Synthesis of new 7-oxycoumarin derivatives as potent and selective monoamine oxidase A inhibitors

Article abstract of DOI:10.1021/jm301014y

New series of 4-methyl and 3,4-dimethyl-7-oxycoumarin derivatives (oxadiazoles, thiadiazoles, triazoles, and thiazolidinones) were designed, synthesized, and evaluated for their monoamine oxidase (MAO) A and B inhibiting effect. All the synthesized compounds showed in vitro high affinity and selectivity toward MAO-A isoenzyme, compared to clorgyline and moclobemide, with K_i values on the picomolar range. Moreover, most of the tested compounds displayed MAO inhibitory effect when tested in vivo. The docking experiments carried out on MAO-A and MAO-B structures proved new information about the enzyme-inhibitor interaction and the potential therapeutic application of 7-oxycoumarin scaffold.

Full text of DOI:10.1021/jm301014y

Article
pubs.acs.org/jmc
Synthesis of New 7‑Oxycoumarin Derivatives As Potent and Selective
Monoamine Oxidase A Inhibitors
Omaima M. Abdelhafez,*,† Kamelia M. Amin,‡ Hamed I. Ali,§ Mohamed M. Abdalla,∥
and Rasha Z. Batran†
†Chemistry of Natural Products Department, National Research Center, Dokki, Egypt
‡Pharmaceutical Chemistry Department, Faculty of Pharmacy, Cairo University, Egypt
§Pharmaceutical Chemistry Department, Faculty of Pharmacy, Helwan University, Egypt
∥Research Unit, Mapco Pharmaceutical Industries Balteim, Egypt
S
* Supporting Information
ABSTRACT: New series of 4-methyl and 3,4-dimethyl-7-
oxycoumarin derivatives (oxadiazoles, thiadiazoles, triazoles,
and thiazolidinones) were designed, synthesized, and evaluated
for their monoamine oxidase (MAO) A and B inhibiting effect.
All the synthesized compounds showed in vitro high affinity
and selectivity toward MAO-A isoenzyme, compared to
clorgyline and moclobemide, with Ki values on the picomolar
range. Moreover, most of the tested compounds displayed
MAO inhibitory effect when tested in vivo. The docking
experiments carried out on MAO-A and MAO-B structures
proved new information about the enzyme−inhibitor inter-
action and the potential therapeutic application of 7-oxy-
coumarin scaffold.
or 4 considers it crucial for modulating MAO-B inhibitory
activity and A/B selectivity.17,18 So far, the aforementioned
studies, encouraged us to assay a large array of 4-methyl (and
3,4-dimethyl)-7-oxycoumarins incorporated with different
bioactive moieties known to have MAO inhibition activity as
oxadiazoles,19,20 thiadiazoles,21,22 triazoles,23 and thiazolidi-
nones23 in order to evaluate their anti-MAO effect in vitro
and in vivo. Finally, docking experiments were carried out on
MAO-A and MAO-B crystallographic structures on the basis of
the significant structural information currently available on
MAOs24−26 in order to analyze the structural requirements for
MAO activity and selectivity.
INTRODUCTION
■
Monoamine oxidases (MAOs) are FAD depending enzymes
responsible for the regulation and metabolism of major
monoamine neurotransmitters (5-hydroxytryptamine (5-HT),
norepinephrine (NE), and dopamine (DA)), modulating their
concentrations in the brain and peripheral tissues.1,2 They are
also involved in the biodegradation of exogenous amines such
as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into
1-methyl-4-phenyl pyridinium (MPP+), a Parkinson producing
neurotoxin.3−5 The MAO enzyme exists in two forms, namely
MAO-A and MAO-B, distinguishable by their molecular
cloning, substrate and inhibitor selectivity, and tissue
distribution.6−9 MAO-A preferentially oxidizes serotonin and
is irreversibly inhibited by low concentrations of clorgyline,7
while that of the B isoform preferentially oxidizes β-phenyl-
ethylamine (PEA) and benzylamine and it is irreversibly
inactivated by low concentrations of L-deprenyl.10 Dopamine,
tyramine, and tryptamine are common substrates for both
MAOs. In fact, human MAO-A inhibitors are antidepressants
and antianxiety agents,11 while human MAO-B inhibitors are
used alone or in combination with other drugs in the therapy of
Alzheimer’s and Parkinson’s diseases.12,13
CHEMISTRY
■
The 7-oxycoumarin derivatives (1a,b), (2a−d), (3a−h), (4a,b),
(5a,b), (6a,b), (7a,b), (8a−d), (9a−d), and (10a,b) were
efficiently synthesized according to the protocols outlined in
Schemes 1−3. The general reaction conditions and the
compounds characterization are described in the Experimental
Section.
The key intermediates, 5-mercapto-1,3,4-oxadiazoles (2a,27
2b), were prepared by refluxing hydrazides (1a,28 1b29) with
carbon disulfide in alcoholic potassium hydroxide solution
while the reaction of the same hydrazides (1a,b) with carbon
Among several MAO inhibitors, some (2H)-1- benzopyran-
2-one derivatives (coumarins) were screened for their good
MAO inhibitory activities.14−16 At the same time, a great deal of
literature data on the importance of substitution of 7-
oxycoumarin nucleus with a methyl group at position 3 and/
Received: July 12, 2012
© XXXX American Chemical Society
A
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disulfide in alcoholic potassium hydroxide at room temperature
followed by cyclization with conc H2SO4, gave the correspond-
ing 5-mercapto-1,3,4-thiadiazole derivatives (2c,27 2d).
In addition, S-alkylation of (2a−d) with diethylaminoethyl-
chloride hydrochloride and/or morpholinoethylchloride hydro-
chloride, in refluxing acetone in the presence of potassium
carbonate, afforded the target diethylaminoethylthio-1,3,4-
oxadiazole compounds (3a,b), diethylaminoethylthio-1,3,4-
thiadiazoles (3c,d), morpholinoethylthio-1,3,4-oxadiazoles
(3e,f), and morpholinoethylthio-1,3,4-thiadiazole derivatives
(3g,h), respectively (Scheme 1).
inhibitors (L-deprenyl 1 μM for MAO-A and clorgyline 1 μM
for MAO-B).32 The inhibitory activities (Ki) and the A-
selectivity (SI) of the tested compounds are depicted in Table
1. All the tested compounds were found to act through a
noncompetitive and reversible mode as demonstrated by the
fact that dialysis for 24 h at 5 °C against 0.1 M potassium
phosphate buffer at pH 7.2 was able to restore 95−100% of the
enzyme activity. The substrate did not compete with the
inhibitor, accordingly, a decrease of Vmax was observed, while
the Km value was unchanged.
Moreover, the in vivo inhibiting properties of the synthesized
compounds (Table 2) were also elucidated using the in vivo
tryptamine seizure potentiation procedure in rats regarding that
monoamine oxidase inhibitors like iproniazid enhance the
seizures caused by an intravenous infusion of tryptamine
hydrochloride in rats.33,34
Scheme 1
DOCKING STUDIES
■
Although significant advances in the design of selective MAOIs
were achieved in the past two decades, a veritable breakthrough
in the field occurred only few years ago with the resolution of
the X-ray crystal structure of human MAO-B (hMAO-B)35 and
rat MAO-A (rMAO-A).36 The high-resolution 3D structure of
the hMAO-B in complex with a large number of selective
inhibitors, covalently bound to the FAD cofactor,37 finally
paved the way to the structure-based design of new modulators
of MAO-B activity. This study was performed using the
advanced and widely distributed molecular grid-based docking
program Autodock 4.238 for docking of flexible ligand within
flexible protein. The target MAO-A enzyme (PDB 2Z5X)25and
MAO-B (PDB 2XFN)39 proteins were involved.
Here, we investigated the AutoDock binding affinities into
MAO-A and MAO-B for the synthesized thirty-two coumarin
derivatives, (1a,b), (2a−d), (3a−h), (4a,b), (5a,b), (6a,b),
(7a,b), (8a−d), (9a−d), and (10a,b). This study was carried
out by differential docking of the compounds into the structure
of human monoamine oxidase A (PDB 2Z5X)25 with its 7-
methoxy-1-methyl-9H-β-carboline (HRM)25 bound ligand and
the human monoamine oxidase B (PDB 2XFN)39 in complex
with 2-(2-benzofuranyl)-2-imidazoline (XCG).39
Condensation of the hydrazides (1a,b) with 4-chlorophenyl-
isothiocyanate afforded the thiosemicarbazide derivatives (4a,30
4b), which were further cyclized with H2SO4 to get 4-
chlorophenylaminothiadiazoles (5a,30 5b) and with chloro-
acetic acid to afford the corresponding iminothiazolidinone
derivatives (6a,b). Moreover, refluxing thiosemicarbazides
(4a,b) with sodium hydroxide yielded the corresponding 5-
mercapto-1,2,4-triazoles (7a,30 7b), which were reacted with
diethylaminoethylchloride hydrochloride and/or morpholinoe-
thylchloride hydrochloride, in acetone in the presence of
potassium carbonate, to give the target diethylaminoethyl thio-
1,3,4-triazoles (8a,b) and morpholinoethylthio-1,3,4-triazole
derivatives (8c,d), respectively (Scheme 2).
As cited in literature,40 if the RMSD (root-mean-square
deviation) of the best docked conformation of the native ligand
is ≤2.0 Å from the experimental one, the used scoring function
is successful. Therefore the validation of the docking accuracy
was investigated for MAO-A and MAO-B enzymes, to inspect
how closely the best docked conformations resemble the bound
ligands in the biological methods.25,39
Furthermore, the Schiff’s bases (9a),28 (9b), (9c),28 and (9d)
were prepared by the reaction of hydrazides (1a,b) with 4-
chlorobenzaldehyde and/or 4-chloroacetophenone. Heterocyc-
lization of the aforementioned Schiff’s bases (9a,b) with
mercaptoacetic acid yielded the corresponding thiazolidinone
derivatives (10a,b) (Scheme 3).
Within MAO-A receptor, the docked ligand 1 (HRM) was
bound hydrophobically with the key amino acids of MAO-A,
and it seemed superimposed on the native ligand within RMSD
of 0.28 Å. The obtained success rates of AutoDock were highly
excellent,as displayed in Table 3, and shown in Figure 1A.
Whereas, the docked ligand 2 (XCG) was bound efficiently into
the target macromolecule of MAO-B identically superimposed
onto the natively bound ligand within 0.68 Å, as cited in Table
4 and shown in Figure 1B.
BIOLOGY
■
The synthesized compounds were tested in vitro for their
MAO-A and MAO-B inhibiting activity using clorgyline (A-
selective, irreversible), moclobemide (A-selective, reversible),
and selegiline (B-selective, irreversible) as reference drugs.
Bovine brain mitochondria isolated according to Basford31 were
used as a source of the two MAO isoforms. MAO-A and MAO-
B activities were determined by a fluorometric assay, using
kynuramine as a substrate, in the presence of their specific
RESULTS AND DISCUSSION
■
Monoamine Oxidase Inhibiting Effect. In Vitro MAO-A
and MAO-B Inhibitory Effect. Generally, all the synthesized
compounds are exceptionally potent and selective MAO-A
inhibitors, and they inhibit MAO-A at a subnanomolar
B
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Scheme 2
Scheme 3
compounds for both MAO-A and B isoforms. The 3,4-
dimethylcoumarin-7-yloxyacetohydrazide (1b) is exceptionally
the most potent MAO-A and MAO-B inhibitor (Ki (MAO-A) =
5.01 pM, Ki (MAO-B) = 0.484 μM). Demethylation of (1b)
results in a dramatic drop of MAO-A and MAO-B inhibition
(1a) (Ki (MAO-A) = 11.20 pM, Ki (MAO-B) = 0.874 μM).
Moreover, S-alkylation of the mercaptothiadiazolyl derivative
(2d) (Ki (MAO-A) = 6.37 pM, Ki (MAO-B) = 0.572 μM) with
both diethylaminoethyl (3d) and morpholinoethyl (3h)
moieties increases the in vitro inhibitory effect for both
MAO-A and B (Ki (MAO-A) = 5.18 and 5.73 pM, Ki (MAO-B)
= 0.496 and 0.535 μM, respectively). Replacement of the
thiadiazole ring with its bioisosteric oxadiazole one (3b) and
(3f) results in a decreased inhibitory activity for both MAO-A
and MAO-B isoforms (Ki (MAO-A) = 6.58 and 6.39 pM, Ki
(MAO-B) = 0.555 and 0.571 μM respectively).
The open chain structures as the thiosemicarbazides (4a)
and (4b) show significant anti-MAO-A and B effects (Ki
(MAO-A) = 7.01, 6.51 pM, Ki (MAO-B) = 0.620, 0.561 μM
respectively). Additionally, compound (9b) proved to be the
most potent in vitro tested Schiff’s base (Ki (MAO-A) = 5.54
pM, Ki (MAO-B) = 0.522 μM).
On the other hand, the thaizolidinone (10a) presents a lower
inhibition activity toward MAO-A and B enzymes than its
imino derivative (6a) (Ki (MAO-A) = 10.9 versus 6.56 pM, Ki
concentration, with Ki values in the picomolar range compared
to clorgyline and moclobemide. On the other hand, the
synthesized compounds exhibit MAO-B inhibiting activity at a
submicromolar concentration, showing an anti-MAO-B effect
greater than selegiline (Table 1).
The majority of 3,4-dimethylcoumarinyl-7-oxy derivatives
show lower Ki values than the 4-methylcoumarinyl-7-oxy target
C
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Table 1. MAO-A and B Inhibitory Activities (Ki; pM), and
Selectivity (SI) of the Tested Compounds
Table 2. In Vivo Tryptamine Seizure Potentiation (ED50;
nM) by Tested Compounds in Rats
a
b
compd
Ki MAO-A
Ki MAO-B (μM)
SI
compd
1a
ED50 (nM)
compd
ED50 (nM)
a
a
a
a
a
a
a
1a
1b
2a
2b
2c
2d
3a
3b
3c
3d
3e
3f
11.2 pM
5.01 pM
12.0 pM
6.40 pM
11.0 pM
6.37 pM
6.57 pM
6.58 pM
10.1 pM
5.18 pM
6.53 pM
6.39 pM
9.81 pM
5.73 pM
7.01 pM
6.51 pM
6.38 pM
6.59 pM
6.56 pM
6.35 pM
6.41 pM
6.61 pM
6.45 pM
6.46 pM
6.41 pM
6.42 pM
8.87 pM
5.54 pM
8.02 pM
6.48 pM
10.9 pM
5.93 pM
0.0540 μM
11.5 μM
3.80 μM
0.874
0.484
0.918
0.570
0.896
0.572
0.556
0.555
0.812
0.496
0.559
0.571
0.792
0.535
0.620
0.561
0.571
0.554
0.557
0.574
0.569
0.553
0.566
0.564
0.569
0.568
0.736
0.522
0.684
0.563
0.853
0.548
58.0
7.80 × 104
9.66 × 104
7.65 × 104
8.91 × 104
8.15 × 104
8.98 × 104
8.47 × 104
8.43 × 104
8.01 × 104
9.58 × 104
8.56 × 104
8.93 × 104
8.07 × 104
9.34 × 104
8.84 × 104
8.62 × 104
8.96 × 104
8.41 × 104
8.49 × 104
9.05 × 104
8.89 × 104
8.36 × 104
8.78 × 104
8.73 × 104
8.87 × 104
8.84 × 104
8.30 × 104
9.42 × 104
8.53 × 104
8.69 × 104
7.86 × 104
9.24 × 104
1.07 × 103
>87
8.05 0. 12
9.14 0. 23
7.85 0. 32
9.87 0. 65
7.95 0. 26
9.55 0. 84
5a
9.67 0.50
68.6 5.4
1b
5b
6a
a
2a
48.3 3.4
a
a
2b
6b
7a
9.26 0.34
9.96 0.88
81.3 6.6
2c
2d
7b
8a
a
3a
52.6 3.5
106
126
5
3
3b
62.7 3.9
8b
8c
a
a
a
a
3c
8.24 0. 36
9.05 0. 36
10.1 0.4
26.5 0.5
3d
8d
9a
a
a
3e
256
4
8.56 0.43
74.6 4.8
a
a
3f
9.78 0. 35
8.33 0. 36
75.7 3. 5
9b
9c
a
3g
3h
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
8c
8d
9a
9b
9c
9d
3g
29.6 0.6
3h
9d
10a
10b
150
5
a
4a
41.4 4.6
8.16 0.32
76.7 2. 2
4b
196
4
iproniazide
64.5 2.2
a
Each ED50 value is the mean (three significant digits) SEM from
five experiments. Level of statistical significance: P < 0.01 with respect
to ED50value of iproniazide as determined by ANOVA/Dunnett’s.
Moreover, p-chlorophenylaminothiadiazolyl- 4-methylcou-
marin (5a) has much higher anti-MAO effect (ED50 = 9.67
nM) compared to the 3,4-dimethylcouamrinyl derivative (5b)
(ED50 = 68.6 nM),which lacks any inhibition effect. In addition,
the mercapto-1,2,4-triazolyl-4-methylcoumarin (7a) demon-
strates the highest in vivo MAO inhibition within the
synthesized traizole series (ED50 = 9.96 nM).
On the other hand, lower ED50 value is observed for the
target 4-methylcoumarinyl Schiff’s base (9a) (ED50 = 8.56 nM)
than the methyl substituted azomethine derivative (9c) (ED50 =
29.6 nM), while the 3,4-dimethylcoumarinyl Schiff ’s base (9b)
completely lacks any inhibition effect (ED50 = 74.6 nM) .
Finally, the 4-methylcoumarinylthiazolidinone (10a) (ED50 =
8.16 nM) shows about 6-fold higher in vivo inhibition activity
than its imino derivative (6a) (ED50 = 48.3 nM). Also, it
displays about 9-fold higher activity than the 3,4-dimethylcou-
marinyl derivative (10b) (ED50 = 76.7 nM). On the contrary,
the 3,4-dimethylcoumarinyliminothiazolidinone derivative (6b)
(ED50 = 9.26 nM) displays much higher potency than the
thiazolidinone congener (10b) (Table 2).
Molecular Modeling Study. AutoDock binding affinities
of the synthesized compounds were evaluated according to
many parameters including: the binding free energies (ΔGb,
kcal/mol), inhibition constants (Ki), hydrogen bonding, and
RMSD values in comparison to the native cocrystallized ligand.
As shown in Table 3, the overall docking results were compared
to the crystal structure of the bound native ligand, where the
compounds revealing the highest binding affinities, i.e., lowest
binding free energies within MAO-A, exhibiting highest
numbers of hydrogen bond interactions into the target receptor
and of the lowest RMSD values were considered as the best
fitted ones. The binding free energies (ΔGb) were revealed up
to −18.55 kcal/mol (Ki, 5.07 fM).
10a
10b
clorgyline
moclobemide
selegiline
>100
0.970
2.50 × 10−1
a
Data represent mean values (three significant digits) for at least three
separate experiments each performed in duplicate. Standard errors
were within 2%. SI (selectivity index) = Ki (MAO-B)/Ki (MAO-A)
b
ratio.
(MAO-B) = 0.853 versus 0.557 μM), while substitution of the
coumarin ring of (10a) with extra 3-methyl group inverses its
MAO inhibiting effects (10b) (Ki (MAO-A) = 5.93 pM, Ki
(MAO-B) = 0.548 μM).
In Vivo Inhibiting Effect. In vivo measurements indicate that
both the acetohydrazide compounds (1a) and (1b) exert a
remarkable inhibitory activity (ED50 = 8.05, 9.14 nM
respectively),being about 7-fold more active than iproniazide
(ED50 = 64.5 nM).
Furthermore, the mercapto-1,3,4 oxadiazoles (2a) and (2b)
and their thiadiazole bioisosters (2c) and (2d) elicit significant
inhibition potencies (ED50 = 7.85, 9.87, 7.95, and 9.55
nM,respectively). In addition, the diethylaminoethyl (3c) and
(3d) and the morpholinoethyl (3g) derivatives present
comparable potencies to the parent thiadiazolyl compounds
(2c) and (2d) (ED50 = 8.24, 9.55, and 8.33 nM,
respectively),while a sharp increase in the ED50 value is
observed for the oxadiazolyl derivatives (3a) and (3e) (52.6
and 256 nM,respectively) over the parent compound (2a).
On applying the flexible docking into MAO-A,the promising
compounds as drug candidates include compounds: (9d), (7b),
(4a), (2c), (2b), (7a), (1b), (1a), (3e), and (2d), which reveal
binding free energies (ΔGb) being in the range of −16.06 to
D
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Table 3. The Best Results of the Flexible Docking Regarding the Binding Free Energies (ΔGb) and Inhibition Constants (Ki) of
Compounds Docked into MAO-A, the Distances and Angles of Hydrogen Bonds between Compounds and Amino Acids
Involved in MAO-A and RMSD from Co-crystallized HRM Native Ligand
hydrogen bonds between atoms of compounds and amino acids of MAO-A
a
b
c
compd
ΔGb (kcal/mol)
Ki (fM)
atom of compd
amino acid
distance (Å)
angle (deg)
RMSD (Å)
1a
−16.74
−16.95
537.23
378.72
2CO
2CO
2CO
2CO
HO of Tyr444
HN of Asn181
HO of Tyr444
HN of Asn181
OC of Ala111
OC of Ala111
HN of Val210
HN of Val210
HO of Tyr444
HN of Asn181
HN of Asn181
OC of Ala111
OC of Gln215
HO of Tyr444
HO of Tyr444
HN of FAD
1.94
1.91
2.09
1.95
2.14
2.27
2.15
2.01
1.89
2.00
2.34
1.98
1.98
2.09
1.98
1.97
2.00
2.48
2.40
2.43
d
142.7
151.9
140.5
166.2
109.3
100.9
141.4
175.0
153.2
142.3
119.4
137.6
115.3
118.0
112.7
123.7
151.2
121.0
153.5
121.0
d
0.90
1.51
1b
a
terminal NH
b
terminal NH
2b
2c
−17.10
−17.10
293.98
294.11
oxadiazole N3
oxadiazole N4
2CO
4.41
1.05
2CO
O (pyrone)
SH (side chain)
terminal SH
2CO
2d
3e
−16.06
−16.31
1680
1110
2.15
1.50
O (pyrone)
2CO
4a
4b
−17.75
−15.49
97.95
4400
1.66
2.52
O (pyrone)
O (pyrone)
O (pyrone)
p-NH
HO of Tyr407
HN of Asn181
HO of Tyr444
HS of Cys323
d
5a
5b
−15.58
−15.82
3780
2540
d
1.67
0.33
2CO
HN of Asn181
HO of Tyr444
HS of Cys323
OC of Gln215
HO of Tyr444
HN of Asn181
HN of Val210
d
1.93
2.08
2.39
2.18
2.35
2.26
2.38
d
131.0
115.6
123.8
124.4
111.3
123.9
133.3
d
2CO
p-NH
7a
7b
8c
−16.96
−17.99
−15.36
229.51
64.72
SH (side chain)
O (pyrone)
O (pyrone)
O (morpholin)
d
1.25
1.33
2.08
5530
9b
9d
−17.78
−18.55
92.40
25.07
3.00
2.26
2CO
HN of Asn181
HO of Tyr444
d
2.25
1.88
146.2
146.9
d
2CO
e
HRM
−15.72
b
3020
d
d
e
0.28
a
c
d
Binding free energy. Inhibition constant. Root mean square deviation. No hydrogen bond detected. XCG: 2-(2-benzofuranyl)-2-imidazoline.
Figure 1. Evaluation of AutoDock 4.2 program by redocking of the native ligands HRM and XCG into MAO-A and MAO-B, as shown in (A) and
(B), respectively. Different runs of the docked HRM ligand into MAO-A, all runs (ball and stick and lines, colored by elements), and the docked
ligand XCG (ball and sticks, colored by element) into MAO-B, all seem superimposed onto the native cocrystallized ones (yellow sticks) within
RMSD 0.28 and 0.68 Å, respectively. The formed hydrogen bonds are shown as green dotted lines.
−18.55 kcal/mol, with RMSD range of 0.90−4.41 Å;moreover,
they exhibit up to four hydrogen bonds.
docked into MAO-A receptor, where they fit similarly within
the binding site, revealing high binding affinity (ΔGb) of
−17.10 and −16.95 kcal/mol, respectively. These docking
results are highly correlated to their biological ones, where their
MAO-A inhibitory activities are 11.0 and 5.01 pM and their in
vivo ED50 are 7.95 and 9.14 nM, respectively.
The analysis of the aforementioned docking results reveals
that there is a direct reasonable correlation between the
AutoDock binding free energy (ΔGb,kcal/mol) and the MAO-
A inhibitory activity (Ki,pM), being of correlation coefficients
(R2) of 0.788 for compounds (1b), (2b,d), (3a,e,g), (4b),
(5a,b), (7a,b), (8c), (9d), and (10a), as illustrated in Figure
2A. Additionally, the coumarin analogues (2c) and (1b) were
As shown in Figure 3, compound (2c) was docked exhibiting
four hydrogen bonds between its O (pyrone), 2-CO,and SH
with OH of Tyr444, NH of Asn181,and CO of Ala111,
E
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Table 4. The Best Results of the Flexible Docking Regarding the Binding Free Energies (ΔGb) and Inhibition Constants (Ki) of
Compounds Docked into MAO-B, the Distances and Angles of Hydrogen Bonds between Compounds and Amino Acids
Involved in MAO-B and RMSD from Co-crystallized XCG Native Ligand
hydrogen bonds between atoms of compounds and amino acids of MAO-B
a
b
c
compd
ΔGb (kcal/mol)
Ki (pM)
atom of compd
amino acid
distance (Å)
angle (deg)
RMSD (Å)
2a
−13.13
−13.84
238.08
71.74
2CO
HO of Tyr435
OC of Pro102
HO of Tyr326
HS of Cys172
HS of Cys172
OC of Leu171
OC of Pro102
HN of Asn203
HO of Tyr326
HO of Tyr326
HO of Ser200
HN of Arg100
HN of Thr201
d
1.95
2.16
1.95
2.15
2.01
2.31
2.07
2.21
2.19
2.49
1.78
2.10
2.25
d
152.9
131.7
139.1
132.0
142.8
150.7
169.3
132.7
152.7
126.7
146.1
115.9
144.1
d
5.44
3.18
SH (terminal)
O (pyrone)
N−N (thiadiazole)
N−N (thiadiazole)
SH (terminal)
terminal SH
2CO
2c
2d
3c
−12.72
−13.30
478.14
177.24
4.56
2.70
N−N (thiadiazole)
C−S (side chain)
thiadiazole CN
morpholine O
O (side chain)
d
3h
−13.08
259.64
4.15
4a
5b
6b
−12.69
−12.65
−13.22
500.54
529.61
203.74
4.51
4.71
5.16
thiazolidinone 5CO
HN of Gly101
OC of Gly101
HN of Thr201
HO of Tyr435
HS of Cys172
HS of Cys172
HO of Tyr326
HO of Tyr326
HO of Tyr326
HN of Gly101
HN of Gly101
HN of Asn203
HN of Arg100
HN of Gly101
OC of Pro102
HO of Tyr326
HN of Gly101
HN of Thr201
HN of Thr201
2.20
1.82
2.35
2.30
2.33
2.00
1.89
2.46
2.04
2.41
2.19
1.93
2.14
2.02
2.23
2.15
2.20
2.38
2.36
2.00
161.5
110.3
147.3
128.1
115.6
127.8
136.0
129.5
116.9
152.5
149.4
168.2
133.4
169.3
112.8
126.0
140.2
135.1
131.1
149.8
−CONH
−HNCO
7a
−14.33
31.18
2-CO
3.58
2-CO
O (pyrone)
N−N (triazole)
triazole CN
triazole CN−N
2CO
7b
8c
−14.42
−12.51
27.00
4.55
3.67
681.54
O (pyrone)
2CO
9a
9b
−14.05
−14.81
50.28
14.03
5.29
5.13
2CO
O (pyrone)
−CONH
−HNCO
O (pyrone)
9c
−14.31
−13.57
32.52
4.73
7-O
9d
113.55
1460
7-O
4.92
0.68
e
XCG
−12.06
NH (imidazole)
OC of Pro102
a
b
c
d
e
Binding free energy. Inhibition constant. Root mean square deviation. No hydrogen bond detected. HRM: 7-methoxy-1-methyl-9H-β-
carboline.
Figure 2. Correlation between MAO-A inhibitory activity (Ki, pM) and AutoDock ΔGb (A) for compounds (1b), (2b,d), (3a,e,g), (4b), (5a,b),
(7a,b), (8c), (9d), and (10a) and between MAO-B inhibitory activity (Ki, μM) and AutoDock ΔGb (B) for compounds (3a,b,e,h), (5b), (6a),
(8a,d), (9b), and (10b), revealing direct relationship of correlation coefficients (R2) being 0.788 and 0.797, respectively.
within RMSD of 1.05 Å, also compound (1b) is bound through
four hydrogen bonds between its 2-CO and terminal NH2
with exactly the same amino acids involved in binding of
compound (2c), within RMSD of 1.51 Å.
F
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vivo tryptamine seizure potentiation procedure in rats, revealed
direct correlation as shown in Figures 5 and 6, where
Figure 3. Mode of binding of compound (2c) (ball and stick, colored
by element) and compound (1b) (yellow sticks) involving flexible
docking into the binding pocket of MAO-A (2Z5X) shown as solid
backbone ribbon with the HRM ligand (blue lines) The hydrogen
bonds are shown as blue and green dashed lines for compound (2c)
and (1b), respectively.
On the other hand, the flexible docking into MAO-B
macromolecule is represented in Table 4, where many
compounds reveal fairly good docking results in comparison
to the natively embedded cocrystallized ligand. The promising
compounds as drug candidates include compounds: (9b), (7b),
(7a), (9c), (9a), (2c), (9d), (3c), (6b), (2a), and (3h), which
reveal binding free energies (ΔGb) within the range of −13.08
to −14.8 kcal/mol, with RMSD range of 2.70−5.44 Å;
moreover, they exhibit up to four hydrogen bonds.
Figure 5. Correlation between in vivo ED50 inhibition of MAO-A
(μM) and AutoDock ΔGb for compounds (1a,b), (2a,c,d), (3c,f,g,h),
(5a), (6a), (7a), (8a,c,d), and (10b), revealing a reasonable direct
correlation coefficients (R2) being 0.729.
The biologically active target compounds (9b) and (3h),
which have almost the same inhibitory activities against MAO-
B, being of 0.522 and 0.535 μM and in vivo ED50 of 74.58 and
75.74 μM, respectively, exhibited low binding free energies
(ΔGb) being of −14.81 and −13.08 kcal/mol, respectively,
upon their docking into MAO-B as shown in detail in Figure 4
Figure 6. Correlation between in vivo ED50 inhibition of MAO-B
(μM) and AutoDock ΔGb for compounds (1a), (2a,c,d), (3b,c),
(6a,b), (8a,b,c), and (10a,b), revealing excellent direct relationship of
correlation coefficients (R2) of 0.889.
Figure 4. AutoDock binding affinities of compounds (9b) (ball and
stick, colored by element) and (3h) (yellow sticks) into MAO-B
(2XFN). The docked inhibitors seem exactly overlapped onto the
native XCG ligand (blue lines). The binding MAO-B pocket is shown
in solid surface and the hydrogen bonds as green dotted lines.
correlation between the in vivo ED50 inhibition of MAO-A
(μM) and the AutoDock ΔGb (kcal/mol) for compounds
(1a,b), (2a,c,d), (3c,f,g,h), (5a), (6a), (7a), (8a,c,d), and
(10b) exhibits highly reasonable direct correlation coefficients
(R2) of 0.729 (Figure 5). To a better extent, the correlation
between the ED50 inhibition of MAO-B (μM) and the
AutoDock ΔGb for compounds (1a), (2a,c,d), (3b,c), (6a,b),
(8a,b,c), and (10a,b) exhibits excellent direct correlation
coefficients (R2) being of 0.889 as shown in Figure 6.
in comparison to the bound native ligand 2. Compound (9b)
exhibits four hydrogen bonds between its moieties and amino
acids: Arg100, Gly101, Prp102, and Tyr326, within RMSD of
5.13 Å, whereas compound (3h) binds by two hydrogen bonds
between its thiazole (CN) and morpholine (O) with amino
acids: Arg100 and Ser200, within RMSD of 4.15 Å.
The analysis of the docking results, revealed a direct
reasonable correlation between the AutoDock binding free
energy (ΔGb; kcal/mol) and the MAO-B inhibitory activity
(μM), being of better correlation coefficients (R2) of 0.797 for
compounds (3a,b,e,h), (5b), (6a), (8a,d), (9b), and (10b), as
illustrated in Figure 2B.
Being that the correlation (R2) between ΔGb and MAO-A
inhibition, is 0.788 and (R2) between ΔGb and ED50 of MAO-A
is 0.729, the aforementioned reasonable correlations between
the molecular simulation and biological MAO-A inhibition,
implied that acetohydrazide (1b), 5-mercapto-1,3,4-thiadiazole
(2d), 5-(2-morpholinoethylthio)-1,3,4-thiadiazole (3g), 5-(4-
Additionally, the results of the in vivo MAO inhibiting
properties (ED50) of the compounds studied involving the in
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chlorophenylamino)-1,3,4-thiadiazole (5a), 4-(4-chlorophen-
yl)-5-mercapto-4H-1,2,4-triazole (7a), and 5-(2-morpholinoe-
thylthio)-4-(4-chlorophenyl)-4H-1,2,4-triazole (8c) represent
to a higher extent the structural prerequisites for the design of
potentially active MAO-A inhibitors.
between the compounds and Ile199 in MAO-B. Loss of
this interaction may explain the weaker MAO-B binding
affinities compared to MAO-A ones.
(iii) The major structural dissimilarity is that MAO-A has a
monopartite substrate cavity of ∼550 Å3 volume and
MAO-B contains a dipartite cavity structure with
volumes of ∼290 Å3 (hydrophobic entrance cavity) and
∼400 Å3 (polar substrate cavity). This means that MAO-
B inhibitors of high affinities must undergo polar and
apolar interactions with the substrate and entrance
cavities, respectively. However, such prerequisites are
not available in the studied coumarins, which have mainly
hydrophobic moieties being of 2-oxo-2H-chromene
aromatic structure and side chains being: acetohydra-
zides, 4-chlorophenylamino, 5-(2-(diethylamino)-
ethylthio) oxadiazoles, 5-(2-morpholinoethylthio) ana-
logues of oxadiazoles, thiadiazoles, and triazoles, whereas
the hydrophilic side chain containing compounds such as
thiosemicarbazide (4a) or acetohydrazide (9a−c) can
reveal some fitting into MAO-B.
On the other hand, ΔGb and MAO-B inhibition are
correlated by (R2) of 0.797; moreover, ΔGb is correlated with
ED50 of MAO-B by (R2) of 0.889. These reasonable
correlations between the molecular simulation and the
biological MAO-B inhibition indicated that 5-(2-
(diethylamino)ethylthio)-1,3,4-oxadiazol (3b), N-(2-(4-chlor-
ophenylimino)-4-oxothiazolidin-3-yl)acetamide (6a), 5-(2-
(diethylamino)ethylthio)-4-(4-chlorophenyl)-4H-1,2,4-triazole
(8a), and N-(2-(4-chlorophenyl)-4-oxothiazolidin-3-yl)-
acetamide (10b) represent to a higher extent the structural
prerequisites for designing potentially active MAO-B inhibitors.
Structure−Activity Relationship (SAR). According to the
molecular simulation results, a significant to mild nonselective
increase of MAO-A and MAO-B inhibitory affinity of both
mercapto-1,3,4-oxadiazole (2b) and their thiadiazole bioisosters
(2c,d) than the parent hydrazide lead (1a) is observed by
replacing acetohydrazide by 5-mercapto-1,3,4-oxadiazole or
1,3,4-thiadiazole. Also a mild increase is observed by
introducing 4-chlorophenylthiosemicarbazides in (4a,b) and
4-(4-chlorophenyl)-5-mercapto-1,2,4-triazoles in (7a,b) and
Schiff’s bases (9a−d). The above-mentioned increase of the
inhibitory affinities may be attributed to the inserted aryl
fragment of (2b,c,d) and (7a,b), which tend to be deeply
embedded and accommodated into the hydrophobic region of
MAO isoenzymes, exhibiting an electrostatic surface attraction
and hydrophobic interactions with their active sites. While such
affinity increase of compounds (4a,b) and (9a,d) may be
attributed to their flexible thiosemicarbazides (4a,b), benzyli-
dene acetohydrazide (9a), or ethylidene acetohydrazide (9d)
which enable them to hydrophilically interact with more
hydrogen binding. The isosteric changes of 2-(4-chloropheny-
limino)-4-oxothiazolidine congener (6b) afford a slight
enhanced MAO-B selective affinity over MAO-A. The
aforementioned docking results matched well with the
biological results (Table 1).
CONCLUSION
■
New series of bioactive 7-oxycoumarin derivatives were
designed, synthesized, and evaluated for their in vitro MAO
inhibitory activity regarding the two isoforms of the enzyme. All
the studied compounds show a very high affinity and selectivity
for the MAO-A isoenzyme, compared to clorgyline and
moclobemide, with Ki values in the picomolar concentration
range. In particular, the acetohydrazide derivative (1b) (Ki
(MAO-A) = 5.01 pM, and SI = 9.66 × 104) and the
diethylaminoethylthio-1,3,4-thiadiazole compound (3d) (Ki
(MAO-A) = 5.18 pM, and SI = 9.58 × 104) are exceptionally
the most potent and selective MAO-A inhibitors. In addition,
most of the target compounds display high potency toward
MAO when tested in vivo. Both 5-mercapto-1,3,4-oxadiazole
(2a) and its thiadiazole bioisoster (2c) display the highest
potencies the in vivo (ED50 = 7.85 and 7.95 nM respectively).
In addition, the docking studies performed on these
compounds reveal that there is a direct reasonable correlation
between the AutoDock binding free energy (ΔGb, kcal/mol)
and the MAO-A inhibitory activity (Ki, pM), being of
correlation coefficients (R2) of 0.788 for compounds (1b),
(2b,d), (3a,e,g), (4b), (5a,b), (7a,b), (8c), (9d), and (10a).
Compound (1b) is bound through four hydrogen bonds
between its 2-CO and terminal NH2 with OH of Tyr444,
NH of Asn181, and CO of Ala111 within RMSD of 1.51 Å.,
Additionally, the results of in vivo MAO inhibiting properties
(ED50) of compounds studied involving in vivo tryptamine
seizure potentiation procedure in rats reveal a direct
correlation, where a correlation between the in vivo ED50
inhibition of MAO-A (μM) and the AutoDock ΔGb (kcal/mol)
for compounds (1a,b), (2a,c,d), (3c,f,g,h), (5a), (6a), (7a),
(8a,c,d), and (10b) exhibits highly reasonable direct correlation
coefficients (R2) of 0.729. Isosteric variations in position 7 of
the studied coumarin derivatives restore a satisfactory MAO
inhibitory affinity and MAO-A/MAO-B selectivity. The results
considering SAR reveal that the higher MAO isoenzymes
binding affinities were obtained with the structure features: 4-
methyl or 3,4-dimethyl-7-oxycoumarin, 4-methylcoumarinylth-
iosemicarbazide, N′-(4-chlorobenzylidene) acetohydrazide
Schiff’s base, whereas such affinity is dropped by the directly
attached 4-chlorophenyl group to the thaizolidinone ring of 4-
Isosteric variations in position 7 of the studied coumarin
derivatives restored satisfactory MAO inhibitory affinity and
MAO-A/MAO-B selectivity. The results considering SAR
reveal that the higher MAO isoenzymes binding affinities are
obtained with the structure features; 4-methyl or 3,4-dimethyl-
7-oxycoumarin, 4-methylcoumarinylthiosemicarbazide, and N′-
(4-chlorobenzylidene) acetohydrazide Schiff’s base, whereas
such affinity is dropped by the directly attached 4-chlorophenyl
group to the thaizolidinone ring of the 4-methylcoumarinyl-7-
oxyacetamide derivative, by the oxadiazole fragment and rarely
by the thiadiazole moiety.
The higher affinity of the studied coumarin analogues to
MAO-A being much more than MAO-B can be explained by:
(i) The structural differences arising from Ile-335 in MAO-A
vs Tyr-326 in MAO-B, where the compounds could not
be accommodated into MAO-B because of their
structural overlap with Tyr-326.
(ii) The active site cavity of MAO-A Phe208 residue was
located at the position occupied by Ile199 in MAO-B. As
a result, a π−π interaction between the studied
compounds and Phe208 significantly enhances their
affinities to MAO-A. While, such interaction is absent
H
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Ar−H). MS m/z (RA %): 404 (M+ + 1) (18%), 190 (5%), 161 (16%),
145 (6%), 99 (100%).
methylcoumarinyl-7-oxyacetamide derivative, by the oxadiazole
fragment, and rarely by the thiadiazole moiety.
7-((5-(2-(Diethylamino)ethylthio)-1,3,4-thiadiazol-2-yl)-
methoxy)-4-methyl-2H-chromen-2-one (3c). Yield 76%; mp
175−7 °C; mol wt 405.53. IR (cm−1, KBr): 3073 (CH aromatic
stretching), 2973, 2937 (CH aliphatic stretching), 1716 (CO, α-
pyrone). 1H NMR (DMSO-d6, δ, ppm): 1.17 (6H, t, 2 CH3CH2), 2.37
(3H, s, CH3), 3.12 (4H, q, 2 CH2CH3), 3.40 (2H, t, CH2N), 3.97 (2H,
t, CH2S), 5.67 (2H, s, OCH2), 6.23 (1H, s, H-3 coumarin), 7.06−7.71
(3H, m, Ar−H). MS m/z (RA %): 405 (M+) (2%), 214 (12%), 150
(19%), 149 (18%), 148 (100%).
7-((5-(2-(Diethylamino)ethylthio)-1,3,4-thiadiazol-2-yl)-
methoxy)-3,4-dimethyl-2H-chromen-2-one (3d). Yield 77%; mp
78−81 °C; mol wt 419.56. IR (cm−1, KBr): 3062 (CH aromatic
stretching), 2967, 2927 (CH aliphatic stretching), 1717 (CO, α-
pyrone). 1H NMR (DMSO-d6, δ, ppm): 1.18 (6H, t, 2 CH3CH2), 2.20
(3H, s, CH3), 2.38 (3H, s, CH3), 3.20 (4H, q, 2 CH2CH3), 2.50 (2H,
t, CH2N), 3.89 (2H, t, CH2S), 5.48 (2H, s, OCH2), 6.89−7.56 (3H, m,
Ar−H). MS m/z (RA %): 420 (M+ + 1) (6%), 173 (6%), 162 (3%),
99 (33%), 86 (100%).
EXPERIMENTAL SECTION
■
Chemistry. Melting points were determined on Electrothermal IA
9000 apparatus and were uncorrected. The infrared (IR) spectra were
recorded using Nexus 670 FT-IR FT-Raman spectrometer as
potassium bromide discs at the National Research Centre. The proton
nuclear resonance (1H NMR) spectra were determined on Varian
mercury 500 MHz spectrometer, using tetramethylsilane (TMS) as the
internal standard, at the National Research Centre. The mass spectra
were performed on JEOL JMS-AX500 mass spectrometer at the
National Research Centre. The reactions were followed by TLC (silica
gel, aluminum sheets 60 F254, Merck) using chloroform−methanol
(9.5:0.5 v/v) as eluent and sprayed with iodine−potassium iodide
reagent. The purity of the newly synthesized compounds was assessed
by TLC and elemental analysis and was found to be higher than 95%.
Preparation of 2-(4-Methyl (and/or 3,4-Dimethyl)-2-oxo-2H-
chromen-7-yloxy) Acetohydrazides (1a,b). Acetohydrazides
(1a)28 and (1b)29 were prepared according to the reported methods.
Preparation of 7-[(5-Mercapto-1,3,4-oxadiazol-2-yl)-
methoxy]-4-methyl (and/or 3,4-Dimethyl) coumarin (2a,b).
Compounds (2a)27 and (2b) were prepared according to Eid et al.27
7-((5-Mercapto-1,3,4-oxadiazol-2-yl)methoxy)-3,4-dimethyl-
2H-chromen-2-one (2b). Yield 72%; mp 220−5 °C; mol wt 304.32.
Crystallization: EtOH. IR (cm−1, KBr): 3089 (CH aromatic
stretching), 2926 (CH aliphatic stretching), 2610 (SH), 1693 (C
O, α-pyrone). 1H NMR (DMSO-d6, δ, ppm): 2.22 (3H, s, CH3), 2.33
(3H, s, CH3), 3.01 (1H, s, SH, D2O exchangeable), 5.41 (2H, s,
OCH2), 6.83−7.55 (3H, m, Ar−H). MS m/z (RA %): 305 (M+ + 1)
(13%), 304 (M+) (69%), 190 (100%), 162 (66%), 147 (16%).
Preparation of 7-[(5-Mercapto-1,3,4-thiadiazol-2-yl)-
methoxy]-4-methyl (and/or 3,4-Dimethyl)coumarins (2c,d).
Compounds (2c)27 and (2d) were prepared according to the reported
method.27
7-((5-(2-Morpholinoethylthio)-1,3,4-oxadiazol-2-yl)-
methoxy)-4-methyl-2H-chromen-2-one (3e). Yield 70%; mp 93−
5 °C; mol wt 403.45. IR (cm−1, KBr): 3069 (CH aromatic stretching),
1
2957, 2833 (CH aliphatic stretching), 1727 (CO, α-pyrone). H
NMR (DMSO-d6, δ, ppm): 2.39 (3H, s, CH3), 2.50 (4H, t, 2 CH2 N
morpholine), 2.77 (2H, t, CH2N), 3.44 (2H, t, CH2S), 3.68 (4H, t, 2
CH2O morpholine), 5.27 (2H, s, OCH2), 6.17 (1H, s, H-3 coumarin),
6.93−7.54 (3H, m, Ar−H). MS m/z (RA %): 403 (M+) (0.2%), 189
(2%), 176 (2%), 147 (6%), 113 (16%), 18(100%).
7-((5-(2-Morpholinoethylthio)-1,3,4-oxadiazol-2-yl)-
methoxy)-3,4-dimethyl-2H-chromen-2-one (3f). Yield 71%; mp
109−110 °C; mol wt 417.48. IR (cm−1, KBr): 3074 (CH aromatic
stretching), 2930, 2861 (CH aliphatic stretching), 1703 (CO, α-
pyrone). 1H NMR (DMSO-d6, δ, ppm): 2.22 (3H, s, CH3), 2.34 (3H,
s, CH3), 2.51 (4H, t, 2 CH2 N morpholine), 2.72 (2H, t, CH2N), 3.40
(2H, t, CH2S), 3.65 (4H, t, 2 CH2O morpholine), 5.25 (2H, s,
OCH2), 6.92−7.55 (3H, m, Ar−H). MS m/z (RA %): 417 (M+) (2%),
189 (3%), 161 (7%), 113 (43%), 100 (100%), 98 (12%).
7-((5-(2-Morpholinoethylthio)-1,3,4-thiadiazol-2-yl)-
methoxy)-4-methyl-2H-chromen-2-one (3g). Yield 67%; mp
250−3 °C; mol wt 419.52. IR (cm−1, KBr): 3065 (CH aromatic
stretching), 2976, 2881 (CH aliphatic stretching), 1719 (CO, α-
pyrone). 1H NMR (DMSO-d6, δ, ppm): 2.37 (3H, s, CH3), 2.60 (4H,
t, 2 CH2 N morpholine), 2.64 (2H, t, CH2N), 3.45 (2H, t, CH2S),
3.49 (4H, t, 2CH2O morpholine), 5.65 (2H, s, OCH2), 6.23 (1H, s, H-
3 coumarin), 7.03−7.70 (3H, m, Ar−H). MS m/z (RA %): 419 (M+)
(1%), 359 (4%), 187 (4%), 176 (7%), 147 (34%), 28 (100%).
7-((5-(2-Morpholinoethylthio)-1,3,4-thiadiazol-2-yl)-
methoxy)-3,4-dimethyl-2H-chromen-2-one (3h). Yield 70%; mp
140−2 °C; mol wt 433.54. IR (cm−1, KBr): 3052 (CH aromatic
stretching), 2966, 2924 (CH aliphatic stretching), 1717 (CO, α-
pyrone). 1H NMR (DMSO-d6, δ, ppm): 2.03 (3H, s, CH3), 2.33 (3H,
s, CH3), 2.35 (4H, t, 2 CH2 N morpholine), 2.61 (2H, t, CH2N), 3.40
(2H, t, CH2S), 3.47 (4H, t, 2 CH2O morpholine), 5.60 (2H, s,
OCH2), 6.99−7.68 (3H, m, Ar−H). MS m/z (RA %): 433 (M+) (2%),
288 (7%), 189 (7%), 161 (27%), 113 (60%), 100 (100%).
7-((5-Mercapto-1,3,4-thiadiazol-2-yl)methoxy)-3,4-dimeth-
yl-2H-chromen-2-one (2d). Yield 78%; mp 260−5 °C; mol wt
320.39. Crystallization: EtOH. IR (cm−1, KBr): 3071 (CH aromatic
stretching), 2874 (CH aliphatic stretching), 2667 (SH), 1671 (CO,
1
α-pyrone). H NMR (DMSO-d6, δ, ppm): 2.21 (3H, s, CH3), 2.31
(3H, s, CH3), 3.01 (1H, s, SH, D2O exchangeable), 5.38 (2H, s,
OCH2), 6.82−7.56 (3H, m, Ar−H). MS m/z (RA %): 320 (M+) (3%),
248 (61%), 220 (25%), 190 (46%), 161 (100%), 147 (32%).
General Procedure for Preparation of 7-((5-(2-(Diethylami-
no)-ethylthio (and/or 2-Morpholinoethylthio)-1,3,4-oxadiazol
(and/or 1,3,4-Thiadiazol)-2-yl)methoxy)-4-methyl (and/or 3,4-
Dimethyl)-2H-chromen-2-ones (3a−h). A mixture of (2a−d)
(0.01 mol), diethylaminoethyl chloride hydrochloride, and/or 4-(2-
chloroethyl)morpholine hydrochloride (0.03 mol) and anhydrous
potassium carbonate (4.2 g, 0.03 mol) in dry acetone (100 mL) was
refluxed while stirring for 10−15 h. The mixture was filtered while hot,
the filtrate was concentrated, and water was added to precipitate the
desired target compounds which were recrystallized from acetone/
water.
7-((5-(2-(Diethylamino)ethylthio)-1,3,4-oxadiazol-2-yl)-
methoxy)-4-methyl-2H-chromen-2-one (3a). Yield 67%; mp 91−
3 °C; mol wt 389.47. IR (cm−1, KBr): 3067 (CH aromatic stretching),
General Procedure for Preparation of 1-(2-(4-Methyl (and/or
3,4-Dimethyl)coumarinyl-7-yloxy)acetyl)-4-(4-chlorophenyl)
Thiosemicarbazides(4a,b). Compounds (4a)30 and (4b) were
prepared according to the reported method.30
1
2967, 2932 (CH aliphatic stretching), 1728 (CO, α-pyrone). H
NMR (DMSO-d6, δ, ppm): 1.07 (6H, t, 2 CH3CH2), 2.39 (3H, s,
CH3), 2.67 (4H, q, 2 CH2CH3), 2.94 (2H, t, CH2N), 3.45 (2H, t,
CH2S), 5.26 (2H, s, OCH2), 6.16 (1H, s, H-3 coumarin), 6.92−7.53
(3H, m, Ar−H). MS m/z (RA %): 390 (M+ + 1) (12%), 211(13%),
174 (15%), 145 (45%), 98 (100%).
1-(2-(3,4-Dimethyl-2-oxo-2H-chromen-7-yloxy)acetyl)-4-(4-
chloro phenyl) Thiosemicarbazide (4b). Yield 88%; mp 207−9
°C; mol wt 431.89. Crystallization: AcOH. IR (cm−1, KBr): 3399,
3315 (NH), 3110 (CH aromatic stretching), 2962 (CH aliphatic
stretching), 1702 (CO, α-pyrone), 1670 (CO), 1242 (CS). 1H
NMR (DMSO-d6, δ, ppm): 1.99 (1H, s, NH, D2O exchangeable), 2.05
(3H, s, CH3), 2.34 (3H, s, CH3), 3.82 (1H, s, NH, D2O exchangeable),
5.23 (2H, s, OCH2), 6.83−7.60 (7H, m, Ar−H), 7.98 (1H, s, NH,
D2O exchangeable). MS m/z (RA %): 433 (M+ + 2) (3%), 431 (M+)
(10%), 429 (9%), 190 (88%), 189 (64%), 161 (100%).
7-((5-(2-(Diethylamino)ethylthio)-1,3,4-oxadiazol-2-yl)-
methoxy)-3,4-dimethyl-2H-chromen-2-one (3b). Yield 65%; mp
78−80 °C; mol wt 403.50. IR (cm−1, KBr): 3065 (CH aromatic
stretching), 2967, 2925 (CH aliphatic stretching), 1714 (CO, α-
pyrone). 1H NMR (DMSO-d6, δ, ppm): 1.00 (6H, t, 2 CH3CH2), 2.15
(3H, s, CH3), 2.34 (3H, s, CH3), 2.56 (4H, q, 2 CH2CH3), 2.83(2H, t,
CH2N), 3.41 (2H, t, CH2S), 5.23 (2H, s, OCH2), 6.87−7.50 (3H, m,
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General Procedure for Preparation of 7-((5-(4-Chlorophe-
nylamino)-1,3,4-thiadiazol-2-yl)methoxy)-4-methyl (and/or
3,4-Dimethyl)coumarins (5a,b). Compounds (5a)30 and (5b)
were prepared according to the reported method.30
CH3CH2), 2.08 (3H, s, CH3), 2.33 (3H, s, CH3), 2.43 (4H, q, 2
CH2CH3), 2.45 (2H, t, CH2N), 3.26 (2H, t, CH2S), 5.23 (2H, s,
OCH2), 6.81−7.62 (7H, m, Ar−H). MS m/z (RA %): 515 (M+ + 2)
(0.13%), 513 (M+) (0.39%), 190 (7%), 99 (100%), 86 (66%).
7-((5-(2-Morpholinoethylthio)-4-(4-chlorophenyl)-4H-1,2,4-
triazol-3-yl)methoxy)-4-methyl-2H-chromen-2-one (8c). Yield
80%; mp 86−89 °C; mol wt 513.01. IR (cm−1, KBr): 3090 (CH
aromatic stretching), 2945, 2850 (CH aliphatic stretching), 1733 (C
O, α-pyrone). 1H NMR (DMSO-d6, δ, ppm): 2.34 (3H, s, CH3), 2.50
(4H, t, 2CH2 N morpholine), 2.76 (2H, t, CH2N), 3.46 (2H, t, CH2S),
3.67 (4H, t, 2CH2O morpholine), 5.08 (2H, s, OCH2), 6.21 (1H, s, H-
3 coumarin), 6.77−7.50 (7H, m, Ar−H). MS m/z (RA %): 515 (M+ +
2) (0.03%), 513 (M+) (0.1%), 176 (4%), 150 (10%), 114 (35%), 113
(100%).
7-((5-(2-Morpholinoethylthio)-4-(4-chlorophenyl)-4H-1,2,4-
triazol-3-yl)methoxy)-3,4-dimethyl-2H-chromen-2-one (8d).
Yield 81%; mp 174−6 °C; mol wt 527.03. IR (cm−1, KBr): 3094
(CH aromatic stretching), 2936, 2863 (CH aliphatic stretching), 1698
(CO, α-pyrone). 1H NMR (DMSO-d6, δ, ppm): 2.17 (3H, s, CH3),
2.35 (3H, s, CH3), 2.49 (4H, t, 2CH2 N morpholine), 2.76 (2H, t,
CH2N), 3.46 (2H, t, CH2S), 3.67 (4H, t, 2CH2O morpholine), 5.08
(2H, s, OCH2), 6.78−7.49 (7H, m, Ar−H). MS m/z (RA %): 529 (M+
+ 2) (0.03%), 527 (M+) (0.1%), 190 (5%), 162 (2%), 114 (19%), 113
(100%).
7-((5-(4-Chlorophenylamino)-1,3,4-thiadiazol-2-yl)-
methoxy)-3,4-dimethyl-2H-chromen-2-one (5b). Yield 88%; mp
207−9 °C; mol wt 413.88. Crystallization: AcOH. IR (cm−1, KBr):
3303 (NH), 3077 (CH aromatic stretching), 2926 (CH aliphatic
1
stretching), 1676 (CO, α-pyrone). H NMR (DMSO-d6, δ, ppm):
2.03 (3H, s, CH3), 2.32 (3H, s, CH3), 5.49 (2H, s, OCH2), 7.09−7.67
(7H, m, Ar−H), 10.58 (1H, s, NH, D2O exchangeable). MS m/z (RA
%): 415 (M+ + 2) (4%), 413 (M+) (12%), 226 (30%), 191 (30%), 190
(100%), 162 (91%).
Preparation of N-(2-(4-Chlorophenylimino)-4-oxothiazoli-
din-3-yl)-2-(4-methyl (and/or 3,4-Dimethyl)coumarin-7-yloxy)-
acetamides (6a,b). A mixture of thiosemicarbazides (4a,b) (0.01
mol), chloroacetic acid (0.01 mol), and anhydrous sodium acetate (0.5
g) in absolute ethanol was refluxed while stirring for about 25 h. The
solution was concentrated, and the precipitated solid was filtered and
crystallized from acetic acid/water.
N-(2-(4-Chlorophenylimino)-4-oxothiazolidin-3-yl)-2-(4-
methyl-2-oxo-2H-chromen-7-yloxy)acetamide (6a). Yield 76%;
mp 225−7 °C; mol wt 457.89. IR (cm−1, KBr): 3225 (NH), 3071
(CH aromatic stretching), 2960 (CH aliphatic stretching), 1723 (C
1
O, α-pyrone), 1665 (CO). H NMR (DMSO-d6, δ, ppm): 2.33
General Procedure for Preparation of Schiff’s Bases (9a−d).
Schiff’s bases (9a),28 (9b), (9c),28 and (9d) were prepared according
to the reported method.28
(3H, s, CH3), 3.75 (2H, s, CH2-thiazolidinone), 5.18 (2H, s, OCH2),
6.17 (1H, s, H-3 coumarin), 6.83−7.58 (7H, m, Ar−H), 10.58 (1H, s,
NH, D2O exchangeable). MS m/z (RA %): 459 (M+ + 2) (12%), 457
(M+) (36%), 443 (25%), 341 (33%), 206 (31%), 50 (100%).
2-(3,4-Dimethyl-2-oxo-2H-chromen-7-yloxy)-N′-(4-
chlorobenzylidene)acetohydrazide (9b). Yield 80%; mp 233−5
°C; mol wt 384.81. Crystallization: AcOH. IR(cm−1, KBr): 3211
(NH),3089 (CH aromatic stretching), 2964, 2854 (CH aliphatic
stretching), 1719 (CO, α-pyrone),1686 (CO), 1626 (CN). 1H
NMR (DMSO-d6, δ, ppm): 2.04 (3H, s, CH3), 2.34 (3H, s, CH3), 5.25
(2H, s, OCH2), 6.92−7.99 (7H, m, Ar−H), 8.00 (1H, s, CHN),
11.7 (1H, s, NH, D2O exchangeable). MS m/z (RA %): 386 (M+ + 2)
(3%), 384 (M+) (10%), 283 (47%), 235 (100%), 219 (53%),
217(50%).
N-(2-(4-Chlorophenylimino)-4-oxothiazolidin-3-yl)-2-(3,4-di-
methyl-2-oxo-2H-chromen-7-yloxy)acetamide (6b). Yield 74%;
mp 170−2 °C; mol wt 471.91. IR (cm−1, KBr): 3290 (NH), 3095
(CH aromatic stretching), 2921 (CH aliphatic stretching), 1705 (C
1
O, α-pyrone), 1609 (CO). H NMR (DMSO-d6, δ, ppm): 2.03
(3H, s, CH3), 2.30 (3H, s, CH3), 3.69 (2H, s, CH2-thiazolidinone),
5.16 (2H, s, OCH2), 6.81−7.63 (7H, m, Ar−H), 10.40 (1H, s, NH,
D2O exchangeable). MS m/z (RA %): 473 (M+ + 2) (2%), 471 (M+)
(6%), 268 (10%), 224 (24%), 147 (36%), 55(91%).
2-(3,4-Dimethyl-2-oxo-2H-chromen-7-yloxy)-N′-(1-(4-
chlorophenyl)ethylidene)acetohydrazide (9d). Yield 78%; mp
228−230 °C; mol wt 398.84. Crystallization: AcOH. IR (cm−1, KBr):
3084 (CH aromatic stretching), 2927 (CH aliphatic stretching), 1707
General Procedure for Preparation of 7-[(4-(4-Chlorophen-
yl)-5-mercapto-1,2,4-triazol-3-yl)methoxy]-4-methyl (and/or
3,4-Dimethyl) Coumarins (7a,b). Compounds (7a)30 and (7b)
were prepared according to the reported method.30
1
(CO, α-pyrone), 1628 (CO), 1611 (CO). H NMR (DMSO-
7-((4-(4-Chlorophenyl)-5-mercapto-4H-1,2,4-triazol-3-yl)-
methoxy)-3,4-dimethyl-2H-chromen-2-one (7b). Yield 88%; mp
220−2 °C; mol wt 413.88. Crystallization: EtOH. IR (cm−1, KBr):
3093 (CH aromatic stretching), 2920 (CH aliphatic stretching), 2550
d6, δ, ppm): 2.04 (3H, s, CH3), 2.25 (3H, s, CH3), 2.33 (3H, s, CH3),
5.28 (2H, s, OCH2), 6.89−7.83 (7H, m, Ar−H), 10.95 (1H, s, NH,
D2O exchangeable). MS m/z (RA %): 400 (M+ + 2) (12%), 398 (M+)
(32%), 211 (34%), 209 (100%), 188 (14%), 163(16%).
1
(SH), 1685 (CO, α-pyrone). H NMR (DMSO-d6, δ, ppm): 2.17
General Procedure for Preparation of 2-(4-Methyl (and/or
3,4-Dimethyl)coumarinyl-7-yloxy)-N-(2-(4-chlorophenyl)-4-ox-
othiazolidin-3-yl)acetamide (10a,b). A homogeneous mixture of
the Schiff’s bases (9a,b) (0.01 mol) and thioglycolic acid (0.92 g, 0.01
mol) in 20 mL of glacial acetic acid was refluxed for about 10 h. The
reaction mixture was triturated with sodium bicarbonate (10%)
solution, and the resulting neutral solution was poured onto crushed
ice .The separated product was filtered off, washed with water, dried,
and recrystallized from ethanol.
(3H, s, CH3), 2.35 (3H, s, CH3), 3.01 (1H, s, SH, D2O exchangeable),
5.08 (2H, s, OCH2), 6.77−7.49 (7H, m, Ar−H). MS m/z (RA %): 415
(M+ + 2) (9%), 413 (M+) (24%), 190 (100%), 162 (26%), 147 (7%).
General Procedure for Preparation of 7-((5-(2-
(Diethylamino)ethylthio) (and/or (2-Morpholinoethylthio))-4-
(4-chlorophenyl)-4H-1,2,4-triazol-3-yl) methoxy)-4-methyl
(and/or 3,4-Dimethyl) Coumarins (8a−d). The target compounds
(8a−d) were prepared from (7a,b) according to the previously
described method for the preparation of compounds (3a−h), and the
synthesized compounds were crystallized from acetone/water.
2-(4-Methyl-2-oxo-2H-chromen-7-yloxy)-N-(2-(4-chloro-
phenyl)-4-oxothiazolidin-3-yl)acetamide (10a). Yield 73%; mp
235−7 °C; mol wt 444.89. IR (cm−1, KBr): 3130 (NH), 3001 (CH
aromatic stretching), 2922, 2853(CH aliphatic stretching), 1722 (C
7-((5-(2-(Diethylamino)ethylthio)-4-(4-chlorophenyl)-4H-
1,2,4-triazol-3-yl)methoxy)-4-methyl-2H-chromen-2-one (8a).
Yield 70%; mp 115−7 °C; mol wt 499.02. IR (cm−1,KBr): 3088
(CH aromatic stretching), 2966, 2932 (CH aliphatic stretching),
1741(CO, α-pyrone). 1H NMR (DMSO-d6, δ, ppm): 1.01 (6H, t, 2
CH3CH2), 2.34 (3H, s, CH3), 2.41 (4H, q, 2 CH2CH3), 2.47 (2H, t,
CH2N), 3.27 (2H, t, CH2S), 5.21 (2H, s, OCH2), 6.19 (1H, s, H-3
coumarin), 6.83−7.60 (7H, m, Ar−H). MS m/z (RA %): 501 (M+ +
2) (20%), 499 (M+) (60%), 427 (67%), 398 (60%), 250 (100%).
7-((5-(2-(Diethylamino)ethylthio)-4-(4-chlorophenyl)-4H-
1,2,4-triazol-3-yl)methoxy)-3,4-dimethyl-2H-chromen-2-one
(8b). Yield 74%; mp 118−120 °C; mol wt 513.05. IR (cm−1, KBr):
3095 (CH aromatic stretching), 2968, 2931 (CH aliphatic stretching),
1702 (CO, α-pyrone). 1H NMR (DMSO-d6, δ, ppm): 1.03 (6H, t, 2
1
O, α-pyrone), 1615 (CO). H NMR (DMSO-d6, δ, ppm): 2.31
(3H, s, CH3), 3.74, 3.87 (2H, dd, CH2 thiazolidinone), 4.79 (2H, s,
OCH2), 5.77 (1H, s, CH thiazolidinone), 6.17 (1H, s, H-3 coumarin),
6.74−7.60 (7H, m, Ar−H), 10.50 (1H, s, NH, D2O exchangeable). MS
m/z (RA %): 446 (M+ + 2) (3%), 444 (M+) (8%), 386 (25%), 312
(21%), 233 (100%), 212 (63%).
2-(3,4-Dimethyl-2-oxo-2H-chromen-7-yloxy)-N-(2-(4-chloro-
phenyl)-4-oxothiazolidin-3-yl)acetamide (10b). Yield 71%; mp
148−150 °C; mol wt 458.91. IR (cm−1, KBr): 3237 (NH), 3001 (CH
aromatic stretching), 2991, 2914(CH aliphatic stretching), 1693 (C
1
O, α-pyrone), 1612 (CO). H NMR (DMSO-d6, δ, ppm): 2.04
(3H, s, CH3), 2.32 (3H, s, CH3), 3.74, 3.89 (2H, dd,CH2
J
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thiazolidinone), 4.79 (2H, s, OCH2), 5.75 (1H, s, CH thiazolidinone),
6.75−7.60 (7H, m, Ar−H), 10.49 (1H, s, NH, D2O exchangeable). MS
m/z (RA %): 460 (M+ + 2) (11%), 458 (M+) (27%), 248 (9%), 247
(100%), 190 (32%), 189 (29%).
Test compounds, standard or vehicle controls, were adminis-
tered intraperitoneally 0.5, 1, 2, and 4 h prior testing. At the
time of testing, 5 mg/kg tryptamine HCl freshly dissolved in
saline was injected intravenously. Immediately after tryptamine
HCl administration, the animals were observed individually for
three minutes for the appearance of clonic “pedalling”
movements of the forepaws which is considered a positive
response. Frequently, these clonic seizures were preceded by a
kyphotic curvature of the spine, but this sign did not constitute
a positive response. In addition to the vehicle control group, a
series of five positive control animals receiving tranylcypromine
at 5 mg/kg ip with a 30 min pretreatment time was subjected to
the test in order to check the effectiveness of the tryptamine
HCl solution which is relatively unstable. A 100% response was
expected. Fresh tryptamine hydrochloride solution should be
prepared hourly as needed. An ED50 was calculated using
probitanalysis.33,34
Molecular Docking. The crystal structures of human
MAO-A in complex with ligand 1 (PDB 2Z5X)25 and the
human MAO-B in complex with ligand 2 (PDB 2XFN)39 were
used for all simulations with the Autodock 4.2 suite.38 All other
docking conditions were as previously published.41 The
constructed 3D structures were energetically minimized by
using MOPAC. AutoDock tool automatically computes
Gasteiger charges and determines rotatable bonds of the ligand
to be able to generate different conformers for the docking.
The grid maps of 60 × 60 × 60 grid points, centered on the
ligands of the complex structures, were used to cover the
binding pockets. A spacing of 0.375 Å was set centered at
41.126, 26.795, and −15.023 Å, respectively for MAO-A, that
encompassed the active site where the cocrystallized ligand 1
was embedded, to be used to guide the docked inhibitors
within MAO-A receptor, and flexible residues: Asn181, Phe208,
Leu337 and Tyr444, whereas, The ligand 2 was centered into
its MAO-B receptor at 50.655, 160.186, and 30.957 Å,
respectively, and flexible residues Pro102, Ile199, Ile316, and
Tyr326 were selected as key amino acids.
BIOLOGY
■
In Vitro Monoamine Oxidase A and B Inhibition.
Mitochondria Preparation. Mitochondria were prepared
according to Basford.31 Reagents: medium A contained 0.4 M
sucrose, 0.001 EDTA, 0.02% polyethersulfone (PES), or
heparin, and pH was adjusted to 6.8−7.0 with KOH; medium
F was made up of the medium A to which Ficoll was added to a
final concentration of 8%.
Calf or beef brains were removed from the animals within 5−
10 min after their death. The brains were immediately placed in
cold medium A, stored on ice, and then transported to the
laboratory. In a cold room, at 5 °C, the cerebral hemispheres
were removed from the brains and the meninges were taken up
with forceps. The gray matter was scraped from the cortices
using a dull spatula. Two brains' yield corresponded to about
100 g of wet tissue, which was homogenized in medium A (2
mL/g of wet tissue). The homogenate was kept at pH 7.0 by
adding some drops of Tris-buffer 2 M; 1 mg of ε-aminocaproic
acid/g of tissue was added, and then the mixture was stirred at
0−4 °C for 15 min. The suspension was diluted with medium A
(20 mL/g of the original tissue), centrifuged first at 184g for 20
min and then at 1153g for 20 min, without transferring of the
supernatant. The residue R1 was discarded while the
supernatant S1 was centrifuged at 12000g for 15 min to yield
a crude mitochondria pellet R2 (the supernatant S2 which is
discarded). The fraction R2 was suspended in medium F (6
mL/g of original tissue), gently homogenized, and centrifuged
at 12000g for additional 30 min. The resulting mitochondria
fraction R3 was washed using 4 mL of medium A/g of original
tissue and again centrifuged at 12000g for 15 min. The final
mitochondria fraction R4 was homogenized in potassium
phosphate buffer pH 7.4, 0.25 M. The yield of mitochondria
protein obtained was between 100 and 140 mg per 50 g wet
weight of the original tissue.
Activity Assay. Monoamine oxidase activity was deter-
mined using kinuramine as a substrate, at four different final
concentrations, ranging from 5 μM to 0.1 mM, by a sensitive
fluorometric assay according to Matsumoto et al.32 In all the
assays, the incubation mixtures contained potassium phosphate
buffer, pH 7.4, mitochondria (6 mg/mL), and drug solutions in
DMSO and were added to the reaction mixture at a final
concentration ranging from 0 to 10−9.
Solutions were preincubated for 30 min before adding the
substrate and then incubated for others 30 min. The inhibitory
activities against MAO-A and MAO-B were determined at
38°C, after incubation of the mitochondrial fractions for 30 min
in the presence of the specific inhibitor (L-deprenyl (1 μM) or
clorgyline (1 μM) to estimate the MAO-A and MAOB activity,
respectively). The addition of percloric acid ended the reaction.
Then the samples were centrifuged at 10000g for 5 min and the
supernatant was added to 2.7 mL of 1N NaOH. Fluorometric
measurements were recorded at λexc.317 nm and λem 393 nm
using a Perkin-Elmer LS 50B spectrofluorometer. Dixon plot
were used to estimate the inhibition constant (Ki) of the
inhibitors. Data are the means of three or more experiments
each performed in duplicate.
The Lamarckian genetic algorithm was used for all molecular
docking simulations. Population size of 300, mutation rate of
0.02, and crossover rate of 0.8 were set as the parameters.
Simulations were performed using up to 2.5 million energy
evaluations with a maximum of 27000 generations. Each
simulation was performed 10 times, yielding 10 docked
conformations.
As a result of AutoDock calculations we obtained the output
file with in our case 10 conformers of the protein−ligand
complex with flexible residues. Each structure was scored and
ranked by the program by its calculated interaction energies
and similarities. The similarity of docked structures was
measured by computing the root-mean-square deviation,
RMSD, between the coordinates of the atoms.
ASSOCIATED CONTENT
■
S
* Supporting Information
Elemental analysis and molecular docking details. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
In Vivo Tryptamine Seizure Potentiation in Rats.
Groups of five male Wistar rats weighing 150−200 g were used.
*Phone: +20 202 37608284. Fax: +20 202 33370931. E-mail:
ommryan@yahoo.com.
K
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Article
(18) Carotti, A.; Altomare, C.; Catto, M.; Gnerre, C.; Summo, L.; De
Marco, A.; Rose, S.; Jenner, P.; Testa, B. Lipophilicity plays a major
role in modulating the inhibition of monoamine oxidase B by 7-
substituted coumarins. Chem. Biodiversity 2006, 3, 134−149.
(19) Maccioni, E.; Alcaro, S.; Cirilli, R.; Vigo, S.; Cardia, M. C;
Sanna, M. L.; Meleddu, R.; Yanez, M.; Costa, G.; Casu, L.; Matyus, P.;
Distinto, S. 3-Acetyl-2,5-diaryl-2,3-dihydro-1,3,4-oxadiazoles: a new
scaffold for the selective inhibition of monoamine oxidase B. J. Med.
Chem. 2011, 54, 6394−6398.
(20) Mazouz, F.; Gueddari, S.; Burstein, C.; Mansuy, D.; Milcent, R.
5-[4-(Benzyloxy) phenyl]-1,3,4-oxadiazol-2(3H)-one derivatives and
related analogues: new reversible, highly potent, and selective
monamine oxidase type B inhibitors. J. Med .Chem. 1993, 36, 1157−
1167.
Notes
The authors declare no competing financial interest.
ABBREVIATIONS USED
FAD, flavin adenine dinucleotide; Ki, inhibition constant; Vmax
maximum velocity; Km, Michaelis constant; PDB, Protein Data
Bank; ED50, median effective dose; DMSO, dimethylsulfoxide;
TLC, thin layer chromatography; MOPAC, Molecular Orbital
PACkage
■
,
REFERENCES
■
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