds 2k and 2l; however,
an a-pyridylmethyl substituent greatly decreased po-
tency (2m). This result mirrors what was found in the
acyclic series. Indeed, other polar substituents also
caused a drop in both antagonist potency and binding
affinity (2q). Substitution at the a-position appears to re-
quire a somewhat lipophilic substituent but not neces-
sarily an aryl group. Both the a-allyl (2n) and the a-
cyclopropylmethyl analogs (2o) exhibited good binding
affinity but only moderate functional antagonism as
compared with benzyl substituted compounds (2d, 2e).
The nature of the R1 substituent seemed to have little ef-
fect on TRPV1 activity except in the case of R1 = OH
(i.e., compound 2p), wherein both binding affinity and
functional antagonism dropped approximately one or-
der of magnitude. Also, the disubstituted phenyl analog
ner as described above to give the requisite racemic ur-
eas 2. Further biological testing of several of the most
potent urea analogs required pure enantiomers. These
were obtained by separation of the racemic mixtures
of the a-substituted-b-phenethyl amines and the a-
substituted-b-aminotetralins either by classical resolu-
tion techniques or by chiral chromatography.9
The phenethyl and tetralin-derived aryl ureas, 1 and 2,
respectively, were evaluated for their ability to modulate
TRPV1 receptor activity in a recombinant HEK293 cell
line using a capsaicin-induced calcium flux assay and
FLIPRTM technology (Molecular Devices, Inc.) under
conditions we have previously reported.10 In addition,
the target compounds were assayed for their binding

6162
M. C. Jetter et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6160–6163
Scheme 3. Reagents and conditions: (a) SOCl2, DCM; (b) CH2 = CH2, AlCl3, DCE, 0 ꢁC; (c) R2CHO, cat piperidine, benzene, heat; (d) NH4OAc,
NaBH3CN, MeOH, heat; (e) pyrrolidine, EtOH; (f) R2CH2Br, CH3CN; (g) HOAc/H2O/DCM/MeOH.
Table 2. Human TRPV1 binding affinities and functional activity of a-
substituted-b-tetralin ureasa
Table 1. Human TRPV1 binding affinities of a-substituted-b-phen-
thylureasa
R2
R2
H
N
H
N
H
N
H
N
Aryl
Aryl
R1
O
O
R1
Aryl = 5-isoquinolyl (5-IsoQ)
1
Aryl = 5-isoquinolyl (5-IsoQ)
or 7-OH-1-naphthyl (7-OH-1-NAP)
C
Aryl
R1
R2
Binding
affinity
Ki (nM)
Functional
activity
IC50 (nM)
C
Aryl
R1
R2
Binding Functional
affinity activity
Ki (nM) IC50 (nM)
1a
1b
1c
1d
1e
1f
5-IsoQ
5-IsoQ
5-IsoQ
5-IsoQ
5-IsoQ
5-IsoQ
OCH3
OCH3
OCH3
CF3
F
—
1290
578
6
680
184
14
2a 7-OH-1- 6-OCH3
NAP
Ph
10
22
60
3-Pyr
Ph
Ph
2b 7-OH-1- 6-F
NAP
4-CF3Ph
360
4
NT
5
Ph
3-CF3Ph
8
20
2c 5-IsoQ
2d 5-IsoQ
2e 5-IsoQ
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4
20
25
F
19
6-OCH3
6-F
3
4
12
17
NT, not tested.
a Data are reported for racemic compounds.
2f
5-IsoQ
6-Br
5-Cl
6-Cl
7-Cl
2
2g 5-IsoQ
2h 5-IsoQ
2
16
63
11
5
2j was 2- to 5-fold less potent at binding to TRPV1.
While there appears to be a requirement for a lipophilic
substituent at R2, the effect of different aryl substituents
on the apparent potency was minimal. In terms of ste-
reochemistry, initial biological results established the
cis diastereomer as the more active isomer (data not
shown). There was ꢀ 5-fold difference in binding po-
tency of the enantiomers but little effect of enantiomers
on the functional potency.
2i
2j
5-IsoQ
5-IsoQ
86
6,7-DiOMe Ph
20
4
230
140
83
2k 5-IsoQ
2l 5-IsoQ
6-F
6-F
2-Thienyl
3-Furanyl
3-Pyridyl
Vinyl
16
1540
2
2m 5-IsoQ
2n 5-IsoQ
2o 5-IsoQ
2p 5-IsoQ
2q 5-IsoQ
2r 5-IsoQ
2s 5-IsoQ
6-OCH3
6-F
6-F
>1000
100
350
200
>1000
36
c-Propyl
Ph
CN
0.8
280
NT
8
6-OH
6-Cl
6-OCH3
6-OCH3
6-OCH3
6-OCH3
6-F
4-OCH3 Ph
4-CF3Ph
4-CN Ph
4-Br Ph
4-CF3 Ph
3-Cl Ph
2
2
21
In summary, we report on a unique series of a-substi-
tuted b-tetralin- and phenethyl-heterocyclic ureas as po-
tent human TRPV1 antagonists12,13 that possess
excellent binding affinity. Due to low aqueous solubility
and extensive in vitro metabolism, further optimization
is underway to demonstrate the potential of the series of
2t
5-IsoQ
17
1
2u 5-IsoQ
2v 5-IsoQ
2w 5-IsoQ
22
10
1
6-OCH3
2
13
NT, not tested.
a Data are reported for racemic compounds.

M. C. Jetter et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6160–6163
6163
meric amine was established by X-ray crystallography of
the amine co-crystallized with a known chiral acid.
TRPV1 antagonists as novel agents for the treatment of
certain types of pain.
10. hTRPV1/HEK cells4 were seeded on poly-D-lysine coated
96-well, black-walled plates (BD 354640) and 2 days later
loaded with Fluo-3/AM for 1 h and subsequently tested
for agonist-induced increases in intracellular Ca2+ levels
using FLIPRTM technology. Cells were challenged with
single concentrations of compound and intracellular Ca2+
was measured for 3 min prior to the addition of CAP to all
wells to achieve a final CAP concentration of 15 nM to
fully activate TRPV1. Antagonist potency was determined
using the protocol described by McDonnell et al. Bioorg.
Med. Chem. 2002, 12, 1189). Data were analyzed using
Prism software to calculate IC50 values.
References and notes
1. Caterina, M. J.; Schumaker, M. A.; Tomaniga, M.; Rosen,
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Kyle, D. J.; Tafesse, L. Exp. Opin. Ther. Patents 2006, 16,
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Carruthers, N. I.. In Annual Reports in Medicinal Chem-
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Vol. 40, pp 185–198.
3. Dax, S.; Dubin, A.; Jetter, M.; Nasser, N.; Shah, C.;
Swanson, D.; Carruthers, N.I. Vanilloid Receptor Antag-
onists: Structure Activity Relationships via Parallel and
Targeted Synthesis. 17th International Symposium on
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4. McDonnell, M. E.; Zhang, S.-P.; Nasser, N.; Dubin, A.
E.; Dax, S. Bioorg. Med. Chem. Lett. 2004, 14, 531.
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Chang, L.; Dax, S. L.; Jetter, M.; Breitenbucher, J. G.;
Liu, C.; Mazur, C.; Lord, B.; Gonzales, L.; Hoey, K.;
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7. (a) Gomtsyan, A.; Bayburt, E. K.; Schmidt, R. G.; Zheng,
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Shin, M.; Kim, J.-M.; Kang, S.-U.; Lim, J.-O.; Choi, H.-
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8. For preparation of aminotetralins see (a) Youngman, M.
A.; Willard, N. M.; Dax, S. L.; McNally, J. J. Syn. Comm.
2003, 33, 2215; (b) McNally, J. J.; Youngman, M. A.;
Lovenberg, T. W.; Nepomuceno, D. H.; Wilson, S. J.;
Dax, S. L. Bioorg. Med. Chem. Lett. 2000, 10, 213; (c)
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11. [3H]-RTX binding assay using hVR1/HEK293 cell mem-
branes. Cloning and generation of stable cell lines
expressing human TRPV1. Human TRPV1 was cloned
and stably expressed in HEK293 cells (hVR1/HEK293) as
described by Grant et al. J. Pharm. Exp. Ther. 2002, 300,
9. Preparation of membranes. Human TRPV1/HEK293
were homogenized with a Polytron twice and centrifuged
at 3000 rpm for 10 min in HEPES buffer containing
20 mM HEPES, pH 7.4, NaCl 5.8 mM, sucrose 320 mM,
MgCl2 2 mM, CaCl2 0.75 mM, and KCl 5 mM. The
supernatant was centrifuged at 18,000 rpm for 20 min. The
pellet was saved in a tube and 10 mL assay buffer was
added into the tube. The pellet and buffer were mixed with
a Polytron. Incubation procedure. Incubations for 60 min
at 37 ꢁC were performed in a total volume of 0.5 mL that
contained 120 lg/mL membrane protein and 0.3–0.6 nM
[3H]-RTX (NEN, Boston) in the HEPES buffer. After
incubation, the samples were cooled on ice and 100 lg of
a-acid glycoprotein was added followed by centrifugation
at 13,000 rpm for 15 min. The supernatant was aspirated
and the tips of tubes were cut off into 6 mL vials.
Nonspecific binding was measured in the presence of
200 nM unlabeled RTX in 4 mL scintillation liquid using a
Packard scintillation counter. Data analysis. Percent (%)
inhibition = (total binding ꢁ total binding in presence of
compound) · 100/(total binding ꢁ nonspecific binding). Ki
values were obtained from Prism (GraphPad, San Diego,
CA) calculated using equation of Cheng–Prusoff
(Ki = IC50/(1 + [Ligand]/Kd).
12. Codd, E.; Dax, S. L.; Jetter, M.; McDonnell, M.; McNally,
J. J.; Youngman, M. Aminotetralin-derived urea modula-
tors of vanilloid VR1 receptor. US 6984647B2.
13. 1-(1-benzyl-6-fluoro-1,2,3,4-tetrahydro-naphthalen-2-yl)-3-
isoquinolin-5-yl-urea (2e): Isoquinolin-5-yl-carbamic acid
phenyl ester (0.005 mol, 1.32 g) was dissolved in 15 mL of
DMSO, followed by the addition of 1-benzyl-6-fluoro-
1,2,3,4-tetrahydro-naphthalen-2-ylamine (0.0044 mol, 1.12 g).
The reaction mixture was stirred at room temperature for
16 h then poured into 50 mL of water containing 10 mL of
1 N NaOH. The precipitated solid was collected by
filtration and purified by chromatography on silica gel
eluting with methylene chloride/3% methanol (v/v). The
obtained product was further purified by recrystallization
from ethyl acetate. Thus title compound (1-(1-benzyl-6-
fluoro-1,2,3,4-tetrahydro-naphthalen-2-yl)-3-isoquinolin-5-
yl-urea) was obtained as an off-white solid (1.25 g,
0.00295 mol). MS (MH+): 426; 1H NMR (MeOH): d
1.35 (m, 1H), 1.9 (m, 1H), 2.1–2.2 (m, 1H), 2.9–3.1 (m, 4H)
3.45 (m, 1H), 4.1–4.2 (m, 1H), 6.7 (t, 1H), 6.8–6.9 (m, 2H),
7.1–7.3 (m, 5H), 7.85 (t, 1H), 8.1 (d, 1H), 8.25 (d, 1H), 8.35
(d, 1H), 8.6 (d, 1H).
9. The racemic amines were resolved by chiral salt formation
with chiral mandelic or tartaric acid. Diastereomeric salt
formation and isolation followed by the efficient determi-
nation of %ee by 1H NMR analysis gave >98% pure
enantiomeric amines that were then converted into the
target ureas. The absolute configuration of the enantio-