Tetrahydropyridine-4-carboxamides as novel, potent transient receptor potential vanilloid 1 (TRPV1) antagonists

Article abstract of DOI:10.1016/j.bmc.2008.08.005

A series of 1,2,3,6-tetrahydropyridyl-4-carboxamides, exemplified by 6, have been synthesized and evaluated for in vitro TRPV1 antagonist activity, and in vivo analgesic activity in animal pain models. The tetrahydropyridine 6 is a novel TRPV1 receptor an

Full text of DOI:10.1016/j.bmc.2008.08.005

Bioorganic & Medicinal Chemistry 16 (2008) 8516–8525
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Tetrahydropyridine-4-carboxamides as novel, potent transient receptor
potential vanilloid 1 (TRPV1) antagonists
*
Brian S. Brown , Ryan Keddy, Guo Zhu Zheng , Robert G. Schmidt, John R. Koenig, Heath A. McDonald,
Bruce R. Bianchi, Prisca Honore, Michael F. Jarvis, Carol S. Surowy, James S. Polakowski,
Kennan C. Marsh, Connie R. Faltynek, Chih-Hung Lee
Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Dept R4PM, AP10-207, 100 Abbott Park Road, Abbott Park, IL 60064-6100, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 1,2,3,6-tetrahydropyridyl-4-carboxamides, exemplified by 6, have been synthesized and eval-
uated for in vitro TRPV1 antagonist activity, and in vivo analgesic activity in animal pain models. The
tetrahydropyridine 6 is a novel TRPV1 receptor antagonist that potently inhibits receptor-mediated
Ca2+ influx in vitro induced by several agonists, including capsaicin, N-arachidonoyldopamine (NADA),
and low pH. This compound penetrates the CNS and shows potent anti-nociceptive effects in a broad
range of animal pain models upon oral dosing due in part to its ability to antagonize both central and
peripheral TRPV1 receptors. The SAR leading to the discovery of 6 is presented in this report.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 24 June 2008
Revised 29 July 2008
Accepted 4 August 2008
Available online 7 August 2008
Keywords:
TRPV1
Vanilloid
Pain
CNS
Tetrahydropyridine
1. Introduction
duced calcium influx and similar anti-nociceptive effects in the com-
plete Freund’s adjuvant (CFA) model9 of inflammatory hyperalgesia
The lipophilic vanilloid capsaicin (1) (Fig. 1) activates primary
sensory nociceptors via a specific cell surface receptor, designated
the transient receptor potential vanilloid 1 receptor (TRPV1).1–3
The TRPV1 receptor has been called a ‘‘polymodal detector” of nox-
ious stimuli since it can be activated in several ways,4 including
vanilloids, heat, and acid (pH < 6).
Knockout mice lacking the TRPV1 receptor revealed a marked
absence of responses evoked by noxious stimuli,1,5 and suggest
TRPV1 may be a viable target for the treatment of pain with small
molecule antagonists. The capsaicin analogs capsazepine6 and 2
(BCTC)7 block activation of the channel in response to ligands, acid,
or heat, and reduce inflammation-induced hyperalgesia in animal
models. Recent reviews have described significant progress in
understanding TRPV1 receptor biology as well as antagonist
medicinal chemistry.8 A growing number of TRPV1 antagonists
which display anti-nociceptive effects in vivo have been identified,
including our earlier lead heterocyclic urea 3 (A-795614).9
Comparison of the analgesic profiles of 2 and 3 showed that 2
exhibited far greater potency in the Chung neuropathic pain
model10 than did 3 despite similar in vitro inhibition of capsaicin-in-
(Table 1). This difference was hypothesized to be due to the higher
CNS distribution of 2 relative to the peripherally-restricted 3.
High-throughput screening of the Abbott compound library
identified the hTRPV1 antagonist 4 (Fig. 2), and hit-to-lead efforts
generated a series of biaryl amides, typified by 5, with improved
in vitro potency. Due to the similarity of these compounds to 2,
they were pursued in order to develop analogs possessing a differ-
ent analgesic profile than that of previous series, and to determine
if TRPV1 antagonists with increased central exposure would broad-
en the scope of anti-nociception.
Other researchers have also reported the discovery of 511 in ef-
forts to improve upon the poor solubility and metabolic instabil-
ity of 2. These reports, as well as our own work, demonstrated
that a phenyl ring provided a suitable steric replacement for the
central piperazine ring, maintaining potent TRPV1 antagonism,
but failing to improve aqueous solubility. Our further exploration
of this region demonstrated that a central tetrahydropyridine ring
offered additional improvements in antagonist potency and phys-
icochemical properties, and yielded compounds with significant
distribution into the CNS. Herein we describe our evaluation of
this new series of 1-heteroaryl-1,2,3,6-tetrahydropyridyl-4-car-
boxamides, and the discovery of 6, a potent, orally bioavailable
TRPV1 antagonist that reduces pain-induced behavior in several
animal models.
* Corresponding author. Tel.: +1 847 937 0750; fax: +1 847 935 5466.
E-mail address: brian.s.brown@abbott.com (B.S. Brown).
Present address: Biogen Idec, 14 Cambridge Center, Cambridge, MA 02142, USA.
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.08.005

B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
8517
O
O
O
Cl
N
NH
MeO
HO
HN
N
H
N
H
N
N
N
N
N
H
3 (A-795614)
2 (BCTC)
1 (Capsaicin)
Figure 1. TRPV1 ligands.
Table 1
Potency, CNS distribution, and efficacy comparison of TRPV1 antagonists
Optimization efforts led to replacement of the central aromatic
ring of these biaryl compounds with the non-aromatic, heterocy-
clic 1,2,3,6-tetrahydropyridyl ring, which afforded compounds
with potency comparable to the best biaryl analogs. A comparison
of the crystal structures of three compounds with different central
rings shows considerable topological similarity between the tetra-
hydropyridyl ring and the piperazine ring of 2 (Fig. 3). In these
cases, the overlap of the extended pi-system leads to a much flatter
conformation of the compounds than for the saturated analog 22b,
in which the carbonyl and amide phenyl ring are orthogonal to the
central piperidine ring. Although these crystal conformations may
not be predictive of receptor-bound conformations, they provide a
possible explanation for the potency differences between the series
and corroborate earlier reports regarding the importance of struc-
tural planarity.11b Related studies have shown a similar decrease in
potency (ꢀ20ꢁ) upon replacement of the piperazine urea nitrogen
with a carbon to give the corresponding piperidine.16 That study
also demonstrated TRPV1 agonism for a related piperidine regio-
isomer, but no corresponding hTRPV1 agonist activity was ob-
served for the tetrahydropyridine analogs examined here.
Because of the acrylamide moiety contained within the tetrahy-
dropyridines, compounds 6, 9g, and 14c were examined for reac-
tivity towards covalent modification using the ALARM NMR
technique.17 The lack of reactivity in the assay indicates covalent
binding to TRPV1 is unlikely. Additionally, in vitro electrophysiol-
ogy experiments have also demonstrated reversible binding for 6.
The 4-t-butylaniline amides provided the best in vitro antago-
nist potencies for each pyridine core, and this moiety was used
to optimize the heterocyclic region. Lipophilic, electron-withdraw-
ing groups at the pyridine 3-position gave the greatest potency
(Table 2). The benefit of the pyridyl nitrogen is shown by the great-
er than tenfold loss in potency between compounds 13b and 20b.
Both pyrimidine and thiazole analogs were also potent. Based on
these SAR studies, the 3-(trifluoromethyl)-pyridine arose as the
optimal substituent for this region. The analogs in Table 2 with
TRPV1 IC50 values <50 nM were evaluated for analgesic efficacy
using the CFA pain model. However, in vivo efficacies only ranged
Compound
hTRPV1
[brain]:[plasma]
CFA ED50
mol/kg, po)
Chung ED50
mol/kg, po)
IC50 (cap, nM)a
(
l
(l
2
3
5.3 1.0
5
8
12
8
>300
14
1
0.008
a
All values are the mean SEM of at least two independent experiments run in
triplicate.
2. Chemistry
The target compounds were prepared as shown in Scheme 1.
The heteroarylation of 7,12 followed by deprotection, enol triflate
formation, and carbonylation comprised the preferred route13 to
the corresponding esters. The desired amides were then formed
either via the acid chlorides following ester hydrolysis and chlori-
nation, or directly by AlMe3-mediated reaction14 with the appro-
priate aniline. Heteroarylation of the corresponding cyclic amines
followed by amide formation provided compounds 18b,c,15a and
22b15b, while 20b was synthesized via the above carbonylation
route starting from 19.
3. Results and discussion
Initial hit-to-lead SAR efforts led to the generation of biaryl ana-
logs such as 5, which incorporated a benzamide ring as a central
aryl moiety and a heterocycle at the phenyl 4-position. As with
the prior research on the biaryl analogs,11 the SAR showed that
pyridines bearing electron-withdrawing groups and pyrimidines
were the heterocycles that generated the best TRPV1 receptor
antagonists. Of the pyridyl substituents examined, 3-fluoro-, 3-
chloro-, and 3-trifluoromethyl groups provided the optimal poten-
cies. The three most important interactions for in vitro functional
activity involve the antagonist heterocyclic nitrogen atom, amide
functionality, and aniline ring substitution. In general, bulky sub-
stituents at the aniline 4-position were preferred, showing in-
creased potency with size in the series t-Bu > Et > Me > H.
from 15% to 39% effect at an oral dose of 30 lmol/kg (e.g., 28% for
O
O
O
NH
NH
CF3
NH
N
N
N
OMe
SO2CF3
5
4
6
Compound
4
5
6
hTRPV1 IC50 (cap, nM)a
147 39 42
9
24
2
Figure 2. TRPV1 antagonists. aAll values are the mean SEM of at least two independent experiments run in triplicate.

8518
B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
O
O
8a-g
CO2Me
h, i
Ar
(a or b or c),
N
O
H
N
or j;
ArNH2
HN
N
d, e,
(f or g)
Het
R
Het
R
7
R
Het=
Het=
8a, CF
8b, Cl
R=
R= 9a, CF3
10a, Cl
3
R= 9b, 6, 9d-g, CF3
10b-d, h-k, Cl
11b, CN
Cl
8c, CN
8d, H
11a, CN
12a, H
N
N
N
12b,c, H
8e, F
13a, F
13b,c, F
8f, Me
14a, Me
14c, Me
Br
S
S
S
15a
8g
N
15b,c
N
N
O
Ar
CO2Na
N
O
Cl
N
H
k, i,
ArNH2
N
N
+
HN
N
N
16
17
18b,c
tBu
tBu
O
F
F
N
N
e, f, j,
H
N
N
ArNH2
19
20b
22b
O
Cl
N
H
CO2Et
l + 8b,
HN
h, i,
ArNH2
N
21
Ar=
F
CF3
N
F
Cl
tBu
SO2CF3 Cl
CF3
CF3
Cl
Cl
Cl
Cl
CN
c
e
g
b
d
f
h
i
j
k
Scheme 1. Syntheses of TRPV1 antagonists. Reagents and conditions: (a) K2CO3, DMSO; (b) Et3N, 160 °C, microwave; (c) Pd2(dba)3ꢂCHCl3, BINAP, KOtBu, toluene, 80 °C,
microwave; (d) HCl; (e) LHMDS, PhNTf2; (f) CO, PdCl2(PPh3)2, Et3N, MeOH; (g) CO, Pd(OAc)2, 2-dicyclohexylphosphino-20-(N,N-dimethylamino)biphenyl, Et3N, MeOH, DMF;
(h) NaOH; (i) (COCl)2, pyr; (j) Me3Al, CH2Cl2; (k) H2O, 90 °C; (l) EtOH, 80 °C.
9b). These poor efficacies were attributed to metabolic or pharma-
cokinetic liabilities arising from the t-butylaniline group, since the
t-butylaniline analogs displayed higher in vitro and in vivo clear-
ances than were generally found for other corresponding analogs.
In SAR studies to mitigate the problems with the t-butylaniline
group, compounds were evaluated both for their in vivo efficacy as
well as in vitro potency (Table 3). Replacing the t-butyl group in 9b
with a trifluoromethylsulfonyl group to give 6 resulted in a four-
fold loss of in vitro potency, but significant anti-nociceptive effi-
cacy. In contrast, the 4-Cl analog 9d and the CF3-containing
analog 9e showed better TRPV1 antagonist potency but somewhat
lower in vivo activity than 6. The pyridylamine amide analog 9f
was synthesized to improve physical and pharmacokinetic proper-
ties, and to reduce the oxidative liability of the aryl ring. A similar
substitution proved effective for related compounds found previ-
ously,16 and this analog did show favorable in vivo efficacy and
clearance, but displayed reduced TRPV1 antagonist potency and
oral bioavailability (F = 3%). A nitrile group (9g) was employed to
reduce the metabolism of the t-butyl group, but this analog
showed reduced in vitro potency, and no improvement of in vivo
efficacy relative to 9b.
Although the chloropyridine 10d showed good in vivo and in vi-
tro activities, it also possessed poor pharmacokinetic properties (t1/
2 = 1.7 h, F = 16%, rat, po) and displayed inhibition of hERG. Addi-
tional amide SAR studies based on 10d demonstrated some toler-
ance for substitution at the aniline 3-position, but low tolerance
for substitution at the 2-position.
For the various heterocycles, the 4-(trifluoromethylsulfo-
nyl)aniline containing analogs showed a similar rank-order of the
in vitro potencies as the 4-t-butylanilines (Table 4), with the 3-(tri-
fluoromethyl)pyridyl compound 6 still providing the most potent
analog. Although each compound in this series showed significant
anti-nociceptive effects in vivo, compound 6 possessed the lowest
efficacious plasma level (EPL) of the compounds examined.
The CNS penetration of these tetrahydropyridyl compounds was
generally good. For the SO2CF3-containing analogs, the brain expo-

B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
8519
O
N
N
N
N
H
Cl
2
hTRPV1 IC50 = 5 1 nM
CF3
N
O
O
O
N
N
S
H
CF3
6
hTRPV1 IC50 = 24 2 nM
O
Cl
N
N
H
N
22b
hTRPV1 IC50 = 196 58 nM
Figure 3. Crystallographic analysis of analog conformations.
Table 2
Effects of heterocycle substitution on 4-t-butylaniline analogs
O
NH
N
9b
10b
11b
12b
13b
15b
18b
20b
Ar
tBu
CF3
Cl
CN
F
F
N
S
Ar
N
N
N
N
N
N
N
IC50 (nM)a
6
1
10
2
78 14
27 13
19
3
14
2
10
1
265 44
a
All values are the mean SEM of at least two independent experiments run in triplicate vs. cap.
sure of 6 ([brain]:[plasma] = 1.5) was intermediate between that of
14c (0.7) and 10c (2.2). The exposure found for 9g (1.2) showed
that the sulfone was not required for good brain penetration.
Although 10c offered the highest degree of CNS penetration, it
demonstrated cardiovascular liabilities upon further testing in
anesthetized rats. Compound 14c also caused adverse cardiovascu-
lar effects, a property absent in the 3-trifluoromethylpyridyl deriv-
ative 6. The favorable cardiovascular attributes due to the CF3
group were also conferred on 9g, but replacement of the aniline
SO2CF3 group by the isobutyronitrile moiety led to poorer pharma-
cokinetic properties. Since 6 displayed the best combination of in
vitro potency, analgesic efficacy, therapeutic plasma concentration,
CNS penetration, and favorable cardiovascular profile, it was cho-
sen for further study.
provide a better correlation to rat pain models. Although reversed
in rank-order, both 6 and 3 displayed similar in vitro potencies
both with regard to each other, and to rat and human TRPV1. As
previously shown,9 the CNS penetrant 6 was more potent than
the peripherally restricted antagonist 3 in the CFA mechanical allo-
dynia, capsaicin-induced secondary mechanical hyperalgesia, and
osteoarthritis pain models (Table 5). In further in vivo studies, 6
also showed full reversal of acute, post-operative pain using a
skin-incision model in rats (ED50 = 20
in a rat model of acute inflammatory thermal hyperalgesia pro-
duced by carrageenan (ED50 = 25 mol/kg). Interestingly, both
compounds were essentially inactive in the Chung model
(ED50 > 300 mol/kg), which was the impetus for determining the
lmol/kg), and full efficacy
l
l
effects of CNS exposure on the scope of anti-nociception. While
this result demonstrates the involvement of multiple factors in
pain pathology, the importance of CNS penetration for broad-spec-
trum efficacy in pain models has been previously elaborated as a
result of some of this work.9 Other studies have also shown
the importance of central TRPV1 receptors in the reversal of
CFA-induced mechanical hyperalgesia,18a and in mediating
referred allodynia induced by a visceral stimulus.18b
Compound 6 also potently inhibited Ca2+ influx induced by
stimuli other than capsaicin, such as the endogenous ligand NADA
(IC50 = 20.2 7.7 nM, 3 lM NADA) and low pH (IC50 = 14.0 2.3
nM, pH 5.5), which may be more relevant to natural pain states.
6 was also evaluated as a ligand for other TRP receptors, but
showed little effect at either hTRPM8 or hTRPA1.9
Compound 6 was efficacious in a number of preclinical models
of both acute and chronic pain.9 IC50 values for rat TRPV1 vs. cap-
saicin were determined for both 6 (17 2 nM) and 3 (30 2 nM) to
The primary challenge to the development of 6 was its very low
aqueous solubility (33 ng/mL). The high permeability of the

8520
B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
Table 3
Effects of aniline substitution
O
CF3
NH
Ar
N
6
9d
9e
9f
9g
N
CN
CF3
Ar
SO2CF3
Cl
CF3
N
IC50 (cap, nM)a
CFA efficacyb
24
58%**
2
19
40%*
2
8
2
42
61%**
5
41
25%*
5
35%**
O
Cl
N
NH
Ar
10d
10h
10i
10j
10k
N
F
Cl
F
F3C
Ar
Cl
Cl
Cl
Cl
Cl
IC50 (cap, nM)a
33
2
78
9
124 18
618 88
2746 783
a
All values are the mean SEM of at least two independent experiments run in triplicate.
30 lmol/kg, po dose in rats, with n = 6/dose group.
p < 0.05 vs. vehicle.
p < 0.01 vs. vehicle.
b
*
**
Table 4
Effects of heterocycles on 4-(SO2CF3)aniline core
SO2CF3
O
N
H
6
10c
13c
14c
15c
18c
N
Ar
CF3
Cl
F
Me
N
S
Ar
N
N
N
N
N
N
IC50 (cap, nM)a
CFA efficacyb
EPL c(ng/mL)
24
2
41
3
67
7
35
2
95 12
37%**
2100
44
6
58%**
200
63%**
280
51%**
900
53%**
960
53%**
380
a
All values are the mean SEM of at least two independent experiments run in triplicate.
30 lmol/kg, po dose in rats, with n = 6/dose group.
Efficacious plasma levels at ED50 in rat CFA experiments 1 h after dosing.
p < 0.01 vs. vehicle.
b
c
**
compound, as shown by Caco-2 membrane permeability studies
(Papp = 28.5 ꢁ 10ꢃ6 cm/s), likely contributed significantly to its
broadoralefficacy. Effortstofinda suitableformulation of 6 revealed
that the compound is highly soluble in organic vehicles (>100
mg/mL in PEG-400). A vehicle composed of 10% ethanol, 20% poly-
sorbate-80, and 70% PEG-400 was employed in the in vivo studies
described above. However, 6 demonstrated non-linear pharmacoki-
netic properties on dose escalation, limiting its exposure to levels
below those required for toxicology studies, and precluding it from
further evaluation as a potential clinical candidate.
ing from its preferential CNS distribution. These findings show 6 to
be a useful standard for evaluating TRPV1 antagonists, and provide
further support for the viability of such antagonists as potential
therapeutics for pain.
4. Experimental
4.1. Determination of TRPV1 antagonist activity
The functional antagonist activity of compounds at the TRPV1
receptorwasdeterminedwithaCa2+influxassaybymeasuringtheef-
fect on capsaicin evoked increase in intracellular Ca2+ levels ([Ca2+]i)
using 1321N1 cells stably expressing recombinant human or rat
In conclusion, 1,2,3,6-tetrahydropyridyl-4-carboxamide TRPV1
antagonists show potent analgesic activity in multiple animal pain
models, with 6 displaying enhanced anti-nociceptive effects result-

B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
8521
Table 5
ED50 values for oral doses of 3 and 6 in various pain models in rats9a
4.4. Skin incision-induced acute thermal hyperalgesia
Paw incision was performed under halothane (2–3%) anesthesia,
using procedures previously described.20 Using aseptic techniques,
the plantar aspect of the left hind paw was placed through a hole
in a sterile plastic drape. A 1-cm longitudinal incision was made
through the skin and fascia, starting 0.5 cm from the proximal edge
of the heel and extending towards the toes, the plantar muscle was
elevated and injured longitudinally leaving the muscle origin and
insertion points intact. After hemostasis with gentle pressure, the
skin was apposed with 2 mattress sutures (5–0 nylon). Animals were
allowed to recover for 2 h before behavioral testing.
Assay
3
6
hTPRV1 (cap, nM)a
rTRPV1 (cap, nM)a
[brain]:[plasma]
14
30
0.008
10
1
2
24
17
1.5
10
6
76
40
8
2
2
Nocifensive behavior ED50 (l
mol/kg)b
CFA-induced thermal hyperalgesia ED50
CFA-induced mechanical allodynia ED50
Secondary mechanical allodynia ED50
MIA-induced osteoarthritis ED50 mol/kg)
(
(
l
l
mol/kg)
mol/kg)
12
300
165
280
>300
(lmol/kg)
(
l
Chung ED50
(l
mol/kg)
>300
a
All values are the mean SEM of at least two independent experiments run in
triplicate.
b
Capsaicin-induced.
4.5. General methods
TRPV1. Allcompoundsweretestedover an11-pointhalf-logconcen-
tration range. Compound solutions were prepared in D-PBS (4ꢁ final
concentration), and diluted serially across 96-well v-bottom tissue
culture plates using a Biomek 2000 robotic automation workstation
1H NMR spectra were obtained at 300 MHz using Me4Si as an
internal standard. Low-resolution mass spectra were recorded on
a Finnigin-4000 instrument, and high-resolution were recorded
on an Agilent LC/MSDTOF instrument. Elemental analyses were ob-
tained from Quantitative Technologies, Inc., and were within 0.4%
of theoretical values unless otherwise noted. Chromatography
was performed with EM Science silica gel 60 (230–400 mesh) or
Analogix Super Flash columns. Reactions were conducted under
an inert N2 atmosphere using commercial high-purity solvents as
received. All materials were obtained and used as-received from
commercial sources unless otherwise noted.
(Beckman–Coulter, Inc., Fullerton, CA). A 0.2 lM solution of the
TRPV1 agonist capsaicin was also prepared in D-PBS. The fluorescent
Ca2+ chelatingdyefluo-4wasusedasanindicatoroftherelativelevels
of[Ca2+]iina96-wellformatusingaFluorescenceImagingPlateRead-
er (FLIPR) (Molecular Devices, Sunnyvale, CA). Cells were grown to
confluency in 96-well black-walled tissue culture plates. Then, prior
to the assay, the cells were loaded with 100
(2 M, in D-PBS) for 1–2 h at 23 °C. Following washing of the cells
(2 ꢁ 1 mL D-PBS per well) to remove extracellular fluo-4 Am, plates
containingthecellsin100 LD-PBSwereplacedinthereadingcham-
lL per well of fluo-4 AM
l
l
4.6. Methyl 1-(3-(trifluoromethyl)pyridin-2-yl)-1,2,3,6-
tetrahydropyridine-4-carboxylate (9a)
ber of the FLIPR instrument. Fifty microliters of the compound solu-
tions were added to the cells at the 10 s time mark of the
experimental run. After 3 min, 50
l
L of the capsaicin solution was
To a solution of 8a (14.2 g, 78 mmol) and 7 (15 mL, 117 mmol)
in DMSO (155 mL) was added K2CO3 (13.0 g, 94 mmol). The reac-
tion mixture was heated to 100 °C for 5 h. After cooling to rt, the
mixture was partitioned between H2O and Et2O. The organic layer
was separated and washed with brine, and then concentrated in
vacuo. The residue was dissolved in concentrated HCl (50 mL)
and stirred overnight. The mixture was then neutralized with
NH4OH (50 mL) and extracted with ether. The organic layer was
dried (Na2SO4), concentrated, and chromatographed (gradient elu-
tion of 10% to 50% Et2O/Hex) to give the corresponding substituted
piperidinone as a white solid (12.4 g, 65%): 1H NMR (300 MHz,
CDCl3) d 8.46 (d, J = 4.6 Hz, 1H), 7.92 (d, J = 7.6 Hz, 1H), 7.07 (dd,
J = 4.6, 7.6 Hz, 1H), 3.59 (t, J = 5.9 Hz, 4H), 2.61 (t, J = 5.9 Hz, 4H).
To a solution of the above 1-(3-(trifluoromethyl)pyridin-2-
yl)piperidin-4-one (7.2 g, 29.5 mmol) and PhNTf2 (11.6 g,
31 mmol) in THF (60 mL) at ꢃ78 °C was added dropwise LHMDS
(1 N in THF, 33 mL, 33 mmol) over 30 min. The mixture was stirred
at this temperature for 1 h and then allowed to warm to rt, concen-
trated, dissolved in 1:1 EtOAc/Hex and then washed with 1 N
NaOH. The organic layer was dried (Na2SO4), concentrated, and
chromatographed (10% to 30% Et2O/Hex gradient elution) to give
the vinyl triflate as a clear oil (7.0 g, 63%): 1H NMR (300 MHz,
CDCl3) d 8.41 (dd, J = 1.4, 4.7 Hz, 1H), 7.89 (dd, J = 1.4, 7.8 Hz, 1H),
7.01 (ddd, J = 1.4, 4.7, 7.8 Hz, 1H), 5.86 (sept, J = 1.5 Hz, 1H), 3.99
(q, J = 3.7 Hz, 2H), 3.55 (t, J = 5.8 Hz, 2H), 2.59–2.66 (m, 2H).
To a 1:1 mixture of MeOH:DMF (80 mL) that had been saturated
with CO, were added the above triflate (7.0 g, 19 mmol), PPh3
(377 mg, 1.4 mmol), Pd(OAc)2 (105 mg, 0.47 mmol), and Et3N
(5.2 mL, 37 mmol). This mixture was stirred under CO (1 atm)
overnight and was then diluted with H2O and extracted with
Et2O, and the combined organic layers were washed with brine,
dried (Na2SO4), concentrated, and chromatographed (10% to 30%
Et2O/Hex gradient elution) to give 9a as a white solid (5.5 g,
19 mmol, quant.): 1H NMR (300 MHz, CDCl3) d 8.40 (dd, J = 1.7,
4.8 Hz, 1H), 7.87 (dd, J = 1.7, 7.8 Hz, 1H), 7.01 (sept, J = 1.7 Hz,
added (0.05 M final concentration, final volume = 200
l
lL) to acti-
vate the TRPV1 receptor. Fluorescence readings were made at 1 to
5 s intervals over the 240 s course of the experimental run. The peak
increase in relative fluorescence units (minus baseline) was calcu-
latedandexpressedasapercentageofthe0.05 lMcapsaicin(control)
response. Curve-fits of the data were solved using a four-parameter
logistic Hill equation in GraphPad PrismÒ (GraphPad Software, Inc.,
San Diego, CA), and IC50 values were calculated.
4.2. Animals
Male Sprague–Dawley rats (Charles River Laboratories, Wil-
mington, MA), weighing 200–320 g were group housed, and given
food and water ad libitum, except before oral administration of
drugs when food was removed for 16 h before dosing.
4.3. Thermal hyperalgesia assessment
Unilateral inflammation was induced by injecting 100
lL of a 1%
solution of k-carrageenan or 150 L of a 50% solution of complete
l
Freund’s adjuvant (CFA) (Sigma Chemical Co., St. Louis, MO) in phys-
iological saline into the plantar surface of the right hindpaw of the
rat. The hyperalgesia to thermal stimulation was determined 2 h
after carrageenan injections or 48 h after CFA injections using a com-
mercially available paw thermal stimulator (UARDG, University of
California, San Diego, CA; Dirig and Yaksh, 1995), modeled after that
described by Hargreaves.19 Animals were placed individually in
Plexiglass cubicles mounted on a glass surface maintained at 30 °C,
and allowed a 30 min habituation period. A thermal stimulus, in
the form of radiant heat emitted from a focused projection bulb,
was then applied to the plantar surface of each hindpaw. In each test
session, each rat was tested in 3 sequential trials at approximately
5 min intervals. Paw withdrawal latencies were calculated as the
mean of the two shortest latencies.

8522
B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
1H), 6.96 (ddd, J = 1.0, 4.8, 7.8 Hz, 1H), 4.03 (q, J = 3.0 Hz, 2H), 3.77
(s, 3H), 3.44 (t, J = 5.4 Hz, 2H), 2.53–2.61 (m, 2H).
J = 8.5 Hz, 2H), 7.60 (d, J = 8.5 Hz, 2H), 7.54 (s, 1H), 7.00 (dd,
J = 7.8, 4.7 Hz, 1H), 6.81 (sept, J = 1.7 Hz, 1H), 4.08 (q,
J = 3.1 Hz, 2H), 3.52 (t, J = 5.6 Hz, 2H), 2.64–2.72 (m, 2H);
HRMS (FAB) calc for C19H15F6N3O (M+) m/z 415.1119; found
415.1117.
4.7. 1-(3-(Trifluoromethyl)pyridin-2-yl)-N-(4-(trifluoro-
methylsulfonyl)phenyl)-1,2,3,6-tetrahydropyridine-4-
carboxamide (6)
4.11. 1-(3-(Trifluoromethyl)pyridin-2-yl)-N-(6-(trifluoro-
methyl)pyridin-3-yl)-1,2,3,6-tetrahydropyridine-4-
carboxamide (9f)
To a solution of 4-(trifluoromethylsulfonyl)-aniline (8.38 g,
37.2 mmol) in CH2Cl2 (90 mL) was added Me3Al (2 N in toluene,
18.6 mL, 37.2 mmol) dropwise. After 30 min, 9a (5.5 g, 18.6 mmol)
in CH2Cl2 (10 mL) was added. The mixture was stirred at rt for 2 h.
The mixture was then diluted with EtOAc and then quenched with
0.5 N HCl. The organic layer was washed with 1 N NaOH, H2O, and
brine, and dried (Na2SO4). The product was chromatographed (0%
to 30% EtOAc/(1:1 CH2Cl2:Hex) gradient elution) and triturated
with Et2O to give 6 as a white solid (7.24 g, 81%): 1H NMR
As for 9b (96%): 1H NMR (300 MHz, DMSO-d6) d 10.32 (s, 1H),
9.01 (d, J = 2.2 Hz, 1H), 8.53 (dd, J = 1.7, 4.8 Hz, 1H), 8.40 (dd,
J = 2.2, 8.3 Hz, 1H), 8.10 (dd, J = 1.7, 7.8 Hz, 1H), 7.87 (d,
J = 8.3 Hz, 1H), 7.19 (ddd, J = 1.0, 4.8, 7.8 Hz, 1H), 6.90 (sept,
J = 1.7 Hz, 1H), 4.02 (q, J = 2.8 Hz, 2H), 3.40 (t, J = 5.4 Hz, 2H),
2.53–2.61 (m, 2H); MS (CI) m/z 417.1 (M+H)+. Anal (C18H14F6N4O)
C, H, N.
(300 MHz, CDCl3)
d 8.43 (dd, J = 1.7, 4.6 Hz, 1H), 8.00 (d,
J = 8.8 Hz, 2H), 7.88–7.92 (m, 3H), 7.75 (br s, 1H), 7.02 (dd, J = 4.6,
7.5 Hz, 1H), 6.85 (sept, J = 1.7 Hz, 1H), 4.09 (q, J = 3.0 Hz, 2H),
3.52 (t, J = 5.4 Hz, 2H), 2.64–2.72 (m, 2H); MS (ESI+) m/z 480.3
(M+H)+. Anal (C19H15F6N3O3S) C, H, N.
4.12. N-(4-(2-Cyanopropan-2-yl)phenyl)-1-(3-(trifluoro-
methyl)pyridin-2-yl)-1,2,3,6-tetrahydropyridine-4-
carboxamide (9g)
4.8. N-(4-tert-Butylphenyl)-1-(3-(trifluoromethyl)pyridin-2-yl)-
1,2,3,6-tetrahydropyridine-4-carboxamide (9b)
As for 9b using 1,1-dimethyl-(4-aminophenyl)-acetonitrile21
(51%): 1H NMR (300 MHz,CDCl3) d ppm 8.43 (dd, J = 4.7, 2.0 Hz,
1H), 7.89 (dd, J = 7.8, 2.0 Hz, 1H), 7.59 (d, J = 8.8 Hz, 2H), 7.42–
7.47 (m, 3H), 7.00 (dd, J = 7.8, 4.7 Hz, 1H), 6.79 (sept, J = 1.7 Hz,
1H), 4.07 (q, J = 3.1 Hz, 2H), 3.53 (t, J = 5.4 Hz, 2H), 2.64-2.71 (m,
2H), 1.72 (s, 6 H); HRMS (ESI-TOF) calc for C22H21F3N4O (M+H+)
m/z 415.17402; found 415.17443.
Ester 9a (3.89 g, 13.5 mmol) was dissolved in MeOH (15 mL)
and THF (30 mL), and stirred with 1 N NaOH (27 mL) for 2 h. Addi-
tional 1 N NaOH (16 mL) was added and stirred for 1 h, followed by
another aliquot (14.5 mL) for 1 h. The mixture was then diluted
with water, and extracted with CH2Cl2. The aqueous layer was then
acidified with conc HCl and extracted with CHCl3. The organic layer
was dried (Na2SO4) and concentrated to give the corresponding
acid as a tan solid (3.00 g, 11.0 mmol, 81%): 1H NMR (300 MHz,
CD3OD) d 8.45 (m, 1H), 7.99 (dd, J = 2.4, 7.8 Hz, 1H), 7.08-7.14
(m, 1H), 7.02 (sept, J = 1.7 Hz, 1H), 3.99 (q, J = 3.1 Hz, 2H), 3.39 (t,
J = 5.6 Hz, 2H), 2.45–2.53 (m, 2H); MS (ESI+) m/z 273.1 (M+H)+.
To a suspension of the acid (0.300 g, 1.10 mmol) and DMF (cat)
in CH2Cl2 (4 mL) was added (COCl)2 (0.14 mL, 1.6 mmol). The mix-
ture was stirred for 90 min, diluted with PhMe (1 mL), concen-
trated to dryness, and dissolved in CH2Cl2 (4 mL). To the solution
were added pyridine (0.14 mL, 1.7 mmol), DMAP (cat), and 4-t-
butylaniline (0.21 mL, 1.3 mmol). The mixture was stirred 1 h, di-
luted with water and extracted with CH2Cl2, dried (Na2SO4), and
purified by flash chromatography (3% EtOAc/CH2Cl2) to give 9b
as a white solid (0.33 g, 0.82 mmol, 74%): 1H NMR (300 MHz,
CDCl3) d 8.42 (dd, J = 1.6, 4.4 Hz, 1H), 7.89 (dd, J = 1.6, 7.5 Hz, 1H),
7.47 (d, J = 8.8 Hz, 2H), 7.36 (d, J = 8.8 Hz, 3H), 6.98 (dd, J = 4.4,
7.5 Hz, 1H), 6.76 (sept, J = 1.7 Hz, 1H), 4.06 (q, J = 2.8 Hz, 2H),
3.53 (t, J = 5.4 Hz, 2H), 2.63–2.70 (m, 2H), 1.31 (s, 9H); MS (ESI+)
m/z 404.4 (M+H)+. Anal (C22H24F3N3O) C, H, N.
4.13. N-(4-tert-Butylphenyl)-1-(3-chloropyridin-2-yl)-1,2,3,6-
tetrahydropyridine-4-carboxamide (10b)
The method used for 9a,b was also used starting with 2,3-
dichloropyridine to give the corresponding acid: 1H NMR
(300 MHz, DMSO-d6) d 12.36 (br s, 1H), 8.20 (dd, J = 1.7, 4.8 Hz,
1H), 7.81 (dd, J = 1.7, 7.8 Hz, 1H), 6.98 (dd, J = 4.8, 7.8 Hz, 1H),
6.94 (sept, J = 1.7 Hz, 1H), 3.98 (q, J = 3.0 Hz, 2H), 3.41 (t,
J = 5.4 Hz, 2H), 2.37–2.45 (m, 2H). A mixture of the acid (120 mg,
70%, 0.35 mmol), 4-t-butylaniline (90.0 mg, 0.6 mmol) and EDCI
(145 mg, 0.75 mmol) in dichloromethane (3 mL) were placed in a
flask under N2. The mixture was stirred at rt overnight, and
quenched with water. The organic layer was separated, and the sol-
vent was removed. The crude product was then purified via col-
umn chromatography (25% EtOAc/hex) to give 10b (95 mg, 74%):
1H NMR (500 MHz, CDCl3) d 8.18 ppm (dd, J = 1.7, 4.7 Hz, 1H),
7.61 (dd, J = 1.7, 7.8 Hz, 1H), 7.46 (d, J = 8.7 Hz, 2H), 7.38 (br s,
1H), 7.35 (d, J = 8.7 Hz, 2H), 6.85 (dd, J = 4.7, 7.8 Hz, 1H), 6.75–
6.78 (m, 1H), 4.10 (q, J = 2.8 Hz, 2H), 3.58 (t, J = 5.6 Hz, 2H), 2.67–
2.71 (m, 2H), 1.30 (s, 9H). HRMS (ESI-TOF) calc for C21H24ClN3O
(M+H)+ m/z 370.16807; found 370.16883.
4.9. N-(4-Chlorophenyl)-1-(3-(trifluoromethyl)pyridin-2-yl)-
1,2,3,6-tetrahydropyridine-4-carboxamide (9d)
4.14. 1-(3-Chloropyridin-2-yl)-N-(4-(trifluoromethylsulfonyl)-
phenyl)-1,2,3,6-tetrahydropyridine-4-carboxamide (10c)
As for 9b (45%): 1H NMR (300 MHz, CDCl3) d 8.42 (dd, J = 1.8,
5.0 Hz, 1H), 7.89 (dd, J = 1.8, 7.8 Hz, 1H), 7.51 (d, J = 9.1 Hz, 2H),
7.43 (br s, 1H), 7.30 (d, J = 9.1 Hz, 2H), 6.99 (dd, J = 5.0, 7.8 Hz,
1H), 6.77 (sept, J = 1.7 Hz, 1H), 4.05 (q, J = 3.0 Hz, 2H), 3.51 (t,
J = 5.4 Hz, 2H), 2.62–2.70 (m, 2H); HRMS (ESI-TOF) calc for
As for 9b (75%): 1H NMR (300 MHz, CDCl3) d 8.19 (dd, J = 1.7,
4.8 Hz, 1H), 8.00 (d, J = 8.8 Hz, 2H), 7.89 (d, J = 8.8 Hz, 2H), 7.82
(br s, 1H), 7.65 (dd, J = 1.7, 7.8 Hz, 1H), 6.85–6.92 (m, 2H), 4.15
(q, J = 3.1 Hz, 2H), 3.60 (t, J = 5.4 Hz, 2H), 2.66–2.73 (m, 2H). MS
(ESI) m/z 446 (M+H)+. Anal. (C18H15ClF3N3O3S) C, H, N.
C
18H15ClF3N3O (M+H)+ m/z 382.09285; found 382.09363.
4.10. N-(4-(Trifluoromethyl)phenyl)-1-(3-(trifluoromethyl)-
4.15. N-(4-Chlorophenyl)-1-(3-chloropyridin-2-yl)-1,2,3,6-
pyridin-2-yl)-1,2,3,6-tetrahydropyridine-4-carboxamide (9e)
tetrahydropyridine-4-carboxamide (10d)
As for 9b (54%): 1H NMR (300 MHz, CDCl3) d ppm 8.43 (dd,
J = 4.7, 1.4 Hz, 1H), 7.89 (dd, J = 7.8, 1.7 Hz, 1H), 7.70 (d,
As for 9b (49%): 1H NMR (500 MHz, CDCl3) d 8.20(dd, J = 1.7,
5.0 Hz, 1H), 7.70 (dd, J = 1.7, 7.5 Hz, 1H), 7.62 (br s, 1H), 7.54 (d,

B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
8523
J = 9.1 Hz, 2H), 7.30 (d, J = 9.1 Hz, 2H), 6.92 (dd, J = 5.0, 7.5 Hz, 1H),
4.22. 1-(Pyridin-2-yl)-N-(4-(trifluoromethylsulfonyl)phenyl)-
6.76 (sept, J = 1.9 Hz, 1H), 4.16 (q, 2.8 Hz, 2H), 3.64 (t, J = 5.6 Hz,
2H), 2.66–2.72 (m, 2H). MS (ESI) m/z 350 (M+H)+. Anal
(C17H15Cl2N3OꢂHCl+0.75 CH2Cl2) C, H, N.
1,2,3,6-tetrahydropyridine-4-carboxamide (12c)
As for 9a,b (37%): 1H NMR (300 MHz, DMSO-d6) d 10.48 (br s,
1H), 8.12–8.17 (m, 3H), 8.08 (d, J = 9.1 Hz, 2H), 7.57 (ddd, J = 2.0,
7.1, 9.2 Hz, 1H), 6.91–6.96 (m, 1H), 6.88 (d, J = 8.8 Hz, 1H), 6.66
(ddd, J = 0.7, 5.1, 7.1 Hz, 1H), 4.20 (q, J = 3.1 Hz, 2H), 3.74 (t,
J = 5.8 Hz, 2H), 2.49 (buried); MS (CI) m/z 412 (M+H)+. Anal
(C18H16F3N3O3S+0.15 CF3CO2H) C, H, N.
4.16. N-(4-Chloro-3-fluorophenyl)-1-(3-chloropyridin-2-yl)-
1,2,3,6-tetrahydropyridine-4-carboxamide (10h)
As for 9b (44%): 1H NMR (300 MHz, DMSO-d6) d ppm 10.05
(s, 1H), 8.22 (dd, J = 4.7, 1.7 Hz, 1H), 7.83–7.85 (m, 2H), 7.50–
7.53 (m, 2H), 7.01 (dd, J = 7.8, 4.7 Hz, 1H), 6.80–6.85 (m, 1H),
4.02 (q, J = 2.9 Hz, 2H), 3.45 (t, J = 5.4 Hz, 2H), 2.52–2.59 (m,
2H); MS (ESI+) m/z 366 (M+H)+. Anal (C17H14Cl2FN3O+0.6
CH2Cl2) C, H, N.
4.23. N-(4-tert-Butylphenyl)-1-(3-fluoropyridin-2-yl)-1,2,3,6-
tetrahydropyridine-4-carboxamide (13b)
As for 9a,b (37%): 1H NMR (300 MHz, CDCl3) d 8.02 (dt, J = 1.7,
4.8 Hz, 1H), 7.46 (d, J = 8.5 Hz, 2H), 7.39 (br s, 1H), 7.36 (d,
J = 8.5 Hz, 2H), 7.27 (ddd, J = 1.4, 7.8, 13.2 Hz, 1H), 6.73–6.80 (m,
2H), 4.22 (q, J = 3.1 Hz, 2H), 3.72 (t, J = 5.4 Hz, 2H), 2.61–2.69 (m,
2H), 1.31 (s, 9H); MS (ESI+) m/z 354 (M+H)+. Anal
(C21H24FN3O+0.21 CF3CO2H) C, H, N.
4.17. 1-(3-Chloropyridin-2-yl)-N-(3,4-dichlorophenyl)-1,2,3,6-
tetrahydropyridine-4-carboxamide (10i)
Asfor9b(47%):1HNMR(300 MHz, DMSO-d6)d ppm10.01 (s, 1H),
8.22 (dd, J = 4.7, 1.7 Hz, 1H), 8.07 (d, J = 2.4 Hz, 1H), 7.83 (dd, J = 7.8,
1.7 Hz, 1H), 7.67 (dd, J = 8.8, 2.4 Hz, 1H), 7.57 (d, J = 8.8 Hz, 1H), 7.01
(dd, J = 7.8, 4.7 Hz, 1H), 6.80–6.84 (m, 1H), 4.02 (q, J = 2.8 Hz, 2H),
3.45 (t, J = 5.4 Hz, 2H), 2.52–2.59 (m, 2H); MS (ESI+) m/z 382
(M+H)+. Anal (C17H14Cl3N3O+0.65 CF3CO2H) C, H, N.
4.24. 1-(3-Fluoropyridin-2-yl)-N-(4-(trifluoromethylsulfonyl)-
phenyl)-1,2,3,6-tetrahydropyridine-4-carboxamide (13c)
As for 9a,b (35%): 1H NMR (300 MHz, CDCl3) d7.97–8.05 (m, 3H),
7.90 (d, J = 8.8 Hz, 2H), 7.83 (br s, 1H), 7.30 (ddd, J = 1.7, 7.8,
13.2 Hz, 1H), 6.84–6.88 (m, 1H), 6.80 (ddd, J = 3.0, 4.7, 7.8 Hz,
1H), 4.25 (q, J = 3.0 Hz, 2H), 3.74 (t, J = 5.8 Hz, 2H), 2.62–2.69 (m,
2H); MS (ESI+) m/z 430 (M+H)+. Anal (C18H15F4N3O3S+0.25
CF3CO2H) C, H, N.
4.18. N-(4-Chloro-2-fluorophenyl)-1-(3-chloropyridin-2-yl)-
1,2,3,6-tetrahydropyridine-4-carboxamide (10j)
As for 9b (19%): 1H NMR (400 MHz, DMSO-d6) d ppm 9.60
(s, 1H), 8.22 (d, J = 1.5 Hz, 1H), 7.82 (dd, J = 7.8, 1.7 Hz, 1H),
7.58 (t, J = 8.4 Hz, 1H), 7.49 (dd, J = 10.4, 2.5 Hz, 1H), 7.26–
7.29 (m, 1H), 7.00 (dd, J = 7.7, 4.6 Hz, 1H), 6.84–6.88 (m, 1H),
4.02 (q, J = 2.8 Hz, 2H), 3.46 (t, J = 5.5 Hz, 2H), 2.52–2.58 (m,
2H); MS (ESI+) m/z 366 (M+H)+. Anal (C17H14Cl2FN3O+0.45
CF3CO2H) C, H, N.
4.25. 1-(3-Methylpyridin-2-yl)-N-(4-(trifluoromethyl-
sulfonyl)phenyl)-1,2,3,6-tetrahydropyridine-4-carboxamide
(14c)
A mixture of 8f (5.0 mL, 45.8 mmol), Pd2dba3ꢂCHCl3 (0.958 g,
0.926 mmol), rac-BINAP (1.43 g, 2.30 mmol), NaOtBu (8.51 g,
88.6 mmol), and 7 (5.6 mL, 44 mmol) in PhMe (135 mL) was heated
to 100 °C for 3.5 h, diluted with EtOAc, washed with water and
brine, dried (Na2SO4), and filtered through silica with 70% Et2O/
Hex to give 11.5 g of impure substituted pyridine as a red oil. This
material was stirred in conc. HCl (60 mL) for 6 h, quenched with
conc NH4OH (80 mL), diluted with EtOAC, washed with water
and brine, dried (Na2SO4), and filtered through silica with 80%
Et2O/Hex to give the impure corresponding ketone as a red oil
(7.35 g), which was used without further purification.
4.19. N-(4-Chloro-2-(trifluoromethyl)phenyl)-1-(3-chloropyridin-
2-yl)-1,2,3,6-tetrahydropyridine-4-carboxamide (10k)
As for 9b (9%): 1H NMR (400 MHz, DMSO-d6) d ppm 9.57 (s, 1H),
8.22 (dd, J = 4.8, 1.7 Hz, 1H), 7.81–7.84 (m, 2H), 7.78 (dd, J = 8.6,
2.5 Hz, 1H), 7.52 (d, J = 8.3 Hz, 1H), 7.00 (dd, J = 7.8, 4.8 Hz, 1H),
6.81–6.84 (m, 1H), 4.02 (q, J = 2.8 Hz, 2H), 3.46 (t, J = 5.4 Hz, 2H),
2.52–2.57 (m, 2H); HRMS (ESI-TOF) calc for
C18H14Cl2F3N3O
(M+H)+ m/z 416.05388; found 416.05440.
To a solution of the crude ketone (7.35 g, 38.6 mmol) and
PhNTf2 (13.9 g, 39.0 mmol) in THF (60 mL) at ꢃ78 °C was added a
solution of LHMDS in THF (1 N, 33 mL, 33 mmol) dropwise. The
mixture was stirred at this temperature for 5 min and allowed to
warm to rt with stirring for 2 h. The mixture was then concen-
trated, dissolved in 1:1 EtOAc/Hex, washed with 1 N NaOH, sat
aq NaHCO3, and brine. The organic layer was dried (Na2SO4), and
concentrated to give the crude triflate as a brown solid (13.2 g,
ꢀquant), which was used without purification. This residue,
Pd(OAc)2 (0.263 g, 1.17 mmol), 2-dicyclohexylphosphino-20-(N,N-
dimethylamino)biphenyl (0.921 g. 2.34 mmol), and Et3 N (12 mL,
86 mmol) was dissolved in a 1:1 solution of MeOH:DMF (80 mL)
that had been saturated with CO, and the mixture was stirred un-
der CO (1 atm) overnight. The mixture was concentrated, diluted
with EtOAc, washed with water and brine, dried (Na2SO4), concen-
trated, and chromatographed (10–40% Et2O/Hex) to give 14a as a
black gummy oil (4.73 g, 20.4 mmol, 53%).
4.20. N-(4-tert-Butylphenyl)-1-(3-cyanopyridin-2-yl)-1,2,3,6-
tetrahydropyridine-4-carboxamide (11b)
As for 9a,b (21%): 1H NMR (300 MHz, DMSO-d6) d ppm 9.66
(br s, 1H), 8.42 (dd, J = 2.0, 4.7 Hz, 1H), 8.09 (dd, J = 2.0, 7.8 Hz,
1H), 7.68 (d, J = 8.8 Hz, 2H), 7.32 (d, J = 8.8 Hz, 2H), 6.93 (dd,
J = 4.7, 7.8 Hz, 1H), 6.73–6.78 (m, 1H), 4.28 (q, J = 3.0 Hz, 2H),
3.81 (t, J = 5.4 Hz, 2H), 2.53–2.61 (m, 2H), 1.26 (s, 9H); HRMS
(ESI-TOF) calc for C22H24N4O (M+H)+ m/z 361.20229; found
361.20228.
4.21. N-(4-tert-Butylphenyl)-1-(pyridin-2-yl)-1,2,3,6-tetrahy-
dropyridine-4-carboxamide (12b)
As for 9a,b (33%): 1H NMR (300 MHz, DMSO-d6) d 9.67 (br s,
1H), 8.14 (dd, J = 1.7, 4.8 Hz, 1H), 7.52–7.61 (m, 3H), 7.32 (d,
J = 8.8 Hz, 2H), 6.86 (d, J = 8.5 Hz, 2H), 6.76–6.80 (m, 1H), 6.65
(dd, J = 4.8, 6.8 Hz, 1H), 4.14 (q, J = 3.0 Hz, 2H), 3.73 (t, J = 5.4 Hz,
2H), 2.44–2.52 (buried m, 2H), 1.26 (s, 9H); MS (CI) m/z 336
(M+H)+. Anal (C21H25N3O+0.11 CF3CO2H) C, H, N.
To a solution of 4-(trifluoromethylsulfonyl) aniline (3.79 g,
16.8 mmol) in CH2Cl2 (17 mL) was added Me3Al (2 N in Hex,
8.4 mL, 16.8 mmol) dropwise. After 1 h, 14a (1.95 g, 8.4 mmol) in
CH2Cl2 (5 mL) was added. The mixture was stirred at 40 C for 2 h,

8524
B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
diluted with EtOAc and quenched with 1 N HCl. The organic layer
was washed with 1 N NaOH, sat aq NaHCO3, and then brine, dried
(Na2SO4), concentrated, and chromatographed (40–100% Et2O/
Hex) to give 14c as a yellow solid (1.24 g, 2.90 mmol, 35%): 1H
6.82–6.87 (m, 1H), 6.57 (t, J = 4.8 Hz, 1H), 4.48 (q, J = 2.7 Hz, 2H),
4.06 (t, J = 5.8 Hz, 2H), 2.57–2.64 (m, 2H); MS (ESI+) m/z 413
(M+H)+. Anal (C17H15F3N4O3S) C, H, N.
NMR (300 MHz, CDCl3)
d
8.19 (d, J = 4.4 Hz, 1H), 8.00 (d,
4.30. N-(4-tert-Butylphenyl)-1-(2-fluorophenyl)-1,2,3,6-tetrahy-
J = 8.8 Hz, 2H), 7.93 (d, J = 8.8 Hz, 2H), 7.51 (d, J = 7.1 Hz, 1H),
6.94 (dd, J = 5.4, 7.5 Hz, 1H), 6.86–6.91 (m, 1H), 4.04 (q, J = 2.7 Hz,
2H), 3.88 (t, J = 5.4 Hz, 2H), 2.59–2.67 (m, 2H), 2.34 (s, 3H); MS
(ESI+) m/z 426 (M+H)+. Anal (C19H18F3N3O3S) H, N, C: calcd,
53.64; found, 53.21.
dropyridine-4-carboxamide (20b)
To a solution of 1-(2-fluoro-phenyl)-piperidin-4-one (0.98 g,
5.1 mmol) and PhNTf2 (1.89 g, 5.3 mmol) in THF (10 mL) at
ꢃ78 °C was added LHMDS (1 N in THF, 5.6 mL, 5.6 mmol) dropwise
over 30 min. The mixture was stirred at this temperature for
30 min and then allowed to warm to RT over 1 h. The solvent
was then removed in vacuo and the residue was dissolved in a
1:1 mixture of EtOAc and Hex and then washed with 1 N NaOH.
The organic layer was dried over Na2SO4 and then filtered through
a plug of silica gel eluted with 1:1 EtOAc/Hex, which was used
without further purification. To a solution of this crude triflate in
1:1 MeOH/DMF (20 mL) that had been saturated with CO was
added 2-dicyclohexylphosphino-20-(N,N-dimethylamino)biphenyl
(177 mg, 0.45 mmol), Pd(OAc)2 (34 mg, 0.15 mmol), and Et3N
(1.6 mL, 10.2 mmol). This mixture was stirred under CO (1 atm)
overnight and then partitioned between H2O and Et2O. The organic
layer was washed with brine and then dried over Na2SO4, and con-
centrated in vacuo. The product was passed through a plug of silica
gel eluting with CH2Cl2 to give 1.09 g of the corresponding ester as
pale oil (4.63 mmol, 91%).
4.26. N-(4-tert-Butylphenyl)-1-(thiazol-2-yl)-1,2,3,6-
tetrahydropyridine-4-carboxamide (15b)
As for 9a,b (29%): 1H NMR (300 MHz, DMSO-d6) d ppm 9.71 (s,
1H), 7.58 (d, J = 8.8 Hz, 2H), 7.32 (d, J = 8.8 Hz, 2H), 7.20 (d,
J = 3.7 Hz, 1H), 6.86 (d, J = 3.7 Hz, 1H), 6.71–6.76 (m, 1H), 4.10 (q,
J = 2.7 Hz, 2H), 3.62 (t, J = 5.8 Hz, 2H), 2.50–2.56 (buried m, 2H),
1.26 (s, 9H); MS (DCI+) m/z 342 (M+H)+. Anal (C19H23N3OS+0.25
CF3CO2H) C, H, N.
4.27. 1-(Thiazol-2-yl)-N-(4-(trifluoromethylsulfonyl)phenyl)-
1,2,3,6-tetrahydropyridine-4-carboxamide (15c)
As for 9a,b (14%): 1H NMR (300 MHz, DMSO-d6) d ppm 10.52 (s,
1H), 8.05–8.16 (m, 4H), 7.20 (d, J = 3.4 Hz, 1H), 6.86–6.90 (m, 2H),
4.15 (q, J = 2.5 Hz, 2H), 3.63 (t, J = 5.8 Hz, 2H), 2.52–2.59 (buried m,
To a solution of 4-t-butylaniline (158 lL, 1.0 mmol) in CH2Cl2
2H); HRMS (ESI-TOF) calcd for
418.05014; found 418.05059.
C
16H14F3N3O3S2 (M+H)+ m/z
(7.5 mL) was added Me3Al (2 N, in toluene, 0.5 mL, 1.0 mmol) drop-
wise. The mixture was stirred for 30 min. and then the above
methyl ester (117 mg, 0.497 mmol) was added and the mixture
was heated to reflux overnight. After cooling to 0 °C the reaction
was quenched by the careful addition of 1 N HCl and then ex-
tracted with EtOAc. The organic layer was then washed with 1 N
NaOH, brine, dried (Na2SO4), concentrated, and chromatographed
(0% to 4% EtOAc/CH2Cl2 gradient elution) to give 20b as a white so-
lid (167 mg, 0.473 mmol, 95%): 1H NMR (300 MHz, DMSO-d6) d
9.66 (s, 1H), 7.60 (d, J = 9.0 Hz, 2H), 7.32 (d, J = 9.0 Hz, 2H), 7.09–
7.19 (m, 3H), 6.94–7.02 (m, 1H), 6.73–6.75 (m, 1H), 3.76 (q,
J = 3.0 Hz, 2H), 3.24 (t, J = 5.8 Hz, 2H), 2.53 (buried m, 2H), 1.27
(s, 9H); MS (DCI) m/z 353 (M+H)+. Anal (C22H25N2OF+0.20
CF3CO2H) C, H, N.
4.28. N-(4-tert-Butylphenyl)-1-(pyrimidin-2-yl)-1,2,3,6-
tetrahydropyridine-4-carboxamide (18b)
A mixture of 17 (0.570 g, 4.98 mmol), and isoguvacine, sodium
salt (1.2 g, 8.2 mmol) in water (7 mL) was heated to 90 °C and stir-
red for 4 h. Additional isoguvacine, sodium salt (0.52 g, 3.3 mmol)
was then added and stirred overnight. The mixture was diluted
with water and extracted with CH2Cl2. The aqueous layer was
acidified with conc HCl (pH 3) and extracted with CHCl3. The or-
ganic layer was dried (Na2SO4) and concentrated to give 1-(pyrim-
idin-2-yl)-1,2,3,6-tetrahydropyridine-4-carboxylic acid as a white
solid (0.564 g, 2.75 mmol, 55%): 1H NMR (300 MHz, CD3OD) d
8.43 (d, J = 4.8 Hz, 2H), 7.02 (sept, J = 1.7 Hz, 1H), 6.74 (t,
J = 4.8 Hz, 1H), 4.39 (q, J = 3.0 Hz, 2H), 3.97 (t, J = 5.8 Hz, 2H),
2.40–2.47 (m, 2H).
4.31. N-(4-tert-Butylphenyl)-1-(3-chloropyridin-2-
yl)piperidine-4-carboxamide (22b)
A solution of 1-(pyrimidin-2-yl)-1,2,3,6-tetrahydropyridine-4-
carboxylic acid (0.282 g, 1.37 mmol) and oxalyl chloride (0.17 mL,
1.9 mmol) in CH2Cl2 (9 mL) with DMF (2 drops) was stirred for
30 min and concentrated. The tan solid was dissolved in CH2Cl2
(9 mL) to which was added pyridine (0.16 mL, 2.0 mmol) and 4-t-
butylaniline (0.26 mL, 1.6 mmol). The mixture was stirred 3 h, con-
centrated, and partitioned between 1 N HCl and EtOAc. The organic
layer was washed with brine, dried (Na2SO4), concentrated, and
chromatographed (15% EtOAc/CH2Cl2) to give 18b as a tan solid
(0.360 g, 1.07 mmol, 78%): 1H NMR (300 MHz, CDCl3) d 8.35 (d,
J = 4.8 Hz, 2H), 7.47 (dt, J = 2.0, 8.8 Hz, 2H), 7.35 (dt, J = 2.0,
8.8 Hz, 2H), 7.35 (buried br s, 1H), 6.75 (sept, J = 1.7 Hz, 1H), 6.54
(t, J = 4.8 Hz, 1H), 4.44 (q, J = 3.0 Hz, 2H), 4.04 (t, J = 5.5 Hz, 2H),
2.55–2.63 (m, 2H), 1.31 (s, 9H); MS (ESI+) m/z 337 (M+H)+. Anal
(C20H24N4O) C, H, N.
A solution of 21 (2.9 mL, 19 mmol) and 8b (1.4 g, 9.5 mmol) in
EtOH (50 mL) was stirred at 85 °C for 3 days, concentrated, and
chromatographed (20% EtOAc/Hex) to give the corresponding
aminopyridine as a yellow oil (1.84 g, 6.85 mmol, 72%). A mixture
of the aminopyridine (0.202 g, 0.75 mmol) and 1 N NaOH
(2.25 mL, 2.25 mmol) in MeOH (5 mL) was stirred for 2 h, concen-
trated, and quenched with 1 N HCl (3 mL). The suspension was
dissolved in EtOAc and washed with brine. The organic layer
was dried (Na2SO4) and concentrated to give the crude acid as a
clear oil (203 mg, 0.84 mmol) which was used without purifica-
tion. A solution of the crude acid and oxalyl chloride (0.22 mL,
2.5 mmol) in CH2Cl2 (10 mL) with DMF (2 drops) was stirred for
30 min and concentrated. The tan solid was dissolved in THF
(20 mL), to which was added Et3N (0.18 mL, 1.3 mmol) and 4-t-
butylaniline (0.138 g, 0.93 mmol). The mixture was stirred over-
night, concentrated, and partitioned between 1 N HCl and EtOAc.
The organic layer was washed with brine, dried (Na2SO4), concen-
trated, and chromatographed (30% EtOAc/Hex) to give 22b as a
yellow film (0.157 g, 0.42 mmol, 50%): 1H NMR (300 MHz, CDCl3)
d 8.19 (dd, J = 1.4, 4.9 Hz, 1H), 7.59 (dd, J = 1.7, 7.6 Hz, 1H), 7.45
(d, J = 8.8 Hz, 2H), 7.35 (d, J = 8.8 Hz, 2H), 7.15 (br s, 1H), 6.84
4.29. 1-(Pyrimidin-2-yl)-N-(4-(trifluoromethylsulfonyl)-
phenyl)-1,2,3,6-tetrahydropyridine-4-carboxamide (18c)
As for 18b (65%): 1H NMR (300 MHz, CDCl3) d 8.36 (d, J = 4.8 Hz,
2H), 8.00 (d, J = 8.8 Hz, 2H), 7.90 (d, J = 8.8 Hz, 2H), 7.72 (br s, 1H),

B. S. Brown et al. / Bioorg. Med. Chem. 16 (2008) 8516–8525
8525
(dd, J = 4.9, 7.6 Hz, 1H), 3.90–3.95 (m, 2H), 2.85–2.95 (m, 2H),
2.39–2.50 (m, 1H), 2.01–2.09 (m, 4H), 1.31 (s, 9H); MS (DCI) m/
z 372.1 (M+H)+. Anal. (C21H26ClN3O + 0.05 H2O) C, H, N.
leadership. We also thank the Structural Chemistry group for ana-
lytical support.
References and notes
Combustion analyses
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Compound
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C
C
H
N
H
N
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6 (C19H15F6N3O3S)
9b (C22H24F3N3O)
9f (C18H14F6N4O)
10c (C18H15ClF3N3O3S)
10d (C17H15Cl2N3O.HCl+0.75
CH2Cl2)
10h (C17H14Cl2FN3O+0.6
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10i (C17H14Cl3N3O+0.65
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10j (C17H14Cl2FN3O+0.45
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12b (C21H25N3O+0.11
CF3CO2H)
12c (C18H16F3N3O3S+0.15
CF3CO2H)
13b (C21H24FN3O+0.21
CF3CO2H)
13c (C18H15F4N3O3S+0.25
CF3CO2H)
14c (C19H18F3N3O3S)
15b (C19H23N3OS+0.25
CF3CO2H)
18b (C20H24N4O)
18c (C17H15F3N4O3S)
20b (C22H25N2OF+ 0.20
CF3CO2H)
47.60 3.15 8.77 47.60 2.90 8.69
65.50 6.00 10.42 65.47 5.67 10.16
51.86 3.09 13.28 51.93 3.39 13.46
48.49 3.39 9.42 48.35 3.08 9.29
47.55 3.93 9.37 47.39 3.85 9.16
50.67 3.67 10.07 50.54 3.95 10.25
48.12 3.23 9.20 48.01 3.38 9.18
51.49 3.49 10.06 51.57 3.53 9.91
73.24 7.27 12.08 73.27 6.88 12.15
51.29 3.80 9.81 51.31 3.40 9.64
68.17 6.47 11.13 68.29 6.85 10.73
48.53 3.36 9.18 48.17 3.03 9.07
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53.64 4.26 9.88 53.21 3.91 9.65
63.30 6.33 11.36 63.31 6.33 11.20
70.27 7.25 16.39 70.57 7.56 16.00
49.51 3.67 13.59 49.28 3.50 13.35
71.70 6.77 7.47 71.88 6.68 7.57
22b (C21H26ClN3O+0.05 H2O) 67.66 7.06 11.27 67.27 7.02 11.10
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Acknowledgments
The authors acknowledge Mike Kort, Anil Vasudevan, and Phil
Kym for their assistance in preparing this manuscript and project