Pyrazoline-based mycobactin analogues as MAO-inhibitors

Article abstract of DOI:10.1016/j.bmcl.2008.10.084

3,5-Diaryl carbothioamide pyrazolines designed as mycobactin analogs (mycobacterial siderophore) were reported to be potent antitubercular agents under iron limiting condition in our earlier study. Clinical complications of newly introduced antibiotic Linezolid, due its MAO inhibitory activity, prompted us to evaluate our compounds for their MAO-inhibitory activity against rat liver MAO-A and MAO-B as pyrazolines were reported to be antidepressants and MAO inhibitors. The present study carried out with this pilot library of 32 compounds will provide us with necessary information for designing antitubercular molecules with reduced MAO-inhibitory activity and also help us in identifying a selective MAO-B inhibitor which has potential clinical utility in neurodegenerative disorders. Thirty-two compounds analyzed has shown spectrum of activity from selective to nonselective against two isoforms of rat liver MAO-A and MAO-B and also as competitive, reversible to non-competitive, irreversible. It is also interesting to note that anti-tubercular compound 11, 14 and 16 were also found to be selective inhibitors of rat liver MAO-B. Docking studies with human MAO shows that compound 11 interacts with the catalytic site of both the isoforms, suggesting compound 11 as nonselective inhibitor of human MAO isoforms.

Full text of DOI:10.1016/j.bmcl.2008.10.084

Bioorganic & Medicinal Chemistry Letters 18 (2008) 6362–6368
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Pyrazoline-based mycobactin analogues as MAO-inhibitors
a
b,
Venkatesan Jayaprakash a, , Barij N. Sinha , Gulberk Ucar , Ayse Ercan b
*
a Department of Pharmaceutical Sciences, Birla Institute of Technology, Mesra, Ranchi 835215, Jharkhand, India
b Department of Biochemistry, Faculty of Pharmacy, Hacettepe University, 06100 Sıhhıye, Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 July 2008
Revised 23 September 2008
Accepted 20 October 2008
Available online 1 November 2008
3,5-Diaryl carbothioamide pyrazolines designed as mycobactin analogs (mycobacterial siderophore)
were reported to be potent antitubercular agents under iron limiting condition in our earlier study.
Clinical complications of newly introduced antibiotic Linezolid, due its MAO inhibitory activity,
prompted us to evaluate our compounds for their MAO-inhibitory activity against rat liver MAO-A
and MAO-B as pyrazolines were reported to be antidepressants and MAO inhibitors. The present study
carried out with this pilot library of 32 compounds will provide us with necessary information for
designing antitubercular molecules with reduced MAO-inhibitory activity and also help us in identi-
fying a selective MAO-B inhibitor which has potential clinical utility in neurodegenerative disorders.
Thirty-two compounds analyzed has shown spectrum of activity from selective to nonselective against
two isoforms of rat liver MAO-A and MAO-B and also as competitive, reversible to non-competitive,
irreversible. It is also interesting to note that anti-tubercular compound 11, 14 and 16 were also
found to be selective inhibitors of rat liver MAO-B. Docking studies with human MAO shows that
compound 11 interacts with the catalytic site of both the isoforms, suggesting compound 11 as non-
selective inhibitor of human MAO isoforms.
Keywords:
Mycobaction analogs
Aryl carbo-thioamide pyrazolines
MAO inhibitors
Docking
Ó 2008 Elsevier Ltd. All rights reserved.
Our group has reported 32 new 3,5-diaryl carbothioamide pyr-
azolines having structural similarities to siderophores of Mycobac-
terium tuberculosis (Mycobactin) and Yersinia pestis (Yersinibactin)
in search of novel antimicrobials against them targeting critical
pathways to iron scarcity adaptation.1 Dual activity of drugs con-
taining hydrazine derived hetero-cycles, which are available for
clinical use (antibacterial with MAO inhibitory activity and MAO
inhibitors with antibacterial activity) were reviewed and reported
by many research groups.2,3 Dual activity targeting different bio-
chemical pathway of a pathogen generally provides a potent anti-
bacterial agent. On the other hand, antibacterial drug acting on
host’s biochemical pathway will lead to clinical complications dur-
ing long term therapy. Linezolid, an oxazolidinone antibiotic, has a
major safety concern due to its reversible non-selective human
MAO inhibitory activity.4
which has potential clinical utility in neurodegenerative disorders.
Since results obtained using rat MAO cannot be extrapolated to hu-
man MAO, docking studies were also performed with human MAO
using Autodock4.
Very few pyrazolines were reported with hydroxylphenyl sub-
stitution in 3rd and 5th position with antibacterial23–29, anti-
tubercular30–32 and MAO inhibitory activity.13 The presence of
2-hydroxyphenyl substitution in the 3rd position of pyrazoline
imparts metal chelating property33 and 4-hydroxyphenyl substitu-
tion in the 3rd and 5th position of pyrazoline imparts antioxidant
property to the molecule.34 Considering the effectiveness of multi-
functional selective MAO-B inhibitor with iron chelating and
anti-oxidant property in the treatment of neurodegenerative disor-
der, we strongly believe a molecule from our pilot library of 32 com-
pounds with selective MAO-B inhibitory activity will be of great
interest towards development of effective Neuroprotective agents.
3,5-Diaryl-1-carbothioamide-pyrazoline derivatives (1–32)
were synthesized from 20-hydroxy chalcone derivatives as per
Scheme 1 as reported earlier.1 Hydroxy chalcones were prepared
through Claisen–Schmidt Condensation. Pyrazoline derivatives
were then obtained by condensing 20-hydroxy chalcones with
hydrazine hydrate (80%). The final compounds 1–31 were ob-
tained by the reaction of pyrazoline derivatives with phenyl/
substituted phenyl isothiocyanates and Compound 32 was ob-
tained by the reaction of chalcone with thiosemicarbazide in
alkaline medium. All the intermediates were characterized by
The above mentioned considerations prompted us to evaluate
our compounds for their MAO inhibitory activity, since pyrazolines
were reported to have anti-depressant5–12 and MAO inhibitory
activity.13–22 This will provide us with necessary information for
designing anti-tubercular molecules with reduced MAO-inhibitory
activity and also help us in identifying a selective MAO-B inhibitor
* Corresponding author. Tel.: +91 651 2275843.
E-mail addresses: venkatesanj@bitmesra.ac.in (V. Jayaprakash), gulberk@hacet-
tepe.edu.tr (G. Ucar).
Tel.: +90 312 3052553; fax: +90 312 3114777.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.10.084

V. Jayaprakash et al. / Bioorg. Med. Chem. Lett. 18 (2008) 6362–6368
6363
R
R
N
1
R
R
O
3
R
R
O
R
2
2
a
b
R
R
3
4
R
4
N
H
R
1
R
R
1
Pyrazoline
e, b, c
Chalcone
d
c
R
R
1
R
R
R
X
1
R
R
3
1
2
R
3
R
2
N
R
N
S
4
R
4
N
N
N
N
HN
S
S
HN
R
H N
5
2
R
5
11
R
6
R
6
X = O or S
8-9
1-7, 10 and 12-32
Scheme 1. *Synthesis of compounds 1–32. Reagents and conditions: (a) i—R2, R3, R4-C6H2–CHO, aq NaOH (60%), stirring at rt 4–48 h, ii—ice cold HCl (6 N), pH adjusted to 2;
(b) NH2NH2/H2O (80%) excess, C2H5OH, reflux 3–6 h; (c) R5, R6-C6H3-NCS, C2H5OH or CH3OH, reflux 15–30 min.; (d) i—NH2NHC(S)NH2, NaOH excess, CH3OH, reflux 8 h, ii—ice
cold HCl (3 N), pH adjusted between 2 and 4; (e) thiophene-2-carboxaldehyde or furfuraldehyde followed by step (b) and (c). Adopted and modified from Ref. 1.
*
IR spectroscopic analysis and elemental analysis for CHNS. In the
Table 1
elemental analysis, the observed values were within 0.4% of the
1
3
calculated values. Final compounds were characterized by 1H
NMR and FAB-MS. Structure of compounds synthesized was pre-
sented in Table 1.
R
R
N
5
2
R
R
A
4
R
B
MAO was purified from the rat liver and total MAO activity
was measured spectrophotometrically according to the method
of Holt.35 Assay mixture contained a chromogenic solution con-
sisted of vanillinic acid, 4-aminoantipyrin and peroxidase type
II in potassium phosphate buffer, pH 7.6. Assay mixture was
pre-incubated with substrate p-tyramine before addition of
enzyme. The reaction was initiated by the addition of homoge-
nate and increase in absorbance was monitored at 498 nm at
37 °C for 60 min. Molar absorption coefficient of 4654 Mꢀ1 cmꢀ1
was used to calculate the initial velocity of the reaction. Results
were expressed as nmol hꢀ1 mgꢀ1. For selective measurement of
MAO-A and MAO-B activities, homogenates were incubated with
the substrate p-tyramine following the inhibition of one of the
MAO isoform with selective inhibitors. After inhibition of
homogenates with selective inhibitors, total MAO activity was
determined by method of Holt. Newly synthesized compounds
were dissolved in DMSO and used in the concentration range
N
6
S
R
C
NH
*
R
Compound
R
R1
R2
R3
R4
R5
R6
1
2
3
4
5
6
7
8
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–OH
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–OH
–OH
–OH
–OH
–H
–H
–H
–OH
–OH
–H
–H
–Cl
–H
–OH
–H
–OMe
–H
2-Thiophenyl
2-Furfuryl
–H
–H
–OH
–H
–OH
–H
–OH
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–Cl
–H
–OH
–H
–OMe
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H–
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
–H
–H
–H
–H
–H
–H
–H
–H
–OMe
–OMe
–OMe
–OMe
–OMe
–H
–H
–H
–H
–OMe
–H
–OMe
–H
–H
–OH
–OH
–H
–OH
–H
–H
–H
–OH
–H
–OH
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–OMe
–OMe
–OMe
–OMe
–OMe
–Me
–Me
–Me
–H
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OMe
–OMe
–Me
–Me
–H
–OMe
–Me
–H
–OMe
–H
–OMe
–H
–H
–H
–H
–H
–H
–H
–H
of 1–1000 lM. Inhibitors were then incubated with purified
MAO at 37° C for 0–60 min prior to adding to the assay mixture.
Reversibility of the inhibition of MAO by these compounds was
assessed by dilution. Kinetic data for interaction of the enzyme
with this compound was determined using Microsoft Excel pack-
age program. IC50 values were determined from plots of residual
activity percentage, calculated in relation to a sample of the en-
zyme treated under the same conditions without inhibitor, ver-
sus inhibitor concentration [I].
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–OH
–H
–OH
–OH
–OH
–OH
–H
–H
–H
–OH
–H
–H
–H
–H
–OH
–H
All of the newly synthesized compounds (1–32) inhibited the
total MAO activity of rat liver homogenates. The IC50
(lM) and Ki
(lM) values of these compounds were presented in Table 2. and
Table 3, respectively. Lineweaver-Burk plot for the inhibition of
rat liver MAO-A by compound 7 was presented in Figure 1. It
is interesting to note the activity profile of the library molecules,
eight compounds were found to be non-selective (25–32), seven
were found to be selective for MAO-B (11–17) and seventeen
–H
–H
–OMe
–OH
*
Adopted and modified from Ref. 1.

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V. Jayaprakash et al. / Bioorg. Med. Chem. Lett. 18 (2008) 6362–6368
Table 2
IC50 values corresponding to the inhibition of rat liver MAO isoforms by the newly synthesized 3,5-diaryl-1-carbothioamide-pyrazoline derivatives (1–32).*
Compound
IC50 for MAO-A**
(lM)
IC50 for MAO-B**
(
lM)
MAO inhibitory Selectivity
Preincubation
0
Preincubation
60 min
Preincubation
0
Preincubation
60 min
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
60.35 4.55
49.10 3.00
60.16 5.33
80.22 5.55
80.10 6.50
87.60 5.66
39.20 2.30
31.20 2.35
74.12 5.37
82.16 7.23
479.18 28.56
456.75 29.36
490.36 25.33
472.20 29.90
405.45 20.30
480.30 35.22
500.01 38.80
77.70 5.23
65.54 5.80
88.60 7.40
90.12 7.60
84.45 6.27
91.20 6.82
96.50 8.66
203.36 15.50
190.21 14.20
240.79 18.86
181.77 15.41
255.60 19.47
240.20 17.43
200.05 13.35
240.22 19.73
432.26 18.60
6.16 034
49.16 3.50
20.05 3.56
23.18 1.58
58.10 3.63
67.22 5.80
74.20 6.76
2.84 0.19
480.32 19.56
470.34 23.20
450.12 35.79
475.06 45.10
498.12 25.55
431.0 12.05
489.00 47.90
481.56 30.56
450.12 29.90
490.22 36.42
45.13 3.20
77.20 5.80
89.60 5.55
75.50 6.31
70.88 6.30
77.96 6.40
82.00 6.02
455.45 29.93
481.00 30.54
490.45 30.70
499.50 32.20
488.20 33.41
476.35 30.25
480.22 30.40
200.55 17.30
219.60 18.44
286.32 20.24
225.33 18.63
201.10 19.60
210.18 18.75
223.88 20.35
244.57 19.44
5.05 0.95
439.20 25.11
455.23 27.10
400.30 29.25
420.34 34.20
400.05 23.35
419.30 26.76
415.20 40.85
385.75 22.10
440.30 28.60
486.28 30.12
19.45 1.02
35.55 3.10
48.60 3.80
40.78 3.66
41.10 3.50
37.70 3.05
46.12 3.70
450.60 30.27
477.22 31.50
481.12 29.99
490.23 30.30
475.50 29.58
470.38 33.90
455.80 28.89
144.47 10.85
170.52 12.75
201.30 16.65
170.55 13.36
170.22 16.32
180.27 13.92
180.44 12.36
197.56 14.88
3.85 0.23
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Selective for MAO-A
Non-selective
Non-selective
Non-selective
Non-selective
Non-selective
Non-selective
Non-selective
Non-selective
Selective for MAO-B
Selective for MAO-A
Selective for MAO-B
Selective for MAO-A
5.56 0.45
33.41 2.85
32.10 3.00
466.20 30.12
450.80 30.40
475.56 30.12
470.50 40.21
400.56 29.60
400.20 31.10
475.50 30.56
40.07 3.56
48.90 4.02
50.64 4.30
65.60 5.13
53.36 4.40
58.60 4.20
69.55 5.74
150.60 10.88
144.48 9.30
170.46 13.60
147.80 10.66
180.23 14.20
188.51 13.34
170.26 12.74
200.56 13.30
390.20 17.23
2.05 0.19
Pargyline***
Clorgyline***
Selegiline***
Moclobemide***
410.15 16.78
7.56 0.35
496.22 30.15
400.90 15.54
2.01 0.15
480.12 21.05
516.10 19.25
5.58 0.28
499.01 18.20
3.90 0.19
*
The IC50 values were determined from the kinetic experiments in which p-tyramine was used at 500
M to determine the isoenzymes A and B.
Each value represents the mean SEM of three independent experiments.
IC50 values corresponding to the inhibition of MAO isoforms by clorgyline and moclobemide as selective MAO-A inhibitors, and pargyline and selegiline as selective MAO-B
lM to measure MAO-A and 2.5 mM to measure MAO-B. Pargyline or
clorgyline were added at 0.50
l
**
***
inhibitors were also determined to assess the inhibitory potencies of the novel compounds.
were found to be selective for MAO-A (1–10 and 18–24). All the
seventeen MAO-A selective inhibitors were found to be compet-
itive and reversible. Compound 7 and 8 (IC50: 2.84 0.19 and
substitution with methoxy group, the difference was significant,
para-methoxy substitution was found to be potent. When ring B
was replaced with thiophene or furan ring, selectivity towards
MAO-A was retained and thiophene substitution was found to
be potent, but not better than para-methoxy phenyl substitution.
Ortho-methoxy, para-hydroxy di-substitution in ring B also fa-
vors selectivity towards MAO-A, once again when ring C is
unsubstituted. Selectivity towards MAO-B was favored when ring
C was absent. In the presence of ring C, para-methyl or para-
methoxy substitution favors selectivity towards MAO-B. It is
interesting to note that compounds 11 and 14 were the only
two which are competitive and reversible in this series while
other five were non-competitive and irreversible. Except com-
pound 11, difference in substitution in compounds 12–17 shows
no great difference in activity.
Docking studies were performed with human MAO isoforms
using Autodock4. Selective inhibitors 7, 8, 9, 11, 14, 16 along with
Linezolid and crystallographic models 2BXR for human MAO-A and
2BYB for human MAO-B were considered for docking study. Marvin
Sketch (Chemaxon), Protein Preparation Wizard (Schrodinger Inc.)
and Open Babel were used for ligand and protein preparation. Top
scoring molecules from the largest cluster were considered for
interaction studies. Estimated free energy of binding (kcal/mol)
was presented in Table 4. and detailed method of computational
approach adopted is presented in Supplementary materials.
5.56 0.45
lM, respectively, Table 2.) were the potent MAO-A
inhibitors in this series, inhibitory activity of compound 7 was
found to be better than moclobemide (IC50
:
3.90 0.19
lM)
and equivalent to clorgyline (IC50: 2.05 0.19
l
M), respectively
(Table 2.). Whereas only two (11 and 14) out of seven MAO-B
selective inhibitors were found to be competitive and reversible,
while other five (12–13 and 15–17) were noncompetitive and
irreversible. Compound 11 (IC50: 19.45 1.02
the potent MAO-B inhibitor in this series and was found to be
5 and 7 times less potent than pargyline (IC50: 3.85 0.23 M)
and selegiline (IC50: 2.01 0.15 M), respectively (Table 2.).
lM, Table 2.) was
l
l
Structure–activity relationship within this small library re-
veals that ortho-methyl or ortho-methoxy substitution in ring C
abolishes selectivity towards isoforms irrespective of substitution
in ring A and B. ortho-hydroxy substitution in ring A has no role
in selectivity towards isoforms, but ortho, para-dihydroxy substi-
tution favors selectivity towards MAO-A that to when ring C was
unsubstituted. In ring B, ortho or para mono-substitution with
hydroxy, methoxy or chloro groups favors selectivity towards
MAO-A when ring C is unsubstituted. Substitution in ortho posi-
tion of ring B with chloro or hydroxy group was found to better
than substitution in para position, but not significant. Whereas

V. Jayaprakash et al. / Bioorg. Med. Chem. Lett. 18 (2008) 6362–6368
6365
Table 3
Experimental kinetic parameters obtained by the inhibition of rat liver MAO isoforms by 3,5-diaryl–1-carbothioamide-pyrazoline derivatives (1–32).
Compound
Experimental Kivalues (
lM)
Selectivity, inhibition type and reversibility of the inhibition
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
40.22 3.00
18.60 1.56
20.14 1.78
48.45 3.08
50.45 45.12
63.55 5.40
2.50 0.15
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-B, competitive, reversible
Selective for MAO-B, noncompetitive, irreversible
Selective for MAO-B, noncompetitive, irreversible
Selective for MAO-B, competitive, reversible
Selective for MAO-B, noncompetitive, irreversible
Selective for MAO-B, noncompetitive, irreversible
Selective for MAO-B, noncompetitive, irreversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-B, competitive, reversible
Selective for MAO-A, competitive, reversible
Selective for MAO-B, competitive, reversible
Selective for MAO-A, competitive, reversible
6.13 0.48
27.53 2.52
30.55 3.90
15.20 1.22
34.70 2.86
40.64 3.99
36.21 3.05
39.18 3.45
35.00 2.85
42.89 3.49
62.74 5.55
60.54 5.70
75.12 5.90
79.19 6.05
71.14 5.82
80.00 7.25
85.45 7.23
3.25 0.21
1.99 0.10
1.90 0.08
2.25 0.15
Pargyline
Clorgyline
Selegiline
Moclobemide
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Control
12uM
10uM
6uM
2uM
-20
-15
-10
-5
0
5
10
15
20
-0.01
1/Tyramine, mM-1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
y = 0.0051x + 0.016
R² = 0.9946
-5
0
5
10
15
[I]
Figure 1. Lineweaver–Burk plot for the inhibition of rat liver MAO-A by the compound 7 with 60 min of preincubation at 37 °C. p-Tyramine was used as substrate in the
concentration range of 10–100 M. Replot of Y-intercepts vs I and apparent Ki value are shown in the second graph.
l

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V. Jayaprakash et al. / Bioorg. Med. Chem. Lett. 18 (2008) 6362–6368
Table 4
whereas ring B was positioned in hydrophobic pocket delimited
by ILE180, ILE335, LEU337, MET350 and PHE352 (pocket 3). Sul-
phur in thicarbamoyl group in compound 11 was found to posi-
tion itself towards the aromatic cage formed by FAD, TYR407
and TYR444. Interactions of compound 11 with MAO-A were
shown in Figure 2a. Estimated binding free energy of compounds
7, 8, 9, 14 and 16 were all found to be lower than compound 11
with single hydrogen bond interaction of hydroxyl oxygen of
ring A with amino nitrogen of SER209. In compounds 7, 8 and
9 ring A was positioned in pocket 3, ring B in pocket 1 and ring
C in pocket 2, where as in compounds 24 and 34 ring A in pock-
et 2, ring B in pocket 3 and ring C in pocket 1.
Docking scores of compounds 7–9, 11, 14, 16 and Linezolid.
Compound
Estimated free energy of binding
hMAO-A (2BXR)
hMAO-B (2BYB)
7
8
9
11
14
16
Linezolid
ꢀ9.07
ꢀ9.33
ꢀ9.31
ꢀ8.27
ꢀ9.40
ꢀ8.97
ꢀ9.07
ꢀ5.42
ꢀ7.83
ꢀ8.43
ꢀ8.69
ꢀ4.36
ꢀ4.76
ꢀ5.42
Complex of compound 11 with MAO-B, hydrogen bonding
interactions were found between: amino hydrogen of compound
11 with hydroxyl oxygen of TYR398 (this also allows the position-
ing of ring B of compound 11 in aromatic cage formed by FAD,
TYR398 and TYR435) and hydroxyl hydrogen of ring A with hydro-
xyl oxygen of TYR326. Interactions of compound 11 with MAO-B
were shown in Figure 2b. Comparatively narrow active site cavity
favors the positioning of ring B in aromatic cage of MAO-B. Hydro-
xyl functional group in para position of ring B further favors hydro-
phobic interaction of its phenyl ring with phenyl rings of TYR398
and TYR435. In compounds 7, 8 and 9 both ring B and C were posi-
tioned in aromatic cage, also ring B methoxy oxygen of compound
7 and furan oxygen of compound 9 were found to have hydrogen
bonding interaction with CYS172. In compounds 24 and 34 ring
Estimated binding free energy for Linezolid with human
MAO-A (2BXR) was found to be higher than with human MAO-
B (2BYB), as expected. Interestingly the compound 11 was found
to interact with the catalytic site of both isomers with apprecia-
bly equal but slightly better estimated binding free energy to-
wards MAO-B. Complex of compound 11 with MAO-A,
hydrogen bonding interactions were found between: amino
hydrogen of compound 11 with side chain carbonyl group of
ASN181, hydroxyl hydrogen in ring A with amino hydrogen of
SER209. Both the aromatic ring A and B were away from aro-
matic cage formed by FAD, TYR407 and TYR444 (pocket 1). Ring
A was positioned in hydrophobic pocket delimited by GLY71,
GLN74, ARG206, ILE207, PHE208, GLU216 and TRP441 (pocket 2)
Figure 2. (a) Interaction of compound 11 with human MAO-A (2BXR), (b) Interaction of compound 11 with human MAO-B (2BYB). FAD shown in green color and hydrogen
bonds in yellow dotted lines.

V. Jayaprakash et al. / Bioorg. Med. Chem. Lett. 18 (2008) 6362–6368
6367
Table 5
MAO-B inhibitory and antitubercular activity of compounds 11–17.
b
b
b
Compounda
IC50 (
l
M) Preincubation 60 mina
MAO inhibitory selectivitya
Compound
IC50
(l
M)
IC50GAST-D-Fe/IC50GAST-D
GAST-D
GAST-D-Fe
11
12
13
14
15
16
17
19.45 1.02
35.55 3.10
48.60 3.80
40.78 3.66
41.10 3.50
37.70 3.05
46.12 3.70
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
Selective for MAO-B
32
30
31
10
15
12
17
8
24
500
28
>500
27
417 83
1
125
42
500
167 42
>500
208 42
>500
0
4
0
16
2
1
6
nd
8
6
0
5
3
>1
a
Table 2 in this article.
Reproduced from Ref. 1.
b
A was positioned in aromatic cage, which is favored by the hydro-
gen bonding interaction between hydroxyl oxygen of ring B and
hydroxyl hydrogen of TYR398.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2008.10.084.
Two unsubstituted aromatic rings were found to be conve-
niently accommodated in aromatic cage of MAO-B (compound
8 and 9), while a ring with substitution drastically reduces esti-
mated binding free energy (compound 7). When all the three
rings were substituted only one ring was accommodated in
aromatic cage of MAO-B, which forces other two ring to be
accommodated in the narrow cavity leading to poor estimated
binding free energy. In other words these factors make them
selective towards MAO-A. Only compounds 8, 9 and 11 were
found to be non-selective towards human MAO-A and B with
good estimated binding free energy on both the isoforms, while
all other compounds studied were found to be selective towards
human MAO-A. Observations from docking studies comply with
the statement of De Colibus et al. that ‘‘results from investigation
of one mammalian form of MAO cannot be unambiguously
extrapolated to other mammalian forms.36
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