Characterization of the binding site of the histamine H3 receptor. 2. Synthesis, in vitro pharmacology, and QSAR of a series of monosubstituted benzyl analogues of thioperamide

Article abstract of DOI:10.1021/jm981106w

A series of monosubstituted benzyl analogues of the histamine H₃ receptor antagonist thioperamide were synthesized and evaluated for their histamine H₃ receptor activity on the guinea pig jejunum. Incorporation of Cl, Br, and I at th

Full text of DOI:10.1021/jm981106w

1754
J . Med. Chem. 2000, 43, 1754-1761
Ch a r a cter iza tion of th e Bin d in g Site of th e Hista m in e H3 Recep tor . 2. Syn th esis,
in Vitr o P h a r m a cology, a n d QSAR of a Ser ies of Mon osu bstitu ted Ben zyl
An a logu es of Th iop er a m id e
Albert D. Windhorst,*,# Henk Timmerman,† Edward A. Worthington,# Greetje J . Bijloo,† Paul H. J . Nederkoorn,†
Wiro M. P. B. Menge,† Rob Leurs,† and J acobus D. M. Herscheid#
Radionuclide Center, Vrije Universiteit, De Boelelaan 1085c, 1081 HV, Amsterdam, The Netherlands, and Leiden/ Amsterdam
Center for Drug Research (LACDR), Division of Medicinal Chemistry, Vrije Universiteit, De Boelelaan 1083,
1081 HV, Amsterdam, The Netherlands
Received October 19, 1998
A series of monosubstituted benzyl analogues of the histamine H3 receptor antagonist
thioperamide were synthesized and evaluated for their histamine H3 receptor activity on the
guinea pig jejunum. Incorporation of Cl, Br, and I at the ortho position of the benzyl moiety
led to an increase of the pA2 value, whereas the same substituents at the para position led to
a decrease. However, a fluorine substituent gave a strong decrease in pA2, regardless of the
position. Molecular modeling revealed a QSAR with a correlation (r ) 0.93) between the pA2
and the dihedral angle between the thiourea and the benzyl moiety and the calculated electron
density on the substituted carbon atom. To verify whether this QSAR model had a predictive
value, the ortho tert-butyl and methyl analogues were synthesized and evaluated. Indeed it
was shown that the predicted pA2 values of these two compounds were in accordance with the
measured pA2 values.
In tr od u ction
based on ab initio quantum-chemical calculations, has
been developed in our laboratory, reported by De Esch
et al.13
The histamine H3 receptor in the central nervous
system (CNS) has been extensively investigated by in
vitro pharmacological methods. These experiments sug-
gest that the H3 receptor plays an important role in
regulating the function of histamine as a neurotrans-
mitter.1,2 The H3 receptor acts as an autoreceptor3
regulating the synthesis and release of histamine from
histaminergic neurons, and it acts as a heteroreceptor
regulating the release of noradrenaline,4 serotonin,5
acetylcholine,6 and dopamine7 from the respective sys-
tems.
Especially since the H3 receptor is involved in the
regulation of the release of several neurotransmitters,
its role in the physiology of neuronal disorders deserves
further investigation. The development of H3 ligands
suitable for positron emission tomography (PET) or
single photon emission computed tomography (SPECT)
by labeling these ligands with 18F or 76Br for PET and
123I for SPECT could be of great help in such studies.
We have selected thioperamide (1) as a template for the
development of such labeled ligands. From in vitro
This regulatory effect of the H3 receptor can be of
great importance for drug therapies in neuronal abnor-
malities occurring e.g. in Parkinson’s disease (dopa-
minergic system), Alzheimer’s disease (cholinergic sys-
tem), schizophrenia, and depression (serotonergic system)
and probably in learning and memory disorders. Both
agonists and antagonists of the H3 receptor might
become useful in therapies for CNS disorders as has
been proposed in several reviews.8,9
pharmacology it is known that thioperamide is both a
relatively selective and a highly potent H3 antagonist.14
Furthermore, ex vivo binding studies have shown that
thioperamide is able to cross the blood-brain barrier
(BBB), e.g. after sc administration.15 From qualitative
structure-activity relationship (QSAR) studies10,11 it is
clear that the cyclohexane part of thioperamide may be
replaced with a (halogenated) benzyl group without
losing H3 receptor activity. Because such derivatives
have not yet been fully described,16 we synthesized and
evaluated the compounds 2a -o listed in Table 1 for
their histamine H3 antagonistic activity with two goals:
to investigate the SAR for the “lipophilic tail” of thio-
Not much is known however about the histamine H3
receptor itself. It is located in the central as well as
peripheral nervous systems. It has a relatively low
abundancy in the brain and has not been cloned yet.
Some qualitative binding models for antagonists have
been described by Vollinga et al.10 and Stark et al.,11
and an agonist binding model has been presented by
Ho¨ltje et al.12 Recently, a general ligand-based model,
* Corresponding author. Tel: 020 444 9107. Fax: 020 444 9121.
E-mail: bwindhorst@rnc.vu.nl.
#
Radionuclide Center.
† LACDR.
10.1021/jm981106w CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/13/2000

Binding Site Characterization of Histamine H3 Receptor
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 9 1755
Sch em e 1a
a
(i) N,N-Dimethylsulfamoyl chloride, triethylamine, toluene, rt, 93%; (ii) (a) n-butyllithium, chlorotrimethylsilane, tetrahydrofuran,
-65 °C, (b) n-butyllithium, N-benzyl-4-piperidone, tetrahydrofuran, -65 °C, (c) 1 M HCl, rt, 54% (a + b + c); (iii) ammonium formate,
10% Pd/C, methanol, reflux, 88%; (iv) 30% HBr, reflux, 74%; (v) H2, 10% Pd/C, methanol, rt, 100%.
Sch em e 2a
Sch em e 4a
a
(i) 1,1′-Thiocarbonyl-2,2′-(1H)-pyridone, diisopropylethylamine,
a
(i) CuCN, dimethylformamide, 83%; (ii) see Scheme 3.
dichloromethane, rt, 63-98%; (ii) 7, diisopropylethylamine, etha-
nol, rt, 10-81%.
the formate ion as hydrogen donor,19 resulting in 5 in
quantitative yield. Acidic hydrolysis of the dimethyl-
sulfamoyl group in 30% HBr also gave elimination of
the tertiary alcohol. The resulting 1,2,5,6-tetrahydro-
pyridine 6 was hydrogenated to giving the desired
compound 4-(1H-imidazol-4-yl)piperidine dihydrobro-
mide (7) in a 24% overall yield, calculated from imid-
azole.
Sch em e 3a
Compound 7 was reacted with substituted benzyl
isothiocyanates 9a -o according to Scheme 2. Benzyl
isothiocyanates 9g-m were commercially available, and
benzyl isothiocyanates 9a -f,n ,o were synthesized from
the commercially available substituted benzylamines
8a -f,n ,o and 1,1′-thiocarbonyldi[(1H)-pyridone]20,21
(Scheme 2), whereas 2- and 4-iodobenzylamines (8a ,c)
were obtained by the selective reduction of the corre-
sponding 2- and 4-iodobenzonitriles (10a ,b) with exactly
1 equiv of AlH3, generated by the addition of 0.5 mol
equiv of concentrated sulfuric acid to LiAlH4 in THF22
(Scheme 3). Other methods for the reduction of 2- and
4-iodobenzonitriles (10a ,b) were not effective. Raney-
Ni reduction in acid media did not reduce the nitrile;
Raney-Ni reduction under basic conditions was possible
but gave consistently deiodinated side product. The
reduction with NaBH4 and CoCl2 gave similar results.
Only by using ALH3, deiodination could be limited to
about 10%. This deiodinated product could be separated
from the target compounds 8a ,c by flash column chro-
matography.
a
(i) Tetrahydrofuran,
0 °C; (ii) tetrahydrofuran, rt, 45%
(i + ii).
peramide and to obtain a suitable lead for further
development as a PET or SPECT ligand for the hista-
mine H3 receptor.
Ch em istr y
The syntheses of the compounds 2a -o are given in
Schemes 1-4.
Syn th esis. 4-(1H-Imidazol-4-yl)piperidine dihydro-
bromide (7) was synthesized according to Vollinga10
(Scheme 1). Imidazole was protected at the N-1 position
with the dimethylsulfamoyl group according to litera-
ture procedures.17,18 For the selective electrophilic ad-
dition of N-benzyl-4-piperidone at the 5-position, the
2-position was first protected in situ with the trimeth-
ylsilane group. After acidic workup compound 4 was
isolated in moderate yield. The benzyl group was
removed by a catalytic hydrogen-transfer reaction with
The 2-tert-butylbenzylamine (8n ) was prepared ac-
cording to Scheme 4; 2-bromo-1-tert-butylbenzene23 (11)
was reacted with CuCN to give 2-tert-butylbenzonitrile24
(10c), which was reduced to 2-tert-butylbenzylamine
(8n ) with AlH3 using the same procedure as for 2- and
4-iodobenzonitriles (10a ,b). Compounds 2a -m ,o were

1756 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 9
Windhorst et al.
Ta ble 1. Histamine H3 Antagonistic Activity Expressed as the
pA2 Value and Molecular Modeling Results (æ and δ) of 2a -oa
F igu r e 1. Dihedral angle æ (bold) used in the QSAR analysis.
model. The pA2 values of all the compounds are listed
in Table 1.
pA2 ((SEM)
(N ) 4)
compd
R
formula
æ
δ
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2-I
3-I
4-I
C
C
C
C
C
C
C
C
C
C
C
C
C
16H19IN4S‚0.5C4H4O4 8.13 (0.15)
16H19IN4S‚0.5C4H4O4 7.80 (0.14)
16H19IN4S‚0.5C4H4O4 6.78 (0.06)
16H19BrN4S‚0.5C4H4O4 7.84 (0.18)
16H19BrN4S‚0.5C4H4O4 7.47 (0.17)
16H19BrN4S‚0.5C4H4O4 6.47 (0.06)
16H19ClN4S‚0.5C4H4O4 8.21 (0.09)
16H19ClN4S‚0.5C4H4O4 7.41 (0.05)
16H19ClN4S‚0.5C4H4O4 7.21 (0.08)
16H19FN4S‚0.5C4H4O4 6.04 (0.14)
16H19FN4S‚0.5C4H4O4 6.44 (0.13)
16H19FN4S‚0.5C4H4O4 6.25 (0.14)
-152.8 -0.58
-131.4 -0.64
-84.2 -0.61
-162.5 -0.02
-119.2 -0.08
-108.8 -0.05
-168.5 0.14
-118.9 0.08
-122.2 0.11
-118.0 0.73
-111.9 0.65
-118.8 0.66
-110.1 -0.23
-155.7 0.21
From the antagonistic activities of 2a -m we observed
a clear influence of the substituent on the benzene ring
on the pA2 value. This is in contradiction to other,
qualitative, receptor models which state that for this
part of the general structure of H3 antagonists, the “tail”
of our compounds, only lipophilicity is of importance.
Indeed for a series of isothiourea (clobenpropit), thiourea
(burimamide), and related compounds such a relation-
ship has been found.26,27 In a series of imidazolyl alkyl
ethers (iodoproxyfan), the 2- and 3-iodo isomers have
been synthesized and tested for H3 antagonistic activity;
no significant influence of the position of the iodo
substituent upon affinity for the H3 receptor has been
found.28 From this perspective it is remarkable that the
2-iodo compound 2a is 15 times more active then its
4-iodo isomer 2c. The same trend was found for the
brominated and chlorinated analogues, but not for the
fluorine-containing derivatives. Furthermore, introduc-
tion of an iodine, bromine, or chlorine substituent in the
para position leads to a decrease in H3 antagonistic
activity compared to the unsubstituted 2m , which is in
contrast to the SAR that has been found in the cloben-
propit series, where para substitution increases the H3
receptor activity. In the case of fluorine substitution,
all three isomers were less active then 2m ; the three
isomers are about equipotent.
These results prompted us to propose that in this
series of compounds a steric factor is partly determinant
for the H3 antagonistic activity. Next to this, the results
of fluorine-substituted compounds indicate the possible
involvement of an electronic factor. To quantify these
findings a classical QSAR method was used to establish
a possible correlation between the biological activity of
the compounds 2a -m and steric and electronic param-
eters, as well as other parameters. However, no statisti-
cally significant correlations were found, which could
have been caused by the relatively small size of the
dataset.
Next, we performed a molecular modeling study to
optimize the geometries of each of the compounds 2a -m
to compare these optimized geometries in correlation
with the biological activities of the compounds 2a -m .
For this modeling study we started to optimize the
geometry of the unsubstituted benzyl analogue 2m and
used the optimized structure as a template for the
optimization of the other substituted analogues 2a -l.
Results of this molecular modeling approach, the dihe-
dral angles æ and the electron densities δ, are given in
Table 1. The dihedral angle æ was defined as depicted
in Figure 1 as the angle between the phenyl group and
the thiourea moiety and the electron density δ as the
electron density of the substituted carbon atom of the
phenyl ring. The optimized geometries of relevant
compounds are shown in Figures 2-4. These modeling
results show that in the case of ortho substitution
(2a ,d ,g), the phenyl moiety is turned out of the plane
2-Br
3-Br
4-Br
2-Cl
3-Cl
4-Cl
2-F
3-F
4-F
H
16H20N4S‚0.5C4H4O4
7.32 (0.16)
7.54 (0.18)
(calcd 7.64)
7.02 (0.10)
(calcd 6.83)
2-t-Bu C20H28N4S
2o
2-Me 17H22N4S‚0.5C4H4O4
C
-114.3 0.19
aæ was defined as depicted in Figure 1 to express the angle
between the phenyl group and the thiourea moiety; the electron
density δ was defined as the electron density of the substituted
carbon atom of the phenyl ring.
isolated and recrystallized as their fumaric acid salts;
2n was isolated and recrystallized as the free base
(Table 1).
Molecu la r Mod elin g. The geometries of 2a -o were
optimized as follows. The starting point was the opti-
mized geometry of the 4-[(1H-imidazol-4-yl)piperidinyl]-
thiourea moiety (including the aspartate) as generated
by De Esch et al.13 Starting from this template, only
the geometry of the added substituted benzyl moiety
needed to be optimized. Starting geometries were
generated and partially optimized using Chem-X (Chemi-
cal Design Ltd., Oxford, U.K.). Subsequently, the ge-
ometries were fully optimized using the Amsterdam
Density Functional program package (v 2.03a) according
to the same procedure as has been described previ-
ously.13
P h a r m a cology
The histamine H3 activity of 2a -o was determined
using the method desribed by Vollinga et al.25 Briefly,
the pA2 value was determined in an in vitro test system,
based on the concentration-dependent inhibitory effect
of H3 agonists on electrically evoked contractile re-
sponses (acetylcholine release) of guinea pig jejunum
preparations. The experiment has been performed four
times in duplicate. As agonist (R)-R-methylhistamine
was used (pD2 ) 7.8 ((0.2), N ) 12). The Schild slopes
were not significantly different from unity.
Resu lts a n d Discu ssion
Compounds 2a -o were obtained in moderate to good
yields and have been tested for their antagonistic
activity at the histamine H3 receptor. Initially we
synthesized only 2a -m as model compounds for the
development of a potential PET or SPECT ligand. After
it became clear that a QSAR model could be derived (see
further), we synthesized 2n ,o to validate this QSAR

Binding Site Characterization of Histamine H3 Receptor
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 9 1757
substituted compounds 2j-l do not contribute to this
correlation. Omitting 2j-l from eq 1 improved the
correlation indeed:
pA2 ) -0.016((0.003)æ + 5.382(( 0.428) (2)
(n ) 10, r ) 0.87, s ) 0.26, F ) 24.26)
The correlation found in eq 2 indicates that the
dihedral angle æ is of importance for the H3 antagonistic
activity of 2a -i,m . However, the results from the
fluorine compounds 2j-l had been omitted. To include
2j-l we also investigated the influence of electronic
effect of the substituent, expressed as the electron
density on the substituted carbon atom (see Table 1).
This electron density δ alone correlates with the pA2
according to eq 3:
F igu r e 2. Optimized geometry of 2m according to the method
of De Esch et al.13 This geometry was used as a starting point
for the geometry optimization of 2a -l,n ,o.
pA2 ) -0.96((0.34)δ + 7.20(0.15)
(n ) 13, r ) 0.65, s ) 0.55, F ) 7.88)
(3)
Combination of the dihedral angle æ and the electron
density on the substituted carbon atom δ revealed a very
good correlation with the H3 antagonistic activity of the
compounds:
pA2 ) -0.02((0.003)æ - 0.93((0.17)δ +
4.72(( 0.44) (4)
F igu r e 3. Optimized geometries of the 2-iodo (2a ), 2-bromo
(2d ), 2-chloro (2g), and 2-fluoro (2j) analogues and the unsub-
stituted 2m . It can clearly be seen that the 2-fluorobenzyl
moiety does not turn out of the plane of the benzyl moiety of
2m , while the substituted benzyl moieties of 2a ,d ,g do turn
out of the plane.
(n ) 13, r ) 0.93, s ) 0.28, F ) 31.57)
To validate these findings we synthesized compounds
2n ,o. We selected the tert-butyl substituent, because
this substituent combines a large steric hindrance effect
to give a large dihedral angle æ, with a relatively small
electronic contribution upon the electron density δ in
comparison to 2m . The methyl group was selected
because it has only a marginal effect on the electron
density δ and on the dihedral angle æ in comparison
with 2m (Figure 4). The predicted pA2 values of these
two compounds are for 2n 7.64 and for 2o 6.83. The
measured values, 7.54 and 7.02, respectively, compare
with the predicted values, and thus we conclude that
the QSAR model is valid. When the measured values
of compounds 2n ,o are included in eq 4, the final
correlation of the pA2 with æ and δ becomes:
F igu r e 4. Optimized geometries of the 2-tert-butyl (2n ) and
2-methyl (2o) analogues added to the optimized geometries of
Figure 3. From this view it can be seen that the 2-tert-
butylbenzyl moiety of 2n turns out of the plane of the benzyl
moiety of 2m , whereas the 2-methylbenzyl moiety of 2o does
not.
pA2 ) -0.02((0.003)æ - 0.93((0.16)δ +
4.81((0.42) (5)
(n ) 15, r ) 0.93, s ) 0.26, F ) 36.57)
Con clu sion
when compared to the unsubstituted benzyl compound
2m (Figure 3). We tried to correlate the dihedral angle
between the thiourea moiety and the phenyl group for
2a -m with the pA2 value and obtained the following
equation, where æ is the dihedral angle:
We have shown that for the series 2a -o a QSAR
model is valid and that this relationship is in contradic-
tion to other SAR studies with related series of H3
antagonists found in the literature. We conclude that
the ‘different’ results of Vollinga10 and Stark11,28 can be
explained by the existence of two separate “lipophilic”
pockets, as has been proposed by De Esch et al.13 We
further conclude that the fluorine-containing compounds
2j-l are not suited for development as PET ligands,
since the H3 antagonistic activity is too low. The 2- or
pA2 ) -0.020(( 0.006)æ + 4.645(( 0.832) (1)
(n ) 13, r ) 0.64, s ) 0.26, F ) 9.79)
In eq 1 compounds 2a -m were included. However it
is clear from the modeling study that the fluorine-

1758 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 9
Windhorst et al.
4-(1H-Im id a zol-4-yl)-1,2,5,6-tetr a h yd r op yr id in e Dih y-
d r obr om id e, 6. Compound 5 (15.00 g, 58 mmol) was refluxed
for 3 h in 50 mL of 30% HBr. The hydrobromic acid was
removed under reduced pressure and the residue was dissolved
in 150 mL of ethanol, 1 mL of concentrated sulfuric acid was
added and the reaction mixture was refluxed for 2 h. After
the solvent was removed under reduced pressure, the solid
material was washed three times with 50 mL of acetone
yielding 13.34 g (43 mmol, 74%) of 6. Rf (methanol/triethyl-
amine: 9/1) ) 0.42. Mp ) 291-292 °C. 1H NMR (D2O): δ )
2.65-2.80 (m, 2H, tetrahydropyridine-H5), 3.52 (t, J ) 6.7 Hz,
2H, tetrahydropyridine-H6), 3.90 (s, 2H, tetrahydropyridine-
H2), 6.58-6.72 (m, 1H, tetrahydropyridine-H3), 7.52 (s, 1H,
imidazole-H4), 8.74 (s, 1H, imidazole-H2).
4-(1H-Im idazol-4-yl)piper idin e Dih ydr obr om ide, 7. Com-
pound 6 (13.00 g, 42 mmol) was dissolved in 25 mL of methanol
and 1 mL of water, 1.30 g of 10% Pd/C was added and the
reaction mixture was hydrogenated for 4 h at 50 bar H2 in a
bomb at room temperature. The catalyst was removed by
filtration over Celite and the filtrate was evaporated to give
13.15 g (42 mmol) of 7. Rf (methanol/triethylamine: 9/1) )
0.38. Mp ) 275-278 °C. 1H NMR (D2O): δ ) 1.70-2.00 (m,
2H, piperidine-H3ax,5ax), 2.20-2.40 (m, 2H, piperidine-H3eq,5eq),
3.11-3.32 (m, 3H, piperidine-H2 ax,4,6ax), 3.45-3.61 (m, 2H,
piperidine-H2eq,6eq), 7.48 (s, 1H, imidazole-H4), 8.61 (s, 1H,
imidazole-H2).
2-ter t-Bu tylben zon itr ile, 10c. Compound 11 (5.00 g, 23
mmol) was added to 2.38 g (26 mmol) of CuCN in 5 mL of
dimethylformamide. The reaction mixture was refluxed for 4
h. After cooling to room temperature 5 mL of diethylamine
and 15 mL of water were added. This aqueous layer was
extracted five times with 25 mL of diethyl ether. The combined
diethyl ether layers were extracted with 25 mL of a 10% NaCN
in water solution and subsequently with 15 mL of water. The
organic layer was dried, the solvent evaporated and the
product was obtained from the residu by Kugelrohr distillation
at 60-70 °C (at 10 mmHg) as a colorless oil. Yield ) 3.07 g
(19 mmol, 83%). 1H NMR (CDCl3): δ ) 1.48 (s, 9H, tert-butyl),
7.15-1.31 (m, 1H, phenyl-H5), 7.40-7.56 (m, 2H, phenyl-
H3,4), 7.63 (d, J ) 8.0 Hz, 1H, phenyl-H6).
3-iodo-substituted derivatives 2b,c are candidates for
SPECT ligands, because they show good H3 antagonistic
activity.
Exp er im en ta l Section
1H NMR spectra were recorded on a Bruker AC 200 (at
200.13 MHz); chemical shifts (δ) are determined relative to
the solvent and converted to the TMS scale using δ ) 2.50 for
DMSO-d6, 3.35 for CD3OD, and 7.26 for CDCl3. Abbreviations
used in description of NMR spectra: s ) singlet, d ) doublet,
t ) triplet, dd ) double doublet, dt ) double triplet, m )
multiplet, bs ) broad singlet. Melting points were measured
on a Mettler FP-5 mounted with a FP-52 microscope and are
uncorrected. Flash column chromatography was performed
with Baker silica gel 60. Thin-layer chromatography (TLC) was
performed on Merck TLC plates (silica gel 60, F254, 0.25 mm);
amines were detected using ninhydrin. Amides were detected
using the Reindol-Hoppe coloring procedure, giving purple
spots for NH- or NH2-containing compounds. For all end
products elemental analyses were within 0.4% of the theoreti-
cal values. The commercial available benzyl isothiocyanates
were purchased from Lancaster and all other chemicals from
Aldrich; solvents were purchased from Riedel-de Haen.
Dichloromethane was distilled from CaH2 and stored over CaO.
Tetrahydrofuran was distilled from LiAlH4 and stored over Na
wire. n-Hexane was distilled before use. All reactions were
carried out under a nitrogen atmosphere.
1-Ben zyl-4-[1-(N,N-d im eth ylsu lfa m oyl)im id a zol-4-yl]-
4-h yd r oxyp ip er id in e, 4. Compound 3 (26.28 g, 0.15 mol) was
dissolved in 500 mL of tetrahydrofuran and cooled to -65 °C.
100 mL (0.16 mol) of a 1.6 M solution of n-butyllithium in
hexanes was added dropwise keeping the temperature between
-65 and -60 °C and was stirred for another 15 min at -65
°C. Then 20.11 mL (0.15 mol) of chlorotrimethylsilane was
added dropwise at -65 °C. The reaction mixture was allowed
to warm to room temperature and stirred for 1 h. This solution
was cooled again to -65 °C and 100 mL (0.16 mol) of a 1.6 M
solution of n-butyllithium in hexanes was added keeping the
reaction temperature between -65 and -60 °C. The reaction
mixture was stirred for 45 min before 26.52 mL (0.15 mol) of
N-benzyl-4-piperidone was added dropwise at -65 °C. The
reaction was allowed to warm to room temperature overnight.
Next, the reaction mixture was poured into 1250 mL of water
and THF was evaporated under reduced pressure. The aque-
ous residue was extracted three times with 700 mL of
dichloromethane. The dichloromethane layers were dried over
Na2SO4 and evaporated under reduced pressure. The residue
was suspended in 300 mL of 1 M hydrochloric acid, stirred for
30 min at ambient temperature and extracted two times with
150 mL of diethyl ether. The aqueous layer was basified
(pH > 10) with K2CO3 and extracted three times with 150 mL
of dichloromethane. The dichloromethane layers were dried
over Na2SO4 and evaporated under reduced pressure. The
crude product was purified by flash column chromatography
with ethyl acetate/triethylamine (9/1) as the eluent to give
29.52 g of 4 (81 mmol, 54%) as a yellow oil. Rf (ethyl acetate/
triethylamine: 9/1) ) 0.29. 1H NMR (CDCl3): δ ) 2.72-3.51
(m, 8H, piperidine-H), 2.97 (s, 6H, CH3), 4.37 (s, 1H, OH), 4.42
(s, 2H, CH2), 7.28 (s, 1H, im-H4), 7.38-7.60 (m, 5H, phenyl-
H), 7.81 (s, 1H, im-H2).
2-Iod oben zyla m in e Hyd r och lor id e, 8a . LiAlH4 (1.60 g,
42 mmol) of was suspended in 25 mL of THF. The mixture
was cooled to 0 °C and 2.10 g (21 mmol) of concentrated
sulfuric acid was added dropwise with vigorous stirring. The
suspension was stirred for 1 h at 0 °C, before a solution of
4.06 (20 mmol) of 2-iodobenzonitrile in 10 mL of THF was
added dropwise. Stirring was continued for 1 h and the
reaction was stopped by the addition of 10 mL of water
followed by the addition of 25 mL of 2.5 M of NaOH. The
reaction mixture was filtered and the organic layer was
separated. The water layer was extracted two times with 20
mL of diethyl ether. The combined organic layers were dried
over Na2SO4 and evaporated. The product was purified by flash
column chromatography with dichloromethane/hexane (1/1) as
the eluent, yielding 2.10 g (9.0 mmol, 45%) of 8a . Rf (dichlo-
1
romethane/n-hexane: 1/1) ) 0.15. H NMR (CDCl3): δ ) 1.50
(s, 2.2H, NH2‚HCl), 3.82 (s, 2H, CH2), 6.91 (m, 1H, phenyl-
H5), 7.30 (m, 2H, phenyl-H4,6), 7.78 (d, J ) 7.9 Hz, phenyl-
H3).
4-Iod oben zyla m in e Hyd r och lor id e, 8c. Compound 8c
was prepared from 4-iodobenzonitrile according to the same
procedure as for 8a yielding 2.78 g (12 mmol, 60%). Rf
(dichloromethane/n-hexane: 1/1) ) 0.27. 1H NMR (CDCl3):
δ ) 1.50 (bs, 1.9H, NH2), 3.78 (s, 2H, CH2), 7.00 (d, J ) 8.4
Hz, 2H, phenyl-H2,6), 7.59 (d, J ) 8.4 Hz, phenyl-H3,5).
2-ter t-Bu tylben zyla m in e, 8n . Compound 8n was prepared
from 3.01 g (19 mmol) of 10c according to the same procedure
as for 8a yielding 2.44 g (15 mmol, 79%) of 8n . 1H NMR
(CDCl3): δ ) 1.50 (s, 9H, tert-butyl), 4.06 (s, 2H, CH2), 7.13
(m, 2H, phenyl-H3,6), 7.35 (m, 2H, phenyl-H4,5).
4-[1-(N,N-Dim eth ylsu lfa m oyl)im id a zol-4-yl]-4-h yd r ox-
yp ip er id in e, 5. Compound 4 (25.00 g, 69 mmol) was dissolved
in 250 mL of methanol and 2.50 g of 10% Pd/C and 28.00 g
(0.45 mol) of ammonium formate were added. The reaction
mixture was refluxed for 6 h. After cooling to room tempera-
ture the reaction mixture was filtered over Celite and the
filtrate was evaporated under reduced pressure to yield 15.75
g (61 mmol, 88%) of 5. This product was pure enough to use
in the next reaction step. Rf (ethyl acetate/methanol: 9/1) )
0.27. 1H NMR (CDCl3): δ ) 1.80-1.98 (m, 2H, piperidine-
H3ax,5ax), 2.03-2.19 (m, 2H, piperidine-H3eq,5eq), 2.81-2.88 (m,
2H, piperidine-H2 ax,6ax), 2.97 (s, 6H, CH3), 2.94-3.16 (m, 3H,
piperidine-H2 eq,6eq and OH), 6.92 (s, 1H, imidazole-H4), 7.70
(s, 1H, imidazole-H2).
2-Iod oben zyl Isoth iocya n a te, 9a . 1,1′-Thiocarbonyl-2,2′-
(1H)-pyridone (0.71 g, 3.0 mmol) was dissolved in 15 mL of
dichloromethane and 0.60 mL (3.5 mmol) of diisopropylethyl-
amine was added. To this mixture was added dropwise a

Binding Site Characterization of Histamine H3 Receptor
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 9 1759
solution of 0.59 g (2.5 mmol) of 8a and 1.80 mL (10.5 mmol) of
diisopropylethylamine in 10 mL of dichloromethane at ambient
temperature. The mixture was stirred for a additional 30 min
after which the reaction mixture was washed twice with 15
mL of brine and once with 15 mL of 1 M HCl. The organic
layer was dried over Na2SO4 and evaporated to dryness. The
product was purified with flash column chromatography with
dichloromethane as the eluent, yielding 0.65 g (2.4 mmol, 80%)
of 2b. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.32.
Mp ) 131-133 °C. 1H NMR (DMSO-d6): δ ) 1.45-1.66 (m,
2H, piperidine-H3ax,5ax), 1.93-2.07 (m, 2H, piperidine-H3eq,5eq),
3.08-3.58 (m, 5H, piperidine-H2,4,6), 4.68-4.80 (m, 2.8H,
CH2, thiourea-NH), 6.43 (s, 1H, fumaric acid), 7.12 (t, 3J )
3
7.7 Hz, 1H, phenyl-H5), 7.31 (d, J ) 7.7 Hz, 1H, phenyl-H6),
3
7.47 (s, 1H, imidazole-H5), 7.58 (d, J ) 7.8 Hz, 1H, phenyl-
H4), 7.65 (s, 1H, phenyl-H2), 8.39 (bs, 1H, imidazole-NH), 9.00
(s, 1H, imidazole-H2). 13C NMR (CD3OD): δ ) 32.3 (piperidine-
4), 34.6 (CH2), 49.1 (piperidine-3,5), 50.5 (piperidine-6), 55.9
(piperidine-2), 108.6 (phenyl-3), 120.8 (imidazole-5), 128.4
(phenyl-4), 129.5 (phenyl-5), 129.8 (phenyl-6), 133.6 (phenyl-
2), 136.1 (phenyl-4), 138.9 (phenyl-2), 143.8 (phenyl-1). Anal.
(C16H19IN4S‚0.5C4H4O4) C, H, N.
1
of 9a . H NMR (CDCl3): δ ) 4.59 (s, 2H, CH2), 6.94-7.09 (m,
1H, phenyl-H5), 7.35-7.47 (m, 2H, phenyl-H4,6) 7.83-7.96 (m,
1H, phenyl-H3).
3-Iod oben zyl Isoth iocya n a te, 9b. Compound 8b (0.2 g,
0.75 mmol) was reacted according to the same procedure as
for 9a to yield 0.19 g (0.69 mmol, 92%) of 9b. 1H NMR (CDCl3):
δ ) 4.67 (s, 2H, CH2), 7.13-7.25 (m, 2H, phenyl-H5,6), 7.63
(m, 2H, phenyl-H2,4).
4-Iod oben zyl Isoth iocya n a te, 9c. Compound 8c (0.19 g,
0.71 mmol) was reacted according to the same procedure as
for 9a to yield 0.13 g (0.45 mmol, 63%) of 9c. 1H NMR
(CDCl3): δ ) 4.54 (s, 2H, CH2), 7.00 (d, J ) 7.8 Hz, 2H, phenyl-
H2,6), 7.39 (d, J ) 7.8 Hz 2H, phenyl-H3,5).
2-Br om oben zyl Isoth iocya n a te, 9d . Compound 8d (0.19
g, 0.88 mmol) was reacted according to the same procedure as
for 9a to yield 0.18 g (0.77 mmol, 88%) of 9d . 1H NMR
(CDCl3): δ ) 4.68 (s, 2H, CH2), 7.25 (m, 2H, phenyl-H4,6),
7.45 (m, 2H, phenyl-H3,5).
3-Br om oben zyl Isoth iocya n a te, 9e. Compound 8e (0.22
g, 0.99 mmol) was reacted according to the same procedure as
for 9a to yield 0.22 g (0.97 mmol, 98%) of 9e. 1H NMR
(CDCl3): δ ) 4.65 (s, 2H, CH2), 7.20 (m, 2H, phenyl-H5,6),
7.49 (m, 2H, phenyl-H2,4).
N-(4-Iod oben zyl)-N′-[4-(1H-im id a zol-4-yl)p ip er id in yl]-
th iou r ea Hem ifu m a r a te, 2c. Compound 9c (125 mg, 0.45
mmol) was reacted with 140 mg (0.45 mmol) of 7 according to
the same procedure as for 2a to yield 111 mg (0.23 mmol 51%)
of 2c. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.43.
1
Mp ) 140-144 °C. H NMR (CD3OD): δ ) 1.60-1.70 (m, 2H,
piperidine-H3ax,5ax), 1.90-2.14 (m, 2H, piperidine-H3eq,5eq),
2.85-3.12 (m, 1H, piperidine-H4), 3.13-3.27 (m, 4H, piperi-
dine-H2,6), 4.84 (s, 2H, CH2), 6.54 (s, 1H, fumaric acid), 6.94
3
(s, 1H, imidazole-H5), 7.12 (d, J ) 8.0 Hz, 2H, phenyl-H2,6),
7.63 (d, 3J ) 8.0 Hz, 2H, phenyl-H3,5), 7.86 (s, 1H, imidazole-
H2), 8.39 (bs, 1H, imidazole-NH). 13C NMR (CD3OD): δ ) 32.7
(piperidine-4), 35.5 (CH2), 49.3 (piperidine-3,5), 50.2 (piperi-
dine-2,6), 92.6 (phenyl-4), 115.8 (imidazole-5), 130.7 (phenyl-
2,6), 135.7 (imidazole-4), 138.4 (phenyl-3,5), 140.8 (imidazole-
2), 141.7 (phenyl-1), 182.7 (CdS). MS: 427 (M + 1), 303, 169,
164, 152, 146, 113. Anal. (C16H19IN4S‚0.5C4H4O4) C, H, N.
N-(2-Br om oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2d . Compound 9d (71 mg, 0.31
mmol) was reacted with 100 mg (0.31 mmol) of 7 according to
the same procedure as for 2a to yield 72 mg (0.16 mmol, 52%)
of 2d . Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.37.
Mp ) 151-154 °C. 1H NMR (DMSO-d6): δ ) 1.65-1.82 (m,
2H, piperidine-H3ax,5ax), 2.01-2.19 (m, 2H, piperidine-H3eq,5eq),
2.95-3.15 (m, 1H, piperidine-H4), 3.16-3.29 (m, 4H, piperi-
dine-H2,6), 4.85 (s, 2H, CH2), 6.45 (s, 1H, fumaric acid), 7.10-
7.20 (m, 1H, phenyl-H5), 7.24-7.32 (m, 2H, phenyl-H4,6), 7.38
4-Br om oben zyl Isoth iocya n a te, 9f. Compound 8f (0.18
g, 0.80 mmol) was reacted according to the same procedure as
for 9a to yield 0.17 g (0.77 mmol, 96%) of 9f. 1H NMR
(CDCl3): δ ) 4.61 (s, 2H, CH2), 7.19 (d, J ) 7.9 Hz, 2H, phenyl-
H2,6), 7.45 (d, J ) 7.9 Hz, 2H, phenyl-H3,5).
2-ter t-Bu t ylb en zyl Isot h iocya n a t e, 9n . Compound 8n
1.00 g (6.1 mmol) was reacted according to the same procedure
as for 9a to yield 1.23 g (6.0 mmol, 98%) of 9n . 1H NMR
(CDCl3): δ ) 1.32 (s, 9H, tert-butyl), 4.92 (s, 2H, CH2), 7.20
(m, 2H, phenyl-H3,6), 7.38 (m, 2H, phenyl-H3,5).
3
(s, 1H, imidazole-H5), 7.55 (d, J ) 8.0 Hz, phenyl-H3), 8.85
N-(2-Iod oben zyl)-N′-[4-(1H-im id a zol-4-yl)p ip er id in yl]-
th iou r ea Hem ifu m a r a te, 2a . Compound 7 (0.25 g, 0.80
mmol) and 0.3 mL (1.6 mmol) of diisopropylethylamine were
dissolved in 10 mL of ethanol. To this solution was added
dropwise a solution of 0.22 g (0.80 mmol) of 9a in 10 mL of
ethanol. The reaction mixture was stirred at room temperature
for 18 h. The solvent was evaporated under reduced pressure
and the product was isolated by flash column chromatography
with ethyl acetate/methanol/triethylamine (7/2/1) as the eluent
to yield 259 mg (0.61 mmol). The free base was dissolved in
as little methanol as possible and then a saturated solution of
fumaric acid in diethyl ether was added dropwise until the
pH was around 4. The precipitate was filtered off and
recrystallized from methanol/acetone to yield 158 mg (0.33
mmol, 41%) of 2a . Rf (ethyl acetate/methanol/triethylamine:
7/2/1) ) 0.35. Mp ) 150-152 °C. 1H NMR (DMSO-d6): δ )
1.43-1.61 (m, 2H, piperidine-H3ax,5ax), 1.90-2.08 (m, 2H,
piperidine-H3eq,5eq), 3.07-3.25 (m, 4H, piperidine-H2,6), 3.61
(s, 1H, piperidine-H4), 4.64 (bs, 1H, thiourea-NH), 4.77 (d, 2H,
(s, 1H, imidazole-H2). MS: 381 (M + 1), 299, 203, 167, 152,
115, 95, 78. Anal. (C16H19BrN4S‚0.5C4H4O4) C, H, N.
N-(3-Br om oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2e. Compound 9e (71 mg, 0.31
mmol) was reacted with 100 mg (0.31 mmol) of 7 according to
the same procedure as for 2a to yield 67 mg (0.15 mmol, 48%)
of 2e. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.35.
1
Mp ) 138-139 °C. H NMR (CD3OD): δ ) 1.55-1.70 (m, 2H,
piperidine-H3ax,5ax), 2.00-2.10 (m, 2H, piperidine-H3eq,5eq),
2.91-3.15 (m, 1H, piperidine-H4), 3.13-3.26 (m, 4H, piperi-
dine-H2,6), 4.84 (s, 2H, CH2), 6.45 (s, 1H, fumaric acid), 6.96
(s, 1H, imidazole-H5), 7.06 (t, 3J ) 7.7 Hz, 1H, phenyl-H5),
7.32 (d, 3J ) 7.7 Hz, 1H, phenyl-H6), 7.57 (d, 3J ) 7.8 Hz,
phenyl-H4), 7.69 (s, 1H, phenyl-H2), 7.91 (s, 1H, imidazole-
H2). 13C NMR (CD3OD): δ ) 34.7 (CH2), 48.9 (piperidine-3),
49.1 (piperidine-5), 49.4 (piperidine-6), 49.8 (piperidine-2),
116.0 (piperidine-5), 123.2 (phenyl-3), 127.4 (phenyl-6), 130.8
(phenyl-5), 131.1 (phenyl-4), 131.5 (phenyl-2), 135.4 (piperi-
dine-4), 140.2 (piperidine-2), 143.6 (phenyl-1), 182.8 (CdS).
MS: 381 (M + 1), 363, 320, 299, 259, 205, 194, 152. Anal.
(C16H19BrN4S‚0.5C4H4O4) C, H, N.
3
2J ) 13 Hz, CH2), 6.52 (s, 1H, fumaric acid), 6.97 (t, J ) 7.5,
1H, phenyl-H5), 7.08 (d, 3J ) 6.8 Hz, 1H, phenyl-H4), 7.31 (d,
3J ) 7.4 Hz, 1H, phenyl-H6), 7.49 (s, 1H, imidazole-H5), 7.78
3
(d, J ) 6.8 Hz, 1H, phenyl-H3), 8.37 (bs, 1H, imidazole-NH),
N-(4-Br om oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2f. Compound 9f (71 mg, 0.31
mmol) was reacted with 100 mg (0.31 mmol) of 7 according to
the same procedure as for 2a to yield 98 mg (0.22 mmol, 71%)
of 2f. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.39.
9.07 (s, 1H, imidazole-H2). 13C NMR (MeOD): δ 32.7 (piperi-
dine-4), 35.6 (CH2), 49.4 (piperidine-5), 49.7 (piperidine-3), 50.1
(piperidine-6), 55.4 (piperidine-2), 98.5 (phenyl-2), 115.7 (imid-
azole-5), 129.2 (phenyl-4), 129.7 (phenyl-6), 135.8 (imidazole-
4), 138.4 (imidazole-2), 140.4 (phenyl-3), 142.1 (phenyl-1). Anal.
(C16H19IN4S‚0.5C4H4O4) C, H, N.
1
Mp ) 145-147 °C. H NMR (CD3OD): δ ) 1.50-1.72 (m, 2H,
piperidine-H3ax,5ax), 1.89-2.07 (m, 2H, piperidine-H3eq,5eq),
2.85-3.02 (m, 1H, piperidine-H4), 3.12-3.24 (m, 4H, piperi-
dine-H2,6), 4.88 (s, 2H, CH2), 6.49 (s, 1H, fumaric acid), 6.88
N-(3-Iod oben zyl)-N′-[4-(1H-im id a zol-4-yl)p ip er id in yl]-
th iou r ea Hem ifu m a r a te, 2b. Compound 9b (88 mg, 0.31
mmol) was reacted with 7 (100 mg, 0.31 mmol) according to
the same procedure as for 2a to yield 75 mg (0.15 mmol, 48%)
3
(s, 1H, imidazole-H5), 7.26 (d, J ) 7.3 Hz, 2H, phenyl-H2,6),
7.44 (d, 3J ) 7.3 Hz, 1H, phenyl-H3,5), 7.70 (s, 1H, imidazole-

1760 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 9
Windhorst et al.
H2). 13C NMR (CD3OD): δ ) 29.5 (CH2), 31.5 (piperidine-4),
48.0 (piperidine-3,5), 52.0 (piperidine-2,6), 112.7 (phenyl-4),
115.0 (imidazole-5), 128.6 (phenyl-3,5), 131.1 (phenyl-2,6),
134.5 (phenyl-1), 139.8 (imidazole-4), 145.6 (imidazole-2), 181.4
(CdS). MS: 381 (M + 1), 296, 256, 242, 217, 211, 203, 196,
164, 152, 146, 97. Anal. (C16H19BrN4S‚0.5C4H4O4) C, H, N.
of 2m . Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.42.
1
Mp ) 120-124 °C. H NMR (CD3OD): δ ) 1.55-1.83 (m, 2H,
piperidine-H3ax,5ax), 2.10-2.29 (m, 2H, piperidine-H3eq,5eq),
3.02-3.44 (m, 5H, piperidine-H2,4,6), 4.81 (s, 2H, CH2), 6.40
(s, 1H, fumaric acid), 7.19-7.57 (m, 5H, phenyl-H + imidazole-
H5), 8.55 (s, 1H, imidazole-H2). MS: 319 (M + 1), 164, 152,
146, 113, 96, 86. Anal. (C16H19FN4S‚0.5C4H4O4) C, H, N.
N-Ben zyl-N′-[4-(1H-im id a zol-4-yl)p ip er id in yl]th iou r ea
Hem ifu m a r a te, 2m . Compound 9m (149 mg, 1.00 mmol) was
reacted with 313 mg (1.00 mmol) of 7 according to the same
procedure as for 2a to yield 125 mg (0.35 mmol, 35%) of 2m .
Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.30.
N-(2-Ch lor oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2g. Compound 9g (57 mg, 0.31
mmol) was reacted with 100 mg (0.31 mmol) of 7 according to
the same procedure as for 2a to yield 75 mg (0.19 mmol, 62%)
of 2g. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.41.
1
Mp ) 124-125 °C. H NMR (CD3OD): δ ) 1.55-1.78 (m, 2H,
1
Mp ) 161-165 °C. H NMR (CD3OD): δ ) 1.60-1.78 (m, 2H,
piperidine-H3ax,5ax), 1.88-2.07 (m, 2H, piperidine-H3eq,5eq),
3.04-3.34 (m, 3H, piperidine-H2ax,4,6ax), 4.70-4.90 (m, 2H,
piperidine-H2eq,6eq), 4.85 (s, 2H, CH2), 6.42 (s, 1H, fumaric
acid), 7.21-7.41 (m, 4H, phenyl-H), 7.45 (s, 1H, imidazole-H5),
8.25 (s, 1H, imidazole-H2). Anal. (C16H19ClN4S‚0.5C4H4O4) C,
H, N.
piperidine-H3ax,5ax), 2.15-2.36 (m, 2H, piperidine-H3eq,5eq),
2.99-3.30 (m, 5H, piperidine-H2,4,6), 4.51 (s, 2H, CH2), 6.46
(s, 1H, fumaric acid), 6.99 (s, 1H, imidazole-H5), 7.25-7.48
(m, 4H, phenyl-H), 8.34 (s, 1H, imidazole-H2). MS: 301 (M +
1), 180, 154, 152, 144, 126, 112, 98, 86, 78. Anal. (C16H20N4S‚
0.5C4H4O4) C, H, N.
N-(3-Ch lor oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2h . Compound 9h (57 mg, 0.31
mmol) was reacted with 100 mg (0.31 mmol) of 7 according to
the same procedure as for 2a to yield 98 mg (0.25 mmol, 81%)
of 2h . Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.38.
N-(2-ter t-Bu tylben zyl)-N′-[4-(1H-im id a zol-4-yl)p ip er i-
d in yl]th iou r ea , 2n . Compound 9n (1.03 g, 5.00 mmol) was
reacted with 1.57 g (5.0 mmol) of 7 according to the same
procedure as for 2a to yield 170 mg (0.48 mmol, 10%) of 2n .
The free base was recrystallized from ethyl acetate. Rf (ethyl
acetate/methanol: 3/1) ) 0.39. Mp ) 197-199 °C. 1H NMR
(CDCl3): δ ) 1.35 (s, 9H, tert-butyl), 1.51-1.75 (m, 2H,
piperidine-H3ax,5ax), 1.95-2.15 (m, 2H, piperidine-H3eq,5eq),
2.61-2.96 (m, 1H, piperidine-H4), 3.01-3.23 (m, 2H, piperi-
dine-H2ax,6ax), 4.50-4.65 (m, 2H, piperidine-H2eq,6eq), 4.91 (d,
3J ) 4.3 Hz, CH2), 5.50 (bs, 0.9H, NH), 6.63 (s, 1H, imidazole-
H5), 7.05-7.25 (m, 3H, phenyl-H4,5,6), 7.30-7.40 (m, 1H,
phenyl-H3), 7.48 (d, 4J ) 1.2 Hz, imidazole-H2). 13C NMR (CD3-
OD): δ ) 20.4 (CH3), 30.6 (CH2), 33.1 (piperidine-4), 35.6 (tert-
butyl-C), 47.5 (piperidine-3,5), 49.5 (piperidine-2,6), 113.5
(imidazole), 126.4 (phenyl), 127.7 (phenyl), 131.5 (phenyl),
134.5 (phenyl), 135.6 (imidazole-4), 138.6 (phenyl-2), 148.6
(phenyl-1), 181.0 (CdS). Anal. (C20H28N4S) C, H, N.
1
Mp ) 130-133 °C. H NMR (CD3OD): δ ) 1.56-1.72 (m, 2H,
piperidine-H3ax,5ax), 1.78-2.01 (m, 2H, piperidine-H3eq,5eq),
2.85-3.11 (m, 1H, piperidine-H4), 3.28-3.34 (m, 2H, piperi-
dine-H2ax,6ax), 4.77 (m, 2H, piperidine-H2eq,6eq), 4.93 (s, 2H,
CH2), 6.40 (s, 1H, fumaric acid), 6.81 (s, 1H, imidazole-H5),
7.14-7.30 (m, 3H, phenyl-H4,5,6), 7.34-7.40 (m, 1H, phenyl-
H2), 7.57 (s, 1H, imidazole-H2). Anal. (C16H19ClN4S‚0.5C4H4O4)
C, H, N.
N-(4-Ch lor oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2i. Compound 9i (57 mg, 0.31
mmol) was reacted with 100 mg (0.31 mmol) of 7 according to
the same procedure as for 2a to yield 71 mg (0.18 mmol, 58%)
of 2i. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.45.
1
Mp ) 119-123 °C. H NMR (CD3OD): δ ) 1.56-1.70 (m, 2H,
N-(2-Meth ylben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2o. Compound 9o (163 mg, 1.00
mmol) was reacted with 313 mg (1.00 mmol) of 7 according to
the same procedure as for 2a to yield 204 mg (0.55 mmol, 55%)
of 2o. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.30.
Mp ) 171-172 °C. 1H NMR (DMSO-d6): δ ) 1.41-1.65 (m,
2H, piperidine-H3ax,5ax), 2.14-2.33 (m, 2H, piperidine-H3eq,5eq),
2.72 (s, 3H, CH3), 2.81-3.00 (m, 1H, piperidine-H4), 3.10-
3.20 (m, 2H, piperidine-H2ax,6ax), 4.60-4.80 (m, 4H, piperidine-
H2eq,6eq and CH2), 6.53 (s, 1H, fumaric acid), 6.82 (s, 1H,
imidazole-H5), 7.11-7.30 (m, 4H, phenyl-H), 7.62 (s, 1H,
imidazole-H2), 8.01 (bs, 1H, NH). Anal. (C17H22N4S‚0.5C4H4O4)
C, H, N.
piperidine-H3ax,5ax), 1.90-2.10 (m, 2H, piperidine-H3eq,5eq),
2.90-3.20 (m, 1H, piperidine-H4), 3.23-3.30 (m, 4H, piperi-
dine-H2,6), 4.83 (s, 2H, CH2), 6.42 (s, 1H, fumaric acid), 6.82
(s, 1H, imidazole-H5), 7.20 (d, J ) 7.9 Hz, 2H, phenyl-H2,6),
7.43 (d, J ) 7.9 Hz, 2H, phenyl-H3,5), 7.59 (s, 1H, imidazole-
H2). Anal. (C16H19ClN4S‚0.5C4H4O4) C, H, N.
N-(2-Flu or oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2j. Compound 9j (167 mg, 1.00
mmol) was reacted with 313 mg (1.00 mmol) of 7 according to
the same procedure as for 2a to yield 176 mg (0.47 mmol, 42%)
of 2j. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.48.
1
Mp ) 111-114 °C. H NMR (CD3OD): δ ) 1.62-1.88 (m, 2H,
piperidine-H3ax,5ax), 2.10-2.31 (m, 2H, piperidine-H3eq,5eq),
3.10-3.34 (m, 5H, piperidine-H2,4,6), 4.70 (s, 2H, CH2), 6.49
(s, 1H, fumaric acid), 7.05-7.48 (m, 5H, phenyl-H + imidazole-
H5), 8.34 (s, 1H, imidazole-H2). 13C NMR (CD3OD): δ ) 31.7
(piperidine-4), 38.8 (CH2), 48.9 (piperidine-3,5), 50.3 (piperi-
dine-6), 55,9 (piperidine-2), 115.7 (imidazole-5), 116,2 (phenyl-
3), 125.1 (phenyl-5), 126.0 (phenyl-4), 129.9 (phenyl-6), 131.9
(phenyl-1), 135.2 (imidazole-4), 138.7 (imidazole-2). MS: 319
(M + 1), 287, 285, 234, 194, 164, 152, 126, 115, 102, 186. Anal.
(C16H19FN4S‚0.5C4H4O4) C, H, N.
Ack n ow led gm en t. Franciscus G. J . Custers, An-
drea C. van der Stolpe, and Mohamed-Aziz Gaffar are
greatly acknowledged for the synthesis of 7, 2n , and 2o,
respectively. The research of Dr. Rob Leurs was made
possible by a fellowship from the Royal Netherlands
Academy of Arts and Sciences.
Refer en ces
N-(3-Flu or oben zyl)-N′-[4-(1H-im idazol-4-yl)piper idin yl]-
th iou r ea Hem ifu m a r a te, 2k . Compound 9k (167 mg, 1.00
mmol) was reacted with 313 mg (1.00 mmol) of 7 according to
the same procedure as for 2a to yield 154 mg (0.41 mmol, 41%)
of 2j. Rf (ethyl acetate/methanol/triethylamine: 7/2/1) ) 0.38.
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Mp ) 128-129 °C. H NMR (CD3OD): δ ) 1.56-1.78 (m, 2H,
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