The synthesis and biological evaluation of quinolyl-piperazinyl piperidines as potent serotonin 5-HT1A antagonists

Article abstract of DOI:10.1021/jm1000908

As part of an effort to identify 5-HT_1A antagonists that did not possess typical arylalkylamine or keto/amido-alkyl aryl piperazine scaffolds, prototype compound 10a was identified from earlier work in a combined 5-HT _1A antagonist/SSRI program. This quinolyl-piperazinyl piperidine analogue displayed potent, selective 5-HT_1A antagonism but suffered from poor oxidative metabolic stability, resulting in low exposure following oral administration. SAR studies, driven primarily by in vitro liver microsomal stability assessment, identified compound 10b, which displayed improved oral bioavailability and lower intrinsic clearance. Further changes to the scaffold (e.g., 10r) resulted in a loss in potency. Compound 10b displayed cognitive enhancing effects in a number of animal models of learning and memory, enhanced the antidepressant-like effects of the SSRI fluoxetine, and reversed the sexual dysfunction induced by chronic fluoxetine treatment.

Full text of DOI:10.1021/jm1000908

4066 J. Med. Chem. 2010, 53, 4066–4084
DOI: 10.1021/jm1000908
The Synthesis and Biological Evaluation of Quinolyl-piperazinyl Piperidines as Potent Serotonin
5-HT1A Antagonists
Wayne E. Childers, Jr.,*,† Lisa M. Havran,† Magda Asselin,† James J. Bicksler,† Dan C. Chong,† George T. Grosu,†
Zhongqi Shen,† Magid, A. Abou-Gharbia,†, Alvin C. Bach, III,† Boyd L. Harrison,† Natasha Kagan,† Teresa Kleintop,†
Ronald Magolda,†,^ Vasilios Marathias,† Albert J. Robichaud,† Annmarie L. Sabb,† Mei-Yi Zhang,† Terrance H. Andree,‡
Susan H. Aschmies,‡ Chad Beyer,‡ Thomas A. Comery,‡ Mark Day,‡ Steven M. Grauer,‡ Zoe A. Hughes,‡
Sharon Rosenzweig-Lipson,‡ Brian Platt,‡ Claudine Pulicicchio,‡ Deborah E. Smith,‡ Stacy J. Sukoff-Rizzo,‡
Kelly M. Sullivan,‡ Adedayo Adedoyin,§ Christine Huselton,§ and Warren D. Hirst‡
§
†Chemical Sciences, ‡Neuroscience, and Drug Safety and Metabolism, Pfizer Global Research and Development, CN-8000, Princeton,
New Jersey 08543-8000. Current Address: Molder Center for Drug Discovery Research, Temple University School of Pharmacy, Philadelphia,
Pennsylvania 19140. ^ Deceased.
Received January 21, 2010
As part of an effort to identify 5-HT1A antagonists that did not possess typical arylalkylamine or keto/
amido-alkyl aryl piperazine scaffolds, prototype compound 10a was identified from earlier work in a
combined 5-HT1A antagonist/SSRI program. This quinolyl-piperazinyl piperidine analogue displayed
potent, selective 5-HT1A antagonism but suffered from poor oxidative metabolic stability, resulting in
low exposure following oral administration. SAR studies, driven primarily by in vitro liver microsomal
stability assessment, identified compound 10b, which displayed improved oral bioavailability and lower
intrinsic clearance. Further changes to the scaffold (e.g., 10r) resulted in a loss in potency. Compound
10b displayed cognitive enhancing effects in a number of animal models of learning and memory,
enhanced the antidepressant-like effects of the SSRI fluoxetine, and reversed the sexual dysfunction
induced by chronic fluoxetine treatment.
Introduction
Several lines of evidence suggest that 5-HT1A receptors are
involved in learning and memory.4,5 The 5-HT1A receptor is
expressed in abundance in several brain regions thought to be
associated with learning and memory, such as the hippocam-
pus, frontal cortex, and septum.6 These receptors are poised to
modulate cholinergic neurotransmission via both direct and
indirect signaling. Postsynaptic 5-HT1A receptors provide
inhibitory tone to the cholinergic projections from the nucleus
basalis of Maynert to the frontal cortex and hippocampus.
Presynaptic 5-HT1A receptors in the dorsal raphe modulate
serotonergic neurotransmission to the prefrontal cortex
(where they control excitatory glutamatergic signals) and
the locus cerruleus (where they control adrenergic signaling).
A 5-HT1A antagonist would be expected to directly block
inhibitory tone in the nucleus basalis while, at the same time,
indirectly stimulate excitatory tone from the prefrontal cortex
and locus ceruleus via blockade of autoreceptors in the dorsal
raphe. The net result would be an increase in cholinergic
signaling from the nucleus basalis to the frontal cortex.
Consistent with this hypothesis, administration of 5-HT1A
antagonists enhanced glutamate and acetylcholine release.7-9
This enhancement on cholinergic neurotransmission corre-
lated with improvement in animal models of cognition.
5-HT1A antagonists have also been explored as potential
adjunctive therapies for selective serotonin reuptake inhibitor
(SSRI) antidepressants. SSRIs are extensively used to treat
depression. However, as a class, they suffer from a delayed
onset of antidepressant action10 and a number of side effects,
including sexual dysfunction.11 The delay in onset of clinical
a
The 5-HT1A receptor is arguably the most thoroughly
studied of all the serotonin receptor subtypes. A plethora of
information on this receptor has been generated since its
discovery in 19811 and subsequent cloning in 1988.2 The
receptor possesses a tertiary structure typical of 7-transmem-
brane G-protein coupled receptors (GPCRs), with multiple
sites for glycosylation and phosphorylation. It is located both
presynaptically, where it functions as an inhibitory somato-
dendritic autoreceptor and postsynaptically, where it also
functions as an inhibitory receptor. The rat 5-HT1A receptor
is 89% homologous to the human protein and resembles its
human counterpart both pharmacologically and in terms of
anatomical localization. The 5-HT1A receptor has been an
important drug discovery target in the brain for nearly two
decades and continues to attract attention.3
*To whom correspondence should be addressed. Phone: (215)-862-
0580. Fax: (732)-274-4505. E-mail: wchilders@yahoo.com.
a Abbreviations: 5-HT, 5-hydroxytryptamine; 8-OH-DPAT, 8-hydro-
xy-2-(di-n-propylamino)-tetralin; Aβ, beta-amyloid; AMP, adeonosine
monophosphate; APP, amyloid precursor protrein; BINAP, tetrakis-
(triphenylphosphino)-1,1-binapthyl; B/P, brain to plasma; CHO, Chi-
nese hamster ovary; CYMAP, dicyclohexylphosphine-20-(N,N-dime-
thylamino)-biphenyl; Emax, maximum enhancing effect level; GPCR,
G-protein coupled receptor; GTPγS, guanosine 50-O-[γ-thio]tripho-
sphate; HPLC, high pressure liquid chromatography; Imax, maximum
inhibitory effect level; MED, minimal effective dose; NADPH, nicoti-
namide adenine dinucleotide phosphate; OB, olfactory bulbectomy; PK,
pharmacokinetic; SAR, structure-activity relationship; SSRI, selective
serotonin reuptake inhibitor.
r
pubs.acs.org/jmc
Published on Web 05/05/2010
2010 American Chemical Society

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4067
Figure 2. Aryl-piperazine 5-HT1A antagonists and partial agonists.
Figure 1. Representative 5-HT1A antagonists.
efficacy is thought to occur because the high density of inhi-
bitory 5-HT1A autoreceptors in the target forebrain regions
compensates for the elevations in synaptic 5-HT induced by
acute SSRI treatment.12 Chronic SSRI treatment is required
to see positive effects and the 2-4 week delay in onset of
action is thought to represent the time needed for desensitiza-
tion of the autoreceptors to occur. Clinical evidence with
pindolol suggests that coadministration of a 5-HT1A antago-
nist may shorten this delay,13 although the data with pindolol
may be confounded by the compound’s β-adrenergic antago-
nist activity.14 There is conflicting clinical evidence regarding
whether 5-HT1A antagonistsmay be useful adjuctive therapies
for ameliorating SSRI-induced sexual dysfunction, but encou-
raging data from animal models is beginning to emerge.15
Selective 5-HT1A antagonists reported to date generally fall
into two structural classes. The first class (Figure 1) is the aryl
alkyl amines, exemplified by compounds like (S)-U-301 (1)
and robalzotan (2). The second structural class is the aryl
piperazines (Figure 1), represented by compounds like LY-
426965 (3) and WAY-100635 (4). We recently reported ontwo
potent, selective orally active 5-HT1A antagonists possessing
this moiety (Figure 2), lecozotan (5)16 and WAY-101405 (6).7
Similar aryl piperazine analogues (Figure 2), such as adatan-
serin (7)17 and BMY 7378 (8),18 display partial agonist
activity, especially in the dorsal raphe where the high degree
of receptor reserve seen for presynaptic 5-HT1A autoreceptors
amplifies small levels of intrinsic activity. One of the structural
features that may promote potent, full antagonist activity in
compounds3-6 isthe presence of a pendent aryl orheteroaryl
group located in proximity to the carbonyl moiety. The carbox-
amide grouping of compounds like 5-8 represents a poten-
tial site for metabolic hydrolysis and/or chemical instability.
In our continuing search for 5-HT1A antagonists, we explored
structural scaffolds that did not possess a carboxamide
moiety.
Figure 3. Recently identified 5-HT1A antagonists.
antagonists.22 These compounds, exemplified by 9 (Figure
3), displayed potent affinity for both the human serotonin
transporter (measured as displacement of [3H]-paroxetine)
and the human 5-HT1A receptor and a variety of intrinsic
activities in an in vitro functional model (inhibition of GTPγS
binding to the human 5-HT1A/G-protein complex). In the
course of prosecuting this series, wesynthesized the previously
undisclosed quinolyl-piperazinyl piperidine analogue 10a
(Figure 3). Compound 10a was surprisingly devoid of sero-
tonin transporter affinity yet maintained potent affinity and
full antagonist activity at the 5-HT1A receptor. To our know-
ledge, this compound represents one of the first potent, select-
ive aryl piperazine-based 5-HT1A antagonists that does not
possess an amide/ketone moiety. Previous work22 had shown
that substitution in the 6-position of the quinolylpiperazinyl
ring system was particularly favorable for producing com-
pounds that profiled in vitro as potent, full 5-HT1A anta-
gonists, so we kept the 6-methoxy group constant for the
purposes of the SAR studies that are the subject of this
manuscript.
Chemistry
Target compounds 10a-r were prepared by condensation
of 5-methoxy-7-(1-piperazinyl)quinoline 15 and appropriate
quinolinylpiperidinones 18a-r under reductive amination
conditions (Scheme 1).23
Compound 15 was synthesized in four steps (Scheme 2)
from3-chloro-4-aminophenol(11) ina sequence thatinvolved
a Skraup reaction24 to give 12, followed by methylation of the
phenol to provide 13. Treatment of 13 with a monoprotected
piperazine derivative under modified Buchwald-Hartwig
conditions25,26 afforded 14, which was deprotected to give
15. Required quinolinylpiperidones 18a-r were prepared by
deprotecting ketals 17a-r. Intermediates 17a-d and 17f-r
were obtained from 8-haloquinolines 16a-d and 16f-r, res-
pectively, by treatment with 1,4-dioxa-8-azaspiro[4,5]decane
More recently, compounds prepared as dual-acting 5-HT1A
antagonists/SSRIs have been reported.19 These compounds,
which often consist of combinations of 5-HT1A pharmaco-
phores and SSRI pharmacophores (see, for example, Hatzen-
buhler et al.20,21), do not possess all three structural features
inherent in selective 5-HT1A antagonists like 3-6 (i.e., the aryl
piperazine, the substituted amide/ketone, and the pendent
aryl/heteroaryl grouping). We recently disclosed our work
on a series of quinolylpiperazines as mixed SSRI-5-HT1A

4068 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
under modified Buchwald-Hartwig conditions (Scheme 3).
When the halogen leaving group was bromine, tetrakis-
(triphenylphosphino)-1,1-binapthyl (BINAP) was used as a
catalyst, whereas dicyclohexylphosphine-20-(N,N-dimethyl-
amino)-biphenyl (CYMAP) was preferred when the leaving
group was chlorine. Compound 17e was obtained by conden-
sation of 7,8-difluoroquinoline 16e with 1,4-dioxa-8-azaspiro-
[4,5]decane to give a mixture of protected piperidinones which
was separated by chromatography to yield the desired 7-
fluoro isomer (Scheme 4). The required haloquinolines 16a-r
were obtained from commercial sources or were prepared via
a variety of published methods from appropriatelysubstituted
commercially available haloanilines.
In Vitro Metabolism/Metabolite ID. Microsomal stability
was determined by incubating test compounds with rat or
human liver microsomes at 37 ꢀC for 20 min in the presence
of NADPH or a NADPH regenerating system. Structural
identification of microsomal metabolites was accomplished
by incubating test compounds with rat or human liver
microsomes at 37 ꢀC for 15 min in the presence of NADPH.
Concentrated supernatants were subjected to LC/MS/MS
analysis. Major components were isolated by HPLC, and
their structures were confirmed by NMR analysis.
In Vitro. 5-HT1A data were generated using membranes
from CHO cells stably transfected with the human 5-HT1A
receptor as previously described.7,27 Affinity for the human
5-HT1A receptor was assessed as the test compound’s ability
to inhibit binding of [3H]-8-OH DPAT. In vitro 5-HT1A
intrinsic activity was measured as the test compound’s ability
to block 8-OH DPAT-induced inhibition of forskolin-
stimulated increases in cyclic AMP. Data are expressed in
nM as IC50 values, with the maximum percent inhibition of
the 8-OH DPAT effect expressed as an Imax value. Com-
pounds with Imax values of 95-100 are considered to be full
Scheme 3a
Receptor Occupancy. In vivo receptor occupancy was
determined by measuring the displacement of [3H]-WAY-
100635 from rat hippocampus and cortex by test com-
pounds.7 The cerebellum was used as a reference tissue for
nonspecific binding of [3H]-WAY-100635 which, under the
present conditions, accounted for 15% to 18% of the total
binding.
Pharmacokinetics. The pharmacokinetic profile of test
compounds was asssessed in rats following a 1 mg/kg iv or
3 mg/kg po dose. Plasma or brain homogenate concentra-
tions were determined following protein precipitation with
acetonitrile by LC/MS/MS using an internal standard.
a Reagents and conditions: (i) for X = Cl, 1,4-dioxa-8-azaspiro-4,
5-decane, tert-butoxide, CYMAP, Pd2(dba)3; For X = Br, 1,4-dioxo-
8-azaspiro-4,5-decane, tert-butoxide, BINAP, Pd2(dba)3; (ii) 2N NCl/
diethyl ether.
Scheme 4a
Scheme 1a
a Reagents and conditions: (i) 1,4-dioxa-8-azaspiro-4,5-decane, 120
ꢀC; (ii) separation of 7- and 8-fluororegioisomers by flash chromato-
graphy; (iii) 2N HCl/diethyl ether.
a Reagents and conditions: (i) NaBH3CN, room temperature, over-
night.
Scheme 2a
a Reagents and conditions: (i) Fe2(SO4)3, glycerol, H3BO3, H2SO4, 150 ꢀC; (ii) CH3I, K2CO3; (iii) tert-butoxycarbonylpiperazine, sodium tert-
butoxide, CYMAP, Pd2(dba)3; (iv) 4N HCl/dioxane.

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4069
antagonists, while compounds with Imax values significantly
less than 100 are considered to be partial agonists.
potency for the5-HT1A receptor asthatseen withthe standard
5-HT1A antagonist 4 and showed no intrinsic activity in the
functional cyclic AMP-based assay. However, stability data
from rat and human microsomal preparations predicted that
the compound might not possess optimal pharmacokinetic
parameters. A rat PK study (Table 2) confirmed this assess-
ment. Administration of 10a was characterized by high clear-
ance and a short half-life. The peak plasma concentration
following a 3 mg/kg oral dose was moderate (in the range of
200-300 nM), although significant brain penetration was
seen following a 3 mg/kg intravenous dose (B/P = 2.8). A
study was undertaken to identify the potential sites of oxida-
tive metabolism. Compound 10a was incubated with rat and
human liver microsomes, and the major metabolites were
identified by LC/MS/MS and NMR. The results are summar-
ized in Figure 4. Minor metabolites in both species included
the des-methyl metabolite 19 and metabolites 20 and 21,
where hydroxylation had occurred on the piperidinyl group.
The major metabolite in both species was the 5-hydroxyqui-
nolyl derivative 22.
SAR studies were initiated to block metabolism on the
5-position of the quinoline appended to the piperidine group
(Table 1). Substituting the 5-position with a fluorine group (to
give compound 10b) retained potent 5-HT1A full antagonist
activity but resulted in only a marginal increase in stability in
the human microsomal assay. Substitutions in the 6- and
7-positions of the quinoline ring induced some degree of
intrinsic activity in the in vitro cAMP assay, suggesting that
these compounds were partial agonists. Surprisingly, even a
fluoro substituent in the 7-position resulted in a significant
loss in 5-HT1A affinity, suggesting the possibility of electronic
or torsional requirements for that region of the scaffold. As
with compound 10a, none of the analogues showed significant
5-HT uptake inhibitory activity.
In Vivo. In vivo microdialysis was used to confirm the
5-HT1A antagonist activity of test compounds by measuring
their effect on 5-HT release in the frontal cortex. The tech-
nique was also used to assess the effect of test compounds on
acetylcholine release in the hippocampus. The pro-cognitive
effects of test compounds were examined in a number of
animal models of learning and memory. The ability of test
compounds to enhance recognition memory was assessed
using a novel object recognition model. The Atlantis water
maze model was used to examine compound effects on
hippocampal-based spatial memory. Test compounds were
also evaluated for their ability to enhance contextual
memory in transgenic Tg2576 mice overexpressing a mutated
form of human amyloid precursor protein (APP) using a
contextual fear conditioning model.
In addition to assessment in a battery of cognitive tests,
compounds were examined for their ability to enhance the
antidepressant-like effects or inhibit the sexual dysfunction
side effects of the SSRI fluoxetine. In vivo microdialysis was
used to examine the effect of test compounds on fluoxetine-
induced 5-HT release in the rat frontal cortex. The ability of
compounds were evaluated for their ability to enhance
antidepressant-like behavioral effects induced by fluoxetine
was assessed using a rat olfactory bulbectomy model and
schedule-induced polydipsia, a model of obsessive/compul-
sive behavior. Finally, test compounds were examined for
their ability to inhibit the decrease in rat penile erections
caused by fluoxetine.
Results and Discussion
Compound 10a displayed a desirable in vitro pharmacolo-
gical profile (Table 1). The compound displayed similar
Another metabolite identification study was performed to
determine the sites of metabolism for 10b. The results are
summarized in Figure 5. Once again, des-methylation of the
methoxy group to give the metabolite 23 was a minor pathway
in rat and human microsomes. The major pathway involved
the formation of the 3-hydroxy derivative 26 via the 2,3-
dihydroxy metabolite 25. The formation of 25 was hypothe-
sized to occur through a proposed 2,3-epoxy intermediate 24.
The structure of 24 was tentatively assigned by LC/MS/MS,
but the metabolite was too unstable to be fully characterized
by NMR.
Table 1. SAR of the Quinoline “B”-Ring
5-HT1A
cAMP
IC50 Imax
(nM)a (%)a
microsomal t1/2 (min)
Ki
(nM)a
compd
R1
RLMb
HLMc
An effort was then undertaken to block this alternate
metabolic pathway. An initial SAR study examining the
effects of substitution on the “A”-ring of the quinoline in
the absence of the 5-fluoro substitutient was performed. The
results are summarized in Table 3. Compounds containing
typical leaving groups in the 2- and 4-position of the quinoline
ring were excluded to avoid potential side reactions. Substitu-
tion in the 2-position (e.g., compounds 10f and 10g) main-
tained good 5-HT1A potency and antagonist activity,
4d
0.9
0.40
0.40
3.4
7.1
3.9
100
100
100
82
>1
2
>1
3
10a
10b
10c
10d
10e
H
5-F
6-F
6-Br
7-F
2.7
2
6
46.5
10
2
4
0.61
276
73
61
2
2
331
3
3
a Data are the results of at least three repetitions. b RLM = rat liver
microsomes. c HLM = human liver microsomes. d Data taken from
Childers, W. E., et al.53
Table 2. PK Parameters of Compounds 10a, 10b, and 10ra
1 mg/kg (iv)
3 mg/kg (po)
CL (mL/min/kg)
V
ss (L/kg)
Cmax (ng/mL)
Tmax (h)
T1/2 (h)
AUC (h ng/mL)
3
F (%)
B/P
10a
10b
10r
38.7
15.0
9.0
2.8
2.6
2.5
130
247
417
1.0
0.8
2.0
1.2
1.1
4.8
360
472
27
33
60
2.8
1.3
0.2
3758
a CL = intrinsic clearance;Vss = volume ofdistribution. AUC= calculatedarea under the curve fromt = 0 tot = ¥; F(%) = percent bioavailability
following oral administration. B/P = brain to plasma ratio.

4070 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
Figure 4. Microsomal metabolism of compound 10a.
Figure 5. Microsomal metabolism of compound 10b.
although the potency in the functional assay was around 10-
fold lower that that seen with the unsubstituted analogue 10a.
Substitution of fluorine in the 3-position of the “A”-ring
retained antagonist activity, but larger groups in the 3- and
4- positions of the “A”-ring (compounds 10i-k) imparted
partial agonist activity. Results with 2,4-bis substitution were
variable, with the dimethyl analogue 10l profiling as a full
antagonist and the 2-trifluoromethyl-4-methoxy derivative
10m showing partial agonist activity. It was not expected that
“A”-ring substitution would dramatically increase metabolic
stability, given likelihood of hydroxylation on the 5-position.
Nevertheless, some encouraging results were obtained with
3- and 2,4-bis substitution (compounds 10j and 10m, res-
pectively) where increases in stability were seen in human
microsomal preparations.
Finally, the effects of “A”-ring substitution in the pre-
sence of the 5-fluoro group were examined (Table 4).
Substitution in the 2-position did little to improve meta-
bolic stability. Substitution in the 3-position could en-
hance stability in both rat and human microsomes,
although the size of the substituent influenced its impact.
The 3-trifluoromethyl derivative 10o showed an increase
in stability while the 3-fluoro analogue 10p was not
particularly stable. Unfortunately, as with the des-fluoro
compounds 10i and 10j, the 3-substituted 5-fluoro analo-
gues profiled as partial agonists. Compounds with sub-
stituents in the 2- and 4-positions profiled as antagonists,
and an appropriate choice of metabolically stable substit-
uents (such as those seen in 10r) led to a compound with
enhanced stability in both rat and human microsomal

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4071
preparations. As with the B-ring substituted analogues,
A-ring substituted derivatives showed no inhibitory activity
on 5-HT uptake.
To assess intrinsic activity in vivo, compounds 10b and 10r
wereexaminedfor theireffectsonrat corticalserotoninrelease
in a series of microdialysis studies (Figure 6). Previous studies
have shown that this assay is sensitive to small degrees of
5-HT1A intrinsic activity.28 In this assay, the full 5-HT1A
agonist 8-OH-DPAT induced a significant decrease in extra-
cellular 5-HT levels through its action on presynaptic 5-HT1A
autoreceptors. When doses were at 10 mg/kg po, compounds
10b and 10r had no effect on extracellular 5-HT levels on their
own. However, pretreatment with 10b (P = 0.049) or 10r
(P = 0.048) completely blocked the effect of 8-OH-DPAT.
These data are indicative of full antagonist activity, and the
results are similar to those obtained with other 5-HT1A
antagonists.7,16
Table 3. SAR of the Quinoline “A”-Ring
microsomal
5-HT1A
cAMP
IC50 Imax
(nM)a (%)a RLMb HLMc
t1/2 (min)
Ki
(nM)a
compd
R2
Animal Models of Cognition
4d
0.9
7.1
47
23
5.6
5.9
30
100
100
100
100
78
<1
<1
2
<1
3
A 5-HT1A antagonist would be expected to enhance learn-
ing andmemoryby enhancing cholinergic(and glutamatergic)
neurotransmission.29 We have previously shown that systemic
administration of 5-HT1A antagonists can enhance the release
of both glutamate9 and acetylcholine7,9 in brain regions
known to degenerate in Alzheimer’s disease. As a representa-
tive of the series, compound 10b was examined for its effects
onmodulating acetylcholine levels using in vivomicrodialysis.
The results are presented in Figure 7. A 10 mg/kg oral dose of
10b caused a significant increase in the level of acetylchloine in
the rat dorsal hippocampus. The pharmacodynamic effect of
10b correlatedwithitsplasmaPKprofile, achieving maximum
effect at around 40 min postadministration and lasting for
approximately 2-3 h. These data suggest that the brain PK
profile for 10b tracks closely with that seen in the plasma.
Compounds 10b and 10r were considered for more detailed
profiling. The lower potency of 10r relative to 10b, coupled
10f
10g
10h
10i
10j
10k
10l
10m
2-CH3
2-CF3
0.54
1.8
3
3-F
3-CH3
0.79
0.46
1.2
2
2
2
2
3-CF3
4-CH3
44
85
4
10
2
0.61
0.63
2.1
1.4
4.8
2
2,4-CH3
2-CF3 4-OCH3
98
78
4
<1
13
30
4
a Data are the results of at least three repetitions. b RLM = rat liver
microsomes. c HLM = human liver microsomes. d Data taken from
Childers, W. E. et al.53
Table 4. SAR of 5-Fluoroquinolylpiperazine Analogues
microsomal
t1/2 (min)
5-HT1A
cAMP
Ki
(nM)a
IC50
(nM)a
Imax
(%)a
compd
R2
RLMb
HLMc
4d
0.9
3.6
7.1
7.0
15
100
100
34
>1
3
>1
3
10n
10o
10p
10q
10r
2-CF3
3-CF3
3-F
0.87
0.47
177
2.0
9
27
5
20
54
<1
3
2,4-CH3
2-CF3
4-OCH3
2.8
9.1
100
94
3
15
12
a Data are the results of at least three repetitions. b RLM = rat liver
microsomes. c HLM = human liver microsomes. d Data taken from
Childers, W. E., et al.53
Figure 7. Effect of compound 10b (10 mg/kg po) on rat hippocam-
pal acetylcholine levels.
Figure 6. Effect of compounds 10b and 10r (10 mg/kg po) on rat cortical 5-HT levels.

4072 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
Figure 8. (a) Effect of 10b novel object recognition; (b) receptor occupancy of 10b in rat cortex and hippocampus.
Figure 9. Reversal of MK-801-induced deficit in novel object
recognition by 10b.
Figure 10. Reversal of scopolamine-induced deficit in novel object
recognition by 10b.
withsolubility issues andlower CNS penetration (likelydue to
the compound’s increased lipophilicity, data not shown), led
us to deprioritize 10r. Compounds 10b was therefore profiled
for its effect in the novel object recognition test, a memory test
based on exploratory activity.30 Animals are allowed to
explore a pair of identical objects (training) and then returned
to their home cages. After a period of time, the animals are
presented with one previously explored “familiar” object and
an unexplored “novel”object”. The animal will spontaneously
explore the novel object more than the familiar one. Memory
for the familiar object is recorded as greater time spent
exploring the novel object. When the time between training
and the trial is increased to 48 h, the animal no longer
remembers the familiar object and will spend equal amounts
of time exploring both objects during the trial. Compounds
10b was able to reverse the time-induced cognitive deficit, with
the MED (minimal effective dose) for 10b being 0.3 mg/kg po
(Figure 8). Compound 10b was effective in this model when
receptor occupancy was in the 20-30% range. A selectivity
profile (NovaScreen) for compound 10b (data not shown)
revealed that the compound had no significant affinity for 55
receptors, ion channels transporters, and enzyme binding sites
at concentrations up to 1 uM, supporting the assertion that
the compound’s pro-cognitive efficacy in this model, even at
relatively low receptor occupancy, was due to its 5-HT1A
antagonist activity.
Figure 11. Cognitive-enhancing synergy of 10b and donepazil in
novel object recognition.
10b coadministered with a subeffective dose of the clinically
used acetylcholinesterase inhibitor donepazil reversed the
48 h delay-induced deficit (Figure 11), suggesting a possible
synergy between the two mechanisms.
The impressive in vivo potency of compound 10b in the
novel object recognition model encouraged us to test the
compound in additional cognition models. 10b was evaluated
in the Atlantis water maze, a hippocampal-dependent spatial
memory task (Figure 12).31 In this variation of the classic
water maze test, animals do not have ready access to the
escape platform but must spend a predetermined amount of
“dwell time” in a “trigger zone”, which encompasses the spot
in which a pneumatically activated platform rises from the
bottom of the water tank. Increasing dwell times over training
sessions is a way to nonpharmacologically increase the diffi-
culty of the task, thus providing for an expanded window to
see improvements with test compounds. On the first training
day, vehicle- and drug-treated rats (3 and 10 mg/kg po) lear-
ned the location of the escape platform, using the extra-maze
Memory deficits in the novel object recognition model can
also be induced by treatment with a glutamatergic antagonist
like MK-801 (dizocilpine) or a cholinergic antagonist like
scopolamine prior to training. Compound 10b was able to
reverse both the MK-801-induced deficit (Figure 9) and the
scopolamine-induced deficit (Figure 10), with MED values of
1.0 mg/kg po (P < 0.05) and 0.3 mg/kg po (P < 0.05),
respectively. In addition, a subeffective dose of compound

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4073
Figure 12. Cognitive enhancing effects of 10b in the Atlantis water maze model: (a) training/dosing schedule; (b) training phase; (c) memory
trials.
cues, from trial 1 to trial 4, as reflected by the progressive
decrease in the mean escape latency (Figure 12b). As the task
became progressively more demanding on the subsequent
days, when the dwell time over the trigger zone increased to
2 s and then to 3 s, the vehicle and 3 mg/kg groups found it
harder to locate the platform. In contrast, the 10 mg/kg po
group demonstrated an improvement by trial 4 (P’s =
0.009-0.015), or earlier, demonstrating a positive effect on
the encoding of spatial memory. There was not significant
effect of drug treatment on swim speed (data not shown). The
retention of this memory was assessed in a drug-free probe test
conducted 5 days after the conclusion of acquisition training.
Animals were placed back in the water maze without the
platform. As can be seen in Figure 12c, the group treated with
Figure 13. Cognitive enhancing effect of 10b on contextual mem-
ory in Tg2576 mice.
10 mg/kg po of compound 10b spent significantly greater
percentage of time in the previously targeted zone than
vehicle- or 3 mg/kg-treated animals (P=0.0003).
Animal Models of Depression
Our next goal was to assess the potential efficacy of
compound 10b in a cognition model with at least some of
the hallmarks of Alzheimer’s disease present. Tg2576 mice
overexpress a mutated form of APP and show increased
Aβ40 and Aβ42/43 and plaque deposition at 9-12 months of
age.32 These animals display behavioral deficits that corre-
late with soluble β-amyloid species, which may be one of the
contributing factors to cognitive decline and neurodegene-
ration in Alzheimer’s patients. Dineley and co-workers
reported that Tg2576 mice show hippocampal-dependent
conditioning deficits beginning at 20 weeks of age.33 These
deficits can be monitored using a contextual fear condition-
ing (CFC) model in which animals are trained to associate a
mild foot shock with an auditory cue (the context) and then
later display memory for the context by freezing when
presented with the auditory cue in the absence of the
shock.34 As can be seen in Figure 13, compound 10b, when
administered 1 h prior to training, was able to improve
contextual memory in the CFC model, with an MED of
0.3 mg/kg po (P < 0.05).
Although currently available SSRIs like fluoxetine acutely
inhibit the 5-HT transporter and elevate 5-HT levels in
midbrain regions, there is little or no elevation of 5-HT in
desired target forebrain regions until an adaptive desensitiza-
tion of the inhibitory 5-HT1A autoreceptors has occurred.35
This delayed effect on forebrain 5-HT is thought to contribute
to the delayed onset of clinical efficacy suffered by SSRIs like
fluoxetine.12 It has been hypothesized that cotherapy of a
5-HT1A antagonist with an SSRI might maximize serotoner-
gic function by inhibiting feedback inhibition of neuronal
firing and immediately increasing synaptic levels of 5-HT in
the forebrain regions. In support of this hypothesis, acute
treatment with fluoxetine had no significant effect on cortical
5-HT levels.36 Chronic fluoxetine treatment was required to
increase forebrain 5-HT, and these increases correlated with
desensitization of 5-HT1A autoreceptors in the dorsal raphe.37,38
However, cotreatment with the 5-HT1A antagonist 4 accele-
rated the fluoxetine-induced increases in cortical 5-HT. These
neurochemical effects seem to correlate behaviorally, at least

4074 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
in some models. For example, cotreatment with 4 accelerated
the antidepressant-like effect of the SSRI paroxetine in the rat
olfactory bulbectomy model.39
had no effect on drinking alone. However, compound 10b
dose-dependently inhibited adjunctive water intake when
coadministered with the subefffective dose of fluoxetine, with
an MED value of 3 mg/kg po in this study (P < 0.001).
The rat olfactory bulbectomy (OB) model has been widely
used to profile potential antidepressant agents.42 In this
model, bilateral removal of the olfactory bulbs results in a
characteristic increase in locomotor activity. Many of the
neurochemical, endocrine, and immunological changes indu-
ced in this model correspond with those seen in clinical
depression. Treatment with many classes of antidepressant
agents, including SSRIs, result in a reduction in OB-induced
hyperlocomotor activity. However, chronic treatment with
the antidepressant agent is required for efficacy, which corre-
lates withthe typical delayed onset of actionseen inthe clinical
setting. For example, 14 days of treatment is required to see
efficacy in this model with fluoxetine. Co-treatment with 4 has
been shown to accelerate the antihyperlocomotor effect seen
with the SSRI paroxetine in the OB model.
We therefore examined the effects of compound 10b on
fluoxetine-induced 5-HT release in the rat frontal cortex using
in vivo microdialysis (Figure 14). Treatment with 10b alone
had no effect on cortical 5-HT levels. As expected, acute
fluoxetine treatment had no significant effect on cortical
5-HT levels. However, coadministration of 10b (10 mg/kg
po) together with fluoxetine resulted in an immediate, signi-
ficant increase in cortical 5-HT, which peaked at around
120% over baseline (P=0.02).
Schedule-induced polydipsia has been used as a model of
obsessive compulsive behavior and is responsive to treatment
with SSRIs like fluoxetine.40 When food pellets are delivered
to rats on a schedule of one every two minutes for a period of
two hours, the animals will develop a repetitive drinking
behavior resulting in consumption of water that is 5-10-fold
greater than baseline levels. Chronic treatment with fluoxetine
prior to the trial inhibits this obsessive drinking behavior, and
it has been shown that cotreatment with 4 can accelerate this
activity.41 To examine the potential enhancing effects of 10b
on fluoxetine in this model, an initial dose-response study
was performed with fluoxetine (Figure 15a). A 5.6 mg/kg ip
dose of fluoxetine was shown to have no significant effect. A
dose-response with compound 10b in combination with a 5.6
mg/kg ip dose of fluoxetine was then performed. As can been
seen from Figure 15b, a 10 mg/kg po dose of compound 10b
Compound 10b was assessed for its enhancing effects on a
subeffective dose of fluoxetine in the OB model (Figure 16).
Bulbectomy resulted in an approximately 25% significant
increase in locomotor activity compared to sham-surgery con-
trol animals when evaluated beginning at 14 days postsurgery.
Figure 14. 10b enhances the acute effect of fluoxetine on rat cortical
5-HT levels.
Figure 16. 10b (10 mg/kg po) enhances the antidepressant-like
effect of fluoxetine on olfactory bulbectomized rats.
Figure 15. 10b enhances the effect of fluoxetine on adjuvant drinking in schedule-induced polydipsia: (a) fluoxetine dose-response; (b) effect
of 10b/fluoxetine combination on SIP.

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4075
A dose-response curve (data not shown) identified a 5.6 mg/
kg ip dose given once daily for 7 days as a subeffective dose of
fluoxetine. This dose produced a small, nonsignificant decre-
ase in locomotor activity compared to treatment with vehicle
in bulbectomized rats. A 7-day cotreatment with fluoxetine
(5.6 mg/kg ip) and 10b (10 mg/kg po) provided a significant
reduction in locomotor activity, returning the total distance
moved back to sham control levels (P < 0.05).
Sexual dysfunction is one of the leading causes of anti-
depressant discontinuation.11 The role of 5-HT1A receptors in
sexual function is still poorly understood, but a small number
of clinical trials have demonstrated an improvement in SSRI-
induced sexual dysfunction by treatment with the 5-HT1A
partial agonist buspirone.43,44 That data, coupled with the
recent clinical report of failure of the 5-HT1A agonist VML-
670 to ameliorate SSRI-induced sexual dysfunction,45 suggest
that the 5-HT1A antagonist-like properties of buspirone may
contribute to the compound’s beneficial effects on SSRI-
induced sexual dysfunction.
We recently reported on a rat noncontact penile erection
model of sexual dysfunction46 and demonstrated that either
chronic or acute cotreatment with 5-HT1A antagonists ame-
lioratethefluoxetine-induced decrease in erectionsseeninthat
model.47 Compound 10b was examined in this model (see
Supporting Information). Following 14 day treatment, fluox-
etine (10 mg/kg ip, once daily) produced a 54% decrease in the
number of noncontact penile erections relative to vehicle
treated controls. Compound 10b (10 mg/kg po), when admi-
nistered either acutely on day 14 or chronically with fluoxetine
on days 1-14, reversed the SSRI-induced decrease in non-
contact penile erections, returning them essentially to sham
control levels. By itself, compound 10b had no effect on
noncontact penile erections.
INOVA spectrometer. The chemical shifts (δ) are reported in
parts per million (ppm) downfield from zero relative to the resi-
dual chloroform signal (7.26 ppm) or DMSO signal (2.49 ppm).
Coupling constants are reported in hertz (Hz), and the exchange-
able protons from HCl are not reported. Mass spectra were
recorded on either a Hewlett-Packard 5995A, a Finnigan Trace
MS, or a Micromass LCT spectrometer. Purity of tested com-
pounds was assessed by reversed-phase high pressure liquid
chromatography on a C18 column using two separate solvent
systems: (1) A, 10 mM ammonium bicarbonate in water (pH 9.5),
B, 50:50 acetonitrile:methanol, gradient of 85/15 A/B to 5/95 A/B
over 2 min; (2) A, 10 mM ammonium formate in water (pH 3.5),
B, 50:50 acetonitrile:methanol, gradient of 85/15 A/B to 5/95 A/B
over 2 min. Detection was performed by UV analysis at both 215
and 254 nm. All compounds were shown to be >95% pure.
Structures were confirmed by high resolution mass spectrometry
on an Agilent TOF instrument. Unless otherwise noted below,
reagents were obtained from commercial sources and were used
without further purification. Chromatographic purifications
were performed by flash chromatography using Baker 40 μm
silica gel. Some of the procedures described below were originally
presented in the patent literature.23
General Chemical Procedures. The synthesis of 10a illus-
trates the general procedure used to prepare compounds
10a-r.
6-Methoxy-8-{4-[1-(8-quinolinyl)-4-piperidinyl]-1-piperazinyl}-
quinoline Trihydrochloride (10a). To a solution of 15 (0.250 g,
1.03 mmol) in methanol (15 mL) was added 18a (0.279 g, 1.023
mmol) followed by sodium cyanoborohydride (0.126 g, 2.00
mmol). The resulting reaction mixture was stirred at room
temperature overnight. The reaction mixture was concentrated
on a rotary evaporator and the residue taken up in ethyl acetate.
The organic layer was washed with water, dried over anhydrous
sodium sulfate, filtered, and concentrated on a rotary evapora-
tor. The resulting residue was purified by flash chromatography
on silica gel (5% methanol/ethyl acetate) to give the desired
product, which was dissolved in methanol and treated with
excess 2N HCl in diethyl ether to afford the trihydrochloride
salt (0.229 g, 40% yield) as a yellow solid: mp=241-243 ꢀC. 1H
NMR (DMSO-d6) δ 9.15 (d, J=4.2 Hz, 1H), 8.95 (d, J=4.0 Hz,
1H), 8.88 (d, J=6.6 Hz, 1H), 8.85-8.93 (m, 1H), 7.97 (d, J=7.8
Hz, 1H), 7.88-7.95 (m, 2H), 7.82-7.93 (m, 2H), 7.78 (d, J=7.9
Hz, 1H), 7.60 (s, 1H), 3.92 (s, 3H), 3.70-3.98 (m, 2H), 3.39-3.78
(m, 9H), 3.12 (t, J=13.7 Hz, 2H), 2.40-2.52 (m, 2H), 2.25-2.90
(m, 2H). MS (ESIþ) (m/z) 454 ([M þ H]þ).
Conclusion
SAR around prototype compound 10a led to the identifica-
tion of a series of quinolyl-piperazinyl piperidines that dis-
played potent 5-HT1A antagonist activity. Stability in rat and
human liver microsomes was used as a predictive screen to
help guide the SAR directed at enhancing metabolic stability.
Identification of the primary paths of oxidative metabolism
was crucial to the success of this effort. Unfortunately,
structural changes that significantly improved metabolic sta-
bility also decreased in vitro affinity and potency and led to a
reduction in CNS penetration. Compound 10b displayed
potent 5-HT1A antagonist activity both in vitro and in vivo
and was selected for detailed profiling. The compound stimu-
lated acetylcholine release in the rat frontal cortex and
displayed cognitive enhancing activity in a number of animal
models of learning and memory, including a contextual fear
conditioning model in transgenic Tg2576 mice. In addition,
compound 10b was able to accelerate the antidepressant-like
neurochemical and behavioral effects of fluoxetine and to
reverse the sexual dysfunction induced by chronic fluoxetine
treatment in a rat noncontact penile erection model. Despite
the limited metabolic stability seen for 10b, successful deve-
lopment of sustained release formulations48,49 has allowed us
to advance the compound to phase 1 clinical trials.
The following compounds were prepared using a similar
procedure.
5-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl} Quinoline Trihydrochloride (10b). Prepared from 15
and 18b in 56% overall yield and obtained as a yellow solid:
mp=226-230 ꢀC. 1H NMR (DMSO-d6) δ 9.04 (dd, J1=4.3 Hz,
J2=1.6 Hz, 1H), 8.92 (d, J=3.7 Hz, 1H), 8.65-8.78 (m, 1H),
8.54 (dd, J1 = 7.5 Hz, J2 = 1.2 Hz, 1H), 7.76-7.88 (m, 1H),
7.66-7.74 (m, 1H), 7.35-7.50 (m, 2H), 7.30-7.43 (m, 1H),
7.16-7.26 (m, 1H), 3.91 (s, 3H), 3.84-3.95 (m, 2H), 3.57-3.88
(m, 6H), 3.43-3.58 (m, 1H), 3.42 (t, J=12.1 Hz, 2H), 2.96-3.13
(m, 2H), 2.30-2.42 (m, 2H), 2.18-2.32 (m, 2H). MS (ESIþ)
(m/z) 472 ([M þ H]þ).
6-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl} Quinoline Trihydrochloride (10c). Prepared from 15
and 18c in 41% overall yield and obtained as a yellow solid:
mp=222-225 ꢀC. 1H NMR (DMSO-d6) δ 8.85-8.98 (m, 2H),
8.60-8.73 (m, 1H), 8.38 (d, J=8.3 Hz, 1H), 7.74-7.85 (m, 1H),
7.59 (dd, J1 = 8.4 Hz, J2 = 4.4 Hz, 1H), 7.25-7.42 (m, 2H),
7.06-7.24 (m, 2H), 4.09 (d, J = 11.3 Hz, 2H), 3.91 (s, 3H),
3.54-3.80 (m, 5H), 3.28-3.52 (m, 4H), 2.84 (t, J=11.6 Hz, 2H),
2.25-2.37 (m, 2H), 2.07-2.21 (m, 2H). MS (ESIþ) (m/z) 472
([M þ H]þ).
Experimental Section
Melting points were recorded on a Thomas-Hoover capillary
melting point apparatus and are uncorrected. 1H NMR spectra
were recorded on a Varian Unity Plus 400 or a Varian 500 Unity
6-Bromo-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl} Quinoline Trihydrochloride (10d). Prepared from 15

4076 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
and 18d in 47% overall yield and obtained as a yellow solid:
mp=230-234 ꢀC. 1H NMR (DMSO-d6) δ 8.83-8.94 (m, 2H),
8.62-8.74 (m, 1H), 8.35 (dd, J1=8.4 Hz, J2=1.3 Hz, 1H), 7.84
(d, J=1.8 Hz, 1H), 7.73-7.84 (m, 1H), 7.58 (dd, J1=8.3 Hz, J2=
4.3 Hz, 1H), 7.25-7.37 (m, 1H), 7.27 (m, 1H), 7.03-7.12 (m,
1H), 4.07 (d, J=11.1 Hz, 2H), 3.90 (s, 3H), 3.58-3.82 (m, 6H),
3.39-3.53 (m, 1H), 3.30-3.42 (m, 2H), 2.85 (t, J=11.6 Hz, 2H),
2.25-2.35 (m, 2H), 2.05-2.19 (m, 2H). MS (ESIþ) (m/z) 533
([M þ H]þ).
(dd, J1=8.2 Hz, J2=1.7 Hz, 1H), 7.62 (d, J=7.8 Hz, 1H), 7.46 (t,
J=8.0 Hz, 1H), 7.25-7.38 (m, 1H), 7.1-7.24 (m, 2H), 6.82 (s,
1H), 6.70-6.78 (m, 1H), 4.09 (d, J=11.7 Hz, 2H), 3.90 (s, 3H),
3.40-3.61 (m, 5H), 3.08-3.20 (m, 4H), 2.82 (t, J=11.5 Hz, 2H),
2.68 (s, 3H), 2.02-2.19 (m, 4H). MS (ESIþ) (m/z) 468 ([M þ
H]þ).
8-{4-[4-(6-Methoxyquinolin-8-yl)piperazin-1-yl]piperidin-1-yl}-
2,4-dimethylquinoline Trihydrochloride (10l). Prepared from 15
and 18l in 52% overall yield and obtained as a yellow solid: mp=
240-244 ꢀC. 1H NMR (DMSO-d6) δ 8.83 (d, J=4.4 Hz, 1H),
8.58 (d, J=8.2 Hz, 1H), 8.07 (d, J=7.8 Hz, 1H), 7.81-7.90 (m,
2H), 7.78 (s, 1H), 7.70-7.77 (m, 1H), 7.26 (d, J=1.7 Hz, 1H),
7.15 (d, J=2.1 Hz, 1H), 3.89 (s, 3H), 3.85 (d, J=11.5 Hz, 2H),
3.55-3.78 (m, 6H), 3.40-3.50 (m, 2H), 3.28-3.37 (m, 1H), 3.04
(t, J=11.6 Hz, 2H), 2.95 (s, 3H), 2.84 (s, 3H), 2.20-2.43 (m, 4H).
MS (ESIþ) (m/z) 482 ([M þ H]þ).
7-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl} Quinoline Trihydrochloride (10e). Prepared from 15
and 18e in 50% overall yield and obtained as a yellow solid:
mp=214-217 ꢀC. 1H NMR (DMSO-d6) δ 9.03-9.12 (m, 1H),
8.87-8.96 (m, 1H), 8.42-8.54 (m, 1H), 7.90-8.02 (m, 1H),
7.65-7.80 (m, 1H), 7.54-7.72 (m, 3H), 7.12-7.23 (m, 1H),
6.95-7.045 (m, 1H), 3.88 (s, 3H), 3.40-4.03 (m, 10H),
3.36-3.52 (m, 1H), 3.26-3.41 (m, 2H), 2.40-2.57 (m, 2H),
2.15-2.25 (m, 2H). MS (ESIþ) (m/z) 472 ([M þ H]þ).
4-Methoxy-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl}-2-(trifluoromethyl)-quinoline Trihydrochloride (10m).
Prepared from 15 and 18m in 37% overall yield and obtained as
a yellow solid: mp = 244-248 ꢀC. 1H NMR (DMSO-d6) δ
8.81-8.86 (m, 1H), 8.50-8.62 (m, 1H), 7.75 (d, J = 7.5 Hz,
1H), 7.56 (t, J=7.9, 1H), 7.36 (s, 1H), 7.28 (d, J=7.6 Hz, 1H),
7.20-7.29 (m, 1H), 7.06-7.13 (m, 1H), 4.10 (s, 3H), 3.75-4.15
(m, 5H), 3.89 (s, 3H), 3.70 (d, J=11.2 Hz, 2H), 3.42-3.62 (m,
2H), 3.24-3.38 (m, 2H), 2.82 (t, J=11.8 Hz, 2H), 2.27-2.38 (m,
2H), 1.98-2.12 (m, 2H). MS (ESIþ) (m/z) 552 ([M þ H]þ).
5-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl}-2-(trifluoromethyl)-quinoline Trihydrochloride (10n).
Prepared from 15 and 18n in 46% overall yield and obtained as a
yellow solid: mp=239-241 ꢀC. 1H NMR (DMSO-d6) δ 8.92 (d,
J=4.5 Hz, 1H), 8.67-8.80 (m, 1H), 8.71 (d, J=7.9 Hz, 1H), 8.02
(d, J=8.7 Hz, 1H), 7.80-7.91 (m, 1H), 7.50 (t, J=8.8 Hz, 1H),
7.37 (s, 1H), 7.16-7.30 (m, H), 4.00 (d, J=12.1 Hz, 2H), 3.91 (s,
3H), 3.57-3.73 (m, 6H), 3.40-3.55 (m, 1H), 3.33-3.43 (m, 2H),
2.84 (t, J=11.5 Hz, 2H), 2.30-2.40 (m, 2H), 2.00-2.14 (m, 2H).
MS (ESIþ) (m/z) 540 ([M þ H]þ).
8-{4-[4-(6-Methoxyquinolin-8-yl)piperazin-1-yl]piperidin-1-yl}-
2-methylquinoline Trihydrochloride (10f). Prepared from 15 and
18f in 58% overall yield and obtained as a yellow solid: mp=
235-237 ꢀC. 1H NMR (DMSO-d6) δ 8.87 (d, J=2.2 Hz, 1H),
8.61-8.75 (m, 2H), 7.90 (d, J=8.3 Hz, 1H), 7.65-7.83 (m, 4H),
7.37 (D, J=2.0 Hz, 1H), 7.22 (d, J=1.9 Hz, 1H), 3.92 (s, 3H),
3.72-3.83 (m, 2H), 3.42-3.76 (m, 7H), 3.33 (t, J=10.9 Hz, 2H),
3.07-3.19 (m, 2H), 2.58-2.79 (m, 4H). MS (ESIþ) (m/z) 468
([M þ H]þ).
8-{4-[4-(6-Methoxyquinolin-8-yl)piperazin-1-yl]piperidin-1-yl}-
2-(trifluoromethyl) Quinoline Trihydrochloride (10g). Prepared
from 15 and 18g in 39% overall yield and obtained as a yellow
solid: mp=245-248 ꢀC. 1H NMR (DMSO-d6) δ 8.81-8.85 (m,
1H), 8.53-8.63 (m, 2H), 7.92 (d, J=8.5 Hz, 1H), 7.67-7.74 (m,
1H), 7.60-7.66 (m, 2H), 7.30 (dd, J1=8.2 Hz, J2=4.1 Hz, 1H),
7.25-7.29 (m, 1H), 7.07-7.11 (m, 1H), 4.12 (d, J=11.2 Hz, 2H),
3.89 (s, 3H), 3.70-3.81 (m 2H), 3.41-3.79 (m, 5H), 3.25-3.38
(m, 2H), 2.35 (t, J=1.2 Hz, 2H), 2.30-2.39 (m, 2H), 2.04-2.10
(m, 2H). MS (ESIþ) (m/z) 522 ([M þ H]þ).
5-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl}-3-(trifluoromethyl)-quinoline Trihydrochloride (10o).
Prepared from 15 and 18o in 40% overall yield and obtained as a
yellow solid: mp=239-243 ꢀC. 1H NMR (DMSO-d6) δ 9.26 (d,
J=2.1 Hz, 1H), 8.85-8.93 (m, 1H), 8.79 (s, 1H), 8.86-8.71 (m,
1H), 7.70-7.85 (m, 1H), 7.50 (t, J=8.9 Hz, 1H), 7.36 (dd, J1=
8.5 Hz, J2=5.3 Hz, 1H), 7.25-7.33 (m, 1H), 7.10-7.20 (m, 1H),
3.93 (d, J = 11.8 Hz, 2H), 3.90 (s, 3H), 3.52-3.88 (m, 6H),
3.38-3.54 (m, 1H), 3.30-3.42 (m, 2H), 2.83 (t, J=11.7 Hz, 2H),
2.25-2.41 (m, 2H), 2.04-2.18 (m, 2H). MS (ESIþ) (m/z) 540
([M þ H]þ).
3-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl} Quinoline Trihydrochloride (10h). Prepared from 15
and 18h in 20% overall yield and obtained as a yellow solid:
mp=234-236 ꢀC. 1H NMR (DMSO-d6) δ 8.87-8.94 (m, 2H),
8.63-8.73 (M, 1H), 8.20 (dd, J1 = 9.6 Hz, J2 = 2.9 Hz, 1H),
7.74-7.86 (m, 1H), 7.53-7.62 (m, 2H), 7.25-7.40 (m, 2H),
7.15-7.23 (m, 1H), 4.03 (d, J = 12.2 Hz, 2H), 3.90 (s, 3H),
3.58-3.79 (m, 6H), 3.45-3.57 (m, 1H), 3.33-3.44 (m, 2H), 3.39
(t, J=12.4 Hz, 2H), 2.30-2.40 (m, 2H), 2.06-2.22 (m, 2H). MS
(ESIþ) (m/z) 472 ([M þ H]þ).
8-{4-[4-(6-Methoxyquinolin-8-yl)piperazin-1-yl]piperidin-1-yl}-
3-methylquinoline Trihydrochloride (10i). Prepared from 15 and
18i in 44% overall yield and obtained as a yellow solid: mp=
232-235 ꢀC. 1H NMR (DMSO-d6) δ 8.93 (s, 1H), 8.81-8.87 (m,
1H), 8.45-8.57 (m, 2H), 7.60-7.72 (m, 2H), 7.60-7.68 (m, 1H),
7.52-7.63 (m, 1H), 7.19-7.27 (m, 1H), 7.02-7.13 (m, 1H), 3.89
(s, 3H), 3.80-3.95 (m, 2H), 3.69-3.81 (m, 2H), 3.53-3.72 (m,
4H), 3.45-3.58 (m, 1H), 3.30-3.44 (m, 2H), 2.53 (s, 3H), 2.93-
3.06(m,2H),2.25-2.40(m,4H).MS(ESIþ) (m/z) 468([Mþ H]þ).
8-{4-[4-(6-Methoxyquinolin-8-yl)piperazin-1-yl]piperidin-1-yl}-
3-(trifluoromethyl) Quinoline Trihydrochloride (10j). Prepared
from 15 and 18j in 33% overall yield and obtained as a yellow
solid: mp=244-247 ꢀC. 1H NMR (DMSO-d6) δ 9.16 (d, J=2.3
Hz, 1H), 8.83-8.95 (m, 2H), 8.53-8.67 (m, 1H), 7.70-7.83 (m,
2H), 7.65 (t, J=7.8 Hz, 1H), 7.41 (d, J=7.4 Hz, 1H), 7,23-7,32
(m, 1H), 7.06-7.16 (m, 1H), 4.10 (d, J=1.5 Hz, 2H), 3.91 (s, 3H),
3.79-4.05 (m, 2H), 3.64-3.75 (m, 3H), 3.45-3.73 (m, 2H),
3.30-3,42 (m, 2H), 2.87 (t, J=11.3 Hz, 2H), 2.30-2.42 (m, 2H),
2.05-2.18 (m, 2H). MS (ESIþ) (m/z) 522 ([M þ H]þ).
3,5-Difluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl}quinoline Trihydrochloride (10p). Prepared from 15
and 18p in 51% overall yield and obtained as a yellow solid:
mp=232-234 ꢀC. 1H NMR (DMSO-d6) δ 8.99 (d, J=2.9 Hz,
1H), 8.80-8.86 (m, 1H), 8.49-8.61 (m, 1H), 8.23 (dd, J1=9.2
Hz, J2=2.8 Hz, 1H), 7.64-7.74 (m, 1H), 7.40 (t, J=8.9 Hz, 1H),
7.19-7.27 (m, 1H), 7.15 (dd, J1 = 8.7 Hz, J2 = 5.4 Hz, 1H),
7.03-7.13 (m, 1H), 3.94 (d, J = 11.7 Hz, 2H), 3.89 (s, 3H),
3.39-3.89 (m, 6H), 3.25-3.38 (m, 2H), 3.20-3.34 (m, 1H), 2.81
(t, J=11.5 Hz, 2H), 2.25-2.39 (m, 2H), 2.04-2.15 (m, 2H). MS
(ESIþ) (m/z) 490 ([M þ H]þ).
5-Fluoro-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-1-yl]pipe-
ridin-1-yl}-2,4-dimethylquinoline Trihydrochloride (10q). Pre-
pared from 15 and 18q in 36% overall yield and obtained as a
yellow solid: mp=236-240 ꢀC. 1H NMR (DMSO-d6) δ 8.82-
8.90 (m, 1H), 8.53-8.65 (m, 1H), 7.64-7.78 (m, 1H), 7.42-7.60
(m, 2H), 7.29-7.41 (m, 1H), 7.20-7.31 (m, 1H), 7.06-7.16 (m,
1H), 3.89 (s, 3H), 3.70-3.94 (m, 4H), 3.48-3.74 (m, 5H),
3.30-3.45 (m, 2H), 2.77 (s, 3H), 2.73-2.82 (m, 2H), 2.72 (s,
3H), 2.23-2.45 (m, 4H). MS (ESIþ) (m/z) 500 ([M þ H]þ).
5-Fluoro-4-methoxy-8-{4-[4-(6-methoxyquinolin-8-yl)piperazin-
1-yl]piperidin-1-yl}-2-(trifluoromethyl)quinoline Trihydrochlor-
ide (10r). Prepared from 15 and 18r in 22% overall yield and
8-{4-[4-(6-Methoxyquinolin-8-yl)piperazin-1-yl]piperidin-1-yl}-
4-methylquinoline Trihydrochloride (10k). Prepared from 15 and
18k in 37% overall yield and obtained as a yellow solid: mp=
1
230-234 ꢀC. H NMR (DMSO-d6) δ 8.69-8.80 (m, 2H), 8.00

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4077
obtained as a yellow solid: mp=251-254 ꢀC. 1H NMR (DMSO-
d6) δ 8.77-8.85 (m, 1H), 8.42-8.58 (m, 1H), 7.63-7.712 (m,
1H), 7.42 (s, 1H), 7.30-7.46 (m, 1H), 7.15-7.29 (m, 2H),
7.0-7.09 (m, 1H), 4.08 (s, 3H), 3.90-3.96 (m, 2H), 3.90 (s,
3H), 3.53-3.81 (m, 6H), 3.40-3.53 (m, 1H), 3.25-3.29 (m, 2H),
2.79 (t, J=11.7, 2H), 2.24-2.38 (m, 2H), 1.95-2.11 (m, 2H). MS
(ESIþ) (m/z) 560 ([M þ H]þ).
purification: mp=105-107 ꢀC. 1H NMR (chloroform-d) δ 8.71
(dd, J1=4.2 Hz, J2=2.4 Hz, 1H), 7.98 (dd, J1=8.4 Hz, J2=1.7
Hz, 1H), 7.25-7.35 (m, 1H), 6.78 (d, J=2.7 Hz, 1H), 6.69 (d, J=
2.7 Hz, 1H), 3.90 (s, 3H), 3.35-3.48 (m, 4H), 3.15-3.24 (m, 4H),
(2.05 (br s, 1H). MS (ESIþ) (m/z) 224 ([M þ H]þ).
8-Chloro-5-fluoroquinoline (16b). To a stirred mixture of
2-chloro-5-fluoroaniline (5.0 g, 34.3 mmol) and m-nitrobenzene
sulfonic acid sodium salt (11.0 g, 48.9 mmol) and glycerol (6.0 g,
65.2 mmol) was added dropwise 70% sulfuric acid (20 mL). The
reaction temperature was then raised to 140 ꢀC and stirred at
that temperature for 2 h. The reaction mixture was cooled to
room temperature, poured into water, filtered through a bed of
celite, made slightly basic (pH=8-9) with 50% aqueous sodium
hydroxide, and extracted three times with dichloromethane (75
mL). The combined organic layers were dried over anhydrous
magnesium sulfate, filtered, and concentrated on a rotary
evaporator. The residue was purified by flash chromatography
on silica gel (100% dichloromethane) to afford the desired
product (3.70 g, 59% yield) as a white solid. 1H NMR (DMSO-
d6) δ 9.04 (dd, J1=4.3 Hz, J2=1.7 Hz, 1H), 8.47 (dd, J1=8.4 Hz,
J2=1.6 Hz, 1H), 7.84-7.934 (m, 1H), 7.65-7.71 (m, 1H), 7.40
(t, J=8.5 Hz, 1H). MS (ESIþ) (m/z) 182 ([M þ H]þ).
Synthesis of 6-Methoxy-8-piperazinoquinoline (15). 8-Chloro-
6-hydroxyquinoline (12). To a 500 mL 3-neck round-bottom
flask was added, in order, iron(II) sulfate (2.0 g, 13.2 mmol),
4-amino-3-chlorophenol hydrochloride (6.4 g, 35.5 mmol),
nitrobenzene (2.9 mL), and a solution of boric acid (3.0 g, 48.5
mmol) in glycerol (16 mL). The stirred mixture was cooled in an
ice bath, and concentrated sulfuric acid (9.0 mL) was added
dropwise. The ice bath was then removed and the stirred mixture
cautiously heated to 120 ꢀC for 2 h, then at 150 ꢀC for 20 h. The
reaction mixture was cooled to room temperature and then
poured onto ice. The resulting aqueous mixture was neutralized
with solid potassium carbonate, and the desired product preci-
pitated as a light-brown solid. The solid was collected by
vacuum filtration, washed with water and hexane, and dried in
vacuo to provide the desired product as a tan solid (7.0 g, 77%
yield). 1H NMR (DMSO-d6) δ 10.37 (s, 1H), 8.77 (d, J=4.3 Hz,
1H), 8.23 (d, J=8.4 Hz, 1H), 7.35-7.52 (m, 2H), 7.17 (s, 1H).
MS (ESI-) (m/z) 178 ([M - H]-).
8-Bromo-6-fluoroquinoline (16c). To a mixture of 2-bromo-
4-fluoroaniline (6.8 g, 35.8 mmol), glycerol (6.8 g, 73.8 mmol),
and m-nitrobenzene sulfonic acid sodium salt (12.8 g, 56.8
mmol) was added 70% sulfuric acid (30 mL) dropwise. The
reaction temperature was raised to 150 ꢀC for 4 h. The mixture
then was cooled to room temperature, poured into ice water, and
was neutralized with 50% aqueous sodium hydroxide solution.
The mixture was then extracted three times with dichloro-
methane (100 mL). The combined organics were washed with
brine and dried over anhydrous magnesium sulfate to yield 3.1 g
(37%) of the desired product as an off-white solid, which was
used without further purification: 1H NMR (DMSO-d6) δ 8.99
(dd, J1=4.2 Hz, J2=1.2 Hz, 1H), 8.43 (dd, J1=8.4 Hz, J2=1.6
Hz, 1H), 8.20 (dd, J1=8.4 Hz, J2=2.8 Hz, 1H), 7.90 (dd, J1=9.1
Hz, J2=2.8 Hz, 1H), 7.67 (dd, J1=8.4 Hz, J2=4.2 Hz, 1H). MS
(ESIþ) (m/z) 226, 228 ([M þ H]þ).
8-Chloro-6-methoxyquinoline (13). To a solution of 12 (3.3 g,
18.4 mmol) in dimethylformamide (30 mL) was added anhy-
drous potassium carbonate (3.8 g, 27.5 mmol), followed by
iodomethane (5.2 g, 36.6 mmol). The mixture was stirred at
room temperature overnight. Water 200 mL) was added, and the
resulting mixture was extracted three times with dichloro-
methane (75 mL). The combined organic layers were dried over
anhydrous magnesium sulfate, filtered, and concentrated on a
rotary evaporator. The resulting residue was purified by flash
chromatography on silica gel (100% dichloromethane) to afford
the desired product (2.2 g, 62% yield) as a beige solid:
1
mp=74-75 ꢀC. H NMR (chloroform-d) δ 8.89 (dd, J1=4.3
Hz, J2=1.8 Hz, 1H), 8.07 (dd, J1=8.3 Hz, J2=1.8 Hz, 1H), 7.54
(d, J=2.8 Hz, 1H), 7.36-7.49 (m, 1H), 7.02 (d, J=2.8 Hz, 1H),
3.93 (s, 3H). MS (ESIþ) (m/z) 180 ([M þ H]þ).
8-Fluoro-6-Bromoquinoline (16d). To a mixture of 4-bromo-
2-fluoroaniline (6.8 g, 35.8 mmol), glycerol (6.8 g, 73.8 mmol),
and m-nitrobenzene sulfonic acid sodium salt (12.8 g, 56.8
mmol) was added 70% sulfuric acid (30 mL) dropwise. The
reaction temperature was raised to 150 ꢀC for 4 h. The mixture
then was cooled to room temperature, poured into ice water, and
was neutralized with 50% aqueous sodium hydroxide solution.
The mixture was then extracted three times with dichloro-
methane (100 mL). The combined organics were washed with
brine and dried over anhydrous magnesium sulfate to yield 4.1 g
(50%) of the desired product as a tan solid, which was used
without further purification. 1H NMR (DMSO-d6) δ 8.98 (dd,
J1=4.3 Hz, J2=1.5 Hz, 1H), 8.38-8.43 (m, 1H), 8.15 (d, J=1.8
Hz, 1H), 7.87 (dd, J1=10.4 Hz, J2=2.1 Hz, 1H), 7.68 (dd, J1=
8.4 Hz, J2=4.1 Hz, 1H). MS (ESIþ) (m/z) 226, 228 ([M þ H]þ)
7,8-Difluoroqinoline (16e). To a stirred mixture of 2,3-difluoro-
aniline (3.57 g, 27.7 mmol), glycerol (5.55 g, 60.3 mmol), and
m-nitrobenzene sulfonic acid sodium salt (10.12 g, 45.0 mmol)
was added dropwise 70% sulfuric acid (20 mL). The resulting
mixture was heated to 135 ꢀC and then stirred at that tempera-
ture for 3.5 h. The reaction was cooled to room temperature,
poured onto ice, and made slightly basic (pH=8-9) with 50%
aqueous sodium hydroxide. The aqueous mixture was extracted
three times with diethyl ether (75 mL). The combined organic
layers were washed with brine, dried over anhydrous magne-
sium sulfate, filtered, and concentrated on a rotary evaporator.
The desired compound (4.13 g, 90% yield) was obtained as a
light-brown solid and was pure enough to use in subsequent
reactions without further purification. 1H NMR (DMSO-d6)
δ 9.00 (dd, J1=4.3 Hz, J2=1.5 Hz, 1H), 8.49 (dd, J1=8.5 Hz,
J2=1.4 Hz, 1H), 7.85-7.95 (m, 1H), 7.71-7.79 (m, 1H), 7.60-
7.71 (m, 1H). MS (ESIþ) (m/z) 166 ([M þ H]þ).
6-Methoxy-8-[1-(tert-butoxycarbonyl)-4-piperazino]quinoline
(14). To a mixture of 13 (2.7 g, 14.0 mmol) in anhydrous
tetrahydrofuran (50 mL) under a nitrogen atmosphere was
added tris(dibenzylideneacetone)dipalladium (0) (Pd2(dba)3,
0.064 g, 0.07 mmol), sodium tert-butoxide (1.9 g, 5.21 mmol),
2-dicylcohexylphosphine-20-(N,N-dimethylamino)biphenyl
(CYMAP, 0.08 g, 0.20 mmol), and tert-butoxycarbonylpiper-
azine (3.4 g, 15.3 mmol). The resulting mixture was stirred at
reflux for 5 h and then cooled to room temperature. The reaction
mixture was diluted with diethyl ether, filtered through a pad of
celite, and concentrated on a rotary evaporator. The resulting
residue was purified by flash chromatography on silica gel
(100% dichloromethane) to afford the desired product (4.4 g,
% yield) as a beige solid: mp=92-93 ꢀC. 1H NMR (chloroform-
d) δ 8.72 (dd, J1=4.2 Hz, J2=1.9 Hz, 1H), 8.00 (dd, J1=8.2 Hz,
J2=1.8 Hz, 1H), 7.33 (dd, J1=8.2 Hz, J2=4.2 Hz, 1H), 6.78 (d,
J=2.7 Hz, 1H), 6.72 (d, J=2.5 Hz, 1H), 3.91 (s, 3H), 3.73-3.84
(m, 4H), 3.28-3.40 (M, 4H), 1.50 (s, 9H). MS (ESIþ) (m/z) 344
([M þ H]þ).
6-Methoxy-8-piperazinoquinoline (15). To a solution of 14
(4.0 g, 11.7 mmol) in 1,4-dioxane (20 mL) was added 4N HCl/
dioxane (10 mL). The resulting mixture was stirred at room
temperature overnight, during which time a white precipitate
formed. The precipitate was collected by vacuum filtration,
dissolved in water, and neutralized with 2.5 N aqueous sodium
hydroxide. The resulting aqueous mixture was extracted three
times with dichloromethane (50 mL). The combined organic
layers were dried over anhydrous sodium sulfate, filtered, and
concentrated on a rotary evaporator to give the desired product
(2.8 g, 98% yield) as a tan solid which was used without further

4078 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
8-Bromo-2-methylquinoline (16f). A mixture of 2-bromoani-
line (4.27 g, 24.8 mmol) and crotonaldehyde (2.20 g, 25.0 mmol)
in 6N aqueous HCl (12.4 mL) was stirred at reflux overnight.
The reaction mixture was cooled to room temperature, made
basic (pH=10) by addition of 2.5 N aqueous sodium hydroxide,
and extracted four times with dichloromethane (50 mL). The
combined organic layers were washed with water and brine,
dried over anhydrous sodium sulfate, filtered, and concentrated
on a rotary evaporator. The residue was purified by flash chro-
matography on silica gel (30% ethyl acetate/hexane) to afford
the desired product 2.10 g, 39% yield) as a yellow oil. 1H NMR
(chloroform-d) δ 7.98-8.06 (m, 2H), 7.73 (dd, J1=8.1 Hz, J2=
1.5 Hz, 1H), 7.28-7.37 (m, 2H), 2.81 (s, 3H). MS (ESIþ) (m/z)
222, 224 ([M þ H]þ).
acetonitrile (3 mL) dropwise over 5 min. The resulting reaction
mixture was stirred at 65 ꢀC for 15 min and then cooled to room
temperature. The reaction was poured into cold 20% aqueous
sodium hydroxide solution and extracted three times with
diethyl ether (30 mL). The organic layer was concentrated on
a rotary evaporator and purified by flash chromatography on
silica (5% EtOAc/hexane) to give 0.027 g (17%) of the desired
8-bromo-5-fluoroquinoline as a light-yellow solid. 1H NMR
(DMSO-d6) δ 9.05 (d, J=3.4 Hz, 1H), 8.37 (dd, J1=5.5 Hz, J2=
2.6 Hz, 1H), 8.13 (d, J=7.5 Hz, 1H), 8.02 (d, J=8.2 Hz, 1H), 7.56
(t, J=7.5 Hz, 1H). MS (ESIþ) (m/z) 226, 228 ([M þ H]þ).
8-Bromo-3-methylquinoline (16i). A mixture of 2-bromoani-
line (4.56 g, 26.5 mmol) and methacrolein (3.10 g, 39.8 mmol) in
6N aqueous HCl (13 mL) was stirred at reflux overnight. The
reaction mixture was cooled to room temperature, made basic
(pH=10) by addition of 50% aqueous sodium hydroxide, and
extracted three times with dichloromethane (50 mL). The com-
bined organic layers were washed with water and brine, dried
over anhydrous sodium sulfate, filtered, and concentrated on a
rotary evaporator. The residue was purified by flash chroma-
tography on silica gel (15% ethyl acetate/hexane) to afford the
8-Bromo-2-(trifluoromethyl)quinoline (16g). Compound 16g
was prepared using the sequence described by Cottet, et al.50 The
compound was isolated as a white solid by recrystallization from
hexane. 1H NMR (chloroform-d) δ 8.42 (d, J=8.4 Hz, 1H), 8.22
(dd, J1=7.6 Hz, J2=1.4 Hz, 1H), 7.92 (d, J=8.1 Hz, 1H), 7.81 (d,
J=8.4 Hz, 1H),7.55-7.63 (m, 1H). MS (ESIþ) (m/z) 276, 278
([M þ H]þ).
1
8-Bromo-3-fluoroquinoline (16h). To a solution of 3-amino-
quinoline (1.00 g, 6.94 mmol) in 48% fluoroboric acid (10 mL) at
0 ꢀC was added sodium nitrate (0.60 g, 14.49 mmol) dissolved in
water (2 mL). The reaction was stirred at 0 ꢀC for 1 h. The
reaction was cooled to room temperature, and the resulting
yellow precipitate was collected by vacuum filtration, washed
with cold ethanol and cold diethylethyl ether, and dried in
vacuo. The dried yellow precipitate was suspended in toluene
(10 mL) and heated at 110 ꢀC for 1 h. The cooled reaction
mixture was poured into ice water. The mixture was treated with
diethyl ether to dissolve the resulting brown precipitate, and the
layers were separated. The aqueous was made basic with 2.5 N
aqueous sodium hydroxide solution and extracted three times
with ethyl acetate (50 mL). The combined organic layers were
dried over anhydrous sodium sulfate, filtered, and concentrated
on a rotary evaporator. The residue was purified by flash
chromatography on silica gel (5% ethyl acetate/hexane) to give
0.64 g (63%) of 3-fluoroquinoline as clear oil. 1H NMR
(DMSO-d6) δ 8.90 (d, J=2.9 Hz, 1H), 8.22 (dd, J1=9.6 Hz,
J2=2.8 Hz, 1H), 8.03 (d, J=8.7 Hz, 1H), 7.96 (dd, J1=8.1 Hz,
J2=1.4 Hz, 1H), 7.72 (t, J=7.7 Hz, 1H), 7.65 (t, J=8.0 Hz, 1H).
MS (ESIþ) (m/z) 148 ([M þ H]þ).
desired product 2.15 g, 46% yield) as a yellow oil. H NMR
(chloroform-d) δ 8.76 (s, 1H), 7.85 (d, J=7.4 Hz, 1H), 7.76 (s,
1H), 7.57 (d, J=8.2 Hz, 1H), 7.23 (t, J=7.5 Hz, 1H), 2.41 (s, 3H).
MS (ESIþ) (m/z) 222, 224 ([M þ H]þ).
8-Bromo-3-(trifluoromethyl)quinoline (16j). To a solution of
8-bromoquinoline (1.0 g, 4.81 mmol) in glacial acetic acid (6 mL)
was added, portionwise, N-iodosuccinimide (1.08 g, 4.81 mmol).
The resulting mixture was stirred at 70 ꢀC overnight, cooled to
room temperature, and concentrated on a rotary evaporator.
The residue was taken up in dichloromethane and washed with
saturated aqueous sodium bicarbonate and brine. The organic
layer was dried over anhydrous sodium sulfate, filtered, and
concentrated on a rotary evaporator. The residue was purified
by flash chromatography on silica gel (5% ethyl acetate/hexane)
to afford the intermediate 8-bromo-3-iodoquinoline (0.79 g,
1
49% yield) as a white solid. H NMR (chloroform-d) δ 9.12
(d, J=2.0 Hz, 1H), 8.52 (d, J=2.1 Hz, 1H), 8.03 (dd, J1=7.5 Hz,
J2=1.3 Hz, 1H), 7.66 (dd, J1=-8.1 Hz, J2=2.1 Hz, 1H), 7.39 (t,
J=7.7 Hz, 1H). MS (ESIþ) (m/z) 334, 336 ([M þ H]þ).
A mixture of copper(I) iodide (0.25 g, 1.32 mmol) and
potassium fluoride (0.077 g, 1.32 mmol) was placed under a
high vacuum and heated until the solid assumed a slightly green
color. The cooled solid mass was suspended in anhydrous N-
methylpyrrolidinone (5 mL) and then treated with the pre-
viously described 8-bromo-3-iodoquinoline (0.40 g, 1.20 mmol),
followed by trifluoromethyltrimethylsilane (0.17 g, 1.20 mmol).
The resulting mixture was stirred under a nitrogen atmosphere
at 50 ꢀC overnight. The mixture was then cooled to room
temperature and poured into 15% aqueous ammonium hydro-
xide. The aqueous mixture was extracted four times with diethyl
ether (25 mL). The combined organic layers were washed with
water and brine, dried over anhydrous sodium sulfate, filtered,
and concentrated on a rotary evaporator. The residue was
purified by flash chromatography on silica gel (4:1 hexane/ethyl
acetate) to afford the desired product 16j (0.27 g, 33% yield) as a
brown oil. 1H NMR (chloroform-d) δ 9.18 (d, J=2.0 Hz, 1H),
8.43 (s, 1H), 8.17 (dd, J1=7.5 Hz, J2=1.1 Hz, 1H), 7.88 (d, J=
8.1 Hz, 1H), 7.50 (t, J=7.9 Hz, 1H). MS (ESIþ) (m/z) 276, 278
([M þ H]þ).
A solution of 3-fluoroquinoline (0.64 g, 4.35 mmol) in con-
centrated sulfuric acid (3.75 mL) was cooled to 0 ꢀC. Fuming
nitric acid was added dropwise. The reaction was warmed to
room temperature and stirred for 1 h, then poured onto ice. The
resulting mixture was made basic with 50% aqueous sodium
hydroxide solution and extracted three times with ethyl acetate
(50 mL). The combined organic layers were washed with brine,
dried over anhydrous sodium sulfate, filtered, and concentrated
on a rotary evaporator to give 0.81 g (97% yield) of a 1:3 mixture
of 3-fluoro-8-nitroquinoline and 3-fluoro-5-nitroquinoline as a
clear oil, which was used in the next step without further
purification: MS (ESIþ) (m/z) 193 ([M þ H]þ).
To the mixture of 3-fluoro-8-nitroquinoline and 3-fluoro-
5-nitroquinoline (0.81 g, 4.23 mmol) in ethyl acetate (20 mL) was
added 10% Pd/C (0.3 g). The mixture was hydrogenated at 55
psi in a Parr reactor for 1 h. The suspension was filtered through
celite to remove the catalyst, concentrated on a rotary evapora-
tor, and purified by flash chromatography on silica gel (30%
EtOAc/hexane) to give 8-amino-3-fluoroquinoline (0.12 g, 17%
yield) as a white solid. 1H NMR (DMSO-d6) δ 8.70 (d, J=2.9
Hz, 1H), 8.00 (dd, J1=10.1 Hz, J2=2.8 Hz, 1H), 7.31 (t, J=7.9
Hz, 1H), 7.02 (d, J=8.1 Hz, 1H), 6.79 (d, J=7.7 Hz, 1H), 5.98 (br
s, 2H). MS (ESIþ) (m/z) 163 ([M þ H]þ).
8-Bromo-4-methylquinoline (16k). To a mixture of 2-bromo-
aniline (7.00 g, 40.7 mmol) and methyl vinyl ketone (4.00 mL g,
48.8 mmol) in ethanol/water (37 mL/7 mL) was added zinc
chloride (1.35 g, 10.1 mmol) and iron(III) chloride (1.10 g,
6.5 mmol). The resulting mixture was stirred at reflux over-
night. The reaction mixture was cooled and treated with etha-
nol (50 mL), followed by 12% aqueous sodium hydroxide
(50 mL). The resulting inorganic white precipitate was removed
by vacuum filtration, and the filtrate was extracted twice with
dichloromethane (100 mL). The combined organic extracts were
A mixture of copper(II) bromide (0.123 g, 0.57 mmol) and
tert-butyl nitrite (0.09 g, 0.86 mmol) in dry acetonitrile (5 mL)
was stirred and heated to 65 ꢀC. To that mixture was added a
solution of 3-fluoroquinolin-8-amine (0.09 g, 0.57 mmol) in dry

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4079
washed with brine, dried over anhydrous sodium sulfate, filte-
red, and concentrated on a rotary evaporator. The residue was
purified by flash chromatography on silica gel (15% ethyl
acetate/hexane) to afford the desired product (3.45 g, 38% yield)
as an off-white solid. 1H NMR (chloroform-d) δ 8.87 (d, J=4.3
Hz, 1H), 8.03 (d, J=7.4 Hz, 1H), 7.96 (d, J=8.5 Hz, 1H), 7.39
(t, J=7.9 Hz, 1 H), 7.27 (d, J=4.4 Hz, 1H), 2.70 (s, 3H). MS
(ESIþ) (m/z) 222, 224 ([M þ H]þ).
To phosphorus oxybromide (6.4 g, 23.00 mmol)) heated at
75 ꢀC was slowly added 8-chloro-5-fluoro-2-(trifluoromethyl)-
quinolin-4-ol (3.04 g, 11.45 mmol) and the temperature was
raised to 150 ꢀC for 2 h. After cooling to room temperature, the
reaction was poured over ice and three times extracted with ethyl
acetate (100 mL). The combined organic layers were washed
with brine, dried over anhydrous magnesium sulfate, filtered,
and concentrated on a rotary evaporator. The crude product
was purified by flash chromatography on silica gel (10% ethyl
acetate in hexane) using hexane/ethyl acetate to give 4-bromo-8-
chloro-5-fluoro-2-(trifluoromethyl)quinoline (3.13 g, 83% yield)
as an off-white solid. 1H NMR (DMSO-d6) δ 8.50 (s, 1H),
8.12-8.18 (m, 1H), 7.67-7.75 (m, 1H). MS (ESIþ) (m/z) 328,
330 ([M þ H]þ).
8-Bromo-2,4-dimethylquinoline (16l). A mixture of 2-bromo-
aniline (4.00 g, 23.3 mmol) and 3-penten-2-one (65%, 4.18 mL,
27.9 mmol) in concentrated HCl (50 mL) was stirred at reflux for
12 h. The reaction mixture was cooled to room temperature and
then cooled in an ice bath and made basic (pH=10) by addition
of 5 N aqueous sodium hydroxide. The resulting aqueous mix-
ture was extracted three times with dichloromethane (75 mL).
The combined organic layers were washed with water and brine,
dried over anhydrous sodium sulfate, filtered, and concentrated
on a rotary evaporator. The residue was purified by flash chro-
matography on silica gel (10% ethyl acetate/hexane) to afford
the desired product 2.15 g, 46% yield) as a white solid. 1H NMR
(chloroform-d) δ 7.97 (d, J=7.3 Hz, 1H), 7.88 (d, J=8.2 Hz,
1H), 7.29(t, J=7.8 Hz, 1H), 7.15 (s, 1H), 2.73 (s, 3H), 2.63 (s,
3H). MS (ESIþ) (m/z) 236, 238 ([M þ H]þ).
A stirred mixture of 1.6 n-butyl lithium/hexane (6.8 mL, 10.8
mmol) in dry tetrahydrofuran (10 mL) under a nitrogen atmo-
sphere was cooled to -78 ꢀC with a dry ice/acetone bath. A
solution of 4-bromo-8-chloro-5-fluoro-2-(trifluoromethyl)qui-
noline (2.9 g, 8.8 mmol) in dry tetrahydrofuran (15 mL) was
added dropwise over 15 min. The resulting reaction mixture
was stirred at -78 ꢀC for 20 min and then quenched by addition
of methanol (2 mL). The reaction was warmed to room
temperature, poured into brine, and partially concentrated
on a rotary evaporator to remove the tetrahydrofuran. The
resulting aqueous mixture was extracted twice with ethyl
acetate (75 mL). The combined organic layers were dried over
anhydrous sodium sulfate, filtered, and concentrated on a
rotary evaporator. The crude residue was purified by flash
chromatography on silica gel (20% dichloromethane in
hexane) to provide 16n (1.1 g, 50% yield) as a white solid. 1H
NMR (DMSO-d6) δ 8.83 (d, J=8.7 Hz, 1H), 8.13 (d, J=8.7 Hz,
1H), 8.05-8.15 (m, 1H), 7.62 (t, J=8.7 Hz, 1H). MS (ESIþ)
(m/z) 250 ([M þ H]þ).
8-Bromo-4-methoxy-2-(trifluoromethyl)quinoline (16m). A so-
lution of ethyl 4,4,4-trifluoroacetoacetate (4.0 mL, 27.3 mmol)
in polyphosphoric acid (22) was heated to 100 ꢀC. 2-Bromoani-
line (4.47 g, 26.0 mmol) was added slowly to the stirred reaction.
The resulting mixture was heated to 150 ꢀC and then stirred at
that temperature overnight. The reaction was then cooled to
room temperature, and water was added carefully. The resulting
tan precipitate was collected by vacuum filtration, washed with
water, and dissolved in ethyl acetate. The ethyl acetate solution
was washed with brine, dried over anhydrous magnesium
sulfate, filtered, and concentrated on a rotary evaporator. The
crude product was purified by flash chromatography on silica
gel (4:1 hexane/ethyl acetate) to give 8-bromo-2-(trifluoromethyl)-
quinolin-4-ol (4.76 g, 63% yield) as an off-white solid. 1H NMR
(DMSO-d6) δ 12.60 (s, 1H), 8.16-8.22 (m, 2H), 7.52 (t, J=8.2
Hz, 1H), 7.19 (s, 1H). MS (ESIþ) (m/z) 291, 293 ([M - H]-).
To a solution of 8-bromo-2-(trifluoromethyl)quinolin-4-ol
(0.50 g, 1.71 mmol) in acetone (15 mL) was added anhydrous
potassium carbonate (0.50 g, 3.60 mmol), followed by iodo-
methane (0.53 g, 3.76 mmol). The resulting mixture was stirred
at reflux for 1.5 h. An additional aliquot of iodomethane (0.53 g,
3.76 mmol) was added, and reflux was continued for an addi-
tional hour. The reaction was cooled to room temperature,
poured onto ice, and extracted three times with ethyl acetate
(50 mL). The combined organic layers were dried over anhy-
drous magnesium sulfate, filtered, and concentrated on a rotary
evaporator to give 16m (0.42 g, 79% yield) as a beige solid, which
was used without further purification. 1H NMR (DMSO-d6) δ
8.18-8.27 (m, 2H), 7.58 (t, J=8.0 Hz, 1H), 7.47 (s, 1H), 4.15 (s,
3H). MS (ESIþ) (m/z) 305, 307 ([M þ H]þ).
8-Chloro-5-fluoro-3-(trifluoromethyl)quinoline (16o). To a
stirred mixture of 2-chloro-5-fluoroaniline (5.00 g, 34.3 mmol),
glycerol (6.00 g, 65.2 mmol), and m-nitrobenzene sulfonic acid
sodium salt (11.0 g, 48.9 mmol) was added dropwise 70%
sulfuric acid. The reaction was then heated to 140 ꢀC and stirred
at that temperature for 2 h. The mixture was cooled to room
temperature and then poured into water, filtered through a bed
or celite, made slightly basic (pH = 8-9) with 50% aqueous
sodium hydroxide, and extracted three times with dichloro-
methane (75 mL). The combined organic layers were dried over
anhydrous magnesium sulfate, filtered, and concentrated on a
rotary evaporator. The residue was purified by flash chroma-
tography on silica gel (100% dichloromethane) to afford the
1
desired product (3.70 g, 59% yield) as a white solid. H NMR
(DMSO-d6) δ 9.04 (dd, J1=4.3 Hz, J2=1.7 Hz, 1H), 8.47 (dd,
J1=8.4 Hz, J2=1. Hz, 1H), 7.84-7.92 (m, 1H), 7.65-7.71 (m,
1H), 7.40 (t, J=8.5 Hz, 1H). MS (ESIþ) (m/z) 182 ([M þ H]þ).
To a solution of 8-chloro-5-fluoroquinoline (3.50 g, 19.3
mmol) in glacial acetic acid (50 mL) was added, portionwise,
N-iodosuccinimide (4.34 g, 19.3 mmol). The resulting mixture
was stirred at 70 ꢀC overnight, cooled to room temperature, and
concentrated on a rotary evaporator. The residue was taken up
in dichloromethane and washed with saturated aqueous sodium
bicarbonate and brine. The organic layer was dried over an-
hydrous sodium sulfate, filtered, and concentrated on a rotary
evaporator. The residue was purified by flash chromatography
on silica gel (5% ethyl acetate/hexane) to afford the intermediate
8-bromo-5-fluoro-3-iodoquinoline (1.68 g, 28% yield) as an off-
white solid. 1H NMR (chloroform-d) δ 9.16 (d, J=2.1 Hz, 1H),
8.79 (d, J=2.1 Hz, 1H), 7.70-7.77 (m, 1H), 7.317 (t, J=8.8 Hz,
1H). MS (ESIþ) (m/z) 308 ([M þ H]þ).
8-Chloro-5-fluoro-2-(trifluoromethyl)quinoline (16n). A solu-
tion of 4,4,4-trifluoroacetoacetate (4 mL, 27.3 mmol) in poly-
phosphoric acid (22 mL) was heated to 100 ꢀC. 2-Chloro-5-
fluoroaniline (3.78 g, 26.0 mmol) was added portionwise to the
stirred solution. The resulting reaction mixture was heated to
150 ꢀC and then stirred at that temperature overnight. The
reaction was cooled to room temperature, and water was added
carefully. The resulting light-brown precipitate was collected by
vacuum filtration, washed with water, and dissolved in ethyl
acetate. The ethyl acetate solution was washed with water and
brine, dried over anhydrous magnesium sulfate, filtered, and
concentrated on a rotary evaporator. The residue was purified
by flash chromatography on silica gel (4:1 ethyl acetate/hexane)
to afford 8-chloro-5-fluoro-2-(trifluoromethyl)quinolin-4-ol
A mixture of copper(I) iodide (2.07 g, 10.9 mmol) and
potassium fluoride (0.63 g, 10.9 mmol) was placed under a high
vacuum and heated until the solid assumed a slightly green
color. The cooled solid mass was suspended in anhydrous N-
methylpyrrolidinone (20 mL) and then treated with the pre-
viously described 8-bromo-5-fluoro-3-iodoquinoline (1.68 g,
1
(3.54 g, 51% yield) as an off-white solid. H NMR (DMSO-
d6) δ 12.74 (br s, 1H), 7.94-8.01 (m, 1H), 7.37 (7.34-7.43 (m,
1H), 7.23 (s, 1H). MS (ESIþ) (m/z) 264 ([M - H]-).

4080 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
5.47 mmol), followed by trifluoromethyltrimethylsilane (2.33 g,
16.4 mmol). The resulting mixture was stirred under a nitrogen
atmosphere at 50 ꢀC overnight. The mixture was then cooled to
room temperature and poured into 15% aqueous ammonium
hydroxide. The aqueous mixture was extracted four times with
diethyl ether (50 mL). The combined organic layers were washed
with water and brine, dried over anhydrous sodium sulfate,
filtered, and concentrated on a rotary evaporator. The residue
was purified by flash chromatography on silica gel (5% ethyl
acetate/hexane) to afford the desired product 16o (0.56 g, 41%
yield) as an off-white solid. 1H NMR (chloroform-d) δ 9.23 (s,
1H), 8.73 (s, 1H), 7.84-7.94 (m, 1 h), 7.29 (t, J=8.6 Hz, 1H). MS
(ESIþ) (m/z) 250 ([M þ H]þ).
washed with water and brine, dried over anhydrous sodium
sulfate, filtered, and concentrated on a rotary evaporator. The
residue was purified by flash chromatography on silica gel (60%
ethyl acetate/hexane) to afford the desired product (2.42 g, 60%
yield) as a light-yellow solid. 1H NMR (chloroform-d) δ
7.84-7.91 (m, 1H), 7.12 (s, 1H), 6.95-7.04 (m, 1H), 2.77 (d,
J=7.1 Hz (fluorine coupling), 3H), 2.71 (s, 3H). MS (ESIþ)
(m/z) 254, 256 ([M þ H]þ).
8-Chloro-5-fluoro-4-methoxy-2-(trifluoromethyl)quinoline (16r).
A solution of 4,4,4-trifluoroacetoacetate (4 mL, 27.3 mmol) in
polyphosphoric acid (22 mL) was heated to 100 ꢀC. 2-Chloro-
5-fluoroaniline (3.78 g, 26.0 mmol) was added portionwise to the
stirred solution. The resulting reaction mixture was heated to
150 ꢀC and then stirred at that temperature overnight. The
reaction was cooled to room temperature, and water was added
carefully. The resulting light-brown precipitate was collected by
vacuum filtration, washed with water, and dissolved in ethyl
acetate. The ethyl acetate solution was washed with water and
brine, dried over anhydrous magnesium sulfate, filtered, and
concentrated on a rotary evaporator. The residue was purified
by flash chromatography on silica gel (4:1 hexane/ethyl acetate)
to afford 8-chloro-5-fluoro-2-(trifluoromethyl)quinolin-4-
ol (3.54 g, 51% yield) as an off-white solid. 1H NMR (DMSO-
d6) δ 12.74 (br s, 1H), 7.94-8.01 (m, 1H), 7.37 (7.34-7.43 (m,
1H), 7.23 (s, 1H). MS (ESIþ) (m/z) 264 ([M - H]-).
8-Bromo-3,5-difluoroquinoline (16p). Flash chromatography
of the mixture of 5-amino-8-fluoroquinoline and 8-amino-3-
fluoroquinoline obtained in the synthesis of 16h on silica gel
(30% ethyl acetate/hexane) afforded 5-amino-3-fluoroquino-
line as a light-brown solid in 53% yield. 1H NMR (DMSO-d6) δ
8.79 (d, J=2.8 Hz, 1H), 8.35 (dd, J1=10.9 Hz, J2=2.8 Hz, 1H),
7.39 (t, J=8.0 Hz, 1H), 7.21 (d, J=8.4 Hz, 1H), 6.73 (d, J=7.5
Hz 1H), 5.94 (br s, 2H). MS (ESIþ) (m/z) 163 ([M þ H]þ).
3,5-Difluoroquinoline was obtained as a tan solid in 63%
yield by treatment of 5-amino-3-fluoroquinoline with 48%
fluoroboric acid using the procedure described for preparing
3-fluoroquinoline in the synthesis of 16h. The crude reaction
residue was purified by flash chromatography on silica using 5%
ethyl acetate/hexane: 1H NMR (chloroform-d) δ 8.86 (d, J=8.5
Hz, 1H), 8.02 (dd, J1=8.5 Hz, J2=2.6 Hz, 1H), 7.96 (d, J=8.6
Hz, 1H), 7.60-7.71 (m, 1H), 7.26-7.35 (m, 1H). MS (ESIþ)
(m/z) 166 ([M þ H]þ).
To a solution of 8-chloro-5-fluoro-2-(trifluoromethyl)quino-
lin-4-ol (3.54 g, 13.3 mmol, preparation described in the synth-
esis of 16n) in acetone (75 mL) was added anhydrous potassium
carbonate (3.88 g, 28.0 mmol), followed by iodomethane (1.8
mL, 28.9 mmol). The resulting mixture was stirred at reflux for
1.5 h. An additional aliquot of iodomethane (1.8 mL, 28.9
mmol) was added, and reflux was continued for an additional
1 h. The reaction was cooled to room temperature, poured onto
ice, and extracted three times with ethyl acetate (50 mL). The
combined organic layers were dired over anhydrous magnesium
sulfate, filtered, and concentrated on a rotary evaporator. The
desired 16r (3.72 g, 100% yield) was isolated as a yellow solid
and was pure enough to use in subsequent reactions without
further purification. 1H NMR (DMSO-d6) δ 8.00-8.05 (m, 1H),
7.53 (s, 1H), 7.43-7.50 (m, 1H), 4.12 (s, 3H). MS (ESIþ) (m/z)
280 ([M þ H]þ).
3,5-Difluoro-8-nitroquinoline was obtained as a yellow solid
in 48% yield from 3,5-difluoroquinoline by treatment with
fuming nitric acid in concentrated sulfuric acid using the pro-
cedure described for preparing 3-fluoro-8-nitroquinoline in the
synthesis of 16h. The product was obtained by vacuum filtration
of the aqueous mixture and was pure enough to use in subse-
quent reactions. 1H NMR (DMSO-d6) δ 9.16 (d, J=2.4 Hz, 1H),
8.52 (dd, J1=8.8 Hz, J2=2.8 Hz, 1H), 8.30-8.38 (m, 1H), 7.68 (t,
J=8.7). MS (ESIþ) (m/z) 211 ([M þ H]þ).
8-Amino-3,5-difluoroquinoline was obtained as a white solid
in 83% yield by hydrogenation of 3,5-difluoro-8-nitroquinoline
over 10% Pd/C at 55 psi. The crude reaction residue was purified
by flash chromatography on silica gel using 30% ethyl acetate/
hexane. 1H NMR (DMSO-d6) δ 8.77 (d, J=2.8 Hz, 1H), 8.06
(dd, J1 = 9.6 Hz, J2 = 2.8 Hz, 1H), 7.19 (t, J = 9.2 Hz, 1H),
6.67-6.73 (m, 1H), 5.82 (br s, 2H). MS (ESIþ) (m/z) 181 ([M þ
H]þ).
The synthesis of 8-(1,4-dioxa-8-azaspiro[4,5]dec-8-yl)quino-
line (17a) illustrates the general sequence used to prepare
compounds 17a, 17c-d, 17f-m and 17p-q.
8-(1,4-Dioxa-8-azaspiro[4,5]dec-8-yl)quinoline (17a). A solu-
tion of commercially available 8-bromoquinoline (16a) (4.0 g,
19.2 mmol) in anhydrous tetrahydrofuran (20 mL) was purged
with nitrogen for 10 min and then placed under a nitro-
gen atmosphere. To the stirred solution was added tris-
(dibenzylideneacetone)dipalladium (0) (Pd2(dba)3, 0.2 g, 0.02
mmol), sodium tert-butoxide (2.6 g, 27.1 mmol), tetrakis-
(triphenylphosphino)-1,1-binapthyl (BINAP, 0.1 g, 0.16 mmol),
and 1,4-dioxa-8-azaspiro-4,5-decane (3.3 g, 23.1 mmol). The
resulting mixture was stirred at reflux for 3 h and then cooled to
room temperature. The reaction mixture was diluted with
diethyl ether, filtered through a pad of celite, and concentrated
on a rotary evaporator. The resulting residue was purified by
flash chromatography on silica gel (4:1 hexane/ethyl acetate)
afforded the desired product (3.0 g, 58% yield) as a brown oil.
1H NMR (DMSO-d6) δ 8.83 (d, J=4.2 Hz, 1H), 8.26 (d, J=5.5
Hz, 1H), 7.40-7.51 (m, 3H), 7.15 (d, J=7.2 Hz, 1H), 3.89 (s,
4H), 3.36 (t, J=5.4 Hz, 4H), 1.83 (t, J=5.4 Hz, 4H). MS (ESIþ)
(m/z) 244 ([M þ H]þ).
To a solution of 8-amino-3,5-difluoroquinoline (0.05 g, 0.28
mmol) in water (2 mL) was added concentrated hydrobromic
acid (5 mL) and cooled to 0 ꢀC. To the reaction was added
sodium nitrite (0.038 g, 0.55 mmol) in water (1 mL). The
resulting mixture was poured into a solution of copper(I)
bromide (0.12 g, 0.84 mmol) in concentrated hydrobromic acid
(5 mL). The reaction was stirred at room temperature overnight.
The reaction was poured into cold 20% aqueous sodium
hydroxide solution and extracted three times with diethyl ether
(20 mL). The combined organic layers were concentrated on a
rotary evaporator to give 0.061 g (89%) of 8-bromo-3,5-difluoro-
quinoline as a yellow oil, which was used without further
1
purification. H NMR (DMSO-d6) δ 9.10 (d, J=2.8 Hz, 1H),
8.38 (dd, J1=8.9 Hz, J2=2.8 Hz, 1H), 8.05-8.12 (m, 1H), 7.46 (t,
J=8.8 Hz, 1H). MS (ESIþ) (m/z) 244, 246 ([M þ H]þ).
8-Bromo-5-fluoro-2,4-dimethylquinoline (16q). A mixture of
2-bromo-5-fluoroaniline (3.0 g, 15.8 mmol) and 3-penten-2-one
(65%, 2.44 g, 18.9 mmol) in concentrated HCl (30 mL), was
stirred at reflux overnight. The reaction mixture was cooled to
room temperature and then cooled in an ice bath. The pH was
adjusted to 10 with 2.5 N aqueous sodium hydroxide, and the
resulting aqueous mixture was extracted three times with di-
chloromethane (50 mL). The combined organic layers were
The following compounds were prepared using a similar
procedure:
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-6-fluoroquinoline (17c).
Prepared from 16c in 36% overall yield and obtained as an off-
white solid. 1H NMR (DMSO-d6) δ 8.80 (dd, J1=4.1 Hz, J2=1.7
Hz, 1H), 8.25 (dd, J1=8.3 Hz, J2=1.7 Hz, 1H), 7.45-7.58 (m,
1H), 7.20-7.31 (m, 1H), 6.98 (dd, J1=11.8 Hz, J2=2.7 Hz, 1H),

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4081
3.93 (s, 4H), 3.46 (t, J=5.6 Hz, 4H), 1.84 (t, J=5.6 Hz, 4H). MS
(ESIþ) (m/z) 289 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-5-fluoro-quinoline (17b).
To a solution of 16b (2.25 g, 12.4 mmol) in anhydrous tetra-
hydrofuran (40 mL), flushed with nitrogen, and kept under a
nitrogen atmosphere, was added tris(dibenzylideneacetone)-
dipalladium (0) (Pd2(dba)3, 0.417 g, 0.02 mmol), sodium tert-
butoxide (01.66 g, 16.3 mmol), 2-dicyclohexylphosphine-20-(N,
N-dimethylamino)biphenyl (CYMAP, 0.072 g, 0.02 mmol), and
1,4-dioxa-8-azaspiro-4,5 decane (2.10 mg, 14.7 mmol). The
resulting mixture was stirred at 70 ꢀC overnight. The reaction
was cooled to room temperature, diluted with diethyl ether,
filtered through a plug of silica gel, and concentrated on a rotary
evaporator. The resulting residue was purified by flash chroma-
tography on silica gel (40% ethyl acetate/hexane) to afford the
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-6-bromoquinoline (17d).
Prepared from 16d in 94% overall yield and obtained as a brown
oil. 1H NMR (DMSO-d6) δ 8.86 (d, J=4.1 Hz, 1H), 8.25 (d, J=
8.4 Hz, 1H), 7.74 (d, J=2.1 Hz, 1H), 7.50-7.55 (m, 1H), 7.15 (s,
J=2.1 Hz, 1H), 3.93 (s, 4H), 3.44 (t, J=5.2 Hz, 4H), 1.84 (t, J=
5.4 Hz, 4H). MS (ESIþ) (m/z) 348, 350 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-2-methylquinoline (17f).
Prepared from 16f in 52% overall yield and obtained as a brown
oil. 1H NMR (chloroform-d) δ 7.95 (d, J = 8.5 Hz, 1H),
7.28-7.46 (m, 2H), 7.15 (d, J = 7.1 Hz, 1H), 7.05-7.11 (m,
1H), 4.00 (s, 4H), 3.47 (t, J=5.6 Hz, 4H), 2.71 (s, 3H), 2.04 (t, J=
5.6 HZ, 4H). MS (ESIþ) (m/z) 285 ([M þ H]þ).
1
desired product (2.10 g, 60% yield) as a beige solid. H NMR
(DMSO-d6) δ 8.92 (d, J=4.1 Hz, 1H), 8.38 (d, J=8.4 Hz, 1H),
7.55-7.61 (m, 1H), 7.21-7.30 (m, 1H), 7.06-7.14 (m, 1H), 3.89
(s, 4H), 331 (t, J=5.3 Hz, 4H), 1.82 (t, J=5.3 Hz, 4H). MS
(ESIþ) (m/z) 289 ([M þ H]þ)
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-2-(trifluoromethyl)quino-
line (17g). Prepared from 16g in 63% overall yield and obtained
1
as a yellow oil. H NMR (DMSO-d6) δ 8.86 (d, J = 8.6 Hz,
1H),7.91 (d, J=8.4 Hz, 1H), 7.55-7.68 (m, 2H), 7.17-7.32 (m,
1H), 3.93 (s, 4H), 3.44 (t, J=5.5 Hz, 4H), 1.83 (t, J=5.5 Hz, 4H).
MS (ESIþ) (m/z) 339 ([M þ H]þ).
The following compounds were prepared using a similar
procedure.
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-5-fluoro-2-(trifluoromethyl)-
quinoline (17n). Prepared from 16n in 44% overall yield and
obtained as a yellow oil. 1H NMR (DMSO-d6) δ 8.70 (d, J=8.7
Hz, 1H), 8.01 (d, J = 8.7 Hz, 1H), 7.48 (t, J = 9.6 Hz, 1H),
7.19-7.27 (m, 1H), 3.92 (s, 4H), 3.35 (t, J=5.6 Hz, 4H), 1.85 (t,
J=5.6 Hz, 4H). MS (ESIþ) (m/z) 357 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-5-fluoro-3-(trifluoro-
methyl)quinoline (17o). Prepared from 16o and isolated as a
beige solid in 30% yield. 1H NMR (chloroform-d) δ 9.10 (d, J=
2.2 Hz, 1H), 8.64 (d, J=2.1 Hz, 1H), 7.10-7.25 (m, 2H), 4.00 (s,
4H), 3.39 (t, J=4.9 Hz, 4H), 2.02 (t, J=4.9 Hz, 4H). MS (ESIþ)
(m/z) 357 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-3-fluoroquinoline (17h).
Prepared from 16h in 82% overall yield and obtained as a yellow
oil. 1H NMR (DMSO-d6) δ 8.85 (d, J=3.0 Hz, 1H), 8.14 (dd,
J1=9.7 Hz, J2=2.9 Hz, 1H), 7.44-7.52 (m, 2H), 7.12 (t, J=4.6
Hz, 1H), 3.91 (s, 4H), 3.36 (t, J=5.2 Hz, 4H), 1.84 (t, J=5.2 Hz,
4H). MS (ESIþ) (m/z) 289 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-3-methylquinoline (17i).
Prepared from 16i in 67% overall yield and obtained as a brown
oil. 1H NMR (chloroform-d) δ 8.73 (d, J=2.2 Hz, 1H), 7.82 (d,
J=1.2 Hz, 1H), 7.28-7.42 (m, 2H), 7.08 (dd, J1=7.3 Hz, J2=1.5
Hz, 1H), 4.00 (s, 4H), 3.46 (t, J=5.8 Hz, 4H), 2.05 (t, J=5.8 Hz,
4H). MS (ESIþ) (m/z) 285 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-5-fluoro-4-methoxy--2-
(trifluoromethyl)quinoline (17r). Prepared from 16r and isolated
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-3-(trifluoromethyl)quino-
line (17j). Prepared from 16j in 78% overall yield and obtained
as a beige solid. 1H NMR (chloroform-d) δ 9.07 (d, J=2.3 Hz,
1H), 8.38 (s, 1H), 7.45-7.58 (m, 2H), 7.28 (dd, J1=7.2 Hz, J2=
1.6 Hz, 1H), 4.03 (s, 4H), 3.48 (t, J=5.5 Hz, 4H), 2.43 (s, 3H),
2.05 (t, J=5.5 Hz, 4H). MS (ESIþ) (m/z) 339 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-4-methylquinoline (17k).
Prepared from 16k in 52% overall yield and obtained as a brown
oil. 1H NMR (chloroform-d) δ 8.72 (d, J=4.3 Hz, 1H), 7.59 (d,
J=8.4 Hz, 1H), 7.42 (t, J=7.7 Hz, 1H), 7.05-7.12 (m, 2H), 4.00
(s, 4H), 3.44 (t, J=4.8 Hz, 4H), 2.65 (s, 3H), 2.04 (t, J=4.9 Hz,
4H). MS (ESIþ) (m/z) 285 ([M þ H]þ).
1
as a beige solid in 64% yield. H NMR (DMSO-d6) δ 7.38 (s,
1H), 7.25-7.32 (m, 1H), 7.13-7.18 (m, 1H), 4.06 (s, 3H), 3.88 (s,
4H), 3.31 (t, J=5.5 Hz, 4H), 1.80 (t, J=5.5 Hz, 4H). MS (ESIþ)
(m/z) 387 ([M þ H]þ).
7-(1,4-Dioxa-8-azaspiro[4,5]dec-8-yl)-8-fluoroquinoline (17e).
A mixture of 16e (0.50 g, 3.03 mmol) and dioxa-8-azaspiro-4,5-
decane (5 mL, 39.1 mmol) was stirred at 120 ꢀC for 48 h. The
reaction was cooled to room temperature, poured into water, and
extracted three times with diethyl ether (30 mL). The combined
organic layers were dried over anhydrous sodium sulfate, filtered,
and concentrated on a rotary evaporator to give a residue consist-
ing of a mixture of 7- and 8-substituted regioisomers. The residue
was subjected to flash chromatography on silica gel. Elution with
30% ethyl acetate/hexane afforded the desired 8-(1,4-dioxa-8-
azaspiro[4,5]dec-8-yl)-7-fluoroquinoline (17e, 0.39 g,) as a yellow
oil. 1H -NMR (DMSO-d6) δ 8.80 (dd, J1=4.2 Hz, J2=1.5 Hz, 1H),
8.24 (d, J=8.3 Hz, 1H), 7.66 (d, J=8.9 Hz, 1H), 7.44 (t, J=8.4 Hz,
1H), 7.34-7.39 (m, 1H), 3.89 (s, 4H), 3.27 (t, J=5.1 Hz, 4H), 1.77
(t, J=5.1 Hz, 4H). MS (ESIþ) (m/z) 289 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-2,4-dmethylquinoline (17l).
Prepared from 16l in 43% overall yield and obtained as a brown
oil. 1H -NMR (chloroform-d) δ 7.55 (d, J1=8.4 Hz, 1H), 7.37 (t,
J=7.9 Hz, 1H), 7.13 (d, J=8.6 Hz, 1H), 7.09 (s, 1H), 4.02 (s, 4H),
3.47 (t, J=5.6 Hz, 4H), 2.68 (S, 3H), 2.62 (s, 3H), 2.05 (t, J=5.6
Hz, 4H). MS (ESIþ) (m/z) 299 ([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-4-methoxy-2-(trifluoro-
methyl)quinoline (17m). Prepared from 16m in 71% overall yield
and obtained as a yellow oil. 1H -NMR (DMSO-d6) δ 7.68 (d, J=
8.3 Hz, 1H), 7.51 (t, J=7.8 Hz, 1H), 7.32 (s, 1H), 7.20 (d, J=7.7
Hz, 1H), 4.08 (s, 3H), 3.89 (s, 4H), 3.37 (t, J=5.1 Hz, 4H), 1.82 (t,
J=5.1 Hz, 4H). MS (ESIþ) (m/z) 369 ([M þ H]þ).
The eluent was switched to 50% ethyl acetate/hexane and the
undesired 7-(1,4-dioxa-8-azaspiro[4,5]dec-8-yl)-8-fluoroquino-
line eluted and was obtained as a white solid (0.23 g). The
structures of both regioisomers were assigned by 1H NMR and
confirmed with a nuclear Overhauser effect spectroscopy ex-
periment (data not shown).
The synthesis of 1-quinolin-8-yl-pipiridin-4-one (18a). illus-
trates the general sequence used to prepare compounds 18a-r.
1-Quinolin-8-yl-pipiridin-4-one (18a). To a solution of 17a (4.0
g, 14.8 mmol) in tetrahydrofuran (10 mL) was added 2N HCl/
diethyl ether (10 mL). The resulting mixture was stirred at room
temperature overnight. The resulting reaction mixture was
diluted with water (100 mL), made basic with 2.5 N aqueous
sodium hydroxide, and extracted three times with dichloro-
methane (100 mL). The combined organic layers were dried
over anhydrous sodium sulfate, filtered, and concentrated on a
rotary evaporator to give the desired product (3.2 g, 95% yield)
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-3,5-difluoroquinoline (17p).
Prepared from 16 h in 39% overall yield and obtained as a
yellow oil. 1H -NMR (DMSO-d6) δ 8.55 (d, J=2.9 Hz, 1H), 7.70
(d, J=2.9 Hz, 1H), 6.98-7.15 (m, 2H), 3.90 (s, 4H), 2.82 (t,
J=5.6 Hz, 4H), 1.82 (t, J=5.6 Hz, 4H). MS (ESIþ) (m/z) 307
([M þ H]þ).
8-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)-5-fluoro-2,4-dimethyl-
quinoline (17q). Prepared from 16q in 30% overall yield and
obtained as a brown oil. 1H -NMR (chloroform-d) δ 7.10-7.16
(m, 1H), 6.95-7.05 (m, 2H), 3.99 (s, 4H), 3.34 (t, J=5.3 Hz, 4H),
2.77 (s, 3H), 2.72 (s, 3H), 2.04 (t, J=5.3 Hz, 4H). MS (ESIþ) (m/
z) 317 ([M þ H]þ).
The synthesis of 17b illustrates the general method used to
prepare compounds 17b, 17n-o and 17r.

4082 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
as a yellow oil which was used without further purification. 1H
NMR (chloroform-d) δ 8.92 (dd, J1=4.2 Hz, J2=1.7 Hz, 1H),
8.14 (dd, J1=8.4 Hz, J2=1.9 Hz, 1H), 7.35-7.53 (m, 3H), 7.17
(dd, J1=6.8 Hz, J2=1.9 Hz, 1H), 3.70 (t, J=6.2 Hz, 4H), 2.79 (t,
J=6.1 Hz, 4H). MS (ESIþ) (m/z) 227 ([M þ H]þ).
1-[4-Methoxy-2-(trifluoromethyl)quinolin-8-yl]piperidin-4-one
(18m). Prepared from 17m in 65% yield and obtained as an off-
white solid. H -NMR (DMSO-d6) δ 7.75 (d, J=8.2 Hz, 1H),
1
7.57 (t, J=8.0 Hz, 1H), 7.38 (s, 1H), 7.30 (d, J=7.7 Hz, 1H), 4.12
(s, 3H), 3.68 (t, J=5.9 Hz, 4H), 2.59 (t, J=5.9 Hz, 4H). MS
(ESIþ) (m/z) 325 ([M þ H]þ).
The following compounds were prepared using a similar
procedure.
1-[5-Fluoro-2-(trifluoromethyl)quinolin-8-yl]piperidin-4-one
(18n). Prepared from 17n in 79% yield and obtained as a yellow
solid. 1H NMR (DMSO-d6) δ 8.71 (d, J=8.7 Hz, 1H), 8.02 (d,
J=8.8 Hz, 1H), 7.49 (t, J=8.7 Hz, 1H), 7.24-7.30 (m, 1H), 3.62
(t, J=6.0 Hz, 4H), 2.57 (t, J=6.9 Hz, 4H). MS (ESIþ) (m/z) 313
([M þ H]þ).
1-(5-Fluoroquinolin-8-yl)piperidin-4-one (18b). Prepared from
17b in 91% yield and obtained as a tan solid. 1H NMR (DMSO-
d6) δ 8.95-9.00 (m, 1H), 8.43 (dd, J1=8.5 Hz, J2-2.4 Hz, 1H),
7.59-7.65 (m, 1H), 7.32 (t, J=9.1 Hz, 1H), 7.13-7.19 (m, 1H),
3.58 (t, J=6.0 Hz, 4H), 2.58 (t, J=6.0 Hz, 4H). MS (ESIþ) (m/z)
245 ([M þ H]þ).
1-[5-Fluoro-3-(trifluoromethyl)quinolin-8-yl]piperidin-4-one
(18o). Prepared from 17o in 71% yield and obtained as a yellow
solid. 1H NMR (chloroform-d) δ 9.12 (d, J=2.2 Hz, 1H), 8.66
(d, J=2.2 Hz, 1H), 7.10-7.25 (m, 2H), 3.61 (t, J=6.0 Hz, 4H),
2.74 (t, J=6.0 Hz, 4H). MS (ESIþ) (m/z) 313 ([M þ H]þ).
1-(3,5-Difluoroquinolin-8-yl)piperidin-4-one (18p). Prepared
1-(6-Fluoroquinolin-8-yl)piperidin-4-one (18c). Prepared from
17c in 66% yield and obtained as a white solid. 1H NMR
(DMSO-d6) δ 8.79 (dd, J1=4.2 Hz, J2=1.7 Hz, 1H), 8.25 (dd,
J1=8.4 Hz, J2=1.8 Hz, 1H), 7.45-7.53 (m, 1H), 7.25 (dd, J1=
9.0 Hz, J2=2.8 Hz, 1H), 7.02 (dd, J1=11.6 Hz, J2=2.8 Hz, 1H),
3.72 (t, J=6.1 Hz, 4H), 2,56 (t, J=6.1 Hz, 4H). MS (ESIþ) (m/z)
245 ([M þ H]þ).
1
in 68% yield from 17p and obtained as a yellow oil. H NMR
(DMSO-d6) δ 8.51 (d, J=2.8 Hz, 1H), 7.68 (d, J=2.8 Hz, 1H),
7.13-7.27 (m, 2H), 3.65 (t, J=5.8 Hz, 4H), 2.69 (t, J=5.8 Hz,
4H). MS (ESIþ) (m/z) 263 ([M þ H]þ).
1-(6-Bromoquinolin-8-yl)piperidin-4-one (18d). Prepared from
17d in 79% yield and obtained as a yellow oil. 1H NMR
(DMSO-d6) δ 8.89 (dd, J1=4.1 Hz, J2=1.8 Hz, 1H), 8.28 (dd,
J1=8.5 Hz, J2=1.8 Hz, 1H), 7.80 (d, J=2.1 Hz, 1H), 7.54-7.58
(m, 1H), 7.22 (d, J=2.1 Hz, 1H), 3.72 (t, J=6.0 Hz, 4H), 2.59 (t,
J=6.0 Hz, 4H). MS (ESIþ) (m/z) 305, 307 ([M þ H]þ).
1-(7-Fluoroquinolin-8-yl)piperidin-4-one (18e). Prepared from
17e in 80% yield and obtained as a yellow oil. 1H NMR (DMSO-d6)
δ8.88 (dd, J1=4.2 Hz, J2=1.7 Hz, 1H), 8.31 (dd, J1=8.3 Hz, J2=1.8
Hz, 1H), 7.63-7.69 (m, 1H), 7.42-7.50 (m, 2H), 3.66 (t, J=6.0 Hz,
4H), 2.53 t, J=6.0 Hz, 4H). MS (ESIþ) (m/z) 245 ([M þ H]þ).
1-(2-Methylquinolin-8-yl)piperidin-4-one (18f). Prepared from
17f in 95% yield and obtained as a yellow oil. 1H NMR
(chloroform-d) δ 8.00 (d, J=8.4 Hz, 1H), 7.32-7.41 (m, 1H),
7.25 (d, J=8.4 Hz, 1H), 7.05-7.17 (m, 2H), 3.70 (t, J=5.9 Hz,
4H), 2.76 (t, J=5.9 Hz, 4H), 2.73 (s, 3H). MS (ESIþ) (m/z) 241
([M þ H]þ).
1-[5-Fluoro-2,4-dimethylquinolin-8-yl]piperidin-4-one (18q).
Prepared from 17q in 65% yield and obtained as a yellow oil.
1H NMR (chloroform-d) δ 7.54-7.60 (m, 1H), 7.06-7.15 (m,
1H), 6.99-7.05 (m, 1H), 3.58 (t, J=6.0 Hz, 4H), 2.79 (t, J=
6.0 Hz, 4H), 2.77 (s, 3H), 2.69 (s, 3H). MS (ESIþ) (m/z) 244
([M þ H]þ).
1-[5-Fluoro-4-methoxy-2-(trifluoromethyl)quinolin-8-yl]pipe-
ridin-4-one (18r). Prepared from 17r in 77% yield and obtained
1
as a light-yellow solid. H NMR (DMSO-d6) δ 7.44 (s, 1H),
7.32-7.40 (m, 1H), 7.22-7.28 (m, 1H), 4.10 (s, 3H), 3.56 (t,
J=5.8 Hz, 4H), 2.57 (t, J=5.8 Hz, 4H). MS (ESIþ) (m/z) 343
([M þ H]þ).
Radioligand Binding Assays. Affinity for the human 5-HT1A
receptor was determined using a previously described method27
and employing a Chinese hampster ovary (CHO) cell line stably
transfected with the human 5-HT1A receptor and [3H]-8-OH-
DPAT as the standard radioligand. Results are expressed as Ki
values and are the average of at least three repetitions.
1-[2-(Trifluoromethyl)-quinolin-8-yl]piperidin-4-one (18g). Pre-
1
pared from 17g in 13% yield and obtained as a yellow oil. H
NMR (DMSO-d6) δ 8.64 (d, J = 8.3 Hz, 1H), 7.82 (d, J = 8.4
Hz, 1H), 7.33-7.42 (m, 1H), 7.12-7.20 (m, 1H), 7.04-7.14 (m,
1H), 3.62 (t, J = 5.8 Hz, 4H), 2.57 (t, J = 6.2 Hz, 4H). MS
(ESIþ) (m/z) 295 ([M þ H]þ).
cAMP Accumulation Assays. Intrinsic activity at the human
5-HT1A receptor was measured using a cAMP accumulation
assay in a CHO cell line stably transfected with the human
5-HT1A receptor.27 Details for the procedures used in this
manuscript are available in the Supporting Information.
Microsomal Stability Studies. Microsomal stability of
the compounds was determined by incubating compounds
with rat or human liver microsomes at 37 ꢀC for 20 min in the
presence of NADPH or a NADPH regenerating system.
Details for this procedure area available in the Supporting
Information.
Pharmacokinetic Studies. The pharmacokinetics of test com-
pounds were determined in male Sprague-Dawley rats after a
single 1 mg/kg iv dose (in 2% Tween 80) or a single 3 mg/kg po
dose (in 2% Tween 80/0.5% methylcellulose). Details for these
procedures are available in the Supporting Information.
In Vivo Microdialysis. In vivo microdialysis studies were
carried out as previously described with some modifications.7
Details for these procedures used in this manuscript are avail-
able in the Supporting Information.
Novel Object Recognition. Compound 10b was assessed for its
ability to improve cognitive function (recognition memory) in a
rat novel object recognition model as previously described.7
Details for this procedures used in this manuscript are available
in the Supporting Information.
Atlantis Water Maze. The Atlantis water maze model has
been described elsewhere.7 Details for this procedures used in
this manuscript are available in the Supporting Information.
Contextual Fear Conditioning. The contextual fear condition-
ing (CFC) model using male Tg2576 mice has been described
1-[3-Fluoroquinolin-8-yl]piperidin-4-one (18h). Prepared from
17h in 48% yield and obtained as a yellow oil. 1H NMR
(DMSO-d6) δ 8.81 (d, J=2.6 Hz, 1H), 8.10 (dd, J1=9.1 Hz,
J2=2.5 Hz, 1H), 7.39-7.47 (m, 2H), 7.08 (t, J=5.2 Hz, 1H), 3.38
(t, J=5.6 Hz, 4H), 1.88 (t, J=5.6 Hz, 4H). MS (ESIþ) (m/z) 245
([M þ H]þ).
1-(3-Methylquinolin-8-yl)piperidin-4-one (18i). Prepared from
17i in 96% yield and obtained as a yellow oil. 1H NMR
(chloroform-d) δ 8.76 (s, 1H), 7.88 (s, 1H), 7.32-7.42 (m, 2H),
7.05-7.16 (m, 1H), 3.67 (t, J=5.9 Hz, 4H), 2.76 (t, J=5.9 Hz,
4H), 2.49 (s, 3H). MS (ESIþ) (m/z) 241 ([M þ H]þ).
1-[3-(Trifluoromethyl)-quinolin-8-yl]piperidin-4-one (18j). Pre-
1
pared from 17j in 65% yield and obtained as a yellow oil. H
NMR (chloroform-d) δ 9.08 (d, J=2.2 Hz, 1H), 8.40 (s, 1H),
7.53-7.60 (m, 2H), 7.21-7.30 (m, 1H), 3.70 (t, J=5.9 Hz, 4H),
2.76 (t, J=5.9 Hz, 4H). MS (ESIþ) (m/z) 295 ([M þ H]þ).
1-(4-Methylquinolin-8-yl)piperidin-4-one (18k). Prepared from
17k in 92% yield and obtained as a brown oil. 1H NMR
(chloroform-d) δ 8.73 (d, J=4.3 Hz, 1H), 7.63 (d, J=8.4 Hz,
1H), 7.43 (t, J=7.7 Hz,, 1H), 7.15-7.25 (m, 1H), 7.14 (d, J=7.7
Hz, 1H), 3.65 (t, J=6.0 Hz, 4H), 2.75 (t, J=6.0 Hz, 4H), 2.66
(s, 3H). MS (ESIþ) (m/z) 241 ([M þ H]þ).
1-2,4-Dimethylquinolin-8-yl)piperidin-4-one (18l). Prepared
1
from 17l in 75% yield and obtained as an off-white solid. H
NMR (chloroform-d) δ 7.62 (d, J=8.4 Hz, 1H), 7.40 (t, J=7.9 Hz,
1H), 7.10-7.18 (m, 2H), 3.69 (t, J=6.0 Hz, 4H), 2.78 (t, J=6.0 Hz,
4H), 2.70 (s, 3H), 2.64 (s, 3H). MS (ESIþ) (m/z) 255 ([M þ H]þ).

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10 4083
elsewhere.51 Details for this procedures used in this manuscript
are available in the Supporting Information.
Schedule-Induced Polydipsia. The experimental details of the
schedule-induced polydipsia model have been published
elsewhere.52 Details for the procedures used in this manuscript
are available in the Supporting Information.
Olfactory Bulbectomy. Test compounds were examined for
their effects on olfactory bulbectomy-induced hyperactivity in
the absence and presence of fluoxetine, a selective serotonin
reuptake inhibitor. The experimental details of this model have
been published elsewhere.52 Details for the procedures used in
this manuscript are available in the Supporting Information.
Fluoxetine-Induced Sexual Dysfunction. The experimental
details for performing this model have been published
elsewhere.46 Data and an experimental description can be found
in the Supporting Information.
(10) Katz, M. M.; Tekell, J. L.; Bewden, C. L.; Branna, S.; Houston, J.
P.; Berm;an, N.; Fraer, A. Onset and early behavioral effects of
pharmacologically different antidepressants and placebo in depres-
sion. Neuropsychopharmacology 2004, 29, 566–579.
(11) Clayton, A. H.; Pradko, J. F.; Croft, J. A.; Montano, C. B.;
Leadbetter, R. A.; Bolden-Watson, C.; Bass, K. I.; Donahue, R.
M. J.; Jamerson, B. D.; Metz, A. Prevalence of sexual dysfunction
among newer antidepressants. J. Clin. Psychiatry 2002, 63, 357–
366.
(12) Kreiss, D. S.; Lucki, I. Effects of acute and repreated administra-
tion of antidepressant drugs on extracellular levels of 5-hydroxy-
tryptamine measured in vivo. J. Pharamcol. Exp. Ther. 1995, 274,
866–876.
(13) Blier, P.; Bergeron, R. J. The use of pindolol to potentiate
antidepressant medication. J. Clin. Psychiatry 1998, 59 (Suppl. 5),
16–23.
(14) Gartside, S. E.; Clifford, E. M.; Cowen, P. J.; Sharp, T. Effects of
(-) tertatolol, 9-0-penbutolol and (() pindolol in combination
with paroxetine on presynaptic 5-HT function: an in vivo micro-
dialysis and electrophysiological study. Br. J. Pharmacol. 1999,
127, 145–152.
(15) Sukoff-Rizzo, S. J.; Schechter, L. E.; Rosenzweig-Lipson, S. A
novel approach for predicting antidepressant-induced sexual dys-
function in rats. Psychopharmacology 2008, 195, 459–467.
(16) Childers, W. E. J.; Harrison, B. L.; Abou-Gharbia, M. A.; Raje, S.;
Parks, V.; Pangalos, M. N.; Schechter, L. E. Lecozotan Hydro-
chloride. Drugs Future 2007, 32, 399–407.
(17) Abou-Gharbia, M. A.; Childers, W. E., Jr.; Fletcher, H.;
McGaughey, G.; Patel, U.; Webb, M. B.; Yardley, J.; Andree, T.;
Boast, C.; Kucharik, R. J.; Marquis, K.; Morris, H.; Scerni, R.;
Moyer, J. A. Synthesis and SAR of adatanserin: novel adamantyl
aryl- and heteroarylpiperazines with dual serotonin 5-HT1A and
5-HT2 activity as potent anxiolytic and antidepresant agents.
J. Med. Chem. 1999, 42, 5077–5094.
(18) Yocca, F. D.; Hyslop, D. K.; Smith, D. W.; Maayani, S. BMY
7378, a buspirone analog with hgih affinity, selectivity and low
intrinsic activity at the 5-HT1A receptor in rat and guinea pig
hippocampal membranes. Eur. J. Pharmacol. 1987, 137, 293–294.
(19) Butler, S. G.; Meegan, M. J. Recent developments in the design of
anti-depressive therapies: targeting the serotonintransporter. Curr.
Med. Chem. 2008, 15, 1737–1761.
(20) Hatzenbuhler, N. T.; Baudy, R.; Evrard, D. A.; Failli, A.;
Harrison, B. L.; Lenecek, S.; Mewshaw, R. E.; Saab, A.; Shah,
U.; Sze, J.; Zhang, M.; Zhou, D.; Chlenov, M.; Kagen, M.;
Golembieski, J.; Hornby, G.; Lai, M.; Smith, D. L.; Sullivan, K.
M.; Schechter, L. E.; Andree, T. H. Advanced toward new anti-
depressants with dual serotonin transporter and 5-HT1A receptor
affinity within a class of 3-aminochroman derivatives. Part 2.
J. Med. Chem. 2008, 51, 6980–7004.
(21) Hatzenbuhler, N. T.; Evrard, D. A.; Harrison, B. L.; Huryn, D.;
Ingram, J.; Kraml, C.; Matter, J. F.; Mewshaw, R. E.; Zhou, D.;
Hornby, G.; Lin, Q.; Smith, D. L.; Sullivan, K. M.; Schechter,
L. E.; Andree, T. A. Synthesis and biological evaluation of novel
compounds within a class of 3-aminochroman derivatives with
dual 5-HT1A receptor and serotonin transporter activity. J. Med.
Chem. 2006, 49, 4785–4789.
(22) Asselin, M.; Grosu, G.; Childers, W.; Schecher, L.; Harrison, B.;
Sabb, A. Smith, D.; Hirst, W.; Andres, T. Design and synthesis of
novel substituted aryl- and heteroaryl-4-(piperidin-4-yl) pipera-
zines as serotonergic agents. 41st National Organic Chemsitry
Symposium, Boulder, June 7-11, 2009, B11.
(23) Asselin, M.; Grosu, T. G.; Sabb, A. L.; Childers, W. E.; Havran, L.
M.; Shen, Z.; Bicksler, J. J.; Chong, D. C. Piperazine-piperidine
antagonists and agonists of the 5-HT1A receptor. U.S. Patent
7,671,056, 2006.
(24) Skraup, Z. H. Eine synthese des chinolins. Chem. Ber. 1880, 13,
2086.
(25) Guram, A. S.; Buchwald, S. L. Palladium-Catalyzed Aromatic
Aminations with in Situ Generated Aminostannanes. J. Am. Chem.
Soc. 1994, 116, 7901–7902.
(26) Louie, J.; Hartwig, J. F. Palladium-catalyzed synthesis of aryl-
amines from aryl halides. Mechanistic studies lead to coupling in
the absence of tin reagents. Tetrahedron Lett. 1995, 36, 3609–3612.
(27) Dunlop, J.; Zhang, Y.; Smith, D. E.; Schechter, L. E. Character-
ization of the 5-HT1A Receptor Functional Coupling in Cells
Expressing the Human 5-HT1A Receptor as Assessed with the
Cytosensor Microphysiometer. J. Pharmacol. Toxicol. Methods
1998, 40, 47–55.
(28) Assie, M. B.; Kiek, W. Effects of 5-HT1A receptor antagonists on
hippocampal 5-hydroxy-tryptamine levels: (S)-WAY-100135 but
not WAY-100635 has partial agonist properties. Eur. J. Pharmacol.
1996, 304, 15–21.
Acknowledgment. The authors thank the members of the
Discovery Analytical Chemistry group for their assistance in
the spectroscopicconfirmation of the compounds described in
this manuscript.
Supporting Information Available: Detailed experimental
protocols for the pharmacology assays and a graph depicting
the effect of compound 10b on fluoxetine-induced sexual dys-
function. This material is available free of charge via the Internet
at http://pubs.acs.org.
References
(1) Pedigo, N. W.; Yamamura, H. I.; Nelson, D. I. Discrimination of
multiple [3H] 5-hydroxytryptamine binding sites by the neuroleptic
spiperone in rat brain. J. Neurochem. 1981, 36, 220–226.
(2) Fargin, A.; Raymond, J. R.; Lohse, M. J.; Kobilka, B. K.; Caron,
M. G.; Lefkowitz, R. J. The genomic clone G-21 which ersembles a
β-adrenergic reeptor sequence encodes the 5-HT1A receptor. Nat-
ure 1988, 335, 358–360.
(3) Lacivita, E.; Leopoldo, M.; Berardi, F.; Perrone, R. 5-HT1A
receptor, an old target for new therapeutic agents. Curr. Top.
Med. Chem. 2008, 8, 1024–1034.
(4) King, M. V.; Marsden, C. A.; Fone, K. C. F. A role for the
5-HT1A, 5-HT4 and 5-HT6 receptors in learning and memory.
Trends Pharmacol. Sci. 2008, 29, 482–492.
(5) Ogren, S. O.; Erikkson, T. M.; Elvander-Tottie, E.; D’Addario, C.;
Ekstrom, J. C.; Svenningsson, P.; Meister, B.; Kehr, J.; Stiedl, O.
The role of 5-HT1A receptors in learning and memory. Behav. Brain
Res. 2008, 195, 54–77.
(6) Chalmers, D. T.; Watson, S. J. Comparative anatomical distribu-
tion of 5-HT1A messenger-RNA and 5-HT1A binding in rat brain;
a combined in situ hybridisation in vitro receptor autoradiography
study. Brain Res. 1991, 561, 51–60.
(7) Hirst, W. D.; Andree, T. H.; Aschmies, S.; Childers, W. E.;
Comery, T. A.; Dawson, L. A.; Day, M.; Feingold, I. B.; Grauer,
S. M.; Harrison, B. L.; Hughes, Z. A.; Kao, J.; Kelly, M. G.; van der
Lee, H.; Rosenzweig-Lipson, S.; Saab, A. L.; Smith, D. L.;
Sullivan, K.; Sukoff-Rizzo, S. J.; Tio, C.; Zhang, M.-Y.; Schechter,
L. E. Correlating efficacy in rodent cognition models with in vivo
5-hydroxytryptamine1A receptor occupancy by a novel antagonist,
(R)-(2-methyl)-(4-indolyl-1-piperazinyl)ethyl)-N-(2-pyridinyl)-cyclo-
hexane carboxamide (WAY-101405). J. Pharmacol. Exp. Ther.
2008, 325, 134–145.
(8) Millan, M. J.; Gobert, A.; Roux, S.; Porsolt, R.; Meneses, A.; Carli,
M.; Di Cara, B.; Jaffard, R.; Rivet, J.-M.; Lestage, P.; Mocaer, E.;
Peglion, J.-L.; dekeyne, A. The serotonin1A receptor partial
agonist S15535 [4-(benzodioxan-5-yl)-1-(indan-2-yl)piperazine]
enhances cholinergic transmission and cognitive runction in rode-
nts: a combinedneurochemicaland behavioral analysis. J. Pharma-
col. Exp. Ther. 2004, 311, 190–203.
(9) Schechter, L. E.; Smith, D. L.; Rosenzweig-Lipson, S.; Sukoff,
S. J.; Dawson, L. A.; Marquis, K.; Jones, D.; Piesla, M.; Andree,
T.; Nawoschik, S.; Harder, J. A.; Womack, M. D.; Buccafusco, J.;
Terry, A. V.; Hoebel, B.; Rada, P.; Kelly, M.; Abou-Gharbia, M.;
Barrett, J. E.; Childers, W. Lecozotan (SRA-333): a selective
serotonin 1A receptor antagonist that enhances the stimulated
release of glutamate and acetylcholine in the hippocampus and
possesses cognitive-enhancing properties. J. Pharmacol. Exp. Ther.
2005, 314, 1274–1289.

4084 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 10
Childers et al.
(29) Bowen, D. M.; Francis, P. T.; Chessel, I. P.; Webster, M. T.
Neurotransmission;the link integrating Alzheimer’s disease?
Trends Neurosci. 1994, 17, 149–150.
(30) Ennaceur, A.; Delacour, J. A new one-trial test for neurobiological
studies of memory in rats. 1: behavioral data. Behav. Brain Res.
1988, 31, 47–59.
(31) Day, M.; Langston, R. F. Post-training N-methyl-D-aspartate
receptor blockade offers protection from retrograde interference
but does not affect consolidation of weak and strong memory
traces in water maze. Neuroscience 2006, 137, 19–28.
(32) Hsiao, K.; Chapman, P.; Nilson, S.; Eckman, C.; Harigaya, Y.;
Younkin, Y.; Yang, F.; Cole, G. Correlative memory deficits, Aβ
elevation and amyloid plaques in transgenic mice. Science 1996,
274, 99–102.
(33) Dineley, K. T.; Xia, X.; Bui, D.; Sweatt, D.; Zheng, H. Accelerated
plaque accumulations, associative learning deficits, and up-regula-
tion of R7 nicotinic receptor protein in transgenic mice co-expres-
sing mutant human Presenilin-1 and amyloid precursor protein.
J. Biol. Chem. 2002, 227, 22768–22780.
(42) Kelly, J. P.; Wrynn, A. S.; Leonard, B. E. The olfactory bulbectomy
rat model of depression;an update. Pharmacol. Ther. 1997, 74,
299–315.
(43) Landen, M.; Erikkson, E.; Agren, H.; Fahlen, T. Effects of
buspirone on sexual dysfunction in depressed patients treated with
selective serotonin reuptake inhibitors. J. Clin. Psychopharmacol.
1999, 19, 268–271.
(44) Norden, M. J. Buspirone treatment of sexual dysfunction asso-
ciated with selective serotonin reuptake inhibitors. Depression
1994, 2, 109–112.
(45) Baldwin, D.; Hutchinson, J.; Donaldson, K.; Shaw, B.; Smithers,
A. Selective serotonin re-uptake inhibitor treatment-emergent sex-
ual dysfunction: randomized double-blind placebo-controlled
parallel-group fixed-dose study of a potential adjuvant compound.
J. Psychopharmacol. 2008, 22, 55–63.
(46) Sukoff-Rizzo, S. J.; Schechter, L. E.; Rosenzweig-Lipson, S. A
novel approach for predicting antidepressant-induced sexual dys-
function in rats. Psychopharmacology 2008, 195, 459–467.
(47) Sukoff-Rizzo, S. J.; Pulicicchio, C.; Malberg, J. E.; Andree, T. H.;
Stack, G. P.; Hughes, Z. A.; Schechter, L. E.; Rosenzweig-Lipson,
S. 5-HT1A receptor antagonism reverses and prevents fluoxetine-
induced sexual dysfunction in rats. J. Neuropsychopharmacol. 2009,
12, 1045–1053.
(34) Corcoran, K. A.; Lu, Y.; Turner, R. S.; Maren, S. Overexpression
of hAPP-swe impairs rewarded alteration and contextual fear
conditioning in a transgenic mouse model of Alzheimer’s disease.
Learn. Mem. 2002, 9, 243–252.
(35) Blier, P.; De Montigny, C.; Chaput, Y. Modifications of the
serotonergic system by antidepressant treatment: implications for
the therapeutic response in major depression. J. Clin. Psychophar-
macol. 1987, 7, 24S–35S.
(36) Dawson, L. A.; Nguyen, H. Q. Effects of 5-HT1A antagonists on
fluoxetine-induced changes in extracullular serotonin concentra-
tions in rat frontal cortex. Eur. J. Pharmacol. 1998, 314, 41–46.
(37) Dawson, L. A.; Nguyen, J. Q.; Smith, D. L.; Schechter, L. E. Effect
of chronic fluoxetine and WAY-100635 treatment on serotonergic
neurotransmission in the frontal cortex. J. Psychopharmacol. 2002,
16, 145–152.
(48) Wen, H.; Goolcharran, C.; Ghosh, K.; Nagi, A. Sustained-release
tablet formulations of piperazine-piperidine antagonists and ago-
nists of the 5-HT1A receptor having enhanced intestinal dissolu-
tion. Patent WO 2008101139, 8/21/2008.
(49) Ku, M. S.; Dulin, W. A.; Lin, Y. A. Controlled-release formulation
of piperazine-piperidine antagonists and agonists of the 5-HT1A
receptor having enhanced intestinal dissolution. Patent WO
2008067399, 6/6/2008.
(50) Cottet, F.; Marull, M.; Lefebvre, O.; Schlosser, M. Recommend-
able routes to trifluoro-substituted pyridine- and quinolinecar-
boxylic acids. Eur. J. Org. Chem. 2003, 1559–1568.
(38) Czachura, J. F.; Rasmussen, K. Effect of acute and chronic
administration of fluoxetine on the activity of serotonergic neurons
in the dorsal raphe nucleus of the rat. Naunyn-Schmiedeberg’s Arch.
Pharmacol. 2000, 362, 266–275.
(39) Cryan, J. F.; McGrath, C.; Leonard, B. E.; Norman, T. R. Onset of
the effects of the 5-HT1A antagonist, WAY100635, alone and in
combination with paroxetine, on olfactory bulbectomy and 8-OH-
DPAT-induced changes in the rat. Pharmacol. Biochem. Behav.
1999, 63, 333–338.
(40) Woods, A.; Smith, C.; Szewczak, M.; Dunn, R. W.; Cornfelt,
M.; Corbett, R. Selective serotonin reuptake inhibitors decrease
schedule-induced polydipsia in rats: a potential model for obses-
sive compulsive disorder. Psychopharmacology 1993, 112, 195–
198.
(41) Hogg, S.; Dalvi, A. Acceleration of onset of action in schedule-
induced polydipsia: combination of SSRI and 5-HT1A and 5-HT1B
receptor antagonists. Pharmacol., Biochem. Behav. 2004, 77,
69–75.
(51) Comery, T. A.; Martone, R. L.; Achmies, S.; Atchinson, K. P.;
Diamantidis, G.; Gong, X.; Zhou, H.; Kreft, A. F.; Pangalos, M.
N.; Sonnenberg-Reines, J.; Jacobsen, J. S.; Marquis, K. L. Acute
g-secretase inhibition improves contextual fear conditioning in the
Tg2576 mouse model of Alzheimer’s disease. J. Neurosci. 2005, 25,
8898–8902.
(52) Rosenzweig-Lipson, S; Sabb, A.; Stack, G.; Mitchel, P.; Lucki, I.;
Malberg, J. E.; Grauer, S.; Brennan, J.; Cryan, J. F.; Sukoff-Rizzo,
S. J.; Dunlop, J.; Barrett, J. E.; Marquis, K. L. Antidepressant-like
effects of the novel, selective, 5-HT2C receptor agonist WAY-
163909 in rodents. Psychopharmacology 2008, 192, 159–170.
(53) Childers, W. E.; Abou-Gharbia, M. A.; Kelly, M. G.; Andree, T.
H.; Harrison, B. L.; Ho, D. M.; Hornby, G.; Huryn, D. M.;
Potestio, L.; Rosenzweig-Lipson, S. J.; Schmid, J.; Smith, D. L.;
Sukoff, S. J.; Zhang, G.; Schechter, L. E. Synthesis and Biological
Evaluation of Benzodioxanylpiperazine Derivatives as Potent
Serotonin 5-HT1A Antagonists: The Discovery of Lecozotan.
J. Med. Chem. 2005, 48, 3467–3470.