Synthesis and evaluation of structurally constrained quinazolinone derivatives as potent and selective histamine H3 receptor inverse agonists

Article abstract of DOI:10.1021/jm800569w

A series of structurally constrained derivatives of the potent H ₃ inverse agonist 1 was designed, synthesized, and evaluated as histamine H₃ receptor inverse agonists. As a result, the N-cyclobutylpiperidin-4-yloxy group as in 2f wa

Full text of DOI:10.1021/jm800569w

J. Med. Chem. 2008, 51, 6889–6901
6889
Synthesis and Evaluation of Structurally Constrained Quinazolinone Derivatives as Potent and
Selective Histamine H3 Receptor Inverse Agonists
Tsuyoshi Nagase, Takashi Mizutani, Etsuko Sekino, Shiho Ishikawa, Sayaka Ito, Yuko Mitobe, Yasuhisa Miyamoto,
Ryo Yoshimoto, Takeshi Tanaka, Akane Ishihara, Norihiro Takenaga, Shigeru Tokita, and Nagaaki Sato*
Tsukuba Research Institute, Merck Research Laboratories, Banyu Pharmaceutical Co., Ltd., Okubo 3, Tsukuba 300-2611, Japan
ReceiVed May 15, 2008
A series of structurally constrained derivatives of the potent H3 inverse agonist 1 was designed, synthesized,
and evaluated as histamine H3 receptor inverse agonists. As a result, the N-cyclobutylpiperidin-4-yloxy
group as in 2f was identified as an optimal surrogate structure for the flexible 1-pyrrolidinopropoxy group
of 1. Subsequent optimization of the quinazolinone core of 2f revealed that substitution at the 5-position of
the quinazolinone ring influences potency. Representative derivatives 5a and 5s showed improved potency
in a histamine release assay in rats and a receptor occupancy assay in mice.
Introduction
Histamine plays a variety of physiological roles in the
CNSa and peripheral tissues. In the CNS, histaminergic neurons
are exclusively localized in the tuberomammillary nucleus of
the hypothalamus but project widely throughout the CNS.1 There
are four known G protein-coupled receptors for histamine: H1,
H2, H3, and H4.2 The histamine receptors have unique signal
transduction pathways and distribution, which has led to the
discovery of a variety of physiological roles for histamine. Of
these receptors, H3 is predominantly expressed in the CNS, while
H1 and H2 are expressed in both central and peripheral tissues.3,4
Figure 1. Structures and antagonistic activities of nonimidazole H3
antagonists and inverse agonists. Antagonistic activities were determined
by inhibition of R-R-methylhistamine-induced binding of [35S]GTPγS
at human H3 receptor. The values represent the mean ( SE for n g 3.
The H4 receptor is predominantly expressed in inflammatory
cells, suggesting its critical role in the regulation of inflammatory
and immune responses.5
The H3 receptor was discovered pharmacologically in
19836 and genetically identified in 1999.3 The genetic
identification of the H3 receptor gained much attention and
redirected both the detailed pharmacological characterization
of the receptor and efforts from academia to the pharmaceuti-
cal industry to find drugs that bind specifically to H3.7
Signaling through the H3 receptor activates G proteins that
inhibit adenylate cyclase activity and reduce intracellular
cAMP levels.3,8 In the CNS, the H3 receptor is localized on
the presynaptic membrane as an autoreceptor and negatively
regulates the release and synthesis of histamine.6 In addition,
the H3 receptor is known to modulate the release of other
neurotransmitters such as norepinephrine, dopamine, acetyl-
choline, serotonin, and GABA.9 The H3 receptor signals
constitutively, which serves to tonically suppress target
neuronal activities such as histamine release to baseline
levels.10 Agonist-induced signaling that occurs in the presence
of elevated histamine levels further suppresses histamine
release. While classical antagonists would interfere with
histamine-mediated negative feedback, H3 receptor inverse
agonists have been demonstrated to decrease constitutive H3
signaling, thus blocking the tonic inhibition of histamine
release and further potentiating histaminergic effects. Because
of the effects of H3 signaling on multiple neuronal transmit-
ters, it has been suggested that H3 antagonists/inverse agonists
could be effective therapeutics for several CNS-related
disorders.11 In animal models, H3 receptor antagonists/inverse
agonists have been shown to enhance wakefulness and
attentive and cognitive behavior while reducing feeding and
body weight.12,13 Moreover, very recently it has been reported
that 25 (BF2.649) (Figure 1), a potent and selective H3
receptor inverse agonist, suppressed the excessive daytime
sleep of narcoleptic patients.14
First-generation imidazole-based H3 antagonists have
inhibitory activity on cytochrome P450 enzymes, which may
result in drug-drug interactions with coadministered drugs
by reducing hepatic clearance.15 Current efforts have focused
on nonimidazole classes of H3 receptor antagonists/inverse
agonists with the potential to reduce these liabilities. Since
the identification of the H3 receptor genes, various classes
of nonimidazole H3 receptor antagonists have been developed
to target H3 receptors in the CNS.7,12,16 Several of them,
including 25,14,17 26 (ABT-239),18 and 27 (GSK189254)19
(Figure 1), have entered clinical trials to evaluate their effec-
tiveness in treating CNS disorders such as excessive daytime
sleepiness, schizophrenia, and cognitive dysfunction.
Starting from the previously reported potent H3 inverse
agonist 1 (Figure 1),20 a series of structurally constrained ana-
logues were prepared and evaluated, aimed at improving its
potency. This approach was previously demonstrated by the
* To whom correspondence should be addressed. Phone: +81-29-877-
2004. Fax: +81-29-877-2029. E-mail: nagaaki_sato@merck.com.
a Abbreviations: P-gp, P-glycoprotein; SD rat, Sprague-Dawley rat;
SAR, structure-activity relationship; hERG, human ether-a-go-go-related
gene; HEK, human embryonic kidney; CNS, central nervous system; Ts,
4-toluenesulfonyl; Ms, methanesulfonyl; DIAD, diisopropyl azodicarboxy-
late; DEAD, diethyl azodicarboxylate.
10.1021/jm800569w CCC: $40.75
2008 American Chemical Society
Published on Web 10/08/2008

6890 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21
Nagase et al.
Scheme 1a
a Reagents: (a) DEAD, PPh3, THF; (b) trifluoroacetic acid, CHCl3; (c) R2R3CHI, K2CO3, DMF, 60 °C; (d) R2R3CO, ZnCl2, NaBH3CN, MeOH.
Scheme 2a
a Reagents: (a) 6, DIAD, PPh3, THF; (b) MsCl, Et3N, CH2Cl2; (c) pyrrolidine, K2CO3, DMF, 80 °C; (d) DIAD, PPh3, PhCO2H, THF; (e) K2CO3,
MeOH.
Scheme 3a
a Reagents: (a) 6, DIAD, PPh3, THF; (b) 10% HCl aq, THF; (c) pyrrolidine, ZnCl2, NaBH3CN, MeOH.
Johnson & Johnson group, in which an N-alkylpiperidin-4-yloxy
group was systematically investigated as a structurally con-
strained replacement for the amimopropoxy group and an
N-isopropylpiperidin-4-yloxy group was successfully identi-
fied.21 In the present SAR study, additional novel structurally
constrained tethers were designed and synthesized to replace
the flexible aminopropoxy group of 1, and the N-cyclobutylpi-
peridin-4-yloxy group22 as in 2f was identified as a useful
surrogate structure. The quinazolinone core of 2f was subse-
quently optimized to find potent analogues 5a-s. Compounds
5a and 5s were profiled in vivo and shown to have good
pharmacokinetic profiles and potent efficacy. In this report, the
design, synthesis, SAR of the structurally constrained quinazoli-
none class of H3 inverse agonists, and in vivo evaluation of the
potent derivatives 5 are described.
Chemistry
The synthetic route for the derivatives reported herein is
described in Schemes 1-4. Scheme 1 outlines the synthesis of
compounds 9b and 2a-l. Known compounds 623 and 7 were
coupled by the Mitsunobu reaction24 to give ethers 8, followed
by deprotection of the tert-butoxycarbonyl group to furnish
amines 9. The amino group of compounds 9 was alkylated with
the desired iodoalkane (method c) or reductively alkylated with
the desired ketones in the presence of sodium cyanoborohydride
and zinc chloride (method d) to furnish 2a-l. Preparation of

Quinazolinones as Histamine H3 Receptor InVerse Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21 6891
Scheme 4a
a Reagents: (a) 7b, NaH, DMF; (b) trifluoroacetic acid, CHCl3; (c) cyclobutanone, ZnCl2, NaBH3CN, MeOH; (d) (i) H2, 10% Pd/C, MeOH, (ii) TsOH ·H2O;
(e) AcOH, rt.
analogue 3a and its corresponding diastereomer 3b is illustrated
in Scheme 2. Cyclopentane-1,3-diol (10) and compound 6 were
coupled to give alcohol 11 as a single diastereomer in 99% yield.
Mesylation of the hydroxy group of 11 was followed by the
displacement with pyrrolidine to furnish amine 3a in good yield.
The corresponding diastereomer 3b was prepared by the
inversion of the hydroxy group configuration in compound 11
by the Mitsunobu protocol. The benzoate group of product 13
was cleaved, and the resulting hydroxy group was mesylated
and displaced with pyrrolidine to give diastereomer 3b in good
yield. The relative stereochemistry of diastereomers 3a and 3b
has not yet been established. The preparation of compound 4 is
shown in Scheme 3. Coupling reaction between 4,4-ethylene-
dioxycyclohexanol (16) and 6, followed by hydrolysis of the
ketal under acidic conditions, afforded the ketone 18, which
was reductively aminated with pyrrolidine to give amines 4a
and 4b after the separation of the diastereomeric mixture. The
quinazolinone ring-modified derivatives were conveniently
prepared as depicted in Scheme 4. Compound 7b was coupled
with 4-fluoronitrobenzene (19) in the presence of sodium hydride
followed by deprotection of the tert-butoxycarbonyl group to
afford the amine 21. Reductive alkylation of piperidine 21 with
cyclobutanone followed by reduction of the nitro group of
intermediate 22 gave the aniline 23, which was conveniently
isolated as a tosylate salt. Finally, the amino group of compound
23 was reacted with the desired substituted- or aza-benzoxazi-
nones 24a-s20,25 to furnish the derivatives 5a-s.
of compound 1 (hH3, IC50 ) 1.7 nM) (Figure 1) might be further
improved by imparting structural constraints to the flexible
propoxy moiety. In addition to the previously studied N-alkyl-
piperidin-4-yloxy group,21 novel structurally constrained tethers
were designed to have a cyclic structure in the aminopropoxy
region, conserving the three-carbon tether between the oxygen
and nitrogen atoms of the aminopropoxy moiety (Table 1).
First, we prepared a variety of N-substituted piperidinyloxy
derivatives 2a-h. N-Substitution is essential for activity because
the nonsubstituted derivative 9b is devoid of potency. The ethyl
derivative 2b displayed the highest activity (IC50 ) 49 nM)
among the unbranched alkyl derivatives 2a-d. Further extension
of the alkyl chain was not attempted due to the decreased
binding affinities of analogues 2c and 2d. The isopropyl
derivative 2e was 3-fold more potent than the ethyl derivative
2b. The cyclobutyl derivative 2f (IC50 ) 1.5 nM) showed a
10-fold improvement over 2e, while ring expansion as in
analogues 2g and 2h resulted in decreases in potency.
Second, the piperidine was replaced by pyrrolidine and
azacycloheptane (2i-l), which affects the direction of the
N-alkyl substituent. The cyclobutyl and cyclopentylpyrrolidine
derivatives (2i and 2j) displayed significantly decreased activi-
ties. The azacycloheptane derivatives 2k and 2l were somewhat
less potent than the corresponding piperidine derivatives 2f and
2g. Further ring expansion was not attempted because undesir-
able hERG activity was observed for compounds 2k and 2l,
possibly attributed to an increase in lipophilicity for those
analogues.
Finally, the nitrogen atom was incorporated in the distal ring
as in cycloalkyl analogues 3 and 4. The cyclopentyl derivative
3a showed a potent H3 activity (IC50 ) 3.4 nM) with a
satisfactory hERG activity. The corresponding diastereomer 3b
was less potent. The cyclohexyl derivatives 4a and 4b were
prepared even though they have a four-carbon tether. The trans-
isomer 4a showed good activity despite its four-carbon tether,
and the corresponding cis-isomer 4b was significantly less potent
than 4a. In this structurally constrained design, the cyclobu-
tylpiperidinyloxy structure 2f was identified as a potent sub-
structure. It should be noted that racemic 3a has the potential
for additional improvement by modification of the size of the
two rings.
Results and Discussion
The compounds were tested using the [35S]GTPγS binding
assay in membranes isolated from cells transfected with cloned
H3 receptors.20 All the quinazolinone derivatives reported herein
reduced the basal GTPγS binding, indicating that they are
inverse agonists. Selected compounds were evaluated for hERG
K+ channel inhibitory activity in the [35S]N-[(4R)-1′-[(2R)-6-
cyano-1,2,3,4-tetrahydro-2-naphthalenyl]-3,4-dihydro-4-
hydroxyspiro[2H-1-benzopyran-2,4′-piperidin]-6-yl]methane-
sulfonamide binding assay to assess cardiac QTc prolongation
liability.26 We recently discovered the quinazolinone class of
histamine H3 receptor inverse agonists and identified the clinical
development candidate 1 (Figure 1).20 The essential pharma-
cophore of the quinazolinone derivatives is the aminopro-
poxyphenyl portion that is a common structural motif recognized
by a number of research groups. We envisioned that the potency
Further optimization of 2f by the modification of the
quinazolinone group is summarized in Table 2. The fluorine-
substituted derivatives 5a-e displayed improved activities

6892 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21
Table 1. In Vitro Profiles of Compounds 1, 2-4, and 9ba
Nagase et al.
Table 2. In Vitro Potency of Compounds 5a-sa
b
compd
R
human H3 (IC50, nM)
hERG (IC50, µM)c
2f
H
5-F
6-F
7-F
8-F
6,7-diF
5-Cl
6-Cl
7-Cl
1.5 ( 0.3
0.55 ( 0.04
1.2 ( 0.1
1.3 ( 0.1
0.84 ( 0.12
0.91 ( 0.06
0.34 ( 0.14
1.5 ( 0.2
3.0 ( 0.5
1.7 ( 0.1
1.2 ( 0.3
1.5 ( 0.1
1.8 ( 0.4
4.2 ( 1.0
14 ( 1
>10
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
5s
>10
>10
>10
>10
>10
>10
5.4 ( 0.2
3.9 ( 0.3
3.3 ( 0.8
>10
8-Cl
5-OCH3
6-OCH3
7-OCH3
8-OCH3
5-Aza
6-Aza
7-Aza
8-Aza
5-CH3
5-CF3
>10
>10
>10
>10
2.0 ( 0.4
1.8 ( 0.2
1.6 ( 0.2
0.27 ( 0.08
0.33 ( 0.05
>10
>10
>10
>10
>10
a The values represent the mean ( SE for n g 3. b Inhibition of R-R-
methylhistamine-induced binding of [35S]GTPγS at human H3 receptor.
c Inhibition of [35S]N-[(4R)-1′-[(2R)-6-cyano-1,2,3,4-tetrahydro-2-naphtha-
lenyl]-3,4-dihydro-4-hydroxyspiro[2H-1-benzopyran-2,4′-piperidin]-6-yl-
]methanesulfonamide binding to hERG in HEK293 cells.
Table 3. Pharmacokinetic Parameters of 5a, 5r, and 5sa
IV Clp
PO AUC0-∞
Cmax
compd
species
(mL/min/kg)
(µM·h)
(µM)
F (%)
5a
rat
dog
monkey
rat
dog
monkey
rat
dog
11
44
27
25
17
17
24
13
26
6.2
0.05
1.7
2.33
5.6
0.08
1.66
1.3
1.3
53
4.8
37
40
76
1
33
46
11
0.02
0.38
0.56
1.1
0.02
0.42
0.28
0.05
5r
5s
monkey
0.15
a The reported data are an average generated after 1 mg/kg iv and 3
mg/kg po doses in n ) 3 animals/dose for rats and 0.3 mg/kg iv and 1
mg/kg po doses in n ) 3 animals/dose for dogs and monkeys.
not effective in improving potency. The derivatives with an
electron-donating methoxy substituent (5j-m) did not show
noticeable improvement. Regarding the aza derivatives, the 5-aza
derivative 5n showed a significant decrease in potency while
the other aza derivatives 5o-q were tolerated. Encouraged by
the improved potency demonstrated by the 5-chloro and fluoro
derivatives (5a and 5f), 5-methyl and 5-trifluoromethyl deriva-
tives 5r and 5s were prepared and found to possess 5-fold more
potent activities than 2f. This enhancement of potency by the
5-substitution of the quinazolinone ring is specific to these
N-cyclobutylpiperidinyloxy derivatives and was not observed
in the flexible propoxy derivatives.20 Compounds 5a, 5r, and
5s were demonstrated to reduce basal GTPγS binding with EC50
values of 1.1, 0.34, and 0.71 nM, respectively, indicating that
these three compounds are inverse agonists.
The representative potent 5-substituted derivatives 5a, 5r, and
5s were evaluated in pharmacokinetic studies (Table 3). All three
compounds showed suitable pharmacokinetic profiles for in vivo
evaluation in SD rats. The systemic exposure of compound 5a
in rats was much higher (AUC0-∞ ) 6.2 µM·h, Cmax ) 1.3
µM) than those of compounds 5r and 5s. The pharmacokinetic
profile of compound 5a in dogs, however, was very poor, which
a The values represent the mean ( SE for n g 3. b Inhibition of R-R-
methylhistamine-induced binding of [35S]GTPγS at human H3 receptor.
c Inhibition of [35S]N-[(4R)-1′-[(2R)-6-cyano-1,2,3,4-tetrahydro-2-naphtha-
lenyl]-3,4-dihydro-4-hydroxyspiro[2H-1-benzopyran-2,4′-piperidin]-6-yl-
]methanesulfonamide binding to hERG in HEK293 cells. d Not determined.
compared to the parent 2f. The 5-fluoro 5a (IC50 ) 0.55 nM)
was the most potent derivative. In the chloro derivatives 5f-i,
the 5-chloro derivative 5f was 4-fold more potent than the parent
2f, while chloro substitution at the other positions (5g-i) was

Quinazolinones as Histamine H3 Receptor InVerse Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21 6893
Table 4. Brain Penetration and P-gp Susceptibility of 5a, 5r, and 5s
brain penetration in SD ratsa
P-gp susceptibilityb
ratio
brain/plasma
transcellular transport ratio (B-to-A)/(A-to-B)
compd
plasma (µM)
brain (nmol/g)
CSF (µM)
CSF/brain
mouse mdr1a
human MDR1
5a
5r
5s
2.4
1.4
0.7
7.6
3.2
2.3
0.95
0.10
0.11
3.2
2.3
3.3
0.13
0.03
0.05
1.8
1.0
2.5
1.0
0.9
0.7
a The concentrations were determined at 2 h after 10 mg/kg oral administration. The values represent the mean for n ) 3 animals. b Transcellular transport
ratio ((B-to-A)/(A-to-B)) in human MDR1- and mouse mdr1a-transfected LLC-PK1 cell line. The values represent the mean for n ) 3. The value above 3.0
indicates that a compound is a P-gp substrate.
Table 5. Binding Affinities of Compounds 5a, 5r, and 5s for the
seems to be necessary for the H3 inverse agonists to exhibit
significant elevation of brain histamine in rats.30
Human, Rat, and Mouse H3 Receptorsa
H3 binding affinity (Ki, nM)b
As a first step in estimating efficacious plasma levels in
humans, we decided to study receptor occupancy of 5a and 5s
in mice in detail. As shown in Table 4, 5a and 5s are not human
P-gp substrates but may be weak mouse P-gp substrates. Hence,
brain exposure and receptor occupancy studies in P-gp-deficient
mdr1a (-/-) and wild type mdr1a (+/+) CF-1 mice31 were
carried out. The plasma and brain concentrations were deter-
mined 2 h after oral administration of 0.3 mg/kg of 5a and 1
mg/kg of 5s in mdr1a (-/-) and mdr1a (+/+) CF-1 mice
(Table 6). The comparison of the brain-to-plasma ratios in mdr1a
(-/-) and mdr1a (+/+) CF-1 mice clearly suggests that P-gp-
mediated efflux has a considerable influence on brain penetration
of 5a and 5s in CF-1 mice. The brain-to-plasma ratios for 5a
and 5s in mdr1a (-/-) CF-1 mice were 9.4 and 13, which are
about 5-fold higher than those in mdr1a (+/+) CF-1 mice (1.9
for 5a and 2.6 for 5s).
Next, the receptor occupancy-brain concentration relation-
ships were studied in CF-1 mice (Figure 3). The brain
concentrations that are required to achieve 90% receptor
occupancy (brain Occ90) for 5a and 5s were determined to be
0.28 and 0.15 nmol/g, respectively. The plasma Occ90 values
were estimated from the brain Occ90 values and the brain-to-
plasma ratios (plasma Occ90 ) brain Occ90/brain-to-plasma
ratio), and the results are shown in Table 6. The estimated
plasma Occ90 values in Table 6 suggest that the plasma Occ90
values in humans might be as low as 30 nM for 5a and 11 nM
for 5s. On the basis of the human P-gp transcellular transport
ratios for 5a and 5s, it is assumed that the effect of P-gp-
mediated efflux is negligible in humans. Investigation of receptor
occupancy in other higher species by noninvasive receptor
occupancy determination methods such as the positron emission
tomography is necessary to confirm these predictions. Examina-
tion of the relationship between the degree of receptor occupancy
and efficacy in animal models using 5a and 5s is in progress.
compd
human
rat
mouse
5a
5r
5s
6.8 ( 1.9
1.7 ( 0.4
3.6 ( 0.7
6.0 ( 0.7
1.8 ( 0.1
2.3 ( 0.1
8.4 ( 1.0
3.9 ( 0.6
3.9 ( 0.5
a The values represent the mean ( SE for n g 3. b Displacement of
[3H]N-R-methylhistamine binding to cell membranes expressing recombinant
H3 receptors.
is most likely due to the significantly higher clearance value.
Compounds 5r and 5s showed good systemic exposure and oral
bioavailability in dogs. In contrast, the pharmacokinetic profiles
of 5s and 5r in monkeys were poor, whereas 5a exhibited a
fair profile in monkeys. It should be noted that the clearance
value of 5a in monkeys is the highest (Clp ) 27 mL/min/kg)
among the three derivatives, so the poor pharmacokinetic profiles
of 5r and 5s may be caused by monkey-specific absorption
problems.
The compounds were studied for their ability to penetrate
the CNS using several assays. The brain and cerebrospinal fluid
(CSF) levels in SD rats 2 h following 10 mg/kg oral administra-
tion of 5a, 5r, and 5s were examined (Table 4). All the
derivatives displayed good brain and CSF exposure. P-gp
susceptibility was evaluated28 as a pivotal factor for brain
penetration, and none of them were found to be substrates for
human P-gp (MDR1) (Table 4). Compounds 5a and 5s might
be very weak substrates for mouse P-gp (mdr1a); see further
discussion below regarding mouse P-gp susceptibility. Com-
pounds 5a and 5s were confirmed to have excellent selectivity
with respect to other histamine receptor subtypes (IC50 > 10
µM for hH1, hH2, and hH4) and to a panel of 115 diverse,
unrelated binding sites (IC50 >1 µM for all the binding sites
tested). The binding affinities of compounds 5a, 5r, and 5r for
the human, rat, and mouse H3 receptors are summarized in Table
5. The compounds showed potent binding affinities, and no
significant species difference in binding affinity was observed.
Summary
Having demonstrated excellent potency, selectivity, pharma-
cokinetic profile, and brain penetration, 5a and 5s were tested
for brain histamine release in SD rats. In our histamine release
assay,29 the test compound (po) and pargyline (ip), a monoamine
oxidase inhibitor, were codosed in SD rats. After 2 h, the whole
brain was rapidly removed, and the concentration of tele-
methylhistamine, a major extracellular metabolite of histamine,
was measured. Significant and dose-proportional elevation of
tele-methylhistamine was observed in the rat brain after oral
administration of 5a and 5s (Figure 2).
Brain histamine H3 receptor occupancy was evaluated by an
ex vivo receptor occupancy method for correlation with the
observed histamine elevation. The brain H3 receptor was shown
to be highly occupied (>90%) 2 h following oral administration
of 1 mg/kg of 5a and 5s. A high degree of receptor occupancy
A series of structurally constrained analogues of potent H3
inverse agonist 1 were designed, synthesized, and evaluated as
histamine H3 receptor inverse agonists. As a result, the N-cy-
clobutylpiperidin-4-yloxy group as in compound 2f was identi-
fied as an optimal surrogate structure for the flexible 3-(1-
pyrrolidinyl)propoxy group of lead compound 1. Subsequent
optimization of the quinazolinone 2f revealed that substitution
at the 5-position of the quinazolinone ring markedly enhances
in vitro potency. Representative analogues 5a and 5s had
excellent selectivity with respect to other histamine receptor
subtypes and to 115 diverse unrelated binding sites. Compounds
5a and 5s showed satisfactory pharmacokinetic profiles and brain
penetrability in the preclinical animals. Two hours following
oral administration of 5a and 5s in SD rats, a dose-proportional
and statistically significant increase of brain histamine levels

6894 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21
Nagase et al.
Figure 2. Brain tele-methylhistamine levels in SD rats after oral administration of 5a and 5s. Values are means ( SE, determined from five
experiments. * P < 0.05 and ** P < 0.01 (ANOVA Dunnett) compared with the vehicle control.
Table 6. Brain Penetration and Plasma Occ90 Values of 5a and 5s in
P-gp-deficient mdr1a (-/-) and Wild Type mdr1a (+/+) CF-1 Micea
istration of compound 5s at a dose of 100 mg/kg caused no
treatment-related changes in psychomotor activities, motor
activities, muscle tone, CNS excitation, autonomic responses,
and reflexes.27 Further profiling of 5a and 5s is in progress to
select an improved clinical candidate from this class, and
updated results will be reported in due course.
plasmab
(µM)
brainb
(nmol/g)
brain/
plasma
compd
plasmac Occ90d (nM)
5a
mdr1a (+/+) 0.032 ( 0.002 0.062 ( 0.002
mdr1a (-/-) 0.028 ( 0.001 0.260 ( 0.039
mdr1a (+/+) 0.012 ( 0.001 0.031 ( 0.002
1.9
9.4
2.6
144
30
58
5s
mdr1a (-/-) 0.010 ( 0.002 0.137 ( 0.014 13
11
Experimental Section
a The brain and plasma concentrations were obtained 2 h following oral
administration of 5a (0.3 mg/kg) and 5s (1 mg/kg) in mice. b The values
represent the mean ( SE for n ) 3. c The ratios were obtained from the
mean values. d Plasma Occ90 was calculated by brain Occ90/brain to plasma
ratio. The brain Occ90 values for 5a and 5s are 0.28 nmol/g and 0.15 nmol/
g, respectively (Figure 3).
Chemistry. General Procedures. Unless otherwise noted, all
solvents, chemicals, and reagents were obtained commercially
and used without purification. The 1H NMR spectra were
obtained at 400 MHz on a MERCURY-400 (Varian) or JMN-
AL400 (JEOL) spectrometer, with chemical shift (δ, ppm)
reported relative to TMS as an internal standard. Mass spectra
were recorded with electron-spray ionization (ESI) or atmo-
spheric pressure chemical ionization (APCI) on a Waters
micromass ZQ, micromass Quattro II, or micromass Q-Tof-2
instrument. Flash chromatography was carried out with pre-
packed silica gel columns (KP-Sil silica) from Biotage. Prepara-
tive thin-layer chromatography was performed on a TLC Silica
gel 60 F (Merck KGaA). Preparative HPLC purification was
carried out on a YMC-Pack Pro C18 (YMC, 50 mm × 30 mm
id), eluting with a gradient of CH3CN/0.1% aqueous CF3CO2H
at a flow rate of 40 mL/min. Purity of target compounds was
determined by HPLC with the two different eluting methods as
follows. Analytical HPLC was performed on a SPELCO Ascentis
Express (4.6 mm × 150 mm id), eluting with a gradient of (A)
0.1% H3PO4/CH3CN ) 95/5 to 10/90 over 7 min followed by
10/90 isocratic over 1 min and (B) 10 mM potassium phosphate
buffer (pH 6.6)/CH3CN ) 95/5 to 20/80 over 7 min followed
by 20/80 isocratic over 1 min (detection at 210 nm). High
resolution mass spectra were recorded with electron-spray
ionization on a micromass Q-Tof-2 instrument.
General Procedure for the Preparation of 2a–e via Alkylation.
3-(4-[(1-Ethyl-4-piperidinyl)oxy]phenyl)-2-methyl-4(3H)-quinazoli-
none (2b). To a mixture of 9b (50 mg, 0.15 mmol) and potassium
carbonate (42 mg, 0.30 mmol) in dry DMF (1 mL) was added
ethyl iodide (23 mg, 0.15 mmol) under a nitrogen atmosphere,
and the mixture was stirred at room temperature for 1 h. The
resulting mixture was partitioned between ethyl acetate and 1
N NaOH. The layers were separated, and the aqueous layer was
extracted with ethyl acetate twice. The combined organic layers
were washed with 1 N NaOH and brine, dried over sodium
sulfate, and concentrated. The residue was purified by silica gel
column chromatography with 3% CHCl3 in methanol to give 2b
as a colorless solid (25 mg, 46%); HPLC purity (99.2%). 1H
NMR (400 MHz, CDCl3) δ 1.12 (3H, J ) 6.8 Hz), 1.83-1.95
(2H, m), 2.02-2.10 (2H, m), 2.26 (3H, s), 2.26-2.39 (2H, m),
2.45 (2H, q, J ) 7.2 Hz), 2.72-2.81 (2H, m), 4.35-4.43 (1H,
m), 7.03 (2H, d, J ) 8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.44
(1H, t, J ) 8.0 Hz), 7.65 (1H, d, J ) 8.0 Hz), 7.74 (1H, t, J )
8.0 Hz), 8.25 (1H, d, J ) 8.0 Hz); MS (ESI) m/z 364 (M +
H)+. HRMS (M + H)+ calcd for C22H26N3O2, 364.2025; found,
364.2020.
Figure 3. The brain concentration-receptor occupancy relationship
of (a) 5a and (b) 5s in CF-1 mice. Receptor occupancy and exposure
were determined 2 h following oral administration of vehicle or
compound 5a or 5s (0.1, 0.3, 1, and 3 mg/kg). See Supporting
Information for experimental details.
was observed, indicating that the brain H3 receptors were highly
occupied (>90%). The plasma Occ90 for 5s in humans was
estimated to be as low as 11 nM based on P-gp susceptibility
and the receptor occupancy studies in P-gp-deficient mdr1a
(-/-) and wild type mdr1a (+/+) CF-1 mice. The potential
cardiovascular effects of compound 5s were evaluated in
anesthetized and ventilated dogs.27 At 3 mg/kg iv dosing (Cmax
) 3.2 µM), no adverse treatment-related cardiovascular effects
were observed. Regarding gross behavior in mice, oral admin-

Quinazolinones as Histamine H3 Receptor InVerse Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21 6895
2-Methyl-3-(4-[(1-methyl-4-piperidinyl)oxy]phenyl)-4(3H)-
quinazolinone (2a). Compound 2a was prepared from methyl iodide
and 9b using the procedure described for 2b as a colorless solid
m), 7.03 (2H, d, J ) 8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.44 (1H,
t, J ) 7.2 Hz), 7.65 (1H, d, J ) 7.6 Hz), 7.74 (1H, t, J ) 7.2 Hz),
8.25 (1H, d, J ) 7.6 Hz). MS (ESI) m/z 418 (M + H)+. HRMS
(M + H)+ calcd for C26H32N3O2, 418.2495; found, 418.2505.
3-(4-[(1-Cyclohexyl-4-piperidinyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2h). Compound 2h was prepared from cyclohex-
anone and 9b using the procedure described for 2f as a colorless
solid (48% yield); HPLC purity (99.5%). 1H NMR (400 MHz,
CDCl3) δ 1.18-1.30 (6H, m), 1.78-1.90 (6H, m), 2.01-2.08 (2H,
m), 2.26 (3H, s), 2.27-2.36 (1H, m), 2.42-2.51 (2H, m), 2.81-2.89
(2H, m), 4.30-4.38 (1H, m), 7.03 (2H, d, J ) 8.8 Hz), 7.13 (2H,
d, J ) 8.8 Hz), 7.44 (1H, t, J ) 8.0 Hz), 7.65 (1H, d, J ) 8.0 Hz),
7.74 (1H, t, J ) 8.0 Hz), 8.25 (1H, d, J ) 8.0 Hz). MS (ESI) m/z
418 (M + H)+. HRMS (M + H)+ calcd for C26H32N3O2, 418.2495;
found, 418.2505.
3-(4-[(1-Cyclobutyl-3-pyrrolidinyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2i). Compound 2i was prepared from cyclobutanone
and 9a using the procedure described for 2f as a beige solid (21%
yield); HPLC purity (97.4%). 1H NMR (400 MHz, CDCl3) δ
1.68-1.78 (2H, m), 1.94-2.07 (5H, m), 2.25 (3H, s), 2.30-2.35
(1H, m), 2.46-2.52 (1H, m), 2.71-2.76 (2H, m), 2.86-2.91 (1H,
m), 2.93-3.00 (1H, m), 4.83-4.87 (1H, m), 6.96 (2H, d, J ) 8.8
Hz), 7.12 (2H, d, J ) 8.8 Hz), 7.44 (1H, t, J ) 8.1 Hz), 7.64 (1H,
d, J ) 8.1 Hz), 7.74 (1H, t, J ) 8.1 Hz), 8.24 (1H, d, J ) 8.1 Hz).
MS (ESI) m/z 376 (M + H)+. HRMS (M + H)+ calcd for
C23H26N3O2, 376.2025; found, 376.2019.
3-(4-[(1-Cyclopentyl-3-pyrrolidinyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2j). Compound 2j was prepared from cyclopen-
tanone and 9a using the procedure described for 2f as a colorless
oil (18% yield); HPLC purity (97.9%). 1H NMR (400 MHz, CDCl3)
δ 1.45-1.57 (4H, m), 1.66-1.88 (4H, m), 1.98-2.05 (1H, m), 2.25
(3H, s), 2.31-2.36 (1H, m), 2.46-2.52 (1H, m), 2.52-2.61 (1H,
m), 2.79-2.84 (2H, m), 3.00-2.97 (1H, m), 4.82-4.87 (1H, m),
6.96 (2H, d, J ) 8.8 Hz), 7.12 (2H, d, J ) 8.8 Hz), 7.44 (1H, t, J
) 8.1 Hz), 7.64 (1H, d, J ) 8.1 Hz), 7.74 (1H, t, J ) 8.1 Hz), 8.24
(1H, d, J ) 8.1 Hz). MS (ESI) m/z 390 (M + H)+. HRMS (M +
H)+ calcd for C24H28N3O2, 390.2182; found, 390.2185.
3-(4-[(1-Cyclobutyl-4-azepanyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2k). Compound 2k was prepared from cyclobu-
tanone and 9c using the procedure described for 2f as a pale-yellow
oil (28% yield); HPLC purity (99.3%). 1H NMR (400 MHz, CDCl3)
δ 1.57-2.18 (12H, m), 2.24 (3H, s), 2.39-2.50 (2H, m), 2.53-2.62
(2H, m), 2.85-2.95 (1H, m), 4.54-4.61 (1H, m), 6.96 (2H, d, J )
8.8 Hz), 7.10 (2H, d, J ) 8.8 Hz), 7.43 (1H, t, J ) 8.0 Hz), 7.63
(1H, d, J ) 7.2 Hz), 7.72 (1H, t, J ) 7.2 Hz), 8.23 (1H, d, J ) 8.0
Hz). MS (ESI) m/z 404 (M + H)+. HRMS (M + H)+ calcd for
C25H30N3O2, 404.2338; found, 404.2346.
1
(13% yield); HPLC purity (95.1%). H NMR (400 MHz, CDCl3)
δ 1.91-1.99 (2H, br m), 2.06-2.18 (2H, br m), 2.27 (3H, s),
2.36-2.51 (2H, br m), 2.39 (3H, s), 2.74-2.82 (2H, br m),
4.40-4.46 (1H, br m), 7.05 (2H, d, J ) 8.8 Hz), 7.16 (2H, d, J )
8.8 Hz), 7.47 (1H, t, J ) 7.8 Hz), 7.67 (1H, d, J ) 7.8 Hz), 7.77
(1H, td, J ) 7.8, 1.5 Hz), 8.27 (1H, dd, J ) 7.8, 1.5 Hz). MS
(ESI) m/z 350 (M + H)+. HRMS (M + H)+ calcd for C21H24N3O2,
350.1869; found, 350.1865.
2-Methyl-3-(4-[(1-propyl-4-piperidinyl)oxy]phenyl)-4(3H)-
quinazolinone (2c). Compound 2c was prepared from n-propyl
iodide and 9b using the procedure described for 2b as a colorless
solid (48% yield); HPLC purity (95.6%). 1H NMR (400 MHz,
CDCl3) δ; 0.93 (3H, t, J ) 7.3 Hz), 1.55-1.69 (2H, br m),
1.88-1.97 (2H, br m), 2.06-2.18 (2H, br m), 2.27 (3H, s),
2.31-2.49 (4H, br m), 2.76-2.85 (2H, br m), 4.37-4.46 (1H, br
m), 7.04 (2H, d, J ) 8.8 Hz), 7.15 (2H, d, J ) 8.8 Hz), 7.47 (1H,
td, J ) 7.8, 1.5 Hz), 7.67 (1H, d, J ) 7.8 Hz), 7.77 (1H, td, J )
7.8, 1.5 Hz), 8.27 (1H, dd, J ) 7.8, 1.5 Hz). MS (ESI) m/z 378 (M
+ H)+. HRMS (M + H)+ calcd for C23H28N3O2, 378.2168; found,
378.2182.
3-(4-[(1-Butyl-4-piperidinyl)oxy]phenyl)-2-methyl-4(3H)-quinazoli-
none (2d). Compound 2d was prepared from n-butyl iodide and
9b using the procedure described for 2b as a colorless solid (43%
yield); HPLC purity (99.8%). 1H NMR (400 MHz, CDCl3) δ 0.93
(3H, t, J ) 7.2 Hz), 1.28-1.39 (2H, m), 1.46-1.54 (2H, m),
1.83-1.93 (2H, m), 2.01-2.10 (2H, m), 2.26 (3H, s), 2.26-2.39
(4H, m), 2.72-2.81 (2H, m), 4.33-4.41 (1H, m), 7.03 (2H, d, J )
8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.44 (1H, t, J ) 8.0 Hz), 7.65
(1H, d, J ) 8.0 Hz), 7.74 (1H, t, J ) 8.0 Hz), 8.25 (1H, d, J ) 8.0
Hz); MS (ESI) m/z 392 (M + H)+. HRMS (M + H)+ calcd for
C24H30N3O2, 392.2338; found, 392.2337.
3-(4-[(1-Isopropyl-4-piperidinyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2e). Compound 2e was prepared from i-propyl iodide
and 9b using the procedure described for 2b as a colorless solid
1
(36% yield); HPLC purity (98.7%). H NMR (400 MHz, CDCl3)
δ 1.07 (6H, d, J ) 6.4 Hz), 1.82-1.92 (2H, m), 2.02-2.11 (2H,
m), 2.26 (3H, s), 2.37-2.46 (2H, m), 2.72-2.84 (3H, m), 4.31-4.40
(1H, m), 7.03 (2H, d, J ) 8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.44
(1H, t, J ) 8.0 Hz), 7.65 (1H, d, J ) 8.0 Hz), 7.74 (1H, t, J ) 8.0
Hz), 8.25 (1H, d, J ) 8.0 Hz). MS (ESI) m/z 378 (M + H)+. HRMS
(M + H)+ calcd for C23H28N3O2, 378.2182; found, 378.2186.
Representative Procedure for the Preparation of 2f-l via
Reductive Amination. 3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phe-
nyl)-2-methyl-4(3H)-quinazolinone (2f). To a stirred solution of 9b
(370 mg, 1.10 mmol) and cyclobutanone (155 mg, 2.20 mmol) in
methanol (10 mL) was added a solution of zinc chloride (409 mg,
3.00 mmol) and sodium cyanoborohydride (189 mg, 3.00 mmol)
in methanol (6 mL) at room temperature, and the mixture was stirred
at room temperature for 1 h. The resulting mixture was concentrated,
and the residue was partitioned between ethyl acetate and water.
The layers were separated, and the aqueous layer was extracted
with ethyl acetate twice. The combined organic layers were washed
with water, dried over sodium sulfate, and concentrated. The residue
was purified by preparative HPLC to provide 2f as a colorless solid
(165 mg, 39%); HPLC purity (99.6%). 1H NMR (400 MHz, CDCl3)
δ 1.63-1.76 (2H, m), 1.84-1.95 (4H, m), 1.99-2.10 (4H, m),
2.14-2.23 (2H, m), 2.26 (3H, s), 2.59-2.67 (2H, m), 2.70-2.79
(1H, m), 4.33-4.41 (1H, m), 7.01 (2H, d, J ) 8.8 Hz), 7.44 (1H,
t, J ) 8.0 Hz), 7.65 (1H, d, J ) 8.4 Hz), 7.74 (1H, t, J ) 7.6 Hz),
8.24 (1H, d, J ) 7.6 Hz). MS (ESI) m/z 390 (M + H)+. HRMS
(M + H)+ calcd for C24H28N3O2, 390.2182; found, 390.2185.
3-(4-[(1-Cyclopentyl-4-piperidinyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2g). Compound 2g was prepared from cyclopen-
tanone and 9b using the procedure described for 2f as a colorless
solid (42% yield); HPLC purity (95.4%). 1H NMR (400 MHz,
CDCl3) δ 1.25-1.48 (2H, m), 1.52-1.61 (2H, m), 1.66-1.73 (2H,
m), 1.83-1.93 (4H, m), 2.01-2.12 (2H, m), 2.25 (3H, s), 2.32-2.40
(2H, m), 2.49-2.58 (1H, m), 2.79-2.95 (2H, m), 4.33-4.41 (1H,
3-(4-[(1-Cyclopentyl-4-azepanyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (2l). Compound 2l was prepared from cyclopentanone
and 9c using the procedure described for 2f as a colorless oil (39%
yield); HPLC purity (96.1%). 1H NMR (400 MHz, CDCl3) δ
1.55-2.22 (14H, br m), 2.26 (3H, s), 2.38-2.49 (1H, br m),
2.89-3.25 (4H, br m), 4.69-4.72 (1H, br m), 7.01 (2H, d, J ) 9.3
Hz), 7.16 (2H, d, J ) 8.8 Hz), 7.45-7.49 (1H, m), 7.67 (1H, d, J
) 7.8 Hz), 7.75-7.79 (1H, m), 8.27 (1H, dd, J ) 8.0, 1.2 Hz).
MS (ESI) m/z 418 (M + H)+. HRMS (M + H)+ calcd for
C26H32N3O2, 418.2495; found, 418.2491.
2-Methyl-3-[4-([3-(1-pyrrolidinyl)cyclopentyl]oxy)phenyl]-4(3H)-
quinazolinone (3a). A mixture of 12 (550 mg, 1.33 mmol),
pyrrolidine (474 mg, 6.7 mmol), and potassium carbonate (277 mg,
2.0 mmol) in dry DMF (10 mL) was stirred at 80 °C for 14 h under
a nitrogen atmosphere. The resulting mixture was poured into water
and extracted with ethyl acetate three times. The combined organic
extracts were washed with water, dried over magnesium sulfate,
and concentrated. The residue was purified by silica gel column
chromatography with 5% methanol in CHCl3 to give 3a as a
1
colorless solid (143 mg, 28%); HPLC purity (99.2%). H NMR
(400 MHz, CDCl3) δ 1.57-1.67 (1H, m), 1.79-1.82 (4H, m),
1.85-1.92 (2H, m), 2.03-2.08 (1H, m), 2.14-2.19 (1H, m),
2.22-2.30 (1H, m), 2.24 (3H, s), 2.53-2.56 (4H, br m), 2.76-2.83
(1H, m), 4.81-4.86 (1H, m), 6.96 (2H, d, J ) 8.8 Hz), 7.11 (2H,

6896 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21
Nagase et al.
d, J ) 8.8 Hz), 7.44 (1H, t, J ) 8.1 Hz), 7.66 (1H, d, J ) 8.1 Hz),
7.73 (1H, t, J ) 8.1 Hz), 8.23 (1H, d, J ) 8.1 Hz). MS (ESI) m/z
390 (M + H)+. HRMS (M + H)+ calcd for C24H28N3O2, 390.2182;
found, 390.2166.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-6-fluoro-2-methyl-
4(3H)-quinazolinone (5b). Compound 5bwas prepared from 6-fluoro-
2-methyl-4H-3,1-benzoxazin-4-one (24b) and 23 tosylate using the
procedure described for 5s as a colorless solid (48% yield); HPLC
purity (97.3%). 1H NMR (400 MHz, CDCl3) δ 1.63-1.75 (2H,
m), 1.84-1.92 (4H, m), 2.01-2.12 (4H, m), 2.16-2.24 (2H, m),
2.25 (3H, s), 2.61-2.70 (2H, m), 2.72-2.81 (1H, m), 4.36-4.42
(1H, m), 7.04 (2H, d, J ) 8.8 Hz), 7.14 (2H, d, J ) 8.8 Hz),
7.45-7.51 (1H, m), 7.68 (1H, dd, J ) 4.8, 8.8 Hz), 7.89 (1H, dd,
J ) 3.2, 8.0 Hz). MS (ESI) m/z 408 (M + H)+. HRMS (M + H)+
calcd for C24H27N3O2F, 408.2087; found, 408.2094.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-7-fluoro-2-methyl-
4(3H)-quinazolinone (5c). Compound 5c was prepared from 7-fluoro-
2-methyl-4H-3,1-benzoxazin-4-one (24c) and 23 tosylate using the
procedure described for 5s as a colorless solid (72% yield); HPLC
purity (99.8%). 1H NMR (400 MHz, CDCl3) δ 1.65-1.75 (2H,
m), 1.82-1.96 (4H, m), 2.00-2.11 (4H, m), 2.14-2.24 (2H, m),
2.25 (3H, s), 2.60-2.68 (2H, m), 2.72-2.79 (1H, m), 4.36-4.41
(1H, m), 7.04 (2H, d, J ) 8.4 Hz), 7.12-7.20 (3H, m), 7.31 (1H,
dd, J ) 2.0,9.6 Hz), 8.27 (1H, dd, J ) 6.0, 8.4 Hz). MS (ESI) m/z
408 (M + H)+. HRMS (M + H)+ calcd for C24H27N3O2F,
408.2087; found, 408.2090.
2-Methyl-3-[4-([3-(1-pyrrolidinyl)cyclopentyl]oxy)phenyl]-4(3H)-
quinazolinone (3b, Diastereomer of 3a). Compound 3b was
prepared from 15 and pyrrolidine using the procedure described
1
for 3a as a colorless solid (47% yield); HPLC purity (98.1%). H
NMR (400 MHz, CDCl3) δ 1.77-1.96 (9H, m), 2.01-2.07 (1H,
m), 2.26 (3H, s), 2.43-2.50 (1H, m), 2.56-2.61 (4H, br m),
4.80-4.74 (1H, m), 6.96-7.01 (2H, m), 7.13 (2H, d, J ) 8.8 Hz),
7.44-7.48 (1H, m), 7.67 (1H, d, J ) 8.3 Hz), 7.74-7.78 (1H, m),
8.27 (1H, dd, J ) 8.0, 1.2 Hz). MS (ESI) m/z 390 (M + H)+.
HRMS (M + H)+ calcd for C24H28N3O2, 390.2182; found,
390.2179.
cis-2-Methyl-3-(4-([4-(1-pyrrolidinyl)cyclohexyl]oxy)phenyl)-
4(3H)-quinazolinone (4a) and trans-2-Methyl-3-(4-([4-(1-pyrrolidi-
nyl)cyclohexyl]oxy)phenyl)-4(3H)-quinazolinone (4b). Compounds
4a (cis-isomer) and 4b (trans-isomer) were synthesized from 18
and pyrrolidine using a similar procedure described for 2f.
Purification by silica gel column chromatography with 20% f 50%
ethyl acetate in hexanes followed by preparative HPLC afforded
4a as a colorless solid (260 mg, 46%) and 4b as a colorless solid
(180 mg, 32%). The stereochemistry of each isomer was determined
by NOE experiments. For cis-isomer (4a), HPLC purity (96.0%).
1H NMR (400 MHz, CDCl3) δ 1.40-1.66 (4H, m), 1.77-1.81 (4H,
m), 2.04-2.10 (3H, m), 2.12-2.20 (2H, m), 2.25 (3H, s), 2.60-2.63
(4H, br s), 4.19-4.26 (1H, m), 7.00 (2H, d, J ) 8.8 Hz), 7.11 (2H,
d, J ) 8.8 Hz), 7.44 (1H, t, J ) 8.1 Hz), 7.65 (1H, d, J ) 8.1 Hz),
7.74 (1H, t, J ) 8.1 Hz), 8.25 (1H, d, J ) 8.1 Hz). MS (ESI) m/z
404 (M + H)+. HRMS (M + H)+ calcd for C25H30N3O2, 404.2338;
found, 404.2351. For trans-isomer (4b), HPLC purity (98.2%). 1H
NMR (400 MHz, CDCl3) δ 1.59-1.83 (10H, br m), 2.10-2.15
(3H, m), 2.26 (3H, s), 2.62 (4H, br s), 4.53-4.56 (1H, br m), 7.03
(2H, d, J ) 9.3 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.44-7.48 (1H, m),
7.67 (1H, d, J ) 7.8 Hz), 7.74-7.78 (1H, m), 8.27 (1H, dd, J )
8.0, 1.2 Hz). MS (ESI) m/z 404 (M + H)+. HRMS (M + H)+
calcd for C25H30N3O2, 404.2338; found, 404.2343.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-8-fluoro-2-methyl-
4(3H)-quinazolinone (5d). Compound 5d was prepared from
8-fluoro-2-methyl-4H-3,1-benzoxazin-4-one (24d) and 23 tosylate
using the procedure described for 5s as a colorless solid (60% yield);
1
HPLC purity (99.0%). H NMR (400 MHz, CDCl3) δ 1.66-1.75
(2H, m), 1.84-1.95 (4H, m), 2.02-2.11 (4H, m), 2.17-2.28 (2H,
m), 2.31 (3H, s), 2.61-2.68 (2H, m), 2.75-2.80 (1H, m), 4.37-4.43
(1H, m), 7.05 (2H, d, J ) 9.3 Hz), 7.14 (2H, d, J ) 9.3 Hz),
7.42-7.37 (1H, m), 7.47-7.52 (1H, m), 8.05 (1H, d, J ) 7.8 Hz).
MS (ESI) m/z 408 (M + H)+. HRMS (M + H)+ calcd for
C24H27N3O2F, 408.2087; found, 408.2106.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-6,7-difluoro-2-
methyl-4(3H)-quinazolinone (5e). Compound 5e was prepared from
6,7-difluoro-2-methyl-4H-3,1-benzoxazin-4-one (24e) and 23 to-
sylate using the procedure described for 5s as a colorless solid (67%
yield); HPLC purity (99.6%). 1H NMR (400 MHz, CDCl3) δ
1.66-1.75 (2H, m), 1.83-1.95 (4H, m), 2.00-2.11 (4H, m),
2.16-2.24 (2H, m), 2.24 (3H, s), 2.60-2.68 (2H, m), 2.72-2.79
(1H, m), 4.35-4.42 (1H, m), 7.04 (2H, d, J ) 8.4 Hz), 7.13 (2H,
d, J ) 8.4 Hz), 7.44 (1H, dd, J ) 6.8, 10.4 Hz), 8.01 (1H, dd, J )
8.4, 9.6 Hz). MS (ESI) m/z 426 (M + H)+. HRMS (M + H)+
calcd for C24H26N3O2F2, 426.1993; found, 426.1998.
5-Chloro-3-(4-[(1-cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methyl-
4(3H)-quinazolinone (5f). Compound 5f was prepared from 5-chloro-
2-methyl-4H-3,1-benzoxazin-4-one (24f) and 23 tosylate using the
procedure described for 5s as a colorless solid (53% yield); HPLC
purity (99.6%). 1H NMR (400 MHz, CDCl3) δ 1.63-1.77 (2H,
m), 1.82-1.96 (4H, m), 1.99-2.09 (4H, m), 2.13-2.23 (2H, m),
2.23 (3H, s), 2.58-2.66 (2H, m), 2.69-2.79 (1H, m), 4.33-4.40
(1H, m), 7.00 (2H, d, J ) 8.8 Hz), 7.12 (2H, d, J ) 8.8 Hz), 7.43
(1H, dd, J ) 1.6, 7.2 Hz), 7.52-7.61 (2H, m). MS (ESI) m/z 424
(M + H)+. HRMS (M + H)+ calcd for C24H27N3O2Cl, 424.1792;
found, 424.1785.
6-Chloro-3-(4-[(1-cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methyl-
4(3H)-quinazolinone (5g). Compound 5g was prepared from 6-chloro-
2-methyl-4H-3,1-benzoxazin-4-one (24g) and 23 tosylate using the
procedure described for 5s as a colorless solid (20% yield); HPLC
purity (98.6%). 1H NMR (400 MHz, CDCl3) δ 1.66-1.79 (2H,
m), 1.83-1.99 (4H, m), 2.00-2.12 (4H, m), 2.15-2.30 (5H, m),
2.59-2.71 (2H, m), 2.72-2.84 (1H, m), 4.40 (1H, br s), 7.04 (2H,
d, J ) 8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.61 (1H, d, J ) 8.8 Hz),
7.69 (1H, dd, J ) 8.8, 2.4 Hz), 8.22 (1H, d, J ) 2.4 Hz). MS (ESI)
m/z 424 (M + H)+. HRMS (M + H)+ calcd for C24H27N3O2Cl,
424.1792; found, 424.1794.
Representative Procedure for the Preparation of 5a-s. 3-(4-
[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methyl-5-(trifluoro-
methyl)-4(3H)-quinazolinone (5s). A mixture of 23 tosylate (20.0
g, 47.8 mmol), 2-methyl-5-(trifluoromethyl)-4H-3,1-benzoxazin-
4-one (24s; 10.95 g, 47.8 mmol) in acetic acid (110 mL) was stirred
at room temperature for 30 h. The resulting mixture was concen-
trated, and the residue was partitioned between ethyl acetate and 2
N NaOH. The layers were separated, and the aqueous layer was
extracted with ethyl acetate twice. The combined organic extracts
were washed with 2 N NaOH and brine, dried over sodium sulfate,
and concentrated. The residue was purified by silica gel chroma-
tography with 0% f 2% methanol in CHCl3 followed by recrys-
tallization from ethyl acetate to afford 5s as a colorless solid (13.7
1
g, 63%); HPLC purity (99.6%). H NMR (400 MHz, CDCl3) δ
1.63-1.77 (2H, m), 1.82-1.96 (4H, m), 1.98-2.09 (4H, m),
2.13-2.23 (2H, m), 2.26 (3H, s), 2.58-2.66 (2H, m), 2.70-2.79
(1H, m), 4.33-4.40 (1H, m), 7.01 (2H, d, J ) 8.8 Hz), 7.12 (2H,
d, J ) 8.8 Hz), 7.77 (1H, d, J ) 8.0 Hz), 7.82-7.88 (2H, m). MS
(ESI) m/z 458 (M + H)+. HRMS (M + H)+ calcd for
C25H27N3O2F3, 458.2055; found, 458.2045.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-5-fluoro-2-methyl-
4(3H)-quinazolinone (5a). Compound 5a was prepared from 5-fluoro-
2-methyl-4H-3,1-benzoxazin-4-one (24a) and 23 tosylate using the
procedure described for 5s as a colorless solid (50% yield); HPLC
purity (99.2%). 1H NMR (400 MHz, CDCl3) δ 1.65-1.75 (2H,
m), 1.83-1.93 (4H, m), 2.00-2.11 (4H, m), 2.13-2.24 (2H, m),
2.24 (3H, s), 2.60-2.68 (2H, m), 2.72-2.79 (1H, m), 4.36-4.41
(1H, m), 7.04 (2H, d, J ) 8.8 Hz), 7.08-7.14 (3H, m), 7.46 (1H,
d, J ) 8.0 Hz), 7.65-7.71 (1H, m). MS (ESI) m/z 408 (M + H)+.
HRMS (M + H)+ calcd for C24H27N3O2F, 408.2087; found,
408.2101.
7-Chloro-3-(4-[(1-cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methyl-
4(3H)-quinazolinone (5h). Compound 5h was prepared from
7-chloro-2-methyl-4H-3,1-benzoxazin-4-one (24h) and 23 tosylate
using the procedure described for 5s as a colorless solid (61% yield);
1
HPLC purity (99.6%). H NMR (400 MHz, CDCl3) δ 1.65-1.74

Quinazolinones as Histamine H3 Receptor InVerse Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21 6897
(2H, m), 1.84-1.93 (4H, m), 2.01-2.08 (4H, m), 2.15-2.22 (2H,
m), 2.25 (3H, s), 2.60-2.67 (2H, m), 2.71-2.79 (1H, m), 4.35-4.40
(1H, m), 7.04 (2H, d, J ) 9.3 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.41
(1H, dd, J ) 8.5, 2.2 Hz), 7.66 (1H, d, J ) 2.0 Hz), 8.19 (1H, d,
J ) 8.8 Hz). MS (ESI) m/z 424 (M + H)+. HRMS (M + H)+
calcd for C24H27N3O2Cl, 424.1792; found, 424.1803.
8-Chloro-3-(4-[(1-cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methyl-
4(3H)-quinazolinone (5i). Compound 5i was prepared from 8-chloro-
2-methyl-4H-3,1-benzoxazin-4-one (24i) and 23 tosylate using the
procedure described for 5s as a colorless solid (69% yield); HPLC
purity (99.0%). 1H NMR (400 MHz, CDCl3) δ 1.65-1.76 (2H,
m), 1.85-1.93 (4H, m), 2.01-2.08 (4H, m), 2.15-2.22 (2H, m),
2.33 (3H, s), 2.60-2.67 (2H, m), 2.71-2.79 (1H, m), 4.41-4.36
(1H, m), 7.04 (2H, d, J ) 8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.38
(1H, t, J ) 8.0 Hz), 7.84 (1H, dd, J ) 7.8, 1.5 Hz), 8.19 (1H, dd,
J ) 8.3, 1.5 Hz). MS (ESI) m/z 424 (M + H)+. HRMS (M + H)+
calcd for C24H27N3O2Cl, 424.1792; found, 424.1786.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-5-methoxy-2-methyl-
4(3H)-quinazolinone (5j). Compound 5j was prepared from 5-meth-
oxy-2-methyl-4H-3,1-benzoxazin-4-one (24j) and 23 tosylate using
the procedure described for 5s as a beige solid (82% yield); HPLC
purity (99.7%). 1H NMR (400 MHz, CDCl3) δ 1.63-1.77 (2H,
m), 1.82-1.96 (4H, m), 1.98-2.09 (4H, m), 2.12-2.23 (2H, m),
2.21 (3H, s), 2.58-2.67 (2H, m), 2.69-2.79 (1H, m), 3.94 (3H,
s), 4.33-4.40 (1H, m), 6.85 (1H, d, J ) 8.8 Hz), 6.99 (2H, d, J )
8.8 Hz), 7.08 (2H, d, J ) 8.8 Hz), 7.21 (1H, d, J ) 8.0 Hz), 7.62
(1H, t, J ) 8.0 Hz). MS (ESI) m/z 420 (M + H)+. HRMS (M +
H)+ calcd for C25H30N3O3, 420.2287; found, 420.2289.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-6-methoxy-2-methyl-
4(3H)-quinazolinone (5k). Compound 5k was prepared from
6-methoxy-2-methyl-4H-3,1-benzoxazin-4-one (24k) and 23 tosy-
late using the procedure described for 5s as a colorless solid (69%
yield); HPLC purity (99.7%). 1H NMR (400 MHz, CDCl3) δ
1.64-1.74 (2H, m), 1.85-1.96 (4H, m), 2.01-2.13 (4H, m),
2.15-2.24 (2H, m), 2.23 (3H, s), 2.60-2.72 (2H, m), 2.72-2.81
(1H, m), 3.91 (3H, s), 4.35-4.42 (1H, brs), 7.04 (2H, d, J ) 6.8
Hz), 7.13 (2H, d, J ) 6.8 Hz), 7.36 (1H, dd, J ) 3.2, 9.2 Hz), 7.61
(1H, d, J ) 9.2 Hz), 7.63 (1H, d, J ) 3.2 Hz). MS (ESI) m/z 420
(M + H)+. HRMS (M + H)+ calcd for C25H30N3O3, 420.2287;
found, 420.2302.
(2H, td, J ) 2.0, 8.8 Hz), 7.67 (1H, dd, J ) 8.3, 4.4 Hz), 8.00 (1H,
dd, J ) 8.3, 1.5 Hz), 8.84 (1H, dd, J ) 4.4, 1.5 Hz). MS (ESI) m/z
391 (M + H)+. HRMS (M + H)+ calcd for C23H27N4O2, 391.2134;
found, 391.2144.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methylpyrido[4,3-
d]pyrimidin-4(3H)-one (5o). Compound 5o was prepared from
2-methyl-4H-pyrido[4,3-d][1,3]oxazin-4-one (24o) and 23 tosylate
using the procedure described for 5s as a pale-yellow solid (27%
yield); HPLC purity (97.4%). 1H NMR (400 MHz, CDCl3) δ
1.63-1.77 (2H, m), 1.82-1.96 (4H, m), 1.99-2.11 (4H, m),
2.14-2.24 (2H, m), 2.29 (3H, s), 2.60-2.68 (2H, m), 2.70-2.80
(1H, m), 4.33-4.41 (1H, m), 7.03 (2H, d, J ) 8.8 Hz), 7.11 (2H,
d, J ) 8.8 Hz), 7.47 (1H, d, J ) 5.2 Hz), 8.82 (1H, d, J ) 5.2 Hz),
9.45 (1H, s). MS (ESI) m/z 391 (M + H)+. HRMS (M + H)+
calcd for C23H27N4O2, 391.2134; found, 391.2122.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methylpyrido[3,4-
d]pyrimidin-4(3H)-one (5p). Compound 5p was prepared from
2-methyl-4H-pyrido[3,4-d][1,3]oxazin-4-one (24p) and 23 tosylate
using the procedure described for 5s as a colorless solid (11% yield);
1
HPLC purity (98.1%). H NMR (400 MHz, CDCl3) δ 1.63-1.77
(2H, m), 1.82-1.95 (4H, m), 1.99-2.11 (4H, m), 2.15-2.23 (2H,
m), 2.29 (3H, s), 2.60-2.69 (2H, m), 2.73-2.83 (1H, m), 4.36-4.43
(1H, m), 7.03 (2H, d, J ) 8.8 Hz), 7.12 (2H, d, J ) 8.8 Hz), 8.01
(1H, dd, J ) 0.8, 5.6 Hz), 8.65 (1H, d, J ) 5.2 Hz), 9.09 (1H, d,
J ) 0.8 Hz). MS (ESI) m/z 391 (M + H)+. HRMS (M + H)+
calcd for C23H27N4O2, 391.2134; found, 391.2134.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methylpyrido[2,3-
d]pyrimidin-4(3H)-one (5q). Compound 5q was prepared from
2-methyl-4H-pyrido[2,3-d][1,3]oxazin-4-one (24q) and 23 tosylate
using the procedure described for 5s as a colorless solid (8% yield);
1
HPLC purity (99.7%). H NMR (400 MHz, CDCl3) δ 1.63-1.77
(2H, m), 1.82-1.95 (4H, m), 1.99-2.11 (4H, m), 2.15-2.23 (2H,
m), 2.34 (3H, s), 2.60-2.68 (2H, m), 2.70-2.80 (1H, m), 4.33-4.41
(1H, m), 7.03 (2H, d, J ) 8.8 Hz), 7.12 (2H, d, J ) 8.8 Hz), 7.39
(1H, dd, J ) 4.4, 8.0 Hz), 8.56 (1H, dd, J ) 2.0, 7.6 Hz), 8.96
(1H, dd, J ) 2.4, 4.8 Hz). MS (ESI) m/z 391 (M + H)+. HRMS
(M + H)+ calcd for C23H27N4O2, 391.2134; found, 391.2122.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-2,5-dimethyl-4(3H)-
quinazolinone (5r). Compound 5r was prepared from 2,5-dimethyl-
4H-3,1-benzoxazin-4-one (24r) and 23 tosylate using the procedure
described for 5s as a colorless solid (70% yield); HPLC purity
(99.9%). 1H NMR (400 MHz, CDCl3) δ 1.63-1.75 (2H, m),
1.82-1.96 (4H, m), 1.99-2.10 (4H, m), 2.13-2.22 (2H, m), 2.22
(3H, s), 2.58-2.67 (2H, m), 2.69-2.79 (1H, m), 2.81 (3H, s),
4.33-4.40 (1H, m), 7.02 (2H, d, J ) 8.8 Hz), 7.11 (2H, d, J ) 8.8
Hz), 7.19 (1H, d, J ) 8.0 Hz), 7.48 (1H, d, J ) 8.0 Hz), 7.57 (1H,
t, J ) 8.0 Hz). MS (ESI) m/z 404 (M + H)+. HRMS (M + H)+
calcd for C25H30N3O2, 404.2338; found, 404.2343.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-7-methoxy-2-methyl-
4(3H)-quinazolinone (5l). Compound 5l was prepared from 7-meth-
oxy-2-methyl-4H-3,1-benzoxazin-4-one (24l) and 23 tosylate using
the procedure described for 5s as a pale-yellow solid (68% yield);
1
HPLC purity (99.2%). H NMR (400 MHz, CDCl3) δ 1.65-1.76
(2H, m), 1.83-1.95 (4H, m), 2.00-2.09 (4H, m), 2.15-2.23 (2H,
m), 2.24 (3H, s), 2.60-2.68 (2H, m), 2.71-2.79 (1H, m), 3.93
(3H, s), 4.35-4.41 (1H, m), 7.06-7.01 (4H, m), 7.14 (2H, d, J )
9.3 Hz), 8.16 (1H, d, J ) 8.8 Hz). MS (ESI) m/z 420 (M + H)+.
HRMS (M + H)+ calcd for C25H30N3O3, 420.2287; found,
420.2294.
3-(4-[(1-tert-Butoxycarbonyl-4-piperidinyl)oxy]phenyl)-2-methyl-
4(3H)-quinazolinone (8b). To a stirred solution of 6 (1.0 g, 3.96
mmol), N-(tert-butoxycarbonyl)-4-piperidinol (7b; 956 mg, 4.75
mmol), and triphenylphosphine (1.56 g, 5.94 mmol) in THF (2 mL)
was added diethyl azodicarboxylate (1.17 mL, 5.94 mmol) dropwise
at 0 °C under a nitrogen atmosphere. The mixture was allowed to
warm to room temperature and stirred for 48 h. The resulting
mixture was concentrated, and the residual oil was taken up into
diethyl ether. The resulting precipitates were removed by filtration,
and the filtrate was concentrated. The residue was purified by silica
gel column chromatography with 30% ethyl acetate in hexanes to
give 8b as a light-brown solid (1.10 g, 64%). 1H NMR (400 MHz,
CDCl3) δ 1.48 (9H, s), 1.76-1.84 (2H, br m), 1.92-1.99 (2H, br
m), 2.26 (3H, s), 3.34 (2H, br m), 3.66-3.75 (2H, br m), 4.48-4.56
(1H, m), 7.03 (2H, d, J ) 9.2 Hz), 7.14 (2H, d, J ) 9.2 Hz),
7.51-7.55 (1H, m), 7.63 (1H, d, J ) 8.0 Hz), 7.72-7.77 (1H, m),
8.25 (1H, dd, J ) 8.0, 1.2 Hz). MS (ESI) m/z 436 (M + H)+.
3-(4-[(1-tert-Butoxycarbonyl-3-pyrrolidinyl)oxy]phenyl)-2-meth-
yl-4(3H)-quinazolinone (8a). Compound 8a was prepared from
compound 6 and N-(tert-butoxycarbonyl)-3-pyrrolidinol (7a) using
the procedure described for 8b as a brown oil. 1H NMR (400 MHz,
CDCl3) δ 1.49 (9H, s), 2.10-2.19 (1H, br m), 2.22-2.29 (1H, br
m), 2.27 (3H, s), 3.50-3.70 (4H, br m), 4.93-4.96 (1H, br m),
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-8-methoxy-2-methyl-
4(3H)-quinazolinone (5m). Compound 5m was prepared from
8-methoxy-2-methyl-4H-3,1-benzoxazin-4-one (24m) and 23 to-
sylate using the procedure described for 5s as a beige solid (87%
yield); HPLC purity (98.8%). 1H NMR (400 MHz, CDCl3) δ
1.67-1.74 (2H, m), 1.84-1.93 (4H, m), 2.00-2.09 (4H, m),
2.15-2.22 (2H, m), 2.32 (3H, s), 2.61-2.66 (2H, m), 2.71-2.79
(1H, m), 4.04 (3H, s), 4.36-4.41 (1H, m), 7.03 (2H, d, J ) 8.8
Hz), 7.14 (2H, d, J ) 8.8 Hz), 7.22 (1H, dd, J ) 8.0, 1.2 Hz), 7.40
(1H, t, J ) 8.0 Hz), 7.85 (1H, dd, J ) 8.0, 1.2 Hz). MS (ESI) m/z
420 (M + H)+. HRMS (M + H)+ calcd for C25H30N3O3, 420.2287;
found, 420.2295.
3-(4-[(1-Cyclobutyl-4-piperidinyl)oxy]phenyl)-2-methylpyrido[3,2-
d]pyrimidin-4(3H)-one (5n). Compound 5n was prepared from
2-methyl-4H-pyrido[3,2-d][1,3]oxazin-4-one (24n) and 23 tosylate
using the procedure described for 5s as a pale-yellow solid (49%
yield); HPLC purity (95.3%). 1H NMR (400 MHz, CDCl3) δ
1.67-1.74 (2H, m), 1.96-1.84 (4H, m), 2.03-2.10 (4H, m),
2.17-2.25 (2H, m), 2.27 (3H, s), 2.59-2.71 (2H, m), 2.73-2.79
(1H, m), 4.36-4.42 (1H, m), 7.05 (2H, td, J ) 2.0, 8.8 Hz), 7.17

6898 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21
Nagase et al.
7.03 (2H, d, J ) 7.3 Hz), 7.18 (2H, d, J ) 7.3 Hz), 7.45-7.49
(1H, m), 7.68 (1H, d, J ) 7.3 Hz), 7.77 (1H, t, J ) 7.3 Hz), 8.27
(1H, dd, J ) 8.0, 1.2 Hz). MS (ESI) m/z 422 (M + H)+.
12 as a pale-yellow solid (553 mg, 86%). 1H NMR (400 MHz,
CDCl3) δ 2.05-2.30 (5H, m), 2.26 (3H, s), 2.44-2.51 (1H, m),
3.02 (3H, s), 4.80-4.83 (1H, m), 5.16-5.23 (1H, m), 6.99 (2H, d,
J ) 9.2 Hz), 7.15 (2H, d, J ) 9.2 Hz), 7.42-7.46 (1H, m), 7.65
(1H, d, J ) 8.0 Hz), 7.74 (1H, t, J ) 8.4 Hz), 8.24 (1H, d, J ) 8.0
Hz). MS (ESI) m/z 415 (M + H)+.
3-(4-[(1-tert-Butoxycarbonyl-4-azepanyl)oxy]phenyl)-2-methyl-
4(3H)-quinazolinone (8c). Compound 8c was prepared from com-
pound 6 and N-(tert-butoxycarbonyl)-4-azepanol (7c) using the
1
procedure described for 8b as a brown oil. H NMR (400 MHz,
3-[4-(2-Methyl-4-oxo-3(4H)-quinazolinyl)phenoxy]cyclopentyl ben-
zoate (13). To a stirred solution of 11 (200 mg, 0.595 mmol),
benzoic acid (109 mg, 0.892 mmol), and triphenylphosphine (234
mg, 0.892 mmol) in THF (2 mL) was added diisopropyl azodicar-
boxylate (173 µL, 0.892 mmol) dropwise at 0 °C under an nitrogen
atmosphere. After being stirred at 0 °C for 10 min, the mixture
was allowed to warm to room temperature and stirred for an
additional 1 h. The resultant mixture was partitioned between water
and ethyl acetate. The layers were separated, and the aqueous layer
was extracted with ethyl acetate three times. The combined organic
extracts were washed with brine, dried over sodium sulfate, and
concentrated. The residue was purified by silica gel column
chromatography with 40% f 100% ethyl acetate in hexanes to
give 13 (377 mg) as a colorless solid. 1H NMR (400 MHz, CDCl3)
δ 1.98-2.10 (2H, m), 2.23-2.46 (4H, m), 2.27 (3H, s), 4.96-5.03
(1H, br m), 5.59-5.63 (1H, m), 7.02 (2H, d, J ) 8.3 Hz), 7.16
(2H, d, J ) 8.8 Hz), 7.44-7.49 (3H, m), 7.57 (1H, t, J ) 7.3 Hz),
7.68 (1H, d, J ) 7.8 Hz), 7.75-7.79 (1H, m), 8.04 (2H, dd, J )
8.5, 1.2 Hz), 8.28 (1H, dd, J ) 7.8, 1.0 Hz). MS (ESI) m/z 441 (M
+ H)+.
CDCl3) δ 1.48 (9H, s), 1.65-1.70 (2H, br m), 1.93-2.02 (3H, m),
2.06-2.16 (1H, m), 2.25 (3H, s), 3.25-3.37 (1H, m), 3.40-3.64
(3H, m), 4.46-4.50 (1H, m), 6.98 (2H, d, J ) 8.8 Hz), 7.13 (2H,
d, J ) 8.0 Hz), 7.44 (1H, t, J ) 8.4 Hz), 7.64 (1H, d, J ) 8.0 Hz),
7.71-7.75 (1H, m), 8.24 (1H, d, J ) 8.0 Hz). MS (ESI) m/z 450
(M + H)+.
2-Methyl-3-[4-(4-piperidinyloxy)phenyl]-4(3H)-quinazolinone (9b).
To a stirred solution of 8b (1.10 g, 2.53 mmol) in CHCl3 (10 mL)
was added trifluoroacetic acid (10 mL), and the mixture was stirred
at room temperature for 30 min. The resulting mixture was
concentrated, and the residue was partitioned between ethyl acetate
and 2 N NaOH. The layers were separated, and the aqueous layer
was extracted with ethyl acetate twice. The combined organic layers
were washed with 2 N NaOH and brine, dried over sodium sulfate,
and concentrated. The residue was vacuum-dried to give 9b as a
slightly purple solid (0.83 g, 98%). 1H NMR (400 MHz, CDCl3) δ
1.67-1.81 (2H, m), 2.01-2.10 (2H, m), 2.26 (3H, s), 2.72-2.80
(2H, m), 3.13-3.20 (2H, m), 4.40-4.47 (1H, m), 7.03 (2H, d, J )
8.8 Hz), 7.13 (2H, d, J ) 8.8 Hz), 7.44 (1H, t, J ) 8.0 Hz), 7.65
(1H, d, J ) 7.6 Hz), 7.74 (1H, t, J ) 7.6 Hz), 8.25 (1H, d, J ) 8.0
Hz). MS (ESI) m/z 336 (M + H)+.
3-(4-[(3-Hydroxycyclopentyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (14, Diastereomer of 11). A mixture of 13 (227 mg,
0.36 mmol) and potassium carbonate (71.2 mg, 0.515 mmol) in
methanol (5 mL) was stirred at room temperature for 8 h under a
nitrogen atmosphere. The resulting mixture was partitioned between
ethyl acetate and water. The layers were separated, and the aqueous
layer was extracted with ethyl acetate twice. The combined organic
layers were washed with 10% aqueous NaHCO3 and brine, dried
over sodium sulfate, and concentrated. The residue was purified
by silica gel column chromatography with 60% f 100% ethyl
acetate in hexanes to give 14 as a pale-yellow solid (80 mg, 66%
2-Methyl-3-[4-(3-pyrrolidinyloxy)phenyl]-4(3H)-quinazolinone
(9a). Compound 9a was prepared from 8a using the procedure
1
described for 9b as a beige solid (34% over 2 steps from 6). H
NMR (400 MHz, CDCl3) δ 2.01-2.20 (2H, m), 2.27 (3H, s),
2.94-3.01 (1H, br m), 3.06-3.11 (1H, br m), 3.19-3.28 (2H, m),
4.87-4.90 (1H, br m), 7.01 (2H, d, J ) 9.3 Hz), 7.16 (2H, d, J )
9.3 Hz), 7.45-7.49 (1H, m), 7.67 (1H, d, J ) 7.8 Hz), 7.75-7.79
(1H, m), 8.27 (1H, dd, J ) 8.0, 1.2 Hz). MS (ESI) m/z 322 (M +
H)+.
1
over 2 steps from 11). H NMR (400 MHz, CDCl3) δ 1.68-1.75
3-[4-(4-Azepanyloxy)phenyl]-2-methyl-4(3H)-quinazolinone (9c).
Compound 9c was prepared from 8c using the procedure described
(1H, m), 1.90-1.97 (1H, m), 2.07-2.21 (3H, m), 2.24-2.33 (1H,
m), 2.26 (3H, s), 4.56-4.60 (1H, m), 4.93-4.98 (1H, m), 6.99
(2H, d, J ) 8.8 Hz), 7.14 (2H, d, J ) 8.8 Hz), 7.44-7.48 (1H, m),
7.67 (1H, d, J ) 7.3 Hz), 7.74-7.79 (1H, m), 8.27 (1H, dd, J )
8.0, 1.2 Hz). MS (ESI) m/z 337 (M + H)+.
1
for 9b as a brown oil (40% over 2 steps from 6). H NMR (400
MHz, CDCl3) δ 1.57-1.68 (1H, m), 1.83-2.22 (5H, m), 2.25 (3H,
s), 2.84-3.06 (4H, m), 4.57-4.62 (1H, m), 6.99 (2H, d, J ) 8.8
Hz), 7.12 (2H, d, J ) 8.8 Hz), 7.43 (1H, t, J ) 8.0 Hz), 7.64 (1H,
d, J ) 8.0 Hz), 7.74 (1H, t, J ) 8.0 Hz), 8.24 (1H, d, J ) 6.4 Hz).
MS (ESI) m/z 350 (M + H)+.
3-[4-((3-[(Methylsulfonyl)oxy]cyclopentyl)oxy)phenyl]-2-methyl-
4(3H)-quinazolinone (15, Diastereomer of 12). Compound 15 was
prepared from 14 using the procedure described for 12 as a colorless
solid (98% yield). 1H NMR (400 MHz, CDCl3) δ 2.01-2.13 (2H,
m), 2.17-2.30 (2H, m), 2.26 (3H, s), 2.37-2.47 (2H, m), 3.04
(3H, s), 4.95-5.00 (1H, m), 5.32-5.37 (1H, m), 6.99 (2H, d, J )
8.8 Hz), 7.16 (2H, d, J ) 9.3 Hz), 7.44-7.49 (1H, m), 7.68 (1H,
d, J ) 7.8 Hz), 7.75-7.79 (1H, m), 8.27 (1H, dd, J ) 8.0, 1.2
Hz). MS (ESI) m/z 415 (M + H)+.
3-[4-(1,4-Dioxaspiro[4.5]dec-8-yloxy)phenyl]-2-methyl-4(3H)-
quinazolinone (17). Compound 17 was prepared from 6 and 4,4-
ethylenedioxycyclohexanol (16) using a similar procedure described
for 8b as a pale-purple solid, which was used for the next reaction
without further purification. 1H NMR (400 MHz, CDCl3) δ
1.62-1.69 (2H, m), 1.91-2.01 (6H, m), 2.27 (3H, s), 3.96-4.01
(4H, m), 4.45-4.49 (1H, m), 7.05 (2H, d, J ) 9.3 Hz), 7.15 (2H,
d, J ) 9.3 Hz), 7.46 (1H, t, J ) 7.6 Hz), 7.67 (1H, d, J ) 7.8 Hz),
7.74-7.79 (1H, m), 8.27 (1H, dd, J ) 8.0, 1.2 Hz); MS (ESI) m/z
393 (M + H)+.
2-Methyl-3-(4-[(4-oxocyclohexyl)oxy]phenyl)-4(3H)-quinazoli-
none (18). To a solution of 17 (1.59 g) in THF (5 mL) was added
10% hydrochloric acid (10 mL), and the mixture was stirred at
room temperature for 3 h. After being neutralized with 2 N NaOH,
the mixture was extracted with ethyl acetate three times. The
combined organic layers were washed with brine, dried over sodium
sulfate, and concentrated. The residue was purified by silica gel
column chromatography with 5% methanol in CHCl3 to give 18 as
a light-orange solid (511 mg, 49% yield for 2 steps). 1H NMR
3-(4-[(3-Hydroxycyclopentyl)oxy]phenyl)-2-methyl-4(3H)-
quinazolinone (11). To a stirred solution of 6 (1.0 g, 3.96 mmol),
cyclopentane-1,3-diol (10; 810 mg, 7.93 mmol), and triphenylphos-
phine (1.56 g, 5.95 mmol) in THF (10 mL) was added diisopropyl
azodicarboxylate (1.16 mL, 5.95 mmol) dropwise at 0 °C under a
nitrogen atmosphere, and the mixture was stirred at room temper-
ature for 14 h. The resulting mixture was partitioned between water
and ethyl acetate. The layers were separated, and the aqueous layer
was extracted with ethyl acetate three times. The combined organic
layers were washed with brine, dried over magnesium sulfate, and
concentrated. The residue was purified by silica gel column
chromatography with 50% f 100% ethyl acetate in hexanes to
afford 11 (1.32 g, 99%) as a beige solid. 1H NMR (400 MHz,
CDCl3) δ 1.91-2.20 (6H, m), 2.26 (3H, s), 4.38-4.42 (1H, br m),
4.85-4.89 (1H, br m), 7.03 (2H, d, J ) 8.8 Hz), 7.16 (2H, d, J )
8.8 Hz), 7.46 (1H, td, J ) 7.4, 1.1 Hz), 7.67 (1H, d, J ) 7.8 Hz),
7.74-7.79 (1H, m), 8.27 (1H, dd, J ) 7.8, 1.0 Hz). MS (ESI) m/z
337 (M + H)+.
3-[4-((3-[(Methylsulfonyl)oxy]cyclopentyl)oxy)phenyl]-2-methyl-
4(3H)-quinazolinone (12). To a stirred solution of 11 (520 mg, 1.55
mmol) and triethylamine (0.33 mL, 2.32 mmol) in dichloromethane
(10 mL) was added mesyl chloride (0.12 mL, 1.55 mmol) dropwise
at 0 °C. After being stirred at 0 °C for 5 min, the mixture was
allowed to warm to room temperature and stirred for an additional
10 min. The mixture was diluted with ethyl acetate and washed
with water, dried over magnesium sulfate, and concentrated to give

Quinazolinones as Histamine H3 Receptor InVerse Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21 6899
(400 MHz, CDCl3) δ 2.08-2.16 (2H, m), 2.27 (3H, s), 2.30-2.40
(4H, m), 2.67-2.76 (2H, m), 4.73-4.78 (1H, m), 7.09 (2H, d, J )
8.4 Hz), 7.18 (2H, d, J ) 8.8 Hz), 7.45 (1H, t, J ) 8.0 Hz), 7.65
(1H, d, J ) 7.2 Hz), 7.73-7.77 (1H, m), 8.25 (1H, dd, J ) 8.0,
1.2 Hz). MS (ESI) m/z 349 (M + H)+.
m), 2.09-2.15 (2H, m), 2.19-2.27 (2H, m), 2.34-2.43 (5H, m),
2.52-2.61 (2H, m), 2.86-2.93 (2H, m), 3.34-3.44 (3H, m), 4.52
(1H, brs), 6.70-6.75 (4H, m), 7.21 (2H, d, J ) 7.8 Hz), 7.79 (2H,
d, J ) 7.8 Hz). MS (ESI) m/z 247 (M + H)+.
Cloning and Expression of the Histamine H3 Receptor. Human
histamine H3 receptor (GenBank accession no. AB045369) was
cloned as previously described.32 The DNAs were inserted into
the mammalian expression vector pCAGGS33 (pCAGGS-hH3), and
cells, stably expressing the human histamine H3 receptors, were
generated by transfecting pCAGGS-hH3 into CHO-K1 cells.
HEK293/CRE-ꢀ-lactamase cells expressing rat histamine H3 recep-
tor were prepared as previously described.34
1-tert-Butoxycarbonyl-4-(4-nitrophenoxy)piperidine (20). To a
stirred solution of N-(tert-butoxycarbonyl)-4-piperidinol (7b; 10.0 g,
49.7 mmol) in DMF (50 mL) was added sodium hydride (60%
dispersion in mineral oil, 3.0 g, 75 mmol) portionwise at 0 °C under
a nitrogen atmosphere. After being stirred at 0 °C for 15 min, the
mixture was allowed to warm to room temperature and stirred for
an additional 30 min. To the mixture was added a solution of
4-fluoronitrobenzene (7.71 g, 55 mmol) in DMF (10 mL) dropwise
at 0 °C. The mixture was allowed to warm to room temperature
and stirred for 15 h. After being quenched by the addition of water
(15 mL), the mixture was concentrated. The residue was partitioned
between ethyl acetate (120 mL) and water (120 mL). The layers
were separated, and the aqueous layer was extracted with ethyl
acetate twice. The combined organic layers were washed with water
twice, dried over sodium sulfate, and concentrated. The residual
solid was suspended in a mixture of diisopropylether/hexanes (v/v
) 1/4), and the precipitates were collected by filtration and vacuum-
dried to provide 20 as a pale-yellow solid (12.4 g, 77%). 1H NMR
(400 MHz, CDCl3) δ 1.48 (9H, s), 1.75-1.82 (2H, m), 1.93-1.99
(2H, m), 3.36-3.42 (2H, m), 3.66-3.73 (2H, m), 4.58-4.62 (2H,
m), 6.96 (2H, d, J ) 8.0 Hz), 8.20 (2H, d, J ) 8.0 Hz). MS (ESI)
m/z 323 (M + H)+.
4-(4-Nitrophenoxy)piperidine (21). Compound 20 (10.9 g, 33.8
mmol) was dissolved in 30 mL of trifluoroacetic acid, and the
mixture was stirred at room temperature for 1 h. The resulting
mixture was concentrated, and the residue was partitioned between
ethyl acetate (150 mL) and 2 N NaOH (100 mL). The layers were
separated, and the aqueous layer was extracted with ethyl acetate
twice. The combined organic layers were washed with 1 N NaOH
and brine, dried over sodium sulfate, and concentrated to give 21
as a brown oil (7.5 g, 99%). 1H NMR (400 MHz, CDCl3) δ
1.70-1.79 (2H, m), 2.03-2.09 (2H, m), 2.77-2.83 (2H, m),
3.14-3.20 (2H, m), 4.49-4.55 (1H, m), 6.95 (2H, d, J ) 8.0 Hz),
8.19 (2H, d, J ) 8.0 Hz). MS (ESI) m/z 223 (M + H)+.
1-Cyclobutyl-4-(4-nitrophenoxy)piperidine (22). To a mixture of
21 (7.5 g, 33.8 mmol), zinc chloride (4.61 g, 33.8 mmol), and
cyclobutanone (3.55 g, 50.7 mmol) in methanol (100 mL) was
added sodium cyanoborohydride (3.19 g, 50.7 mmol) portionwise
at room temperature, and the mixture was stirred at room temper-
ature for 5 h. The resulting mixture was concentrated, and the
residue was partitioned between ethyl acetate and 2 N NaOH. The
layers were separated, and the aqueous layer was extracted with
ethyl acetate twice, and the combined organic layers were washed
with 1 N NaOH and brine, dried over sodium sulfate, and
concentrated. The resulting solid was suspended in a mixture of
diisopropylether/hexanes (v/v ) 1/4), and the precipitates were
collected by filtration and vacuum-dried to give 22 (7.5 g, 80%) as
a pale-yellow solid. 1H NMR (400 MHz, CDCl3) δ 1.75-1.86 (1H,
m), 1.87-1.94 (1H, m), 2.07-2.17 (2H, br m), 2.22-2.35 (6H, br
m), 2.92-3.02 (4H, br m), 3.28-3.34 (1H, m), 4.76 (1H, br s),
6.99 (2H, d, J ) 9.2 Hz), 8.18 (2H, d, J ) 9.2 Hz). MS (ESI) m/z
277 (M + H)+.
Ligand Binding Assay. Membrane preparations from the cells
expressing histamine H3 receptors and [3H] N-R-methylhistamine
binding studies were performed as previously described.34
[35S]GTPγS Functional Binding Assay. [35S]GTPγS functional
binding assays were carried out with a minor modification to the
method described previously.34 In brief, membranes were incubated
with 200 pM [35S]GTPγS in 50 mM Tris-HCl, 100 mM NaCl, 5
mM MgCl2, and 10 µM GDP (pH 7.4) containing 1.0 mg of wheat
germ agglutinin-coated SPA beads for 3 h at 25 °C in the presence
or absence of various concentrations of compounds. Membrane-
bound radioactivity was detected by scintillation proximetry with
a TopCount microplate scintillation counter (Packard, Meriden, CT).
Brain Histamine Release Assay. Brain tele-methylhistamine
levels were measured as previously described.29 In brief, 2 h after
treatment with orally administered vehicle (0.5% methylcellulose)
or compounds 5a and 5s (1, 3, and 10 mg /kg), male SD rats
(Charles River, Tokyo, Japan) were decapitated and the brains were
homogenized. After the solid phase extraction, tele-methylhistamine
was analyzed by high performance liquid chromatography with
fluorometry.
Receptor Occupancy by Ex Vivo Autoradiography. Male SD
rats received vehicle or compounds 5a and 5s (1 mg /kg) by oral
gavage. Animals were decapitated 2 h following oral dosing. In
other studies, female mdr1a (+/+) and mdr1a (-/-) CF-1 mice
(Charles River, Tokyo, Japan) were administered vehicle or
compound 5a (0.1, 0.3, and 1 mg /kg) or 5s (0.3, 1, and 3 mg/kg)
by oral gavage and decapitated 2 h following oral dosing. Terminal
blood samples were collected and whole brains were rapidly
removed in all studies. Whole brain tissue was dissected from half
of each brain (for ex vivo autoradiography), and the other half of
the brain was kept for pharmacokinetic analysis of brain concentra-
tions of 5a and 5s. All dissected tissue samples were frozen in dry
ice-cold isopentane and stored at -80 °C until use. Serial coronal
sections, 20 µm in thickness, of the anterior striatal (0.2-1.0 mm
anterior to Bregma) regions were cut by cryostat microtome and
stored at -80 °C. Striatal sections were incubated with 400 pM of
3-([1,1,1-3H]methyl)-2-(4-([3-(1-pyrrolidinyl)propyl]oxy)phenyl)-
4(3H)-quinazolinone (a selective histamine H3 receptor inverse
agonist radioligand) in sodium phosphate buffer for 10 min at room
temperature. Nonspecific binding was defined by the presence of
R-R-methylhistamine (10 µM). Following incubation, the striatum
sections were washed, air-dried, and exposed to beta-Imager
(Biospace, Paris, France) for 6 h. Autoradiographic images were
quantified as photostimulated luminescence (cpm) per mm2 by beta-
Imager. Blood samples were centrifuged to separate the plasma,
and the brain samples were homogenized by ultrasonification with
4 volumes of water. The plasma and brain homogenate samples
were deproteinized with ethanol containing an internal standard.
Compounds 5a and 5s and the internal standard were detected by
LC-MS/MS in a positive ionization mode using the electrospray
ionization probe, and their precursor to product ion combinations
were monitored in Multiple Reaction Monitoring mode.
4-[(1-Cyclobutyl-4-piperidinyl)oxy]aniline p-Toluenesulfonate
(23 Tosylate). Compound 22 (7.5 g, 27 mmol) was hydrogenated
over 3.0 g of 10% Pd/C in methanol (100 mL) under a hydrogen
atmosphere (1 atm) at room temperature for 13 h. The mixture was
filtered through a pad of celite, and the filtrate was concentrated.
The residue was vacuum-dried to give the aniline 23 as a pale-
brown oil (6.5 g, 97%). To a stirred solution of 23 (6.5 g, 26.4
mmol) in ethyl acetate (100 mL) was added a solution of
p-toluenesulfonic acid monohydrate (26.4 mmol) in EtOH (20 mL)
at room temperature. The mixture was heated to reflux for 10 min
to dissolve the precipitates. After being cooled to room temperature,
the resulting precipitates were collected and vacuum-dried to
Pharmacokinetics. Pharmacokinetic characterizations were con-
ducted in male SD rats, male Beagle dogs, and male rhesus monkeys
following single oral and single intravenous administration. In the
three species, single doses of 5a, 5r, and 5s were administered either
intravenously in a vehicle of PEG400/EtOH/H2O ) 50/10/40 or
orally by gavage in a vehicle of 0.5% methylcellurose aqueous
suspension. Doses of 1 (iv) and 3 (po) mg/kg for rats and 0.3 (iv)
1
provide 23 tosylate as a beige solid (10.3 g, 93%). H NMR (400
MHz, CDCl3/CD3OD ) 4/1) δ 1.68-1.79 (1H, m), 1.81-1.90 (1H,

6900 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 21
Nagase et al.
potential for metabolic disorders. J. Pharmacol. Sci. 2006, 101, 12–
and 1 (po) mg/kg for dogs and monkeys were used. Blood samples
for the determination of drug plasma concentrations were obtained
at multiple time points up to 24 h after administration. Blood
samples were centrifuged to separate the plasma, and the plasma
samples were deproteinized with ethanol containing an internal
standard. Compounds 5a, 5r, and 5s and the internal standard were
detected by LC-MS/MS in a positive ionization mode using the
electrospray ionization probe, and their precursor to product ion
combinations were monitored in Multiple Reaction Monitoring
mode.
18.
(14) Lin, J. S.; Dauvilliers, Y.; Arnulf, I.; Bastuji, H.; Anaclet, C.;
Parmentier, R.; Kocher, L.; Yanagisawa, M.; Lehert, P.; Ligneau, X.;
Perrin, D.; Robert, P.; Roux, M.; Lecomte, J. M.; Schwartz, J. C. An
inverse agonist of the histamine H3-receptor improves wakefulness in
narcolepsy: studies in orexin-/-mice and patients. Neurobiol. Dis.
2008, 30, 74–83.
(15) (a) LaBella, F. S.; Queen, G.; Glavin, G.; Durant, G.; Stein, D.;
Brandes, L. J. H3 receptor antagonist, thioperamide, inhibits adrenal
steroidogenesis and histamine binding to adrenocortical microsomes
and binds to cytochrome P450. Br. J. Pharmacol. 1992, 107, 161–
164. (b) Alves-Rodrigues, A.; Leurs, R.; Wu, T. S.; Prell, G. D.; Foged,
C.; Timmerman, H. [3H]-thioperamide as a radioligand for the
histamine H3 receptor in rat cerebral cortex. Br. J. Pharmacol. 1996,
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Coordination of histamine H3 receptor antagonists with human adrenal
cytochrome P450 enzymes. Pharmacology 2002, 66, 128–135.
Acknowledgment. We thank Hirokazu Ohsawa for collect-
ing the high-resolution mass spectral data, Hiroaki Suwa for
HPLC purity analyses, and Dr. Takahiro Fukuroda for cardio-
vascular studies in anesthetized dogs. We also thank Drs.
Nobuyoshi Yasuda, Robert J. DeVita, and Peter T. Meinke
(Merck Research Laboratories, Rahway, NJ) for the editing of
this manuscript.
(16) (a) Berlin, M.; Boyce, C. W. Recent advances in the development of
histamine H3 antagonists. Expert Opin. Ther. Patents 2007, 17, 675–
687. (b) Wijtmans, M.; Leurs, R.; de Esch, I. Histamine H3 receptor
ligands break ground in a remarkable plethora of therapeutic areas.
Expert Opin. InVestig. Drugs 2007, 16, 967–985. (c) Letavic, M.;
Barbier, A. J.; Dvorak, C. A.; Carruthers, N. I. Recent medicinal
chemistry of the histamine H3 receptor. Prog. Med. Chem. 2006, 44,
181–206.
Supporting Information Available: Preparation of benzoxazi-
nones 24e and 24g-i and procedures for safety-related studies,
HPLC retention times and purity for the target compounds, and
HPLC traces for 2f, 5a, 5r, and 5s. This material is available free
of charge via the Internet at http://pubs.acs.org.
(17) (a) Ligneau, X.; Perrin, D.; Landais, L.; Camelin, J.-C.; Calmels,
T. P.G.; Berrebi-Bertrand, I.; Lecomte, J.-M.; Parmentier, R.; Anaclet,
C.; Lin, J.-S.; Bertaina-Anglade, V.; la Rochelle, C. D.; d’Aniello,
F.; Rouleau, A.; Gbahou, F.; Arrang, J.-M.; Ganellin, C. R.; Stark,
H.; Schunack, W.; Schwartz, J.-C. BF2.649 [1-(3-[3-(4-Chlorophe-
nyl)propoxy]propyl)piperidine, hydrochloride], a nonimidazole inverse
agonist/antagonist at the human histamine H3 receptor: preclinical
pharmacology. J. Pharmacol. Exp. Ther 2007, 320, 365–375. (b)
Ligneau, X.; Landais, L.; Perrin, D.; Piriou, J.; Uguen, M.; Denis, E.;
Robert, P.; Parmentier, R.; Anaclet, C.; Lin, J. -S.; Burban, A.; Arrang,
J. -M.; Schwartz, J. C. Brain histamine and schizophrenia: potential
therapeutic applications of H3-receptor inverse agonists studied with
BF2.649. Biochem. Pharmacol. 2007, 73, 1215–1224.
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