Oxazolopyridines and thiazolopyridines as monoamine oxidase B inhibitors for the treatment of Parkinson's disease

Article abstract of DOI:10.1016/j.bmc.2013.05.066

In Parkinson's disease, the motor impairments are mainly caused by the death of dopaminergic neurons. Among the enzymes which are involved in the biosynthesis and catabolism of dopamine, monoamine oxidase B (MAO-B) has been a therapeutic target of Parkinson's disease. However, due to the undesirable adverse effects, development of alternative MAO-B inhibitors with greater optimal therapeutic potential towards Parkinson's disease is urgently required. In this study, we designed and synthesized the oxazolopyridine and thiazolopyridine derivatives, and biologically evaluated their inhibitory activities against MAO-B. Structure-activity relationship study revealed that the piperidino group was the best choice for the R¹ amino substituent to the oxazolopyridine core structure and the activities of the oxazolopyridines with various phenyl rings were between 267.1 and 889.5 nM in IC₅₀ values. Interestingly, by replacement of the core structure from oxazolopyrine to thiazolopyridine, the activities were significantly improved and the compound 1n with the thiazolopyridine core structure showed the most potent activity with the IC₅₀ value of 26.5 nM. Molecular docking study showed that van der Waals interaction in the human MAO-B active site could explain the enhanced inhibitory activities of thiazolopyridine derivatives.

Full text of DOI:10.1016/j.bmc.2013.05.066

Bioorganic & Medicinal Chemistry 21 (2013) 5480–5487
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Oxazolopyridines and thiazolopyridines as monoamine oxidase B
inhibitors for the treatment of Parkinson’s disease
Hye Ri Park a, , Jiyoon Kim a,b, , Taekeun Kim c, Seonmi Jo c, Miyoung Yeom a,b, Bongjin Moon b,
Il Han Choo d, Jaeick Lee e, Eun Jeong Lim a, Ki Duk Park a, Sun-Joon Min a, Ghilsoo Nam a,
Gyochang Keum a, C. Justin Lee c,f, ,à, Hyunah Choo a, ,à
⇑
⇑
a Center for Neuro-Medicine, Korea Institute of Science and Technology, Hwarangro 14-gil-5, Seongbuk-gu, Seoul 136-791, Republic of Korea
b Department of Chemistry, Sogang University, Mapo-gu, Seoul 121-742, Republic of Korea
c Center for Functional Connectomics, Korea Institute of Science and Technology, Seongbuk-gu, Seoul 136-791, Republic of Korea
d Department of Neuropsychiatry, School of Medicine, Chosun University, Pilmoondaero 309, Dong-gu, Kwangju 501-759, Republic of Korea
e Doping Control Center, Korea Institute of Science and Technology, Seongbuk-gu, Seoul 136-791, Republic of Korea
f Center for Neural Science, Korea Institute of Science and Technology, Seongbuk-gu, Seoul 136-791, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
In Parkinson’s disease, the motor impairments are mainly caused by the death of dopaminergic neurons.
Among the enzymes which are involved in the biosynthesis and catabolism of dopamine, monoamine oxi-
dase B (MAO-B) has been a therapeutic target of Parkinson’s disease. However, due to the undesirable
adverse effects, development of alternative MAO-B inhibitors with greater optimal therapeutic potential
towards Parkinson’s disease is urgently required. In this study, we designed and synthesized the oxazol-
opyridine and thiazolopyridine derivatives, and biologically evaluated their inhibitory activities against
MAO-B. Structure–activity relationship study revealed that the piperidino group was the best choice for
the R1 amino substituent to the oxazolopyridine core structure and the activities of the oxazolopyridines
with various phenyl rings were between 267.1 and 889.5 nM in IC50 values. Interestingly, by replacement
of the core structure from oxazolopyrine to thiazolopyridine, the activities were significantly improved
and the compound 1n with the thiazolopyridine core structure showed the most potent activity with
the IC50 value of 26.5 nM. Molecular docking study showed that van der Waals interaction in the human
MAO-B active site could explain the enhanced inhibitory activities of thiazolopyridine derivatives.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 23 April 2013
Revised 28 May 2013
Accepted 29 May 2013
Available online 11 June 2013
Keywords:
Monoamine oxidase B
MAO-B
Parkinson’s disease
Oxazolopyridine
Thiazolopyridine
1. Introduction
(L-DOPA), and degraded by catechol-O-methyl transferase (COMT)
or monoamine oxidase (MAO).5 There are two isozymes of MAO,
which are identified as MAO-A and MAO-B.6 Among these, elevated
enzymatic activity of MAO-B results in Parkinson’s disease-like
pathology7 and motor impairments.8
As the life expectancy is increasing, aging and age-related neu-
rodegenerative diseases have become important health problems
in developed countries. Among the age-related neurodegenerative
diseases with no currently available cure, Parkinson’s disease is the
second most common one after Alzheimer’s disease.1 This disease
is characterized by the impairment of motor function such as tre-
mor, rigidity, bradykinesia, gait dysfunction, and postural instabil-
ity.2 The motor symptoms of Parkinson’s disease are mainly caused
by the death of dopaminergic neurons in the substantia Nigra pars
compacta.3 Accordingly, current medications for ameliorating Par-
kinson’s symptoms mostly target dopamine depletion in the
brain.4 Dopamine is a monoamine neurotransmitter which is
MAO-B is a flavin adenine dinucleotide (FAD)-containing en-
zyme, and is located in the mitochondrial outer membranes of glial
cell types and some neuronal population.9 Because MAO-B de-
grades dopamine and at the same time produces toxic by-products
such as hydrogen peroxide and ammonia,10 inhibition of MAO-B is
effective in alleviating the symptoms of Parkinson’s disease.11 In-
deed, selegiline12 and rasagiline,13 which are selective and irre-
versible MAO-B inhibitors, have been prescribed to patients with
Parkinson’s disease. However, these inhibitors are known to cause
undesirable adverse effects such as hallucination and head-
ache.14,15 Moreover, neurotoxic or ineffective metabolites are gen-
erated from these inhibitors, which limit the long term use of those
inhibitors.11,16 Therefore, development of alternative MAO-B
inhibitors with greater optimal therapeutic potential towards
Parkinson’s disease is urgently required.
synthesized by direct conversion of L-3,4-dihydroxyphenylalanine
⇑
Corresponding authors. Tel.: +82 2 958 5157; fax: +82 2 958 5189.
E-mail addresses: cjl@kist.re.kr (C.J. Lee), hchoo@kist.re.kr (H. Choo).
The first two authors contributed equally to this work.
à
These two corresponding authors contributed equally to this work.
0968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.05.066

H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
5481
R1 =
R2 =
N
N
H
H
N
X
H
2-Cl
3-Cl
4-Cl
2-F
3-F
N
H
R1
N
N
R2
4-F
X = O, S
1
N
N
Figure 1. Designed oxazolopyridines and thiazolopyridines 1.
In this study, we focused on oxazolopyridines and thiazolopyri-
dines to find new MAO-B inhibitors which possibly can be applied
to patients with Parkinson’s disease in the future. Previously, oxaz-
olopyridine derivatives with aryl or heteroaryl substitution were
employed as inhibitors of the MAO-B, and as molecular probes
for assessing MAO-B levels in living patients via positron emission
tomography (PET) tracer technology.17 However, other derivatives
of oxazolopyridines and any derivatives of thiazolopyridines have
not been tested on MAO-B yet. Thus, in this study, we prepared no-
vel oxazolopyridine and thiazolopyridine derivatives 1 by intro-
duction of amino functionalities and halogen substituents to the
oxazolopyridine core and the 2-phenyl substituent of the oxazolo-
pyridine scaffold, respectively (Fig. 1). Herein, we report prepara-
tion of a novel series of oxazolopyridine or thiazolopyridine
derivatives and evaluation of their inhibitory activities against
MAO-B.
3-amine 2 underwent acylation with various substituted benzoyl
chlorides in acetonitrile to afford N-(2,6-dichloropyridin-3-
yl)benzamide derivatives 3 in 59–99% yields. To synthesize the
oxazolopyridines, the benzamides 3 were cyclized in the presence
of sodium carbonate in DMF to give oxazolopyridines 4 in 60–95%
yields. The oxazolopyridines 4 were converted to the desired oxaz-
olopyridines 1 by reaction with various amines. However, the com-
pound 1a with N-methylamino group as R1 was obtained from the
oxazolopyridine 4 upon treatment with N,N-benzylmethylamine
followed by debenzylation under acidic conditions. The benzam-
ides 3 were also treated with Lawesson’s reagent under basic con-
ditions, which led to thiazolopyridines 5 in 50–80% yield.18 With
the same procedure as amination of oxazolopyridines 4, the de-
sired thiazolopyridines 1 (X = S) were obtained in 7–80% yields.
2.2. Inhibition of human MAO-B
The synthesized compounds were biologically evaluated
against human MAO-B (hMAO-B). The potential effects of the com-
pounds were investigated by measuring the amount of H2O2 pro-
duced by MAO-B from a human MAO-B substrate (benzylamine)
and our test compound using the Amplex RedÒ MAO assay kit.19
2. Results and discussion
2.1. Chemistry
Oxazolopyridine or thiazolopyridine derivatives were synthe-
sized in three steps as shown in Scheme 1. 2,6-Dichloro-pyridin-
The prepared compounds were initially screened at 10 lM, and
R2
H
NH2
Cl
N
N
O
a
b
O
Cl
N
Cl
N
R2
Cl
N
Cl
2
4
3
R2 = H, F or Cl
c
d
N
X
N
d
R1
N
R2
Cl
R2
S
N
5
1 X = O or S
Compd
1a
X
O
O
O
O
O
O
O
O
R1
R2
H
Compd
1i
X
O
O
O
O
S
R1
R2
N-methylamino
N-cyclohexylamino
N-benzylamino
1-piperidino
1-piperidino
1-piperidino
1-piperidino
1-piperidino
1-piperidino
1-piperidino
1-piperidino
4-F
2-Cl
3-Cl
4-Cl
H
H
1b
1j
H
1c
1k
N,N-benzylmethylamino
1-azepino
H
1d
1l
H
1d
1m
1n
1-piperidino
H
S
2-F
2-Cl
4-Cl
1f
1-piperidino
2-F
3-F
S
1g
1o
1-piperidino
S
1h
1p
Scheme 1. Synthesis of oxazolopyridines and thiazolopyridines. Reagents and conditions: (a) R2PhCOCl, CH3CN, 80 °C, 59–99%; (b) Na2CO3, DMF, 110 °C, 60–95%; (c)
Lawesson’s reagent, DBU, toluene, 110 °C then K2CO3, DMF, 160 °C, 50–80%; (d) amines with R1 group, DMF, reflux, or N,N-benzylmethylamine, DMF, reflux then H2SO4, 7–
80%.

5482
H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
Table 2
the IC50 values were estimated only for the compounds of which
%inhibitions at this concentration were higher than 50%.
hMAO-B inhibition results for the synthesized compounds 1f–1p
2-Phenyloxazolopyridine derivatives 1a–1f with various amino
substituents were initially tested against hMAO-B, and the results
are shown in Table 1. The compounds 1a, 1c, and 1d with small or
aromatic R1 substituents such as N-methylamino, N-benzylamino,
and N,N-benzylmethylamino groups showed no inhibitory activi-
ties against hMAO-B. In contrast, amino groups with aliphatic rings
like N-cyclohexylamino and 1-piperidino as R1 substituents pro-
vided the corresponding oxazolopyridines (1b and 1f) with signif-
icantly increased inhibitory activities. The IC50 values of the
compounds 1b and 1f were 2539.2 and 1372.8 nM, respectively.
The compound 1e with 1-azepino group as R1 showed only mar-
N
R2
X
N
N
b
Compd
X
R2
%Inhibition at 10
l
Ma IC50 (in
lM)
Fold increasec
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
Selegiline
O
O
O
O
O
O
O
S
H
86.8
94.9
89.7
93.4
1372.8 48.4
665.1 8.5
271.8 15.4
270.3 22.1
267.1 2.7
334.5 4.8
889.5 24.2
356.0 21.6
26.5 1.3
1.0
2.1
5.1
5.1
5.1
4.1
1.5
3.9
51.8
8.0
3.8
2-F
3-F
4-F
2-Cl 96.3
3-Cl 91.7
4-Cl 69.8
95.5
92.7
2-Cl 95.1
4-Cl 84.2
97.4
ginal activity with 57.9% inhibition at 10 lM. Among the com-
H
4-F
pounds 1a–1f, the compound 1f is the most active. Therefore, we
fixed R1 as 1-piperidino group and modified the phenyl ring on
the compound 1f to obtain more active compounds against
hMAO-B.
S
S
S
171.4 5.7
357.9 19.3
1.3 0.03
d
—
To improve inhibitory potency against hMAO-B, positional
scanning of the halogen substitution on the phenyl ring of the com-
pound 1f with piperidino group was conducted and the results are
summarized in Table 2. The oxazolopyridines 1g–1l with a halogen
substituent showed better inhibitory activities against hMAO-B
than the compound 1f with a simple phenyl ring. In the case of
the compounds 1g–1i with a fluorine substituent, substitution at
the ortho-position led to slightly improved activity with an IC50 va-
lue of 665.1 nM. Interestingly, the fluorine atom substituted at the
meta- and para-position provided the resulting compounds 1h and
1i with high hMAO-B inhibitory activities (IC50 = 271.8 and
270.3 nM, respectively). On the other hand, when a chlorine substi-
tuent was introduced, the 4-substituted derivative 1l showed the
lowest inhibitory activity among the series with an IC50 value of
889.5 nM. The compound 1j with the chlorine substituent at the
ortho-position of aromatic ring was more potent (IC50 = 267.1 nM)
than the compound 1l. The compound 1k with meta-chloro substi-
tuent showed similar IC50 value as that of the compound 1j.
a
%Inhibition against hMAO-B at 10
All IC50 values shown in the table are expressed as mean SEM from four
l
M.
b
experiments.
c
Fold increase = IC50 of 1f/IC50 of the compound modified (1g ꢀ 1p, respectively).
d
Not determined.
Finally, we introduced sulfur atom to the core oxazolopyridine
ring to provide the thiazolopyridine derivatives 1m–1p. The bio-
logical results are shown in Table 2. The compound 1m showed
more potent inhibitory activity than its oxazolopyridine congener
1f with an IC50 value of 356 nM. Other compounds (1n–1p)
showed similar increase in inhibitory activity compared with their
oxazolopyridine counterparts. The hMAO-B inhibitory activities of
the thiazolopyridine derivatives 1o and 1p with a chlorine substi-
tuent were considerably higher (IC50 = 171.4 and 357.9 nM, respec-
tively) than the corresponding oxazolopyridines 1j and 1l
(IC50 = 267.1 and 889.5 nM, respectively). Interestingly, the thiaz-
olopyridine 1n with a fluorine substituent at the para-position of
the phenyl ring showed the most potent hMAO-B activity with
an IC50 value of 26.5 nM. Based on the increased activities of the
thiazolopyridines, it could be assumed that the change of atom size
and/or electronegativity at the core structure caused by substitu-
tion of oxygen with sulfur might influence the bioactivity against
hMAO-B. These compounds 1f–1p were also assayed for hMAO-A
inhibitory activity. All tested compounds showed no inhibitory
Table 1
Activities of the oxazolopyridines 1a–1f with a phenyl ring against hMAO-B
N
O
R1
N
activities against hMAO-A at 10 lM. Therefore, the oxazolopyri-
dines 1f–1l and the thiazolopyridines 1m–1p are determined as
selective hMAO-B inhibitors.
b
Compd
R1
%Inhibition at 10
19.0
l
Ma
IC50 (nM)
HN
1a
NDc
HN
2.3. Molecular docking study
1b
79.1
2539.2 62.4
For molecular docking study, two compounds ln and li were se-
lected. The compound 1n is the most potent MAO-B inhibitor in
these series of the compounds and the compound 1i is exactly
the same as the compound 1n except with oxazolopyridine core
structure. Comparison between the binding modes of the two com-
pounds ln and li could provide insights to figure out the improved
inhibitory activities by replacement of the core structure from
oxazolopyridine to thiazolopyridine. Molecular docking study
was carried out in order to understand the energetically preferred
conformations adopted by the compounds 1i and 1n inside the
hMAO-B binding pocket and thereby the key factor for the im-
proved inhibitory activities of the thiazolopyridines. Crystallo-
graphic structure of hMAO-B (PDB code 2V60)20 from the Protein
Data Bank was used as a template for docking experiments because
the ligand inside of the crystal structure of MAO-B is a coumarin
derivative which is a reversible inhibitor like our MAO-B inhibitors
HN
N
1c
4.8
3.7
NDc
NDc
1d
1e
1f
57.9
86.8
NDc
N
1372.8 48.4
N
a
%Inhibition against hMAO-B at 10
All IC50 values shown in the table are expressed as mean SEM from four
l
M.
b
experiments.
c
Not determined.

H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
5483
1i and 1n and has similar structural properties: a fused ring system
and similar size.
in the compound 1i with a distance of 3.8 Å (Fig. 2a) and the sulfur
atom in the compound 1n with a distance of 3.3 Å (Fig. 2b), respec-
tively. The van der Waals surfaces of the sulfur atom in Cys172 and
the sulfur atom in the compound 1n are closer to each other than
the corresponding surfaces in the binding mode of the compound
1i (Fig. 2c), which indicates that the compound 1n has stronger
van der Waals interaction with Cys172 than the compound 1i
and thereby more potent inhibitory activity against hMAO-B.
The MAO-B inhibitors 1i and 1n were successfully docked to the
MAO-B active site, of which the GLIDE energies are À29.2 and
À34.2 kcal/mol, respectively and the two inhibitors occupied the
entrance hydrophobic cleft formed by Pro102, Cys172, Ile199, Ile
316, Tyr326, and Phe343 (Fig. 2). The binding modes of the two
inhibitors 1i and 1n are shown in Figure 2. The two inhibitors were
shown to form no specific interaction except van der Waals inter-
action as a key interaction between the inhibitors and hMAO-B.
Due to different van der Waals radii of oxygen atom and sulfur
atom, the van der Waals surfaces of the compounds 1i and 1n
are distinctive, and Cys172 in the active site of hMAO-B plays an
important role in distinguishing binding modes of the two com-
pounds. The sulfur atom in Cys172 is nearest to the oxygen atom
3. Conclusion
The oxazolopyridine and thiazolopyridine derivatives 1a–1p
were designed, synthesized and biologically evaluated as inhibitors
of MAO-B enzyme. The structure–activity relationship study re-
vealed that the piperidino group was the best choice as R1 group,
and the activities of the oxazolopyridines with various aromatic
rings were between 267.1 and 889.5 nM in IC50 values. Interest-
ingly, by replacement of the core structure from oxazolopyridine
to thiazolopyridine, the activities were significantly improved
and the most potent compound was 1n of which an IC50 value
was 26.5 nM. Molecular docking study showed that van der Waals
interaction in the hMAO-B active site could explain the enhanced
inhibitory activities of thiazolopyridine derivatives. Based on this
study, an extensive SAR (structure–activity relationship) study of
the compound 1n to obtain improved pharmacological profiles
with in vivo activity in Parkinon’s disease animal model is
warranted.
4. Experimental section
4.1. Chemicals and instrumentation
All starting materials and reagents were purchased from Sig-
ma–Aldrich, TCI, Fluka, Lancaster and Acros, and used without fur-
ther purification. Analytical thin layer chromatography was
performed on silica gel 60 F254 purchased from Merck. Column
chromatography was performed using silica gel grade 230–400
(Merck Kieselgel 60 Art 9385). Nuclear magnetic resonance spectra
were recorded on Bruker Advance 400 (or 300) spectrometer at
400 MHz (or 300 MHz) for 1H NMR and at 100 MHz for 13C NMR
with tetramethylsilane as an internal standard. Chemical shifts
are reported as s (singlet), d (doublet), t (triplet), q (quartet), m
(multiplet) or br s (broad singlet). Coupling constants are reported
in hertz (Hz). The chemical shifts are reported as parts per million
(d) relative to the solvent peak. The high-resolution mass spectrum
was performed on a LTQ Orbitrap (Thermo Electron Corporation).
4.2. General procedure for preparation of 3a–3g
Substituted benzoyl chloride (1.1 equiv) was added dropwise to
a solution of the 2.6-dichloro-pyridin-3-amine (1 equiv) in acetoni-
trile at 0 °C. The resulting mixture was stirred for 6 h at 80 °C. After
cooling down to room temperature, the solvent was removed un-
der reduced pressure. The crude compound was dissolved in meth-
anol, and then white solid was recrystallized from methanol to give
desired product.
4.2.1. N-(2,6-Dichloropyridin-3-yl)benzamide (3a)
The desired product was obtained in 90% yield: 1H NMR
(400 MHz, MeOD) d 8.29 (d, J = 8.4 Hz, 1H), 8.00–7.98 (m, 2H),
7.62 (t, J = 6.1 Hz, 1H), 7.57–7.50 (m, 3H).
Figure 2. Binding modes of (a) 1i and (b) 1n inside of the hMAO-B active site. (c)
Two compounds 1i and 1n were overlapped to compare binding modes and van der
Waals surface. Van der Waals surfaces of Cys172, the oxygen of li, and the sulfur of
ln were expressed with net shapes.
4.2.2. N-(2,6-Dichloropyridin-3-yl)-2-fluorobenzamide (3b)
The desired product was obtained in 95% yield: 1H NMR
(400 MHz, CDCl3) d 9.15 (d, J = 17.2 Hz, 1H), 8.93 (d, J = 8.8 Hz,

5484
H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
1H), 8.16 (td, J = 8.0, 2.0 Hz, 1H), 7.60–7.54 (m, 1H), 7.35–7.30 (m,
2H), 7.22 (dd, J = 12.4, 0.8 Hz, 1H).
4.3.6. 5-Chloro-2-(3-chlorophenyl)oxazolo[5,4-b]pyridine (4f)
The desired product was obtained in 63% yield: 1H NMR
(300 MHz, CDCl3) d 8.29 (s, 1H), 8.50 (dd, J = 2.9, 4.6 Hz, 1H), 8.06
(d, J = 8.2 Hz, 1H), 7.63–7.51 (m, 2H), 7.45 (d, J = 8.2 Hz, 1H)
4.2.3. N-(2,6-Dichloropyridin-3-yl)-3-fluorobenzamide (3c)
The desired product was obtained in 60% yield: 1H NMR
(300 MHz, CDCl3) d 8.93 (d, J = 8.5 Hz, 1H), 8.37 (s, 1H), 7.68 (t,
J = 7.5 Hz, 2H), 7.57 (q, J = 8.0 Hz, 1H), 7.41–7.34 (m, 2H).
4.3.7. 5-Chloro-2-(4-chlorophenyl)oxazolo[5,4-b]pyridine (4g)
The desired product was obtained in 60% yield: 1H NMR
(400 MHz, CDCl3)
d 8.51 (dd, J = 1.8, 5.1 Hz, 2H), 8.01 (d,
J = 8.2 Hz, 1H), 7.54 (dd, J = 1.8, 5.2 Hz, 2H), 7.40 (d, J = 8.2 Hz, 1H)
4.2.4. N-(2,6-Dichloropyridin-3-yl)-4-fluorobenzamide (3d)
The desired product was obtained in 94% yield: 1H NMR
(300 MHz, CDCl3) d 8.72 (d, J = 4.5 Hz, 1H), 8.24 (s, 1H), 7.72 (d,
J = 8.0 Hz, 2H), 7.46 (d, J = 8.1 Hz, 2H), 7.28 (d, J = 8.0 Hz, 1H).
4.4. General procedure for preparation of 5a–d
Lawesson’s reagent (1.5 equiv) was added to a solution of
substituted N-(2,6-dichloropyridin-3-yl)benzamide (1 equiv) in
toluene. The resulting mixture was stirred for 5 h at 110 °C and
monitored with TLC. After cooling down to room temperature,
1.8-diazabicylo[5.4.0]undec-7-ene (3 equiv) was added and the
reaction mixture was allowed to stir for 60 h. The solvent was re-
moved under reduced pressure, and the residue was dissolved in
DMF. After adding K2CO3 (3 equiv), the reaction mixture was stir-
red for 3 h at 160 °C. After completion of the reaction, as monitored
by TLC, the reaction mixture was cooled to room temperature and
partitioned between ethyl acetate and water. The mixture was ex-
tracted with ethyl acetate. The combined organic layers were dried
over MgSO4, filtered, and evaporated. The residue was purified by
column chromatography (hexane:EtOAc = 20:1) on silica gel to ob-
tain the desired product.
4.2.5. 2-Chloro-N-(2,6-dichloropyridin-3-yl)benzamide (3e)
The desired product was obtained in 75% yield: 1H NMR
(300 MHz, CDCl3) d 8.98 (d, J = 8.6 Hz, 1H), 8.68 (s, 1H), 7.80 (d,
J = 6.7 Hz, 1H), 7.56–7.52 (m, 2H), 7.49–7.45 (m, 1H), 7.39 (d,
J = 8.6 Hz, 1H).
4.2.6. 3-Chloro-N-(2,6-dichloropyridin-3-yl)benzamide (3f)
The desired product was obtained in 59% yield: 1H NMR
(400 MHz, MeOD) d 8.22 (d, J = 8.3 Hz, 1H), 7.97 (t, J = 1.9 Hz, 1H),
7.90–7.88 (m, 1H), 7.62–7.61 (m, 1H), 7.5 (dd, J = 7.9, 11.6 Hz, 2H).
4.2.7. 4-Chloro-N-(2,6-dichloropyridin-3-yl)benzamide (3g)
The desired product was obtained in 99% yield: 1H NMR
(300 MHz, CDCl3) d 8.93 (d, J = 4.7 Hz, 1H), 8.34 (s, 1H), 7.89 (d,
J = 8.3 Hz, 2H), 7.56 (d, J = 8.3 Hz, 2H), 7.39 (d, J = 8.6 Hz, 1H).
4.4.1. 5-Chloro-2-phenylthiazolo[5,4-b]pyridine (5a)
The desired product was obtained in 50% yield: 1H NMR
(400 MHz, CDCl3) d 8.22 (d, J = 8.5 Hz, 1H), 8.09–8.07 (m, 2H),
7.55–7.50 (m, 3H), 7.45 (d, J = 8.5 Hz, 1H).
4.3. The general procedure for preparation of 4a–4g
Na2CO3 (1 equiv) was added to a solution of substituted N-(2,6-
dichloropyridin-3-yl)benzamide (1 equiv) in DMF. The resulting
mixture was stirred at 160 °C for 24 h. After completion of the
reaction, as monitored by TLC, the reaction mixture was cooled
to room temperature and partitioned between ethyl acetate and
water. The mixture was extracted with ethyl acetate. The com-
bined organic layers were dried over MgSO4, filtered, and evapo-
rated. The residue was purified by column chromatography
(hexane:EtOAc = 20:1) on slica gel to obtain the desired product.
4.4.2. 5-Chloro-2-(4-fluorophenyl)thiazolo[5,4-b]pyridine (5b)
The desired product was obtained in 73% yield: 1H NMR
(300 MHz, CDCl3) d 8.24 (d, J = 8.5 Hz, 1H), 8.14–8.08 (m, 2H),
7.49 (d, J = 8.5 Hz, 1H), 7.30–7.21 (m, 2H).
4.4.3. 5-Chloro-2-(2-chlorophenyl)thiazolo[5,4-b]pyridine (5c)
The desired product was obtained in 80% yield: 1H NMR
(300 MHz, CDCl3) d 8.26–8.21 (m, 1H), 8.15 (d, J = 8.6 Hz, 1H),
7.61–7.57 (m, 1H), 7.51–7.44 (m, 2H), 7.36 (d, J = 8.6 Hz, 1H).
4.3.1. 5-Chloro-2-phenyloxazolo[5,4-b]pyridine (4a)
The desired product was obtained in 95% yield: 1H NMR
(300 MHz, CDCl3) d 8.30 (d, J = 6.4 Hz, 2H), 8.05 (d, J = 8.2 Hz, 1H),
7.67–7.57 (m, 3H), 7.43 (d, J = 8.2 Hz, 1H).
4.4.4. 5-Chloro-2-(4-chlorophenyl)thiazolo[5,4-b]pyridine (5d)
The desired product was obtained in 73% yield: 1H NMR
(300 MHz, CDCl3) d 8.10–8.00 (m, 3H), 7.56–7.44 (m, 3H)
4.3.2. 5-Chloro-2-(2-fluorophenyl)oxazolo[5,4-b]pyridine (4b)
The desired product was obtained in 95% yield: 1H NMR
(300 MHz, CDCl3) d 8.24–8.23 (m, 1H), 8.13–8.09 (m, 1H), 7.67–
7.59 (m, 1H), 7.47–7.29 (m, 3H).
4.5. N-Methyl-2-phenyloxazolo[5,4-b]pyridin-5-amine (1a)
To a solution of 4a (200 mg, 0.9 mmol) in DMF (3 ml), N-ben-
zylmethylamine (1.2 ml, 9.0 mmol) was added and stirred at
135 °C for 4 h. After completion of the reaction, as monitored by
TLC, the reaction mixture was cooled to room temperature, and
then solvent was removed reduced pressure. The mixture was di-
luted with saturated NaHCO3 solution and extracted with CH2Cl2.
The combined organic layers were dried over MgSO4, filtered,
and evaporated. The residue was dissolved in 95% H2SO4 (0.5 ml)
and refluxed for 12 h. After cooling to room temperature, the reac-
tion flask was basified with diluted sodium hydroxide solution un-
til a pH of 10. The reaction mixture was extracted with CH2Cl2, the
combined organic layers were dried over MgSO4, filtered, and
evaporated to give afford 1a (109 mg, 0.5 mmol, 54% yield): 1H
NMR (300 MHz, CDCl3) d 8.24–8.20 (m, 2H), 7.83 (d, J = 8.6 Hz,
1H), 7.55–7.51 (m, 3H), 6.46 (d, J = 8.6 Hz, 1H), 4.75 (s, 1H), 3.07
(d, J = 5.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz) d 159.43, 158.76,
157.12, 130.54, 129.22, 128.40, 127.41, 126.87, 124.21, 104.22,
4.3.3. 5-Chloro-2-(3-fluorophenyl)oxazolo[5,4-b]pyridine (4c)
The desired product was obtained in 80% yield: 1H NMR
(300 MHz, CDCl3) d 8.07 (d, J = 8.1 Hz, 2H), 7.97 (d, J = 9.1 Hz, 1H),
7.57 (q, J = 8.0 Hz, 1H), 7.44 (d, J = 8.2 Hz, 1H), 7.36–7.30 (m, 1H).
4.3.4. 5-Chloro-2-(4-fluorophenyl)oxazolo[5,4-b]pyridine (4d)
The desired product was obtained in 73% yield: 1H NMR
(300 MHz, CDCl3) d 8.32–8.26 (m, 2H), 8.04 (d, J = 8.2 Hz, 1H),
7.43 (d, J = 8.2 Hz, 1H), 7.32–7.21 (m, 2H).
4.3.5. 5-Chloro-2-(2-chlorophenyl)oxazolo[5,4-b]pyridine (4e)
The desired product was obtained in 75% yield: 1H NMR
(300 MHz, CDCl3) d 8.20 (d, J = 8.6 Hz, 1H), 7.99 (d, J = 8.2 Hz, 1H),
7.65 (d, J = 8.1 Hz, 1H), 7.45–7.33 (m, 3H).

H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
5485
29.11; HRMS (ESI) m/z calcd for C13H12N3O [M+H]+ 226.0975;
found: 226.0976.
reaction mixture was cooled to room temperature, and then sol-
vent was removed reduced pressure. The mixture was diluted with
saturated NaHCO3 solution and extracted with CH2Cl2. The com-
bined organic layers were dried over MgSO4, filtered, and evapo-
rated. The residue was purified by column chromatography
(hexane:CH2Cl2:EtOAc = 20:1:1) on slica gel to give afford 1e
(70 mg, 0.2 mmol, 57% yield): 1H NMR (300 MHz, CDCl3) d 8.24–
8.20 (m, 2H), 7.82 (d, J = 8.8 Hz, 1H), 7.54–7.50 (m, 3H), 6.54 (d,
J = 8.9 Hz, 1H), 3.74 (t, J = 5.9 Hz, 4H), 1.88 (s, 4H), 1.63–1.59 (m,
4H); 13C NMR (CDCl3, 75 MHz) d 162.33, 156.34, 130.60, 129.56,
128.81, 127.60, 126.76, 123.06, 103.10, 48.35, 27.70, 27.11; HRMS
(ESI) m/z calcd for C18H20N3O [M+H]+ 294.1601; found: 294.1603.
4.6. N-Cyclohexyl-2-phenyloxazolo[5,4-b]pyridin-5-amine (1b)
To solution of 4a (50 mg, 0.2 mmol) in DMF (2 ml), cyclohexyl-
amine (0.2 ml, 2.0 mmol) was added and stirred at 35 °C for 4 h.
After completion of the reaction, as monitored by TLC, the reaction
mixture was cooled to room temperature, and then solvent was re-
moved reduced pressure. The mixture was diluted with saturated
NaHCO3 solution and extracted with CH2Cl2. The combined organic
layers were dried over MgSO4, filtered, and evaporated. The residue
was purified by column chromatography (hexane:CH2Cl2:
EtOAc = 20:1:1) on slica gel to give afford 1b (20 mg, 0.07 mmol,
34% yield): 1H NMR (300 MHz, MeOD) d 8.12–8.11 (m, 2H), 7.70
(d, J = 8.7 Hz, 1H), 7.57–7.53 (m, 3H), 6.54 (d, J = 8.7 Hz, 1H), 3.79
(s, 1H), 2.08 (d, J = 12.2 Hz, 2H), 1.83 (dd, J = 3.9, 5.7 Hz, 2H), 1.71
(d, J = 13.2 Hz, 1H), 1.52–1.42 (m, 2H), 1.30 (t, J = 12.0 Hz, 3H);
13C NMR (CDCl3, 75 MHz) d 159.64, 158.75, 156.05, 130.74,
129.71, 128.84, 127.48, 126.81, 124.17, 105.51, 50.41, 33.34,
4.9. General procedure for preparation of 1f–1p
To solution of substituted phenyloxazolopyridine or phenyl-
thiazolopyridine (1 equiv) in DMF, piperidine (10 equiv) was added
and stirred at 35 °C for 4 h. After completion of the reaction, as
monitored by TLC, the reaction mixture was cooled to room tem-
perature, and then solvent was removed reduced pressure. The
mixture was diluted with saturated NaHCO3 solution and extracted
with CH2Cl2. The combined organic layers were dried over MgSO4,
filtered, and evaporated. The residue was purified by column chro-
matography (hexane:CH2Cl2:EtOAc = 20:1:1) on slica gel to ob-
tained the desired product.
25.79, 24.89; HRMS (ESI) m/z calcd for
C
18H20N3O [M+H]+
294.1601; found: 294.1604.
4.7. N-Benzyl-2-phenyloxazolo[5,4-b]pyridin-5-amine (1c)
To solution of 4a (100 mg, 0.9 mmol) in DMF (3 ml), benzyl-
amine (0.4 ml, 4 mmol) was added and stirred at 35 °C for 4 h.
After completion of the reaction, as monitored by TLC, the reaction
mixture was cooled to room temperature, and then solvent was re-
moved reduced pressure. The mixture was diluted with saturated
NaHCO3 solution and extracted with CH2Cl2. The combined organic
layers were dried over MgSO4, filtered, and evaporated. The residue
4.9.1. 2-Phenyl-5-(piperidin-1-yl)oxazolo[5,4-b]pyridine (1f)
The desired product was obtained in 26% yield: 1H NMR
(300 MHz, CDCl3) d 8.22–8.16 (m, 2H), 7.80 (d, J = 8.7 Hz, 1H),
7.83–7.47 (m, 3H), 6.70 (d, J = 8.7 Hz, 1H), 3.63 (s, 4H), 1.68 (s,
6H); 13C NMR (CDCl3, 75 MHz) d 159.33, 159.19, 157.32, 130.85,
129.65, 128.88, 127.42, 126.86, 123.93, 104.80, 46.91, 25.50,
24.65; HRMS (ESI) m/z calcd for C17H18N3O [M+H]+ 280.1444;
found: 280.1446.
was
purified
by
column
chromatography
(hex-
ane:CH2Cl2:EtOAc = 20:1:1) on slica gel to give afford 1c (30 mg,
0.1 mmol, 25% yield): 1H NMR (300 MHz, CDCl3) d 8.24–8.21 (m,
2H), 7.82 (d, J = 8.6 Hz, 1H), 7.55–7.51 (m, 3H), 7.46–7.31 (m,
5H), 6.46 (d, J = 8.6 Hz, 1H), 5.04 (s, 1H), 4.67 (d, J = 5.7 Hz, 2H);
13C NMR (CDCl3, 75 MHz) d 159.49, 159.14, 156.41, 138.75,
130.92, 129.89, 128.89, 128.76, 127.50, 127.37, 126.90, 124.87,
4.9.2. 2-(2-Fluorophenyl)-5-(piperidin-1-yl)oxazolo[5,4-
b]pyridine (1g)
The desired product was obtained in 9% yield: 1H NMR
(300 MHz, CDCl3) d 8.20 (t, J = 1.6 Hz, 1H), 7.89 (d, J = 8.9 Hz, 1H),
7.53–7.46 (m, 1H), 7.33–7.24 (m. 2H), 6.73 (d, J = 8.9 Hz, 1H),
3.67 (s, 4H), 1.72 (s, 6H); 13C NMR (CDCl3, 100 MHz) d 160.49
(J = 257 Hz), 159.01, 157.51, 155.20 (J = 6 Hz), 132.20 (J = 8 Hz),
129.88 (J = 30 Hz), 129.72, 124.40 (J = 3 Hz), 123.71, 117.00
(J = 21 Hz), 115.81 (J = 10 Hz), 104.91, 46.83, 25.49, 24.63; HRMS
(ESI) m/z calcd for C17H17FN3O [M+H]+ 298.1350; found: 298.1352.
105.46, 46.57; HRMS (ESI) m/z calcd for
C
19H16N3O [M+H]+
302.1288; found: 302.1290.
4.8. N-Benzyl-N-methyl-2-phenyloxazolo[5,4-b]pyridin-5-
amine (1d)
To solution of 4a (200 mg, 0.4 mmol) in DMF (3 ml), N-ben-
zylmethylamine (1.2 ml, 9.0 mmol) was added and stirred at
35 °C for 4 h. After completion of the reaction, as monitored by
TLC, the reaction mixture was cooled to room temperature, and
then solvent was removed reduced pressure. The mixture was di-
luted with saturated NaHCO3 solution and extracted with CH2Cl2.
The combined organic layers were dried over MgSO4, filtered,
and evaporated. The residue was purified by column chromatogra-
phy (hexane:CH2Cl2:EtOAc = 20:1:1) on slica gel to give afford 1d
(218 mg, 0.7 mmol, 80% yield): 1H NMR (300 MHz, CDCl3) d 8.25–
8.21 (m, 2H), 7.85 (d, J = 8.8 Hz, 1H), 7.54–7.50 (m, 3H), 7.39–
7.27 (m, 5H), 6.58 (d, J = 8.8 Hz, 1H), 4.91 (s, 2H), 3.21 (s, 3H);
13C NMR (CDCl3, 75 MHz) d 159.37, 158.96, 156.68, 138.05,
130.83, 129.75, 128.88, 128.68, 128.25, 127.45, 127.18, 127.04,
126.86, 123.88, 103.70, 53.97, 37.02; HRMS (ESI) m/z calcd for
4.9.3. 2-(3-Fluorophenyl)-5-(piperidin-1-yl)oxazolo[5,4-
b]pyridine (1h)
The desired product was obtained in 19% yield: 1H NMR
(300 MHz, CDCl3) d 8.00 (d, J = 7.8 Hz, 1H), 7.90 (d, J = 8.0 Hz, 1H),
7.84 (d, J = 8.9 Hz, 1H), 7.53–7.18 (m, 1H), 7.21 (t, J = 5.9 Hz, 1H),
6.73 (d, J = 8.9 Hz, 1H), 3.67 (s, 4H), 1.72 (s, 6H); 13C NMR (CDCl3,
75 MHz) d 162.97 (J = 245 Hz), 159.36, 157.85, 130.56 (J = 8.1 Hz),
129.84, 129.57, 123.75, 122.52, 117.74 (J = 21.2 Hz), 105.01,
46.86, 25.50, 24.64; HRMS (ESI) m/z calcd for C17H17FN3O [M+H]+
298.1350; found: 298.1352.
4.9.4. 2-(4-Fluorophenyl)-5-(piperidin-1-yl)oxazolo[5,4-
b]pyridine (1i)
The desired product was obtained in 11% yield: 1H NMR
(300 MHz, CDCl3) d 8.11 (d, J = 9. 1 Hz, 2H), 7.92 (d, J = 8.2 Hz,
1H), 7.33 (t, J = 8.1 Hz, 1H), 7.36 (d, J = 9.1 Hz, 2H), 3.43 (s, 4H),
1.72 (s, 6H); 13C NMR (CDCl3, 75 MHz) d 164.40 (J = 250 Hz),
162.33, 158.33, 157.29, 129.60, 128.97 (J = 8.7 Hz), 123.82,
123.78, 116.12 (J = 22.0 Hz), 104.83, 46.91, 25.48, 24.63; HRMS
(ESI) m/z calcd for C17H17FN3O [M+H]+ 298.1350; found: 298.1353.
C
20H18N3O [M+H]+ 316.1444; found: 316.1446.
4.8.1. 5-(Azepan-1-yl)-2-phenyloxazolo[5,4-b]pyridine (1e)
To solution of 4a (97 mg, 0.4 mmol) in DMF (2 ml), hexamethy-
leneimine (0.5 ml, 4.0 mmol) was added and stirred at 35 °C for
4 h. After completion of the reaction, as monitored by TLC, the

5486
H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
4.9.5. 2-(2-Chlorophenyl)-5-(piperidin-1-yl)oxazolo[5,4-
b]pyridine (1j)
25.61, 24.68; HRMS (ESI) m/z calcd for C17H17ClN3S [M+H]+
330.0826; found: 330.0828.
The desired product was obtained in 18% yield: 1H NMR
(300 MHz, CDCl3) d 8.19–8.16 (m, 1H), 7.91 (d, J = 8.9 Hz, 1H),
7.59–7.56 (m, 1H), 7.44–7.41 (m, 2H), 6.73 (d, J = 8.9 Hz, 1H),
3.67 (s, 4H), 1.72 (s, 6H); 13C NMR (CDCl3, 75 MHz) d 159.10,
157.59, 156.67, 132.87, 131.47, 131.19, 131.15, 130.19, 126.88,
126.18, 123.62, 104.93, 46.56, 25.51, 24.66; HRMS (ESI) m/z calcd
for C17H17ClN3O [M+H]+ 314.1055; found: 314.1057.
4.10. Human MAO-B assay
Human recombinant MAO-B enzyme prepared from insect cells
was obtained from Sigma-Aldrich. Benzylamine hydrochloride
(Sigma) was used as substrate for the enzyme. Sodium phosphate
buffer (0.05 M, pH 7.4) was used for all the enzyme reactions and
dilutions. The final volume of the enzyme reactions was 200
and each reaction contained benzylamine hydrochloride, various
concentrations of the test inhibitors (0.01–100 M) and 1% DMSO
as co-solvent. The potential effects of the test drugs on hMAO-B
activity were investigated by measuring their effects on the pro-
duction of H2O2 from benzylamine, using the Amplex RedÒ MAO
assay kit (Invitrogen).
Briefly, 0.1 ml of sodium phosphate buffer (0.05 M, 7.4 pH) con-
taining the test drugs (new compounds or reference inhibitors) in
various concentrations and adequate amounts of recombinant
ll,
4.9.6. 2-(3-Chlorophenyl)-5-(piperidin-1-yl)oxazolo[5,4-
b]pyridine (1k)
l
The desired product was obtained in 56% yield: 1H NMR
(300 MHz, CDCl3) d 8.22 (s, 1H), 8.09 (d, J = 6.5 Hz, 1H), 7.84 (d,
J = 8.8 Hz, 1H), 7.47 (s, 2H), 6.72 (d, J = 8.9 Hz, 1H), 3.67 (s, 4H),
1.72 (s, 6H); 13C NMR (CDCl3, 75 MHz) d 159.36, 127.67, 157.46,
135.03, 130.70, 130.16, 129.83, 129.17, 126.85, 124.79, 123.74,
105.02, 46.86, 25.49, 24.63; HRMS (ESI) m/z calcd for C17H17ClN3O
[M+H]+ 314.1055; found: 314.1057.
hMAO-B (0.5
96-well plate. After this incubation period, the reaction was started
by adding (final concentrations) 200
M Amplex RedÒ reagent,
1 U/ml horseradish peroxidase, and 1 mM benzylamine hydrochlo-
ride. The production of H2O2 and, consequently, of resorufin, was
quantified at 37 °C in a multidetection microplate fluorescence
reader (TECAN) based on the fluorescence generated (absorbance,
570 nm).
Control experiments were carried out simultaneously by replac-
ing the test drugs (new compounds and reference inhibitors) with
appropriate dilutions of the vehicles. In addition, the possible
capacity of the above test drugs to modify due to nonenzymatic
inhibition (e.g., for directly reaction with Amplex RedÒ reagent)
was determined by adding these drugs to solutions containing only
the Amplex RedÒ reagent in a sodium phosphate buffer.
The specific fluorescence absorbance (used to obtain the final
results) was calculated after subtraction of the background activ-
ity, which was determined from vials containing all components
except the hMAO-B, which was replaced by a sodium phosphate
buffer solution.
ll, 71 U/mg) were incubated for 1 h at 37 °C in a
4.9.7. 2-(4-Chlorophenyl)-5-(piperidin-1-yl)oxazolo[5,4-
b]pyridine (1l)
l
The desired product was obtained in 17% yield: 1H NMR
(300 MHz, CDCl3) d 8.14 (d, J = 8.7 Hz, 2H), 7.83 (d, J = 8.9 Hz, 1H),
7.50 (d, J = 8.7 Hz, 2H), 6.72 (d, J = 8.9 Hz, 1H), 3.67 (s, 4H), 1.72
(s, 6H); 13C NMR (CDCl3, 75 MHz) d 162.34, 158.15, 157.37,
136.93, 129.72, 129.24, 128.04, 125.94, 123.80, 104.95, 46.87,
25.50, 24.64; HRMS (ESI) m/z calcd for C17H17ClN3O [M+H]+
314.1055; found: 314.1058.
4.9.8. 2-Phenyl-5-(piperidin-1-yl)thiazolo[5,4-b]pyridine (1m)
The desired product was obtained in 73% yield: 1H NMR
(300 MHz, CDCl3) d 8.04 (d, J = 9.2 Hz, 3H), 7.51–7.48 (m, 3H),
6.84 (d, J = 9.2 Hz, 1H), 3.67 (s, 4H), 1.71 (s, 6H); 13C NMR (CDCl3,
75 MHz)
d 161.81, 157.72, 157.58, 139.55, 134.25, 131.22,
130.24, 128.96, 126.85, 106.53, 46.73, 25.63, 24.71; HRMS (ESI)
m/z calcd for C17H18N3S [M+H]+ 296.1216; found: 296.1220.
4.9.9. 2-(4-Fluorophenyl)-5-(piperidin-1-yl)thiazolo[5,4-
b]pyridine (1n)
4.11. Docking study
The desired product was obtained in 35% yield: 1H NMR
(300 MHz, CDCl3) d 8.04–7.99 (m, 3H), 7.18 (t, J = 6.4 Hz, 2H),
6.84 (d, J = 9.2 Hz, 1H), 3.69 (d, J = 4.8 Hz, 4H), 1.72 (s, 6H); 13C
All docking studies were performed with Maestro 7.5 package
(Schrödinger, Inc.) and carried out on the X-ray crystal structure
of hMAO-B (PDB code 2V60) which was obtained from the Protein
Data Bank. Three dimensional structures of the compounds 1i and
1n were prepared by build module of Maestro 7.5 and then the
constructed 3D structures of 1i and 1n were minimized with con-
jugate gradient method, OPLS-AA (Optimized Potentials for Liquid
Simulations-All Atom) force field, and GB/SA continuum water
model. The crystal structure of hMAO-B was prepared for docking
with the Protein Preparation Wizard workflow of Maestro 7.5 to
assign the charge state of ionizable residues, add hydrogens, and
carry out energy minimization. The docking was performed by
using GLIDE 4.0 (http://www.schrodinger.com). The grid was made
by applying a van der Waals radii scaling factor of 1.00 with a par-
tial charge cut-off of less than 0.25e and the co-crystal ligand was
used to center docking box with a size capable of accommodating
ligands with a length of 620 Å. The docking calculations were per-
formed with Glide standard precision (SP) mode, and ten best
poses for each ligand were retained.
NMR (CDCl3, 75 MHz)
d 164.00 (J = 249 Hz), 160.50, 157.76,
157.58, 139.51, 131.16, 130.63 (J = 3.3 Hz), 128.70 (J = 8.4 Hz),
116.03(J = 21.9 Hz), 106.53, 46.72, 25.61, 24.69; LC/MS (ESI) m/z
calcd for C17H17FN3S [M+H]+ 314.1122; found: 314.1124.
4.9.10. 2-(2-Chlorophenyl)-5-(piperidin-1-yl)thiazolo[5,4-
b]pyridine (1o)
The desired product was obtained in 7% yield: 1H NMR
(300 MHz, CDCl3) d 8.19–8.13 (m, 1H), 8.08 (d, J = 9.2 Hz, 1H),
7.57–7.51 (m, 1H), 7.45–7.36 (m, 2H), 6.87 (d, J = 9.2 Hz, 1H),
3.70 (s, 4H), 1.72 (s, 6H); 13C NMR (CDCl3, 75 MHz) d 159.47,
157.63, 154.07, 148.84, 131.94, 131.03, 130.45, 130.37, 123.97,
123.48, 121.13, 105.22, 46.77, 25.50, 24.64; HRMS (ESI) m/z calcd
for C17H17ClN3S [M+H]+ 330.0826; found: 330.0829.
4.9.11. 2-(4-Chlorophenyl)-5-(piperidin-1-yl)thiazolo[5,4-
b]pyridine (1p)
The desired product was obtained in 35% yield: 1H NMR
(300 MHz, CDCl3) d 8.03–7.95 (m, 3H), 7.47 (d, J = 8.4 Hz, 3H),
7.47 (d, J = 8.4 Hz, 2H), 6.84 (d, J = 9.2 Hz, 1H), 3.68 (s, 4H), 1.72
(s, 6H); 13C NMR (CDCl3, 75 MHz) d 160.26, 157.81, 157.62,
139.49, 136.11, 132.82, 131.25, 129.15, 127.97, 106.63, 46.70,
Acknowledgement
This research was supported by the KIST Institutional Program
(2E24183 and 2E23770).

H. R. Park et al. / Bioorg. Med. Chem. 21 (2013) 5480–5487
5487
13. Rabey, J. M.; Sagi, I.; Huberman, M.; Melamed, E.; Korczyn, A.; Giladi, N.;
Inzelberg, R.; Djaldetti, R.; Klein, C.; Berecz, G. Clin. Neuropharmacol. 2000, 23,
324.
14. Vezina, P.; Mohr, E.; Grimes, D. Can. J. Neurol. Sci. 1992, 19, 142.
15. Stern, M. B.; Marek, K. L.; Friedman, J.; Hauser, R. A.; LeWitt, P. A.; Tarsy, D.;
Olanow, C. W. Mov. Disord. 2004, 19, 916.
16. Dimpfel, W.; Hoffmann, J. BMC Pharmacol. 2011, 11, 2.
17. Barrow, J.; Harrison, S.; Mulhearn, J.; Sur, C.; Williams, D. L.; Wolkenberg, S.
WO 155,017, 2009, A2.
18. Kempson, J.; Spergel, S. H.; Guo, J.; Quesnelle, C.; Gill, P.; Belanger, D.;
Dyckman, A. J.; Li, T.; Watterson, S. H.; Langevine, C. M.; Das, J.; Moquin, R. V.;
Furch, J. A.; Marinier, A.; Dodier, M.; Martel, A.; Nirschl, D.; Kirk, K. V.; Burke, J.
R.; Pattoli, M. A.; Gillooly, K.; McIntyre, K. W.; Chen, L.; Yang, Z.; Marathe, P. H.;
Wang-Iverson, D.; Dodd, J. H.; McKinnon, M.; Barrish, J. C.; Pitts, W. J. J. Med.
Chem. 2009, 52, 1994.
References and notes
1. de Lau, L. M. L.; Breteler, M. M. B. Lancet Neurol. 2006, 5, 525.
2. Jankovic, J. J. Neurol. Neurosurg. Psychiatry 2008, 79, 368.
3. German, D. C.; Manaye, K.; Smith, W. K.; Woodward, D. J.; Saper, C. B. Ann.
Neurol. 1989, 26, 507.
4. Gardian, G.; Vecsei, L. Int. J. Clin. Pharmacol. Ther. 2010, 48, 633.
5. Fahn, S. Mov. Disord. 2008, 23, S497.
6. Bach, A. W. J.; Lan, N. C.; Johnson, D. L.; Abell, C. W.; Bembenek, M. E.; Kwan, S.
W.; Seeburg, P. H.; Shih, J. C. Proc. Natl. Acad. Sci. U.S.A. 1988, 85, 4934.
7. Mallajosyula, J. K.; Kaur, D.; Chinta, S. J.; Rajagopalan, S.; Rane, A.; Nicholls, D.
G.; Di Monte, D. A.; Macarthur, H.; Andersen, J. K. PLoS ONE 2008, 3, e1616.
8. Lieu, C. A.; Chinta, S. J.; Rane, A.; Andersen, J. K. PLoS ONE 2013, 8, e54200.
9. Levitt, P.; Pintar, J. E.; Breakefield, X. O. Proc. Natl. Acad. Sci. U.S.A. 1982, 79,
6385.
10. Bortolato, M.; Chen, K.; Shih, J. C. Adv. Drug Delivery Rev. 2008, 60, 1527.
11. Fernandez, H. H.; Chen, J. J. Pharmacotherapy 2007, 27, 174S.
12. Pålhagen, S.; Heinonen, E.; Hagglund, J.; Kaugesaar, T.; Maki-Ikola, O.; Palm, R.
Neurology 2006, 66, 1200.
19. Chimenti, F.; Secci, D.; Bolasco, A.; Chimenti, P.; Bizzarri, B.; Granese, A.;
Carradori, S.; Yánez, M.; Orallo, F.; Ortuso, F.; Alcaro, S. J. Med. Chem. 2009, 52,
1935.
20. Binda, C.; Wang, J.; Pisani, L.; Caccia, C.; Carotti, A.; Salvati, P.; Edmondson, D.
E.; Mattevi, A. J. Med. Chem. 2007, 50, 5848.