3-[5-(4,5-Dihydro-1H-imidazol-2-yl)-furan-2-yl]phenylamine (Amifuraline), a promising reversible and selective peripheral MAO-A inhibitor

Article abstract of DOI:10.1021/jm060605r

On the basis of the observation that the central side effects of MAO inhibitors may represent a major limit for their use in pathological processes involving peripheral MAOs, we investigated the possibility of generating novel inhibitors able to target sp

Full text of DOI:10.1021/jm060605r

5578
J. Med. Chem. 2006, 49, 5578-5586
3-[5-(4,5-Dihydro-1H-imidazol-2-yl)-furan-2-yl]phenylamine (Amifuraline), a Promising
Reversible and Selective Peripheral MAO-A Inhibitor
Francesco Gentili,§ Nathalie Pizzinat,† Catherine Ordener,† Sophie Marchal-Victorion,† Agne`s Maurel,† Robert Hofmann,‡
Pierre Renard,‡ Philippe Delagrange,‡ Maria Pigini,§ Angelo Parini,† and Mario Giannella*,§
Dipartimento di Scienze Chimiche, UniVersita` degli Studi di Camerino, Via S. Agostino 1, 62032 Camerino, Italy, INSERM U 388,
Institut Louis Bugnard. IFR31, CHU Rangueil, 1 aVenue Jean Poulhes, 31403 Toulouse, France, and ADIR, 1, rue Carle He´bert,
92415 CourbeVoie Cedex (France)
ReceiVed May 22, 2006
On the basis of the observation that the central side effects of MAO inhibitors may represent a major limit
for their use in pathological processes involving peripheral MAOs, we investigated the possibility of generating
novel inhibitors able to target specifically peripheral MAOs. To address this issue, we designed compounds
7-28. From biological results, the 2-(5-phenyl-furan-2-yl)-4,5-dihydro-1H-imidazole (Furaline, 17) proved
to be a suitable lead. In fact, in enzyme assays on homogenate preparation from rat liver and HEK cells
expressing MAO-A or MAO-B, compounds possessing the frame of 17 behaved as selective and reversible
MAO-A inhibitors. Interestingly, in in vivo studies the amino derivative 21 (Amifuraline), endowed with
good hydrophilic character, was able to significantly inhibit liver but not brain MAO-A.
Introduction
the potential cytotoxic effect of H2O2 in nigral cells in
Parkinson’s disease,12 the cell events following MAO-dependent
H2O2 production in physiological conditions are still unknown.
In a first series of results, we showed that in various peripheral
living cells, including renal mesangial and proximal tubule cells,
degradation of small quantities of substrate by MAO-A or
MAO-B induces H2O2 production that was not fully scavenged
by intracellular antioxidants and therefore may behave as an
intracellular messenger.13 This possibility was confirmed by
further experiments showing that, depending on concentrations,
H2O2 produced by MAOs is responsible for the receptor-
independent proliferative and apoptotic effects of dopamine.10,11
The relevance of this novel MAO mechanism of action in vivo
was demonstrated in a model of renal ischemia-reperfusion in
which animal treatment with a MAO inhibitor largely prevented
the post-reperfusion oxidative stress and renal damage.14 These
findings, along with other results showing the important role
of ROS generated by MAOs in heart,15 adipose tissue,16
macrophages,17 and skeletal muscle,18 pointed to the relevance
of peripheral MAOs in various pathological processes and their
potentiality as pharmacological targets.
Monoamine oxidase inhibitors (MAOIs) have been exten-
sively used in the therapy of psychiatric and neurodegenerative
disorders including Parkinson’s disease, Alzheimer’s dementia,
depression syndrome, and panic disorders.19 However, the use
of these drugs has been limited by some centrally mediated side
effects such as the serotonin syndrome,20 dizziness, light-
headedness, blurred vision, and weakness. In addition, it has
been reported that MAOIs may potentiate the effects of alcohol
and other drugs that slow the central nervous system, such as
antihistamines, cold medicine, allergy medicine, sleep aids,
medicine for seizures, tranquilizers, some pain relievers, and
muscle relaxants.21-23
Monoamine oxidases (MAOs) are FAD-containing enzymes
catalyzing the oxidation of endogenous (e.g. norepinephrine,
dopamine, serotonin) and exogenous amines to the correspond-
ing aldehyde and ammonia.1 Currently, two MAO isoforms,
encoded by separate genes sharing a common intron/exon
organization,1-3 have been identified based on substrate speci-
ficity: MAO-A preferentially metabolizes serotonin and
kynuramine, whereas MAO-B has a greater affinity for phen-
ylethylamine and benzylamine.4 The two MAO isoforms can
be also differentiated according to their inhibition by synthetic
compounds: clorgyline and moclobemide for MAO-A and
selegiline and lazabemide for MAO-B.5
Although MAOs are widely distributed in various organs,
most of the studies concerning their functional properties and
involvement in pathological processes have been mainly focused
on the central nervous system. These studies showed that MAOs
play a major role in regulating brain concentrations of biogenic
amines, and their abnormalities have been involved in various
psychiatric and neurodegenerative disorders.6 In the periphery,
MAO-A and MAO-B are differently expressed in a variety of
organs: MAO-A is predominant in heart, adipose tissue, and
skin fibroblasts, MAO-B is the major form found in platelet
and lymphocytes, whereas both isoenzymes are expressed in
kidney and liver.7
We and other authors have shown that the kidney displays
one of the highest MAO activities.8,9 As reported for the central
nervous system, MAOs regulate the availability of renal
dopamine and serotonin and, consequently, their activity on renal
function. We have recently identified an additional MAO
mechanism of action involving reactive oxygen species (ROS)
production and the consequent induction of intracellular oxida-
tive stress.10,11
These central side effects of MAOIs may represent a major
limit for their use in pathological processes involving peripheral
MAOs. On the basis of this observation, we decided to design
a strategy to synthesize novel MAOIs able to target specifically
peripheral MAOs. In the absence of any accurate SAR studies
which might lead us to suppose structural deviations between
the peripheral and central isoenzymes, our strategy was inspired
Hydrogen peroxide (H2O2) is one of the reaction products
generated by MAOs during substrate degradation. Except for
* To whom correspondence should be addressed. Phone: +39 0737
402257. Fax +39 0737 637345. E-mail: mario.giannella@unicam.it.
§ Universita` degli Studi di Camerino.
† INSERM U 388, Toulouse.
‡ ADIR, Courbevoie Cedex.
10.1021/jm060605r CCC: $33.50 © 2006 American Chemical Society
Published on Web 08/01/2006

Peripheral MAO-A Inhibitor
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18 5579
Chart 3. Furaline Modifications
Chart 1. Structural Formulas of MAO Inhibitors 1-5 and
Dopamine (6)
Chart 2. Imidazoline Derivatives Designed as MAO Inhibitors
first series (7-19) showed great differences in the kind of
substituent inserted at position 2 of the imidazoline ring. In fact,
the aromatic function has been represented either by the simple
phenyl, dihydronaphthalene, or the more hydrophilic azaryl
(pyridine or quinoline) nuclei that, hindering the hemato-
encephalic barrier crossing, prevented central side effects; the
central spacer was represented by alkylic, amidic, as in
moclobemide, and oxygenated (epoxydic or furanic), as in
brofaromine, functions. In particular, the molecules shown in
panel A, clearly inspired by moclobemide (2), allowed us to
evaluate the effects of the distance between the aromatic and
imidazoline functions (compounds 7 and 8) and the increase of
hydrophilicity by substitution of the phenyl with the pyridyl
ring (compound 9). The electronic effects promoted by the
amidic function were partly simulated by a single double bond
(compounds 10-12) or a constraint structure (13 and 14), as
reported in panel B. Instead, the epoxides 15 and 16, and the
furan-2,5-derivative 17, shown in panel C, were inspired by
brofaromine (3). Finally, bifemelane (4) was the model for the
derivatives of panel (D) (compounds 18 and 19).
by known compounds which displayed low toxicity and relative
selectivity, such as 3-(imidazolin-2-yl)thioxanthen-9-one 10,10-
dioxide (1), moclobemide (2), brofaromine (3), bifemelane (4),
and lazabemide (5).24 These inhibitors share a common phar-
macophore, represented by a basic group and a suitably spaced
aryl ring.25 The same structural features are found in dopamine
(6), a MAO-A and MAO-B substrate (Chart 1).
As our major goal was to obtain a novel lead compound, we
designed, prepared, and tested compounds 7-19 (Chart 2, panels
A-D), in which the basic function that supports the primary
interaction at the catalytic site, was simulated by the imidazoline
ring. This choice was made for two reasons: first because this
ring is present in some efficacious MAOIs as, for example, the
already mentioned compound 1,26 and second because the I2-
imidazoline binding sites (I2-IBS) seem allosterically connected
with the MAO isoforms.27 To perform an adequate structure-
activity relationship (SAR) investigation, the compounds of this
Subsequently, on the basis of the obtained results, we
designed, synthesized, and tested the second series of com-
pounds 20-28 (Chart 3). Compounds 7,28 8,29 10 and 13,30 12,31
18,32 and 1933 were already known, but their potential inhibitory
properties toward MAOs had never been described. In addition,
compounds 21, 22 and 25 were carefully studied in vitro and
in vivo assays.
Chemistry. Compounds 15-17, 22, 23, 25, 26, 28, and 30
were synthesized according to standard methods by condensation
of suitable nitriles with ethylenediamine, 1,2-diaminopropane,
or 2,3-diamino-propionic acid methyl ester. [2-(5-Phenyl-furan-
2-yl)-4,5-dihydro-1H-imidazol-4-yl]-methanol (27) was obtained
through a NaBH4 reduction of the corresponding carbomethoxy
derivative 30 (Scheme 1).

5580 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18
Gentili et al.
Scheme 1a
a Reagents: (a) HClg/MeOH; H2NCH(COOCH3)CH2NH2; (b) HClg/MeOH; H2NCH(CH3)CH2NH2; (c) HClg/MeOH; H2NCH2CH2NH2; (d) CH3ONa/
CH3OH, H2NCH2CH2NH2; (e) H2NCH2CH2NH2/TsOH, ∆, (f) NaBH4, EtOH.
Scheme 2a
a Reagents: (a) H2NCH2CH2NH2/∆; (b) Al(CH3)3, toluene, ∆, H2NCH2CH2NH2; (c) H2, Pd/C.
Imidazolines 9, 11, 14, 20, and 24 were synthesized from
suitable methyl esters by treatment with ethylenediamine alone
(compound 9) or in the presence of trimethylaluminum (com-
pounds 11, 14, 20, and 24). 3-[5-(4,5-Dihydro-1H-imidazol-2-
yl)-furan-2-yl]phenylamine (21) was obtained through catalytic
hydrogenation over Pd/C of the corresponding nitro-derivative
20 (Scheme 2).
inhibition of [14C]tyramine oxidation, of compounds 7-19 and
their calculated hydrophilicity (Clog P)34 are reported. Within
this series a significant activity was observed for compounds
13 (40% inhibition at 10 µM) and 17 (50% inhibition at 10
µM). As shown by CLog P, compound 17 displayed a
lipophilicity about 20-fold lower than that calculated for
compound 13. These observations proposed compound 17
(Furaline) as a possible lead for the design of peripheral MAO
inhibitors.
Results and Discussion
Moreover, the I2-IBS affinity value of furaline (17), deter-
mined following previously described procedures,35 was pKi )
7.68. Therefore, the more interesting compounds such as 13
(pKi I2 7.95)36 and 17 showed high I2-IBS affinity. Nevertheless,
since some compounds such as 10 (pKi I2 8.72)36 and 16 (pKi
To select a potential lead, we performed a first screening in
vitro on homogenates from rat liver, a tissue containing MAO-A
and MAO-B, using [14C]tyramine, a common substrate for both
MAO isoenzymes, at two compound concentrations (0.1 and
10 µM). In Table 1 the inhibitory properties, expressed as % of

Peripheral MAO-A Inhibitor
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18 5581
Table 1. MAO Inhibition of Imidazolines 7-19a
of portion X of the ligand is critical for activity: substituents
with electron-withdrawing effects (+σ) in this portion (Chart
3), probably weakening the charge-transfer interaction with the
isoalloxazine nucleus of the flavin cofactor,39 might decrease
inhibitory activity, as observed for the NO2 group (20).
Analogously, the substitution of the phenyl group of furaline
(17) with the pyridine nucleus (28) appears to be unfavorable.
In fact, it is known that the nitrogen atom of the pyridine ring
and the NO2 group of the phenyl ring possess similar polarities
and electron-withdrawing effects. On the contrary, substituents
with null or negative σ values (CH2OH or NH2 group,
respectively), are compatible with the activity (compounds 21
and 22). According to known analogies among pentatomic
systems (furane, thiophene, and pyrrole), the inhibitory activity
does not appear affected by the type of heteroatom of the spacer
(portion Y) (compounds 23 and 24); also the replacement of
the furan ring of the model 17 with the pyridine nucleus,
endowed with basic character, proved to be acceptable (com-
pound 25). Finally, the good activity displayed by 26 allows us
to hypothesize the presence in the enzymatic protein of a little
lipophilic pocket near the site interacting with portion Z of the
ligand.
% inhib of
[14C]tyramine oxidation
compd
0.1 µM
10 µM
calcd Log Pb
ref
7
8
9
0
25
0
0
25
0
0.00
1.30
0.22
1.54
2.90
0.18
2.49
0.48
1.41
0.94
1.14
4.13
4.47
28
29
-
30
-
31
30
-
-
-
-
32
33
10
11
12
13
14
15
16
17
18
19
10
0
0
10
0
25
5
5
5
10
25
5
5
40
0
25
15
50
15
10
a Experiments were performed in liver homogenate preparations. Values
are the means of two experiments performed in triplicate. b Data from ACD/
Labs 7.00 Release. Product Ver. 7.09, 03 Nov. 2003.34
Table 2. MAO Inhibition of Imidazolines 17, 20-28a
% inhib of
[14C]tyramine oxidation
compd
0.1 µM
10 µM
calcd Log Pb
Then, with the aim of defining the role played by new
template 17 in the reversible and selective MAO-A and MAO-B
inhibition of preferential peripheral character, its most hydro-
philic derivatives, compounds 21 and 22 (ClogP - 0.42 and
-0.04, respectively) were selected for an in-depth study. In this
study, was also included compound 25 that, even if it showed
a more lipophilic character than 21 and 22 (ClogP 1.28), allowed
us to evaluate the effects induced by additional interactions
between basic pyridine nitrogen of the spacer (portion Y) and
enzymatic protein.
17
20
21
22
23
24
25
26
27
28
5
10
30
0
50
15
60
90
50
55
50
55
25
0
1.14
0.67
-0.42
-0.04
2.05
0.74
1.28
1.64
0.40
5
10
10
10
15
0
-0.03
a,b See Table 1.
Their MAO inhibition properties were measured in HEK-
transfected cell extracts expressing selectively MAO-A (HEK-
MAO-A) or MAO-B (HEK-MAO-B) (Figure 1A) and were
further confirmed on homogenate preparations from rat liver
using [14C]5-hydroxytryptamine ([14C]5-HT) and [14C]phenyl-
ethylamine ([14C]PEA) as substrates for MAO-A and MAO-B,
respectively (Figure 1B). The results in Figure 1A show that
compounds 21, 22, and 25 reduced [14C]tyramine oxidation
obtained on HEK-MAO-A significantly. Conversely, [14C]-
tyramine oxidation obtained on HEK-MAO-B was poorly
affected in the presence of these compounds. In liver mem-
branes, the IC50 of 21, 22, and 25 for inhibition of [14C]5-HT
oxidation was 0.6 ( 0.15 µM, 1.2 ( 1.1 µM, and 1.8 ( 1.6
µM, respectively (Figure 1B). Studies on inhibition of liver
homogenate [14C]PEA oxidation were performed in the presence
of 0.1 µM of clorgyline to prevent the metabolism of PEA by
MAO-A as previously reported in rat mesangial cells or rat
heart.40,41 As shown in Figure 1B, compounds 21, 22, and 25
poorly inhibited [14C]PEA oxidation at concentrations up to 10
µM. These results show that compounds 21, 22, and 25 display
MAO-A selectivity in vitro.
I2 7.55) displayed high I2-IBS affinity but negligible inhibitory
properties, we suggest that peripheral MAO inhibitory properties
are not necessarily linked to I2-IBS affinity, contrary to what
was observed for the central MAO inhibition produced by BU
series compounds.37
On the basis of our results, to confirm the lead validity, to
enhance possibly its potency and selectivity, and to highlight
the potential interactions with ancillary enzymatic proteins sites,
we performed some conservative structural modifications at the
three portions X, Y, and Z of furaline (17) (Chart 3). These
modifications included (i) introduction in the meta and para
positions of the phenyl ring of substituents with different
hydrophilic and electronic contributions38 such as NO2 (20) or
NH2 (21) and CH2OH (22) (modifications in X); (ii) isosteric
substitution of the furan ring with thiophene (23), pyrrole (24)
and pyridine (25) nuclei (modification in Y); (iii) introduction
of CH3 (26) or CH2OH (27) groups in position 4 of the
imidazoline nucleus (modification in Z); (iv) simultaneous
isosteric substitutions of portions X and Y with the pyridine
nuclei (28). Instead, the imidazoline nucleus modifications, such
as N-methylation, enlargement, or oxidation to the imidazole
ring, that in the previous studies of Harfenist et al. proved to
be unfavorable,26 have not been designed.
As reported in Table 2, most of the new derivatives
(compounds 21-26), displayed similar and significant inhibitory
properties on homogenates from rat liver, comparable to that
of lead. This result confirmed that furaline (17), selected as a
model, represents a really suitable new template and an
important basis for future work on peripheral MAO inhibitors.
Nevertheless, for the design of new derivatives inspired by
17, Table 2 allows several useful considerations. The aromaticity
Next we evaluated whether compounds 21, 22, and 25
behaved as reversible or irreversible inhibitors. This is a crucial
point in view of their potential clinical development, as it is
well-known that irreversible MAOIs have severe side effects
(i.e. the “cheese effect”) that preclude their use in therapy. In
attempting this, we incubated liver homogenates with 10 µM
of compounds 21, 22 or 25 for 20 min and then we washed the
homogenates by sequential dilution and centrifugation. After
20 min incubation with compounds 21, 22 or 25, [14C]5-HT
oxidation was reduced by 85%, 79%, and 53%, respectively,
as compared to untreated membranes. After membrane washing,

5582 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18
Gentili et al.
Figure 1. Inhibitory properties of compounds 21, 22, and 25 toward MAO-A and MAO-B. Effect of two concentrations of compounds, 0.1 µM,
10 µM, on measured MAO-A or MAO-B activity in stably transfected HEK cells expressing MAO-A or MAO-B cDNA (A). Deamination of 200
µM 5-HT (MAO-A) or 20 µM PEA (MAO-B) by the rat liver homogenates was determined in the presence of increasing concentrations of compounds
21 (squares), 22 (circles), and 25 (triangles). Symbols represent the means of three experiments per group, and vertical lines show SEM. ND: not
determined (less than 50% inhibition). The table of IC50 values determined using GraphPad PRISM software (B). *** P < 0.001, ** P < 0.01,
between MAO activity in vehicle and inhibitor-treated HEK cells homogenates.
about 80% of the enzyme activity was recovered for each
condition, indicating that MAO-A inhibition by these three
compounds (21, 22, and 25) was reversible (Figure 2).
for rat treatment, 21 prevalently inhibits liver MAO-A. Similar
results were obtained using 22 although the MAO-A inhibition
in liver was less relevant than that found using 21.
Therefore, our results in vitro and in vivo, interestingly
highlighted that compounds bearing the typical structure of
furaline (17) and with appropriate physicochemical properties,
such as the promising amino derivative 21 (Amifuraline), could
target prevalently peripheral MAO-A. This peculiarity could be
extremely interesting in pathological situations in which it is
suitable to selectively inhibit peripheral MAO-A and avoid
central side effects. For example, this could be the case of the
post-ischemia-reperfusion syndromes responsible for organ
failure (liver, kidney, and heart) occurring after transplantation,
angioplasty, or hypovolemic shock. Indeed, we showed that
cardiac and renal damage after reperfusion was greatly prevented
by animal pretreatment with MAO inhibitors. It is conceivable
that the use of selective peripheral MAO-A inhibitors could be
expanded to other peripheral pathologies in which this enzyme
may be involved.
To define the ability of 21, 22, and 25 to inhibit MAOs in
vivo, we treated rats with three intraperitoneal injections (50
mg/kg) of compounds, and we measured residual MAO-A and
MAO-B activities present in a homogenate preparation from
liver and brain. As expected from in vitro studies, rat treatment
with 21 and 22 did not considerably modify MAO-B activity
in brain and liver homogenates (Figure 3). In contrast, compound
25, which did not significantly inhibit [14C]PEA degradation in
vitro, decreased brain MAO-B after rat treatment. This indicates
that compound 25, displaying higher lipophilicity than 21 and
22, not only crosses the blood-brain barrier (as also demon-
strated by the brain MAO-A inhibition, Figure 3) but also
metabolic modification occurring in vivo may confer to this
compound the ability to interact with MAO-B. On the basis of
these observations, compound 25 is not suitable to specifically
target peripheral MAO-A in vivo. In contrast, administration
of 21 significantly decreased MAO-A activity in liver (36%).
Interestingly, we did not observe any significant MAO-A
inhibition in brain homogenates, indicating that, at the dose used
In conclusion, our study opens new perspectives for the design
of a novel subclass of MAO-A inhibitors, with more selective
peripheral effects and less centrally evoked side effects.

Peripheral MAO-A Inhibitor
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18 5583
the lack of unusual features) were obtained for all compounds
reported and are consistent with the assigned structures. The
microanalyses were performed by the Microanalytical Laboratory
of our department. The elemental composition of the compounds
agreed to within (0.4% of the calculated value. Chromatographic
separations were performed on silica gel columns (Kieselgel 40,
0.040-0.063 mm, Merck) by flash chromatography. The term
“dried” refers to the use of anhydrous sodium sulfate. Compounds
were named following the IUPAC rules proposed by Beilstein-
Institut AutoNom (version 2.1), a software for systematic names
in organic chemistry.
Pyridine-2-carboxylic Acid (4,5-Dihydro-1H-imidazol-2-yl-
methyl)-amide (9). To a solution of [(pyridine-2-carbonyl)-amino]-
acetic acid methyl ester42 (1.79 g, 9.22 mmol) in absolute EtOH (9
mL) was added a solution of ethylenediamine (6.21 mL, 92.2 mmol)
in EtOH dry (9 mL). The mixture was refluxed for 4 h. The
evaporation of the solvent gave pyridine-2-carboxylic acid [(2-
amino-ethylcarbamoyl)-methyl]-amide (1.5 g, 73% yield) that,
dissolved in xylene (30 mL), was refluxed with vigorous stirring
and water removal for 25 h. Evaporation of the solvent gave a
residue which was purified by flash chromatography using cyclo-
hexane/AcOEt/MeOH/33% NH4OH (2:5:1:0.1) as eluent. The free
base (0.5 g, 36% yield) was transformed into the oxalate salt, which
Figure 2. Reversible effect of compounds 21, 22, and 25 on MAO
activity inhibition. MAO-A activity recovered in liver homogenate
following incubation with 10 µM of compound 21, 22, or 25 before
and after washing. Vehicle-treated homogenate was submitted to the
same washing protocol and used as control for MAO-A activity
recovered in compounds treated liver homogenate after washing.
Activity measured in the presence of 10 µM compounds was compared
to unwashed vehicle-treated homogenates. Values are from duplicate
experiments and are presented as percentage of vehicle-treated liver
homogenates. *** P < 0.001 between % of MAO activity remaining
in inhibitor-treated homogenates before and after washing.
1
was recrystallized from MeOH, mp 192.5-193.5 °C. H NMR
(DMSO) δ 3.82 (s, 4, NCH2CH2N), 4.38 (d, 2, CH2), 7.18-8.23
(m, 4, ArH), 9.42 (t, 1, CONH, exchangeable with D2O) 10.13 (s
br, 1, NH, exchangeable with D2O). Anal. (C10H12N4O‚H2C2O4)
C, H, N.
2-((E)-3-Phenyl-allyl)-4,5-dihydro-1H-imidazole (11). A solu-
tion of ethylenediamine (0.505 mL, 7.5 mmol) in dry toluene (2.6
mL) was added dropwise to a mechanically stirred solution of 2 M
trimethylaluminum (3.76 mL, 7.52 mmol) in dry toluene (6.3 mL)
at 0 °C in nitrogen atmosphere. After being stirred at room
temperature for 1 h, the solution was cooled to 0 °C and a solution
of (E)-4-phenyl-but-3-enoic acid methyl ester43 (0.70 g; 3.78 mmol)
in dry toluene (5 mL) was added dropwise. The reaction mixture
was heated to 110 °C for 8 h, cooled to 0 °C, and quenched
cautiously with MeOH (1.8 mL) followed by H2O (0.4 mL). After
addition of CHCl3 (14 mL), the mixture was left for 30 min at
room temperature to ensure the precipitation of the aluminum salts.
The mixture was filtered, and the organic layer was evaporated.
The residue was purified by flash chromatography using cyclo-
hexane/CHCl3/MeOH/33% NH4OH (8:8:2.5:2.5) as eluent (0.1 g,
13% yield) and then transformed into the oxalate salt which was
recrystallized from EtOH/Et2O, mp 151-152 °C. 1H NMR (DMSO)
δ 3.48 (d, 2, CH2), 3.85 (s, 4, NCH2CH2N), 6.36 (dd, 1, CH2CH),
6.68 (d, 1, CH), 7.28-7.51 (m, 5, ArH), 9.15 (br, 1, NH,
exchangeable with D2O). Anal. (C12H14N2‚H2C2O4) C, H, N.
6-(4,5-Dihydro-1H-imidazol-2-yl)-quinoline (14). It was pre-
pared from quinoline-6-carboxylic acid methyl ester44 via the
procedure described for 11. The free base (45% yield) was
transformed into the oxalate salt which was recrystallized from
1
MeOH-EtOH (3:7), mp 228.5-229 °C. H NMR (D2O) δ 4.06
(s, 4, NCH2CH2N), 7.68-8.99 (m, 6, ArH). Anal. (C12H11N3‚
H2C2O4) C, H, N.
cis-2-(3-Phenyl-oxiranyl)-4,5-dihydro-1H-imidazole (15). A
mixture of cis-3-phenyl-oxirane-2-carbonitrile45 (0.44 g, 3.0 mmol),
sodium methoxide (0.014 g, 0.26 mmol), and MeOH (2 mL) was
stirred for 4 h. On cooling to 0-10 °C, a solution of ethylenedi-
amine (0.22 mL, 3.36 mmol) in MeOH (1 mL) was added dropwise
with stirring; after a few minutes a solution of HCl in MeOH (1.043
mL of 3 N solution, 3.13 mmol) was added dropwise and the
mixture was allowed to warm to room temperature. After 48 h, the
solvent was evaporated and the residue was taken up in AcOEt.
The organic solution was washed with H2O, dried over Na2SO4,
and evaporated to give a residue that was purified by flash
chromatography using cyclohexane/AcOEt/MeOH/33% NH4OH (7:
Figure 3. MAO activity on liver and brain homogenate preparation
from rats treated, as reported in experimental protocol, with compounds
21, 22, and 25. MAO-A was measured with 200 µM [14C] 5HT and
MAO-B with 20 µM [14C] PEA in the presence of 0.1 µM clorgyline.
An asterisk indicates groups that differed significantly from vehicle-
treated animals: *P < 0.05, **P < 0.01.
Experimental Protocols
Chemistry. Melting points were taken in glass capillary tubes
in a Bu¨chi SMP-20 apparatus and are uncorrected. IR and NMR
spectra were recorded on Perkin-Elmer 297 and Varian EM-390
instruments, respectively. Chemical shifts are reported in parts per
million (ppm) relative to tetramethylsilane (TMS), and spin
multiplicities are given as s (singlet), d (doublet), t (triplet), q
(quartet), or m (multiplet). IR spectral data (not shown because of
1
4:1:0.1) as eluent (0.2 g, 36% yield), mp 105-106 °C. H NMR
(CDCl3) δ 3.37 (m, 4, NCH2CH2N), 4.03 (d, 1, CH), 4.30 (d, 1,
ArCH), 7.31-7.42 (m, 5, ArH), 4.38 (s, 1, NH, exchangeable with
D2O). Anal. (C11H12N2O) C, H, N.

5584 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18
Gentili et al.
trans-2-(3-Phenyl-oxiranyl)-4,5-dihydro-1H-imidazole (16). It
was prepared from trans-3-phenyl-oxirane-2-carbonitrile46 via the
procedure described for 15. The free base was purified by flash
chromatography using cyclohexane/AcOEt/MeOH/33% NH4OH (7:
4:1:0.1) as eluent. The free base (42% yield) was transformed into
the oxalate salt, which was recrystallized from 2-PrOH/Et2O, mp
(d, 1, J ) 4 Hz, PhCCHCH), 8.05 (d, 1, J ) 4 Hz, PhCCH), 4.98
(br, 1, NH, exchangeable with D2O). Anal. (C13H12N2S‚H2C2O4)
C, H, N.
2-(5-Phenyl-1H-pyrrol-2-yl)-4,5-dihydro-1H-imidazole (24). It
was prepared from 5-phenyl-1H-pyrrole-2-carboxylic acid methyl
ester50 via the procedure described for 11. The free base was purified
by flash chromatography using cyclohexane/AcOEt/MeOH/33%
NH4OH (4:6:1:0.1) as eluent (35% yield) and then transformed into
the oxalate salt which was recrystallized from MeOH/Et2O, mp
220.8-222°C. 1H NMR (DMSO) δ 3.95 (s, 4, NCH2CH2N), 6.82
(d, 1, J ) 3.82 Hz, PhCCHCH), 7.31 (d, 1, J ) 3.82 Hz, PhCCH),
7.39-7.92 (m, 5, ArH), 10.38 (br, 1, NHCH2, exchangeable with
D2O), 12.88 (s br, 1, NH, exchangeable with D2O). Anal. (C13H13N3‚
2H2C2O4) C, H, N.
5-(4,5-Dihydro-1H-imidazol-2-yl)-2-phenyl-pyridine (25). A
mixture of 2-aminoethylammonium toluene-p-sulfonate (6.79 g,
27.6 mmol) and 6-phenyl-nicotinonitrile45 (0.5 g, 2.76 mmol) was
heated at 200 °C for 2 h. After cooling and addition of MeOH, the
solvent was evaporated to give a residue that was purified by flash
chromatography using cyclohexane/AcOEt/MeOH/33% NH4OH (6:
4:1:0.1) as eluent. The free base (0.25 g, 42% yield) was
transformed into the oxalate salt which was recrystallized from
EtOH, mp 236.5-236.6 °C. 1H NMR (DMSO) δ 4.05 (s, 4, NCH2-
CH2N), 7.52 (m, 8, ArH), 10.35 (br s, 1, NH, exchangeable with
D2O). Anal. (C14H13N3‚H2C2O4) C, H, N.
4-Methyl-2-(5-phenyl-furan-2-yl)-4,5-dihydro-1H-imidazole
(26). It was prepared from 5-phenyl-furan-2-carbonitrile47 and 1,2-
diaminopropane via the procedure described for 17. The free base
(57% yield) was then transformed into the oxalate salt which was
recrystallized from EtOH/Et2O, mp 223.8-224 °C. 1H NMR
(DMSO) δ 1.39 (d, 3, CH3), 3.55 (dd, 1, NCH), 4.04-4.43 (m, 2,
NCH2), 7.33 (d, 1, J ) 3.5 Hz PhCCHCH), 7.72 (d, 1, J ) 3.5 Hz,
PhCCH) 7.45-7.95 (m, 5, ArH), 10.55 (br s, 1, NH, exchangeable
with D2O). Anal. (C14H14N2O‚H2C2O4) C, H, N.
[2-(5-Phenyl-furan-2-yl)-4,5-dihydro-1H-imidazol-4-yl]-metha-
nol (27). A mixture of 30 (0.38 g; 1.41 mmol) and NaBH4 (0.059
g; 1.55 mmol) in dry EtOH (10 mL) was stirred at room temperature
for 1 h under nitrogen atmosphere. The solvent was evaporated,
and the residue was purified by flash chromatography using
cyclohexane/CHCl3/MeOH/33% NH4OH (4:5:1:0.1) as eluent. The
free base (0.3 g, 86% yield) was transformed into the oxalate salt
which was recrystallized from MeOH/Et2O, mp 216-216.5 °C. 1H
NMR (DMSO) δ 3.51-4.11 (m, 4, NCH2, CH2OH), 4.42 (m, 1,
CH), 4.80 (s, 1, OH, exchangeable with D2O), 7.34 (d, 1, J ) 3.5
Hz PhCCHCH), 7.79 (d, 1, J ) 3.5 Hz, PhCCH), 7.48-8.03 (m,
5, ArH), 10.82 (br s, 1, NH, exchangeable with D2O). Anal.
(C14H14N2O2‚H2C2O4) C, H, N.
5-(4,5-Dihydro-1H-imidazol-2-yl)-[2,3′]bipyridinyl (28). It was
prepared from [2,3′]bipyridyl-5-carbonitrile51 via the procedure
described for 25. The free base was purified by flash chromatog-
raphy using CHCl3/MeOH/33% NH4OH (9:1:0.1) as eluent (65%
yield) and transformed into the oxalate salt which was recrystallized
from EtOH/Et2O, mp 232.5-236 °C. 1H NMR (DMSO) δ 4.05 (s,
4, NCH2CH2N), 7.58-9.38 (m, 7, ArH), 10.45 (br s, 1, NH,
exchangeable with D2O). Anal. (C13H12N4‚H2C2O4) C, H, N.
Acetic Acid 4-(5-Cyano-furan-2-yl)-benzyl Ester (29). 5-(4-
Hydroxymethyl-phenyl)-furan-2-carbaldehyde52 (2.5 g; 12.4 mmol),
hydroxylamine hydrochloride (1.75 g; 25 mmol), and sodium acetate
(2.05 g; 25 mmol) in a stirred mixture of ethanol (7 mL) and water
(0.7 mL) were heated under reflux for 5 h and then poured into
cold water and extracted with CHCl3; the organic phase was washed
with H2O. Removal of dried solvent gave 5-(4-hydroxymethyl-
phenyl)-furan-2-carbaldehyde oxime (2.53 g; 94% yield). 1H NMR
(DMSO) δ 4.52 (s, 2, CH2), 4.50 (s, 1, OH), 7.11 (d, 1, J ) 3.5 Hz
PhCCHCH), 7.28 (d, 1, J ) 3.5 Hz PhCCH), 7.42-7.75 (2 d, 4,
ArH), 11.9 (s, 1, N-OH).
1
139-140 °C. H NMR (DMSO) δ 3.87 (s, 4, NCH2CH2N), 4.26
(d, 1, CH), 4.42 (d, 1, ArCH), 7.38-7.52 (m, 5, ArH), 8.48 (s, 1,
NH, exchangeable with D2O). Anal. (C11H12N2O‚H2C2O4) C, H,
N.
2-(5-Phenyl-furan-2-yl)-4,5-dihydro-1H-imidazole (Furaline)
(17). HCl was bubbled through a stirred and cooled (0 °C) solution
of 5-phenyl-furan-2-carbonitrile47 (0.71 g, 4.14 mmol) and MeOH
(0.35 mL, 8.29 mmol) in dry CHCl3 (7 mL) for 45 min. After 12
h at 0 °C, dry ether was added to the reaction mixture to give the
intermediate imidate, which was filtered (0.76 g; 77.8% yield). This
solid (0.76 g, 3.22 mmol) was added to a cooled (0 °C) and stirred
solution of ethylenediamine (0.26 mL, 3.99 mmol) in absolute EtOH
(15.5 mL). After 1 h, concentrated HCl (a few drops) in abs EtOH
(7 mL) was added to the reaction mixture, which was stored
overnight in the refrigerator. It was then diluted with abs EtOH
(13 mL) and heated at 75 °C for 5 h. After cooling, the solid was
collected and discarded and the filtrate was concentrated and filtered
again. The filtrate was evaporated to dryness to give a residue that
was purified by flash chromatography using cyclohexane/AcOEt/
MeOH/33% NH4OH (7:3:1:0.1) as eluent. The free base (0.57 g;
65% yield) was then transformed into the oxalate salt which was
recrystallized from MeOH, mp 179-180 °C. 1H NMR (DMSO) δ
4.00 (s, 4, NCH2CH2N), 7.37 (d, 1, J ) 3.5 Hz, PhCCHCH), 7.78
(d, 1, J ) 3.5 Hz, PhCCH), 7.49-8.04 (m, 5, ArH), 4.58 (br, 1,
NH) exchangeable with D2O). Anal. (C13H12N2O‚H2C2O4) C, H,
N.
2-[5-(3-Nitro-phenyl)-furan-2-yl]-4,5-dihydro-1H-imidazole (20).
It was prepared from 5-(3-nitro-phenyl)-furan-2-carboxylic acid
methyl ester48 via the procedure described for 11. The free base
(40% yield) was transformed into the oxalate salt which was
1
recrystallized from H2O, mp 249-249.5 °C. H NMR (DMSO) δ
3.35 (s, 4, NCH2CH2N), 7.08 (d, 1, J ) 3.5 Hz, PhCCHCH), 7.38
(d, 1, J ) 3.5 Hz, PhCCH), 7.74-8.60 (m, 4, ArH), 7.13 (br, 1,
NH, exchangeable with D2O). Anal. (C13H11N3O3‚H2C2O4) C, H,
N.
3-[5-(4,5-Dihydro-1H-imidazol-2-yl)-furan-2-yl]-phenyl-
amine (21). Imidazoline 20 (1 g, 3.89 mmol) was hydrogenated in
MeOH for 12 h at room temperature under pressure (40 psi) using
10% Pd on charcoal as catalyst. Following catalyst removal, the
evaporation of the solvent gave a residue that was purified by flash
chromatography using cyclohexane/AcOEt/MeOH/33% NH4OH (4:
6:1:0.1) as eluent. The free base (0.35 g, 40% yield) was
transformed into the oxalate salt which was recrystallized from
1
EtOH/Et2O, mp 178.6-179.8 °C. H NMR (DMSO) δ 4.00 (s, 4,
NCH2CH2N) 4.48 (s br, 2, NH2, exchangeable with D2O) 6.67 (d,
1, J ) 3.5 Hz, PhCCHCH), 7.13 (d, 1, J ) 3.5 Hz, PhCCH), 7.09-
7.72 (m, 4, ArH), 10.68 (br, 1, NH, exchangeable with D2O). Anal.
(C13H13N3O‚1.5H2C2O4) C, H, N.
{4-[5-(4,5-Dihydro-1H-imidazol-2-yl)-furan-2-yl]-phenyl}-
methanol (22). It was prepared from 29 via the procedure described
for 17. The free base was purified by flash chromatography using
cyclohexane/AcOEt/MeOH/33% NH4OH (5:4:1:0.1) as eluent (67%
yield) and transformed into the oxalate salt which was recrystallized
from 2-PrOH, mp 219.5-220 °C. 1H NMR (DMSO) δ 3.77 (s, 4,
NCH2CH2N), 4.71 (s, 2, CH2), 6.72 (d, 1, J ) 3.5 Hz PhCCHCH),
7.03 (d, 1, J ) 3.5 Hz, PhCCH), 7.38-7.67 (2 d, 4, ArH), 9.58 (s,
1, OH, exchangeable with D2O), 10.35 (br s, 1, NH, exchangeable
with D2O). Anal. (C14H14N2O2‚H2C2O4) C, H, N.
2-(5-Phenyl-thiophen-2-yl)-4,5-dihydro-1H-imidazole (23). It
was prepared from 5-phenyl-thiophene-2-carbonitrile49 via the
procedure described for 17. The free base was purified by flash
chromatography using cyclohexane/AcOEt/MeOH/33% NH4OH (3:
5:1:0.1) as eluent (65% yield) and transformed into the oxalate salt
which was recrystallized from MeOH, mp 223-223.5 °C. 1H NMR
(DMSO) δ 3.97 (s, 4, NCH2CH2N), 7.48-7.76 (m, 5, ArH), 7.75
5-(4-Hydroxymethyl-phenyl)-furan-2-carbaldehyde oxime (2.53
g; 11.65 mmol) was stirred under reflux for 3 h in acetic anhydride
(25 mL). The cooled solution was poured into ice water and
extracted with CHCl3; the organic phase was washed with H2O.
Removal of dried solvent gave a residue which was purified by

Peripheral MAO-A Inhibitor
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 18 5585
flash chromatography using cyclohexane/EtOAc (9:1) as eluent to
give 29 (2.53 g; 90% yield). 1H NMR (CDCl3) δ 2.13 (s, 3, CH3),
5.15 (s, 2, CH2), 6.75 (d, 1, J ) 3.5 Hz PhCCHCH), 7.18 (d, 1, J
) 3.5 Hz PhCCH), 7.45-7.71 (2 d, 4, ArH).
Supporting Information Available: Elemental analyses. This
material is available free of charge via the Internet at http://
pubs.acs.org.
2-(5-Phenyl-furan-2-yl)-4,5-dihydro-1H-imidazole-4-carboxy-
lic Acid Methyl Ester (30). It was prepared from 5-phenyl-furan-
2-carbonitrile47 and 2,3-diamino-propionic acid methyl ester via the
procedure described for 17. The free base was purified by flash
chromatography using cyclohexane/AcOEt/MeOH/33% NH4OH (6:
4:1:0.1) as eluent (42% yield) and transformed into the oxalate salt
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