Novel nonimidazole histamine H3 receptor antagonists: 1-(4-(phenoxymethyl)benzyl)piperidines and related compounds

Article abstract of DOI:10.1021/jm021084k

In an extension of very recently published studies on successful imidazole replacements in some series of histamine H₃ receptor antagonists, we report on a new class of lipophilic nonimidazole antagonist having an aliphatic tertiary amino moiet

Full text of DOI:10.1021/jm021084k

J . Med. Chem. 2003, 46, 1523-1530
1523
Novel Non im id a zole Hista m in e H3 Recep tor An ta gon ists:
1-(4-(P h en oxym eth yl)ben zyl)p ip er id in es a n d Rela ted Com p ou n d s
Tibor Miko´,§ Xavier Ligneau,| Heinz H. Pertz,§ C. Robin Ganellin, J ean-Michel Arrang,†
J ean-Charles Schwartz,| Walter Schunack,§ and Holger Stark*,‡
Institut fu¨r Pharmazie, Freie Universita¨t Berlin, Ko¨nigin-Luise-Strasse 2+4, 14195 Berlin, Germany, Bioprojet Biotech,
4 rue du Chesnay Beauregard BP 96205, 35762 Saint Gre´goire Cedex, France, Department of Chemistry, Christopher Ingold
Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ , U.K.; Unite´ de Neurobiologie et Pharmacologie
Mole´culaire, Centre Paul Broca de l’INSERM, 2ter rue d’Ale´sia, 75014 Paris, France, and Institut fu¨r Pharmazeutische
Chemie, J ohann Wolfgang Goethe-Universita¨t, Biozentrum, Marie-Curie-Strasse 9, 60439 Frankfurt am Main, Germany
Received October 30, 2002
In an extension of very recently published studies on successful imidazole replacements in
some series of histamine H3 receptor antagonists, we report on a new class of lipophilic
nonimidazole antagonist having an aliphatic tertiary amino moiety connected to a benzyl
template substituted in the 4-position by a phenoxymethyl group. The structural modifications
were performed with the intention to avoid possible negative side effects reported for other
series of antagonists. The novel compounds combine different characteristics of recently
developed histamine H3 receptor antagonists. The compounds were screened for their affinity
in a binding assay for the human histamine H3 receptor stably expressed in CHO-K1 cells
and tested for their in vivo potency in the central nervous system of mice after oral
administration. Different substitution patterns on the phenoxy group were used to optimize
in vitro and/or in vivo potency leading to some compounds with low nanomolar affinity and
high oral in vivo potency. Modifications of the basic piperidino moiety were performed by ring
expansion, contraction, and opening. Selected compounds exhibited selectivity in functional
assays on isolated organs of guinea-pig for H3 vs H1 and H2 receptors. Unexpectedly, some of
the novel antagonists also showed a slight preference for the human histamine H3 receptor
compared to their affinities for the guinea-pig H3 receptor.
In tr od u ction
Histamine H3 receptors were first identified by Ar-
rang et al. as autoreceptors on histaminergic neurons
in rat brain cortex.1 While histamine acts as a neu-
rotransmitter at postsynaptic H1 and H2 receptors,
activation of the presynaptically localized histamine H3
receptor exerts a negative feedback on histamine syn-
thesis and release in histaminergic neurons.2,3 In ad-
dition, H3 receptors were found to be presynaptic
heteroreceptors modulating the release of other neuro-
transmitters.4-7 The physiological role of the recently
cloned H4 receptor is currently under investigation in
different laboratories.8,9 Due to the important role of the
H3 receptor in (patho)physiological conditions, antago-
nists are proposed to have a therapeutic use in neuro-
logical disorders and psychiatric diseases such as schizo-
F igu r e 1.
phrenia, attention-deficit hyperactivity disorder (ADHD),
dementia, epilepsy, obesity, and narcolepsy.10 To sup-
in rodents as well as in man has opened a new chapter
port this suggestion GT-2331 (cipralisant, formerly
Perceptin) has been described as entering phase II in
clinical trials for the treatment of ADHD.11,12
The recent cloning of rodent and especially human
H3 receptors and the identification of different isoforms
in the understanding of the role of the third histamine
receptor subtype.13-18 There are also new insights in
receptor-ligand interactions.19,20 For the last years
several attempts to replace the imidazole moiety com-
mon to most classes in this field have been carried
out.21-24 We reported the successful discovery of UCL
1972 (Ki (rat) ) 39 ( 11 nM; ED50 (mouse) ) 1.1 ( 0.6
mg/kg po; Figure 1) as a novel prototype for nonimida-
zole histamine H3 receptor antagonists with relatively
high in vivo activity.25 These results inspired our
investigations to replace imidazole by a piperidino group
in different classes of known H3 receptor antagonists26
* To whom correspondence should be addressed. Tel.: +49-69-798
29302. Fax.: +49-69-798 29258. E-mail: h.stark@pharmchem.uni-
frankfurt.de.
§ Freie Universita¨t Berlin.
| Bioprojet Biotech.
University College London.
† Centre Paul Broca de l’INSERM.
‡ J ohann Wolfgang Goethe-Universita¨t Frankfurt am Main.
10.1021/jm021084k CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/07/2003

1524 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8
Miko´ et al.
Sch em e 1. General Procedure for Mitsunobu Type
to reveal general patterns for their pharmacological
behavior and to avoid possible therapeutic drawbacks
such as poor absorption, poor penetration through the
blood-brain barrier, interaction with CYP 450 isoen-
zymes, and/or hepatic toxicity, although these param-
eters are beyond the scope of this paper. Compared to
the related imidazole-containing H3 receptor antago-
nists, almost all of these novel nonimidazole compounds
have an aminoalkyl moiety in common but with differ-
ent chain length and chain structures. The development
of UCL 2190 is one example of this replacement
strategy, ciproxifan27 being lead structure (Figure 1).26
Recently another scaffold was synthesized containing
a 4-((1H-imidazol-4-yl)methy)benzyl template (com-
pounds A, B; Figure 1).28 These imidazole-containing
analogues with different functionalities (from Schering
Plough) show strong similarities to our own 3-(1H-
imidazol-4-yl)propyl series. The trimethylene chain was
exchanged with a p-xylene-R,R′-diyl moiety. Urea de-
rivative compound A can be compared to FUB 172,29
and the benzyl ether compound B can be compared to
the proxyfan series, iodoproxyfan being the most promi-
nent reference compound.30 Since iodoproxyfan shows
partial agonist properties, we followed the replacement
strategy in the proxifan series: a phenoxy moiety in-
stead of a benzyloxy moiety. Supported by the promising
results of UCL 2190, this series seemed more encourag-
ing than other leads. Here we report on the development
of a novel class of nonimidazole histamine H3 receptor
antagonists based on a 4-(phenoxymethyl)benzylamine
template. As in the related imidazole-containing series
where optimized substitution patterns were described
to be different to that found in the proxifan series, we
investigated numerous substituents and substitution
patterns on the phenoxy group. In addition, some
changes were performed on the alkyl groups at their
amino functionality. Displacement experiments were
performed with all compounds at human histamine H3
receptors stably expressed in CHO-K1 cells.19,31 In vivo
screening was performed after oral administration to
mice, measuring the level of the main histamine me-
tabolite, Nτ-methylhistamine, in the cerebral cortex.32
Results from this in vivo screening reflect numerous
pharmacodynamic and pharmacokinetic parameters
leading to a general rating of compounds. The failure
of in vivo potency can have different reasons which were
not investigated. The most interesting compounds were
also tested in functional models on isolated organs of
Phenyl Ethersa
a
(a) (i) Piperidine, Ti[OCH(CH3)2]4, NaBH3CN, MeOH, (ii)
NaBH4, AlCl3, diglyme; (b) Ph3P, DEAD, THF.
Sch em e 2. General Procedure for Compounds with
Different Amine Moietiesa
a
(a) 4-Hydroxyacetophenone, K2CO3, acetone; (b) K2CO3, cor-
responding secondary amine, EtOH.
increased reducing power, which is as potent as lithium
aluminum hydride, but relatively nonhazardous. Ether
formation with the corresponding commercially avail-
able phenol derivatives was then performed using a
Mitsunobu-type procedure.37 Although this reaction
provides a convenient way for variations in the substi-
tution pattern on the phenoxy group and for purification
of the products due to small amounts of side products,
different methods for preparation were performed. For
amine variations, compounds 28 and 36-38 were
prepared by SN2 reaction of p-R,R′-dibromoxylene in
excess with 4-hydroxyacetophenone, resulting in 1-(4-
(4-(bromomethyl)benzyloxy)phenyl)ethanone (Precursor
II) as main product (Scheme 2), and then the final
compounds were obtained by alkylation of the related
amines. Compound 29 was synthesized by SNAR reac-
tion of 4-fluorophenyl-cyclopropylmethanone with 1,4-
benzenedimethanol to the intermediate cyclopropyl-(4-
(4-(hydroxymethyl)benzyloxy)phenyl)methanone. Con-
33
guinea-pig for H3 and/or for H1 and H2 receptor
potencies.34
Ch em istr y
Syn th esis. The key intermediate for the preparation
of different ethers was 4-(piperidinomethyl)benzyl al-
cohol, which was prepared in two steps from 4-formyl-
benzoic acid methyl ester. First reductive amination was
carried out with piperidine and titanium(IV) isopro-
poxide as Lewis acid catalyst,35 a method that provides
a mild and effective way to alkylate amines with
aldehydes. The remaining ester group of the resulting
4-(piperidinomethyl)benzoic acid methyl ester was re-
duced to the corresponding benzyl alcohol (Precursor I,
Scheme 1) with NaBH4 in diglyme in the presence of
aluminum chloride.36 The combination of a borohydride
with aluminum chloride results in a system with

Nonimidazole Histamine H3 Receptor Antagonists
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8 1525
Ta ble 1. Structures, Chemical Data, and Pharmacological Results of Substituted 1-(4-(Phenoxymethyl)benzyl)piperidines for in Vitro
Affinity at Human Histamine H3 Receptor and Oral Antagonist Potency in Vivo in Mice
b
yield
(%)
mp
(°C)
Kia
(nM)
ED50
no.
R1
R2
formula
Mr
(mg/kg) xj ( sxj
1
2
3
4
5
6
7
8
H
F
Cl
Cl
Cl
Cl
Br
I
H
H
H
F
Cl
CH3
H
H
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
19H23NO ‚ C2H2O4‚0.25H2O
19H22FNO ‚C2H2O4
375.6
389.2
405.6
423.6
31
20
60
55
52
27
42
10
43
19
41
51
20
26
16
13
46
44
43
32
26
29
50
40
47
49
35
19
9
135
143
165
150
121
113
178
176-177
162-164
139
147-148
147
227
123
124
95
167
42
114
107
126
125
149
334
163
257
87
≈30
≈15
19H22ClNO‚C2H2O4
>10
19H21ClFNO‚C2H2O4
19H21Cl2NO‚C2H2O4‚0.25H2O 444.6
>10
>10
20H24ClNO‚C2H2O4
19H22BrNO‚C2H2O4
19H22INO‚C2H2O4‚0.25H2O
20H25NO‚C2H2O4
419.6
450.0
501.6
385.2
443.6
399.2
385.2
399.2
413.2
411.2
413.2
436.2
425.2
450.2
439.2
474.7
475.2
473.2
400.1
419.7
467.7
481.7
413.2
439.2
467.2
342.7
442.2
536.2
558.2
563.2
>10
>10
>10
9
CH3
CF3
CH3
H
C2H5
C3H7
-CH2CH2CH2-
CH(CH3)2
C4H9
-CH2CH2CH2CH2-
C5H11
cyclopentyl
CH2C6H5
CH2CH2C6H5
CHdCHC6H5
OCH3
OC3H7
OC6H5
1.8 ( 0.4
>10
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
H
20H22F3NO‚C2H2O4‚0.25H2O
21H27NO‚C2H2O4
CH3
CH3
H
4.8 ( 0.8
≈20
20H25NO‚C2H2O4
21H27NO‚C2H2O4
136
2.2 ( 0.5
4.3 ( 0.9
1.9 ( 0.4
3.0 ( 1.0
2.8 ( 1.2
3.5 ( 1.5
3.0 ( 1.1
3.1 ( 0.6
>10
H
22H29NO‚C2H2O4
142-143
154-155
136-137
131
165-167
125
C22H27NO‚C2H2O4
C
C
H
H
22H29NO‚C2H2O4
23H31NO‚C2H2O4‚0.5H2O
253
169
92
C23H29NO‚C2H2O4
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
24H33NO‚C2H2O4‚0.5H2O
24H31NO‚C2H2O4
1130
159
201
238
890
761
119
88
530
550
84
66
157
55
129
27
2.8
26H29NO‚C2H2O4‚0.75H2O
27H31NO‚C2H2O4
116-117
170-171
190
145
145
≈30
27H29NO‚C2H2O4
20H24NO2‚C2H2O4
>10
≈20
22H29NO2‚C2H2O4‚0.25H2O
25H27NO2‚C2H2O4‚0.25H2O
26H29NO2‚C2H2O4‚0.25H2O
21H25NO2‚C2H2O4
≈10
151
>10
OCH2C6H5
C(dO)CH3
159-160
136-137
194
144-145
156-157
158
155-156
198-199
136
>30
3.9 ( 1.9
5.9 ( 1.2
2.8 ( 0.9
≈5
C(dO)-cyclopropyl
C(dO)-cyclopentyl
C(dNOH)-CH3
C(dNOCH3)-CH3
imidazol-1-yl
piperidinomethyl
(phenylamino)methyl
23H27NO2‚C2H2O4
25H31NO2‚C2H2O4
21H26N2O2‚0.25H2O
22H28N2O2‚C2H2O4
22H25N3O‚2C2H2O4‚0.5H2O
23H34N2O‚2C2H2O4
25H30N2O‚2C2H2O4‚0.5H2O
40
95
89
37
20
19
6.4 ( 0.6
4.0 ( 1.3
9.6 ( 4.5
≈10
90
thioperamide
clobenpropit
ciproxifan
60c
1.0 ( 0.5d
26 ( 7d
0.14 ( 0.03d
0.24 ( 0.06e
2.4c
46c
87c
acetoproxifan
a
[
125I]Iodoproxyfan binding assay with membranes from CHO-K1 cells stably expressing the human H3 receptor (logKi SEM e 0.2).19,31
Central H3 receptor screening in vivo after oral administration to mice ( SEM.32 c Reference 39. Reference 27. e Reference 47.
b
d
version of alcohol into chloride was performed with
by measuring the displacement curves of [125I]iodoproxy-
fan at human histamine H3 receptors stably expressed
in CHO cells.19,31 Influence of the substitution pattern
on the phenoxy group is shown in Table 1, whereas the
influence of the amino-containing moiety is shown in
Table 2. The parent compound 1 showed moderate
nanomolar affinity at the human H3 receptor. Halogen,
small alkyl, or methoxy substitutions in the 4-position
increased affinities, demonstrating that electron-with-
drawing properties (cf. substituents on phenyl group of
compounds in Figure 1) had limited, if any, influence
on receptor binding (2, 3, 7-10, 13, and 24). Effects of
additional substitution in the meta-position to p-
monochloro 3 can be examined with 4-6. Additional
chlorination (5) decreased affinity, whereas fluorination
(4) and methylation (6) gave an increase. Comparing
the mono- and dimethylated derivatives 9, 11, and 12
showed a beneficial effect of substitution in the para-
position. A tendency for decreased affinities is seen in
the series of para-alkylated compounds roughly in order
of increasing steric bulk (9 f 13 ≈ 17 f 20 f 14 ≈
thionyl chloride followed by piperidine alkylation. Cy-
clopentyl-(4-hydroxyphenyl)methanone, as an interme-
diate for 30, was prepared by Friedel-Crafts-acylation
of phenol with AlCl3 at ambient temperature in ni-
trobenzene. A mixture of ortho- and para-isomers was
separated by column chromatography. The phenol de-
rivative for the synthesis of 22 was obtained by catalytic
hydrogenation of 4-hydroxystilbene according to stan-
dard procedures. Methoxime and oxime derivatives 31
and 32 were achieved by heating compound 28 in
absolute solvent with O-methylhydroxylammonium chlo-
ride or hydroxylammonium chloride under basic condi-
tions, respectively. The phenol precursor for 34 and 35
was obtained by reductive amination of piperidine or
aniline, respectively, with 4-hydroxybenzaldehyde ac-
cording to standard procedures.
P h a r m a cologica l Resu lts a n d Discu ssion
In Vit r o Bin d in g Assa y a t Clon ed H u m a n H3
Recep tor s. The affinity of compounds was determined

1526 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8
Miko´ et al.
Ta ble 2. Structures, Physical Data, and Pharmacological Screening Results of 4-(4-(Acetyl)phenoxymethyl)benzyl Derivatives for in
Vitro Affinity at the Human Histamine H3-Receptor and Oral Antagonist Potency in Vivo in Mice
b
yield
(%)
mp
(°C)
Kia
(nM)
ED50
no.
R
formula
Mr
(mg/kg) xj ( sxj
36
37
38
azepan-1-yl
pyrrolidino
(H5C2)2N-
C
22H27NO2‚HCl‚0.25H2O
378.2
404.0
347.6
34
10
26
198-199
157-158
254-255
37
26
91
4.3 ( 2.2
1.9 ( 1.0
3.4 ( 0.8
C20H23NO2‚C2H2O4‚0.25H2O
C20H25NO2‚HCl
a
[
125I]Iodoproxyfan binding assay with membranes from CHO-K1 cells stably expressing the human H3 receptor (log Ki SEM e 0.2).19,31
Central H3 receptor screening in vivo after oral administration to mice ( SEM.32
b
16 f 19). In contrast to the weak influence of an
additional m-methyl substituent (11) to 9 or that of
chain elongations (13, 14, 17, and 19) of 9, ring forma-
tion to 5-indanyl (15) or 1,2,3,4-tetrahydronaphthyl
moieties (18) clearly enhanced affinities comparable to
that of the dihalogenated derivative 4. An even larger
difference was seen by comparison of compounds 19 and
20, both having pentyl groups. Whereas the n-alkyl
compound 19 showed a dramatic loss in affinity, the
related cycloalkyl compound 20 was active in almost the
same concentration range as the smaller alkyl deriva-
tives 16, 14, and the parent compound 1. Introduction
of phenylalkyl substituents to create even bulkier
moieties (21-23) led to results comparable to those
obtained for the alkyl series. Conversion into dialkylated
p-hydroquinone compounds (24-27) was effective for
alkyl but not for phenylalkyl substituents. Surprisingly,
the propyloxy compound 25 showed higher affinity than
that of the shorter methoxy compound 24. In the series
of compounds containing an acyl moiety (28-30) the
ciproxifan analogue showed low nanomolar affinity at
the human receptor. Conversion of acetoproxifan (FUB
372) into the corresponding oxime (imoproxifan) or
methoxime derivative resulted in a drastic increase in
affinity.38 Unfortunately, the oxime derivatives 31 and
32 did not become more active than the corresponding
acetyl derivative 28. One might speculate that the
differences in structure-activity relationships between
the series described here and the proxifan series are
strong indications for differences in receptor-ligand
interactions and a different mode of binding. Com-
pounds 33-35 containing substituents with basic prop-
erties showed good affinities. Compound 34, as the most
basic compound, exhibited the highest affinity in this
series, displaying a similar value to that of clobenpro-
pit.39 Compound 34, with two benzylpiperidine struc-
tures, may possess two potential bioisosteric interaction
areas to the imidazole binding site of the H3 receptor
protein and therefore may display higher affinity. In a
second approach we determined the influence of replac-
ing the piperidine ring by similar structures (Table 2).
While an expansion of the ring size to a seven-
membered azepane (36) had almost no influence on
affinity, decreased ring size to a pyrrolidine ring tended
to slightly enhance activity. Keeping the same number
of carbon atoms, but opening the ring to a diethylamino
moiety (38), was not advantageous.
target area and influence the central nervous system
(CNS). All novel compounds were screened for their
modulating effects on Nτ-methylhistamine levels in the
brain cortex of Swiss mice after oral administration
(Tables 1, 2). Parent compound 1 as well as the
halogenated derivatives 2-8 showed weak or lacking
in vivo potency as was also the case for the compounds
of the proxyfan series in this test model. The same was
true for the electron-withdrawing substituted trifluo-
romethyl derivative 10 and the m-methyl-substituted
derivative 12. Aromatic moieties and/or ether structures
(21-27, and 35) led to weak or missing in vivo potency
with the exception of 33. Relatively high antagonist in
vivo potencies below 5 mg/kg were achieved with the
alkylated compounds 9, 11, and 13-20. Although the
differences were not statistically significant, the smaller
alkylated derivatives showed higher in vivo potency
compared to the compounds with longer alkyl chains.
A direct correlation between chain length and in vivo
results was not detectable (results not shown). It might
be concluded that lipophilicity, metabolic stability, and
steric receptor-ligand interaction are three important
parameters among others which have an important
influence on in vivo potency. The calculated partition
coefficient values (LogP)40 varied in a range from 3.21
(37) to 6.51 (23) (xj ) 4.86 ( 0.62) and showed no direct
correlation to in vitro or in vivo potencies (results not
shown). Surprisingly, in vivo the pentyl derivative 19
was as potent as the related cyclopentyl derivative 20
which showed more than 5 times higher binding affinity
than 19. One might argue that these findings are caused
by species differences in the test models, but many other
reasons can also been taken into account. Compounds
28-34 showed moderate to good antagonist in vivo
potencies without having a correlation to their in vitro
affinities. The substituent on the phenoxy group and
its position had marked influence on in vivo potency.
On the other hand, it seems remarkable that all
acylated derivatives, despite the structure of their amino
group (28, 36-38), showed any in vivo potency (Tables
1, 2). This result is somewhat surprising since, for a long
time, the imidazole nucleus seemed to be essential for
H3 receptor affinity, and now we find numerous bioiso-
steric replacements with relative small changes in
affinities and in vivo potencies. To exclude effects on
the main histamine-metabolizing enzyme in brain,
histamine N-methyltransferase [EC 2.1.1.8], which may
interfere with the in vivo data, compound 28 was tested
as the single example, showing relative weak affinity
In Vivo Scr een in g on Sw iss Mice. For drug design
of centrally active drugs, it is essential that these
compounds are distributed after absorption into their

Nonimidazole Histamine H3 Receptor Antagonists
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8 1527
Ta ble 3. Potency of Selected Compounds at Histamine
Receptor Subtypes
constants in hertz, and the number of protons (Az, azepanyl;
Cyp, cyclopropyl; Im, imidazolyl; Ind, indanyl; Pip, piperidino;
Ph, phenyl; Pyr, pyrrolidino; Xyl, para-R,R′-xylenediyl). Mass
spectra were obtained on EI-MS Finnigan MAT CH7A and
Finnigan MAT 711 (high-resolution mass spectra) spectrom-
eters (resolving power 12 500). Elemental analyses (C, H, N)
for all compounds were measured on Perkin-Elmer 240 B or
Perkin-Elmer 240 C instruments and are within (0.4% of the
theoretical values for all compounds. Column chromatography
or flash column chromatography were carried out using silica
gel 62-200 µm or 20-63 µm (Merck), respectively. TLC was
performed on silica gel PF254 plates (Merck), and the spots were
detected by UV spectroscopy (wavelength 254 nm) and visual-
ized with Dragendorff reagent. Abbreviations for solvents are
the following: Et2O, diethyl ether; EtOH, ethanol; EtOAc,
ethyl acetate; MeOH, methanol; PE, petroleum ether (bp 40-
60 °C); TEA, triethylamine; THF, tetrahydrofuran. Only
spectra of prominet intermediate products and the most
interesting compounds are shown (9, 15, 28-29, 31, 33-34,
36, and 37).
H3
pA2
H2
pA2
H1
pA2
a
b
c
no.
28
30
31
32
33
34
36
37
7.21
7.51
7.07
6.54
7.80
7.42
7.51
7.74
4.99
5.34
4.85
5.40
5.10
5.46
5.11
5.03
a
Functional H3 receptor assay on guinea-pig ileum (SEM e
0.2).33 Functional H2 receptor test on guinea-pig atrium
(SEM e 0.2).34 c Functional H1 receptor test on guinea-pig ileum
(SEM e 0.2).34
b
on rat enzyme (IC50 value of 10.4 ( 1.3 µM) (for test
assay and discussion, see ref 41).
4-(P ip er id in om eth yl)ben zoic Acid Meth yl Ester . A
mixture of 4-formylbenzoic acid methyl ester (3.2 g, 20 mmol),
piperidine (1.7 g, 20 mmol), and titanium(IV) isopropoxide (7.4
mL, 25 mmol) in 20 mL of MeOH was stirred at room
temperature. After 3 h, sodium cyanoborohydride (0.84 g, 13.4
mmol) was added, and the solution was stirred overnight.
Water was added, and the resulting inorganic precipitate was
filtered and washed with EtOH. The filtrate was then con-
centrated in vacuo, and the residue was purified by flash
column chromatography (eluent: EtOAc/hexane, 1:1, saturated
with ammonia) to give a colorless oil. Yield 65%; 1H NMR
(CDCl3) δ 7.97 (d, J ) 8.0 Hz, 2H, Ph-2-H, Ph-6-H), 7.39 (d,
J ) 8.0 Hz, 2H, Ph-3-H, Ph-5-H), 3.90 (s, 3H, CH3), 3.50 (s,
2H, CH2N), 2.33-2.39 (m, 4H, Pip-2-H, Pip-6-H), 1.50-1.61
(m, 4H, Pip-3-H, Pip-5-H), 1.38-1.45 (m, 2H, Pip-4-H); MS
m/z 233 ([M•+], 64), 202 (9), 149 (62), 121 (15), 98 (100), 84
(97), 42 (21). Anal. (C14H19NO2).
Scr een in g of Select ed Com p ou n d s a t Ot h er
F u n ction a l Hista m in e Su br ecep tor Mod els. Se-
lected compounds have been evaluated for their activity
in a functional model for the histamine H3 receptor on
the guinea-pig ileum (Table 3).33 Activity of compounds
1, 9, 11, 14, 15, 21, 22, and 26 was not exactly deter-
mined due to high muscarinic M3 receptor antagonist
activity in this test model42 but were calculated to have
pA2 values e6.8. The results on guinea-pig ileum mostly
showed slightly lower values than the binding affinities
at human H3 receptors, which is in accordance with
previously reported results. Only imidazolyl compound
33 showed slightly higher potency in the guinea-pig
assay than in the human test model. The number of
results is much too low to draw any conclusions on
species specificity.
4-(P ip er id in om et h yl)p h en ylm et h a n ol (P r ecu r sor I).
4-(Piperidinomethyl)benzoic acid methyl ester (3 g, 15 mmol)
was dissolved in 50 mL of diglyme together with sodium
borohydride (0.95 g, 15 mmol). A freshly prepared solution of
aluminum chloride in diglyme was then slowly added drop-
wise. Then the solution was heated under reflux for 24 h. The
solution was poured into ice and filtered. The filtrate was then
concentrated in vacuo to give a colorless oil, which was
additionally purified by flash column chromatography (elu-
ent: EtOAc/hexane:1/1, saturated with ammonia). Yield 82%;
1H NMR (CF3COOD) δ 7.58 (d, J ) 8.2 Hz, 2H, Ph-2-H, Ph-
6-H), 7.48 (d, J ) 8.2 Hz, 2H, Ph-3-H, Ph-5-H), 6.54-6.84 (m,
1H, Pip-N+), 4.92 (s, 2H, CH2O), 4.38 (d, J ) 9.3 Hz, 2H,
CH2N), 3.67 (d, J ) 11.5 Hz, 2H, Pip-2-Heq, Pip-6-Heq), 3.05
(s, 2H, Pip-2-Hax, Pip-6-Hax), 2.80 (d, J ) 14.9 Hz, 2H, Pip-3-
Furthermore, compounds 28, 31, 32, and 37 have
been tested for their antagonist activity at H1 and H2
receptors in functional tests on isolated organs of
guinea-pig (Table 3).34 Results indicate moderate to good
preference of the H3 vs H1 and H2 receptors.
Con clu sion s
We have successfully replaced the imidazole ring of
compounds of the 4-((1H-imidazol-4-yl)methy)benzyl
series by a piperidino group or related secondary amino
groups. The compounds represent a new class of non-
imidazole histamine H3 receptor antagonists, some of
which display low nanomolar affinities at the human
H3 receptor and high antagonist in vivo potencies in the
CNS of mice after oral application. Structure-activity
relationships are similar but somewhat different to
those obtained in the previously reported series of
imidazole-containing H3 receptor antagonists. Species
differences have to be taken into account with the
pharmacological data. The compounds tested showed
moderate to good selectivity for the H3 receptor vs H1
and H2 receptors.
H
eq, Pip-5-Heq), 1.99 (d, J ) 13.8 Hz, 1H, Pip-4-Heq), 1.82-
1.91 (m, 2H, Pip-3-Hax, Pip-5-Hax), 1.54-1.64 (m, 1H, Pip-4-
Hax); MS m/z 205 ([M•+], 27), 188 (26), 121 (100), 98 (77), 84
(64), 42 (15). Anal. (C13H19NO).
Gen er a l Syn th etic P r oced u r e for Mitsu n obu -Typ e
Eth er F or m a tion (1-27, 30, a n d 33-35). Triphenylphos-
phine (0.65 g, 2.5 mmol) was dissolved with 4-(piperidinometh-
yl)phenylmethanol (0.51 g, 2.5 mmol) and the corresponding
phenol (2.5 mmol) in 15 mL of dry THF under argon atmo-
sphere. After the mixture was cooled for 5 min in an ice bath,
diethyl azodicarboxylate (DEAD, 0.48 mL, 2.6 mmol) was
slowly added, and the solution was stirred for 72 h at room
temperature. The solvent was removed under reduced pressure
and the product purified via flash column chromatography
(eluent: EtOAc/hexane, 1:1, saturated with ammonia). The oil
obtained was dried in vacuo and then crystallized as hydrogen
oxalate in EtOH/Et2O.
Exp er im en ta l Section
Ch em istr y. Gen er a l P r oced u r es. Melting points were
determined on an Electrothermal Bu¨chi 512 or 545 apparatus
and are uncorrected. For all compounds, 1H NMR spectra were
recorded on a Bruker DPX 400 (400 MHz) spectrometer.
Chemical shifts are expressed in parts per million downfield
from internal standard Me4Si as a reference. 1H NMR data
are reported in the following order: multiplicity (s, singlet; d,
doublet; t, triplet; and m, multiplet), approximate coupling
1-(4-(4-Meth ylp h en oxym eth yl)ben zyl)p ip er id in e (9).
1H NMR (CF3COOD) δ 7.64 (d, J ) 7.9 Hz, 2H, Xyl-2-H, Xyl-
6-H), 7.49 (d, J ) 7.9 Hz, 2H, Xyl-3-H, Xyl-5-H), 7.17 (d, J )
8.3 Hz, 2H, Ph-3-H, Ph-5-H), 6.99 (d, J ) 8.3 Hz, 2H, Ph-2-H,
Ph-6-H), 6.77-6.81 (m, 1H, Pip-N+), 5.29 (s, 2H, CH2O), 4.37

1528 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8
(d, J ) 5.3 Hz, 2H, CH2N), 3.67 (d, J ) 11.9 Hz, 2H, Pip-2-
Miko´ et al.
Hz, 2H, Pip-2-Heq, Pip-6-Heq), 3.00-3.08 (m, 2H, Pip-2-Hax, Pip-
6-Hax), 2.77 (s, 3H, CO-CH3), 2.09 (d, J ) 14.9 Hz, 2H, Pip-
3-Heq, Pip-5-Heq), 1.99 (d, J ) 13.5 Hz, 1H, Pip-4-Heq), 1.82-
1.92 (m, 2H, Pip-3-Hax, Pip-5-Hax), 1.55-1.64 (m, 1H, Pip-4-
H
eq, Pip-6-Heq), 3.00-3.08 (m, 2H, Pip-2-Hax, Pip-6-Hax), 2.32
(s, 3H, CH3), 2.09 (d, J ) 14.9 Hz, 2H, Pip-3-Heq, Pip-5-Heq),
1.99 (d, J ) 13.8 Hz, 1H, Pip-4-Heq), 1.82-1.92 (m, 2H, Pip-
3-Hax, Pip-5-Hax), 1.55-1.64 (m, 1H, Pip-4-Hax); MS m/z 295
([M•+], 23), 188 (100), 104 (27), 98 (7), 84 (11), 45 (16). Anal.
C, H, N.
1-(4-(In d a n -5-yloxym eth yl)ben zyl)p ip er id in e (15). 1H
NMR (DMSO-d6) δ 7.48 (s, 4H, Xyl-2-H, Xyl-3-H, Xyl-5-H, Xyl-
6-H), 7.10 (d, J ) 8.2 Hz, 1H, Ind-6-H), 6.88 (s, 1H, Ind-2-H),
6.75 (dd, J 1 ) 2.3 Hz, J 2 ) 5.8 Hz, 1H, Ind-7-H), 5.07 (s, 2H,
CH2O), 4.13 (s, 2H, CH2N), 2.90-3.05 (m, 4H, Ind-3-H, Ind-
5-H), 2.74-2.82 (m, 4H, Pip-2-H, Pip-6-H), 1.95-2.03 (m, 2H,
Ind-4-H), 1.64-1.72 (m, 4H, Pip-3-H, Pip-5-H), 1.45-1.54 (m,
2H, Pip-4-H); MS m/z 321 ([M•+], 25), 188 (100), 104 (17), 98
(3), 84 (6), 45 (7). Anal. C, H, N.
H
ax); MS m/z 323 ([M•+], 24), 188 (100), 153 (13), 104 (33), 98
(17), 84 (24), 45 (10). Anal. C, H, N.
1-(4-(4-(Azep a n e-1-ylm et h yl)b en zyloxy)p h en yl)et h a -
n on e (36). 1H NMR (CF3COOD) δ 8.12 (d, J ) 8.9 Hz, 2H,
Ph-2-H, Ph-6-H), 7.64 (d, J ) 8.1 Hz, 2H, Xyl-2-H, Xyl-6-H),
7.52 (d, J ) 8.1 Hz, 2H, Xyl-3-H, Xyl-5-H), 7.16 (d, J ) 8.9
Hz, 2H, Ph-3-H, Ph-5-H), 6.99-7.11 (m, 1H, Az-N+), 5.32 (s,
2H, CH2O), 4.44 (d, J ) 5.6 Hz, 2H, CH2N), 3.67-3.72 (m, 2H,
Az-2-Heq, Az-7-Heq), 3.26-3.34 (m, 2H, Az-2-Hax, Az-7-Hax), 2.76
(s, 3H, CO-CH3), 2.06-2.11 (m, 2H, Az-3-Heq, Az-6-Heq), 1.95-
2.01 (m, 2H, Az-3-Hax, Az-6-Hax), 1.80-1.92 (m, 4H, Az-4-H,
Az-5-H); MS m/z 337 ([M•+], 35), 239 (7), 202 (100), 104 (67),
98 (62), 42 (36). Anal. C, H, N.
1-(4-(4-(P ip er id in om eth yl)ben zyloxy)p h en yl)-1H-im id -
1
a zole (33). H NMR (CF3COOD) δ 8.84 (s, 1H, Im-2-H), 7.68
1-(4-(4-(P yr r olid in om et h yl)b en zyloxy)p h en yl)et h a -
n on e (37). 1H NMR (CF3COOD) δ 8.12 (d, J ) 8.8 Hz, 2H,
Ph-2-H, Ph-6-H), 7.65-7.8 (m, 1H, Pyr-N+), 7.64 (d, J ) 7.9
Hz, 2H, Xyl-2-H, Xyl-6-H), 7.52 (d, J ) 7.9 Hz, 2H, Xyl-3-H,
Xyl-5-H), 7.16 (d, J ) 8.8 Hz, 2H, Ph-3-H, Ph-5-H), 5.32 (s,
2H, CH2O), 4.46 (d, J ) 5.9 Hz, 2H, CH2N), 3.74-3.79 (m, 2H,
Pyr-2-Heq, Pyr-5-Heq), 3.26-3.35 (m, 2H, Pyr-2-Hax, Pyr-5-Hax),
2.77 (s, 3H, CO-CH3), 2.27-2.36 (m, 2H, Pyr-3-Heq, Pyr-4-
Heq), 2.19-2.25 (m, 2H, Pyr-3-Hax, Pyr-4-Hax); MS m/z 309
([M•+], 13), 174 (100), 104 (31), 84 (14), 70 (14), 45 (12). Anal.
C, H, N.
(s, 1H, Im-5-H), 7.63-7.66 (m, 3H, Xyl-2-H, Xyl-6-H, Im-4-
H), 7.51-7.54 (m, 4H, Xyl-3-H, Xyl-5-H, Ph-3-H, Ph-5-H), 7.29
(d, J ) 8.7 Hz, 2H, Ph-2-H, Ph-6-H), 6.77-6.81 (m, 1H, Pip-
N+), 5.31 (s, 2H, CH2O), 4.38 (d, J ) 4.6 Hz, 2H, CH2N), 3.71
(d, J ) 12.0 Hz, 2H, Pip-2-Heq, Pip-6-Heq), 3.02-3.10 (m, 2H,
Pip-2-Hax, Pip-6-Hax), 2.09 (d, J ) 14.8 Hz, 2H, Pip-3-Heq, Pip-
5-Heq), 2.02 (d, J ) 13.8 Hz, 1H, Pip-4-Heq), 1.83-1.93 (m, 2H,
Pip-3-Hax, Pip-5-Hax), 1.59-1.65 (m, 1H, Pip-4-Hax); MS m/z
347 ([M•+], 9), 264 (57), 188 (100), 160 (32), 104 (46), 84 (22).
Anal. C, H, N.
1-(4-(4-(P ip er id in om eth yl)p h en oxym eth yl)ben zyl)p i-
p er id in e (34). 1H NMR (CF3COOD) δ 7.63 (d, J ) 8.0 Hz,
2H, Xyl-2-H, Xyl-6-H), 7.50 (d, J ) 8.0 Hz, 2H, Xyl-3-H, Xyl-
5-H), 7.41 (d, J ) 8.6 Hz, 2H, Ph-3-H, Ph-5-H), 7.17 (d, J )
8.6 Hz, 2H, Ph-2-H, Ph-6H), 6.69-6.80 (m, 2H, Pip-N+), 5.28
(s, 2H, CH2O), 4.38 (d, J ) 5.4 Hz, 2H, CH2N), 4.31 (d, J ) 5.3
Hz, 2H, Ph-CH2N), 3.60-3.75 (m, 4H, Pip-2-Heq, Pip-6-Heq),
2.97-3.09 (m, 4H, Pip-2-Hax, Pip-6-Hax), 2.09 (d, J ) 14.7 Hz,
4H, Pip-3-Heq, Pip-5-Heq), 1.99 (d, J ) 13.8 Hz, 2H, Pip-4-Heq),
1.84-1.94 (m, 4H, Pip-3-Hax, Pip-5-Hax), 1.54-1.64 (m, 2H, Pip-
4-Hax); MS m/z 378 ([M•+], 12), 295 (49),188 (100), 104 (36), 98
(18), 84 (18), 45 (66). Anal. C, H, N.
1-(4-(4-(Br om om eth yl)ben zyloxy)ph en yl)eth an on e (P r e-
cu r sor II). p-R,R′-Dibromoxylene (5.88 g, 20 mmol) was stirred
in 100 mL of acetone together with 4-hydroxyacetophenone
(0.68 g, 5 mmol) and potassium carbonate (0.82 g, 6 mmol)
under reflux for 12 h. The solvent was removed under reduced
pressure and the residue purified by column chromatography
(eluent: CH2Cl2/PE/MeOH, 60:38:2). Yield 71%; mp 105 °C; 1H
NMR (CDCl3): δ 7.91-7.95 (m, 2H, Ph-3-H, Ph-5-H), 7.36-
7.44 (m, 4H, Xyl-2-H, Xyl-3-H, Xyl-5-H, Xyl-6-H), 6.97-7.01
(m, 2H, Ph-2-H, Ph-6-H), 5.12 (s, 2H, CH2O), 4.50 (s, 2H, CH2-
Br), 2.55 (s, 3H, CH3), MS m/z 318 ([M•+], 7), 239 (12), 104
(100), 78 (10), 43 (9). Anal. (C16H15BrO2).
Gen er a l Syn th etic P r oced u r e for Com p ou n d s w ith
Differ en t Am in e Moieties (28, 36-38). 1-(4-(4-(Bromometh-
yl)benzyloxy)phenyl)ethanone (Precursor II, 0.95 g, 3 mmol)
and the corresponding amine (6 mmol) were dissolved in 20
mL of EtOH and heated for 12 h in the presence of potassium
carbonate (1.38 g, 10 mmol). The solvent was evaporated and
the residue dissolved in 30 mL of EtOAc. The organic layer
was washed with water and extracted with 1 N hydrochloric
acid (3 × 15 mL). In the case of compounds 36 and 38 a white
precipitate was formed. This precipitate was collected and
dried to give the hydrochloride salts. In the case of compounds
28 and 37 the aqueous layer was alkalized and extracted with
EtOAc (3 × 20 mL). The solvent was removed and the resulting
crude product crystallized as a salt of oxalic acid from EtOH/
Et2O after purification by column chromatography (eluent:
EtOAc/TEA, 99:1).
Cyclop r op yl-(4-(4-(p ip er id in om eth yl)ben zyloxy)p h en -
yl)m eth a n on e (29). 1,4-Benzenedimethanol (4.14 g, 30 mmol)
in 30 mL of THF was added dropwise to a suspension of
sodium hydride (25 mmol, 60% dispersion in paraffin oil) in
30 mL of THF with a catalytic amount of tetrabutylammonium
iodide and 15-crown-5. After stirring for 15 min, cyclopropyl-
(4-fluorophenyl)methanone (3.28 g, 20 mmol) was added
dropwise, and the solution was refluxed for 2 days. Water was
added carefully and the solvent removed under reduced
pressure. The residue was purified by column chromatography
on silica gel (eluent: CH2Cl2/MeOH, 98:2) resulting in cyclo-
p r op yl-(4-(4-(h yd r oxym eth yl)ben zyloxy)p h en yl)m eth a -
1
n on e. Yield 38%; mp 100 °C; H NMR (DMSO-d6) δ 8.02 (d,
J ) 8.8 Hz, 2H, Ph-3-H, Ph-5-H), 7.41 (d, J ) 7.9 Hz, 2H, Xyl-
3-H, Xyl-5-H), 7.33 (d, J ) 7.9 Hz, 2H, Xyl-2-H, Xyl-6-H), 7.12
(d, J ) 8.8 Hz, 2H, Ph-2-H, Ph-6-H), 5.19 (s, 2H, CH2O), 4.49
(s, 2H, CH2OH), 2.82-2,86 (m, 1H, Cyp-1-H), 0.97 (d, J ) 6.1
Hz, 4H, Cyp-2-H, Cyp-3-H); MS m/z 282 ([M•+], 4), 121 (100),
104 (1), 93 (18), 41 (3). Anal. (C18H18O3). The resulting ether
(1.12 g, 4 mmol) was dissolved in 30 mL of dry THF, stirred
at 0 °C, and thionyl chloride (0.95 g, 8 mmol) was added
dropwise. After 1 h at ambient temperature, the mixture was
warmed to 60 °C for 2 h. The solvent and the excess of thionyl
chloride were evaporated, and the residue was purified by
column chromatography on silica gel (eluent: CH2Cl2/MeOH,
95:5) resulting in cyclop r op yl-(4-(4-(ch lor m eth yl)ben zyl-
oxy)p h en yl)m eth a n on e. Yield 96%; mp 111-112 °C; 1H
NMR (DMSO-d6) δ 8.03 (d, J ) 9.3 Hz, 2H, Ph-3-H, Ph-5-H),
7.4 (d, J ) 7.9 Hz, 2H, Xyl-3-H, Xyl-5-H), 7.34 (d, J ) 7.9 Hz,
2H, Xyl-2-H, Xyl-6-H), 7.13 (d, J ) 9.3 Hz, 2H, Ph-2-H, Ph-
6-H), 5.21 (s, 2H, CH2O), 4.49 (s, 2H, CH2-Cl), 2.82-2.87 (m,
1H, Cyp-1-H), 0.97 (d, J ) 6.1 Hz, 4H, Cyp-2-H, Cyp-3-H); MS
m/z 300 ([M•+], 7), 265 (2), 139 (100), 104 (27), 77 (9), 41 (4).
Anal. (C18H17ClO2). The product (0.6 g, 2 mmol) was dissolved
in 40 mL of EtOH and heated with piperidine (0.34 g, 4 mmol)
and potassium carbonate (0.82 g, 6 mmol) for 12 h under
reflux. The solvent was removed and EtOAc (50 mL) added
and washed with 0.5 N sodium carbonate solution (15 mL).
The organic layer was extracted with 0.5 N hydrochloric acid
(3 × 15 mL). The aqueous layer was alkalized and extracted
with EtOAc. The solvent was removed and the residue crystal-
lized as a salt of oxalic acid from EtOH/Et2O. 1H NMR (DMSO-
d6) δ 8.04 (d, J ) 8.3 Hz, 2H, Ph-3-H, Ph-5-H), 7.52 (d, J )
3.8 Hz, 4H, Xyl-2-H, Xyl-3-H, Xyl-5-H, Xyl-6-H), 7.14 (d, J )
8.3 Hz, 2H, Ph-2-H, Ph-6-H), 5.24 (s, 2H, CH2O), 4.13 (s, 2H,
CH2N), 2.84-2.89 (m, 5H, Pip-2-H, Pip-6-H, Cyp-1-H), 1.67-
1-(4-(4-(P ip e r id in om e t h yl)b e n zyloxy)p h e n yl)e t h a -
n on e (28). 1H NMR (CF3COOD) δ 8.12 (d, J ) 8.7 Hz, 2H,
Ph-2-H, Ph-6-H), 7.64 (d, J ) 7.8 Hz, 2H, Xyl-2-H, Xyl-6-H),
7.49 (d, J ) 7.8 Hz, 2H, Xyl-3-H, Xyl-5-H), 7.16 (d, J ) 8.7
Hz, 2H, Ph-3-H, Ph-5-H), 6.77-6.81 (m, 1H, Pip-N+), 5.32 (s,
2H, CH2O), 4.37 (d, J ) 5.2 Hz, 2H, CH2N), 3.71 (d, J ) 11.9

Nonimidazole Histamine H3 Receptor Antagonists
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8 1529
1.69 (m, 4H, Pip-3-H, Pip-5-H), 1.45-1.49 (m, 2H, Pip-4-H),
0.99 (d, J ) 5.8 Hz, 4H, Cyp-2-H, Cyp-3-H); MS m/z 349 ([M•+],
23), 265 (<1), 188 (100), 153 (8), 104 (43), 98 (15), 84 (20), 69
(10), 42 (7). Anal. C, H, N.
tion period of 1 h with washings every 10 min, the preparations
were stimulated for 30 min with rectangular pulses of 15 V
and 0.5 ms at a frequency of 0.1 Hz. Viability of the muscle
strips was monitored by addition of the H3 receptor agonist
(R)-R-methylhistamine (100 nM), which caused a relaxation
of the twitch response of more than 50 up to 100%. After wash
out, reequilibration, and 30 min field stimulation, a cumulative
concentration-response curve to (R)-R-methylhistamine (1-
1000 nM) was constructed. Subsequently, the preparations
were washed intensively and reequilibrated for 20-30 min in
the absence of the antagonist under study. During the incu-
bation period, the strips were stimulated continuously for 30
min. Finally, a second concentration-response curve to (R)-
R-methylhistamine was obtained.31,33 The rightward displace-
ment of the curve to the H3 receptor agonist evoked by the
antagonist under study was corrected with the mean shift
monitored by daily control preparations in the absence of the
antagonist. All compounds were tested in concentrations not
blocking ileal M3 receptors. The pharmacological tests were
performed at least in triplicate.
1-(4-(4-P ip er id in om eth ylben zyloxy)p h en oxy)eth a n on -
oxim e (31). Compound 28 (0.2 g, 0.5 mmol) was dissolved
together with hydroxylamine hydrochloride (0.7 g, 1 mmol) and
K2CO3 (1.6 g, 1.2 mmol) in 20 mL of absolute EtOH and heated
under reflux until no initial compound was detectable with
TLC. The solvent was removed and the remaining material
purified by flash column chromatography (eluent: EtOAc) to
1
give a white solid. H NMR (CF3COOD) δ 7.81 (d, J ) 7.7 Hz,
2H, Ph-3-H, Ph-5-H), 7.63 (d, J ) 7.5 Hz, 2H, Xyl-2-H, Xyl-
6-H), 7.51 (d, J ) 7.5 Hz, 2H, Xyl-3-H, Xyl-5-H), 7.25 (d, J )
7.7 Hz, 2H, Ph-2-H, Ph-6-H), 6.77-6.81 (m, 1H, Pip-N+), 5.31
(s, 2H, CH2O), 4.38 (s, 2H, CH2N), 3.71 (d, J ) 11.9 Hz, 2H,
Pip-2-Heq, Pip-6-Heq), 3.01-3.09 (m, 2H, Pip-2-Hax, Pip-6-Hax),
2.86 (s, 3H, CNOHCH3), 2.10 (d, J ) 14.7 Hz, 2H, Pip-3-Heq
,
Pip-5-Heq), 1.99 (d, J ) 13.6 Hz, 1H, Pip-4-Heq), 1.83-1.93 (m,
2H, Pip-3-Hax, Pip-5-Hax), 1.55-1.64 (m, 1H, Pip-4-Hax); MS
m/z 338 ([M•+], 10), 321 (37), 188 (100), 104 (25), 98 (6), 84 (7).
Anal. C, H, N.
In Vitr o Scr een in g a t Oth er Hista m in e Recep tor s.
Selected compounds were screened for histamine H2 receptor
activity on the isolated spontaneously beating guinea-pig right
atrium as well as for H1 receptor activity on the isolated
guinea-pig ileum by standard methods described by Hirschfeld
et al.34 Each pharmacological test was performed at least in
triplicate, but the exact type of interaction was not determined
in each case. The given values represent the mean.
P h a r m a cology. Gen er a l Meth od s. Hista m in e H3 Re-
cep tor An ta gon ist Activity In Vivo in Mou se. In vivo
testing was performed after oral administration of the com-
pound to Swiss mice as described by Garbarg et al.32 Brain
histamine turnover was assessed by measuring the level of
the main metabolite of histamine, Nτ-methylhistamine. Mice
were fasted for 24 h before treatment. Animals were decapi-
tated 90 min after treatment, and the cerebral cortex was
isolated. The cortex was homogenized in 10 volumes of ice-
cold perchloric acid (0.4 M). The Nτ-methylhistamine level was
measured by radioimmunoassay.43 By oral treatment with 3
mg/kg of ciproxifan the maximum Nτ-methylhistamine level
was obtained and related to the level reached with the
administered drug, and the ED50 value was calculated as mean
values with SEM.44 The pharmacological tests were performed
at least in triplicate.
Ack n ow led gm en t. This work was supported by the
Fonds der Chemischen Industrie, Verband der Chemis-
chen Industrie, Frankfurt/Main, Germany. We thank
I. Walter for carrying out pharmacological testing for
guinea-pig H1, H2, and H3 values and M. Berg for
synthesizing the first batches of compounds 28 and 37.
Refer en ces
125I]Iod op r oxyfa n Bin d in g Assa y on Sta bly Tr a n s-
(1) 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.
[
fected CHO-K1 Cells. Potency of the novel compounds 7-18
was investigated in a radioligand binding assay described by
Ligneau et al.31 Transfected CHO-K1 cells were washed and
harvested with a PBS medium. They were centrifuged (140 g,
10 min, +4 °C) and then homogenized with a Polytron in the
ice-cold binding buffer (Na2HPO4/KH2PO4, c ) 50 mmol/L,
pH ) 7.5). The homogenate was centrifuged (23 000 × g, 30
min, +4 °C) and the pellet obtained resuspended in the binding
buffer to constitute the membrane preparation used for the
binding assays. Aliquots of the membrane suspension (5-15
µg protein) were incubated for 60 min at 25 °C with [125I]-
iodoproxyfan (c ) 25 pmol/L) alone, or together with competing
drugs dissolved in the same buffer to give a final volume of
200 µL. Incubations were performed in triplicate and stopped
by four additions (5 mL) of ice-cold medium, followed by rapid
filtration through glass microfiber filters (GF/B Whatman,
Clifton, NJ ) presoaked in polyethylene imine (ω ) 0.3%).
Radioactivity trapped on the filters was measured with a LKB
(Rockville, MD) gamma counter (efficiency: 82%). Specific
binding was defined as that inhibited by imetit (c ) 1 µmol/
L), a specific H3 receptor agonist.31 Ki values were determined
according to the Cheng-Prusoff equation.45 Data are presented
as the mean of experiments performed at least in triplicate.
Histam in e H3 Receptor An tagon ist Activity on Gu in ea-
P ig Ileu m .33 Strips of guinea-pig ileal longitudinal muscle
with adhering myenteric plexus, approximately 2 cm in length
and proximal to the ileocaecal junction, were prepared as
described previously.46 The strips were mounted isometrically
under a tension of approximately 7.5 ( 2.0 mN in 20 mL of
organ baths filled with modified Krebs-Henseleit solution of
the following composition (mM): NaCl 117.9, KCl 5.6, CaCl2
2.5, MgSO4 1.2, NaH2PO4 1.3, NaHCO3 25.0, D-glucose 5.5, and
choline chloride 0.001, aerated with 95% O2/5% CO2 (V/V) and
kept at 37 °C. Mepyramine (1 µM) was present throughout
the experiment to block ileal H1 receptors. After an equilibra-
(2) Arrang, J . M.; Garbarg, M.; Schwartz, J . C. Autoinhibition of
Histamine Synthesis Mediated by Presynaptic H3-Receptors.
Neuroscience 1987, 23, 149-157.
(3) Arrang, J . M.; Garbarg, M.; Schwartz, J . C. Autoregulation of
Histamine Release in Brain by Presynaptic H3-Receptors.
Neuroscience 1985, 15, 553-562.
(4) Schlicker, E.; Fink, K.; Detzner, M.; Gothert, M. Histamine
Inhibits Dopamine Release in the Mouse Striatum via Presyn-
aptic H3-Receptors. J . Neural Transm. Gen. Sect. 1993, 93, 1-10.
(5) Schlicker, E.; Betz, R.; Gothert, M. Histamine H3-Receptor-
Mediated Inhibition of Serotonin Release in the Rat Brain
Cortex. Naunyn Schmiedeberg’s Arch. Pharmacol. 1988, 337,
588-590.
(6) Clapham, J .; Kilpatrick, G. J . Histamine H3-Receptors Modulate
the Release of [3H]-Acetylcholine from Slices of Rat Entorhinal
Cortex: Evidence for the Possible Existence of H3-Receptor
Subtypes. Br. J . Pharmacol. 1992, 107, 919-923.
(7) 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.
(8) Nakamura, T.; Itadani, H.; Hidaka, Y.; Ohta, M.; Tanaka, K.
Molecular Cloning and Characterization of a New Human
Histamine Receptor, HH4R. Biochem. Biophys. Res. Commun.
2000, 279, 615-620.
(9) 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.
(10) Leurs, R.; Blandina, P.; Tedford, C.; Timmerman, H. Therapeutic
Potential of Histamine H3 Receptor Agonists and Antagonists.
Trends Pharmacol. Sci. 1998, 19, 177-183.
(11) (a) Ali, S. M.; Tedford, C. E.; Gregory, R.; Handley, M. K.; Yates,
S. L.; Hirth, W. W.; Phillips, J . G. Design, Synthesis, and
Structure-Activity Relationships of Acetylene-Based Histamine
H
3 Receptor Antagonists. J . Med. Chem. 1999, 42, 903-909. (b)
http://www.gliatech.com/pages/corp-info/2000financials.pdf.

1530 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 8
Miko´ et al.
(12) Schwartz, J . C.; Arrang, J . M. Histamine. In Neuropsychophar-
macology: The Fifth Generation of Progress; Davis, K. L.,
Charney, D., Coyle, J . J ., Nemeroff, C., Eds.; Lipincott Williams
& Wilkins: Philadelphia, 2002; pp 179-190.
(13) Tardivel-Lacombe, J .; Rouleau, A.; Heron, A.; Morisset, S.; Pillot,
C.; Cochois, V.; Schwartz, J . C.; Arrang, J . M. Cloning and
Cerebral Expression of the Guinea Pig Histamine H3 Receptor:
Evidence for Two Isoforms. Neuroreport 2000, 11, 755-759.
(14) Lovenberg, T. W.; Pyati, J .; Chang, H.; Wilson, S. J .; Erlander,
M. G. Cloning of Rat Histamine H3 Receptor Reveals Distinct
Species Pharmacological Profiles. J . Pharmacol. Exp. Ther. 2000,
293, 771-778.
(15) Lovenberg, T. W.; Roland, B. L.; Wilson, S. J .; J iang, X.; Pyati,
J .; Huvar, A.; J ackson, M. R.; Erlander, M. G. Cloning and
Functional Expression of the Human Histamine H3 Receptor.
Mol. Pharmacol. 1999, 55, 1101-1107.
(16) Morisset, S.; Sasse, A.; Gbahou, F.; Heron, A.; Ligneau, X.;
Tardivel-Lacombe, J .; Schwartz, J . C.; Arrang, J . M. The Rat
H3 Receptor: Gene Organization and Multiple Isoforms. Bio-
chem. Biophys. Res. Commun. 2001, 280, 75-80.
Receptor Antagonists: Amine Derivatives. Pharmazie 1997, 52,
419-423.
(30) Stark, H.; Purand, K.; Hu¨ls, A.; Ligneau, X.; Garbarg, M.;
Schwartz, J . C.; Schunack, W. [125I]Iodoproxyfan and Related
Compounds: A Reversible Radioligand and Novel Classes of
Antagonists with High Affinity and Selectivity for the Histamine
H3 Receptor. J . Med. Chem. 1996, 39, 1220-1226.
(31) Ligneau, X.; Garbarg, M.; Vizuete, M. L.; Diaz, J .; Purand, K.;
Stark, H.; Schunack, W.; Schwartz, J . C. [125I]Iodoproxyfan, a
New Antagonist to Label and Visualize Cerebral Histamine H3
Receptors. J . Pharmacol. Exp. Ther. 1994, 271, 452-459.
(32) 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.
(33) Schlicker, E.; Kathmann, M.; Reidemeister, S.; Stark, H.;
Schunack, W. Novel Histamine H3 Receptor Antagonists: Af-
finities in an H3 Receptor Binding Assay and Potencies in Two
Functional H3 Receptor Models. Br. J . Pharmacol. 1994, 112,
1043-1048.
(17) (a) Morisset, S.; Rouleau, A.; Ligneau, X.; Gbahou, F.; Tardivel-
Lacombe, J .; Stark, H.; Schunack, W.; Ganellin, C. R.; Schwartz,
J . C.; Arrang, J . M. High Constitutive Activity of Native H3
Receptors Regulates Histamine Neurons in Brain. Nature 2000,
408, 860-864. (b) Drutel, G.; Peitsaro, N.; Karlstedt, K.;
Wieland, K.; Smit, M. J .; Timmerman, H.; Panula, P.; Leurs, R.
Identification of Rat H3 Receptor Isoforms with Different Brain
Expression and Signaling Properties. Mol. Pharmacol. 2001, 59,
1-8.
(34) Hirschfeld, J .; Buschauer, A.; Elz, S.; Schunack, W.; Ruat, M.;
Traiffort, E.; Schwarz, J . C. Iodoaminopotentidine and Related
Compounds: A New Class of Ligands with High Affinity and
Selectivity for Histamine H2 Receptors. J . Med. Chem. 1992, 35,
2231-2238.
(35) Mattson, R. J .; Pham, K. M.; Leuck, D. J .; Cowen, K. A. An
Improved Method for Reductive Alkylation of Amines using
Titanium(IV)-isopropoxide and Sodium Cyanoborohydride. J .
Org. Chem. 1990, 55, 2552-2554.
(18) Wellendorf, P.; Goodman, M. W.; Burstein, E. S.; Nash, N. R.;
Brann, M. R.; Weiner, D. M. Molecular Cloning and Pharmacol-
ogy of Functionally Distinct Isoforms of the Human Histamine
H3 Receptor. Neuropharmacology 2002, 42, 929-940.
(19) Ligneau, X.; Morisset, S.; Tardivel-Lacombe, J .; Gbahou, F.;
Ganellin, C. R.; Stark, H.; Schunack, W.; Schwartz, J . C.; Arrang,
J . M. Distinct Pharmacology of Rat and Human Histamine H3
Receptors: Role of Two Amino Acids in the Third Transmem-
brane Domain. Br. J . Pharmacol. 2000, 131, 1247-1250.
(20) Uveges, A. J .; Kowal, D.; Zhang, Y.; Spangler, T. B.; Dunlop, J .;
Semus, S.; J ones, P. G. The Role of Transmembrane Helix 5 in
Agonist Binding to the Human H3 Receptor. J . Pharmacol. Exp.
Ther. 2002, 301, 451-458.
(36) Brown, H. C.; Subba Rao, B. C. A New Powerful Reducing Agent-
Sodium Borohydride in the Presence of Aluminum Chloride and
Other Polyvalent Metal Halides. J . Am. Chem. Soc. 1956, 78,
2582-2588.
(37) Mitsunobu, O. The Use of Diethyl Azodicarboxylate and Triphen-
ylphosphine in Synthesis and Transformation of Natural Prod-
ucts. Synthesis 1981, 1-28.
(38) Sasse, A.; Sadek, B.; Ligneau, X.; Elz, S.; Pertz, H. H.; Luger,
P.; Ganellin, C. R.; Arrang, J . M.; Schwartz, J . C.; Schunack,
W.; Stark, H. New Histamine H3-Receptor Ligands of the
Proxifan Series: Imoproxifan and Other Selective Antagonists
with High oral in vivo Potency. J . Med. Chem. 2000, 43, 3335-
3343.
(39) Stark, H.; Sippl, W.; Ligneau, X.; Arrang, J . M.; Ganellin, C. R.;
Schwartz, J . C.; Schunack, W. Different Antagonist Binding
Properties of Human and Rat Histamine H3 Receptors. Bioorg.
Med. Chem. Lett. 2001, 11, 951-954.
(40) (a) CS ChemOffice Ultra 2002 7.0, C., Cambridge, MA. (b) Ghose,
A. K.; Crippen, G. M. Atomic Physicochemical Parameters for
Three-Dimensional-Structure-Directed Quantitative Structure-
Activity Relationships. 2. Modeling Dispersive and Hydrophobic
Interactions. J . Chem. Inf. Comput. Sci. 1987, 27, 21-35.
(41) Apelt, J .; Ligneau, X.; Pertz, H. H.; Arrang, J . M.; Ganellin, C.
R.; Schwartz, J . C.; Schunack, W.; Stark, H. Development of a
New Class of Nonimidazole Histamine H3 Receptor Ligands with
Combined Inhibitory Histamine N-Methyltransferase Activity.
J . Med. Chem. 2002, 45, 1128-1141.
(42) Vollinga, R. C.; Zuiderveld, O. P.; Scheerens, H.; Bast, A.;
Timmerman, H. A Simple and Rapid in vitro Test System for
the Screening of Histamine H3-Ligands. Methods Find. Exp.
Clin. Pharmacol. 1992, 14, 747-751.
(43) Garbarg, M.; Tuong, M. D.; Schwartz, J . C.; Gros, C. Sensitive
Radioimmunoassay for Histamine and Telemethylhistamine in
the Brain. J . Neurochem. 1989, 53, 1724-1730.
(44) (a) Parker, R. B.; Waud, D. R. Pharmacological Estimation of
Drug-Receptor Dissociation Constants. Statistical Evaluation.
I. Agonists. J . Pharmacol. Exp. Ther. 1971, 177, 1-12. (b) Waud,
D. R.; Parker, R. B. Pharmacological Estimation of Drug-
Receptor Dissociation Constants. Statistical Evaluation. II.
Competitive Antagonists. J . Pharmacol. Exp. Ther. 1971, 177,
13-24.
(21) Kiec-Kononowicz, K.; Ligneau, X.; Schwartz, J . C.; Schunack,
W. Pyrazoles as Potential Histamine H3 Receptor Antagonists.
Arch. Pharm. (Weinheim) 1995, 328, 469-472.
(22) Kiec-Kononowicz, K.; Ligneau, X.; Stark, H.; Schwartz, J . C.;
Schunack, W. Azines and Diazines as Potential Histamine H3-
Receptor Antagonists. Arch. Pharm. (Weinheim) 1995, 328, 445-
450.
(23) Walczynski, K.; Guryn, R.; Zuiderveld, O. P.; Timmerman, H.
Non-Imidazole Histamine H3 Ligands, Part 2: New 2-Substi-
tuted Benzothiazoles as Histamine H3 Antagonists. Arch. Pharm.
(Weinheim) 1999, 332, 389-398.
(24) Walczynski, K.; Guryn, R.; Zuiderveld, O. P.; Timmerman, H.
Non-Imidazole Histamine H3 Ligands. Part I. Synthesis of 2-(1-
piperazinyl)- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothia-
zole Derivatives as H3-Antagonists with H1 Blocking Activities.
Farmaco 1999, 54, 684-694.
(25) Ganellin, C. R.; Leurquin, F.; Piripitsi, A.; Arrang, J . M.;
Garbarg, M.; Ligneau, X.; Schunack, W.; Schwartz, J . C.
Synthesis of Potent Non-Imidazole Histamine H3-Receptor
Antagonists. Arch. Pharm. (Weinheim) 1998, 331, 395-404.
(26) Meier, G.; Apelt, J .; Reichert, U.; Graâmann, S.; Ligneau, X.;
Elz, S.; Leurquin, F.; Ganellin, C. R.; Schwartz, J . C.; Schunack,
W.; Stark, H. Influence of Imidazole Replacement in Different
Structural Classes of Histamine H3-Receptor Antagonists. Eur.
J . Pharm. Sci. 2001, 13, 249-259.
(27) Ligneau, X.; Lin, J .; Vanni-Mercier, G.; J ouvet, M.; Muir, J . L.;
Ganellin, C. R.; Stark, H.; Elz, S.; Schunack, W.; Schwartz, J .
C. Neurochemical and Behavioral Effects of Ciproxifan, a Potent
Histamine H3-Receptor Antagonist. J . Pharmacol. Exp. Ther.
1998, 287, 658-666.
(28) (a) Aslanian, R.; Mutahi, M. W.; Shih, N. Y.; McCormick, K. D.;
Piwinski, J . J .; Ting, P. C.; Albanese, M. M.; Berlin, M. Y.; Zhu,
X.; Wong, S.; Rosenblum, S. B.; J iang, Y.; West, R.; She, S.;
Williams, S. M.; Bryant, M.; Hey, J . A. Identification of a Novel,
Orally Bioavailable Histamine H3 Receptor Antagonist Based
on the 4-Benzyl-(1H-imidazol-4-yl) Template. Bioorg. Med.
Chem. Lett. 2002, 12, 937-941. (b) Aslanian, R. G.; Green, M.
J .; Shih, N. Y.; Phenyl-Alkyl Imidazoles as H3-Receptor An-
tagonists. Int. Pat. Appl. WO 95/14 007, May 26, 1995. (c)
Aslanian, R. G.; McCormick, K. D.; Mutahi, M. W. H3 Receptor
Ligands of the Phenyl-Alkyl-Imidazoles Type. Int. Pat. Appl. WO
99/24 405, May 20, 1999.
(45) Cheng, Y. C.; Prusoff, W. H. Relationship Between the Inhibition
Constant (Ki) and the Concentration of Inhibitor which Causes
50% Inhibition (I50) of an Enzymatic Reaction. Biochem. Phar-
macol. 1973, 22, 3099-3108.
(46) Buchheit, K.-H.; Engel, G.; Mutschler, E.; Richardson, B. Study
of the Contractile Effect of 5-Hydroxytryptamine (5-HT) in the
Isolated Longitudinal Muscle Strip from Guinea-Pig Ileum.
Naunyn-Schmiedeberg’s Arch. Pharmacol. 1985, 329, 36-41.
(47) Stark, H.; Sadek, B.; Krause, M.; Hu¨ls, A.; Ligneau, X.; Ganellin,
C. R.; Arrang, J . M.; Schwartz, J . C.; Schunack, W. Novel
Histamine H3-Receptor Antagonists with Carbonyl-Substituted
4-(3-(Phenoxy)propyl)-1H-imidazole Structures like Ciproxifan
and Related Compounds. J . Med. Chem. 2000, 43, 3987-3994.
(29) Stark, H.; Ligneau, X.; Lipp, R.; Arrang, J . M.; Schwartz, J . C.;
Schunack, W. Search for Novel Leads for Histamine H3-
J M021084K