Novel vanilloid receptor-1 antagonists: 3. The identification of a second-generation clinical candidate with improved physicochemical and pharmacokinetic properties

Article abstract of DOI:10.1021/jm070191h

Based on the previously reported clinical candidate, AMG 517 (compound 1), a series of related piperazinylpyrimidine analogues were synthesized and evaluated as antagonists of the vanilloid 1 receptor (VR1 or TRPV1). Optimization of in vitro potency and physicochemical and pharmacokinetic properties led to the discovery of (R)-N-(4-(6-(4-(1-(4-fluorophenyl)ethyl) piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]-thiazol-2-yl)acetamide (16p), a potent TRPV1 antagonist [rTRPV1(CAP) IC₅₀ = 3.7 nM] with excellent aqueous solubility (≥200 μg/mL in 0.01 N HCl) and a reduced half-life (rat t _1/2 = 3.8 h, dog t_1/2 = 2.7 h, monkey t_1/2 = 3.2 h) as compared to AMG 517. In addition, compound 16p was shown to be efficacious at blocking a TRPV1-mediated physiological response in vivo (ED ₅₀ = 1.9 mg/kg, p.o. in the capsaicin-induced flinch model in rats) and was also effective at reducing thermal hyperalgesia induced by complete Freund's adjuvant in rats (MED = 1 mg/kg, p.o). Based on its improved overall profile, compound 16p (AMG 628) was selected as a second-generation candidate for further evaluation in human clinical trials as a potential new treatment for chronic pain.

Full text of DOI:10.1021/jm070191h

3528
J. Med. Chem. 2007, 50, 3528-3539
Novel Vanilloid Receptor-1 Antagonists: 3. The Identification of a Second-Generation Clinical
Candidate with Improved Physicochemical and Pharmacokinetic Properties
Hui-Ling Wang,*,† Jodie Katon, Chenera Balan,† Anthony W. Bannon,‡ Charles Bernard,† Elizabeth M. Doherty,†
Celia Dominguez,† Narender R. Gavva,‡ Vijay Gore,† Vu Ma,† Nobuko Nishimura,† Sekhar Surapaneni,§ Phi Tang,†
Rami Tamir,‡ Oliver Thiel,† James J. S. Treanor,‡ and Mark H. Norman†
Department of Chemistry Research and DiscoVery, Department of Neuroscience, and Department of Pharmacokinetics and Drug Metabolism,
Amgen Inc., One Amgen Center DriVe, Thousand Oaks, California 91320-1799
ReceiVed February 19, 2007
Based on the previously reported clinical candidate, AMG 517 (compound 1), a series of related
piperazinylpyrimidine analogues were synthesized and evaluated as antagonists of the vanilloid 1 receptor
(VR1 or TRPV1). Optimization of in vitro potency and physicochemical and pharmacokinetic properties
led to the discovery of (R)-N-(4-(6-(4-(1-(4-fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]-
thiazol-2-yl)acetamide (16p), a potent TRPV1 antagonist [rTRPV1(CAP) IC50 ) 3.7 nM] with excellent
aqueous solubility (g200 µg/mL in 0.01 N HCl) and a reduced half-life (rat t1/2 ) 3.8 h, dog t1/2 ) 2.7 h,
monkey t1/2 ) 3.2 h) as compared to AMG 517. In addition, compound 16p was shown to be efficacious
at blocking a TRPV1-mediated physiological response in vivo (ED50 ) 1.9 mg/kg, p.o. in the capsaicin-
induced flinch model in rats) and was also effective at reducing thermal hyperalgesia induced by complete
Freund’s adjuvant in rats (MED ) 1 mg/kg, p.o). Based on its improved overall profile, compound 16p
(AMG 628) was selected as a second-generation candidate for further evaluation in human clinical trials as
a potential new treatment for chronic pain.
Introduction
The vanilloid receptor-1 (VR1 or TRPV1) is a nonselective
cation channel belonging to the transient receptor potential
(TRP) super family that plays a role as an integrator of multiple
pain-producing stimuli.1 Over the past several years, TRPV1
has emerged as an exciting target for the treatment of chronic
pain,2 and we have reported the identification and SAR
development of several novel classes of TRPV1 antagonists,
Figure 1. AMG 517 (1) and generic structure (2) used for SAR
investigations of region C.
including cinnamides,3 thiazoles,4 benzimidazoles,5 and pyri-
midines.6,7 Investigations into the latter class of compounds have
not critical for further progression of AMG 517, presented
challenges to the development of this candidate. Therefore, our
goal was to identify a novel second-generation clinical candidate
with a similar pharmacological profile to AMG 517, but with
increased aqueous solubility and a reduced half-life that would
make the compound suitable for QD or BID dosing.
been particularly fruitful and have provided us with a rich supply
of TRPV1 antagonists for further study.
In parts 1 and 2 of this series, we described the structure-
activity relationship (SAR) investigations leading to the dis-
covery of the pyrimidine class of TRPV1 antagonists.6,7 These
studies led to the identification of our first TRPV1 clinical
candidate AMG 517 (1, Figure 1). AMG 517 was chosen for
evaluation in human clinical trials based on its potent efficacy
in pharmacological models and its excellent safety profile. As
this promising candidate progressed into clinical development,
we sought to identify a second-generation TRPV1 antagonist
with an improved profile. The two areas that we felt AMG 517
could be improved upon were its half-life and solubility. In
preclinical studies, AMG 517 was found to be extremely stable
in vitro and in vivo and was shown to have very long half-
lives in multiple species (rat t1/2 ) 31 h, dog t1/2 ) 41 h, monkey
t1/2 ) 62 h).7 Based on this preclinical pharmacokinetic data,
allometric projections predicted a human half-life of 60-120 h
and significant accumulation upon multiple-dose administration.
In addition, AMG 517 was found to have low aqueous solubility
(<1 µg/mL in PBS or 0.01 N HCl).8 These two factors, although
In the previous two reports, we described our SAR investiga-
tions leading to the optimization of the central core, B (oxo-
pyrimidine),6 and the heteroaryl moiety, A (N-acetyl benzothi-
azole,7 1; Figure 1). With these two groups optimized to provide
analogues with exquisite TRPV1 potency, we then turned our
attention to region C of the molecule in attempts to modulate
the physicochemical properties of these antagonists (2; Figure
1). We envisaged that we could effect both half-life and
solubility through modification of the metabolically stable
4-(trifluoromethyl)phenyl moiety. Our strategy was 2-fold: (1)
introduction of saturation into the 4-(trifluoromethyl)phenyl ring
to reduce structural planarity and disrupt crystal-stacking
capability (e.g., compound 2; where Y, Z ) C); and (2)
replacement of the 4-(trifluoromethyl)phenyl group with various
saturated aza-heterocycles (e.g., compound 2; where Y ) N
and Z ) CH, O, or N) to create the potential for salt formation.
Herein, we describe the synthesis and biological evaluation of
a novel series of TRPV1 antagonists based on generic structure
2, which led to the discovery of the second-generation TRPV1
clinical candidate, AMG 628.
* To whom correspondence should be addressed. Tel.: 805-447-4735.
Fax: 805-375-4532. E-mail: huiw@amgen.com.
† Department of Chemistry Research and Discovery.
‡ Department of Neuroscience.
§ Department of Pharmacokinetics and Drug Metabolism.
10.1021/jm070191h CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/22/2007

AMG 628, a Second-Generation Clinical Candidate
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15 3529
Scheme 1a
a Reagents and conditions: (a) Ac2O, toluene, reflux; (b) K2CO3, MeOH, room temperature; (c) NaI, 47% HI, 40 °C; (d) 4,6-difluoropyrimidine (5),
DMSO, room temperature; (e) 4,6-dichloropyrimidine (6), K2CO3, acetone, reflux; (f) 4,6-diiodopyrimidine (7), K2CO3, DMSO, 80 °C; (g) PdCl2(PPh3)2,
Na2CO3, DME/EtOH/H2O (2:1:1), 120 °C, microwave; (h) ammonium formate, Pd(OH)2, n-butanol, 120 °C; (i) 4-(trifluoromethyl)piperidine, morpholine
or piperazines, K2CO3, DMF or DMSO.
Scheme 2a
a Reagents and conditions: (a) 4′-fluoroacetylphenone or 2′-fluoroacetylphenone, Ti(Oi-Pr)4, THF, 75 °C; NaBH4, MeOH, -48 °C to room temperature.
Chemistry
other acetophenones resulted in low yields. Therefore, we
investigated an alternative synthetic route wherein the requisite
N-alkylated piperazines (20a-f, 23, 24, and 26) were prepared
according to Schemes 3 and 4 prior to the condensation with
the pyrimidinyl chloride 9. We found that the yield of final
product could be improved by reversing the sequence in this
manner.
The synthetic routes employed to prepare the saturated
analogues (12 and 13) as well as a majority of the aza-
heterocyclic derivatives (14, 15, 16a-q) are outlined in Scheme
1. Diacetylation of compound 3 with excess acetic anhydride,
followed by selective hydrolysis of the acetate group under basic
conditions, provided acetamide 4. Condensation of acetamide
4 with 4,6-difluoropyrimidine (5) proceeded smoothly at room
temperature in DMSO to give fluoropyrimidine 8 in good yield.
Similarly, coupling of acetamide 4 with 4,6-dichloropyrimidine
(6) or 4,6-diiodopyrimidine (7)9 in the presence of potassium
carbonate generated chloropyrimidine 9 and iodopyrimidine 10,
respectively. Suzuki coupling of boronate 1110 with iodopyri-
midine 10 afforded the desired trifluoromethylcyclohexenyl
analogue 12. Subsequent hydrogenation at high temperature in
the presence of ammonium formate and a catalytic amount of
palladium hydroxide provided the fully saturated analogue 13
as an inseparable mixture of trans- and cis-isomers (1.6:1).11
Direct nucleophilic displacement of the fluorine or chlorine
atoms in intermediates 8 or 9 with a variety of six-membered
cyclic amines provided compounds 14, 15, and 16a-q in good
yields.
The syntheses of piperazine intermediates 20a-f, 23, and 24
are outlined in Scheme 3. N-Boc-piperazine (18) was converted
to N-trifluoroethylpiperazine (20a) by alkylation with 2,2,2-
trifluoroethyl trifluoromethanesulfonate, followed by removal
of the Boc-group under acidic conditions. Alternatively, reduc-
tive amination of N-Boc-piperazine (18) with trimethylacetal-
dehyde and NaBH(OAc)3, followed by Boc-deprotection pro-
vided N-neopentylpiperazine (20b). Due to the poor reactivity
of alkyl aryl ketones with compound 18, imine formation was
conducted in refluxing THF in the presence of Ti(Oi-Pr)4. The
resulting imines were readily reduced with NaBH(OAc)3 to
provide the desired alkylated piperazines 19c-g. The racemic
mixture of Boc-protected piperazine 19g was resolved by chiral
HPLC chromatography with a Chirobiotic TAG column (4.6
× 250 mm) to provide the antipodes 21 and 22. Subsequent
removal of the Boc-groups under acidic conditions gave the
enantiopure piperazines 23 and 24.
In some cases, additional modifications to piperazine deriva-
tive 16a (R1 ) H) were required. For example, compounds 17a
and 17b were prepared by the condensation of 2′- or 4′-
fluoroacetophenones with compound 16a using Ti(Oi-Pr)4
followed by reduction of the resulting imine with NaBH4
(Scheme 2). Unfortunately, this method did not prove to be very
general, and we found that reductive aminations of 16a with
To eliminate the tedious chiral separation step, an alternate
route to the enantiopure piperazines 23 and 24 starting from
commercially available nonracemic amines was developed
(Scheme 4). In addition to providing larger amounts of the chiral
derivatives, this alternate route also allowed us to unambiguously

3530 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15
Wang et al.
Scheme 3a
a Reagents and conditions: (a) CF3CH2OTf, i-Pr2NEt, THF, reflux; (b) trimethylacetaldehyde, AcOH, NaBH(OAc)3, 1,2-dichloroethane, 50 °C; (c)
propiophenone, 3′-fluoroacetophenone, 4′-trifluoromethylacetophenone or 4′-methoxyacetophenone, Ti(Oi-Pr)4, THF, 75 °C; NaBH(OAc)3, MeOH, -48 °C
to room temperature; (d) TFA, CH2Cl2, room temperature; (e) 4′-fluoroacetophenone, Ti(Oi-Pr)4, THF, 75 °C; NaBH(OAc)3, MeOH, -48 °C to room
temperature; (f) rp-HPLC Chirobiotic TAG column (4.6 × 250 mm).
Scheme 4a
Table 1. In Vitro TRPV1 Activities and Aqueous Solubility for
Saturated C-Rings (12 and 13) and Simple Heterocycles (14, 15, and
16a)
a Reagents and conditions; (a) (R)-1-(4-fluorophenyl)ethanamine, (S)-1-
(4-fluorophenyl)ethanamine or 2-phenylpropan-2-amine, i-Pr2NEt, 125 °C;
(b) HBr, 4-hydroxybenzoic acid, room temperature.
assign the absolute stereochemistries for intermediates 23 and
24 and, by extension, the final analogues 16p and 16q.
Cyclization of bis(2-chloroethyl)-4-methylbenzenesulfonamide
(25) with (R)-1-(4-fluorophenyl)ethylamine or (S)-1-(4-fluo-
rophenyl)ethylamine, followed by removal of the p-toluene-
sulfonyl groups using HBr and 4-hydroxybenzoic acid, provided
the enantiopure piperazines 23 and 24, respectively.12 In a
similar manner, 1-(2-phenylpropan-2-yl)piperazine (26) was
prepared from N,N-bis(2-chloroethyl)-4-methylbenzenesulfona-
mide (25) and 2-phenylpropan-2-amine.
Results and Discussion
a IC50 values based on inhibition of capsaicin- (500 nM) or acid- (pH 5)
The compounds prepared in this paper were tested for their
ability to block the capsaicin- (500 nM) or acid- (pH 5) induced
influx of 45Ca2+ into rat TRPV1-expressing Chinese hamster
ovary (CHO) cells. Functional activity is reported as IC50 values
in Tables 1 and 2. All compounds reported herein behaved as
antagonists, as confirmed by separate assays designed to measure
agonist activity.
TRPV1 antagonist activities for the initial set of compounds
examined the effect of ring saturation (compounds 12 and 13)
as well as replacement of the 4-(trifluoromethyl)phenyl group
with simple heterocycles, such as 4-(trifluoromethyl)piperidinyl
(14), morpholine (15), and piperidine (16a; Table 1). For
comparison, the data for AMG 517 (compound 1) is also
included in Table 1. Partial ring saturation of the C-ring of AMG
517 (i.e., 4-(trifluoromethyl)cyclohexenyl analogue 12), resulted
in an approximately 30-fold decrease of potency in the capsaicin-
mediated assay and a 4-fold decrease in the acid-mediated assay.
induced influx of 45Ca2+ into rat TRPV1- expressing CHO cells. (Each
IC50 value reported represents an average of at least two independent
experiments with three replicates at each concentration ((SEM).) b Ther-
modynamic solubility measured in a high-throughput automated format.8
Further reduction of the planarity to the fully saturated cyclo-
hexyl analogue 13 gave an additional reduction in potency in
both assays. These results suggest that the antagonist with a
planar aromatic C-ring affords optimum binding affinity to the
receptor. Nevertheless, we were encouraged by the fact that the
partially saturated and fully saturated analogues 12 and 13
maintained moderate inhibitory activity and showed the antici-
pated improvement in solubility (13 µg/mL and 5 µg/mL in
0.01 N HCl, respectively).
Consequently, we replaced the 4-(trifluoromethyl)phenyl
group of AMG 517 (compound 1) with heterocyclic moieties,
such as piperidines, morpholines, and piperazines (i.e., 14, 15,
and 16a-q), to find a more potent antagonist with better

AMG 628, a Second-Generation Clinical Candidate
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15 3531
Table 2. In Vitro TRPV1 Activities, Aqueous Solubility and In Vivo Clearance for 4-Substituted Piperazinyl Analogues (16a-q, 17a, and 17b)
a IC50 values based on inhibition of capsaicin- (500 nM) or acid- (pH 5) induced influx of 45Ca2+ into rat TRPV1- expressing CHO cells. (Each IC50 value
reported represents an average of at least two independent experiments with three replicates at each concentration ((SEM).) b Thermodynamic solubility
measured in a high-throughput automated format.8 c Study in fed male Sprague-Dawley rats dosed at 1 mg/kg in DMSO with sampling time up to 6 h. n
) 2 animals per study. Interanimal variability was less than or equal to 30%.

3532 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15
Wang et al.
Table 3. Pharmacokinetic Profile and Solubility for Compounds 1, 17a, 16n, 16p, and 16q
solubilitye (µg/mL)
AUC0-∞
(ng‚h/mL)
(iv)a
CL
(L/h/kg)
(iv)a
Vss
t1/2
(h)
AUC0-∞
(ng‚h/mL)
(po)
(L/kg)
F
(%)
HCl
(0.01 N)
cmpd
(iv)a
(iv)a
PBS
SIF
1
5400
1000
720
1200
550
0.19
1.0
1.4
0.8
1.8
1.6
2.9
4.5
2.8
5.7
6.3b
2.4
2.7
2.7
2.5
12 500c
1800d
120d
32
35
3
51
93
<1
g200
g200
g200
g200
<1
5
5
7
31
6.6
34
121
64
17a
16n
16p
16q
3100d
2550d
121
a Study in fed male Sprague-Dawley rats dosed at 1 mg/kg in DMSO with sampling time up to 6 h. n ) 2 animals per study. Interanimal variability was
less than or equal to 30%. b Underestimation of the true half-life of compound 1 due to limited sampling time. c Study in fasted male Sprague-Dawley rats
dosed at 3 mg/kg as a suspension in 5% Tween 80/Oraplus with sampling time up to 8 h. d Study in fasted male Sprague-Dawley rats dosed at 5 mg/kg
as a suspension in 5% Tween 80/Oraplus with sampling time up to 8 h. e Thermodynamic solubility measured in a high-throughput automated format.8
aqueous solubility. The 4-(trifluoromethyl)piperidinyl analogue
14 displayed reasonable potency with an IC50 value of 330 nM
in the capsaicin-mediated assay and 19 nM in the acid-mediated
assay. However, the IC50 values for morpholine analogue 15
and piperazine analogue 16a were greater than 4000 nM in both
assays. This significant reduction in potency was presumably
due to the lack of a lipophilic group in the 4-position of these
analogues. This result is consistent with the SAR established
in the cinnamide series, where we found that a lipophilic group
in this region was important for activity.3
To improve the potency of 16a, a variety of lipophilic groups
were installed in the 4-position of the piperazine C-ring. A
comparison of in vitro potency, aqueous solubility, and clearance
data for these 4-substituted piperazinyl analogues is shown in
Table 2. Initially, the N-isopropyl and N-t-butyl analogues 16b
and 16c were examined based on the similarity in size to the
trifluoromethyl group. A slight improvement in activity was
observed for these compounds as compared to 16a, along with
a significant improvement in solubility as compared to AMG
517. By extending the t-butyl group one carbon atom further
from piperazine ring, a dramatic improvement in potency was
observed. The neopentyl analogue 16d had an IC50 value of 3
nM in the capsaicin assay and an IC50 value of 5 nM in the
acid-mediated assay. Replacement of the neopentyl group with
2,2,2-trifluoroethyl (i.e., 16e) led to a 100-fold decrease of
potency in the capsaicin-mediated assay and a 20-fold decrease
of potency in the acid-mediated assay relative to 16d.
16g (i.e., 16i-l). The addition of a methyl group at this position
led to a 10-fold increase in potency (16i vs 16g); however, as
the size of the group increased to ethyl (16j) and phenyl (16k),
potency decreased. The geminal dimethyl analogue 16l also
showed a significant reduction in potency relative to the
monomethyl analogue 16i.
While the 1-(1-phenylethyl)piperazine analogue 16i showed
excellent potency in both assays (IC50 ) 4.8 nM and 6 nM in
the capsaicin- and acid-mediated assays, respectively) and good
solubility (g200 µg/mL in 0.01 N HCl), the compound suffered
from high in vivo clearance (CLin vivo ) 3.9 L/h/kg). Therefore,
we prepared a series of substituted phenyl analogues of
compound 16i with the intention of blocking metabolism on
the aromatic ring, thus reducing clearance (i.e., 16m-q and
17a,b).
The 2-fluorophenyl analogue 17b showed a 2-fold improve-
ment in potency over compound 16i in both assays. The activity
of the 3-fluorophenyl analogue 16m was 3-fold less than
compound 16i in the capsaicin-mediated assay but was com-
parable to 16i in the acid-mediated assay. Unfortunately, both
17b and 16m exhibited unacceptable in vivo clearance (CLin
vivo > 3 L/h/kg) and offered no advantage over 16i. On the other
hand, the results for the 4-fluorophenyl analogue 17a were more
promising. Compound 17a was equipotent to 16i in the
capsaicin-mediated assay and 2-fold more potent than 16i in
the acid-mediated assay. Moreover, 17a demonstrated a sig-
nificantly lower in vivo clearance (CLin
) 1.1 L/h/kg)
vivo
Although the potency and solubility properties of compound
16d were encouraging, the compound exhibited moderate in
vivo clearance in rats (CLin vivo ) 1.5 L/h/kg) and poor oral
bioavailability (Foral ) 14%). Subsequent metabolite identifica-
tion studies of compound 16d in rat liver microsomes indicated
that the major site of metabolism was oxidation on the neopentyl
group. Therefore, we turned our attention to exploring different
lipophilic groups at the 4-position of piperazine ring with the
goal of maintaining potency and improving clearance. Based
on size and lipophilicity, the phenyl group was initially chosen
to replace the neopentyl moiety. 4-Phenylpiperazine 16f exhib-
ited reasonable potency in the capsaicin- and acid-mediated
assays, with IC50 values of 43 nM and 7.5 nM, respectively.
The influence of adding a linker between the piperazine and
phenyl group was examined. For example, a carbon atom was
inserted between the piperazine and phenyl group to generate
benzylpiperazine analogue 16g. The methylene linker did not
improve on activities in the capsaicin- and acid-mediated assays
in comparison to 16f, however, a significant increase in aqueous
solubility (g200 µg/mL in 0.01 N HCl) was obtained. Extending
the linking group one atom longer (phenethylpiperazine analogue
16h) was not tolerated (IC50 values g4000 nM in both the
capsaicin- and acid-mediated assays). Next we examined the
effect of an additional substituent on the benzylic position of
relative to 16i. The potency of the 4-trifluoromethylphenyl
analogue 16n was similar to 17a and showed improved in vivo
clearance in the rat (CLin vivo ) 1.4 L/h/kg) as well. Analogue
16o, with an electronic-donating methoxy group at the para-
position of the phenyl ring, was less potent than either the
unsubstituted analogue 16i or the analogues with electron-
deficient aromatic rings such as 17b, 16m, 17a, and 16n.
Because of the excellent potency and low clearance demon-
strated by racemate 17a, each of the antipodes were synthesized
for further evaluation (R, 16p, and S, 16q). While both
enantiomers showed comparable in vitro potency, the R-isomer
(16p) was superior in terms of pharmacokinetic profile with
over a 2-fold lower rate of clearance in comparison to the
S-isomer (16q; 0.8 vs 1.8 L/h/kg, respectively).
Pharmacokinetic and Solubility Profiles. Due to the excel-
lent in vitro activities and aqueous solubilities of compounds
17a, 16n, 16p, and 16q, the pharmacokinetic and solubility
profiles of these compounds were evaluated further. A com-
parison with the clinical candidate AMG 517 is shown in Table
3. The data from the preliminary pharmacokinetic studies using
the 6-hour time point are reported for comparison purposes. The
higher rate of clearance translated into a shorter half-life, t1/2
2.7 h for 17a versus 6.4 h for 1. Compound 17a also showed
)

AMG 628, a Second-Generation Clinical Candidate
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15 3533
Figure 2. (a) Effects of compound 16p on capsaicin-induced flinching in rats and corresponding plasma levels (ED50 ) 1.9 mg/kg; n ) 8/group).
(b) Time course of 16p inhibition of capsaicin-induced flinching in rats (10 mg/kg (p.o.); n ) 8/group).
Table 4. Mean Pharmacokinetic Parameters for Compound 16p in
Preclinical Species and Predicted Human Pharmacokinetic Parameters
Based on Allometric Scalinga
CL
(mL/h/kg)
(iv)
Vss
(mL/kg)
(iv)
t1/2
(h)
(iv)
Foral
(%)
species
rat
830b
2600b
4000d
900d
3.8b
51c
83e
12f
dog
2400d
2.7d
monkey
human
(projected)
400d
3.2d
1500-5000
3000
3-15
a Variability for AUC0-∞, CL ,and Vss values ranged from 3 to 19%,
and variability for Foral ranged from 13 to 43% for all species. b Study in
fed male Sprague-Dawley rats dosed at 1 mg/kg in DMSO with sampling
time up to 72 h. c Study in fasted male Sprague-Dawley rats dosed at 5
mg/kg as a suspension in 5% Tween 80/Oraplus. d Study in fed male animal
dosed at 1 mg/kg in 80% PEG-400/H2O. e Study in fasted male animal dosed
at 3 mg/kg in 10% Pluronic F108/ Oraplus. f Study in fasted male animal
dosed at 3 mg/kg in 10% Pluronic F108/H2O.
Figure 3. Dose-response curve with compound 16p in CFA-induced
thermal hyperalgesia.
the enhanced solubility profile of compound 16p, represented
a significant improvement over AMG 517.
good absorption upon oral dosing (AUC0-∞ ) 1800 ng‚h/mL;
Foral ) 35%). In contrast, the trifluoromethyl analogue 16n
showed a reasonable half-life (2.7 h), but it had poor oral
bioavailability (Foral ) 3%) presumably due to high first-pass
metabolism. Compound 16p exhibited low clearance (CLin vivo
) 0.8 L/h/kg), good systemic exposure (AUC0-∞ ) 1200 ng‚
h/mL), and a reasonable half-life (t1/2 ) 2.7 h) when delivered
intravenously. Upon oral administration, compound 16p showed
In Vivo Efficacy. On the basis of its excellent in vitro
potency, selectivity,13 and pharmacokinetic profile, compound
16p was chosen for further in vivo evaluation. The compound
was first tested in an agonist challenge model (capsaicin-induced
flinching in rats) and the results are illustrated in Figure 2.
Compound 16p potently suppressed capsaicin-evoked paw
flinching in rats in a dose-dependent manner with an ED50 of
1.9 mg/kg, p.o. (corresponding to 16p plasma level of ap-
proximately 128 ng/mL; Figure 2a). Because of the significantly
shorter half-life of compound 16p as compared to AMG 517,
we were interested in evaluating the duration of this flinch effect.
For this reason, a time-course experiment was conducted. At a
10 mg/kg (p.o.) dose, compound 16p blocked capsaicin-induced
flinching (Figure 2b) up to 8 h.
As we demonstrated for AMG 517, we found that compound
16p was efficacious at reversing thermal hyperalgesia in the
complete Freund’s adjuvant (CFA) model of inflammation-
induced pain in rats in a dose-dependent manner (Figure 3).
The minimum effect dose (MED) for compound 16p was
approximately 1 mg/kg, corresponding to a plasma level of ∼70
ng/mL.
excellent bioavailability (AUC0-∞ ) 3100 ng‚h/mL, Foral
51%).
)
Because half-life was a key parameter that we sought to
optimize in the second-generation compound, the pharmacoki-
netic studies in rats were repeated with an extended sampling
time (72 h) to get a more accurate t1/2 measurement (Table 4).
Unlike AMG 517, where a substantial difference was observed
in the extended pharmacokinetic studies, the half-life for
compound 16p did not change significantly when the sampling
time was extended to 72 h (t1/2 ) 2.7 h vs 3.8 h). In addition to
examining compound 16p in rats, the pharmacokinetics was also
examined in dogs and monkeys. Compound 16p exhibited
moderate to high clearance and moderate to high volumes of
distribution in all preclinical species examined. The oral
bioavailability ranged from 12 to 83% among the three species.
The human pharmacokinetic parameters projected based upon
allometric scaling of rat and monkey data are also presented in
Table 4. Based on this analysis, compound 16p is projected to
have a significantly shorter half-life than AMG 517 in humans
(3-15 h vs 60-120 h) and would be suitable for QD or BID
dosing. This reduction in predicted human half-life, as well as
Summary
In this investigation we examined a variety of replacements
for the C-ring of AMG 517 in attempts to modulate the
physicochemical properties of our first generation TRPV1
clinical candidate. The SAR of this series of TRPV1 antagonists
demonstrated that replacement of the 4-(trifluoromethyl)phenyl

3534 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15
Wang et al.
in vacuo to give the title compound as a light-yellow solid (1.86 g,
84%). 1H NMR (400 MHz, DMSO-d6): δ 8.61 (s, 2 H). MS (ESI,
pos. ion) m/z: 332 (M + 1).
moiety with saturated rings or heterocycles was effective in
increasing aqueous solubility and modifying the pharmacokinetic
properties. While potency was reduced with the saturated
carbocyclic rings, activity was maintained with substituted
piperazines as the C-ring replacements. Furthermore, we found
that hydrophobic groups in the 4-position of the piperazine ring
gave the best results. This investigation culminated in the
discovery of compound 16p, (R)-N-(4-(6-(4-(1-(4-fluorophenyl)-
ethyl)piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)ac-
etamide. Compound 16p demonstrated excellent in vitro po-
tency, in vivo efficacy, and pharmacokinetic profile with
increased solubility (g200 µg/mL in 0.01 N HCl) and a reduced
half-life (rat t1/2 ) 3.8 h, dog t1/2 ) 2.7 h, monkey t1/2 ) 3.2 h)
as compared to AMG 517. Based on its enhanced overall profile,
compound 16p ((R)-N-(4-(6-(4-(1-(4-fluorophenyl)ethyl)piper-
azin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide; AMG
628) was chosen as our second-generation TRPV1 clinical
candidate for further evaluation as a potential new treatment
for inflammatory pain.14
N-(4-(6-Fluoropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)aceta-
mide (8). A mixture of N-(4-hydroxybenzo[d]thiazol-2-yl)acetamide
(4; 300 mg, 1.4 mmol) and 4,6-difluoropyrimidine (5; 0.17 mL,
1.4 mmol) in DMF (3 mL) was stirred at room temperature for 18
h. The reaction mixture was then diluted with H2O (20 mL), and
the resulting off-white precipitate was collected by filtration and
dried under vacuum to give the title compound (360 mg, 84%). 1H
NMR (400 MHz, DMSO-d6): δ 12.44 (s, 1 H), 8.54 (s, 1 H), 7.94
(d, J ) 7.8 Hz, 1 H), 7.32-7. 40 (m, 2 H), 7.09 (s, 1 H), 2.15 (s,
3 H). MS (ESI, pos. ion) m/z: 305 (M + 1).
N-(4-(6-Chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)aceta-
mide (9). 2,6-Dichloropyrimidine (6; 50.4 g, 340 mmol), K2CO3
(51.4 g, 370 mmol), and benzothiazole (4; 70.4 g, 340 mmol) were
weighed into a 2 L flask equipped with a reflux condenser and a
mechanical stirrer. Acetone (700 mL) was added and the mixture
was heated to reflux while stirring at 450 rpm. HPLC indicated
complete conversion after 15 h. The mixture was cooled to room
temperature and H2O (700 mL) was added. The product precipitated
and the suspension was stirred for 2 h. The solids were isolated by
vacuum filtration. The filter cake was dried in the vacuum oven
(65 °C, 48 h) to obtain the title compound as an off-white solid
(104 g, 96%). Mp: 268-275 °C. 1H NMR (400 MHz, DMSO-d6):
δ 12.43 (s, 1 H), 8.59 (d, J ) 0.8 Hz, 1 H), 7.94 (dd, J ) 7.6, 1.4
Hz, 1 H), 7.51 (d, J ) 0.8 Hz, 1 H), 7.28-7.43 (m, 2 H), 2.15 (s,
3 H). MS (ESI, pos. ion.) m/z: 321 (M + 1).
Experimental Section
Unless otherwise noted, all materials were obtained from
commercial suppliers and used without further purification. An-
hydrous solvents were obtained from Aldrich or EM Science and
used directly. All reactions involving air- or moisture-sensitive
reagents were performed under a nitrogen or argon atmosphere.
All microwave-assisted reactions were conducted with a Smith
Synthesizer from Personal Chemistry, Uppsala, Sweden. All final
compounds were purified to >95% purity as determined by LC/
MS obtained on Agilent 1100 and HP 1100 specrometers. Silica
gel chromatography was performed using either glass columns
packed with silica gel (200-400 mesh, Aldrich Chemical) or
prepacked silica gel cartridges (Biotage or RediSep). Melting points
were determined on a Buchi-545 melting point apparatus and are
uncorrected. 1H NMR spectra were determined with a Bruker 300
MHz or DRX 400 MHz spectrometer. Chemical shifts are reported
in parts per million (ppm, δ units). Low-resolution mass spectral
(MS) data were determined on a Perkin-Elmer-SCIEX API 165
mass spectrometer using ES ionization modes (positive or negative).
Combustion analyses were performed by Atlantic Microlab, Inc.,
Norcross, GA, and were within (0.4% of calculated values, unless
otherwise noted. Combustion analysis and 1H NMR spectra showed
that fractional molar amounts of H2O or organic solvents were
tenaciously retained in some analytical samples, even after pro-
longed drying under reduced pressure.
N-(4-(6-Iodopyrimidin-4-yloxy)benzo[d]thiazol-2-yl)aceta-
mide (10). A mixture of 4,6-diiodopyrimidine (7; 0.72 g, 2.2 mmol),
N-(4-hydroxybenzo[d]thiazol-2-yl)acetamide (4; 0.43 g, 2.0 mmol),
and K2CO3 (0.43 g, 3.0 mmol) in DMSO (3.0 mL) was heated at
80 °C for 1 h. The reaction mixture was cooled to room temperature,
diluted with H2O, and stirred for 18 h. The resulting precipitate
was filtered, washed with H2O, and dried in vacuo to give the title
1
compound as a light-yellow solid (0.85 g, 95%). H NMR (400
MHz, DMSO-d6): δ 12.43 (s, 1 H), 8.42 (s, 1 H), 7.93 (d, J ) 7.8
Hz, 1 H), 7.82 (s, 1 H), 7.23-7.47 (m, 2 H), 2.15 (s, 3 H). MS
(ESI, pos. ion) m/z: 413 (M + 1).
4,4,5,5-Tetramethyl-2-(4-trifluoromethyl-cyclohex-1-enyl)-
[1,3,2]dioxaborolane (11). To a solution of 4-(trifluoromethyl)-
cyclohex-1-enyl trifluoromethanesulfonate (6.1 g, 20 mmol) in
dioxane (100 mL) was added bis(pinacolato)diboron (5.6 g, 22
mmol), potassium acetate (5.9 g, 60 mmol), PdCl2(dppf) (320 mg,
0.6 mmol), and dppf (330 mg, 0.6 mmol) under a nitrogen
atmosphere. The reaction mixture was heated at 80 °C with stirring
for 18 h, cooled to room temperature, and filtered through Celite.
The filtrate was evaporated in vacuo and the residue was purified
by silica gel column chromatography (10% EtOAc/hexane) to give
4.2 g (75%) of the title compound as a white amorphous solid. 1H
NMR (400 MHz, CDCl3): δ 6.52 (d, J ) 2.4 Hz, 1 H), 2.05-2.45
(m, 5 H), 1.93-2.05 (m, 1 H), 1.38-1.51 (m, 1 H), 1.26 (s, 12 H).
MS (ESI, pos. ion) m/z: 277 (M + 1).
N-{4-[6-(4-Trifluoromethyl-cyclohex-1-enyl)-pyrimidin-4-yloxy]-
benzothiazol-2-yl}-acetamide (12). A mixture of N-(4-(6-iodopy-
rimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (10; 220 mg,
0.54 mmol), 4,4,5,5-tetramethyl-2-(4-trifluoromethyl-cyclohex-1-
enyl)-[1,3,2]dioxaborolane (11; 220 mg, 0.81 mmol), PdCl2(PPh3)2
(38 mg, 0.05 mmol), and Na2CO3 (86 mg, 0.81 mmol) in
DME/EtOH/H2O (2:1:1, 3.2 mL) was heated at 120 °C in a
microwave reactor for 15 min. The reaction mixture was cooled
to room temperature and solvents were removed in vacuo. The
residue was purified by silica gel chromatography (gradient:
0-1.0% 2 M NH3 in MeOH/CH2Cl2) to give the title compound
as a white solid (120 mg, 52%). Mp: 130-131 °C. 1H NMR (400
MHz, DMSO-d6): δ 12.42 (s, 1 H), 8.58 (s, 1 H), 7.91 (d, J ) 8.0
Hz, 1 H), 7.37 (t, J ) 8.0 Hz, 1 H), 7.29 (d, J ) 8.0 Hz, 1 H), 7.23
(s, 1 H), 7.07 (s, 1 H), 2.56-2.67 (m, 2 H), 2.46-2.51 (m, 2 H),
2.33 (m, 1 H), 2.14 (s, 3 H), 2.04 (m, 1 H), 1.59 (m, 1 H).
MS (ESI, pos. ion) m/z: 435 (M + 1). Anal. (C20H17F3N4O2S): C,
H, N.
N-(4-Hydroxybenzo[d]thiazol-2-yl)acetamide (4). To a suspen-
sion of 2-aminobenzo[d]thiazol-4-ol (40 g, 240 mmol) in toluene
(400 mL) was added acetic anhydride (220 mL, 2400 mmol) at
room temperature. The reaction mixture was stirred at 115 °C for
22 h. The solvents were evaporated and the residue was azeotroped
with EtOAc to give 2-acetamidobenzo[d]thiazol-4-yl acetate (47
g, 78%) as a tan solid. MS (ESI, pos. ion) m/z: 251 (M + 1). The
suspension of the above solid (47 g) in MeOH (500 mL) was treated
with K2CO3 (52 g, 380 mmol) and stirred at room temperature for
6 h. MeOH was evaporated and the residue was diluted with H2O.
The resulting mixture was neutralized with concd HCl to pH ) 7
and extracted with EtOAc (3×). The combined organic phases were
dried over sodium sulfate, filtered, and concentrated in vacuo to
provide N-(4-hydroxybenzo[d]thiazol-2-yl)acetamide (38 g, 98%)
1
as a tan solid. H NMR (400 MHz, DMSO-d6): δ 12.32 (br s, 1
H), 9.80 (br s, 1 H), 7.33 (d, J ) 7.4 Hz, 1H), 7.09 (dd, J ) 7.4,
7.4 Hz, 1H), 6.82 (d, J ) 7.4 Hz, 1H), 2.18 (s, 3H). MS (ESI, pos.
ion) m/z: 209 (M + 1).
4,6-Diiodo-pyrimidine (7). A mixture of 4,6-dichloropyrimidine
(6; 1.00 g, 6.70 mmol), NaI (1.36 g, 9.00 mmol), and hydriodic
acid (57 wt % in H2O, 20 mL, 151.0 mmol) was heated at 40 °C
with stirring for 1 h. The reaction mixture was stirred at room
temperature for 20 h and basified with 10 N NaOH to pH ) 10.
The resulting precipitate was filtered, washed with H2O, and dried

AMG 628, a Second-Generation Clinical Candidate
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15 3535
trans-N-{4-[6-(4-Trifluoromethyl-cyclohexyl)-pyrimidin-4-
yloxy]-benzothiazol-2-yl}-acetamide and cis-N-{4-[6-(4-Trifluo-
romethyl-cyclohexyl)-pyrimidin-4-yloxy]-benzothiazol-2-yl}-
acetamide (13). To a mixture of N-{4-[6-(4-trifluoromethyl-
cyclohex-1-enyl)-pyrimidin-4-yloxy]-benzothiazol-2-yl}-
acetamide (12; 94 mg, 0.22 mmol) and ammonium formate (270
mg, 4.3 mmol) in n-butanol (4 mL) was added palladium hydroxide
(23 mg, 20 wt % Pd on carbon, wet, Aldrich) at room temperature
under a nitrogen atmosphere. The reaction mixture was heated at
120 °C with stirring for 17 h, cooled to room temperature, filtered
through Celite, and washed with MeOH. The filtrates were
combined and evaporated in vacuo. The residue was purified by
silica gel chromatography (gradient: 0-4.0% MeOH/CH2Cl2) to
give the title compound as a 1:1.6 mixture of cis- and trans-isomers
(45 mg, 48%). 1H NMR (400 MHz, DMSO-d6): δ 12.44 (s, 1 H),
8.62 (s, 1 H), 7.92 (d, J ) 8.0 Hz, 1 H), 7.37 (t, J ) 8.0 Hz, 1 H),
7.29 (t, J ) 7.2 Hz, 1 H), 7.12 (s, 1 H), 2.98 (m, 1 H), 2.33 (m, 1
H), 2.14 (s, 3 H), 2.11 (m, 1 H), 1.98 (m, 3 H), 1.75 (m, 1 H),
1.62 (m, 2 H), 1.41 (m, 1 H) and 1H NMR (400 MHz, DMSO-d6):
δ 12.46 (s, 1 H), 8.58 (s, 1 H), 7.92 (d, J ) 8.0 Hz, 1 H), 7.37
(t, J ) 8.0 Hz, 1 H), 7.29 (t, J ) 7.2 Hz, 1 H), 7.05 (s, 1 H), 2.71
(m, 1 H), 2.33 (m, 1 H), 2.14 (s, 3 H), 2.11 (m, 1 H), 1.98 (m, 3
H), 1.75 (m, 1 H), 1.62 (m, 2 H), 1.41 (m, 1 H). MS (ESI,
pos. ion) m/z: 437 (M + 1). Anal. (C20H19F3N4O2S‚0.5 H2O): C,
H, N.
mg, 1.0 mmol) and 1-isopropylpiperazine (260 mg, 2.0 mmol). The
title compound (260 mg, 63%) was obtained as light-yellow crystals.
Mp: 264-265 °C. H NMR (400 MHz, DMSO-d6) δ 12.47 (s, 1
H), 8.11 (s, 1 H), 7.89 (d, J ) 7.8 Hz, 1 H), 7.37 (t, J ) 8.0 Hz,
1 H), 7.24 (d, J ) 7.0 Hz, 1 H), 6.38 (s, 1 H), 3.61 (br s, 4 H),
2.73 (dt, J ) 12.9, 6.5 Hz, 1 H), 2.49-2.53 (m, 4 H), 2.19 (s, 3
H), 1.03 (d, J ) 6.6 Hz, 6 H). MS (ESI, pos. ion) m/z: 413 (M +
1). Anal. (C20H24N6O2S‚0.2 H2O): C, H, N.
1
N-(4-(6-(4-tert-Butylpiperazin-1-yl)pyrimidin-4-yloxy)benzo-
[d]thiazol-2-yl)acetamide (16c). To a suspension of N-(4-(6-
fluoropyrimidin-4-yloxy)benzo[d]thiazo-2-yl]acetamide (8; 100 mg,
0.33 mmol) in EtOH (2 mL) was added 1-tert-butylpiperazine15
(72 mg, 0.32 mmol). The reaction mixture was heated at 150 °C
for 5 min using a microwave reactor. The reaction mixture was
cooled, the solvents were removed in vacuo, and the residue was
washed with MeOH to give N-(4-(4-tert-butylpiperazinyl)pyrimi-
dine-4-yloxy)benzo[d]thiazo-2-yl]acetamide (65 mg, 46%) as a
1
white amorphous solid. H NMR (400 MHz, CDCl3): δ 9.99 (br
s, 1 H), 8.20 (s, 1 H), 7.68 (d, J ) 7.8 Hz, 1 H), 7.33 (t, J ) 7.8
Hz, 1 H), 7.22 (d, J ) 7.0 Hz, 1 H), 6.02 (s, 1 H), 3.61 (br s, 4 H),
2.65 (br s, 4 H), 2.24 (s, 3 H), 1.11 (s, 9 H). MS (ESI, pos. ion)
m/z: 427 (M + 1). Anal. Calcd for C21H26N6O2S‚1.3H2O: C, 56.06;
H, 6.41; N, 18.68; S, 7.13. Found: C, 56.37; H, 6.10; N, 18.17; S,
7.29.
N-(4-(6-(4-Neopentylpiperazin-1-yl)pyrimidin-4-yloxy)benzo-
[d]thiazol-2-yl)acetamide (16d). To a solution of tert-butyl pip-
erazine-1-carboxylate 18 (8.4 g, 45 mmol) in 1,2-dichloroethane
(100 mL) was added acetic acid (2.7 mL, 47 mmol) at 50 °C, and
the reaction mixture was stirred for 20 min. Trimethylacetaldehyde
(9.5 mL, 70 mmol) was added into the solution, immediately
followed by sodium triacetoxyborohydride (19.2 g, 90 mmol). After
1.5 h, the mixture was allowed to cool to room temperature and
saturated NaHCO3 (300 mL) was added. The organic phase was
separated and the aqueous phase was extracted with CH2Cl2 (2 ×
100 mL). The combined organic phases were dried over sodium
sulfate, filtered, and concentrated in vacuo to provide tert-butyl
4-neopentylpiperazine-1-carboxylate (19b; 12.6 g, 100%) as a pale-
N-(4-(6-(4-(Trifluoromethyl)piperidin-1-yl)pyrimidin-4-yloxy-
)benzo[d]thiazol-2-yl)acetamide (14). To a mixture of N-(4-(6-
chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (9; 300
mg, 0.9 mmol) and K2CO3 (500 mg, 3.6 mmol) in DMF (3.0 mL)
was added 4-(trifluoromethyl)piperidine (400 mg, 1.9 mmol), and
the mixture was heated at 80 °C for 3.5 h. The reaction was then
allowed to cool to room temperature and H2O (1.0 mL) was added.
The resulting precipitates were collected by filtration and washed
with H2O. The resulting solid was suspended in MeOH, collected
by filtration, and dried in vacuo to provide the title compound as
1
an off-white solid (160 mg, 39%). Mp: 327-328 °C. H NMR
(400 MHz, DMSO-d6): δ 12.42 (s, 1 H), 8.09 (s, 1 H), 7.86 (dd,
J ) 7.9, 1.1 Hz, 1 H), 7.33 (t, J ) 7.9 Hz, 1 H), 7.21 (dd, J ) 7.9,
1.1 Hz, 1 H), 6.41 (s, 1 H), 4.48 (d, J ) 11.7 Hz, 2 H), 2.88-2.99
(m, 2 H), 2.61-2.76 (m, 1 H), 2.15 (s, 3 H), 1.88 (d, J ) 11.0 Hz,
2 H), 1.30-1.44 (m, 2 H). MS (ESI, pos. ion) m/z: 438 (M + 1).
Anal. (C19H18F3N5O2S): C, H, N.
1
yellow oil. H NMR (300 MHz, CDCl3): δ 3.33-3.44 (m, 4 H)
2.40-2.51 (m, 4 H), 2.06 (s, 2 H), 1.46 (s, 9 H), 0.87 (s, 9 H). MS
(ESI, pos. ion) m/z: 257 (M + 1).
To a stirred solution of tert-butyl 4-neopentylpiperazine-1-
carboxylate (19b; 11.6 g, 45 mmol) in 70 mL of CH2Cl2 was added
2,2,2-trifluoroacetic acid (30.0 mL, 390 mmol) at room temperature
and the solution was stirred for 18 h. The solvent was evaporated,
and the oily residue was dissolved in CH2Cl2 (100 mL) and treated
with saturated NaHCO3 aqueous solution. The organic layer was
separated, and the aqueous phase was extracted with CH2Cl2 (2 ×
100 mL). The combined extracts were washed with brine (200 mL),
dried over Na2SO4, and concentrated in vacuo to afford 1-neopen-
N-(4-(6-Morpholinopyrimidin-4-yloxy)benzo[d]thiazol-2-yl)-
acetamide (15). This material was prepared according to the
procedure described for compound 14 from morpholine (0.11 mL,
1.2 mmol) and N-(4-(6-chloro-pyrimidin-4-yloxy)-benzothiazol-2-
yl)-acetamide (9; 200 mg, 0.62 mmol). The title compound was
1
obtained as a white solid (150 mg, 66%). Mp: 308-311 °C. H
NMR (400 MHz, DMSO-d6): δ 12.44 (s, 1 H), 8.11 (s, 1 H), 7.86
(d, J ) 7.8 Hz, 1 H), 7.34 (t, J ) 7.8 Hz, 1 H), 7.21 (d, J ) 7.8
Hz, 1 H), 6.38 (s, 1 H), 3.63-3.70 (m, 4 H), 3.54-3.60 (m, 4 H),
2.16 (s, 3 H). MS (ESI, pos. ion) m/z: 372 (M + 1). Anal.
(C17H17N5O3S‚0.2 H2O): C, H, N.
1
tylpiperazine (20b) as a white solid (7.8 g, 60%). H NMR (300
MHz, CDCl3) δ 9.49 (br s, 1 H), 3.02-3.34 (m, 4 H), 2.60-2.95
(m, 4 H), 2.15 (s, 2 H), 0.86 (s, 9 H). MS (ESI, pos. ion) m/z: 157
(M + 1).
N-(4-(6-(Piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-
yl)acetamide (16a). A mixture of N-(4-(6-chloropyrimidin-4-
yloxy)benzo[d]thiazol-2-yl)acetamide (9; 320 mg, 1.0 mmol) and
piperazine (860 mg, 1.0 mmol) in DMF (2.0 mL) was heated at
80 °C for 15 min. The reaction was then allowed to cool to room
temperature and H2O (1.0 mL) was added. The resulting precipitates
were collected by filtration and washed with H2O. The resulting
solid was suspended in MeOH, collected by filtration, and dried in
vacuo to provide the title compound as a light-yellow solid (330
mg, 89% yield). 1H NMR (400 MHz, DMSO-d6): δ 8.07 (s, 1 H),
7.86 (dd, J ) 8.0, 1.0 Hz, 1 H), 7.33 (t, J ) 7.8 Hz, 1 H), 7.20 (dd,
J ) 7.8, 0.8 Hz, 1 H), 6.31 (s, 1 H), 3.48-3.55 (m, 4 H), 2.70-
2.77 (m, 4 H), 2.16 (s, 3 H). MS (ESI, pos. ion) m/z: 371 (M +
1). Anal. (C17H18N6O2S‚0.2 H2O): C, H, N.
To a 5 mL microwave reaction tube was added N-(4-(6-
fluoropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (8; 320 mg,
1.0 mmol) and 1-neopentylpiperazine (20b; 210 mg, 1.34 mmol)
in DMSO (4.0 mL). The reaction was heated at 150 °C for 70 min
in a microwave reactor. The reaction mixture was partitioned
between H2O (50 mL) and EtOAc (30 mL). The aqueous phase
was extracted with EtOAc (2 × 30 mL). The combined organic
phases were washed with H2O (2 × 50 mL) and saturated aqueous
NaCl (50 mL). The organic phase was dried over sodium sulfate,
filtered, and concentrated in vacuo to afford a light-yellow solid
(406 mg). The crude product was purified by silica gel chroma-
tography (10%-80% EtOAc in hexanes) to afford the title
1
compound 16d (230 mg, 51%) as a white solid. H NMR (300
MHz, CDCl3): δ 9.76 (s, 1 H), 8.20 (s, 1 H), 7.68 (d, J ) 7.9 Hz,
1 H), 7.34 (t, J ) 8.0 Hz, 1 H), 7.16-7.24 (m, 1 H), 6.02 (s, 1 H),
3.56 (br s, 4 H), 2.57 (br s, 4 H), 2.24 (s, 3 H), 2.10 (s, 2 H), 0.90
(s, 9 H). MS (ESI, pos. ion) m/z: 441 (M + 1). Anal.
(C22H28N6O2S): C, H, N.
N-(4-(6-(4-Isopropylpiperazin-1-yl)pyrimidin-4-yloxy)benzo-
[d]thiazol-2-yl)acetamide (16b). This material was prepared ac-
cording to the procedure described for compound 14 from N-(4-
(6-chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (9; 320

3536 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15
Wang et al.
N-(4-(6-(4-(2,2,2-Trifluoroethyl)piperazin-1-yl)pyrimidin-4-
yloxy)benzo[d] thiazol-2-yl)acetamide (16e). To a solution of tert-
butyl piperazine-1-carboxylate (18; 500 mg, 2.7 mmol) in THF (20
mL) was added diisopropylethylamine (0.50 mL, 2.7 mmol)
followed by 2,2,2-trifluoroethyl trifluoromethanesulfonate (620 mg,
2.7 mmol), and the reaction mixture was stirred at reflux for 4 h.
The resulting mixture was allowed to cool to room temperature,
concentrated in vacuo, and purified by silica gel column chroma-
tography (gradient: 5-10% MeOH in CH2Cl2) to afford tert-butyl
4-(2,2,2-trifluoroethyl)piperazine-1-carboxylate (19a; 670 mg, 97%)
as a white crystalline solid. To a solution of 19a in CH2Cl2 (50
mL) was added trifluoroacetic acid (5 mL, 65 mmol). The reaction
mixture was stirred at room temperature for 2 h. The solvent was
removed in vacuo. The crude material was dissolved in CH2Cl2
(100 mL) and washed with saturated aqueous NaHCO3 (2 × 100
mL). The organic layer was dried over Na2SO4, filtered, and
concentrated in vacuo to give 1-(2,2,2-trifluoroethyl)piperazine
(20a) as a clear oil (0.40 mg, 91%). 1H NMR (300 MHz, CDCl3):
δ 8.80 (br s, 1 H), 3.83 (br s, 4 H), 3.31 (br s, 2 H), 3.09 (q, J )
9.2 Hz, 2 H), 2.91-3.03 (m, 2 H). MS (ESI, pos. ion) m/z: 169
(M + 1).
N-(4-(6-(4-(1-Phenylethyl)piperazin-1-yl)pyrimidin-4-yloxy)-
benzo[d]thiazol-2-yl)acetamide (16i). This material was prepared
according to the procedure described for compound 14 from 1-(1-
phenylethyl)piperazine (0.24 mL, 1.2 mmol) and N-(4-(6-chloro-
pyrimidin-4-yloxy)-benzothiazol-2-yl)-acetamide (9; 200 mg, 0.62
mmol). The title compound was obtained as a solid (92 mg, 31%).
Mp: 132-135 °C. 1H NMR (400 MHz, DMSO-d6): δ 12.42 (s, 1
H), 8.05 (s, 1 H), 7.84 (dd, J ) 8.0, 1.0 Hz, 1 H), 7.22-7.38 (m,
6 H), 7.19 (dd, J ) 7.8, 1.0 Hz, 1 H), 6.32 (s, 1 H), 3.57 (br s, 4
H), 3.46 (q, J ) 6.6 Hz, 1 H), 2.41-2.48 (m, 2 H), 2.31-2.40 (m,
2 H), 2.15 (s, 3 H), 1.33 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion)
m/z: 475 (M + 1). Anal. (C25H26N6O2S‚0.5 H2O): C, H, N.
N-(4-(6-(4-(1-Phenylpropyl)piperazin-1-yl)pyrimidin-4-yloxy)-
benzo[d]thiazol-2-yl)acetamide (16j). A mixture of piperazine-1-
carboxylic acid tert-butyl ester (18; 500 mg, 2.7 mmol), propiophe-
none (0.54 mL, 4.0 mmol) in THF (2.5 mL) at room temperature
was treated with titanium tetra-isopropoxide (2.4 mL, 8.1 mmol)
under nitrogen and then stirred at 75 °C for 16 h. The reaction
mixture was cooled to -48 °C and then treated with sodium
triacetoxyborohydride (1720 mg, 8.10 mmol) followed by MeOH
(1.3 mL). The resulting mixture was allowed to warm to room
temperature over 1.5 h. The reaction mixture was diluted with
EtOAc (20 mL) and washed with aqueous 1 N NaOH (2 × 30
mL). The organic layer was dried over Na2SO4 and concentrated
under vacuum. The crude material was purified by silica gel
chromatography (gradient: 0-5% MeOH/CH2Cl2) to obtain tert-
butyl 4-(1-phenylpropyl)piperazine-1-carboxylate (19c) as a yellow
oil (510 mg, 62%). 1H NMR (400 MHz, DMSO-d6): δ 7.60-7.57
(m, 2 H), 7.53-7.46 (m, 3 H), 3.54-3.51 (m, 5 H), 2.76 (m, 2 H),
2.50 (m, 2 H), 2.10 (m, 1 H), 1.95 (m, 1 H), 1.60 (s, 9 H), 0.96 (t,
J ) 7.6 Hz, 3 H). MS (ESI, pos. ion) m/z: 305 (M + 1).
A solution of tert-butyl 4-(1-phenylpropyl)piperazine-1-carboxy-
late (19c; 510 mg, 1.71 mmol) in CH2Cl2 (3.5 mL) was treated
with TFA (0.8 mL) at room temperature and stirred for 16 h. The
solvent and excess TFA were removed under vacuum to give 1-(1-
phenylpropyl)piperazine (20c) as a TFA salt. Following the
procedure described for compound 14, the above 1-(1-phenylpro-
pyl)piperazine (20c), N-(4-(6-chloro-pyrimidin-4-yloxy)-benzothia-
zol-2-yl)-acetamide (9; 550 mg, 1.7 mmol), and K2CO3 (940 mg,
6.6 mmol) provided the title compound 16j as an off-white solid
(376 mg, 29% over three steps). Mp: 213-215 °C. 1H NMR (400
MHz, DMSO-d6): δ 12.41 (s, 1 H), 8.03 (s, 1 H), 7.84 (d, J ) 8.0
Hz, 1 H), 7.29-7.38 (m, 3 H), 7.22-7.29 (m, 3 H), 7.17 (d, J )
7.2 Hz, 1 H), 6.29 (s, 1 H), 3.56 (s, 4 H), 3.56 (m, 1 H), 2.30-
2.42 (m, 4 H), 2.14 (s, 3 H), 1.87-1.99 (m, 1 H), 1.66-1.79 (m,
1 H), 0.73 (t, J ) 7.2 Hz, 3 H). MS (ESI, pos. ion) m/z: 489 (M
+ 1). Anal. (C26H28N6O2S‚0.2 H2O): C, H, N.
To a 2.5 mL microwave vial was added 1-(2,2,2-trifluoroethyl)-
piperazine (20a; 0.40 g, 2.9 mmol) and N-(4-(6-fluoropyrimidin-
4-yloxy)benzo[d]thiazol-2-yl)acetamide (8; 0.80 g, 2.6 mmol) in
DMSO (4 mL). The vial was sealed and the solution was stirred at
110 °C for 17 h. The reaction mixture was allowed to reach room
temperature. Water (20 mL) was added to the reaction mixture and
the aqueous phase was extracted with CH2Cl2 (2 × 50 mL). The
combined CH2Cl2 layers were washed with brine (100 mL), dried
over Na2SO4, filtered, and concentrated. The crude material was
purified by silica gel column chromatography (gradient: 20-80%
EtOAc in hexanes) to give the title compound 16e as an off-white
1
solid (0.68 g, 63%). H NMR (300 MHz, DMSO-d6): δ 12.44 (s,
1 H), 8.09 (s, 1 H), 7.86 (d, J ) 7.2 Hz, 1 H), 7.33 (t, J ) 7.9 Hz,
1 H), 7.20 (d, J ) 7.2 Hz, 1 H), 6.38 (s, 1 H), 3.62 (s, 4 H), 3.26
(q, J ) 10 Hz, 2 H), 2.68 (s, 4 H), 2.16 (s, 3 H). MS (ESI, pos.
ion) m/z: 453 (M + 1). Anal. (C19H19F3N6O2S): C, H, N.
N-(4-(6-(4-Phenylpiperazin-1-yl)pyrimidin-4-yloxy)benzo[d]-
thiazol-2-yl)acetamide (16f). This material was prepared according
to the procedure described for compound 14 from 1-phenylpipera-
zine (0.20 mL, 1.3 mmol) and N-(4-(6-chloro-pyrimidin-4-yloxy)-
benzothiazol-2-yl)-acetamide (9; 200 mg, 0.62 mmol). The title
compound was obtained as an off-white solid (200 mg, 73%). Mp:
1
292.0-292.3 °C. H NMR (400 MHz, DMSO-d6): δ 8.12 (s, 1
H), 7.86 (d, J ) 7.8 Hz, 1 H), 7.33 (t, J ) 7.9 Hz, 1 H), 7.19-7.28
(m, 3 H), 6.99 (d, J ) 8.2 Hz, 2 H), 6.82 (t, J ) 7.2 Hz, 1 H), 6.43
(s, 1 H), 3.76 (br s, 4 H), 3.19-3.25 (m, 4 H), 2.15 (s, 3 H). MS
(ESI, pos. ion) m/z: 447 (M + 1). Anal. (C23H22N6O2S‚0.2 H2O):
C, H, N.
N-(4-(6-(4-Benzhydrylpiperazin-1-yl)pyrimidin-4-yloxy)ben-
zo[d]thiazol-2-yl)acetamide (16k). This material was prepared
according to the procedure described for compound 14 from
1-benzhydrylpiperazine (310 mg, 1.2 mmol) and N-(4-(6-chloro-
pyrimidin-4-yloxy)-benzothiazol-2-yl)-acetamide (9; 200 mg, 0.62
mmol). The title compound was obtained as an off-white solid (150
N-(4-(6-(4-Benzylpiperazin-1-yl)pyrimidin-4-yloxy)benzo[d]-
thiazol-2-yl)acetamide (16g). This material was prepared according
to the procedure described for compound 14 from 1-benzylpipera-
zine (0.20 mL, 1.2 mmol) and N-(4-(6-chloro-pyrimidin-4-yloxy)-
benzothiazol-2-yl)-acetamide (9; 200 mg, 0.62 mmol). The title
compound was obtained as a tan solid (150 mg, 52%). Mp: 217-
1
mg, 46%). Mp: 156.0-156.5 °C. H NMR (400 MHz, DMSO-
d6): δ 12.43 (s, 1 H), 8.06 (s, 1 H), 7.84 (dd, J ) 8.2, 0.8 Hz, 1
H), 7.47 (d, J ) 7.4 Hz, 4 H), 7.27-7.35 (m, 5 H), 7.16-7.24 (m,
3 H), 6.32 (s, 1 H), 4.35 (s, 1 H), 3.61 (s, 4 H), 2.37 (s, 4 H), 2.15
(s, 3 H). MS (ESI, pos. ion) m/z: 537 (M + 1). Anal. (C30H28N6O2S‚
2H2O): C, H, N.
1
218 °C. H NMR (400 MHz, DMSO-d6): δ 12.42 (s, 1 H), 8.07
(s, 1 H), 7.85 (dd, J ) 7.9, 0.9 Hz, 1 H), 7.25-7.37 (m, 6 H), 7.20
(dd, J ) 7.8, 0.8 Hz, 1 H), 6.35 (s, 1 H), 3.60 (br s, 4 H), 3.53 (s,
2 H), 2.40-2.45 (m, 4 H), 2.15 (s, 3 H). MS (ESI, pos. ion) m/z:
461 (M + 1). Anal. (C24H24N6O2S): C, H, N.
N-(4-(6-(4-(2-Phenylpropan-2-yl)piperazin-1-yl)pyrimidin-4-
yloxy)benzo[d]thiazol-2-yl)acetamide (16l). A mixture of N,N-
bis(2-chloroethyl)-4-methylbenzenesulfonamide (25; 860 mg, 2.9
mmol), 2-phenylpropan-2-amine (780 mg, 5.8 mmol) in N,N-
diisopropylpropylethylamine (2.0 mL) was heated at 125 °C for 3
d. The reaction was then allowed to cool to room temperature and
partitioned between H2O (20 mL) and CH2Cl2 (20 mL). The
aqueous phase was extracted with CH2Cl2 (2 × 10 mL). The
combined organic phases were washed with H2O (50 mL) and
saturated aqueous NaCl (50 mL). The organic phase was dried over
sodium sulfate, filtered, and concentrated in vacuo. The crude
product was purified by silica gel chromatography (50-100% CH2-
N-(4-(6-(4-Phenethylpiperazin-1-yl)pyrimidin-4-yloxy)benzo-
[d]thiazol-2-yl)acetamide (16h). This material was prepared ac-
cording to the procedure described for compound 14 from
1-phenethylpiperazine (360 mg, 1.90 mmol) and N-(4-(6-chloro-
pyrimidin-4-yloxy)-benzothiazol-2-yl)-acetamide (9; 300 mg, 0.94
mmol). The title compound was obtained as a white solid (21 mg,
5%). Mp: 128-133 °C. 1H NMR (400 MHz, DMSO-d6): δ 12.43
(s, 1 H), 8.08 (s, 1 H), 7.85 (d, J ) 7.8 Hz, 1 H), 7.15-7.36 (m,
7 H), 6.37 (s, 1 H), 3.60 (br s, 4 H), 2.72-2.81 (m, 2 H), 2.54-
2.61 (m, 2 H), 2.50 (s, 4 H), 2.15 (s, 3 H). MS (ESI, pos. ion) m/z:
475 (M + 1). Anal. (C25H26N6O2S‚1.5 H2O): C, H, N.

AMG 628, a Second-Generation Clinical Candidate
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15 3537
Cl2 in hexanes) to afford 1-(2-phenylpropan-2-yl)-4-tosylpiperazine
(790 mg, 76%) as a white foam. H NMR (300 MHz, CDCl3): δ
7.63 (d, J ) 6.8 Hz, 2 H), 7.40 (d, J ) 8.0 Hz, 2 H), 7.34 (d, J )
8.0 Hz, 2 H), 7.25 (m, 2 H), 7.18 (m, 1 H), 2.95 (br s, 4 H), 2.55
(t, J ) 4.6 Hz, 4 H), 2.46 (s, 3 H), 1.30 (s, 6 H). MS (ESI, pos.
ion) m/z: 359 (M + 1).
H), 6.32 (s, 1 H), 3.75 (s, 3 H), 3.56 (br s, 4 H), 3.43 (q, J ) 6.5
Hz, 1 H), 2.39-2.48 (m, 2 H), 2.30-2.39 (m, 2 H), 2.15 (s, 3 H),
1.31 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 505 (M + 1).
Anal. Calcd for C26H28N6O3S‚H2O: C, 59.75; H, 5.79; N, 16.08;
S, 6.14. Found: C, 59.38; H, 5.48; N, 16.66; S, 6.62.
1
(S)-tert-Butyl 4-(1-(4-Fluorophenyl)ethyl)piperazine-1-car-
boxylate (21) and (R)-tert-Butyl 4-(1-(4-Fluorophenyl)ethyl)-
piperazine-1-carboxylate (22). A mixture of 4′-fluoroacetophenone
(1.0 mL, 8.0 mmol) and piperazine-1-carboxylic acid tert-butyl ester
(18; 1.00 g, 5.0 mmol) in THF (3.0 mL) at room temperature was
treated with titanium tetra-isopropoxide (5.0 mL, 16.00 mmol) under
nitrogen and then stirred at 75 °C for 18 h. The reaction mixture
was cooled to -48 °C and then treated with sodium triacetoxy-
borohydride (3.00 g, 16.0 mmol) followed by MeOH (2.0 mL).
The resulting mixture was allowed to warm to room temperature
over 1.5 h. The reaction mixture was diluted with EtOAc (100 mL)
and washed with aqueous 5 N NaOH (4 × 30 mL). The organic
layer was dried over Na2SO4, filtered, and concentrated under
vacuum. The crude material was purified by silica gel chromatog-
raphy (gradient: 0-5% MeOH/ CH2Cl2) to obtain tert-butyl 4-(1-
(4-fluorophenyl)ethyl)piperazine-1-carboxylate (19g) as a yellow
To a mixture of 1-(2-phenylpropan-2-yl)-4-tosylpiperazine (790
mg, 2.2 mmol) and 4-hydroxybenzoic acid was added hydrogen
bromide solution (33 wt % in acetic acid, 8.0 mL) at room
temperature. The reaction mixture was stirred for 4 d at room
temperature. The resulting mixture was cooled to 0 °C followed
by addition of H2O (20 mL) and CH2Cl2 (20 mL). A white
precipitate was formed and removed by filtration. The filter cake
was washed with H2O (3×). The combined aqueous layers were
extracted with CH2Cl2 (2×) and toluene (2×). The aqueous phase
was then cooled to 0 °C, basified with 10 M NaOH aqueous solution
to pH ) 12, and extracted with CH2Cl2 (3×). The combined organic
phases were washed with H2O and brine, dried over sodium sulfate,
filtered, and concentrated in vacuo to afford 1-(2-phenylpropan-2-
1
yl)piperazine (26; 390 mg, 86%) as a white solid. H NMR (400
MHz, CDCl3): δ 7.53 (m, 2 H), 7.30 (m, 2 H), 7.19 (m, 1 H), 2.85
(t, J ) 4.8 Hz, 4 H), 2.45 (t, J ) 4.8 Hz, 4 H), 1.82 (br s, 3 H),
1.33 (s, 6 H). MS (ESI, pos. ion) m/z: 205 (M + 1).
1
oil (0.74 g, 44%). H NMR (400 MHz, DMSO-d6): δ 7.29-7.35
(m, 2 H), 7.10-7.17 (m, 2 H), 3.46 (q, J ) 6.7 Hz, 1 H), 3.27 (br
s, 4 H), 2.26-2.36 (m, 2 H), 2.17-2.26 (m, 2 H), 1.37 (s, 9 H),
1.27 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 309 (M + 1).
Chiral separation of tert-butyl 4-(1-(4-fluorophenyl)ethyl)pip-
erazine-1-carboxylate (19g; 1.29 g) was performed on an Agilent
1100 specrometer by Chirobiotic TAG column (4.6 × 250 mm) at
a 1.0 mL/min flow rate using isocratic MeOH/acetic acid/tri-
ethyamine (100:0.08:0.02). (R)-tert-Butyl 4-(1-(4-fluorophenyl)-
ethyl)piperazine-1-carboxylate (21; 0.49 g, tr ) 13.16 min, 93%
ee) and (S)-tert-butyl 4-(1-(4-fluorophenyl)ethyl)piperazine-1-car-
boxylate (22; 0.42 g, tr ) 8.88 min, 96% ee) were obtained.
(R)-1-(1-(4-Fluorophenyl)ethyl)piperazine (23). Method A: A
solution of (R)-tert-butyl 4-(1-(4-fluorophenyl)ethyl)piperazine-1-
carboxylate (21; 480 mg, 1.5 mmol) in CH2Cl2 (2.0 mL) was treated
with TFA (0.5 mL) at room temperature and stirred for 18 h. The
solvents and excess TFA were removed under vacuum to give (R)-
1-(1-(4-fluorophenyl)ethyl)piperazine (23) as a TFA salt. MS (ESI,
pos. ion) m/z: 209 (M + 1).
Following the procedure described for compound 14, 1-(2-
phenylpropan-2-yl)piperazine (26; 470 mg, 2.3 mmol) and N-(4-
(6-chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (9; 490
mg, 1.5 mmol) provided the title product 16l (450 mg, 92%) as a
light-yellow solid. Mp: 223-224 °C. 1H NMR (400 MHz, DMSO-
d6) δ 12.43 (s, 1 H), 8.06 (s, 1 H), 7.85 (d, J ) 7.8 Hz, 1 H), 7.54
(d, J ) 7.8 Hz, 2 H), 7.33 (q, J ) 7.7 Hz, 3 H), 7.16-7.26 (m, 2
H), 6.32 (s, 1 H), 3.56 (br s, 4 H), 2.45 (s, 4 H), 2.15 (s, 3 H), 1.32
(s, 6 H). MS (ESI, pos. ion) m/z: 489 (M + 1). Anal. (C25H28N6O2S‚
0.3 H2O): C, H, N.
N-(4-(6-(4-(1-(3-Fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-
4-yloxy)benzo[d]thiazol-2-yl)acetamide (16m). Analogous to the
procedure in the preparation of compound 16j, 3′-fluoroacetophe-
none (0.49 mL, 4.00 mmol), piperazine-1-carboxylic acid tert-butyl
ester (18; 500 mg, 2.7 mmol), and N-(4-(6-chloro-pyrimidin-4-
yloxy)-benzothiazol-2-yl)-acetamide (9; 630 mg, 1.9 mmol) pro-
vided the title compound as a white solid (680 mg, 51% over three
steps). Mp: 204 °C. 1H NMR (400 MHz, DMSO-d6): δ 12.42 (s,
1 H), 8.05 (s, 1 H), 7.84 (d, J ) 7.8 Hz, 1 H), 7.34-7.43 (m, 1 H),
7.31 (t, J ) 7.8 Hz, 1 H), 7.13-7.22 (m, 3 H), 7.02-7.12 (m, 1
H), 6.32 (s, 1 H), 3.57 (br s, 4 H), 3.52 (q, J ) 6.8 Hz, 1 H),
2.42-2.48 (m, 2 H), 2.30-2.41 (m, 2 H), 2.14 (s, 3 H), 1.32 (d, J
) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M + 1). Anal.
(C25H25FN6O2S‚0.5 H2O): C, H, N.
Method B: A mixture of N,N-bis(2-chloroethyl)-4-methylben-
zenesulfonamide (39.2 g, 134 mmol; 25), (R)-1-(4-fluorophenyl)-
ethanamine (17.0 g, 122 mmol), and N,N-diisopropylpropylethy-
lamine (42.5 mL) under a nitrogen atmosphere was heated at
125 °C for 20 h. The reaction was then allowed to cool to room
temperature. A mixture of EtOH/H2O (70/30, 100 mL) was added
slowly to the reaction mixture and stirred overnight. The resulting
solid was filtered off and washed with H2O (3 × 50 mL) and
hexanes (2 × 50 mL). The filter cake was suspended in a mixture
of EtOH/H2O (1:1; 120 mL) for 3.5 h. The resulting solid was
collected by filtration, washed with EtOH/H2O (1:1, 2 × 40 mL),
EtOH/H2O (70:30, 30 mL) and hexanes (2 × 40 mL). The solid
was dried in a vacuum oven at 50 °C for 17 h to provide (R)-1-
(1-(4-fluorophenyl)ethyl)-4-tosylpiperazine (35.4 g, 80%). Mp:
129 °C. 1H NMR (400 MHz, CDCl3): δ 7.63 (d, J ) 8.2 Hz, 2 H),
7.33 (d, J ) 8.2 Hz, 2 H), 7.16-7.23 (m, 2 H), 6.92-7.00 (m, 2
H), 3.36 (q, J ) 6.9 Hz, 1 H), 2.89-3.03 (m, 4 H), 2.50-2.62 (m,
2 H), 2.40-2.47 (m, 5 H), 1.29 (d, J ) 6.9 Hz, 3 H). MS (ESI,
pos. ion) m/z: 363 (M + 1).
To a mixture of (R)-1-(1-(4-fluorophenyl)ethyl)-4-tosylpiperazine
(20.0 g, 55.2 mmol) and 4-hydroxybenzoic acid (22.9 g, 165 mmol)
was added hydrogen bromide solution (33 wt. % in acetic acid,
220 mL) at room temperature. The reaction mixture was stirred
under nitrogen atmosphere for 2 d with a mechanical stirrer at room
temperature. Water (200 mL) was slowly added to the reaction
mixture (mildly exothermic), and the reaction mixture was continu-
ally stirred for 2 h. A white precipitate was formed and removed
by filtration. The filter cake was washed with H2O (2 × 50 mL).
The combined acidic aqueous washes were washed with toluene
(4 × 50 mL). The aqueous phase was then cooled to 0 °C, basified
with KOH pellets portionwise until pH > 10, and extracted with
N-(4-(6-(4-(1-(4-(Trifluoromethyl)phenyl)ethyl)piperazin-1-
yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16n). Analo-
gous to the procedure for the preparation of compound 16j, 4′-
trifluoromethyl-acetophenone (750 mg, 4.0 mmol), piperazine-1-
carboxylic acid tert-butyl ester (18; 500 mg, 2.7 mmol), and N-(4-
(6-chloro-pyrimidin-4-yloxy)-benzothiazol-2-yl)-acetamide (9; 610
mg, 1.9 mmol) provided the title compound as a white solid (730
mg, 50% over three steps). Mp: 153-155 °C. 1H NMR (400 MHz,
DMSO-d6): δ 12.42 (s, 1 H), 8.06 (s, 1 H), 7.85 (dd, J ) 8.0, 1.0
Hz, 1 H), 7.71 (d, J ) 8.2 Hz, 2 H), 7.58 (d, J ) 8.2 Hz, 2 H),
7.32 (t, J ) 7.9 Hz, 1 H), 7.19 (dd, J ) 7.8, 0.8 Hz, 1 H), 6.32 (s,
1 H), 3.52-3.64 (m, 5 H), 2.44-2.48 (m, 2 H), 2.30-2.41 (m, 2
H), 2.15 (s, 3 H), 1.34 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion)
m/z: 543 (M + 1). Anal. (C26H25F3N6O2S‚0.5 H2O): C, H, N.
N-(4-(6-(4-(1-(4-Methoxyphenyl)ethyl)piperazin-1-yl)pyrimi-
din-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16o). Analogous to
the procedure in the preparation of compound 16j, 1-(4-methox-
yphenyl)ethanone (600 mg, 4.0 mmol), piperazine-1-carboxylic acid
tert-butyl ester (18; 500 mg, 2.7 mmol), and N-(4-(6-chloro-
pyrimidin-4-yloxy)-benzothiazol-2-yl)-acetamide (9; 590 mg, 1.8
mmol) provided the title compound as a white solid (300 mg, 22%
1
in three steps). Mp: 150-151 °C. H NMR (400 MHz, DMSO-
d6): δ 12.43 (s, 1 H), 8.05 (s, 1 H), 7.85 (d, J ) 7.8 Hz, 1 H), 7.32
(t, J ) 7.8 Hz, 1 H), 7.16-7.26 (m, 3 H), 6.90 (d, J ) 8.6 Hz, 2

3538 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15
Wang et al.
toluene (3 × 50 mL) and EtOAc (50 mL). The combined organic
phases were washed with brine (100 mL), dried over sodium sulfate,
filtered, and concentrated in vacuo to afford (R)-1-(1-(4-fluorophe-
nyl)ethyl)piperazine (23; 10.4 g, 91%) as a pale brown solid. Mp:
12.41 (s, 1 H), 8.06 (s, 1 H), 7.84 (dd, J ) 7.8, 0.8 Hz, 1 H),
7.27-7.40 (m, 3 H), 7.11-7.22 (m, 3 H), 6.32 (s, 1 H), 3.57 (br s,
4 H), 3.50 (q, J ) 6.8 Hz, 1 H), 2.40-2.48 (m, 2 H), 2.30-2.38
(m, 2 H), 2.15 (s, 3 H), 1.31 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos.
ion) m/z: 493 (M + 1). Anal. (C25H25FN6O2S): C, H, N.
N-(4-(6-(4-(1-(2-Fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-
4-yloxy)benzo[d]thiazol-2-yl)acetamide (17b). This material was
prepared according to the procedure described for compound 17a
from N-(4-(6-(piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-
yl)acetamide (16a; 60 mg, 0.16 mmol) and 2′-fluoro-acetylphenone
(0.03 mL, 0.24 mmol). The title compound (29 mg, 37%) was
obtained as a pale-yellow solid. Mp: 203-204 °C. 1H NMR (400
MHz, DMSO-d6): δ 12.43 (s, 1 H), 8.06 (s, 1 H), 7.85 (d, J ) 7.8
Hz, 1 H), 7.48 (t, J ) 7.4 Hz, 1 H), 7.32 (t, J ) 8.0 Hz, 2 H),
7.14-7.26 (m, 3 H), 6.33 (s, 1 H), 3.86 (q, J ) 7.0 Hz, 1 H), 3.58
(br s, 4 H), 2.42-2.48 (m, 2 H), 2.35-2.42 (m, 2 H), 2.15 (s, 3
H), 1.36 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M +
1). Anal. (C25H25FN6O2S): C, H, N.
1
70-71 °C. H NMR (400 MHz, CDCl3): δ 7.26-7.30 (m, 2 H),
6.95-7.06 (m, 2 H), 3.33 (q, J ) 6.8 Hz, 1 H), 2.82-2.88 (m, 4
H), 2.40-2.50 (m, 1 H), 2.28-2.37 (m, 2 H), 2.01-2.09 (m, 2 H),
1.33 (d, J ) 6.8 Hz, 3 H). MS (ESI, pos. ion) m/z: 209 (M + 1).
(S)-1-(1-(4-Fluorophenyl)ethyl)piperazine (24). Method A:
Analogous to the method A in the preparation of compound 23,
(S)-tert-butyl 4-(1-(4-fluorophenyl)ethyl)piperazine-1-carboxylate
(22; 420 mg, 1.4 mmol) provided (S)-1-(1-(4-fluorophenyl)ethyl)-
piperazine (24) as a TFA salt. MS (ESI, pos. ion) m/z: 209
(M + 1).
Method B: Analogous to the method B in the preparation of
compound 23, N,N-bis(2-chloroethyl)-4-methylbenzenesulfonamide
25 (21.0 g, 134 mmol), (S)-1-(4-fluorophenyl)ethanamine (9.0 g,
120 mmol) provided (S)-1-(1-(4-fluorophenyl)ethyl)piperazine (24;
1
7.4 g, 56% over two steps) as a pale-yellow solid. H NMR (400
Acknowledgment. The authors thank Paul Reider, Randy
Hungate, Jean-Claude Louis, and Chris Fibiger for their support
in this research program. Thanks also go to James Davis, Gal
Hever, Rongzhen Kuang, Jue Wang, Dawn Zhu, Shoushu Jiao,
and Ella Magal for conducting the in vivo pharmacology,
Helming Tan and Maggie Reed for the solubility determination,
and Wesley Barnhart for his excellent technical assistance in
conducting the HPLC chiral separation. Finally, we acknowledge
all of our colleagues on the TRPV1 research team (pharma-
ceutics, toxicology, PKDM, process research and development,
analytical support, clinical development).
MHz, CDCl3): δ 7.26-7.30 (m, 2 H), 6.95-7.06 (m, 2 H), 3.33
(q, J ) 6.8 Hz, 1 H), 2.82-2.88 (m, 4 H), 2.40-2.50 (m, 1 H),
2.28-2.37 (m, 2 H), 2.01-2.09 (m, 2 H), 1.33 (d, J ) 6.8 Hz, 3
H). MS (ESI, pos. ion) m/z: 209 (M + 1).
(R)-N-(4-(6-(4-(1-(4-Fluorophenyl)ethyl)piperazin-1-yl)pyri-
midin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16p). A mixture
of N-(4-(6-chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide
(9; 3.0 g, 9.4 mmol), (R)-1-(1-(4-fluorophenyl)ethyl)piperazine (23;
2.0 g, 9.8 mmol, from the procedure described for compound 23,
method B), and Na2CO3 (2.4 g, 9.4 mmol) in DMF (30.0 mL) was
heated at 90 °C for 5.5 h. The reaction mixture was transferred
dropwise to a flask containing H2O (240 mL) and stirred vigorously
for 30 min. The resulting precipitate was collected by filtration and
washed with H2O (1 × 50 mL and 2 × 25 mL) followed by hexanes
(3 × 50 mL). The resulting solid was dried under vacuum to provide
Supporting Information Available: Elemental analysis data
for final compounds 12-15, 16a-q, and 17a,b. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
the title compound as an off-white solid (4.1 g, 88%). H NMR
References
(400 MHz, DMSO-d6): δ 12.41 (s, 1 H), 8.06 (s, 1 H), 7.84 (dd,
J ) 7.8, 0.8 Hz, 1 H), 7.27-7.40 (m, 3 H), 7.11-7.22 (m, 3 H),
6.32 (s, 1 H), 3.57 (br s, 4 H), 3.50 (q, J ) 6.8 Hz, 1 H), 2.40-
2.48 (m, 2 H), 2.30-2.38 (m, 2 H), 2.15 (s, 3 H), 1.31 (d, J ) 6.7
Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M + 1). Anal. (C25H25-
FN6O2S): C, H, N.
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(S)-N-(4-(6-(4-(1-(4-Fluorophenyl)ethyl)piperazin-1-yl)pyri-
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compound 16p from N-(4-(6-chloropyrimidin-4-yloxy)benzo[d]-
thiazol-2-yl)acetamide (9; 430 mg, 1.4 mmol) and (S)-1-(1-(4-
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1
compound was obtained as an off-white solid (271 mg, 41%). H
NMR (400 MHz, DMSO-d6): δ 12.41 (s, 1 H), 8.06 (s, 1 H), 7.84
(dd, J ) 7.8, 0.8 Hz, 1 H), 7.27-7.40 (m, 3 H), 7.11-7.22 (m, 3
H), 6.32 (s, 1 H), 3.57 (br s, 4 H), 3.50 (q, J ) 6.8 Hz, 1 H),
2.40-2.48 (m, 2 H), 2.30-2.38 (m, 2 H), 2.15 (s, 3 H), 1.31 (d, J
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(6-(piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)aceta-
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1
mg, 2%). Mp: 241-242 °C. H NMR (400 MHz, DMSO-d6): δ

AMG 628, a Second-Generation Clinical Candidate
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JM070191H