Novel ligands rationally designed for characterizing I2- imidazoline binding sites nature and functions

Article abstract of DOI:10.1021/jm800400k

The study of two series of 2-aryl-ethylen-imidazolines 3-7 and 8-12 inspired by I₂-IBS ligands phenyzoline (1) and diphenyzoline (2), respectively, confirmed the interesting "positive" or "negative" morphine analgesia modulation displayed by th

Full text of DOI:10.1021/jm800400k

5130
J. Med. Chem. 2008, 51, 5130–5134
Novel Ligands Rationally Designed for Characterizing I2-Imidazoline Binding Sites Nature and
Functions†
Francesco Gentili,‡ Claudia Cardinaletti,‡ Cristian Vesprini,‡ Francesca Ghelfi,‡ Aniket Farande,‡ Mario Giannella,‡
Alessandro Piergentili,‡ Wilma Quaglia,‡ Laura Mattioli,§ Marina Perfumi,§ Alan Hudson,| and Maria Pigini*,‡
Dipartimento di Scienze Chimiche, UniVersita` degli Studi di Camerino, Via S. Agostino 1, 62032 Camerino, Italy, Dipartimento di Medicina
Sperimentale e Sanita` Pubblica, UniVersita` degli Studi di Camerino, Via Madonna delle Carceri, 62032 Camerino, Italy, Department of
Pharmacology, Medical Sciences Building, UniVersity of Alberta, Edmonton, Alberta, Canada
ReceiVed April 7, 2008
The study of two series of 2-aryl-ethylen-imidazolines 3-7 and 8-12 inspired by I2-IBS ligands phenyzoline
(1) and diphenyzoline (2), respectively, confirmed the interesting “positive” or “negative” morphine analgesia
modulation displayed by their corresponding leads and demonstrated that these effects might be correlated
with morphine tolerance and dependence, respectively. By comparative examination of rationally designed
compounds, some analogies between binding site cavity of I2-IBS proteins and R2C-adrenoreceptor emerged.
Chart 1. Imidazolines Structurally Related to Phenyzoline (1)
and Diphenyzoline (2)
Introduction
For over 15 years, the interest of our research group has been
directed to the characterization of the imidazoline binding sites
(IBSa)1 described for the first time by Bousquet in 1984.
Although it has been possible to ascribe the IBS nature to distinct
proteins in human and rat brain, the structures of these binding
proteins have not yet been identified. Nevertheless, the IBS,
classified into I1-IBS and I2-IBS, represent interesting thera-
peutic targets. While the I1-IBS participate in the regulation
of cardiovascular function,1 the I2-IBS appears to be involved
in the Parkinsons’s disease, depression, and modulation of
analgesia as well as tolerance and addiction to opioids.2
Recently, we examined the effect on morphine analgesia
produced by 1 (phenyzoline)3 (Chart 1), which might be
considered as a particularly selective I2-IBS ligand with respect
to I1-IBS and R2-adrenoreceptors (R2-ARs) (pKi I2 ) 8.60; I2/
I1 ) 1479; I2/R2 ) 794)4 and by its ortho phenyl derivative 2
(diphenyzoline) (pKi I2 ) 6.80; I2/I1 ) 40; I2/R2 ) 45), designed
to induce modification of the biological profile of 1.3 The mouse
tail-flick test showed that 1 and 2 significantly enhanced (60%)
and decreased (-41%) morphine analgesia, respectively. The
ability to decrease morphine analgesia had never been observed
before in I2-IBS ligands. Therefore, in the present study, to
confirm the interesting “positive” or “negative” morphine
analgesia modulatory effects observed for 1 and 2, respectively,
and to improve SAR knowledge for better I2-IBS characteriza-
tion, we designed two series of imidazoline molecules: 3-7
and 8-12, based on the leads 1 and 2, respectively (Chart 1).
The already described compounds 3,5 5,6 9,7 and 118 had never
been studied from this point of view. The affinity values of 3-12
at I1-IBS on rat kidney membranes, I2-IBS, and R2-ARs on
rat whole brain membranes were determined. Morphine anal-
gesia modulation was evaluated by the mouse tail-flick test.3
In addition, the lead 1 and imidazoline 9, belonging to the first
and second series, respectively, were examined for their ability
to affect tolerance and dependence development induced by
morphine.
Chemistry
The novel imidazolines 4, 6-8, 10, and 12 were synthesized
according to standard methods (Scheme 1): the imidazolines 4,
6, and 7 by catalytic hydrogenation over Pd/C of the corre-
sponding vinyl precursors, and the imidazoline 8, 10, and 12
by condensation of suitable methyl ester or nitriles with
ethylenediamine in different conditions. The new intermediates
13 and 15 were obtained starting from 3-(2-bromo-phenyl)-
propionic acid or 3-(2-bromo-phenyl)-propionitrile9 with the
suitable commercially available arylboronic acid in the presence
of tetrakis(triphenylphosphine)palladium(0). 14 was obtained by
esterification of 13 with MeOH in presence of H2SO4.
†
This article is dedicated to Dr. Francesco Gentili, who died prematurely
Results and Discussion
at the age of 39.
* To whom correspondence should be addressed. Phone: +39 0737
We have previously demonstrated that the nature of the bridge
between the aromatic portion and imidazoline nucleus played
a crucial role for IBS or R2-ARs selective recognition.4
Therefore, the unsubstituted ethylenic bridge, which proved to
be determinant in inducing high I2-IBS selectivity with regard
to I1-IBS and R2-ARs, was present in all the designed
derivatives. No modification was performed on the imidazoline
402257. Fax: +39 0737 637345. E-mail:maria.pigini@unicam.it.
‡
Dipartimento di Scienze Chimiche, Universita` degli Studi di Camerino.
Dipartimento di Medicina Sperimentale e Sanita` Pubblica, Universita`
§
degli Studi di Camerino.
|
Department of Pharmacology, University of Alberta.
a Abbreviations: IBS, imidazoline binding sites; R2-ARs, R2-adrenore-
ceptors; DA, dopamine; DME, 1,2-dimethoxyethane; MPE, maximum
possible effect.
10.1021/jm800400k CCC: $40.75
2008 American Chemical Society
Published on Web 07/29/2008

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5131
Scheme 1a
involvement of I2-IBS in the morphine analgesia modulatory
effects of 1 and 2 has been demonstrated. In fact, these effects
were not affected by treatment of animals with yohimbine
(selective R2-AR antagonist) or Efaroxan (I1-IBS/R2-AR
antagonist) but were completely reversed by treatment with
idazoxan (I2-IBS/R2-AR antagonist). In addition, 1 and 2
proved to be inactive at all three R2-AR subtypes.3 Therefore,
I2-IBS selectivity with regard to I1-IBS and R2-ARs, observed
in 3-12, and the correlation of the 3-7 series with 1 and 8-12
series with 2, supported the involvement of I2-IBS in the
morphine analgesia modulatory effects of 3-12. The above
results, confirming what was observed for 1 and 2, demonstrated
that the introduction of substituents in the ortho position of the
aromatic ring of 1 induced significant change of its morphine
analgesia modulation.
In previous contributions from our laboratory, we demon-
strated that the introduction of pendant groups in the ortho
position of the aromatic ring of the R2-AR ligand 2-(1-phenoxy-
ethyl)-4,5-dihydro-1H-imidazole, structurally related to 1, caused
decisive biological profile modulation; in this case, from
antagonist to agonist behavior was induced (biphenyline and
analogues).12,13 This observation allows us to suggest that R2-
AR and I2-IBS ligands might interact with their corresponding
binding sites in a similar fashion. In particular, in the above-
mentioned biphenyline series, the interactions formed between
the ortho phenyl or methyl (results not published) or 3-nitro-
phenyl or 3-thienyl pendant groups and the aromatic cluster
present in transmembrane domain 6 of the R2-AR binding cavity
proved to be favorable to trigger high R2C-subtype activation.
Methyl or 3-nitrophenyl groups selectively activated the R2C-
subtype.13 As above-reported, the same ortho phenyl, 3-nitro-
phenyl, methyl, and 3-thienyl pendant groups (compounds 2,
8, 9, and 12, respectively) induced also a change of the
modulatory effect on morphine analgesia displayed by the
unsubstituted precursor 1. Therefore, we suggest that the I2-IBS
proteins amino acid residues domain interacting with the
hydrophobic portions of the I2-IBS ligands might share some
degree of homology with the corresponding aromatic cluster
involved in the R2C-AR activation.13 Moreover, if the pendant
groups, interacting with hydrophobic residues, would lead to
receptor activation, it might be reasonable, as previously
reported,3 to define the I2-IBS ligands 8-12 as “putative
agonists” and, consequently, the compounds 3-7 as “putative
inverse agonists”.
a Reagents: (a) Na2CO3, Pd[(C6H5)3P]4, DME; (b) MeOH, H2SO4; (c)
(CH3)3Al, dry toluene, ethylenediamine, ∆; (d) H2, Pd/C; (e) HClg, MeOH,
ethylenediamine.
nucleus, as the previous observations indicated that the C- or
N-substitution, in structurally related compounds, was detri-
mental for I2-IBS affinity and selectivity.10,11 Consequently,
the derivatives of the two series (3-7 and 8-12) showed
differences exclusively on the aromatic portion (Chart 1). In
this portion, a 2D- and 3D-quantitative SAR study, performed
on a series of imidazoline congeners (tracizoline derivatives),
highlighted that good lipophilicity, extended also to the ortho
position of the phenyl ring, was favorable but not decisive for
significant I2-IBS affinity.7 Consequently, in the designed
imidazoline molecules, the phenyl ring R1 of 1 or the ortho
pendant phenyl group R2 of 2 were replaced by functions of
different lipophilic character (compounds 3-7 and 8-12,
respectively). In particular, among the derivatives of 2 (diphenyzo-
line), as previously made for it,3 the compounds 8, 9, and 12
were rationally designed to verify our hypothesis that I2-IBS
and R2-ARs might present analogies in the nature and orientation
of some critical binding functions.
Among the many approaches investigated to overcome the
undesired side effects of opiate drugs, the synergism with
I2-IBS mediated antinociceptive mechanisms has been re-
ported.2 Therefore, to find new possible therapeutic coadjuvants
in the management of chronic pain with opiate drugs, we wished
to evaluate the effects of the observed I2-IBS mediated
“positive” or “negative” morphine analgesia modulation on
opioid tolerance and dependence. In this study, 1 and 9 were
selected due to their very high I2-IBS affinity and significant
modulatory activity. Analogously to what previously made for
1 and 2,3 the selective involvement of I2-IBS in the morphine
analgesia modulatory effect of 9 has been confirmed (Supporting
Information, Figure 5). Interestingly, both “positive” and
“negative” modulation of the morphine analgesia was found to
attenuate the development of side effects. In particular, in mice
receiving morphine (twice daily for 5 days), the tolerance
development determined the lack of morphine antinociceptive
effect on day 5. In contrast, the pretreatment with 1 inhibited
the tolerance expression phases, and the antinociceptive effect
observed proved similar to that of the morphine alone treated
The affinity and calculated logP values of 1-12, reported in
Table 1, indicated that the presence of portions endowed with
good lipophilicity such as thiophen-2-yl (3), naphthalen-1-yl (5),
cyclohexyl (6), o-tolyl (9), 2-chloro-phenyl (10), and 2-thiophen-
3-yl-phenyl (12) induced in the ligands the highest I2-IBS
affinities. Lower I2-IBS affinities were produced by the
presence of polar portions such as 1H-pyrrol-2-yl (4), 3-pyridyl
(7), and 2-hydroxy-phenyl (11). Although the 3′-nitrobiphenyl-
2-yl (8) and biphenyl-2-yl (2) fractions displayed good lipo-
philicity, they negatively affected I2-IBS affinity, probably
owing unfavorable steric hindrance. The novel derivatives,
except 8, displayed significant I2-IBS selectivity. The data
obtained by the in vivo study corresponded to our expectations.
Indeed, analogously to 1, the compounds of the first series 3-7
exhibited no antinociceptive effect by themselves but increased
morphine analgesia (34, 14, 16, 30, and 23%, respectively)
(Figure 1). The compounds of the second series 8-12, lacking
in analgesic effect by themselves, analogously to 2, reduced
morphine analgesia (-29, -44, -34, -26, and -59%, respec-
tively) (Figure 2). In the previous study,3 the unambiguous

5132 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Brief Articles
Table 1. Binding Affinities,a Selectivity Ratios,b and Calculated logPc of Compounds 1-12
compd
I1-IBSIC50 (nM)
I2-IBSKi (nM)
R2-ARs Ki (nM)
I1/I2 selectivity ratio
R2/I2 selectivity ratio
calcd logP
1
2
3
4
5
6
7
8
3697 ( 230d
6340 ( 272d
2877 ( 592
23890 ( 3829
25812 ( 6017
3569 ( 841
211600 ( 2984
3998 ( 663
7360 ( 898
4255 ( 952
2.5 ( 0.49
158.5 ( 10.3
7.72 ( 1.64
254.3 ( 62.1
1.16 ( 0.32
4.8 ( 0.49
413.6 ( 66.1
251.9 ( 60.1
1.68 ( 0.2
1985 ( 200
7132 ( 250
819.9 ( 131.8
3540 ( 600
381.0 ( 27.1
2962 ( 683
64773 ( 8069
1117.9 ( 436.3
557.7 ( 77.1
295.4 ( 58.2
925.9 ( 163.7
292.7 ( 40.6
1479
40
372.6
94
22252
743.5
511.6
16.0
4381
2836.6
99.3
794
45
2.71
4.47
2.39
1.24
3.94
3.64
1.22
4.00
3.17
3.31
1.98
4.15
106.2
13.9
328.4
617.1
156.6
4.4
332.0
196.9
12.6
32.9
9
10
11
12
1.5 ( 0.9
73.5 ( 12.9
8.89 ( 2.74
7301 ( 1308
6891 ( 868
775.1
a Data for I1-IBS affinity were determined on rat kidney membranes and values expressed in IC50 values (the concentration of ligand that inhibits 50%
of specific binding). I2-IBS and R2-ARs binding was determined on rat brain membranes and values are expressed as Ki values. Data represent the mean
( SEM of 3-5 separate experiments performed in triplicate. b I1/I2 and R2/I2 are the ratios of I1-IBS IC50 and R2-ARs Ki, respectively, to I2-IBS Ki. c Data
from ACD/logP DB version. d Ki values performed on rat pheochromocytoma cells, PC 12.
Figure 1. Effects of 3-7 (10 mg/kg, sc) on morphine (5.0 mg/kg, sc) analgesia in the tail flick test. The reaction latencies were expressed as a
percent of the maximum possible effect (%MPE). To avoid tissue damage, a cutoff latency of 12-15 s was used. Each mouse was tested 1 and
0.5 h before vehicle or compound administration to determine baseline latency. Then mice were sc administered with compounds 3-7 or related
vehicle. Morphine (5.0 mg/kg) or its vehicle were sc administered 30 min later. The antinociceptive activity was evaluated 30 min after morphine
injection. Each column represents the mean ( SEM of 8-10 animals. Significant differences: *p < 0.05, **p < 0.01 compared to morphine treated
group; where not indicated, the difference was not statistically significant.
group on day 1. Pretreatment with 9 proved ineffective (Figure
3). In mice treated with morphine (twice daily for 6 days to
induce opioid dependence), on day 6, the naloxone injection
induced severe signs of withdrawal syndrome, as manifested
by jumping behavior. Interestingly, in mice coadministered with
9, withdrawal signs were significantly reduced (-39%). The
reduction induced by 1 proved less significant (Figure 4). It
has been reported that BFI, currently considered a ligand of
choice for the I2-IBS study, was able to enhance morphine-
induced analgesia14 and displayed central dopamine (DA)
releasing/deplete properties.15 Therefore, to extend our study
and discover novel I2-IBS ligands potentially useful in the
treatment of the DA system alterations on our most interesting
I2-IBS ligands, we intend to investigate the possible correlations
between the ability to modulate the morphine analgesia with
its side effects and influence on DA system functional relevance.
In conclusion, the aryl-ethylen-imidazoline molecules of the
present study (i) extended the knowledge of the ligand structural
characteristics, such as good lipophilicity and suitable steric
hindrance, compatible with significant I2-IBS affinity and
selectivity; (ii) confirmed our previous observation that I2-IBS
ligands, depending on their structure, might behave as “putative
inverse agonists” or “putative agonists”; (iii) demonstrated that
the corresponding effects of morphine analgesia enhancement
or decrease might be correlated with morphine tolerance or
dependence, respectively. Finally, the comparative examination
of rationally designed compounds pointed out some significant
analogies between binding site cavity of I2-IBS proteins and
R2C-AR subtype.
Experimental Section
2-(2-Cyclohexyl-ethyl)-4,5-dihydro-1H-imidazole (6). A solution
of 2-((E)-2-cyclohexyl-vinyl-4,5-dihydro-1H-imidazole7 (0.57 g, 3.2
mmol) in MeOH was hydrogenated for 3 h at rt under pressure (40
psi) using 10% Pd/C (0.6 g) as catalyst. Following catalyst removal
and evaporation of the solvent, the residue was purified by flash
chromatography eluting with CHCl3/MeOH/33% NH4OH (9:1:0.1)
to give the free base (0.54 g, 94% yield), which was transformed
into the oxalate salt and crystallized from EtOH: mp 130-131 °C.
1H NMR (DMSO) δ 0.78-1.72 (m, 13H, C6H11-CH2), 2.45 (m,
2H, CH2), 3.84 (s, 4H, NCH2CH2N), 7.85 (br s, 1H, NH,
exchangeable with D2O). Anal. (C11H20N2 ·H2C2O4) C, H, N.

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5133
Figure 2. Effects of 8 (20 mg/kg) and 9-12 (10 mg/kg) on morphine (5.0 mg/kg, sc) analgesia in the tail-flick test. The reaction latencies were
expressed as a percent of the maximum possible effect (%MPE). To avoid tissue damage, a cutoff latency of 12-15 s was used. Each mouse was
tested 1 and 0.5 h before vehicle or compound administration to determine baseline latency. Then mice were sc administered with compounds
8-12 or related vehicle. Morphine (5.0 mg/kg) or its vehicle were sc administered 30 min later. The antinociceptive activity was evaluated 30 min
after morphine injection. Each column represents the mean ( SEM of 8-10 animals. Significant differences: **p < 0.01 compared to morphine
treated group; where not indicated, the difference was not statistically significant.
Figure 3. Effects of repeated coadministration of 1 and 9 (10 mg/kg)
with morphine on the development of morphine tolerance to analgesia
in mice. Morphine was sc injected twice daily for 5 days at the dose
Figure 4. Effects of repeated coadministration of 1 and 9 (10 mg/kg,
of 10 mg/kg (except for the day of the test when the dose of 5 mg/kg
sc) with morphine (10 mg/kg, sc) on naloxone-precipitated withdrawal
has been used). Compounds 1 and 9 were repeatedly administered 30
syndrome. I2-imidazoline compounds were repeatedly administered, 30
min before every morphine treatment. Morphine antinociceptive effect
min before every morphine treatment, twice daily for 5 days. On the
was assessed both on day 1 and on day 5. Significant differences: *p
sixth day, I2-imidazoline compounds and naloxone (5 mg/kg, ip) were
< 0.05, **p < 0.01 compared to morphine-treated mice; where not
administered 30 min before and 2 h after morphine treatment,
indicated, the difference was not statistically significant.
respectively. The development of dependence on morphine was
determined by frequency of the precipitate withdrawal signs (expressed
as jumping) for 15 min after naloxone injection. Significant differences:
**p < 0.01 compared to morphine-treated mice.
2-[2-(1H-Pyrrol-2-yl)-ethyl]-4,5-dihydro-1H-imidazole (4). This
was prepared from 2-[(E)-2-(1H-pyrrol-2-yl)-vinyl]-4,5-dihydro-
1H-imidazole7 via the procedure described for 6. The reaction
mixture was purified by flash chromatography, and the free base
(85% yield) was transformed into the hydrochloride salt, which
was crystallized from EtOH: mp 146-148 °C. 1H NMR (DMSO)
δ 2.58 (t, 2H, CH2CdN), 2.82 (t, 2H, CH2), 3.62 (s, 4H,
NCH2CH2N), 5.72-6.58 (m, 3H, ArH), 10.68 (br s, 2H, NH,
exchangeable with D2O). Anal. (C9H13N3 ·HCl) C, H, N.
3-[2-(4,5-Dihydro-1H-imidazol-2-yl)-ethyl]-pyridine (7). This was
prepared from 3-[(E)-2-(4,5-dihydro-1H-imidazol-2-yl)-vinyl]-py-
ridine16 via the procedure described for 6. The reaction mixture
was purified by flash chromatography, and the free base (95% yield)
was transformed into the oxalate salt, which was crystallized from
EtOH: mp 140-141 °C. 1H NMR (DMSO) δ 2.80 (t, 2H,
CH2CdN), 3.98 (t, 2H, CH2), 3.88 (s, 4H, NCH2CH2N), 7.32-8.44
(m, 4H, ArH), 10.18 (br s, 1H, NH, exchangeable with D2O). Anal.
(C10H13N3 ·H2C2O4) C, H, N.
2-[2-(3′-Nitro-biphenyl-2-yl)-ethyl]-4,5-dihydro-1H-imidazole (8).
A solution of ethylenediamine (0.42 mL, 6.28 mmol) in dry toluene
(6 mL) was added dropwise to a mechanically stirred solution of 2
M trimethylaluminum (3.2 mL, 6.28 mmol) in dry toluene (4 mL)
at 0 °C in nitrogen atmosphere. After being stirred at rt for 1 h, the
solution was cooled to 0 °C, and a solution of 14 (0.90 g; 3.14
mmol) in dry toluene (8 mL) was added dropwise. The reaction
mixture was heated to 110 °C for 3 h, cooled to 0 °C, and quenched
cautiously with MeOH (0.8 mL) followed by H2O (0.2 mL). After
addition of CHCl3 (5 mL), the mixture was left for 30 min at rt.
The mixture was filtered and the organic layer was extracted with

5134 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Brief Articles
2N HCl. The aqueous layer was made basic with 10% NaOH and
extracted with CHCl3. Removal of dried solvent gave a residue
that was purified by flash chromatography to give the free base
(0.48 g, 52% yield). The oxalate salt was crystallized from EtOH:
Supporting Information Available: Chemical methodology,
biological experiments and elemental analysis results. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
mp 180-182.2 °C. H NMR (DMSO) δ 2.62 (t, 2H, CH2CdN),
References
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(C11H13N3O2 ·H2C2O4 ·0.5H2O) C, H, N.
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Garzon, J. Activation of I2-imidazoline receptors enhances supraspinal
morphine analgesia in mice: a model to detect agonist and antagonist
activities at these receptors. Br. J. Pharmacol. 2000, 130, 146–152.
(15) Sastre-Coll, A.; Esteban, S.; Miralles, A.; Zanetti, R.; Garcia-Sevilla,
J. A. The imidazoline receptor ligand 2-(2-benzofuranyl)-2-imidazoline
is a dopamine-releasing agent in the rat striatum in vivo. Neurosci.
Lett. 2001, 301, 29–32.
2-[2-(2-Chloro-phenyl)-ethyl]-4,5-dihydro-1H-imidazole (10).
HCl was bubbled through the stirred and cooled (0 °C) solution of
3-(2-chloro-phenyl)-propionitrile (0.89 g, 5.35 mmol) in MeOH
(0.43 mL) and dry CHCl3 (9.3 mL) for 45 min. After 12 h at 0 °C,
the solvent was removed in vacuo to give an oil (0.61 g, 2.60 mmol)
that was dissolved in absolute EtOH and added to a cooled (0 °C)
and stirred solution of ethylenediamine (0.22 mL, 3.24 mmol) in
absolute EtOH (12.5 mL). After 1 h, concentrated HCl (0.11 mL)
was added to the reaction mixture, which was stored overnight in
the refrigerator. The crude residue was then diluted with absolute
EtOH (8.6 mL) and heated to 70 °C for 5 h. After cooling, the
solid was collected and discarded and the filtrate was concentrated
and filtered again. The filtrate, evaporated to dryness, gave a residue
that was taken up in CHCl3 (20 mL) and washed with 2N NaOH.
Removal of the dried solvent gave a residue that was purified by
flash chromatography to give the free base (0.40 g, 36% yield over
all). The hydrochloride salt was crystallized from EtOH: mp
157.7-159 °C. 1H NMR (DMSO) δ 2.82 (t, 2H, CH2CdN), 3.12
(t, 2H, CH2), 3.81 (s, 4H, NCH2CH2N), 7.30-7.52 (m, 4H, ArH),
10.18 (br s, 1H, NH, exchangeable with D2O). Anal.
(C11H13ClN2 ·HCl·0.33H2O) C, H, N.
2-[2-(2-Thiophen-3-yl-phenyl)-ethyl]-4,5-dihydro-1H-imidaz-
ole (12). This was prepared from 15 via the procedure described
for 10. The purification by flash chromatography gave the free base
(42% yield), which was transformed into the oxalate salt and
1
crystallized from EtOH: mp 200.3-202.6 °C. H NMR (DMSO)
δ 2.68 (t, 2H, CH2CdN), 2.98 (t, 2H, CH2), 3.78 (s, 4H,
NCH2CH2N), 7.20-7.68 (m, 7H, ArH), 9.66 (br s, 1H, NH,
exchangeable with D2O). Anal. (C15H16N2S·H2C2O4 ·0.25H2O) C,
H, N.
3-(3′-Nitro-biphenyl-2-yl)-propionic acid methyl ester (14).
Na2CO3 (1.13 g, 10.7 mmol), H2O (5.35 mL), and tetrakis-
(triphenylphosphine)palladium(0) (0.255 g, 0.221 mmol) were added
to a solution of 3-(2-bromo-phenyl)-propionic acid (1.00 g, 4.42
mmol) and 3-nitrophenylboronic acid (0.92 g, 5.52 mmol) in DME
(8 mL). The mixture was heated at 90 °C for 14 h in the dark
under nitrogen atmosphere. After cooling to rt the mixture was
poured into AcOEt and ice, acidified and extracted with AcOEt.
Removal of dried solvent gave the 3-(3′-nitro-biphenyl-2-yl)-
propionic acid (13) (0.68 g, 2.51 mmol). 1H NMR (CDCl3) δ 2.52
(t, 2H, CH2), 2.72 (t, 2H, CH2-Ar), 7.22-8.30 (m, 8H, ArH), 11.04
(br s, 1H, COOH, exchangeable with D2O).
13 was converted into the corresponding methyl ester by heating
in CH3OH in the presence of a catalytic amount of H2SO4. After
purification by flash chromatography eluting with cyclohexane/
AcOEt (95:5) compound 14 was obtained as an oil (0.71 g, 2.49
mmol; yield over all 56%). 1H NMR (CDCl3) δ 2.44 (t, 2H, CH2),
2.92 (t, 2H, CH2-Ar), 3.62 (s, 3H, OCH3), 7.18-8.27 (m, 8H,
ArH).
3-(2-Thiophen-3-yl-phenyl)-propionitrile (15). This was prepared
from 3-(2-bromo-phenyl)-propionitrile9 (0.93 g, 4.42 mmol) and
3-thiophenboronic acid (0.7 g, 5.52 mmol) via the procedure
described for 13. Compound 15 was obtained as an oil (60% yield).
1H NMR (CDCl3) δ 2.43 (t, 2H, CH2), 3.04 (t, 2H, CH2-Ar),
7.08-7.43 (m, 7H, ArH).
(16) Ferretti, G.; Dukat, M.; Giannella, M.; Piergentili, A.; Pigini, M.;
Quaglia, W.; Damaj, M. I.; Martin, B. R.; Glennon, R. A. Homoa-
zanicotine: a structure-affinity study for nicotinic acetylcholine (nACh)
receptor binding. J. Med. Chem. 2002, 45, 4724–4731.
Acknowledgment. We thank the MIUR (Rome) and the
University of Camerino.
JM800400K