Discovery of 3-methyl-N-(1-oxy-3′,4′,5′,6′- tetrahydro-2′H-[2,4′-bipyridine]-1′-ylmethyl)benzamide (ABT-670), an orally bioavailable dopamine D4 agonist for the treatment of erectile dysfunction

Article abstract of DOI:10.1021/jm060662k

The goal of this study was to identify a structurally distinct D4-selective agonist with superior oral bioavailability to our first-generation clinical candidate 1a (ABT-724) for the potential treatment of erectile dysfunction. Arylpiperazines such as (heteroarylmethyl)piperazine 1a, benzamide 2, and acetamides such as 3a,b exhibit poor oral bioavailability. Structure-activity relationship (SAR) studies with the arylpiperidine template provided potent partial agonists such as 4d and 5k that demonstrated no improvement in oral bioavailability. Further optimization with the (N-oxy-2-pyridinyl)piperidine template led to the discovery of compound 6b (ABT-670), which exhibited excellent oral bioavailability in rat, dog, and monkey (68%, 85%, and 91%, respectively) with comparable efficacy, safety, and tolerability to 1a. The N-oxy-2-pyridinyl moiety not only provided the structural motif required for agonist function but also reduced metabolism rates. The SAR study leading to the discovery of 6b is described herein.

Full text of DOI:10.1021/jm060662k

7450
J. Med. Chem. 2006, 49, 7450-7465
Discovery of 3-Methyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-ylmethyl)benzamide
(ABT-670), an Orally Bioavailable Dopamine D4 Agonist for the Treatment of Erectile
Dysfunction
Meena V. Patel,* Teodozyj Kolasa, Kathleen Mortell, Mark A. Matulenko, Ahmed A. Hakeem, Jeffrey J. Rohde,
Sherry L. Nelson, Marlon D. Cowart, Masaki Nakane, Loan N. Miller, Marie E. Uchic, Marc A. Terranova,
Odile F. El-Kouhen, Diana L. Donnelly-Roberts, Marian T. Namovic, Peter R. Hollingsworth, Renjie Chang,
Brenda R. Martino, Jill M. Wetter, Kennan C. Marsh, Ruth Martin, John F. Darbyshire, Gary Gintant, Gin C. Hsieh,
Robert B. Moreland, James P. Sullivan, Jorge D. Brioni, and Andrew O. Stewart
Neuroscience Research, Global Pharmaceutical Research and DeVelopment, Abbott Laboratories, 100 Abbott Park Road,
Abbott Park, Illinois 60064-3500
ReceiVed June 2, 2006
The goal of this study was to identify a structurally distinct D4-selective agonist with superior oral
bioavailability to our first-generation clinical candidate 1a (ABT-724) for the potential treatment of erectile
dysfunction. Arylpiperazines such as (heteroarylmethyl)piperazine 1a, benzamide 2, and acetamides such
as 3a,b exhibit poor oral bioavailability. Structure-activity relationship (SAR) studies with the arylpiperidine
template provided potent partial agonists such as 4d and 5k that demonstrated no improvement in oral
bioavailability. Further optimization with the (N-oxy-2-pyridinyl)piperidine template led to the discovery
of compound 6b (ABT-670), which exhibited excellent oral bioavailability in rat, dog, and monkey (68%,
85%, and 91%, respectively) with comparable efficacy, safety, and tolerability to 1a. The N-oxy-2-pyridinyl
moiety not only provided the structural motif required for agonist function but also reduced metabolism
rates. The SAR study leading to the discovery of 6b is described herein.
Introduction
SAR for agonist function appears to be a general trend and is
exhibited by closely related D4 ligands from the arylpiperazines
reported in the literature7b,c where the agonists described are
substituted in the 2-position (ortho) including 2 (PD168077)
(Figure 1). We have reported that acetamide analogues7d such
as 3a,b, related to 2, containing an o-cyanophenyl or 2-pyridinyl
group, also exhibited this substituent effect on the terminal aryl
ring, where even a small substituent such as fluorine or a lone
pair of electrons on the pyridine nitrogen in the meta or para
position showed complete loss of agonist activity. This remark-
able SAR precluded a standard strategy of reducing the
metabolism of the region B aryl ring by introduction of a
halogen or other substituent at the site of metabolism in order
to improve the oral bioavailability. The medicinal chemistry
challenge in this or closely related series was finding substitution
patterns on the region B aryl ring that would maintain agonist
function and suppress the metabolism, thereby providing
increased oral bioavailability.
Dopamine receptors belong to the superfamily of G-protein
coupled receptors (GPCR) and have been classified as D1-like
and D2-like on the basis of their binding properties and their
ability to activate or to inhibit forskolin-induced adenylate
cyclase activity.1 The D1-like receptors include D1 and D5
receptors, and the D2-like receptors include D2, D3, and D4
receptors.2 The dopamine D4 receptor is expressed predomi-
nantly within the central nervous system (CNS), and despite
low abundance relative to the D2 receptor, localization in the
cortex suggests an important functional role. The role of D4
receptor antagonists in CNS disorders such as schizophrenia
has been extensively investigated and it has also been shown
that the D4 receptor could be associated with ADHD, depression,
substance abuse, and cognitive disorders.3,4 Apomorphine, a
nonselective dopamine receptor agonist clinically effective in
the treatment of patients with erectile dysfunction (ED), acts
via a central dopaminergic mechanism.5 We have proposed that
the dopamine D4 receptor subtype is primarily responsible for
the erectogenic efficacy of apomorphine, while the dose-limiting
side effects of nausea and emesis are mediated via the dopamine
D2 subtype.6a,b,d This breakthrough provided the impetus for the
discovery of 1a (ABT-724), a highly selective D4 agonist for
the potential treatment of ED.6c Since the discovery of 1a, our
goal was to identify a structurally distinct, selective D4 agonist
with improved in vitro efficacy and comparable in vivo efficacy
and tolerability in animals but with substantially improved oral
bioavailability.
To attenuate the metabolism of the region B aryl ring (Figure
2), we sought to decrease the electron density and make it less
susceptible to putative oxidation. Our strategy was (1) to replace
the 4-position piperazine nitrogen, which has an electron-
donating resonance effect, with a carbon atom while keeping
the basic nitrogen at the 1-position, which is required for
activity.6c and (2) to deactivate the region B aryl ring (Ar2)
through substituent effects. The arylpiperidine templates gener-
ated by employing these strategies were utilized to conduct
region A SAR studies with methylene, amide, and retroamide
linkers (Figure 2).
SAR studies leading to 1a indicated that the D4 agonist
function was incompatible with substitution other than hydrogen
in the meta or para position of the terminal aryl ring.6c This
According to our strategy, we initially synthesized benzimi-
dazolylmethyl compound 1c, a direct analogue of 1a with the
piperidine core (Figure 2). Region A analogues containing an
amide linker (benzamides), such as compounds 4a-d, and the
retroamide linker analogues (acetamides), represented by 5a-
* To whom correspondence should be addressed: tel +1-847-935-4846;
fax +1-847-935-5466; e-mail meena.v.patel@abbott.com.
10.1021/jm060662k CCC: $33.50 © 2006 American Chemical Society
Published on Web 11/10/2006

ABT-670, an Orally BioaVailable Treatment for ED
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7451
3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-carboxylic acid t-
butyl ester 11d, followed by Boc deprotection with HCl gas.
The benzimidazole analogues of 1a, compounds 1c and 1d,
were synthesized by the same method as compound 1a reported
earlier6c with heteroarylpiperidine cores 12d and 14. Some
benzamide analogues (4a-d) were synthesized by the two-step
methodology reported by Glase et al.7b (method A). We
developed a new one-pot methodology (Scheme 2) avoiding
Pb(OAc)4 used in the synthesis reported by Glase et al.7b This
new one-pot Mannich-type reaction (method B) enabled rapid
access to a large number of region A analogues in good yields.
In this methodology, (N-oxy-2-pyridinyl)piperidine 14 in toluene
was treated with the appropriate benzamides and aqueous
formaldehyde at 80 °C to give benzamides 6a-t in good yield.
Figure 1. Dopamine D4 agonists.
The bromo- and chloroacetamide precursors 17 were obtained
through acylation of commercially available substituted anilines
15 with chloroacetyl bromide or chloride 16a or 16b, by
methodologies7d described in the literature, in 50-70% yield.
Coupling of N-arylchloroacetamides with piperidines was carried
out in toluene at elevated temperatures in the presence of N,N-
diisopropylethyl amine (method A) or by use of K2CO3 in N,N-
dimethylformamide (DMF) at room temperature (method B) to
obtain the acetamides 5a-s and 7a-z (Scheme 3).
In Vitro Activity of Compounds. D4 agonist profile was
measured by use of an in vitro Ca2+ flux assay through GRq0
coupling by FLIPR (fluorometric imaging plate reader)
technology.6c,8 This assay directly measures the activation of
the receptor and provides both a measure of ligand potency and
the agonist efficacy, also called intrinsic activity. One expression
of the agonist potency is given by EC50, the concentration of a
compound giving half its maximal receptor activation. Agonist
efficacy, %E, is the maximum calcium signal achieved by the
compound, with efficacy normalized to the effect of 10 µM
dopamine defined as full efficacy. The Ca2+ flux assay was used
for SAR studies of D4 agonists. In addition to the functional
assay, binding affinities were used to confirm D2/D4 selectivity
on selected compounds. Compounds that activated the D4
receptor with efficacy g80% were defined as full agonists.
SAR of Agonist Potency and Efficacy. To determine the
effect of replacing the piperazine core of 1a with piperidine,
1c (Figure 2) was synthesized. Compound 1c retained the in
vitro potency of 1a but exhibited a 20% loss in agonist efficacy.
A small set of benzamides, 4a-d (Scheme 2, Table 1), was
synthesized with the arylpiperidine templates. The unsubstituted
phenyl analogue 4a did not activate the D4 receptor (%E )
17%). Ortho-substituted phenyl analogues such as the o-methoxy
analogue 4b, exhibited partial agonist activity (%E ) 55%) for
the D4 receptor. Introduction of a heteroaryl group such as the
2-thiazolyl and 2-pyridinyl group provided compounds 4c and
4d. These analogues exhibited higher efficacies of 71% and
67%, respectively, at the D4 receptor relative to the phenyl
analogue 4b.
Data for the corresponding piperidine acetamide analogues,
5a-s, are also shown in Table 1. Among the region B aryl
analogues, the unsubstituted phenyl analogue 5a also exhibited
low efficacy (%E ) 37%) as in the benzamide series. The
o-cyano analogue 5b was twice as effective (%E ) 71%) as an
agonist, and the o-fluoro analogue 5c also had good potency
and efficacy. Electron-donating groups such as methyl (5d) and
methoxy (5e) in the ortho position showed lower potency and
efficacy compared to 5b. The m-fluoro analogue 5f showed a
significant drop in potency and efficacy compared to the o-fluoro
analogue 5c. A complete loss of agonist functional activity was
observed in the para-substituted analogues such as 5h (4-F) and
Figure 2. SAR strategy.
s, were also synthesized from the arylpiperidine templates.
Pyridine N-oxidation of the (2-pyridinyl)piperidine template
would potentially deactivate the pyridine ring toward putative
oxidation and meet the structural requirements of having meta
and para hydrogen substituents on the region B aromatic ring
for agonist activity. The (N-oxy-2-pyridinyl)piperidine template
was utilized to conduct a second SAR study of region A to
obtain benzamides 6a-s and acetamides 7a-z. In this report
we describe the discovery of 6b (ABT-670) a novel, orally
bioavailable, potent, and selective human dopamine D4 receptor
agonist.
Results and Discussion
Chemistry. General schemes 1-3 entail the synthesis of
4-heteroarylpiperidine templates, arylpiperidine benzamides, and
arylpiperidine acetamides. 4-Substituted phenylpiperidines
12a,b,e-k were obtained from commercial sources. The 4-het-
eroarylpiperidines 12c,d,l,m were synthesized by the method
depicted in Scheme 1. Commercially available 1-t-butoxycar-
bonyl-4-piperidinone 8 was converted to its o-triflyl enolate 9a
and then reacted with the appropriate intermediates under Pd-
catalyzed Negishi cross-coupling9a conditions to provide 4-aryltet-
rahydropyridine intermediates 10c,d,m that upon hydrogenation
gave the corresponding arylpiperidines 11c,d. The Boc group
was removed by treatment with TFA to give 12c,d. Compound
12l was synthesized via Pd-mediated Suzuki cross-coupling9b
of 2-chloro-3-cyanopyridine with vinyl boronates 9c, followed
by hydrogenation.
(N-Oxy-2-pyridinyl)piperidine9c 14 was obtained by m-
chloroperbenzoic acid (m-CPBA) oxidation of the 1-oxy-

7452 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
Scheme 1a
a Reagents and conditions: (a) LDA, -78 °C, PhNTf2; (b) ArZnX, Pd(PPh3)4, Negishi cross-coupling conditions; (c) H2/Pd; (d) CF3COOH; (e) m-CPBA,
CH2Cl2; (f) HCl gas, EtOAc; (g) PdCl2dppf, dppf, dioxane, 80 °C; (h) PdCl2dppf, K2CO3, 2-chloro-3-cyanopyridine, DMF, 80 °C.
Scheme 2a
The hydroxy substituent is an exception to this SAR trend for
functional activity. Among the region A analogues (5k-p)
evaluated with the pyridinylpiperidine template, the 3-meth-
ylphenyl analogue 5k exhibited low nanomolar potency and
higher efficacy for the D4 receptor. Other substituents such as
chloro, ethyl, or methoxy (5k-p) reduced agonist efficacy.
Several other region A analogues with various substituents on
the phenyl ring were also synthesized by parallel synthesis with
the (2-pyridinyl)piperidine template (data not shown in this
paper). The in vitro potency and efficacy of these analogues
was lower than that of 5k. These data suggested that a small
alkyl substituent on the region A phenyl ring with the pyridi-
nylpiperidine template provided low nanomolar potency and
good efficacy, exemplified by compound 5k. Region B ana-
logues with other heteroaryl groups such as thiazole (5t)
displayed a loss in agonist efficacy compared to the pyridine
analogue 5k. Comparison of the results from the benzamide
and acetamide analogues shown in Table 1 with the correspond-
ing piperazine analogues6c,7d demonstrates that piperidine is
bioisosteric with piperazine for this class of D4 ligands.
a Reagents and conditions: method A, (a) Pb(OAc)4, Cu(OAc)2, C6H6,
reflux, (b) arylpiperidine, Et3N, CH3CN, 25 °C; method B, benzamide, 37%
aqueous CH2O, K2CO3, toluene, 80 °C.
Scheme 3a
Our second strategy to modulate the electron density of the
aromatic ring, and subsequently attenuate its metabolism, was
via oxidation of the pyridine nitrogen of the (2-pyridinyl)-
piperidine template. Pyridine N-oxidation would inductively
reduce the oxidation potential of the pyridine ring while
maintaining the requirement of a mono-ortho-substituted aryl
ring in region B for functional activity. To test this hypothesis,
we synthesized the (N-oxy-2-pyridinyl)piperidine template 14
and synthesized direct analogues of 1c, 4d, and 5k. The direct
analogue of 1c, 1′-(1H-benzimidazol-2-ylmethyl)-1′,2′,3′,4′,5′,6′-
hexahydro-[2,4′-bipyridine] 1-oxide (1d), was found to be a
potent partial agonist (hD4 EC50 ) 54 nM; %E ) 54%). The
benzamide analogue 6b and its acetamide congener 7a exhibited
nearly full agonist efficacy while maintaining low nanomolar
a Reagents and conditions: (a) 2 N NaOH, CH2Cl2, room temperature;
method A, toluene, N,N-diisopropylethylamine, 80 °C or method B, K2CO3,
DMF, 40 °C; (b) H2/Pd.
5i (4-OCH3). This confirmed the SAR describing the substituent
effect for agonist activity observed in previously reported
arylpiperazine series6c,7d. However the m- and p-hydroxy
analogues 5g and 5j exhibited low nanomolar partial agonist
activity. Compound 5r, the p-hydroxypyridine analogue of 5k,
maintained the low nanomolar potency of 5k and exhibited full
efficacy (%E ) 83%). Additionally the p-hydroxy analogue of
1a, compound 1b (A-425444), which was found to be a major
metabolite10 of 1a, also exhibited partial agonist activity (hD4
EC50 ) 2.4 nM, %E ) 70%; rD4 EC50 ) 13.7 nM, %E ) 66%).
potency (hD4 EC50 ) 89 nM, %E ) 77% for 6b; hD4 EC50
)
32 nM, %E ) 79% for 7a). The in vitro activity of compounds
6b and 7a met our potency and efficacy criteria and therefore
an expanded SAR study of region A was conducted with the

ABT-670, an Orally BioaVailable Treatment for ED
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7453
Table 1. In Vitro Activity of Benzamides and Acetamides in FLIPR Assaya
human D4 FLIPR
compd
R
Ar2
EC50,b nM (SEM)
% efficacyc
1a
2
12.4 ( 1.0
8.3 ( 1.1
12 ( 1
61
62
51
1c
4a
4b
4c
4d
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
5s
2-pyridinyl
phenyl
2-methoxyphenyl
2-thiazole
2-pyridinyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
3-methyl
nad
206 ( 16
9.8 ( 3.5
9 ( 2
170 ( 40
8 ( 2
1.0 ( 0.4
340 ( 20
420 ( 10
512 ( 52
8 ( 1
na
na
70 ( 10
14 ( 2
240 ( 60
145 ( 25
111 ( 41
60 ( 10
40 ( 4
55
71
67
37
71
57
43
43
40
66
phenyl
2-cyanophenyl
2-fluorophenyl
2-methylphenyl
2-methoxyphenyl
3-fluorophenyl
3-hydroxyphenyl
4-fluorophenyl
4-methoxyphenyl
4-hydroxy-phenyl
2-pyridinyl
60
75
50
45
70
70
69
42
83
62
4-chloro-2,6-dimethyl
2,4,6-trichloro
2-ethyl-6-methyl
2-chloro-6-methyl
2-methyl-6-methoxy
3-methyl
2-pyridinyl
2-pyridinyl
2-pyridinyl
2-pyridinyl
2-pyridinyl
6-cyano-2-pyridinyl
2-(5-hydroxy-pyridinyl)
2-thiazolyl
36 ( 6
3.8 ( 0.8
1.0 ( 0.1
3-methyl
3-methyl
a In vitro activity was measured in FLIPR assays, using HEK-293 cells cotransfected with human D4.4 receptor and G-protein GRqo5. b EC50 for agonists
(SEM, n g 3). c Efficacy relative to 10 µM dopamine (100%), SEM ( 1-5%. d na ) no agonist activity up to 10 µM.
Table 2. In Vitro Activity of the (N-oxy-2-pyridinyl)piperidine
(N-oxy-2-pyridinyl)piperidine template utilizing the amide and
Benzamides in the FLIPR Assay+a
retroamide linkers (Tables 2 and 3).
Table 2 shows results of region A SAR studies of the
benzamide series incorporating the (N-oxy-2-pyridinyl)piperi-
dine template. The unsubstituted phenyl analogue 6a showed
partial agonist activity (%E ) 66%). Adding an electron-
donating substituent (methyl group) at the 3-position (6b)
human D4 FLIPR
improved the potency by 9-fold and the efficacy by 10%, while
electron-withdrawing groups in the 3-position, such as CN
analogue 6e and CHdCH2 analogue 6c, displayed slightly
reduced agonist efficacy. Disubstituted analogue 6f, bearing
3-methyl and 4-chloro groups, displayed a significant drop in
potency and efficacy. The potency and efficacy was regained
when a fluoro group was placed at the 4-position (6g) in region
A. The di- and trisubstituted analogues such as 6h-p did not
show improvement in potency and efficacy compared to the
monosubstituted analogue 6b. The heteroaryl (pyridinyl) ana-
logues such as 6q and 6r showed a significant drop in both
potency and efficacy. The 2-thienyl analogue 6s was found to
be a nonagonist (%E < 10%). This region A SAR study
confirmed that a small alkyl substituent in the 3-position,
exemplified by compound 6b, provided optimal potency and
efficacy.
Several (N-oxy-2-pyridinyl)piperidine acetamide analogues
were also examined (Table 3). Compound 7a, a direct analogue
of 5k having a 3-methyl-substituted phenyl group in region A,
also maintained the low nanomolar potency of 5k and exhibited
nearly full agonist activity (%E ) 79%). Substituted phenyl
analogues exhibited nanomolar potency as the substituent was
moved from ortho to meta to para position (7b-k) but they
exhibited lower efficacy compared to 7a (%E ranging from 46%
to 76%). Among the disubstituted analogues, compounds 7r and
compd
aromatic group
EC50,b nM (SEM)
% efficacyc
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
6s
Ph
532 ( 72
89 ( 1
68 ( 8
63
77d
63
54
69
62
67
33
64
59
65
67
56
51
54
67
44
40
nae
Ph (3-CH3)
Ph(3-CHdCH2)
Ph(3-OCH2CH3)
Ph(3-CN)
Ph(3-CH3, 4-Cl)
Ph(3-CH3, 4-F)
Ph(3-Cl, 4-OCF3)
Ph(3,5-di-Cl)
Ph(3-CF3, 4-CH3)
Ph(3,4-di-CH3)
Ph(3-Cl, 4-F)
Ph(3,5-di-CH3)
Ph(2-CH3, 3-OCH3)
Ph(3-OCH3, 4-Cl)
2-napthyl
324 ( 20
840 ( 100
2460 ( 500
50 ( 10
170 ( 10
45 ( 10
85 ( 20
38 ( 4
63 ( 10
90 ( 4
685 ( 100
159 ( 39
115 ( 20
1290 ( 40
3150 ( 7800
4-chloro-3-pyridinyl
2-pyridinyl
2- thienyl
a In vitro activity was measured in FLIPR assays, using HEK-293 cells
cotransfected with human D4.4 receptor and G-protein GRqo5.
b EC50 for
agonists (SEM, n g 3). c Efficacy relative to 10 µM dopamine (100%),
SEM ( 1-5%. d SEM ( 0.6%, n ) 24. e na ) no agonist activity up to
10 µM.
7s, with a combination of a CH3 group and a fluoro or NO2
substituent, maintained agonist activity of the 3-methyl analogue

7454 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
Table 3. In Vitro Activity of the (N-Oxy-2-pyridinyl)piperidine
erazine analogue 1b were selective and potent D4 agonists at
human, ferret, and rat cell lines. These compounds were inactive
as agonists at D2 across the three species and were also inactive
in the human D3 cell line. Although 6b, 7a, and 7r were clearly
selective D4 agonists, they could still have high affinity and
potential antagonist activity at D2 receptor.
Acetamides in the FLIPR Assaya
Binding studies were conducted to determine selectivity based
on binding affinities at D2 and D4 receptors for select com-
pounds. To determine binding affinities at dopamine receptors,
the functional profile of both competing ligand and radioligand
must be considered.7a In general, agonists may show weak
affinities against an antagonist radioligand, whereas antagonists
usually show similar binding competition against both agonist
and antagonist radioligand. The D4 binding affinity of these
compounds were assessed by use of the D4 partial agonist
radioligand [3H]-A-3695088 and a D2-like receptor antag-
onist [3H]spiperone (Table 5). The D2 binding affinities
were determined by use of radiolabeled D2 agonist 7-OH-PIPAT.
The region B unsubstituted phenyl analogue 4a had moderate
binding affinity for the human D2L receptor. The o-methoxy
analogue 4b also had binding affinity for the D2 receptor;
however, it did not activate the D2 receptor (EC50 > 10 000).
Region B pyridinyl analogue 4d exhibited high affinity for the
D4 receptor in the binding assay versus spiperone with a Ki value
of 32 nM and only low affinity for human D2 receptor with a
Ki value of 3.5 µM. Compound 5k also exhibited high selectivity
for the D4 receptor. This data suggested that introduction of a
heteroaryl group in region B provided high D4/D2 selec-
tivity.
Compounds 6b, 7a, 7r, and 1b showed no binding for the
human D2s and D2L receptor isoforms (Ki >10 µM) and they
did not induce nausea or emesis in the ferret model of emesis.6e
The N-oxy-2-pyridinyl analogues 6b, 7a, and 7r exhibit modest
D4 binding affinity with the radioligand used. These binding
affinities are considerably weaker than the EC50 values from
the Ca2+ flux assay (EC50 , Ki), which may indicate a high
agonist efficiency for the D4 receptor.6f This may also reflect a
considerable affinity of the partial agonist radioligand [3H]-A-
369508 for the antagonist conformation. In wider selectivity
studies, both 6b and 7a at 10 µM did not show any activity
against more than 70 different receptors, ion channels, and
neuronal receptors (CEREP11a) including phosphodiesterases
PDE1-6.
human D4 FLIPR
compd
R1
Ph (3-CH3)
Ph (3-CF3)
Ph (3-F)
Ph (4-F)
Ph (2-F)
Ph (3-Cl)
Ph (3-iPrO)
Ph (3-OCF3)
Ph (3-SCH3)
Ph (3-CH2CH3)
Ph (3-Ph)
Ph (3,5-di-Cl)
Ph (2,3-di-Cl)
Ph (2-OCH3, 6-CH3)
Ph (3,5-di-CH3)
Ph (2-CH3, 4-Br)
Ph (3-CH3, 4-F)
Ph (2-CH3, 4-F)
Ph (2-CH3, 5-NO2)
Ph (2,6-di-CH3)
Ph (3-CH3, 2,6-di-Cl)
Ph (2-CH3, 5-Cl)
Ph (2,4-di-F)
Ph (2-CF3, 4-F)
cyclohexyl
EC50,b nM (SEM)
% efficacyc
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
7n
7o
7p
7q
7r
7s
32 ( 2
76 ( 10
160 ( 25
85 ( 10
270 ( 20
62 ( 10
555 ( 100
135 ( 15
100 ( 15
95 ( 30
360- ( 30
160 ( 50
180 ( 20
340 ( 75
52 ( 2
66 ( 16
18 ( 2
60 ( 5
134 ( 34
346 ( 33
346 ( 53
126 ( 22
103 ( 13
473 ( 93
294 ( 52
79
75
70
71
63
76
48
51
56
62
75
68
66
56
76
61
75
84
76
68
62
58
74
65
58
nad
7t
7u
7v
7w
7x
7y
7z
2-pyridinyl
a In vitro activity was measured in FLIPR assays, using HEK-293 cells
cotransfected with human D4.4 receptor and G-protein GRqo5.
b EC50 for
agonists (SEM, n g 3). c Efficacy relative to 10 µM dopamine (100%),
SEM ( 1-5%. d na ) no agonist activity up to 10 µM.
7a. Compound 7y containing a lipophilic cyclohexyl group
showed only partial agonist activity, and compound 7z bearing
a polar pyridinyl group in region A was not an agonist as
observed in the benzamide case. In summary, the 3-methyl
analogue 7a and the disubstituted analogues compounds 7r and
7s exhibited high potency and efficacy.
Selectivity. With the discovery of 1a (ABT-724), it was
demonstrated that the D4 receptor subtype is responsible for
the in vivo erectogenic activity, while the dose-limiting side
effects of nausea and emesis seen in the nonselective dopamine
agonist apomorphine are mediated via the dopamine D2
subtype.6d,h Our goal was to maintain the selectivity of 1a in
order to avoid off-target side effects. The dopamine receptor
subtype activation, as measured by a calcium flux assay of the
lead compounds, is shown in Table 4. N-Oxy-2-pyridinyl
analogues 6b, 7a, and 7r and benzimidazolylmethyl arylpip-
In Vivo Studies. Potent agonists 4d, 5k, 6b, 7a, 7s, and 7r
demonstrated similar in vivo efficacy to 1a in the rat penile
erection assay6d when administered subcutaneously (Table 6).
The in vivo potencies ranged from 0.003 to 1 µmol/kg with
maximal erectile incidence to at least 70-85%. The maximally
efficacious dose of compound 1b was 0.1 µmol/kg. Agonist 6b
robustly induced a high (75%) incidence of erections in male
rats, at a maximally efficacious dose of 0.1 µmol/kg. In this
model, apomorphine also efficiently induced erections in rat at
a high incidence rate (91%).6
Table 4. In Vitro Agonist Activity in Cellular FLIPR Assaysa
EC50 ( SEM, nM (%E)b
compd
human D4
ferret D4
rat D4
human D2
ferret D2
rat D2
human D3
dopamine
apomorphine
6b
7a
7r
1b
2.2 ( 0.2 (100%)
4.3 ( 0.2 (84%)
89 ( 1 (77%)c
32 ( 2 (79%)
2.7 ( 0.3 (100%) 2.4 ( 0.2 (100%) 18 ( 2 (100%)
8 ( 0.4 (100%)
1.1 ( 0.1 (100%)
1.5 ( 0.1 (84%)
160 ( 8 (76%)
5.5 ( 0.3 (87%)
93 ( 3 (78%)
57 ( 3 (80%)
100 ( 5 (76%)
5.8 ( 0.3 (86%) 1.8 ( 0.2 (91%) 0.4 ( 0.1 (103%)
nad
na
na
na
na
na
na
na
na
na
na
na
na
na
na
60 ( 5 (84%)
2.4 ( 0.1 (70%)
5 ( 0.1 (48%)
13.7 ( 0.5 (66%) na
a In vitro activity was measured in FLIPR assays, using HEK cells cotransfected with the target receptor and G protein GRqo5
.
b EC50 for agonists (SEM,
n g 3). Efficacy relative to 10 µM dopamine (100%), SEM ( 1-5%. c SEM ( 0.6%, n ) 24. d na ) no agonist (<10%) activity up to 10 µM.

ABT-670, an Orally BioaVailable Treatment for ED
Table 5. Radioligand Binding Affinity for Select Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7455
compd
human D2L binding Ki,a nM human D4 binding Ki,b nM
apomorphine
3.6
8.9
4a
4b
4d
5k
7a
6b
7r
1b
235
27
3500
2900
>10 000
>10 000
>10 000
>10 000
1.3
32c
8
294
1445
405
17
a Radioligand binding affinity for the dopamine agonists was measured
using membrane expressing the human D2L receptor and functional efficacy
in HEK-293 cells expressing the cloned human D2L receptor and the
chimeric G-protein Gq05. In the D2L binding studies, data represent the mean
Ki calculated from at least four determinations (15% standard error of the
mean (SEM) with [125I]-7-OH-PIPAT as ligand. b Radioligand binding
affinity (Ki, nanomolar) for the DA agonists was measured by use ofthe D4
agonist [3H]-A-369508. Data represent the mean Ki calculated from at least
four determinations ( 15% mean SEM. c Binding assay using a D2-like
receptor antagonist [3H]spiperone, Ki calculated from at least four deter-
minations ( 15% mean SEM.
Table 6. In Vivo Proerectile Activity of Compounds in Rats during 60
Min Following Subcutaneous Injection
max. incidence of
max. effective
dose, µmol/kg, sc
penile erections,
compd
a % ( SEM
6b
0.1
0.1
0.1
0.03
0.3
0.01
0.03
0.1
75 ( 9** (n ) 24)
91 ( 1*** (n ) 32)
75 ( 10*** (n ) 24)
83 ( 10** (n )12)
75 ( 10*** (n ) 12)
83 ( 10** (n ) 12)
67 ( 15** (n ) 12)
60 ( 15* (n ) 12)
apomorphine
5k
4d
7a
7s
7r
1b
a Level of statistical significance relative to control: *p < 0.1; **p <
0.05; ***p < 0.001; n ) number of animals tested.
Table 7. Pharmacokinetic Properties of Lead Compounds in Rat
compd
dosea
T1/2 (h)
F%b (SEM)
4d
4d
5k
5k
5r
7a
7a
7r
sc
po
sc
po
po
scd
pod
pod
0.6
UCc
0.7
UC
UC
0.5
0.3
UC
76 (5)
2 (1)
57 (11)
0
Figure 3. Mean ((SEM, n ) 3) plasma concentrations of 6b, ABT-
670, after a 1 mg/kg intravenous, subcutaneous, or oral dose in (A)
rat, (B) dog, and (C) monkey.
0
61 (4)
11 (1)
7 (1)
The (N-oxy-2-pyridinyl)piperidine analogues such as 6b, 7a,
and 7r from our second strategy were selected for PK evaluation.
Compound 7a exhibited a remarkable improvement in PK
profile compared to 5k with oral bioavailability in rat, dog, and
monkey of 11%, 70%, and 28%, respectively. PK profile of
the benzamide analogue 6b was superior to that of 7a, exhibiting
high oral bioavailability in all three species. Plasma concentra-
tion curves for 6b after intravenous (iv), oral (po), and
subcutaneous (sc) dosing are shown in Figure 3. The calculated
PK parameters across three species are shown in Table 8.
Compound 6b was slowly cleared after iv dosing in rat, dog,
and monkey, with values ranging from 0.74 L/(h‚kg) in rat to
0.2 L/(h‚kg) in dog. SC bioavailability was high in the rat, with
peak concentration of 465 ng/mL and bioavailability of 84%
following a 1 mg/kg dose. Compound 6b reached similar Cmax
and AUC when dosed both po and sc. Dosing po in monkey
and dog at 1 mg/kg dose produced a higher Cmax and AUC with
a calculated oral bioavailability of 91% (Figure 3, Table 8).
This remarkable oral bioavailability of 6b indicated that the
oxidation of the pyridine nitrogen not only had attenuated the
first-pass metabolism of the pyridine ring but also may have
provided improved solubility and absorption.11b
a Pharmacokinetic properties were evaluated in Sprague-Dawley rats, after
administration of 1 mg/kg drug; sc, subcutaneous; po, per os (oral). n ) 3
except as marked. b F ) oral bioavailability, %; data are provided as mean
(SEM). c UC, unable to calculate. d n ) 6.
Clozapine (3 µmol/kg, ip) and haloperidol (1 µmol/kg, ip)
blocked the erectogenic effect of 6b, but domperidone (10 µmol/
kg, ip) did not. These data indicate that the effect is mediated
via central dopaminergic mechanisms, as the peripheral dopam-
ine antagonist domperidone did not block the proerectile effect
of 6b.
Preclinical Pharmacokinetics. Potent partial agonists such
as 4d, 5k, and 5s were selected for pharmacokinetic (PK)
studies. An initial PK study with benzamide 4d and acetamide
5k showed moderate bioavailabilty upon subcutaneous dosing
in rat (Table 7); however, like 1a, the oral bioavailability was
still extremely low. This data suggested that the primary
oxidative metabolism route had not been altered by replacing
the piperazine core with piperidine. An in vitro metabolism study
of 5k showed hydroxylation of the pyridine ring to produce
the major metabolite. The para-hydroxylated analogue of 5k,
compound 5r, also exhibited low oral bioavailability in rat.

7456 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
Table 8. Pharmacokinetics of 6b (ABT-670) after a Single Dose in Rat, Monkey, or Doga
species
doseb
T1/2, h
F% (SEM)
Cmax, ng/mL (SEM)
AUC, ng‚h/mL (SEM)
rat
rat
monkey
dog
sc
po
po
po
1.2
1.8
2.0
2.1
84 (6)
68 (9)
91 (18)
85 (7)
465 (50)
417 (70)
660 (201)
1418 (66)
1138 (81)
922 (121)
2280 (449)
4275 (356)
a Pharmacokinetic data are provided as mean (SEM). b 1.0 mg/kg dose; sc, subcutaneous; po, per os (oral).
Table 9. In Vitro Effects on hERG Current and Cardiac Purkinje Fiber
or cardiovascular liability. Since compound 6b (ABT-670)
exhibited superior PK as well as cardiovascular safety profile,
it was selected for advanced toxicological and safety evaluation
and subsequently selected as a development candidate for
erectile dysfunction.
Repolarizationa
compd dose, ng/mL hERG blockade, % dose, ng/mL Purkinje RP, %
6b
7a
3000
3000
14.5 ( 3.5
44.8 ( 4.6
3000
1600
4.3 ( 1.0
12.0 ( 2.0
a DMSO, 11.0% ( 4.0% block; n ) 4-6 per group.
Experimental Section
In Vitro Effects on HERG Current and Cardiac Purkinje
Fiber Repolarization. Since different classes of dopaminergic
agents can induce both central and peripheral side effects such
as pressor effects on the cardiovascular system, compounds 6b
and 7a were profiled in cardiovascular safety studies. Com-
pounds 6b and 7a were tested by in vitro assays to measure
their effects on hERG tail currents12a as a primary screen (Table
9). Compound 7a exhibited a 45% reduction in hERG current
at 3 µg/mL concentrations indicating that it could have some
cardiovascular liability. In contrast, compound 6b did not reduce
hERG current at the 1 and 3 µg/mL concentrations tested (14.4%
and 14.5% block, respectively) compared to vehicle [dimethyl
sulfoxide (DMSO), 11% block; n ) 4-6 per group].
To evaluate the possible effects of 6b and 7a on ventricular
repolarization, changes in action potential duration (APD) of
canine cardiac Purkinje fibers were assessed in vitro (Table 9).
For compound 6b, no significant prolongation (0.6%) of the
action potential duration was elicited at 1 µg/mL. A higher
concentration of 6b (3 µg/mL) elicited minimal (4.3%) prolon-
gation of the action potential duration that attained statistical
significance. However, the higher concentration of 7a elicited
12% prolongation of the action potential duration.
Chemistry Methods. All solvents were of anhydrous reagent
grade from commercial sources. Unless otherwise noted, all
chemicals and reagents were obtained commercially and used
1
without purification. The H NMR spectra were obtained at 300
MHz on a Nicolet/GE QE300 spectrometer. Chemical shifts are
reported in parts per million (ppm, δ) relative to tetramethylsilane
(TMS) or (trimethylsilyl)propionate-d4 (TSP) as in internal standard.
Mass spectra were obtained on a Kratos MS-50 instrument, in
desorption chemical ionization (DCI)/NH3 mode. Elemental analy-
ses were performed by Robertson Microlit Laboratories, Inc.,
Madison, NJ. Flash chromatography was carried out on silica gel
60 (E. Merck, 230-400 mesh), or prepacked 40 mm silica gel
columns from Biotage. Thin-layer chromatography was performed
on 250 µM silica-coated glass plates from EM Science. Samples
were analyzed by high-performance liquid chromatography (HPLC)-
mass spectrometry (MS)-evaporative light scattering detection
(ELSD) on an Open Access Finnigan Navigator/Agilent 1100/
Sedere Sedex 75 system using a Phenomenex Luna C8 column (5
µm, 2.1 × 50 mm). The elution system used was a gradient of
10-100% over 4.5 min at 1.5 mL/min, and the solvent was either
acetonitrile/0.1% aqueous trifluoroacetic acid (TFA), or acetonitrile/
10 mM ammonium acetate. The MS was operated in the atmo-
spheric pressure chemical ionization (+APCI) mode. Melting points
were determined on a Buchi 510 melting point apparatus and are
uncorrected.
As shown in Table 9, compound 6b did not elicit meaningful
prolongation of canine Purkinje fiber repolarization and it did
not block hERG current at concentrations 200-fold greater than
efficacious plasma concentrations (15 ng/mL at 0.1 µmol/kg
dose). Compound 6b appears to have a large preclinical
cardiovascular safety index. The hERG and Purkinje fiber
repolarization data on 7b indicated low cardiovascular liability.
GeneralProcedureforCompounds4a-c(MethodA): 2-Meth-
oxy-N-(3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-ylmethyl)-
benzamide (4b). Step 1. N-(3-Methylbenzoyl)glycine (10 g, 51.7
mmol), lead tetraacetate (25.25 g, 56.94 mmol), and copper(II)
acetate monohydrate (0.94 g, 5.17 mmol) were combined in toluene
and heated at reflux overnight. The reaction mixture was cooled to
room temperature (rt) and filtered through Celite, and the filtrate
was concentrated under reduced pressure. The residue was purified
by flash column chromatography on silica gel (elution with 25%
EtOAc/hexanes) to provide [(3-methylbenzoyl)amino]methyl acetate
Conclusion
Arylpiperidine acetamides and benzamides have been dis-
covered as a new class of selective D4 agonists. Arylpiperidine
analogues demonstrated the same remarkable SAR trend
observed in the arylpiperazine series reported earlier, wherein
substitution at the meta or para position of the terminal aryl
ring was found to be detrimental to the D4 functional activity,
precluding blockage of the site of metabolism with a substituent.
The N-oxidation of the pyridine ring of (2-pyridinyl)piperidine
provided an alternative pharmacophore that retained structural
requirements for receptor activation. Optimization of region A
provided compound 6b (ABT-670), which exhibited nearly full
agonist activity and demonstrated excellent oral bioavailability
in rat, dog, and monkey (68%, 85%, and 91%, respectively).
In addition to attenuated first-pass metabolism, the remarkable
oral bioavailability may also be a result of better physicochem-
ical properties of the pyridine N-oxide analogue compared to
the pyridine analogue. Compound 6b exhibited erectogenic
activity in rats with no overt side effects such as emesis, nausea,
1
(7.95 g, 74% yield). H NMR (300 MHz, CDCl3) δ 2.10 (s, 3H),
2.40 (s, 3H), 5.45 (d, J ) 9 Hz, 2H), 7.35 (m, 2H), 7.55 (m, 1H),
7.62 (s, 1H); MS (DCI/NH3) m/e 208 (M + H)+
Step 2. 4-(2-Methoxyphenyl)piperidine 12b (286 mg, 1.5 mmol),
[(3-methylbenzoyl)amino]methyl acetate (310 mg, 1 mmol), and
triethylamine (0.42 mL, 3 mmol) were combined in acetonitrile (8
mL) and stirred at rt for 18 h. The reaction mixture was concentrated
under reduced pressure and the residue was purified by flash
chromatography on silica gel (elution with CH2Cl2/CH3OH 9.5:
1
0.5) to provide 4b(285 mg, 56.2% yield). H NMR (300 MHz,
DMSO-d6) δ 1.65 (m, 4H), 2.31 (m, 2H), 2.37 (s, 3H), 2.79 (m,
1H), 2.93 (m, 2H), 3.75 (s, 3H), 4.15 (d, J ) 6 Hz, 2H), 6.90 (m,
2H), 7.15 (m, 2H), 7.36 (m, 2H), 7.68 (m, 2H), 8.69 (t, J ) 6 Hz,
1H); MS (DCI/NH3) m/e 339 (M + H)+; Anal. (C21H26N2O2‚
0.15H2O) C, H, N.
N-(3′,4′,5′,6′-Tetrahydro-2′H-[2,4′-bipyridine]-1′-ylmethyl)-
benzamide (4a) was prepared in the same manner as compound
4b but with substitution of 4-phenylpiperidine in place of 4-(2-
methoxyphenyl)piperidine (90 mg, 62% yield). 1H NMR (300 MHz,

ABT-670, an Orally BioaVailable Treatment for ED
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7457
DMSO-d6) δ 1.70 (m, 4H), 2.31 (m, 2H), 2.36 (s, 3H), 2.45 (m,
1H), 2.95 (m, 2H), 4.17 (d, J ) 6 Hz, 2H), 7.23 (m, 5H), 7.35 (d,
J ) 6 Hz, 2H), 7.69 (m, 2H), 8.71 (m, 1H); MS (DCI-NH3) m/e
309 (M + H)+. Anal. (C20H24N2O) C, H, N.
Preparation of 3-Methyl-N-(4-thiazol-2-ylpiperidin-1-ylm-
ethyl)-benzamide (4c): Step 1. The procedure described below
for 10d was followed, with substitution of 2-thiazolylzinc bromide
in place of 3-methyl-2-pyridylzinc bromide, to provide 3-methyl-
N-(4′-thiazol-2-yl-2′,3′,4′,5′-tetrahydropyridin-1′-ylmethyl)benza-
mide 10c (56% yield). 1H NMR (300 MHz, CDCl3) δ 1.5 (s, 9H),
2.7 (m, 2H), 3.33 (t, J ) 6 Hz, 2H), 4.10 (q, J ) 3 Hz, 2H), 6.60
(m, 1H), 7.21 (d, J ) 3 Hz, 1H), 7.78 (d, J ) 3 Hz, 1H); MS
(DCI/NH3) m/e 267 (M + H)+.
to the residue. Zinc salts were filtered and the organic layer was
separated, washed with brine (300 mL), dried (MgSO4), and
concentrated on the rotary evaporator to give a brown oil.
Purification by flash chromatography with hexanes/EtOAc 6:4 as
eluent gave 9.0 g (64% yield) of the desired product as a colorless
oil. 1H NMR (300 MHz, DMSO-d6) δ 1.43 (s, 9H), 2.56 (m, 2H),
3.54 (t, 2H), 4.04 (m, 2H), 6.08 (m, 1H), 7.25 (dd, 1H), 7.56 (d, J
) 9 Hz, 1H), 7.77 (m, 1H), 8.54 (m, 1H); MS (DCI-NH3) m/e 259
(M + H)+, 277 (M + H + 18)+
(C) 3′,4′,5′,6′-Tetrahydro-2′H-[2,4′-bipyridine]-1′-carboxylic
Acid t-Butyl Ester (11d). 3′,6′-Dihydro-2′H-[2,4′-bipyridine]-1′-
carboxylic acid t-butyl ester (9.0 g) was hydrogenated by use of
10%Pd/C (dry, 900 mg) at 60 psi at room temperature for 1.5 h to
give 8.9 g (99%) of the desired product as a colorless oil. 1H NMR
(300 MHz, DMSO-d6) δ 1.41 (s, 9H), 1.58 (m, 2H), 1.81 (m, 2H),
2.85 (m, 3H), 4.06 (m, 2H), 7.20 (dd, 1H), 7.28 (d, J ) 9 Hz, 1H),
7.70 (m, 1H), 8.48 (m, 1H).
(D) 1′,2′,3′,4′,5′,6′-Hexahydro-2′H-[2,4′-bipyridine] (12d). Com-
pound 11d (6.57 g) was dissolved in EtOAc (50 mL) and cooled
to -78 °C. HCl gas was bubbled through the reaction mixture for
15 min. The reaction mixture was allowed to warm up to room
temperature, upon which an off-white precipitate was formed. This
precipitate was filtered, washed with EtOAc, and dried under high
vacuum to give the dihydrochloride salt (5.03 g, 99%) of the desired
product (12d).
Step 2. A solution of 10c (3.62 g, 13.6 mmol) in 25%
trifluoroacetic acid in CH2Cl2 (30 mL) was stirred at rt for 2 h.
The reaction was concentrated under reduced pressure to afford
4-thiazol-2-yl-1,2,3,6-tetrahydropyridine as a brown oil (1.69 g, 74%
1
yield). H NMR (300 MHz, CDCl3) δ 2.55 (m, 2H), 3.12 (t, J )
6 Hz, 2H), 3.59 (m, 2H), 6.63 (m, 1H), 7.20 (d, J ) 3 Hz, 1H),
7.75 (d, J ) 3 Hz, 1H); MS (DCI/NH3) m/e 167 (M + H)+.
Step 3. The procedure described for 4b was followed, with
substitution of 4-thiazol-2-yl-1,2,3,6-tetrahydropyridine in place of
4-(2-methoxyphenyl)piperidine, to provide 3-methyl-N-{[4-(1,3-
thiazol-2-yl)-3,6-dihydro-1(2H)-pyridinyl]methyl}benzamide as a
1
yellow sticky residue (680 mg, 36% yield). H NMR (300 MHz,
CDCl3) δ 2.4 (s, 3H), 2.8 (m, 2H), 2.95 (t, 2H, 4.5 Hz), 3.42 (m,
2H), 4.5 (d, J ) 6 Hz, 2H), 6.6 (m, 1H), 7.2 (d, J ) 3 Hz, 1H),
7.35 (dd, J ) 4.5 and 1.5 Hz, 2H), 7.49 (m, 1H), 7.52 (s, 1H), 7.78
(d, J ) 3 Hz, 1H); MS (DCI/NH3) m/e 314 (M + H)+.
(E) The procedure described for 4b was followed, with substitu-
tion of compound 12d in place of 12b, to provide the title compound
4d (480 mg, 64% yield). H NMR (300 MHz, DMSO-d6) δ 1.75
1
(m, 4H), 2.31 (m, 2H), 2.36 (s, 3H), 2.59 (m, 1H), 2.95 (m, 2H),
4.17 (d, J ) 6 Hz, 2H), 7.18 (m, 1H), 7.25 (d, J ) 6 Hz, 1H), 7.35
(m, 2H), 7.69 (m, 3H), 8.48 (m, 1H), 8.71 (m, 1H); MS (DCI/
NH3) m/e 310 (M + H)+. Anal. (C19H23N3O‚0.25 H2O): C, H, N.
General Procedure for Compounds 5a-s (Method B): 2-(3′,4′,-
5′,6′-Tetrahydro-2′H-[2,4′-bipyridine]-1′-yl)-N-(m-tolyl)acetamide
(5k). A mixture of 4-(2-pyridinyl)piperidine 12d (900 mg, 3.86
mmol), 2-bromo-N-(m-tolyl)acetamide (880 mg, 3.86 mmol) and
K2CO3 (1.6 g, 11.58 mmol) in DMF (20 mL) was stirred at rt for
18 h. The reaction mixture was poured into water (30 mL) and
extracted with EtOAc (20 mL). The organic layer was washed with
brine (2 × 30 mL), dried over MgSO4, filtered and concentrated
in vacuo, and purified by flash chromatography with EtOAc/EtOH,
9.2:0.8, to give the desired product (850 mg, yield 71%). 1H NMR
(300 MHz, DMSO-d6) δ 1.83 (m, 4H), 2.24 (m, 5H), 2.64 (m, 1H),
2.98 (m, 2H), 3.12 (s, 2H), 3.78 (s, 3H), 6.88 (d, J ) 6 Hz, 1H),
7.20 (m, 2H), 7.30 (d, J ) 6 Hz, 1H), 7.45 (d, J ) 6 Hz, 2H), 7.71
(m, 1H), 8.51 (m, 1H), 9.59 (br s, 1H); MS (DCI-NH3) m/e 310
(M + H)+. Anal. (0.15H2O‚C19H23N3O) C, H, N.
Step 4. 3-Methyl-N-{[4-(1,3-thiazol-2-yl)-3,6-dihydro-1(2H)-
pyridinyl]methyl}benzamide (490 mg, 1.5 mmol) was hydrogenated
with 10% Pd/C catalyst under hydrogen gas pressure (60 psi) for
42 h in methanol. The mixture was filtered and concentrated under
reduced pressure. The residue was purified by flash column
chromatography on silica gel (5% ethanol/EtOAc) to provide the
title compound 4c (100 mg, 22% yield). 1H NMR (300 MHz,
CDCl3) δ 1.85 (dq, J ) 12 and 6 Hz, 2H), 2.20 (m, 2H), 2.40 (s,
3H), 2.48 (m, 2H), 3.10 (m, 3H), 4.35 (d, J ) 6 Hz, 2H), 6.50 (m,
1H), 7.20 (d, J ) 3.3 Hz, 1H), 7.35 (m, 2H), 7.60 (m, 2H), 7.70
(d, J ) 3.3 Hz, 1H); MS (DCI/NH3) m/e 316 (M + H)+. Maleate
salt: Anal. (C17H21N3OS‚1.2C4H4O4) C, H, N.
3-Methyl-N-(3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-yl-
methyl)benzamide (4d): (A) 4-Trifluoromethanesulfonyloxy-
3,6-dihydro-2H-pyridine-1-carboxylic Acid t-Butyl Ester (9a).
To a solution of diisopropylamine (13.4 mL, 96 mmol) in
tetrahydrofuran (THF) (350 mL) at -78 °C was added 1.6 M
n-BuLi in hexanes (60 mL, 96 mmol). The reaction mixture was
stirred for 5 min at -78 °C. A solution of t-butoxycarbonyl-4-
piperidone (16 g, 80 mmol) in THF (100 mL) was added, and the
reaction mixture was stirred for 10 min. Then a solution of
N-phenyltrifluoromethanesulfonimide (31.4 g, 88 mmol) was added.
The reaction mixture was stirred at -78 °C for 30 min and the
cooling bath was removed to warm it up to rt for 1.5 h until all
piperidone was utilized (determined by thin-layer chromatography,
TLC). The reaction was quenched by saturated NaHCO3, followed
by extraction with ethyl ether and 5% citric acid. The organic layer
was then washed with 1 N NaOH (4 × 200 mL), water (2 × 200
mL), and brine (1 × 200 mL), dried over MgSO4, and evaporated
on a rotary evaporator to give a yellowish oil. Purification by flash
chromatography with hexanes/EtOAc 8:2 as eluent gave 18 g (68%
yield) of pure colorless oil. 1H NMR (300 MHz, DMSO-d6) δ 1.41
(s, 9H), 2.41 (m, 2H), 3.54 (t, 2H), 3.98 (m, 2H), 6.02 (m, 1H).
(B) 3′,6′-Dihydro-2′H-[2,4′-bipyridine]-1′-carboxylic Acid t-
Butyl Ester (10d). Pure 4-trifluoromethanesulfonyloxy-3,6-dihydro-
2H-pyridine-1-carboxylic acid t-butyl ester (18 g, 54 mmol) in THF
(∼200 mL) was treated with 2-pyridylzinc bromide (0.5 M solution
in THF; Aldrich, brown color, 124 mL, 62.5 mmol, 1.15 equiv)
followed by Pd(PPh3)4 (from Strem Chemicals) (625 mg). The
reaction mixture was heated at 60 °C for 90 min. All of the triflate
was utilized (checked by TLC). The THF was removed by rotary
evaporation. EtOAc (300 mL) and 1 N NaOH (200 mL) were added
2-(4-Phenylpiperidin-1-yl)-N-(m-tolyl)acetamide (5a) was pre-
pared in the same manner as 5k but with substitution of 4-phe-
nylpiperidine in place of 4-(2-pyridinyl)piperidine (150 mg, 99%
1
yield). H NMR (300 MHz, DMSO-d6) δ 1.76 (m, 4H), 2.28 (m,
5H), 2.51 (m, 1H), 2.98 (m, 2H), 3.12 (s, 2H), 6.88 (d, J ) 6 Hz,
1H), 7.19 (m, 2H), 7.29 (m, 4H), 7.46 (d, 2H), 9.61 (br s, 1H); MS
(DCI-NH3) m/e 39 (M + H)+. Anal. (C20H24N2O‚0.2H2O) C, H,
N.
2-[1-[2-(m-Tolylamino)allyl]piperidin-4-yl]benzonitrile (5b)
was prepared in the same manner as 5k but with substitution of
2-piperidin-4-ylbenzonitrile in place of 4-(2-pyridinyl)piperidine
1
(133 mg, 70% yield). H NMR (300 MHz, DMSO-d6) δ 9.62 (s,
1H), 7.79 (dd, J ) 7.8 and 1.0 Hz, 1H), 7.70 (ddd, J ) 7.8, 7.8,
and 1.4 Hz, 1H), 7.60 (br d, J ) 7.1 Hz, 1H), 7.44 (m, 3H), 7.19
(dd, J ) 7.8 and 7.8 Hz, 1H), 6.88 (br d, J ) 7.5 Hz, 1H), 3.17 (s,
2H), 3.02 (br d, J ) 11.5 Hz, 2H), 2.86 (m, 1H), 2.34 (m, 2H),
2.29 (s, 3H), 1.96-1.75 (m, 4H). MS (DCI/NH3) m/e 334 (M +
H)+. This material was converted to the maleate salt. Anal.
(C21H23N3O‚1.2C4H4O4‚0.2H2O) C, H, N.
2-[4-(2-Fluorophenyl)piperidin-1-yl]-N-(m-tolyl)acetamide (5c)
was prepared in the same manner as 5k but with substitution of
4-(2-fluorophenyl)piperidine in place of 4-(2-pyridinyl)piperidine
(89 mg, 80.9% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.72 (m,
2H), 1.85 (m, 2H), 2.29 (m, 5H), 2.51 (m, 1H), 2.80 (m, 1H), 2.97

7458 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
(m, 2H), 3.12 (s, 2H), 6.88 (d, J ) 6 Hz, 1H), 7.19 (m, 4H), 7.42
(m, 3H), 9.61 (br s, 1H); MS (DCI/NH3) m/e 327 (M + H)+. Anal.
(C20H23FN2O) C, H, N.
N-(4-Chloro-2,6-dimethylphenyl)-2-(3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (5l) was prepared in the same
manner as 5k but with substitution of 2-bromo-N-(4-chloro-2,6-
dimethylphenyl)acetamide in place of 2-bromo-N-(m-tolyl)aceta-
mide (22.9 mg, 25% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.90
(m, 4H), 2.05 (s, 3H), 2.14 (s, 6H), 2.30 (m, 2H), 2.67 (m, 1H),
3.04 (m, 2H), 3.16 (s, 2H), 4.67 (br s, 1H), 6.83 (s, 2H), 7.16 (s,
2H), 7.20 (m, 1H), 7.29 (br d, J ) 7.5 Hz, 1H), 7.72 (ddd, J ) 2.1,
7.5, 7.5 Hz, 1H), 8.48 (m, 1H), 9.27 (br s, 1H); MS (ESI) m/e 358
(M + H)+; Anal. (C20H24ClN3O‚0.35C2H4O2‚0.15H2O) C, H, N.
2-(3′,4′,5′,6′-Tetrahydro-2′H-[2,4′-bipyridine]-1′-yl)-N-(2,4,6-
trichlorophenyl)acetamide (5m) was prepared in the same manner
as 5k but with substitution of 2-bromo-N-(2,4,6-trichlorophenyl)-
acetamide in place of 2-bromo-N-(m-tolyl)acetamide (21.2 mg, 21%
N-(m-Tolyl)-2-[4-(o-tolyl)piperidin-1-yl]acetamide (5d) was
prepared in the same manner as 5k but with substitution of 4-(2-
methylphenyl)piperidine in place of 4-(2-pyridinyl)piperidine (65
mg, 87.8% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.72 (m, 2H),
1.79 (m, 2H), 2.29 (m, 8H), 2.69 (m, 1H), 2.97 (m, 2H), 3.12 (s,
2H), 6.88 (d, J ) 6 Hz, 1H), 7.13 (m, 4H), 7.28 (d, J ) 6 Hz, 1H),
7.47 (m, 2H), 9.61 (br s, 1H); MS (DCI/NH3) m/e 323 (M + H)+.
Anal. (C21H26N2O) C, H, N.
2-[4-(2-Methoxyphenyl)piperidin-1-yl]-N-(m-tolyl)aceta-
mide (5e) (Method A). 4-(2-Methoxyphenyl)piperidine (200 mg,
1 mmol), 2-bromo-N-(3-methylphenyl)acetamide (228 mg, 1 mmol),
and N,N-diisopropylethylamine (0.185 mL, 1.1 mmol) in toluene
(8 mL) were stirred at 60 °C for 18 h. The reaction mixture was
poured into water (30 mL) and extracted with EtOAc (30 mL).
The organic layer was washed with brine (2 × 30 mL), dried over
MgSO4, and filtered, and the filtrate was concentrated under reduced
pressure. The residue was purified by flash chromatography on silica
gel (elution with CH2Cl2/methanol, 9.5:0.5) to provide the title
1
yield). H NMR (300 MHz, DMSO-d6) δ 1.84 (m, 4H), 2.48 (m,
2H), 2.67 (m, 1H), 3.10 (br d, J ) 10.5 Hz, 2H), 3.17 (s, 2H), 7.21
(m, 1H), 7.30 (d, J ) 7.8 Hz, 1H), 7.72 (ddd, J ) 2.1, 7.5, and 7.5
Hz, 1H), 7.77 (s, 2H), 8.48 (m, 1H); MS (ESI) m/e 400 (M + H)+;
Anal. (C18H18Cl3N3O‚0.1C4H4O4‚0.55H2O) C, H, N.
N-(2-Ethyl-6-methylphenyl)-2-(3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-yl)acetamide (5n) was prepared in the same manner
as 5k but with substitution of 2-bromo-N-(2-ethyl-6-methylphenyl)-
acetamide in place of 2-bromo-N-(m-tolyl)acetamide (48.5 mg, 28%
yield). 1H NMR (300 MHz, DMSO-d6) δ 1.08 (t, J ) 7.5 Hz, 3H),
1.90 (m, 4H), 2.14 (s, 3H), 2.32 (m, 2H), 2.50 (q, J ) 7.5 Hz, 2H),
2.68 (m, 1H), 3.04 (br d, J ) 11.4 Hz, 2H), 3.15 (s, 2H), 7.10 (m,
3H), 7.21 (ddd, J ) 1.5, 4.5, and 7.5 Hz, 1H), 7.30 (d, J ) 8.4 Hz,
1H), 7.72 (ddd, J ) 2.1, 7.5, and 7.5 Hz, 1H), 8.28 (m, 1H), 9.22
(br s, 1H); MS (ESI) m/e 338 (M + H)+; Anal. (C21H27N3O‚0.3H2O)
C, H, N.
N-(2-Chloro-6-methylphenyl)-2-(3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (5o) was prepared in the same
manner as 5k but with substitution of 2-bromo-N-(2-chloro-6-
methylphenyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide
(62.8 mg, 36% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.88 (m,
4H), 2.20 (s, 3H), 2.30 (m, 2H), 2.68 (m, 1H), 3.12 (m, 2H), 3.17
(s, 2H), 7.21 (m, 2H), 7.29 (d, J ) 8.4 Hz, 1H), 7.36 (m, 1H), 7.73
(ddd, J ) 2.1, 7.5, and 7.5 Hz, 1H), 8.48 (m, 1H), 9.43 (br s, 1H);
MS (ESI) m/e 344 (M + H)+; Anal. (C19H22ClN3O‚0.1CH2Cl2) C,
H, N.
1
compound (177 mg, 52.3% yield). H NMR (300 MHz, DMSO-
d6) δ 1.71 (m, 4H), 2.28 (m, 5H), 2.89 (m, 1H), 2.96 (m, 2H), 3.13
(s, 2H), 3.78 (s, 3H), 6.91 (m, 3H), 7.20 (m, 3H), 7.45 (m, 2H),
8.69 (s, 1H); MS (DCI/NH3) m/e 339 (M + H)+. Anal. (C21H26N2O2)
C, H, N.
2-[4-(3-Fluorophenyl)piperidin-1-yl]-N-(m-tolyl)acetamide (5f)
was prepared in the same manner as 5k but with substitution of
4-(3-fluorophenyl)piperidine in place of 4-(2-pyridinyl)piperidine
(68 mg, 61.8% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.75 (m,
4H), 2.29 (m, 5H), 2.55 (m, 1H), 2.96 (m, 2H), 3.12 (s, 2H), 6.88
(d, J ) 6 Hz, 1H), 7.01 (m, 1H), 7.14 (m, 3H), 7.35 (m, 1H), 7.45
(m, 2H), 9.61 (br s, 1H); MS (DCI/NH3) m/e 327 (M + H)+. Anal.
(C20H23FN2O) C, H, N.
2-[4-(3-Hydroxyphenyl)piperidin-1-yl]-N-(m-tolyl)aceta-
mide (5g) was prepared in the same manner as 5k but with
substitution of 4-(3-hydroxyphenyl)piperidine in place of 4-(2-
1
pyridinyl)piperidine (190 mg, 60% yield). H NMR (300 MHz,
DMSO-d6) δ 1.61-1.87 (m, 4H), 2.16-2.34 (m, 5H), 2.33-2.46
(m, 1H), 2.88-3.01 (m, 2H), 3.25-3.41 (m, 2H), 6.54-6.61 (m,
1H), 6.62-6.73 (m, 2H), 7.08 (t, 1H), 7.14-7.24 (m, 1H), 7.20 (t,
1H), 7.40-7.51 (m, 2H), 9.19-9.30 (m, 1H), 9.56-9.66 (m, 1H);
MS (DCI/NH3) m/e 325 (M + H)+. Anal. (C20H24N2O2‚0.2H2O)
C, H, N.
N-(2-Methoxy-6-methylphenyl)-2-(3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (5p) was prepared in the same
manner as 5k but with substitution of 2-bromo-N-(2-methoxy-6-
methylphenyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide
1
2-[4-(4-Fluorophenyl)piperidin-1-yl]-N-(m-tolyl)acetamide (5h)
was prepared in the same manner as 5k but with substitution of
4-(4-fluorophenyl)piperidine in place of 4-(2-pyridinyl)piperidine
(38 mg, 22% yield). H NMR (300 MHz, DMSO-d6) δ 1.87 (m,
4H), 2.14 (s, 3H), 2.29 (m, 2H), 2.69 (m, 1H), 3.08 (m, 4H), 3.72
(s, 3H), 6.84 (m, 2H), 7.13 (dd, J ) 8.4 and 8.4 Hz, 1H), 7.20
(ddd, J ) 1.5, 4.5, and 7.5 Hz, 1H), 7.31 (d, J ) 8.4 Hz, 1H), 7.72
(ddd, J ) 2.1, 7.5, and 7.5 Hz, 1H), 8.48 (m, 1H), 8.94 (br s, 1H);
MS (ESI) m/e 340 (M + H)+; Anal. (C20H25N3O‚0.4H2O) C, H,
N.
1
(125 mg, 83.8% yield). H NMR (300 MHz, DMSO-d6) δ 1.75
(m, 4H), 2.29 (m, 5H), 2.55 (m, 1H), 2.96 (m, 2H), 3.12 (s, 2H),
6.88 (d, J ) 7.5 Hz, 1H), 7.13 (m, 3H), 7.31 (m, 2H), 7.45 (m,
2H), 9.61 (br s, 1H); MS (DCI-NH3) m/e 327 (M + H)+. Anal.
(C20H23FN2O) C, H, N.
2-(3-Cyano-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-yl)-
N-(m-tolyl)acetamide (5q): (A) 4-Trifluoromethanesulfonyloxy-
3,6-dihydro-2H-pyridine-1-carboxylic Acid Benzyl Ester (9b).
Benzyl 4-oxo-1-piperidinecarboxylate (0.5 g, 2.1 mmol) and
N-phenyltrifluoromethanesulfonimide (1.15 g, 3.2 mmol) in tet-
rahydrofuran (10 mL) at -78 °C was treated with lithium
hexamethyldisilazide (2.14 mL, 2.1 mmol). After 4 h at -78 °C,
the mixture was quenched with water and extracted with a large
excess of diethyl ether (3×). The ethereal layers were combined,
dried over Na2SO4, and filtered, and the filtrate was concentrated
under reduced pressure. The residue was chromatographed on flash
silica gel (20% EtOAc/hexanes) to provide the title compound
(0.471 g, 60% yield). 1H NMR (300 MHz, CDCl3) δ 2.47 (m, 2H),
3.72 (m, 2H), 4.13 (m, 2H), 5.16 (s, 2H), 5.78 (br m, 1H), 7.36
(m, 5H); MS (ESI) m/e 366 (M + H)+.
2-[4-(4-Methoxyphenyl)piperidin-1-yl]-N-(m-tolyl)aceta-
mide (5i) wasprepared in the same manner as 5k but with
substitution of 4-(4-methoxyphenyl)piperidine in place of 4-(2-
1
pyridinyl)piperidine (120 mg, 83.8% yield). H NMR (300 MHz,
DMSO-d6) δ 1.73 (m, 4H), 2.14-2.35 (m, 5H), 2.38-2.61 (m,
1H), 2.81-2.99 (m, 2H), 3.04-3.18 (m, 2H), 3.61-3.87 (m, 3H),
6.71-7.00 (m, 3H), 7.10-7.29 (m, 3H), 7.36-7.62 (m, 2H), 9.47-
9.71 (m, 1 H); MS (DCI-NH3) m/e 339 (M + H)+. HRMS Calcd
for C21H26N2O2: 339.1994 (M + H)+. Found: 339.2067.
2-[4-(4-Hydroxyphenyl)piperidin-1-yl]-N-(m-tolyl)aceta-
mide (5j) was prepared in the same manner as 5k but with
substitution of 4-(4-hydroxyphenyl)piperidine in place of 4-(2-
pyridinyl)piperidine and NaHCO3 as a base (120 mg, 83.8% yield).
1H NMR (300 MHz, DMSO-d6) δ 1.54-1.89 (m, 4H), 2.14-2.36
(m, 4H), 2.27 (m, 3H), 2.33-2.46 (m, 1H), 2.84-3.02 (m, 2H),
3.04-3.21 (m, 2H), 6.56-6.78 (m, 2H), 6.81-6.94 (m, 1H), 6.97-
7.15 (m, 2H), 7.14-7.26 (m, 1H), 7.36-7.57 (m, 2H), 9.02-9.23
(m, 1H), 9.48-9.76 (m, 1H); MS (DCI-NH3) m/e 325 (M + H)+.
Anal. (C20H24N2O2‚0.2H2O) C, H, N.
(B) 4-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-3,6-di-
hydro-2H-pyridine-1-carboxylic Acid Benzyl Ester (9c). Bis-
(pinacolato)diborane (338 mg, 1.33 mmol), potassium acetate
(356 mg, 3.63 mmol), [1,1′-bis(diphenylphosphino)ferrocene]-
dichloropalladium(II) (PdCl2dppf; 30 mg, 0.04 mmol), and 1,1′-

ABT-670, an Orally BioaVailable Treatment for ED
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7459
bis(diphenylphosphino)ferrocene (20 mg, 0.04 mmol) were com-
bined and treated with compound 9b (440 mg, 1.21 mmol) in
degassed 1,4-dioxane (7 mL). The reaction mixture was heated at
80 °C for 16 h, allowed to cool to 23 °C, diluted with water, and
extracted with CH2Cl2 (3×). The CH2Cl2 extracts were combined,
dried over Na2SO4, and filtered, and the filtrate was concentrated
under reduced pressure. The residue was chromatographed on flash
silica gel (20% EtOAc/hexanes) to provide the title compound (323
mg, 78% yield). 1H NMR (300 MHz, CDCl3) δ 1.25 (s, 12H), 2.24
(m, 2H), 3.52 (dd, J ) 5.7 and 5.7 Hz, 2H), 4.03 (dd, J ) 3 and
6 Hz, 2H), 5.14 (s, 2H), 6.46 (br m, 1H), 7.32 (m, 5H); MS (ESI)
m/e 344 (M + H)+.
DMSO-d6) δ 5.19 (s, 2H), 7.42 (m, 6H), 7.57 (d, J ) 6 Hz, 1H),
8.19 (d, J ) 3 Hz, 1H), MS (DCI/NH3) m/e 365 (M + H)+.
(B) t-Butyl 5-Benzyloxy-3′,6′-dihydro-2′H-[2,4′-bipyridine]-
1′-carboxylate (12m). The 5-benzyloxy-2-bromopyridine (0.33 g,
17.7 mmol) in diethyl ether (10 mL) was added rapidly to a solution
of 2.5 M n-butyllithium (0.98 mL, 1.56 mmol) in diethyl ether (8
mL) at -78 °C. The resulting brown solution was stirred at -78
°C for 10 min. To this was added 0.5 M zinc chloride solution
(2.75 mL, 1.37 mmol), and the reaction mixture was warmed to 0
°C and stirred at 0 °C for 15 min. To this reaction mixture was
added 4-trifluoromethanesulfonyloxy-3,6-dihydro-2H-pyridine-1-
carboxylic acid t-butyl ester (0.5 g, 1.5 mmol) and tetrakis-
(triphenylphosphine)palladium(0) (175 mg, 0.15 mmol). The re-
action was heated to 60 °C for 4 h. The mixture was cooled to rt
and the solvent was removed under reduced pressure. The residue
was partitioned between EtOAc (50 mL) and 1 N sodium hydroxide
(50 mL). The inorganic salts were filtered, and the filtrate was
washed with brine (50 mL), dried (MgSO4), and concentrated on
the rotary evaporator to give a brown oil. The crude compound
was purified by flash column chromatography on silica gel with
80% hexanes/EtOAc as eluent to give 0.209 g (47% yield) of the
desired product 12m as a white solid. 1H NMR (300 MHz, DMSO-
d6) δ 1.42 (s, 9H), 2.52 (m, 2H), 3.51 (t, J ) 6 Hz, 2H), 4.01 (m,
2H), 5.19 (s, 2H), 6.52 (m, 1H), 7.41 (m, 7H), 8.31 (d, J ) 1.5 Hz,
1H), MS (DCI/NH3) m/e 367 (M + H)+.
(C) 2-[5-Benzyloxy-3′,6′-dihydro-2′H-[2,4′-bipyridine]-1′-yl]-
N-(3-methylphenyl)acetamide (12n). A mixture of 5-benzyloxy-
3′,6′-dihydro-2,4′-bipyridine (175 mg, 0.46 mmol), the product from
example 1A (125 mg, 0.54 mmol), and potassium carbonate (164
mg, 1.1 mmol) in DMF (8 mL) was stirred at rt for 18 h. The
reaction mixture was poured into water (30 mL) and extracted with
EtOAc (30 mL). The organic layer was washed with brine (2 × 30
mL), dried over MgSO4, filtered, concentrated under reduced
pressure, and purified by flash column chromatography with 70%
hexanes/EtOAc to give the desired product (105 mg, 55% yield).
1H NMR (300 MHz, DMSO-d6) δ 2.27 (s, 3H), 2.60 (m, 2H), 2.76
(t, J ) 4.5 Hz, 2H), 3.27 (m, 2H), 3.97 (d, J ) 6 Hz, 2H), 5.19 (s,
2H), 6.54 (m, 1H), 6.87 (m, 2H), 7.18 (t, J ) 6 Hz, 2H), 7.42 (m,
7H), 8.31 (d, J ) 3 Hz, 1H), 9.52 (s, 0.5H), 9.64 (s, 0.5H); MS
(DCI/NH3) m/e 414 (M + H)+.
(C) Benzyl 3-Cyano-3′,6′-dihydro-2′H-[2,4′-bipyridine]-1′-
carboxylate 4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-ol Com-
plex (10l). Compound 9c (200 mg, 0.58 mmol), potassium
carbonate (241 mg, 1.75 mmol), PdCl2dppf (29 mg, 0.035 mmol),
and 2-chloro-3-cyanopyridine (85 mg, 0.61 mmol) were combined
in degassed DMF (4 mL). The reaction mixture was heated at 80
°C for 16 h, allowed to cool to 23 °C, and diluted with water and
CH2Cl2, and the layers were separated. The aqueous phase was
extracted with CH2Cl2 (2×). All the CH2Cl2 phases were combined,
dried over Na2SO4, and filtered, and the filtrate was concentrated
under reduced pressure. The residue was chromatographed on flash
silica gel (50% EtOAc/hexanes) to provide the title compound
sufficiently pure to carry on in further reactions (323 mg, 78%
1
yield). H NMR (300 MHz, CDCl3) δ 1.13 (s, 12H), 2.74 (br s,
2H), 3.75 (dd, 2H, J ) 6 Hz), 4.26 (m, 2H), 5.19 (s, 2H), 6.57 (br
m, 1H), 7.32 (m, 6H), 7.98 (dd, J ) 1.8 and 7.8 Hz, 1H), 8.76 (dd,
J ) 1.8 and 4.5 Hz, 1H); MS (ESI) m/e 320 (M + H)+.
(D) 2-(4-Piperidinyl)nicotinonitrile (12l). A steady stream of
H2 was bubbled through a stirred solution of 10l (70 mg, 0.15
mmol), Pd/C (5 mg), and ethanol (2 mL) at 23 °C for 24 h. The H2
bubbling was stopped and N2 was bubbled through for a few
minutes. The reaction mixture was passed through Celite and the
filtrate was concentrated under reduced pressure to provide the title
compound sufficiently pure to carry into further reactions (30 mg).
MS (ESI) m/e 188 (M + H)+.
(E) 2-(3-Cyano-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-
yl)-N-(m-tolyl)acetamide (5q). 2-(4-Piperidinyl)nicotinonitrile 12l
(30 mg, 0.15 mmol), 2-bromo-N-(3-methylphenyl)acetamide (37
mg, 0.16 mmol), and DMF (31 mg, 0.24 mmol) in toluene (3 mL)
were combined and heated at 60 °C. After 16 h, the mixture was
allowed to cool to 23 °C and concentrated under reduced pressure.
The residue was purified by thin-layer chromatography (7% EtOAc/
hexanes) to provide the title compound (9 mg, 17% yield). 1H NMR
(400 MHz, DMSO-d6) δ 1.79 (br d, J ) 12 Hz, 2H), 2.02 (m, 2H),
2.27 (s, 3H), 2.32 (m, 2H), 3.04 (m, 3H), 3.16 (s, 2H), 6.88 (br d,
J ) 8 Hz, 1H), 7.18 (dd, J ) 7.2 and 7.2 Hz, 1H), 7.45 (m, 3H),
8.26 (dd, J ) 1 and 2 Hz, 1H), 8.82 (dd, J ) 1 and 4.4 Hz, 1H),
9.58 (s, 1H); MS (APCI/ESI) m/e 335 (M + H)+.
2-(5-Hydroxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-
yl)-N-(m-tolyl)acetamide (5r): (A) 5-Benzyloxy-2-bromopyri-
dine. 6-Chloropyridin-3-ol (6 g, 46 mmol) in DMF (50 mL) was
treated with benzyl bromide (5.5 mL, 46 mmol) and potassium
carbonate (12.8 mmol), and the reaction mixture was heated to 40
°C for 18 h. The reaction was cooled to rt, poured into brine (200
mL), and extracted with EtOAc (200 mL). The organic layer was
washed with brine (3 × 100 mL), dried over MgSO4, filtered, and
concentrated under reduced pressure to give 5-benzyloxy-2-
chloropyridine. This crude product was dissolved in propionitrile
(50 mL) and treated with trimethylsilyl bromide (12.36 mL, 92
mmol), and the reaction mixture was heated at 100 °C for 113 h.
The reaction mixture was cooled to rt and poured into 2.0 M sodium
hydroxide solution to which 50 g of ice had been added. The
aqueous phase was extracted with diethyl ether (3 × 75 mL). The
organic layers were combined and washed with water (2 × 100
mL) and brine (75 mL), dried over MgSO4, filtered, and concen-
trated under reduced pressure. The crude residue (light brown oil)
was purified by flash column chromatography on silica gel with
8% EtOAc/hexanes as eluent to give 4.72 g of the 5-benzyloxy-
2-bromopyridine as a light yellow solid. 1H NMR (300 MHz,
(D) 2-[4-(5-Hydroxypyridin-2-yl)piperidin-1-yl]-N-(3-meth-
ylphenyl)acetamide (5r). Compound 12n (105 mg, 0.2 mmol) in
methanol (50 mL) was treated with 10% Pd/C (58 mg) at 60 psi
for 16 h. The catalyst was filtered and the filtrate was concentrated
under reduced pressure to give a pale yellow foamy solid. This
crude product was purified by flash column chromatography on
silica gel with 4% ethanol/EtOAc to give the title compound (50
mg, 64% yield). 1H NMR (300 MHz, CDCl3) δ 1.93 (m, 4H), 2.31
(s, 3H), 2.41 (m, 2H), 2.71 (m, 1H), 3.04 (m, 2H), 3.16 (s, 2H),
6.92 (d, J ) 7.5 Hz, 1H), 7.20 (m, 4H), 7.40 (d, J ) 9 Hz, 2H),
8.26 (m, 1H), 9.24 (br s, 1H); MS (DCI/NH3) m/e 326 (M + H)+;
Anal. (C19H23N3O2) C, H, N.
2-(4-Thiazol-2-ylpiperidin-1-yl)-N-(m-tolyl)acetamide (5s): 2-(4-
Thiazol-2-yl-3,6-dihydro-2H-pyridin-1-yl)-N-(m-tolyl)aceta-
mide (12o) was prepared in the same manner as 5k but with
substitution of 4-(1,3-thiazol-2-yl)-3,6-dihydropyridine in place of
1′,2′,3′,4′,5′,6′-hexahydro-2′H-[2,4′-bipyridine] (12d) to provide the
title compound as a yellow sticky residue (450 mg, 62% yield). 1H
NMR (300 MHz, CDCl3) δ 2.3 (s, 3H), 3.8 (m, 2H), 2.9 (m, 2H),
3.31 (s, 2H), 3.4 (m, 2H), 6.6 (m, 1H), 6.9 (m, 1H), 7.2 (m, 1H),
7.25 (d, J ) 3 Hz, 1H), 7.4 (m, 2H), 7.8 (d, J ) 3 Hz, 1H), 9.15
(br s, 1H); MS (DCI/NH3) m/e 314 (M + H)+. This product was
hydrogenated under the same conditions as compound 4c to provide
1
the desired product 5s. H NMR (300 MHz, DMSO-d6) δ 1.8-
1.95 (m, 2H), 2.0-2.15 (m, 2H), 2.22 (s, 3H), 2.25-2.35 (m, 2H),
2.85-2.98 (m, 2H), 3.0 (m, 1H), 3.15 (s, 2H), 6.82 (d, J ) 9 Hz,
1H), 7.18 (t, J ) 7.5 Hz, 1H), 7.45 (m, 2H), 7.6 (d, J ) 3 Hz, 1H),
7.7 (d, J ) 3 Hz, 1H), 9.6 (br s, 1H); MS (DCI/NH3) m/e 316 (M
+ H)+.
General Procedure for Compounds 6a-s (Method B).3-
Methyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-

7460 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
ylmethyl)benzamide (6b): (A) 1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-carboxylic Acid t-Butyl Ester (13). 3′,4′,5′,6′-
Tetrahydro-2′H-[2,4′-bipyridine]-1′-carboxylic acid t-butyl ester (8.9
g, 33.9 mmol) in CH2Cl2 (30 mL) was cooled to 0 °C and treated
with 77% m-chloroperbenzoic acid (10.5 g, 61.06 mmol, 1.8 equiv).
The reaction mixture was stirred at 0 °C for 30 min and then at rt
for 2 h; CH2Cl2 (50 mL) was added to the reaction mixture, which
was washed with saturated NaHCO3 and then with brine, dried over
MgSO4, and concentrated in vacuo. The residue was triturated with
(m, 1H), 4.08 (q, J ) 6 Hz, 2H), 4.18 (d, J ) 6 Hz, 2H), 7.08 (m,
1H), 7.27 (m, 2H), 7.39 (m, 4H), 8.23 (dd, J ) 6 and 1.5 Hz, 1H),
8.72 (t, J ) 6 Hz, 1H); MS (DCI/NH3) m/e 340 (M + H - 16)+;
356 (M + H)+; Anal. (C20H25N3O3‚0.75H2O) C, H, N.
3-Cyano-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)benzamide (6e) was prepared in the same manner as
compound 6b but with substitution of 3-cyanobenzamide in place
1
of 3-methylbenzamide (55 mg, 55% yield). H NMR (300 MHz,
CD3OD) δ 1.73 (dd, J ) 12.5 and 3.6 Hz, 2H), 2.11 (m, 2H), 2.69
(d, J ) 2.0 Hz, 2H), 3.27 (m, 2H), 3.46 (m, 1H), 4.43 (s, 2H), 7.41
(d, J ) 2.4 Hz, 1H), 7.56 (m, 2H), 7.70 (t, J ) 7.8 Hz, 1H), 7.96
(d, J ) 8.8 Hz, 1H), 8.18 (d, J ) 8.1 Hz, 1H), 8.24 (s, 1H), 8.34
(d, J ) 6.4 Hz, 1H), MS (ESI) m/e 337 (M + H)+. HRMS Calcd
for C19H20N4O2Na: 359.14843. Found: 359.1478.
3-Chloro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)benzamide (6f) was prepared in the same manner as
compound 6b but with substitution of 4-chloro-3-methylbenzamide
in place of 3-methylbenzamide (60 mg, 56% yield). 1H NMR (300
MHz, DMSO-d6) δ 2.38 (m, 6H), 2.51 (m, 2H), 2.73 (m, 1H), 2.88
(s, 3H), 4.80 (s, 2H), 7.34 (m, 1H), 7.52 (m, 2H), 7.71 (m, 2H),
7.90 (m, 2H), 9.21 (br s, 1H); MS (ESI) m/e 360 (M + H)+; Anal.
(C19H22ClN3O2‚1.0C2HF3O2) C, H, N.
1
5% CH2Cl2 in hexanes to give a white solid (6.57 g, 72%). H
NMR (300 MHz, DMSO-d6) δ 1.41 (s, 9H), 1.42 (m, 2H), 1.90
(m, 2H), 2.83 (m, 2H), 3.45 (m, 1H), 4.09 (m, 2H), 7.30 (m, 2H),
7.40 (m, 1H), 8.26 (m, 1H).
(B) 1′,2′,3′,4′,5′,6′-Hexahydro-[2,4′-bipyridine] N-Oxide (14).
Compound 13 (6.57 g) was dissolved in EtOAc (150 mL) and
cooled to -78 °C. HCl gas was bubbled through the reaction
mixture for 15 min. The reaction mixture was allowed to warm up
to rt, upon which an off-white precipitate was formed. This
precipitate was filtered, washed with EtOAc, and dried under high
vaccum to give the hydrochloride salt of the desired product
1′,2′,3′,4′,5′,6′-hexahydro-[2,4′-bipyridine] N-oxide (5.04 g, 99%
1
yield). H NMR (300 MHz, DMSO-d6) δ 1.82 (m, 2H), 2.10 (m,
2H), 3.06 (m, 2H), 3.36 (m, 2H), 3.58 (m, 1H), 7.45 (m, 3H), 8.39
(d, J ) 9 Hz, 1H), 9.04 (br s, 1H); MS (DCI-NH3) m/e 179 (M +
H) +, 163 (M + H - 16)+
3-Fluoro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)benzamide (6g) was prepared in the same manner as
compound 6b but with substitution of 4-fluoro-3-methylbenzamide
for 3-methylbenzamide (82 mg, 82.8% yield). 1H NMR (300 MHz,
DMSO-d6) δ 1.52 (m, 2H), 1.89 (d, J ) 12 Hz, 2H), 2.29 (s, 3H),
2.36 (t, J ) 12 Hz, 2H), 2.95 (d, J ) 12 Hz, 2H), 3.19 (m, 1H),
4.17 (d, J ) 6 Hz, 2H), 7.27 (m, 3H), 7.39 (dd, J ) 7.5 and 1.5
Hz, 1H), 7.75 (m, 1H), 7.85 (dd, 7.5 and 1.5 Hz, 1H), 8.23 (dd, J
) 6 and 1.5 Hz, 1H), 8.72 (t, J ) 6 Hz, 1H); MS (DCI/NH3) m/e
328 (M + H - 16)+; 344 (M + H)+; Anal. (C19H22N3FO2) C, H,
N.
(C) 3-Methyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyri-
dine]-1′-ylmethyl)benzamide (6b). 2-Piperidin-4-ylpyridinium N-
oxide hydrochloride (4.16 g, 16.4 mmol) in toluene/dioxane (60
mL/6 mL) was treated with powdered potassium carbonate (2.69
g, 19.37 mmol) at rt and stirred for 30 min. To this mixture were
added 3-methylbenzamide (7.89 g, 58.4 mmol) and 37% aqueous
formaldehyde (4.7 mL, 58 mmol). The reaction mixture was heated
at 80 °C for 3 h, cooled to rt, and treated with additional portions
of 3-methylbenzamide (2.63 g, 19.5 mmol) and 37% formaldehyde
(1.57 mL, 19.5 mmol). The reaction mixture was stirred at 80 °C
for 1 h, cooled, and concentrated under reduced pressure. Toluene
was used to remove the water (2 × 75 mL). To the residue was
added 3% methanol/CH2Cl2, and the inorganic salts were filtered
off. The filtrate was concentrated under reduced pressure. The
residue was purified by flash column chromatography with 10%
methanol/CH2Cl2 followed by 15% methanol/CH2Cl2 to provide
the title compound as a solid (4.53 g, 85% yield). mp 177-180
°C; 1H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 2H), 1.89 (m, 2H),
2.33 (m, 2H), 2.38 (s, 3H), 2.96 (m, 2H), 3.19 (m, 1H), 4.17 (d, J
) 6 Hz, 2H), 7.31 (m, 5H), 7.69 (m, 2H), 8.23 (m, 1H), 8.71 (m,
1H); MS (DCI/NH3) m/e 310 (M + H - 16)+; Anal. (C19H23N3O2)
C, H, N.
3-Chloro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)-4-trifluoromethylbenzamide (6h) was prepared in
the same manner as compound 6b but with substitution of 3-chloro-
4-trifluoromethoxybenzamide in place of 3-methylbenzamide (98
1
mg, 62% yield). H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 2H),
1.89 (d, J ) 12 Hz, 2H), 2.36 (t, J ) 12 Hz, 2H), 2.95 (d, J ) 12
Hz, 2H), 3.20 (m, 1H), 4.18 (d, J ) 6 Hz, 2H), 7.27 (m, 3H), 7.39
(dd, J ) 7.5 and 1.5 Hz, 1H), 7.75 (m, 1H), 7.85 (dd, 7.5 and 1.5
Hz, 1H), 8.23 (dd, J ) 6 and 1.5 Hz, 1H), 8.72 (t, J ) 6 Hz, 1H);
MS (DCI/NH3) m/ e 414 (M + H - 16)+; 430 (M + H)+; Anal.
(C19H19ClF3O3) C, H, N.
3,5-Dichloro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyri-
dine]-1′-ylmethyl)benzamide (6i) was prepared in the same manner
as compound 6b but with substitution of 3,5-dichlorobenzamide
1
N-(1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-ylm-
ethyl)benzamide (6a) waspPrepared in the same manner as
compound 6b but with substitution of benzamide in place of
3-methylbenzamide (27 mg, 30% yield). 1H NMR (300 MHz, CD3-
OD) δ 1.71 (dd, J ) 12.4 and 3.6 Hz, 2H), 2.04 (m, 2H), 2.54 (m,
2H), 3.12 (m, 3H), 3.37 (s, 2H), 7.46 (m, 5H), 7.87 (m, 3H), 8.33
(d, J ) 6.4 Hz, 1H); MS (ESI) m/e 312 (M + H)+; Anal.
(C18H21N3O2•2.0 H2O) C, H, N.
in place of 3-methylbenzamide (46 mg, 33.3% yield). H NMR
(300 MHz, DMSO-d6) δ1.52 (m, 2H), 1.89 (d, J ) 12 Hz, 2H),
2.36 (t, J ) 12 Hz, 2H), 2.95 (d, J ) 12 Hz, 2H), 3.20 (m, 1H),
4.18 (d, J ) 6 Hz, 2H), 7.29 (m, 2H), 7.39 (m, 1H), 7.83 (t, J )
1.5 Hz, 1H), 7.92 (d, J ) 1.5 Hz, 2H), 8.23 (dd, J ) 6 and 1.5 Hz,
1H), 8.98 (t, J ) 6 Hz, 1H); MS (DCI/NH3) m/e 365 (M + H -
16)+; 381 (M + H)+; Anal. (C18H19Cl2N3O2) C, H, N.
4-Methyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)-3-trifluoromethylbenzamide (6j) was prepared in the
same manner as compound 6b but with substitution of 3-trifluo-
romethyl-4-methylbenzamide in place of 3-methylbenzamide (75
mg, 66.3% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 2H),
1.89 (d, J ) 12 Hz, 2H), 2.36 (t, J ) 12 Hz, 2H), 2.95 (d, J ) 12
Hz, 2H), 3.20 (m, 1H), 3.25 (s, 3H), 4.18 (d, J ) 6 Hz, 2H), 7.29
(m, 2H), 7.39 (m, 1H), 7.58 (d, J ) 9 Hz, 1H), 8.08 (d, J ) 9 Hz,
1H), 8.19 (s, 1H), 8.23 (dd, J ) 6 and 1.5 Hz, 1H), 8.98 (t, J ) 6
Hz, 1H); MS (DCI/NH3) m/e 378 (M + H - 16)+; 394 (M + H)+;
Anal. (C20H22F3N3O2‚0.3H2O) C, H, N.
N-(1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-ylm-
ethyl)-3-vinylbenzamide (6c) was prepared in the same manner
as compound 6b but with substitution of 3-vinylbenzamide in place
1
of 3-methylbenzamide (84 mg, 67% yield). H NMR (300 MHz,
CD3OD) δ 1.75 (dd, J ) 12.6 and 3.7 Hz, 2H), 2.10 (d, J ) 12.6
Hz, 2H), 2.63 (m, 2H), 3.21 (m, 2H), 3.46 (m, 1H), 4.38 (s, 2H),
5.34 (d, J ) 11.2 Hz, 1H), 5.90 (d, J ) 17.3 Hz, 1H), 6.81 (dd, J
) 17.6 and 10.9 Hz, 1H), 7.50 (m, 5H), 7.76 (d, J ) 7.5 Hz, 1H),
7.95 (s, 1H), 8.33 (d, J ) 6.4 Hz, 1H), MS (ESI) m/e 338 (M +
H)+. HRMS Calcd for C20H23N3O2Na: 360.4503. Found: 360.1682.
3-Ethoxy-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)benzamide (6d) was prepared in the same manner as
compound 6b but with substitution of 3-ethoxybenzamide in place
3,4-Dimethyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyri-
dine]-1′-ylmethyl)benzamide (6k) was prepared in the same
manner as compound 6b but with substitution of 3,4-dimethylben-
1
1
of 3-methylbenzamide (65 mg, 47% yield). H NMR (300 MHz,
zamide in place of 3-methylbenzamide (85 mg, 89% yield). H
DMSO-d6) δ 1.34 (t, J ) 7.5 Hz, 3H), 1.52 (m, 2H), 1.89 (d, J )
12 Hz, 2H), 2.36 (t, J ) 12 Hz, 2H), 2.95 (d, J ) 12 Hz, 2H), 3.20
NMR (300 MHz, DMSO-d6) δ1.52 (m, 2H), 1.89 (d, J ) 12 Hz,
2H), 2.28 (s, 6H), 2.36 (m, 2H), 2.95 (d, J ) 12 Hz, 2H), 3.20 (m,

ABT-670, an Orally BioaVailable Treatment for ED
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7461
1H), 4.18 (d, J ) 6 Hz, 2H), 7.21 (d, J ) 9 Hz, 1H), 7.29 (m, 2H),
7.39 (m, 1H), 7.62 (d, J ) 9 Hz, 1H), 7.68 (s, 1H), 8.23 (dd, J )
6 and 1.5 Hz, 1H), 8.64 (t, J ) 6 Hz, 1H); MS (DCI/NH3) m/e 324
(M + H - 16)+; 340 (M + H)+; Anal. (C20H25N3O2‚0.3H2O) C,
H, N.
3-Chloro-4-fluoro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bi-
pyridine]-1′-ylmethyl)benzamide (6l) was prepared in the same
manner as compound 6b but with substitution of 3-chloro-4-
fluorobenzamide in place of 3-methylbenzamide (85 mg, 89%
yield). 1H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 2H), 1.89 (d, J
) 12 Hz, 2H), 2.36 (m, 2H), 2.95 (d, J ) 12 Hz, 2H), 3.20 (m,
1H), 4.18 (d, J ) 6 Hz, 2H), 7.24 (m, 2H), 7.39 (dd, J ) 6 and 1.5
Hz, 1H), 7.53 (t, J ) 9 Hz, 1H), 7.93 (m, 1H), 8.13 (dd, J ) 6 and
1.5 Hz, 1H), 8.23 (dd, J ) 6 and 1.5 Hz, 1H), 8.90 (t, J ) 6 Hz,
1H); MS (DCI/ NH3) m/e 348 (M + H - 16)+; 364 (M + H)+;
Anal. (C18H19N3O2ClF‚0.8H2O) C, H, N.
6-Chloro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-
1′-ylmethyl)nicotinamide (6q) was prepared in the same manner
as compound 6b but with substitution of 6-chloronicotinamide in
1
place of 3-methylbenzamide (20 mg, 25% yield). H NMR (300
MHz, DMSO-d6) δ 1.52 (m, 2H), 1.89 (d, J ) 12 Hz, 2H), 2.36
(m, 2H), 2.98 (d, J ) 12 Hz, 2H), 3.22 (m, 1H), 4.19 (d, J ) 6 Hz,
2H), 7.29 (m, 2H), 7.30 (dd, J ) 6 and 1.5 Hz, 1H), 7.65 (d, J )
9 Hz, 1H), 8.26 (m, 2H), 8.88 (d, J ) 3 Hz, 1H), 9.02 (t, J ) 6 Hz,
1H); MS (DCI/NH3) m/e 331 (M + H - 16)+; Anal. (C17H19N4O2-
Cl‚0.4H2O) C, H, N.
Pyridine-2-carboxylic Acid (1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-ylmethyl)amide (6r) was prepared in the same
manner as compound 6b but with substitution of pyridine-2-
carboxylic acid amide in place of 3-methylbenzamide (51 mg, 57%
yield). 1H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 2H), 1.89 (d, J
) 12 Hz, 2H), 2.36 (m, 2H), 2.98 (d, J ) 12 Hz, 2H), 3.18 (m,
1H), 4.22 (d, J ) 6 Hz, 2H), 7.27 (m, 2H), 7.28 (dd, J ) 6 and 1.5
Hz, 1H), 7.63 (m, 1H), 8.03 (m, 1H), 8.22 (dd, J ) 6 and 1.5 Hz,
1H), 8.23 (dd, J ) 6 and 1.5 Hz, 1H), 8.68 (dd, J ) 6 and 1.5 Hz,
1H), 9.02 (t, J ) 6 Hz, 1H); MS (DCI/NH3) m/e 297 (M + H -
16)+; 313 (M + H)+; Anal. (C17H20N4O2‚0.3H2O) C, H, N.
Thiazole-2-carboxylic Acid (1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-ylmethyl)amide (6s) was prepared in the same
manner as compound 6b but with substitution of thiophene-2-
carboxylic acid amide in place of 3-methylbenzamide (100 mg,
56.6% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 2H), 1.89
(d, J ) 12 Hz, 2H), 2.36 (m, 2H), 2.98 (d, J ) 12 Hz, 2H), 3.18
(m, 1H), 4.12 (d, J ) 6 Hz, 2H), 7.18 (dd, J ) 4.5 and 3.0, 1H),
7.28 (m, 2H), 7.39 (dd, J ) 9.0 and 3 Hz, 1H), 7.78 (dd, J ) 4.5
and 1.5 Hz, 1H), 7.85 (dd, J ) 4.5 and 1.5 Hz, 1H), 8.22 (dd, J )
6 and 1.5 Hz, 1H), 8.79 (t, J ) 6 Hz, 1H); MS (DCI/NH3) m/e 297
(M + H - 16)+; 313 (M + H)+. HRMS Calcd for C16H19N3O2-
SNa: 340.1096 (M + H)+. Found: 340.1090
General Procedure for Compounds 7a-z: 2-(1-Oxy-3′,4′,5′,6′-
tetrahydro-2′H-[2,4′-bipyridine]-1′-yl)-N-(m-tolyl)acetamide (7a).
A mixture of 2-bromo-N-(m-tolyl)acetamide (8.903 g, 39.03 mmol),
and 1′,2′,3′,4′,5′,6′-hexahydro-[2,4′-bipyridine] N-oxide (8.38 g,
39.03 mmol) and K2CO3 (10.78 g, 78.06 mmol) in DMF (100 mL)
was stirred at rt for 20 h. The reaction mixture was checked by
TLC. Both starting materials were present along with the product;
therefore, the reaction mixture was heated at 40 °C for 4 h. TLC
still showed starting materials 1 and 2, but to avoid any side
reactions due to prolonged heating, the reaction mixture was worked
up. DMF was removed on the rotary evaporator. The residue was
extracted between brine and EtOAc. The aqueous layer was
extracted with EtOAc (3 × 200 mL). Combined organics were dried
over MgSO4 and concentrated. The residue was purified by flash
chromatography with 4% MeOH in CH2Cl2 to give the desired
product as an off-white solid (8.065 g, 63.5%). 1H NMR (300 MHz,
DMSO-d6) δ 1.80 (m, 2H), 1.91 (m, 2H), 2.30 (m, 5H), 2.99 (m,
2H), 3.14 (s, 2H), 3.25 (m, 1H), 6.88 (d, J ) 7.5 Hz, 1H), 7.19 (t,
J ) 7.5 Hz, 1H), 7.31 (m, 2H), 7.45 (m, 2H), 8.24 (m, 1H), 9.6 (br
s, 1H); MS (DCI-NH3) m/e 310 (M + H - 16)+; 326 (M + H)+.
Anal. (C19H23N3O2) C, H, N.
3,5-Dimethyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyri-
dine]-1′-ylmethyl)benzamide (6m) was prepared in the same
manner as compound 6b but with substitution of 3,5-dimethylben-
1
zamide in place of 3-methylbenzamide (140 mg, 60% yield). H
NMR (300 MHz, CD3OD) δ 1.76 (dd, J ) 12.4 and 3.6 Hz, 2H),
2.11 (d, J ) 12.6 Hz, 2H), 2.36 (s, 6H), 2.66 (m, 2H), 3.23 (d, J
) 12.2 Hz, 2H), 3.47 (m, 1H), 4.38 (s, 2H), 7.22 (s, 1H), 7.41 (m,
1H), 7.52 (m, 2H), 7.56 (m, 2H), 8.34 (d, J ) 6.4 Hz, 1H); MS
(ESI) m/e 340 (M + H)+. HRMS Calcd for C20H25N3O2Na:
362.1844. Found: 362.1839
3-Methoxy-2-methyl-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-ylmethyl)benzamide (6n): 3-Methoxy-2-methyl-
benzamide. A reaction mixture containing 3-methoxy-2-methyl-
benzoic acid (2 g, 12.04 mmol), 1-[3-(dimethylamino)propyl]-3-
ethylcarbodiimidehydrochloride(2.76g,14.4mmol),and1-hydroxybenzo-
triazole hydrate (1.95 g, 14.4 mmol) in chloroform was stirred at
rt for 1 h. The reaction was quenched with 30% ammonium
hydroxide solution (35 mL), and stirring was continued for another
1.5 h. The layers were separated, and the organic phase was dried
over MgSO4, filtered, and concentrated under reduced pressure. The
residue was purified by flash column chromatography on silica gel
(50% EtOAc/hexanes) to afford a white powder (1.2 g, 60% yield).
1H NMR (300 MHz, CDCl3) δ 2.3 (s, 3H), 3.82 (s, 3H), 6.9 (d, J
) 9 Hz, 1H), 7.02 (d, J ) 9 Hz, 1H), 7.18 (t, J ) 9 Hz, 1H); MS
(DCI/NH3) m/e 166 (M + H)+.
Compound 6n was prepared in the same manner as compound
6b but with substitution of 3-methoxy-2-methylbenzamide in place
1
of 3-methylbenzamide (45 mg, 16% yield; white solid). H NMR
(300 MHz, CDCl3) δ 1.45-1.55 (m, 2H), 2.05-2.15 (m, 2H), 2.25
(s, 3H), 2.55-2.65 (m, 2H), 3.05-3.10 (m, 2H), 3.40-3.50 (m,
1H), 3.81 (s, 3H), 4.40 (d, J ) 6 Hz, 2H), 6.4 (br s, 1H), 6.85 (d,
J ) 9 Hz, 1H), 7.0 (d, J ) 9 Hz, 1H), 7.10-7.20 (m, 2H), 7.25-
7.32 (m, 2H), 8.20 (d, J ) 6 Hz, 1H); MS (DCI/NH3) m/e 356 (M
+ H)+; Anal. (C20H25N3O3) C, H, N.
3-Methoxy-4-chloro-N-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-ylmethyl)benzamide (6o) was prepared in the same
manner as compound 6b but with substitution of 4-chloro-3-
methoxybenzamide in place of 3-methylbenzamide (75 mg, 17%
yield; yellow solid). 1H NMR (300 MHz, CDCl3) δ 1.6-1.68 (m,
2H), 2.05-2.20 (m, 2H), 2.50-2.65 (m, 2H), 3.05-3.20 (m, 2H),
3.42-3.55 (m, 1H), 3.98 (s, 3H), 4.40 (d, J ) 6 Hz, 2H), 6.65 (br
s, 1H), 7.15 (m, 1H), 7.2-7.35 (m, 3H), 7.40 (d, J ) 9 Hz, 1H),
7.45 (d, J ) 3 Hz, 1H), 8.22 (d, J ) 6 Hz, 1H); MS (DCI/NH3)
m/e 376 (M + H)+; Anal. (C19H22ClN3O3) C, H, N.
2-(1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-yl)-N-
(3-trifluoromethylphenyl)acetamide (7b) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(3-trifluoromethylphenyl)acetamide in place of 2-bromo-N-(3-
tolyl)acetamide (191 mg, 17% yield). This material was converted
to the maleate salt: 1H NMR (300 MHz, CD3OD) δ 8.39 (br d, J
) 6.5 Hz, 1H), 8.08 (br s, 1H), 7.77 (br d, J ) 8.1 Hz, 1H), 7.65-
7.44 (m, 5H), 6.26 (s, 2H), 4.12 (s, 2H), 3.77 (br d, J ) 11.9 Hz,
2H), 3.69 (ddd, J ) 12.2, 3.4, and 3.4 Hz, 1H), 3.30 (m, 2H), 2.35
(br d, J ) 13.9 Hz, 2H), 2.10 (m, 2H); MS (ESI) m/e 380 (M +
H)+; Anal. (C19H20F3N3O2‚1.2C4H4O4‚0.1H2O) C, H, N.
Naphthalene-2-carboxylic Acid (1-Oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-ylmethyl)amide (6p) was prepared in the
same manner as compound 6b but with substitution of 2-naph-
thoylamide in place of 3-methylbenzamide (75 mg, 56% yield;
1
white solid). H NMR (300 MHz, DMSO-d6) δ 1.56 (q, J ) 12.2
Hz, 1H), 1.57 (q, J ) 11.9 Hz, 1H), 1.92 (d, J ) 11.2 Hz, 2H),
2.41 (t, J ) 11.2 Hz, 2H), 3.02 (d, J ) 11.5 Hz, 2H), 3.25 (m, J
) 12.9 Hz, 1H), 4.24 (d, J ) 5.8 Hz, 2H), 7.30 (m, 2H), 7.40 (dd,
J ) 7.5 and 2.4 Hz, 1H), 7.62 (m, 2H), 8.01 (m, 4H), 8.24 (d, J )
5.8 Hz, 1H), 8.51 (s, 1H), 8.97 (s, 1H); MS (DCI/ NH3) m/e 362
(M + H)+; Anal. (C22H23N3O2‚0.2CH2Cl2‚1.2H2O) C, H, N.
N-(3-Fluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-yl)acetamide (7c) was prepared in the same manner
as compound 7a but with substitution of 2-bromo-N-(3-fluorophe-
nyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide (157 mg,
68% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.68 (m, 2H), 1.92
(d, J ) 5.8 Hz, 2H), 2.30 (m, 2H), 3.01 (m, 2H), 3.19 (s, 2H), 3.25

7462 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
(m, 1H), 6.89 (m, 1H), 7.35 (m, 3H), 7.42 (m, 2H), 7.68 (m, 1H),
8.26 (d, J ) 4.5 Hz, 1H), 9.91 (s, 1H); MS (DCI/NH3) m/e 330 (M
+ H)+. Maleate salt (190 mg): Anal. (C18H20N3O2F‚1.0C4H4O4‚
0.2H2O) C, H, N.
3H), 1.70 (m, 8H), 2.64 (m, 3H), 4.26 (s, 2H), 6.91 (s, 1H), 7.25
(m, 3H), 7.42 (m, 2H), 7.60 (m, 1H), 8.28 (d, J ) 6.1 Hz, 1H);
MS (ESI) m/e 340 (M + H)+. HRMS Calcd for C20H25N3O2:
340.4314 (M + H)+. Found: 340.2020.
N-(4-Fluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-yl)acetamide (7d) was prepared in the same manner
as compound 7a but with substitution of 2-bromo-N-(4-fluorophe-
nyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide (245 mg,
45% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.68 (m, 2H), 1.92
(d, J ) 5.8 Hz, 2H), 2.30 (m, 2H), 3.01 (m, 2H), 3.19 (s, 2H), 3.25
(m, 1H), 6.89 (m, 1H), 7.35 (m, 3H), 7.42 (m, 2H), 7.68 (m, 1H),
8.26 (d, J ) 4.5 Hz, 1H), 9.91 (s, 1H); MS (DCI/NH3) m/e 314 (M
+ H - 16)+; 330 (M + H)+. Maleate salt (190 mg): Anal.
(C18H20N3O2F‚1.0C4H4O4‚1.1H2O) C, H, N.
N-(Biphenyl-3-yl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bi-
pyridine]-1′-yl)acetamide (7k) was prepared in the same manner
as compound 7a but with substitution of N-(biphenyl-3-yl)-2-
bromoacetamide in place of 2-bromo-N-(m-tolyl)acetamide (38.5
mg, 26% yield). 1H NMR (300 MHz, CDCl3) δ 1.73 (m, 2H), 2.09
(m, 2H), 2.55 (m, 2H), 3.08 (m, 2H), 3.22 (s, 2H), 3.48 (m, 1H),
7.19 (m, 4H), 7.39 (m, 3H), 7.61 (m, 5H), 8.28 (d, J ) 6.10 Hz,
1H) 9.21 (s, 1H); MS (ESI) m/e 390 (M + H)+; Anal. (C24H25N3O2)
C, H, N.
N-(3,5-Dichlorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (7l) was prepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(3,5-
dichlorophenyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide
N-(2-Fluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-yl)acetamide (7e) was pPrepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(2-
fluorophenyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide
1
(36 mg, 34% yield). H NMR (300 MHz, DMSO-d6) δ 1.71 (m,
1
(126 mg, 54% yield). H NMR (300 MHz, DMSO-d6) δ 1.68 (m,
2H), 1.92 (m, 2H), 2.30 (m, 2H), 2.98 (m, 2H), 3.19 (s, 2H), 3.25
(m, 1H), 7.30 (m, 2H), 7.42 (m, 1H), 7.80 (d, J ) 3 Hz, 2H), 8.26
(d, J ) 4.5, 1H), 10.05 (s, 1H); MS (DCI/NH3) m/e 365 (M + H
- 16)+; 381 (M + H)+; Anal. calcd for acetate salt (C18H19Cl2N3O2‚
1.0C2H4O2) C, H, N.
2H), 1.92 (d, J ) 6 Hz, 2H), 2.30 (m, 2H), 3.01 (m, 2H), 3.19 (s,
2H), 3.25 (m, 1H), 7.15 (m, 1H), 7.30 (m, 3H), 7.42 (m, 2H), 7.68
(m, 1H), 8.26 (d, J ) 4.5 Hz, 1H), 9.81 (s, 1H); MS (DCI/NH3)
m/e 314 (M + H - 16)+; 330 (M + H)+. Maleate salt (190 mg):
Anal. (C18H20N3O2F‚1.0C4H4O4‚0.2H2O) C, H, N.
N-(2,3-Dichlorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (7m) was prepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(2,3-
dichlorophenyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide
N-(3-Chlorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-
bipyridine]-1′-yl)acetamide (7f) was prepared in the same manner
as compound 7a but with substitution of 2-bromo-N-(3-chlorophe-
nyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide (226 mg,
66% yield). 1H NMR (300 MHz, DMSO-d6) δ 1.68 (m, 2H), 1.92
(d, J ) 5.7 Hz, 2H), 2.30 (m, 2H), 3.01 (m, 2H), 3.19 (s, 2H), 3.25
(m, 1H), 6.89 (m, 1H), 7.35 (m, 3H), 7.42 (m, 2H), 7.68 (m, 1H),
8.26 (d, J ) 4.5 Hz, 1H), 9.91 (s, 1H); MS (DCI/NH3), m/e 330
(M + H - 16)+, 346 (M + H)+. Maleate salt (294 mg): Anal.
(C18H20N3O2Cl‚1.0C4H4O4‚0.2H2O) C, H, N.
1
(25 mg, 22% yield). H NMR (300 MHz, DMSO-d6) δ 1.71 (m,
2H), 1.99 (m, 2H), 2.43 (m, 2H), 3.03 (m, 2H), 3.25 (s, 2H), 3.35
(m, 1H), 7.38 (m, 5H), 8.26 (dd, J ) 4.5 and 1.5 Hz, 2H), 10.15
(s, 1H). MS (DCI/NH3) m/e 365 (M + H - 16)+; 381 (M + H)+.
Anal. calcd for acetate salt (C18H19Cl2N3O2‚1.0C2H4O2) C, H, N.
N-(2-Methoxy-6-methylphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7n) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(2-methoxy-6-methylphenyl)acetamide in place of 2-bromo-N-
(m-tolyl)acetamide (45 mg, 44% yield). 1H NMR (300 MHz,
DMSO-d6) δ 1.71 (m, 2H), 1.99 (m, 4H), 2.15 (m, 3H), 2.30 (m,
2H), 3.10 (m, 1H), 3.15 (s, 2H), 3.75 (s, 3H), 6.86 (dd, J ) 9 and
1.5 Hz, 2H), 7.16 (t, J ) 9 Hz, 1H), 7.30 (m, 2H), 7.45 (m, 1H),
8.26 (dd, J ) 4.5 and 1.5 Hz, 1H), 8.95 (s, 1H); MS (DCI/NH3)
m/e 340 (M + H - 16)+; 356 (M + H)+. Acetate salt was obtained
after purification. HRMS Calcd for C20H26N3O3: 356.4308 (M +
H)+. Found: 356.1969.
N-(3-Isopropoxyphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (7g) was prepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(3-
isopropoxyphenyl)acetamide in place of 2-bromo-N-(m-tolyl)-
1
acetamide (74 mg, 52.8% yield). H NMR (300 MHz, DMSO-d6)
δ 1.26 (d, J ) 6 Hz, 6H), 1.70 (m, 2H), 1.91 (m, 2H), 2.30 (m,
2H), 3.01 (m, 2H), 3.15 (m, 1H), 3.31 (m, 1H), 4.55 (m, 1H), 6.62
(m, 1H), 7.16 (m, 2H), 7.30 (m, 3H), 7.45 (m, 1H), 8.15 (dd, J )
6 and 1.5 Hz, 1H), 9.65 (s, 1H); MS (DCI/NH3) m/e 354 (M + H
- 16)+; 370 (M + H)+; Anal. (C21H27N3O3‚0.4H2O) C, H, N.
N-(3-Trifluoromethoxyphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7h) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(3-trifluoromethoxyphenyl)acetamide in place of 2-bromo-N-(m-
N-(3,5-Dimethylphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (7o) was prepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(3,5-
dimethylphenyl)acetamide in place of 2-bromo-N-(m-tolyl)aceta-
mide (38 mg, 26% yield). 1H NMR (300 MHz, CDCl3) δ 1.88 (d,
J ) 3.39 Hz, 2H), 2.05 (d, J ) 12.55 Hz, 2H), 2.28 (s, 6H), 2.43
(m, 2H), 3.11 (m, 3H), 3.21 (s, 2H), 6.78 (s, 1H), 7.21 (s, 2H),
7.41 (m, 2H), 7.60 (d, J ) 4.07 Hz, 1H), 8.34 (d, J ) 6.44 Hz,
1H); MS (ESI) m/e 340 (M + H)+. HRMS Calcd for C20H25N3O2:
340.1947 (M + H)+. Found: 340.2020.
N-(2-Methyl-4-bromophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7p) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(4-bromo-2-methylphenyl)acetamide in place of 2-bromo-N-(m-
tolyl)acetamide (25 mg, 60% yield). 1H NMR (300 MHz, DMSO-
d6) δ 1.67 (ddd, J ) 24.6, 12.2, and 3.6 Hz, 2H), 1.96 (d, J ) 12.5
Hz, 2H), 2.25 (s, 3H), 2.37 (t, J ) 11.7 Hz, 2H), 3.04 (d, J ) 11.5
Hz, 2H), 3.18 (s, 2H), 3.26 (m, 1H), 7.37 (m, 5H), 7.76 (d, J ) 8.8
Hz, 1H), 8.26 (m, 1H), 9.46 (s, 1H); MS (DCI/NH3) m/e 404/406
(M + H)+; Anal. (C19H22BrN3O2‚0.1K2CO3) C, H, N.
1
tolyl)acetamide (176 mg, 77% yield) as a white solid. H NMR
(300 MHz, DMSO-d6) δ 1.68 (q, J ) 11.9 Hz, 1H), 1.69 (q, J )
12.4 Hz, 1H), 1.91 (d, J ) 11.9 Hz, 2H), 2.31 (t, J ) 11.5 Hz,
2H), 3.00 (d, J ) 11.5 Hz, 2H), 3.19 (s, 2H), 3.28 (m, 1H), 7.05
(m, J ) 8.3, 2.4, 1.0, and 0.9 Hz, 1H), 7.31 (m, 2H), 7.44 (m, 2H),
7.62 (ddd, J ) 8.2, 2.0, and 1.0 Hz, 1H), 7.85 (s, 1H), 8.26 (d, J
) 5.8 Hz, 1H), 10.01 (s, 1H); MS (DCI/NH3) m/e 396 (M + H)+;
Anal. (C19H20F3N3O3‚0.4H2O) C, H, N.
N-(3-Methylsulfanylphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7i) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(3-thiomethylphenyl)acetamide in place of 2-bromo-N-(m-tolyl)-
acetamide (17 mg, 21% yield). 1H NMR (300 MHz, DMSO-d6) δ
1.60-1.78 (m, 2H), 1.63-1.95 (m, 2H), 2.12-2.18 (m, 2H), 2.70
(s, 3H), 2.9-3.12 (m, 2H), 3.22-3.30 (m, 3H), 6.9-7.0 (m, 1H),
7.2-7.3 (m, 2H), 7.3-7.35 (m, 2H), 7.62 (t, J ) 3 Hz, 1H), 7.8 (s,
1H), 8.23-8.27 (m, 1H), 9.75 (s, 1H); MS (DCI/NH3) m/e 358 (M
+ H)+.
N-(3-Methyl-4-fluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7q) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(4-bromo-2-methylphenyl)acetamide in place of 2-bromo-N-(m-
tolyl)acetamide (139 mg, 57% yield). 1H NMR (300 MHz, DMSO-
d6) δ 1.68 (m, 2H), 1.92 (d, J ) 5.8 Hz, 2H), 2.22 (s, 3H), 2.46
(m, 2H), 3.04 (m, 2H), 3.25 (s, 3H), 7.03 (t, J ) 6 Hz, 1H), 7.35
N-(3-Ethylphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bi-
pyridine]-1′-yl)acetamide (7j) was prepared in the same manner
as compound 7a but with substitution of 2-bromo-N-(3-ethylphe-
nyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide (38 mg,
1
26% yield). H NMR (300 MHz, CDCl3) δ 1.24 (t, J ) 7.6 Hz,

ABT-670, an Orally BioaVailable Treatment for ED
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25 7463
(m, 2H), 7.44 (dd, J ) 4.5 and 1.5 Hz, 1H), 7.48 (m, 1H), 7.54
(dd, J ) 4.5 and 1.5 Hz, 1H), 8.26 (d, J ) 4.5 Hz, 1H), 9.79 (s,
1H); MS (DCI/NH3) m/e 328 (M + H - 16)+; 344 (M + H)+.
Maleate salt (171 mg): Anal. (C19H22N3O2F‚1.0C4H4O4) C, H, N.
N-(2-Methyl-4-fluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7r) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(2-methyl-4-fluorophenyl)acetamide in place of 2-bromo-N-(m-
in the same manner as compound 7a but with substitution of
2-bromo-N-(4-fluoro-2-trifluoromethylphenyl)acetamide in place of
2-bromo-N-(m-tolyl)acetamide (120 mg, 14% yield). 1H NMR (300
MHz, CD3OD) δ 1.80 (m, 2H), 2.10 (br d, 2H, 12.5), 2.53 (ddd, J
) 12.2, 12.2, and 2.4 Hz, 2H), 3.12 (br d, J ) 11.5 Hz, 2H), 3.26
(s, 2H), 3.50 (dddd, J ) 12.6, 12.6, 4.1, and 4.1 Hz, 1H), 7.42 (m,
2H), 7.53 (ddd, J ) 8.1, 8.1, and 2.4 Hz, 2H), 7.61 (ddd, J ) 8.5,
8.5, and 1.4 Hz, 1H), 8.15 (dd, J ) 8.8 and 4.7 Hz, 1H), 8.35 (dd,
J ) 6.1 and 1.0 Hz, 1H). MS (DCI/NH3) m/e 398 (M + H)+; Anal.
(C19H19F4N3O2) C, H, N.
1
tolyl)acetamide. H NMR (300 MHz, DMSO-d6) δ 1.68 (m, 2H),
1.92 (d, J ) 5.8 Hz, 2H), 2.24 (s, 3H), 2.36 (m, 2H), 3.04 (d, J )
11.5 Hz, 2H), 3.17 (s, 2H), 3.29 (m, 2H), 7.03 (m, 1H), 7.11 (dd,
J ) 9.7 and 2.9 Hz, 1H), 7.35 (m, 2H), 7.67 (dd, J ) 8.8 and 5.8
Hz, 1H), 8.26 (m, 1H), 9.40 (s, 1H); MS (DCI/NH3) m/e 328 (M
+ H - 16)+; 344 (M + H)+. Maleate salt (856 mg): Anal.
(C19H22N3O2F‚1.0C4H4O4‚0.75H2O) C, H, N.
N-Cyclohexyl-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyri-
dine]-1′-yl)acetamide (7y) was prepared in the same manner as
compound 7a but with substitution of 2-bromo-N-cyclohexylac-
etamide in place of 2-bromo-N-(m-tolyl)acetamide (153 mg, 21%
1
yield). This material was converted to the maleate salt. H NMR
(300 MHz, CD3OD) δ 1.47-1.18 (m, 6H), 1.64 (m, 1H), 1.78 (m,
2H), 1.90 (m, 2H), 2.05 (m, 2H), 2.33 (m, 2H), 3.24 (dd, J ) 12.6
and 2.4 Hz, 1H,), 3.70 (m, 4H), 3.90 (s, 2H), 6.26 (s, 2H), 7.45
(m, 1H), 7.53 (dd, J ) 8.1 and 2.0 Hz, 1H), 7.61 (ddd, J ) 8.5,
8.5,and 1.4 Hz, 1H), 8.37 (dd, J ) 6.4 and 1.0 Hz, 1H). MS (ESI)
m/e 318 (M + H)+. Anal. (C18H27N3O2‚1.2C4H4O4‚0.4H2O‚0.2CH2-
Cl2) C, H, N.
N-(2-Methyl-5-nitrophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7s) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(2-nitro-5-methylphenyl)acetamide in place of 2-bromo-N-(m-
tolyl)acetamide (75% yield) as a yellow solid. 1H NMR (300 MHz,
CDCl3) δ 1.70 (q, J ) 11.9 Hz, 1H), 1.71 (q, J ) 12.4 Hz, 1H),
2.21 (d, J ) 13.2 Hz, 2H), 2.40 (s, 3H), 2.62 (t, J ) 11.9 Hz, 2H),
3.11 (d, J ) 11.9 Hz, 2H), 3.28 (s, 2H), 3.55 (tt, J ) 12.0 and 3.4
Hz, 1H), 7.19 (ddd, J ) 12.9, 6.4, and 2.7 Hz, 1H), 7.31 (m, 2H),
7.91 (dd, J ) 8.1 and 2.4 Hz, 1H), 8.28 (d, J ) 6.4 Hz, 1H), 9.08
(d, J ) 2.4 Hz, 1H), 9.55 (s, 1H); MS (DCI/NH3) m/e 371 (M +
H)+; Anal. (C19H22N4O4‚1.1H2O) C, H, N.
2-(1-Oxy-3′,4′,5′,6′-tetrahydro-2′H-[2,4′-bipyridine]-1′-yl)-N-
pyridin-2-ylacetamide (7z) was prepared in the same manner as
compound 7a but with substitution of 2-chloro-N-pyridin-3-
ylacetamide in place of 2-bromo-N-(m-tolyl)acetamide (392 mg,
1
30% yield). H NMR (300 MHz, CD3OD) δ 1.83 (dd, J ) 12.2
and 3.4 Hz, 1H), 1.91 (dd, J ) 12.2 and 3.4 Hz, 1H), 2.05 (br d,
J ) 11.9 Hz, 2H), 2.44 (ddd, J ) 11.9, 11.9, and 2.4 Hz, 2H), 3.13
(m, 2H), 3.28 (s, 2H), 3.46 (m, 1H), 7.41 (m, 2H), 7.60 (m, 2H),
8.18 (ddd, J ) 8.5, 2.7, and 1.7 Hz, 1H), 8.28 (dd, J ) 5.1 and 1.4
Hz, 1H), 8.34 (br d, J ) 6.4 Hz, 1H), 8.80 (br d, J ) 2.4 Hz, 1H),
MS (DCI/NH3) m/e 313 (M + H)+; Anal. (C17H20N4O2‚0.3 H2O)
C, H, N.
N-(2,6-Dimethylphenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (7t) was prepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(2,6-
dimethylphenyl)acetamide in place of 2-bromo-N-(m-tolyl)aceta-
mide (27 mg, 8% yield). 1H NMR (300 MHz, CD3OD) δ 1.88 (dd,
J ) 12.4 and 3.6 Hz, 2H), 2.07 (m, 2H), 2.22 (s, 6H), 2.50 (m,
2H), 3.11 (m, 3H) 3.21 (s, 2H), 7.10 (m, 1H), 7.42 (m, 2H), 7.58
(m, 1H), 7.86 (m, 1H), 7.93 (d, J ) 2.0 Hz, 1H), 8.34 (d, J ) 6.4
Hz, 1H); MS (ESI) m/e 354 (M + H)+. Anal. (C20H25N3O2) C, H,
N.
FLIPR Assay of Receptor Activation by Agonists. Test
compounds were evaluated for their ability to activate the human
D
4.4 receptors coexpressed with GRqo5 in HEK293 cells according
to the method described by Moreland et al.8
N-(3-Methyl-2,6-dichlorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahy-
dro-2′H-[2,4′-bipyridine]-1′-yl)acetamide (7u) was prepared in
the same manner as compound 7a but with substitution of 2-bromo-
N-(2,6-dichloro-3-methylphenyl)acetamide in place of 2-bromo-N-
Conscious Rat Penile Erection Model. Test compounds were
evaluated for their ability to induce erections in rat according to
the method described by Brioni et al.6b
1
(m-tolyl)acetamide (86 mg, 64% yield; off-white solid). H NMR
hERG Ionic Current Studies. hERG channels were stably
expressed in HEK 293 cells. Cells were maintained in minimal
Eagle medium (MEM) supplemented with 10% fetal bovine serum.
1% penicillin-streptomycin, 2 mM L-glutamine, 0.1 mM nones-
sential amino acids, 1 mM sodium pyruvate, and 200 mg/mL G418.
Medium was changed every 48 h and cells were passaged weekly.
Currents were recorded by use of an Axopatch 200 and pClamp
data acquisition software. Patch pipettes were constructed with
borosilicate glass capillary tubes (resistance 1.8-3.8 MΩ). The
pipet solution contained 125 mM potassium aspartate, 20 mM KCl,
10 mM ethylene glycol bis(â-aminoethyl ether)-N,N,N′,N′-tetraace-
tic acid (EGTA), 1 mM MgCl2, 5 mM N-(2-hydroxyethyl)-
piperazine-N′-2-ethanesulfonic acid (HEPES), and 5 mM MgATP;
pH ) 7.3. The bath solution contained 140 mM NaCl, 5 mM KCl,
1 mM MgCl2, 2 mM CaCl2, 5 mM glucose, and 20 mM HEPES;
pH ) 7.4. Compounds were dissolved in DMSO and then diluted
in the bath solution. Cells were exposed to a single concentration
of drug. DMSO concentrations never exceeded 0.1% (by volume).
Effects of compounds on hERG current were assessed by a
voltage clamp protocol that stepped to -25, 0, 25, and 50 mV for
3 s, followed by a step to -50 mV for 4 s from a holding potential
of -80 mV once every 15 s. Current measurements were made at
36.5-37 °C. IC50 values were calculated from the effect of
compounds on hERG tail current at -50 mV corrected for run
down/DMSO vehicle effects.
(300 MHz, CDCl3) δ 1.72 (q, J ) 12.4 Hz, 1H), 1.73 (q, J ) 12.3
Hz, 1H), 2.17 (d, J ) 12.9 Hz, 2H), 2.39 (s, 3H), 2.56 (t, J ) 11.9
Hz, 2H), 3.25 (d, J ) 12.2 Hz, 2H), 3.27 (s, 2H), 3.58 (t, J ) 12.2
and 3.3 Hz, 1H), 6.57 (d, J ) 8.1 Hz, 1H), 7.17 (m, 4H), 8.27 (d,
J ) 6.4 Hz, 1H), 9.03 (s, 1H); MS (DCI/NH3) m/e 394 (M + H)+;
Anal. (C19H21Cl2N3O2‚1.3H2O) C, H, N.
N-(2-Methyl-5-chlorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-
2′H-[2,4′-bipyridine]-1′-yl)acetamide (7v) was prepared in the
same manner as compound 7a but with substitution of 2-bromo-
N-(5-chloro-2-methylphenyl)acetamide in place of 2-bromo-N-(m-
1
tolyl)acetamide (15 mg, 13% yield). H NMR (300 MHz, CDCl3)
δ 1.68-1.73 (m, 2H), 2.15-2.22 (m, 2H), 2.25 (s, 3H), 2.6 (t, J )
12 Hz, 2H), 3.05-3.18 (m, 2H), 3.22 (s, 2H), 3.50-3.60 (m, 1H),
7.05 (dd, J ) 6 and 3 Hz, 1H), 7.10 (d, J ) 9 Hz, 1H), 7.18-7.2
(m, 1H), 7.22-7.28 (m, 2H), 8.22 (d, J ) 6 Hz, 2H), 9.38 (br s,
1H); MS (DCI/NH3) m/e 360 (M + H)+; Anal. (C19H22ClN3O2‚
0.5H2O) C, H, N.
N-(2,4-Difluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tetrahydro-2′H-
[2,4′-bipyridine]-1′-yl)acetamide (7w) was prepared in the same
manner as compound 7a but with substitution of 2-bromo-N-(2,4-
difluorophenyl)acetamide in place of 2-bromo-N-(m-tolyl)acetamide
1
(1100 mg, 86% yield). H NMR (300 MHz, DMSO-d6) δ 1.50-
1.80 (m, 2H), 1.84-2.02 (m, 2H), 2.20-2.45 (m, 2H), 2.92-3.10
(m, 2H), 3.23-3.39 (m, 3H), 6.94-7.17 (m, 1H), 7.23-7.53 (m,
4H), 7.78-8.01 (m, 1H), 8.16-8.44 (m, 1H), 9.52-9.69 (m, 1H).
MS (DCI/NH3) m/e 332 (M + H - 16)+; 348 (M + H)+; Anal.
(C18H19N3O2F2) C, H, N.
Action Potential Duration Studies. Free-running canine cardiac
Purkinje fibers were removed and placed in a warmed (37 °C)
superfusion chamber (8-10 mL/min) and stimulated (2× threshold,
biphasic waveform, typically 1-2 ms in duration) by use of
platinum electrodes located in the chamber floor. Fibers were
N-(2-trifluoromethyl-4-fluorophenyl)-2-(1-oxy-3′,4′,5′,6′-tet-
rahydro-2′H-[2, 4′-bipyridine]-1′-yl)acetamide (7x) was prepared

7464 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 25
Patel et al.
Ro´nai, Z.; Nemoda, Z.; Gaszner, P.; Sasva´ri-Sze´kely, M.; Guttman,
A.; Kala´sz, H. Curr. Med. Chem. 2002, 9, 793. (f) Powell, S. B.;
Paulus, M. P.; Hartman, D. S.; Godel, T.; Geyer, M. A. RO-10-
5824 is a selective dopamine D4 receptor agonist that increases novel
object exploration in C57 mice. Neuropharmacology 2003, 44, 473-
481.
impaled with 3 M KCl-filled microelectrodes (resistance 10-30
MΩ), and electrical activity was monitored with high-input
impedance electrometers. Studies were initiated after a minimum
of 30 min in vitro equilibration with stimulation. Fibers were
considered suitable for study if the following criteria were satis-
fied: (a) the membrane potential just prior to the action potential
(AP) upstroke was more negative than -80 mV, (b) the AP duration
was between 300 and 500 ms, and (c) the normal automatic rate
did not exceed the stimulation cycle length. The AP duration was
defined as the interval between the maximum upstroke velocity
and 90% of repolarization (APD90). Fibers were exposed to two
concentrations of compounds, with electrophysiological effects at
each concentration evaluated at three different stimulation rates.
Fibers were paced in control bath solution (131 mM NaCl, 18 mM
NaHCO3, 1.8 mM NaH2PO4, 0.5 mM MgCl2, 5.5 mM dextrose, 4
mM KCl, and 2 mM CaCl2) for a minimum of 20 min at a basic
cycle length (BCL) of 2 s, then consecutively paced at 800 and
400 ms for at least 2 min at each rate to establish a baseline AP
recording. Following return to the stimulation BCL of 2 s,
superfusion with the lowest compound concentration was initiated.
After a 25 min drug equilibration period, APs were again obtained
at the three different stimulation rates. The protocol was then
repeated with the higher compound concentration.
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Supporting Information Available: Elemental analysis data
for the compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
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