N-substituted piperidinyl alkyl imidazoles: Discovery of methimepip as a potent and selective histamine H3 receptor agonist

Article abstract of DOI:10.1021/jm049475h

In this study, we continue our efforts toward the development of potent and highly selective histamine H₃ receptor agonists. We introduced various alkyl or aryl alkyl groups on the piperidine nitrogen of the known H₃/H₄ agonist immepip and its analogues (1-3a). We observed that N-methyl-substituted immepip (methimepip) exhibits high affinity and agonist activity at the human histamine H₃ receptor (pK _i = 9.0 and pEC₅₀ = 9.5) with a 2000-fold selectivity at the human H₃ receptor over the human H₄ receptor and more than a 10000-fold selectivity over the human histamine H₁ and H ₂ receptors. Methimepip was also very effective as an H₃ receptor agonist at the guinea pig ileum (pD₂ = 8.26). Moreover, in vivo microdialysis (in rat brain) showed that methimepip reduces the basal level of brain histamine to about 25% after a 5 mg/kg intraperitoneal administration.

Full text of DOI:10.1021/jm049475h

2100
J. Med. Chem. 2005, 48, 2100-2107
N-Substituted Piperidinyl Alkyl Imidazoles: Discovery of Methimepip as a
Potent and Selective Histamine H3 Receptor Agonist
Ruengwit Kitbunnadaj,†,‡ Takeshi Hashimoto,§ Enzo Poli,| Obbe P. Zuiderveld,† Alessandro Menozzi,|
Ryoko Hidaka,§ Iwan J. P. de Esch,† Remko A. Bakker,† Wiro M. P. B. Menge,† Atsushi Yamatodani,§
Gabriella Coruzzi,| Henk Timmerman,† and Rob Leurs*,†
Faculty of Chemistry, Department of Pharmacochemistry, Division of Medicinal Chemistry, Leiden/Amsterdam Center of Drug
Research, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands, Faculty of
Pharmaceutical Sciences, Department of Pharmaceutical Chemistry and Pharmacognosy, Naresuan University,
Phitsanulok, Thailand, Faculty of Medicine, Department of Bioinformatics, Graduate School of Allied Health Sciences,
Osaka University, Osaka, Japan, and Faculty of Medicine, Institute of Pharmacology, University of Parma, Italy
Received July 1, 2004
In this study, we continue our efforts toward the development of potent and highly selective
histamine H3 receptor agonists. We introduced various alkyl or aryl alkyl groups on the
piperidine nitrogen of the known H3/H4 agonist immepip and its analogues (1-3a). We observed
that N-methyl-substituted immepip (methimepip) exhibits high affinity and agonist activity
at the human histamine H3 receptor (pKi ) 9.0 and pEC50 ) 9.5) with a 2000-fold selectivity
at the human H3 receptor over the human H4 receptor and more than a 10000-fold selectivity
over the human histamine H1 and H2 receptors. Methimepip was also very effective as an H3
receptor agonist at the guinea pig ileum (pD2 ) 8.26). Moreover, in vivo microdialysis (in rat
brain) showed that methimepip reduces the basal level of brain histamine to about 25% after
a 5 mg/kg intraperitoneal administration.
Chart 1
Introduction
The histamine receptors, members of G-protein-
coupled receptor (GPCR) families, were initially catego-
rized on the basis of their pharmacological character-
ization, but they are currently classified as H1, H2, H3,
and H4 receptors on the basis of the diversity of their
amino acid sequences.1-4 The histamine H1 and H2
receptors were identified decades ago,5,6 and therapeutic
substances antagonizing the activity of histamine at the
histamine H1 or H2 receptors have been successfully
used for the treatment of allergies7,8 and gastric acid
related diseases,9,10 respectively. The histamine H3
receptor was discovered by Arrang and colleagues in
1983 to modulate the neuronal release of histamine.11
Many studies have shown that the histamine H3 recep-
tor also regulates the release of several other neuro-
transmitters, e.g., acetylcholine,12,13 dopamine,14 nor-
adrenaline,15 and serotonin16 in both the central and
peripheral nervous systems. In 1999, the human his-
tamine H3 receptor cDNA has been cloned by Lovenberg
and colleagues and gene expression analysis has shown
that the H3 receptor is predominantly expressed in the
brain.3
agonists at the H4 receptor showed that many potent
histamine H3 receptor agonists also possess a high
affinity at the H4 receptor. For example, imetit and
immepip (Chart 1), which have been published previ-
ously as selective potent histamine H3 receptor ago-
nists,23,24 exhibit also a high affinity at the histamine
H4 receptor with pKi values of 8.50 and 7.66, respec-
tively.21,25 Since the actual role of the histamine H3
receptor in both central and peripheral nervous systems
may therefore have become obscured due to the lack of
H3 receptor selective agonists, we continued our quest
for compounds with high selectivity and potency at the
human histamine H3 receptor.
We hypothesized that systematic modification of
potent histamine H3 ligands might result in compounds
with increased selectivity and retained high affinity and
agonist efficacy at the H3 receptor. Hence, we investi-
gated some promising potent histamine H3 receptor
ligands and eventually selected immepip, VUF4929, and
VUF5510 (Chart 1) as prototypes. A series of new
compounds with various alkyl or aryl alkyl groups on
the piperidine nitrogen of the selected prototypes were
prepared, as we reasoned that H3 and H4 receptor
agonism might be differentially affected by substitution
of the amine function. In fact, a recent study on indole
piperazines as selective H4 antagonists reported that
In 2000, a new type of histamine receptor (H4) was
discovered using the sequence information of the H3
receptor cDNA.4,17-20 The alignment of amino acid
sequences of the human histamine H3 and H4 receptors
indicates an overall 35% identity21 and a 58% identity
in the TM regions.22 Characterization of several H3
* Author to whom correspondence should be addressed. Tel: (+31)
20 4447600. Fax: (+31) 20 4447610. E-mail: leurs@few.vu.nl.
† Vrije Universiteit Amsterdam.
‡ Naresuan University.
§ Osaka University.
| University of Parma.
10.1021/jm049475h CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/24/2004

Methimepip as a Histamine H3 Receptor Agonist
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2101
Scheme 1. Synthetic Pathway for 1aa
a Reagents and conditions: (i) di-tert-butyl dicarbonate, TEA, CHCl3, room temperature; (ii) oxalyl chloride, DMSO, TEA, DCM, -60
°C to room temperature 5 h; (iii) TosMIC, NaCN, ethanol; (iv) saturated NH3 in ethanol, 90-110 °C, 10-12 atm, 16 h; (v) 1 N HBr, room
temperature 2 h.
Scheme 2. Synthetic Pathway for 2aa
a Reagents and conditions: (i) oxalyl chloride, DMSO, TEA, DCM, -60 °C to room temperature 5 h; (ii) TosMIC, NaCN, ethanol; (iii)
saturated NH3 in ethanol, 90-110 °C, 10-12 atm, 16 h; (iv) 10% Pd/C, HBr, H2 100 atm, 48 h.
Scheme 3. Synthetic Pathway for 1b-g,h, 2b-g, and
3b-ga
Alkylation of the piperidine nitrogen was achieved via
three different methods (A, B, and C, Scheme 3)
depending on the substituent desired. The methylated
amine was prepared following the Eschweiler-Clarke
procedure (method A);27,28 treatment of the amine with
formaldehyde in formic acid at 100 °C gave the desired
product in a good yield. In method B, treatment of the
amine with an alkyl halide in the presence of base
yielded the alkylated product in a moderate yield.
However, this method is not the method of choice since
an alkylation on the imidazole nitrogen may occur as
side reaction. Fortunately, reductive amination (method
C) does not lead to alkylation at the imidazole nitrogen
and proved to be very useful for the synthesis of the
alkylated compounds in this study. Yet, attempts to
synthesize 1-3c via method C failed; the ethylated
product was not obtained. However, treatment of 1-3a
with ethyl iodide in ethanol (1.5 equiv) in the presence
of potassium carbonate at room temperature (method
B) gave the desired product (1-3c) in a good yield (80%)
without an ethylation at the imidazole nitrogen. Com-
pounds 1d-h, 2d-g, and 3d-g were obtained following
method C; treatment of compounds 1-3a with the
corresponding aldehyde or ketone in dichloroethane in
the presence of a very mild reducing agent, sodium
triacetoxyborohydride,29 gave the desired products in
60-75% yield.
a Reagents and conditions: method A, (i) formaldehyde, formic
acid, ∆, 6 h; method B, (i) alkyl iodide, K2CO3, ethanol, 0 °C to
room temperature 16 h; method C, (i) aldehyde or ketone, acetic
acid, DCE, sodium triacetoxyborohydride, room temperature 16
h.
for proper H4 receptor affinity the piperidine ring could
not be substituted with large alkyl groups.26
Chemistry. The synthesis of the compounds is out-
lined in Schemes 1-3. Although the synthesis of im-
mepip (1a) using imidazole as starting chemical has
been published,24 the overall yield was less than 25%.
We therefore developed a new synthetic pathway
(Scheme 1) using a commercially available 2-piperidin-
4-yl ethanol as starting chemical. Treatment of the
piperidine compound with di-tert-butyl dicarbonate
resulted in the protected intermediate alcohol (4), which
was subsequently transformed into the corresponding
aldehyde using a Swern oxidation to give 5 in good yield
(90%). Next, the aldehyde was converted into an imid-
azole ring via two consecutive reactions; TosMIC chem-
istry gave an intermediate oxazoline (6), which was
subsequently treated with ammonia to give 7 in 70%
yield. Deprotection of 7 under acidic conditions gave 1a
in a quantitative yield.
Compound 2a was prepared from 3-pyridin-4-yl pro-
panol following Scheme 2. The hydroxyl group was
transformed into the aldehyde and subsequently con-
verted into an imidazole ring using the method de-
scribed above to give 10 in 70% yield. After hydrogen-
ation under acidic conditions using Pd/C as catalyst, the
product (2a) was obtained in a moderate yield (60%).
Pharmacology. Histamine H1 Receptor Binding
Studies. The affinity (pKi) value was measured by
displacement of [3H]-mepyramine binding to mem-
branes of COS-7 cells transiently expressing the human
histamine H1 receptor (3.2 ( 0.41 pmol/mg of protein)
in the presence of ligand using the procedure described
earlier.30
Histamine H2 Receptor Binding Studies. The
affinity (pKi) value was measured by displacement of
[
125I]-aminopotentidine binding to membranes of CHO
cells stably expressing the human histamine H2 receptor
(1079 ( 313 fmol/mg of protein) in the presence of ligand
using the procedure described earlier.31
Histamine H3 and H4 Receptor Binding Studies.
The affinity (pKi) values were measured by displace-

2102 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Kitbunnadaj et al.
ment of [3H]-NR-methylhistamine (for H3) or [3H]-
histamine (for H4) binding to membranes of SK-N-MC
cells expressing the human H3 or H4 receptor (131 (
11 fmol/mg of protein for H3 and 166 ( 26 fmol/mg of
protein for H4) in the presence of the ligand using the
procedures described previously.25
Functional Assay for Activity at Human Hista-
mine H3 Receptor. Using a cAMP reporter gene assay
as described previously,25 the functional activities of all
ligands were determined on SK-N-MC cells stably
expressing the human histamine H3 receptor.
Functional Studies on the Electrical Field Stimu-
lated Guinea Pig Ileum Contraction. The inhibitory
effects of histamine H3 receptor agonists were deter-
mined on ileum obtained from 25-30 days old Dunkin-
Hartley guinea pigs using the procedure described
earlier.32
results were observed in the VUF5510 (3a) series; an
introduction of various alkyl or aryl alkyl groups on the
piperidine nitrogen of VUF5510 leads to a decrease in
both histamine H3 receptor affinity and agonist activity
(Table 1). However, the introduction of a small group,
i.e., a methyl (3b), does not affect the binding and
functional activity at the human H3 receptor since this
compound still displays a comparable high affinity and
functional activity (pKi of 8.3 and pEC50 of 8.6, Table
1). In agreement with the VUF4929 series, substitution
of the piperidine nitrogen with either an isopropyl or a
cyclohexyl moiety results again in compounds acting as
inverse agonists; compounds 3d and 3e behave as
partial inverse agonists at the human H3 receptor with
pKi of 7.2 and 7.5, respectively. Surprisingly, partial
agonism is observed when a benzyl (3f) or a phenethyl
(3g) group is introduced at the piperidine nitrogen of
VUF5510.
In the immepip (1a) series, an introduction at the
piperidine nitrogen with various alkyl or aryl alkyl
groups also results in a decreased affinity and functional
activity at the human histamine H3 receptor with pKi
values ranging from 7.2 to 9.0 and pEC50 values ranging
from 7.5 to 9.5, respectively. The methyl derivative
(methimepip, 1b), however, possesses only a slightly
decreased affinity and agonist activity (pKi ) 9.0 and
pEC50 ) 9.5) at the human histamine H3 receptor
compared to its prototype immepip (1a, pKi ) 9.3 and
pEC50 ) 9.9, Table 1). A further increase of the sub-
stituent size at the piperidine nitrogen (1c-h) results
in a more than 25-fold decrease in affinity at the
histamine H3 receptor (Table 1). In contrast to what was
observed in the VUF4929 and VUF5510 series, substi-
tution of an isopropyl (1d), cyclohexyl (1e), benzyl (1f),
phenethyl (1g), or phenylpropyl (1h) group at the
piperidine nitrogen of immepip does not affect the
agonistic activity at the human histamine H3 receptor;
compounds 1d-h all display full agonism at the human
H3 receptor (Table 1), although the affinity was greatly
reduced compared to immepip.
Due to the high affinity and functional activity of
N-methyl-substituted immepip (methimepip, 1b) at the
human H3 receptor, this compound was tested further
for its affinity at the other histamine receptor types, i.e.,
the human histamine H1, H2, and H4 receptors. Radio-
ligand displacement studies of methimepip (1b) at the
cloned human H1, H2, and H4 receptors indicated low
affinities for the other three histamine receptor subtypes
(pKi < 5 at the H1 and H2 receptors, and pKi ) 5.7 at
the human H4 receptor, Table 2). Thus, within the class
of histamine receptors methimepip (1b) is identified as
a novel potent and highly selective histamine H3 recep-
tor agonist with a pKi of 9.0 and a pEC50 of 9.5 at the
human H3 receptor stably expressed on SK-N-MC cells.
This new H3 agonist (methimepip) shows a 2000-fold
preference for the human H3 receptor over the human
H4 receptor and a more than 10000-fold preference over
the human H1 and H2 receptors.
Microdialysis in Rat Brain. Characterization of
histamine release from the hypothalamus of male rats
of Wistar strain (8-9 weeks old, Japan SLC) were
measured by in vivo microdialysis using a procedure
described earlier.33
Results and Discussion
Pharmacological Evaluations and Structure-
Activity Relationships. In previous studies we showed
that histamine analogues containing a piperidine ring
in the side chain possess improved affinities and func-
tional activities at the human histamine H3 receptor.25
Immepip was identified as the most potent histamine
H3 receptor agonist with a pKi of 9.3 and a pEC50 of 9.9.
Characterization of immepip at the human histamine
H4 receptor, however, revealed a relative lack of selec-
tivity at the human H3 receptor, since immepip also
possesses high H4 receptor affinity as determined by
[3H]-histamine displacement studies (pKi ) 7.7).25 Due
to the high affinities of the parent compounds at the
human H3 receptor, in this study, analogues of immepip
(1a), VUF4929 (2a), and VUF5510 (3a) were synthe-
sized for the development of selective histamine H3
receptor agonists. The incorporation of various lipophilic
groups at the piperidine nitrogen of the selected com-
pounds (1b-h, 2b-g, and 3b-g) resulted in important
changes in affinity and activity at the human H3
receptor (Table 1). Although some of these compounds
were previously also reported as H3 receptor ligands in
a US patent,34 their pharmacological evaluations at the
human H3 or H4 receptor have not been described. In
the VUF4929 (2a) series, the introduction of various
alkyl or aryl alkyl groups at the piperidine nitrogen of
2a leads to a decreased affinity and functional activity
at the human H3 receptor. Compounds in this series
(2b-g) possess pKi values ranging from 6.8 (2e) to 7.4
(2g) at the H3 receptor as shown in Table 1, and none
of the compounds exhibit full agonistic activity at the
human H3 receptor. The introduction of a benzyl (2f) or
a phenethyl (2g) group even leads to compounds with
moderate affinity but no (inverse) agonist activity. Most
likely these two compounds behave as neutral antago-
nists at the human H3 receptor. Interestingly, the
attachment of a bulky group, i.e., isopropyl (2d) or
cyclohexyl (2e), at the piperidine nitrogen results in a
total loss of histamine H3 receptor agonism, and these
compounds act as partial inverse agonists. Similar
Functional Studies on the Electrical Field Stimu-
lated Guinea Pig Ileum Contraction. In the guinea
pig intestine, histamine H3 receptor agonists inhibit the
electrically evoked acetylcholine release from myenteric
plexus, and thereby modulate subsequent twitch re-
sponses.35-37 The recent discovery of the histamine H4

Methimepip as a Histamine H3 Receptor Agonist
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2103
Table 1. Affinities (pKi) and Functional Activities (pEC50) of Various Ligands for Human Histamine H3 Receptord
a The pKi values were measured by displacement of [3H]-NR-methylhistamine binding to membranes of SK-N-MC cells expressing the
human H3 receptor in the presence of the ligand. b The pEC50 were determined by the inhibition of the cAMP-stimulated â-galactosidase
transcription in SK-N-MC cells stably expressing the human H3 receptor. Results are presented as mean ( SEM of at least three
independent experiments. c R ) intrinsic activity as the ratio of the maximum response of each ligand to the maximum response of histamine
(for agonists) or clobenpropit (for inverse agonists). The positive and negative values represent agonism and inversed agonism, respectively.
dn.d. ) not determined.
receptor, which has high homology to the H3 receptor,
revealed the lack of selectivity of known histamine H3
receptor agonists; e.g., histamine, imetit, and immepip
also show a high affinity on the H4 receptor.25 Poly-
merase chain reaction (PCR) analysis of the histamine
H4 receptor mRNA on several tissues also indicated the
expression of the H4 receptor in the small intestine.4 It
may, therefore, be asked whether the inhibitory re-
sponse observed on the ileum could (partly) be mediated
by activation of the histamine H4 receptor. In order to

2104 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Kitbunnadaj et al.
Table 2. Affinities (pKi) of Methimepip (1b) and Immepip (1a)
for Human Histamine H1, H2, H3, and H4 Receptors
pKi ( SEMa
compound
hH1
<5
hH2
hH3
hH4
methimepip
immepip
<5
9.0 ( 0.1
9.3 ( 0.0
5.7 ( 0.1
7.7 ( 0.0
<5b
a n g 3. b See ref 24.
Figure 1. Effects of the histamine H3 receptor agonists
immepip and methimepip on guinea pig ileal muscle contrac-
tion evoked by electrical field stimulation (EFS). Values are
mean ( SEM of 6 or 7 observations.
Figure 2. Effects of methimepip (circles) and immepip
(squares) on the extracellular histamine concentration in rat
brain determined by microdialysis (A) after an intraperitoneal
answer this question, methimepip (1b), which exhibits
high selectivity at the histamine H3 receptor, was tested
for its activity on the electrically stimulated guinea pig
ileum. Using the procedure described before,32 me-
thimepip (1b) was characterized in comparison with the
potent but less selective H3 receptor agonist immepip
(1a). The results depicted in Figure 1 show that both
immepip and methimepip (1b) inhibit the EFS-evoked
contractions of the guinea pig ileum with a comparable
efficacy (55% inhibition of neurogenic contraction am-
plitude) and potency (pD2 ) 8.40 and 8.26, respectively).
These findings suggest that the inhibitory effect of
intestinal acetylcholine release and consecutive contrac-
tion is most likely mediated through the activation of
the histamine H3 receptor.
Microdialysis Studies in Rat Brain. The hista-
mine H3 receptor was discovered by Arrang and col-
leagues and identified as an autoreceptor in the rat
brain modulating the synthesis and release of hista-
mine.11 Activation of the histamine H3 receptor by
agonists leads to a decrease of the histamine concentra-
tion in the brain. Therefore, methimepip (1b) was
selected for further in vivo studies in comparison with
immepip. Using a previously described microdialysis
technique,33 the level of histamine was determined in
the dialysate collected from rat hypothalamus at 20 min
intervals after the administration of methimepip (1b)
either by intraperitoneal (ip) injection at a dose of 5 mg/
kg or by infusion via the microdialysis probe at a
concentration of 1 × 10-5 M or 1 × 10-6 M. The results
depicted in Figure 2A,B show that both immepip and
methimepip (1b) significantly lowered the level of
histamine in the rat hypothalamus after intraperitoneal
injection or infusion via the microdialysis probe. The
basal level of histamine is reduced to about 25% by the
ip injection or the infusion of either immepip or me-
thimepip (1b). The effect of methimepip (1b) was
antagonized by coinfusion of clobenpropit (Figure 3).
Clobenpropit is known as a potent H3 receptor antago-
nists (pKi ) 9.4) with only limited affinity at the human
(ip) injection of 5 mg/kg or (B) during infusions of 1 × 10-5
M
and/or 1 × 10-6 M solutions via the microdialysis probes.
Values are mean ( SEM of 4 or 5 observations.
Figure 3. The extracellular histamine concentration in rat
brain as determined by microdialysis during an infusion of
methimepip (1 × 10-6 M) and subsequently coinfusion with
clobenpropit (1 × 10-5 M). Values are mean ( SEM of 4 or 5
observations.
H1 and H2 receptor (pKi ) 5.6 and 5.2 respectively),38
whereas it acts as a partial agonist at the human H4
receptor.4
Conclusion
In this study, systematic modification, achieved by the
introduction of various alkyl or aryl alkyl groups on the
piperidine nitrogen of the selected potent histamine H3
receptor agonists immepip (1a), VUF4929 (2a), and
VUF5510 (3a), resulted in the discovery of a new, potent
and selective histamine H3 receptor agonist. The N-
methyl-substituted immepip (methimepip, 1b) retains
high affinity and functional activity at the human H3
receptor (pKi ) 9.0 and pEC50 ) 9.5, Table 1). Radio-
ligand displacement studies of methimepip (1b) at the
other human histamine receptor types (H1, H2, and H4)
reveal a high selectivity of methimepip (1b) for the
human H3 receptor (2000-fold over the human H4
receptor and more than 10000-fold over the human H1
and H2 receptors, Table 2). In contrast, immepip shows

Methimepip as a Histamine H3 Receptor Agonist
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2105
Table 3. Synthetic Methods and Spectroscopic and Analytical Data for Compoundsa
yield
no meth (%)
mp
(°C)
MS
elemental anal.
(C, H, N)
[M + 1]+
1H NMR (D2O)
1b
2b
3b
1c
A
A
A
B
78
72
75
80
156.7-157.3
193.8-194.2
217.4-219.3
128.0-129.8
180.3
194.3
178.4
194.3
δ 8.57 (s, 1H), 7.25 (s, 1H), 3.47 (m, 2H), 2.96 (m, 2H), 2.81 (s,
3H), 2.72 (d, 2H, J ) 6.7 Hz), 1.94 (m, 3H), 1.49 (m, 2H)
δ 8.54 (s, 1H), 7.18 (s, 1H), 3.60 (m, 2H), 2.93 (m, 2H), 2.80 (s,
3H), 2.75 (t, 2H, J ) 7.6 Hz), 2.00 (m, 2H), 1.45-1.68 (m, 5H)
δ 8.62 (s, 1H), 7.40 (s, 1H), 6.30 (s, 1H), 3.52 (m, 2H), 2.90-3.05
(m, 3H), 2.87 (s, 3H), 2.57-2.71 (m, 3H)
δ 8.54 (s, 1H), 7.24 (s, 1H), 3.55 (m, 2H), 3.12 (q, 2H, J ) 7.4 Hz),
2.88 (m, 2H), 2.72 (d, 2H, J ) 6.8 Hz), 1.94 (m, 3H), 1.45
(m, 2H), 1.26 (t, 3H, J ) 7.4 Hz)
δ 8.52 (s, 1H), 7.17 (s, 1H), 3.53 (m, 2H), 3.10 (q, 2H, J ) 7.4 Hz),
2.86 (m, 2H), 2.74 (t, 2H, J ) 7.5 Hz), 2.02 (m, 2H),
1.43-1.67 (m, 5H), 1.26 (t, 3H, J ) 7.5 Hz)
δ 8.61 (s, 1H), 7.40 (s, 1H), 6.27 (s, 1H), 3.63 (m, 2H), 3.19 (q, 2H,
J ) 7.4 Hz), 2.90-3.10 (m, 3H), 2.55-2.70 (m, 3H), 1.29 (t,
3H, J ) 7.4 Hz)
δ 8.54 (s, 1H), 7.23 (s, 1H), 3.56 (m, 3H), 3.35 (m, 2H), 2.78 (d,
2H, J ) 5.6 Hz), 1.97 (m, 3H), 1.74 (m, 2H), 1.39 (d, 6H, J
) 6.7 Hz)
δ 8.52 (s, 1H), 7.17 (s, 1H), 3.41 (m, 3H), 2.95 (m, 2H), 2.74 (t, 2H,
J ) 7.4 Hz), 2.02 (m, 2H), 1.42-1.67 (m, 5H), 1.27 (d, 6H,
J ) 6.7 Hz)
δ 8.57 (s, 1H), 7.37 (s, 1H), 6.26 (s, 1H), 3.47-3.53 (m, 3H),
2.95-3.02 (m, 3H), 2.58-2.72 (m, 3H), 1.26 (d, 6H, J ) 6.8
Hz)
C
10H19N3Br2‚0.7H2O
C
C
C
11H21N3Br2
10H17N3Br2
11H21N3Br2‚2.3H2O
2c
3c
1d
2d
3d
B
B
C
C
C
74
73
67
63
65
204.5-206.1
194.6-197.1
185.7-187.4
224.3-225.9
176.2-178.3
208.4
192.6
208.3
222.3
206.8
C
C
C
C
C
12H23N3Br2
11H19N3Br2
12H23N3Br2‚0.4H2O
13H25N3Br2‚0.4H2O
12H21N3Br2‚2.6H2O
1e
2e
3e
C
C
C
68
65
60
216.5-218.1
232.4-234.5
184.5-185.7
248.5
262.3
246.6
δ 8.55 (s, 1H), 7.23 (s, 1H), 3.45 (m, 2H), 3.00 (m, 3H), 2.70 (d,
2H, J ) 6.6 Hz), 1.64-1.97 (m, 7H), 1.11-1.44 (m, 8H)
δ 8.50 (s, 1H), 7.15 (s, 1H), 3.47 (m, 3H), 2.98 (m, 3H), 2.72 (t, 2H,
J ) 7.2 Hz), 1.61-1.95 (m, 7H), 1.12-1.38 (m, 9H)
δ 8.60 (s, 1H), 7.38 (s, 1H), 6.26 (s, 1H), 3.56 (m, 2H), 3.05-3.16
(m, 4H), 2.54-2.71 (m, 3H), 1.83-1.98 (m, 4H), 1.26-1.48
(m, 6H)
δ 8.59 (s, 1H), 7.52 (m, 5H), 7.27 (s, 1H), 4.30 (s, 2H), 3.53 (m,
2H), 3.02 (m, 2H), 2.74 (d, 2H, J ) 6.8 Hz), 1.95 (m, 3H),
1.44 (m, 2H)
δ 8.49 (s, 1H), 7.44 (m, 5H), 7.14 (s, 1H), 4.23 (s, 2H), 3.45 (m,
2H), 2.92 (m, 2H), 2.71 (t, 2H, J ) 7.4 Hz), 1.96 (m, 2H),
1.49-1.61 (m, 5H)
δ 8.59 (s, 1H), 7.48 (m, 5H), 7.37 (s, 1H), 6.26 (s, 1H), 4.32 (s, 2H),
3.58 (m, 2H), 3.15 (m, 3H), 2.66-2.69 (m, 3H)
δ 8.56 (s, 1H), 7.25-7.38 (m, 6H), 3.62 (m, 2H), 3.38 (m, 2H),
2.92-3.09 (m, 4H), 2.72 (d, 2H, J ) 6.8 Hz), 1.95 (m,
3H),1.48 (m, 2H)
C
C
C
15H27N3Br2‚1.4H2O
16H29N3Br2‚0.3H2O
15H25N3Br2‚2.6H2O
1f
2f
C
C
75
68
241.8-242.4
205.5-206.4
256.3
270.6
C
16H23N3Br2‚1.3H2O
17H25N3Br2‚1.4H2O
C
3f
C
C
70
72
223.8-224.4
219.8-220.4
254.5
270.4
C
16H21N3Br2‚0.9H2O
17H25N3Br2‚1.0H2O
1g
C
2g
C
65
214.3-215.6
284.6
δ 8.52 (s, 1H), 7.35 (m, 5H), 7.17 (s, 1H), 3.60 (m, 2H), 3.34 (m,
2H), 2.89-3.08 (m, 4H), 2.74 (t, 2H, J ) 7.2 Hz), 2.00 (m,
2H), 1.37-1.64 (m, 5H)
δ 8.60 (s, 1H), 7.35-7.41 (m, 6H), 6.27 (s, 1H), 3.65 (m, 2H), 3.37
(t, 2H, J ) 7.2 Hz), 2.93-3.06 (m, 5H), 2.54-2.67 (m, 3H)
δ 8.53 (s, 1H), 7.21-7.34 (m, 6H), 3.50 (m, 2H), 3.05 (m, 2H), 2.99
(m, 2H), 2.67 (m, 4H), 1.86-2.01 (m, 5H),1.43 (m, 2H)
C18H27N3Br2
3g
1h
C
C
64
75
213.8-214.8
196.6-197.6
268.3
284.4
C
17H23N3Br2‚1.8H2O
C18H27N3Br2
a All compounds are hygroscopic.
tography was performed on J. T. Baker Kieselgel 60 under
pressure. Melting points were determined on an Electrother-
mal IA9200 apparatus. Mass spectrometry was performed on
a Finnigan LCQDECA ion-trap mass spectrometer using APCI
technique. 1H spectra were recorded on a Bruker AC-200
spectrometer with the residual undeuterated solvent peak as
reference. Elemental analyses were performed at Mikroana-
lytisches Labor Pascher (Remagen-Bandorf, Germany). Syn-
thetic methods and spectroscopic and analytical data for the
target compounds are shown in Table 3.
only a 45-fold preference for the human H3 receptor over
the human H4 receptor. The microdialysis study in rat
brain shows that both immepip and methimepip (1b)
lower the basal level of histamine in rat hypothalamus
to about 25% after an intraperitoneal injection (5 mg/
kg). Thus, methimepip (1b) is identified as a novel,
potent and highly selective histamine H3 receptor ago-
nist, which will be useful in both in vitro and in vivo
studies.
Methods. 4-(2-Hydroxyethyl)piperidine-1-carboxylic
Acid tert-Butyl Ester (4). To a cold solution of 4-piperidine
ethanol (10 g, 0.08 mol) in 200 mL of CHCl3 was added
dropwise a solution of di-tert-butyl dicarbonate (19 g, 0.09 mol)
and triethylamine (34 mL, 0.24 mol) in 200 mL of CHCl3. The
mixture was stirred in an ice bath for 1 h and subsequently
at room temperature for 16 h. A saturated sodium carbonate
solution (250 mL) was added, the organic layer was collected,
and the aqueous layer was extracted with CHCl3 (2 × 200 mL).
The combined organic layers were dried over sodium sulfate
Experimental Section
Material. Reagents were obtained from commercial sup-
pliers and used without further purification. 3-Pyridin-4-yl-
propanol was purified by distillation under reduced pressure.
VUF5510 (3a) was synthesized using a procedure earlier
described.25 Solvents used were either AR or HPLC grade. Dry
THF and DCM were obtained freshly from distillation over
lithium aluminum hydride and calcium hydride, respectively.
Thin-layer chromatography was carried out on Merck Kieselgel
60 F254 on aluminum sheets, and preparative flash chroma-
1
and evaporated to give 4 as a light-yellow oil (18 g, 98%). H

2106 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Kitbunnadaj et al.
NMR (CDCl3): δ 4.02 (m, 2H), 3.68 (t, 2H, J ) 6.1 Hz), 2.66
(m, 2H), 2.00 (br, s, OH), 1.51-1.70 (m, 5H), 1.46 (s, 9H), 1.07
(m, 2H).
4-[2-(Imidazol-4-yl)-ethyl]pyridine (10). The compound
was synthesized from 9 using the procedure described for the
synthesis of 7. The product 10 was obtained as a light-yellow
1
oil (12.1 g, 70% based on 8). H NMR (CDCl3): δ 8.43 (d, 2H,
4-(2-Oxoethyl)piperidine-1-carboxylic Acid tert-Butyl
Ester (5). A solution of oxalyl chloride (7.4 mL, 0.09 mol) in
100 mL of dry DCM was cooled to -60 °C under an atmosphere
of dry nitrogen. A solution of dimethyl sulfoxide (13.4 mL, 0.19
mol) in 100 mL of DCM was added dropwise, and the mixture
was subsequently stirred for 15 min at -60 °C. Next, a solution
of 4 (18 g, 0.08 mol) in 100 mL of dry DCM was added dropwise
and the mixture stirred for 45 min at -60 °C. Subsequently,
triethylamine (55 mL, 0.40 mol) was added, and the mixture
was warmed to room temperature. The reaction mixture was
washed with water (3 × 200 mL) and dried over sodium
sulfate. The solvent was evaporated under reduced pressure.
After purification by flash column chromatography (EtOAc),
the title compound (5) was obtained as a light-yellow solid (16.5
J ) 6.1 H), 7.55 (s, 1H), 7.07 (d, 2H, J ) 6.1 Hz), 6.68 (s, 1H),
2.94 (m, 4H).
4-[2-(Imidazol-4-yl)-ethyl]piperidine Dihydrobromide
(2a). A solution of 10 (12 g, 0.07 mol) in 10 mL of 5 N HCl
was added to a suspension of 1.2 g of 10% Pd/C in 100 mL of
MeOH. The mixture was hydrogenated under 100 atm of
hydrogen gas for 48 h in a stainless steel bomb. The mixture
was concentrated in vacuo, whereafter a saturated sodium
carbonate solution was added in order to get pH ≈ 12. After
extraction with CHCl3 (3 × 250 mL), the organic solvent was
dried over sodium sulfate and evaporated to obtain a yellow
oil, which was subsequently treated with 1 N HBr (adjusted
pH ≈ 3) and concentrated in vacuo. The product 2a was
recrystallized from EtOH/Et2O as light-yellow solid (14.3 g,
60%). 1H NMR (D2O): δ 8.53 (s, 1H), 7.18 (s, 1H), 3.39 (m,
2H), 2.94 (m, 2H), 2.75 (t, 2H, J ) 7.2 Hz), 1.96 (m, 2H), 1.64
(m, 3H), 1.44 (m, 2H).
General Procedures for the Synthesis of Compounds
1a-h, 2a-g, and 3a-g. Method A. The amine (1a, 2a, or
3a, 1.5 mmol) was added to cold formic acid (25 mL) followed
by slow addition of 0.5 mL of formaldehyde (37% solution
stabilized with methanol). The resulting mixture was refluxed
for 6 h and quenched by addition of saturated sodium carbon-
ate solution until pH ≈ 12. After concentration of the mixture
in vacuo, the residue was washed with CHCl3 (3 × 25 mL).
The combined organic layers were dried over sodium sulfate
and evaporated. The product was purified using flash column
chromatography (5% TEA in MeOH). The purified compound
was subsequently treated with 1 N HBr (adjusted pH ≈ 3),
concentrated in vacuo, and recrystallized from EtOH/Et2O to
give a light-yellow solid.
Method B. A mixture of the amine (1a, 2a, or 3a, 1.5 mmol)
and potassium carbonate (3.75 mmol) in ethanol (50 mL) was
stirred at room temperature for 15 min and cooled to 0 °C in
an ice bath. Ethyl iodide (1.5 mmol) was added dropwise, and
the mixture was stirred at 0 °C for 1 h, followed by 16 h at
room temperature. If the reaction was incomplete, additional
ethyl iodide (0.75 mmol) was added and the mixture was
stirred for another 16 h. After the mixture was concentrated
in vacuo, the residue was washed with CHCl3 (3 × 25 mL)
and filtered. The filtrate was dried over sodium sulfate and
the solvent was evaporated to give the product, which was
purified subsequently using flash column chromatography (5%
TEA in MeOH). The purified product was treated with 1 N
HBr (adjusted pH ≈ 3), concentrated in vacuo, and recrystal-
lized from EtOH/Et2O to give a light-yellow solid.
Method C. The amine (1a, 2a, or 3a, 1.5 mmol) and sodium
carbonate (1.5 mmol) were added to MeOH and warmed to 80
°C for 15 min. The solvent was evaporated under reduced
pressure, and dichloroethane (20 mL) was added. The aldehyde
or ketone (2.25 mmol) was dissolved in 5 mL of dichloroethane
and added to the solution of amine. The resulting mixture was
stirred at room temperature for 15 min, and glacial acetic acid
(0.1 mL) was added. The mixture was stirred for an additional
30 min, and sodium triacetoxyborohydride (2.25 mmol) was
added in a portion and stirred at room temperature for 16 h.
CHCl3 (25 mL) was added, and the reaction was quenched with
saturated sodium carbonate solution. The organic layer was
separated, and the aqueous layer was extracted with CHCl3
(2 × 25 mL). The combined organic layers were dried over
sodium sulfate. The solvent was evaporated, and the product
was purified using flash column chromatography (5% TEA in
MeOH). The purified product was treated with 1 N HBr
(adjusted pH ≈ 3) and then concentrated in vacuo. The product
was recrystallized from EtOH/Et2O to give a light-yellow solid.
1
g, 90%). H NMR (CDCl3): δ 9.76 (s, 1H), 4.08 (m, 2H), 2.64
(m, 2H), 2.34 (dd, 2H, J ) 6.4 and 2.2 Hz), 2.11 (m, 1H), 1.65
(m, 2H), 1.42 (s, 9H), 1.12 (m, 2H).
4-[4-(4-Methylbenzenesulfonyl)-4,5-dihydrooxazol-5-
ylmethyl]piperidine-1-carboxylic Acid tert-Butyl Ester
(6). Finely powdered sodium cyanide (0.4 g, 7 mmol) was added
in one portion to a stirred suspension of tosylmethyl isocyanide
(15.6 g, 0.08 mol) and 5 (16.5 g, 0.07 mol) in 500 mL of absolute
ethanol. Immediately, the reaction mixture became clear, and
the solution was stirred for another 2 h. The solvent was
evaporated under reduced pressure, and 500 mL of CHCl3 was
added. The resulting mixture was filtered, and the filtrate was
concentrated in vacuo to give a brown oil, which was used
immediately for the next step without further purification. 1H
NMR (CDCl3): δ 7.76 (d, 2H, J ) 8.2 Hz), 7.34 (d, 2H, J ) 8.2
Hz), 6.94 (s, 1H), 5.08 (m, 1H), 4.71 (d, 1H, J ) 5.9 Hz), 4.08
(m, 2H), 2.66 (m, 2H), 2.41 (s, 3H), 1.44-1.61 (m, 5H), 1.41 (s,
9H), 1.20 (m, 2H).
4-(Imidazol-4-ylmethyl)piperidine-1-carboxylic Acid
tert-Butyl Ester (7). In a stainless steel bomb, a solution of
6 in 120 mL of absolute ethanol saturated with ammonia was
heated at 90-110 °C for 16 h. After cooling to room temper-
ature, the solvent was evaporated under reduced pressure. The
residue was dissolved in DCM (250 mL) and washed with 10%
sodium carbonate solution (250 mL) and water (2 × 250 mL).
The organic layer was dried over sodium sulfate and concen-
trated under reduced pressure to give a dark brown oil, which
was subsequently treated with activated charcoal. Filtration
and purification using flash column chromatography (MeOH:
DCM, 1:9) resulted in 7 as a light-yellow oil (13.7 g, 70% based
1
on 5). H NMR (CDCl3): δ 7.53 (s, 1H), 6.74 (s, 1H), 4.00 (m,
2H), 2.63 (m, 2H), 2.49 (d, 2H, J ) 6.8 Hz), 1.59-1.73 (m, 3H),
1.41 (s, 9H), 1.10 (m, 2H).
4-(Imidazol-4-ylmethyl)piperidine Dihydrobromide
(1a). Compound 7 (13.7 g, 0.05 mol) was dissolved in 100 mL
of 1 N HBr. The solution was heated at 80 °C for 2 h, and the
solvent was evaporated. The residue was dissolved in 50 mL
of ethanol and precipitated by slow addition of ether. The
product 1a was obtained as an off white solid (10.6 g, 65%).
1H NMR (D2O): δ 8.56 (s, 1H), 7.24 (s, 1H), 3.40 (m, 2H), 2.91
(m, 2H), 2.72 (d, 2H, J ) 6.8 Hz), 1.87-1.94 (m, 3H), 1.40 (m,
2H). mp 233.6-234.8 °C (237-239 °C).39
3-Pyridin-4-yl-propionaldehyde (8). The compound was
synthesized from 4-pyridinepropanol (15 g, 0.11 mol) using the
procedure described for the synthesis of 5. The product 8 was
obtained as a yellow oil (13 g, 87%). 1H NMR (CDCl3): δ 9.80
(s, 1H), 8.47 (d, 2H, J ) 6.0 Hz), 7.10 (d, 2H, J ) 6.0 Hz),
2.75-2.97 (m, 4H).
4-{2-[4-(4-Methylbenzenesulfonyl)-4,5-dihydrooxazol-
5-yl]ethyl}pyridine (9). The compound was synthesized from
8 (13 g, 0.10 mol) using the procedure described for the
synthesis of 6. The product 9 was used immediately for the
next step without further purification. 1H NMR (CDCl3): δ
8.44 (d, 2H, J ) 6.0 Hz), 7.72 (d, 2H, J ) 8.2 Hz), 7.37 (d, 2H,
J ) 8.2 Hz), 7.12 (d, 2H, J ) 6.0 Hz), 6.96 (s, 1H), 4.97 (m,
1H), 4.77 (d, 1H, J ) 5.9 Hz), 2.74 (m, 2H), 2.39 (s, 3H), 1.96
(m, 2H).
Acknowledgment. The authors thank Dr. T. Loven-
berg, Johnson & Johnson Pharmaceutical Research and

Methimepip as a Histamine H3 Receptor Agonist
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2107
(22) Nguyen, T.; Shapiro, D. A.; George, S. R.; Setola, V.; Lee, D. K.;
Cheng, R.; Rauser, L.; Lee, S. P.; Lynch, K. R.; Roth, B. L.;
O’Dowd, B. F. Discovery of a novel member of the histamine
receptor family. Mol. Pharmacol. 2001, 59, 427-433.
(23) Garbarg, M.; Arrang, J. M.; Rouleau, A.; Ligneau, X.; Tuong,
M. D.; Schwartz, J. C.; Ganellin, C. R. S-[2-(4-imidazolyl)ethyl]-
isothiourea, a highly specific and potent histamine H3 receptor
agonist. J. Pharmacol. Exp. Ther. 1992, 263, 304-310.
(24) Vollinga, R. C.; de Koning, J. P.; Jansen, F. P.; Leurs, R.; Menge,
W. M.; Timmerman, H. A new potent and selective histamine
H3 receptor agonist, 4-(1H-imidazol-4-ylmethyl)piperidine. J.
Med. Chem. 1994, 37, 332-333.
(25) Kitbunnadaj, R.; Zuiderveld, O. P.; Esch, I. J. P. D.; Vollinga,
R. C.; Bakker, R.; Lutz, M.; Spek, A. L.; Cavoy, E.; Deltent, M.
F.; Menge, W. M. P. B.; Timmerman, H.; Leurs, R. Synthesis
and Structure-Activity Relationships of Conformationally Con-
strained Histamine H3 Receptor Agonists. J. Med. Chem. 2003,
46, 5445-5457.
(26) Jablonowski, J. A.; Grice, C. A.; Chai, W.; Dvorak, C. A.; Venable,
J. D.; Kwok, A. K.; Ly, K. S.; Wei, J.; Baker, S. M.; Desai, P. J.;
Jiang, W.; Wilson, S. J.; Thurmond, R. L.; Karlsson, L.; Edwards,
J. P.; Lovenberg, T. W.; Carruthers, N. I. The first potent and
selective non-imidazole human histamine H4 receptor antago-
nist. J. Med. Chem. 2003, 46, 3957-3960.
(27) Newman, M. S.; Lloyd, H. A. The reaction of N-methylpiperidine
with alkyl durenecarboxylates. J. Am. Chem. Soc. 1952, 74,
2672-2674.
Development L.L.C., San Diego, CA, for the gift of cells
stably expressing the human histamine H3 or H4 recep-
tor.
Supporting Information Available: Elemental analysis
data for 1b-g,h, 2b-g, and 3b-g. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) Yamashita, M.; Fukui, H.; Sugama, K.; Horio, Y.; Ito, S.;
Mizuguchi, H.; Wada, H. Expression cloning of a cDNA encoding
the bovine histamine H1 receptor. Proc. Natl. Acad. Sci. U.S.A.
1991, 88, 11515-11519.
(2) Gantz, I.; Schaffer, M.; DelValle, J.; Logsdon, C.; Campbell, V.;
Uhler, M.; Yamada, T. Molecular cloning of a gene encoding the
histamine H2 receptor. Proc. Natl. Acad. Sci. U.S.A. 1991, 88,
429-433.
(3) Lovenberg, T. W.; Roland, B. L.; Wilson, S. J.; Jiang, X.; Pyati,
J.; Huvar, A.; Jackson, M. R.; Erlander, M. G. Cloning and
functional expression of the human histamine H3 receptor. Mol.
Pharmacol. 1999, 55, 1101-1107.
(4) Oda, T.; Morikawa, N.; Saito, Y.; Masuho, Y.; Matsumoto, S.
Molecular cloning and characterization of a novel type of
histamine receptor preferentially expressed in leukocytes. J.
Biol. Chem. 2000, 275, 36781-36786.
(5) Ash, A. S. F.; Schild, H. O. Receptor mediating some actions of
histamine. Br. J. Pharmacol. 1966, 188, 219-227.
(6) Black, J. W.; Duncan, W. A. M.; Durant, G. J.; Ganellin, C. R.;
Parsons, M. E. Definition and antagonism of histamine H2
receptors. Nature 1972, 236, 385-390.
(7) Kaliner, M. A.; Check, W. A. Non-sedating antihistamines.
Allergy Proc. 1988, 9, 649-663.
(28) Lee, S. S.; Wu, W. N.; Wilton, J. H.; Beal, J. L.; Doskotch, R. W.
Longiberine and O-methyllongiberine, dimeric protoberberine-
benzyl tetrahydroisoquinoline alkaloids from Thalictrum longi-
stylum(1). J. Nat. Prod. 1999, 62, 1410-1414.
(8) Simons, F. E. Recent advances in H1 receptor antagonist
treatment. J. Allergy Clin. Immunol. 1990, 86, 995-999.
(9) Ivey, K. J. Control of gastric acid secretion by histamine H2
receptor antagonists; a pharmacological dream come true. Aust.
N. Z. J. Med. 1974, 4, 521-524.
(29) Abdel-Magid, A. F.; Maryanoff, C. A.; Carson, K. G. Reductive
amination of aldehydes and ketones by using sodium triacetoxy-
borohydride. Tetrahedron Lett. 1990, 31, 5595-5598.
(30) Govoni, M.; Bakker, R. A.; van de Wetering, I.; Smit, M. J.;
Menge, W. M.; Timmerman, H.; Elz, S.; Schunack, W.; Leurs,
R. Synthesis and pharmacological identification of neutral
histamine H1 receptor antagonists. J. Med. Chem. 2003, 46,
5812-5824.
(31) Alewijnse, A. E.; Smit, M. J.; Rodriguez Pena, M. S.; Verzijl, D.;
Timmerman, H.; Leurs, R. Modulation of forskolin-mediated
adenylyl cyclase activation by constitutively active GS-coupled
receptors. FEBS Lett. 1997, 419, 171-174.
(32) Poli, E.; Pozzoli, C.; Coruzzi, G.; Bertaccini, G. Signal transducing
mechanisms coupled to histamine H3 receptors and R2 adreno-
ceptors in the guinea pig duodenum: possible involvement of
N-type Ca2+ channels. J. Pharmacol. Exp. Ther. 1994, 270, 788-
794.
(33) Jansen, F. P.; Mochizuki, T.; Yamamoto, Y.; Timmerman, H.;
Yamatodani, A. In vivo modulation of rat hypothalamic hista-
mine release by the histamine H3 receptor ligands, immepip and
clobenpropit. Effects of intrahypothalamic and peripheral ap-
plication. Eur. J. Pharmacol. 1998, 362, 149-155.
(10) Pounder, R. Histamine H2 receptor antagonists. Bailliere’s Clin.
Gastroenterol. 1988, 2, 593-608.
(11) Arrang, J. M.; Garbarg, M.; Schwartz, J. C. Auto-inhibition of
brain histamine release mediated by
a novel class H3 of
histamine receptor. Nature 1983, 302, 832-837.
(12) Poli, E.; Stark, H.; Bertaccini, G. Histamine H3 receptor activa-
tion inhibits acetylcholine release from the guinea pig myenteric
plexus. Agents Actions 1991, 33, 167-169.
(13) Giorgetti, M.; Bacciottini, L.; Bianchi, L.; Giovannini, M. G.;
Cecchi, M.; Blandina, P. GABAergic mechanism in histamine
H3 receptor inhibition of K+ evoked release of acetylcholine from
rat cortex in vivo. Inflammation Res. 1997, 46, S33-34.
(14) Oishi, R.; Nishibori, M.; Itoh, Y.; Shishido, S.; Saeki, K. Is
monoamine turnover in the brain regulated by histamine H3
receptors? Eur. J. Pharmacol. 1990, 184, 135-142.
(15) Fink, K.; Schlicker, E.; Gothert, M. N-methyl-D-aspartate
(NMDA)-stimulated noradrenaline (NA) release in rat brain
cortex is modulated by presynaptic H3 receptors. Naunyn
Schmiedeberg’s Arch. Pharmacol. 1994, 349, 113-117.
(16) Monti, J. M.; Jantos, H.; Ponzoni, A.; Monti, D. Sleep and waking
during acute histamine H3 agonist BP 294 or H3 antagonist
carboperamide (MR 16155) administration in rats. Neuropsy-
chopharmacology 1996, 15, 31-35.
(34) Shih, N. Y.; Green, M. J. Imidazolealkyl substituted with a six
membered nitrogen containing heterocyclic ring. U.S. Patent
5,932,596, 1993.
(35) Trzeciakowski, J. P. Inhibition of guinea pig ileum contractions
mediated by a class of histamine receptor resembling the H3
subtype. J. Pharmacol. Exp. Ther. 1987, 243, 874-880.
(36) Leurs, R.; Brozius, M. M.; Smit, M. J.; Bast, A.; Timmerman,
H. Effects of histamine H1-, H2- and H3-receptor selective drugs
on the mechanical activity of guinea-pig small and large
intestine. Br. J. Pharmacol. 1991, 102, 179-185.
(37) Bertaccini, G.; Morini, G.; Coruzzi, G.; Schunack, W. Histamine
H3 receptors in the guinea pig ileum: evidence for a postjunc-
tional location. J. Physiol. (Paris) 2000, 94, 1-4.
(38) Esbenshade, T. A.; Krueger, K. M.; Miller, T. R.; Kang, C. H.;
Denny, L. I.; Witte, D. G.; Yao, B. B.; Fox, G. B.; Faghih, R.;
Bennani, Y. L.; Williams, M.; Hancock, A. A. Two novel and
selective nonimidazole histamine H3 receptor antagonists
A-304121 and A-317920: I. In vitro pharmacological effects. J.
Pharmacol. Exp. Ther. 2003, 305, 887-896.
(39) Harusawa, S.; Koyabu, S.; Inoue, Y.; Sakamoto, Y.; Araki, L.; et
al. An efficient and convenient synthesis of 4-vinylimidazoles
using a novel Horner-Wadsworth-Emmons (HWE) reagent:
synthesis studies toward novel histamine H3 ligands. Synthesis
2002, 2002, 1072-1078.
(17) Nakamura, T.; Itadani, H.; Hidaka, Y.; Ohta, M.; Tanaka, K.
Molecular cloning and characterization of a new human hista-
mine receptor, HH4R. Biochem. Biophys. Res. Commun. 2000,
279, 615-620.
(18) Coge, F.; Guenin, S. P.; Rique, H.; Boutin, J. A.; Galizzi, J. P.
Structure and expression of the human histamine H4 receptor
gene. Biochem. Biophys. Res. Commun. 2001, 284, 301-309.
(19) Liu, C.; Ma, X.; Jiang, X.; Wilson, S. J.; Hofstra, C. L. Blevitt,
J.; Pyati, J.; Li, X.; Chai, W.; Carruthers, N.; Lovenberg, T. W.
Cloning and pharmacological characterization of a fourth his-
tamine receptor H4 expressed in bone marrow. Mol. Pharmacol.
2001, 59, 420-426.
(20) Zhu, Y.; Michalovich, D.; Wu, H.; Tan, K. B.; Dytko, G. M.,
Mannan, I. J.; Boyce, R.; Alston, J.; Tierney, L. A.; Li, X.; Herrity,
N. C.; Vawter, L.; Sarau, H. M.; Ames, R. S.; Davenport, C. M.;
Hieble, J. P.; Wilson, S.; Bergsma, D. J.; Fitzgerald, L. R.
Cloning, expression, and pharmacological characterization of a
novel human histamine receptor. Mol. Pharmacol. 2001, 59,
434-441.
(21) Morse, K. L.; Behan, J.; Laz, T. M.; West, R. E., Jr.; Greenfeder,
S. A.; Anthes, J. C.; Umland, S.; Wan, Y.; Hipkin, R. W.;
Gonsiorek, W.; Shin, N.; Gustafson, E. L.; Qiao, X.; Wang, S.;
Hedrick, J. A.; Greene, J.; Bayne, M.; Monsma, F. J., Jr. Cloning
and characterization of a novel human histamine receptor. J.
Pharmacol. Exp. Ther. 2001, 296, 1058-1066.
JM049475H