6-Phenoxy-2-phenylbenzoxazoles, novel inhibitors of receptor for advanced glycation end products (RAGE)

Article abstract of DOI:10.1016/j.bmc.2015.05.022

Receptor for advanced glycation end products (RAGE) is known to be involved in the transportation of amyloid β (Aβ) peptides and causes the accumulation of Aβ in the brain. Moreover, recent studies suggest that the interactions between RAGE and Aβ peptides may be the culprit behind Alzheimer's disease (AD). Inhibitors of the RAGE-Aβ interactions would not only prevent the accumulation of toxic Aβ in the brain, and but also block the progress of AD, therefore, have the potential to provide a 'disease-modifying therapy'. In this study, we have developed a series of 6-phenoxy-2-phenylbenzoxazole analogs as novel inhibitors of RAGE. Among these derivatives, we found several effective inhibitors that block the RAGE-Aβ interactions without causing significant cellular toxicity. Further testing showed that compound 48 suppressed Aβ induced toxicity in mouse hippocampal neuronal cells and reduced Aβ levels in the brains of a transgenic mouse model of AD after oral administration.

Full text of DOI:10.1016/j.bmc.2015.05.022

Bioorganic & Medicinal Chemistry xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
6-Phenoxy-2-phenylbenzoxazoles, novel inhibitors of receptor
for advanced glycation end products (RAGE)
Kwanghyun Choi a,b, Kwang Su Lim a, Juhee Shin a, Seo Hee Kim a, Young-Ger Suh a, Hyun-Seok Hong b,
Hee Kim b, Hee-Jin Ha b, Young-Ho Kim b, Jiyoun Lee c, Jeewoo Lee a,
⇑
a Laboratory of Medicinal Chemistry, Research Institute of Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul 151-742, South Korea
b Medifron DBT, Sandanro 349, Danwon-Gu, Ansan-City, Gyeonggi-Do 425-839, South Korea
c Department of Global Medical Science, Sungshin University, Seoul 142-732, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Receptor for advanced glycation end products (RAGE) is known to be involved in the transportation of
amyloid b (Ab) peptides and causes the accumulation of Ab in the brain. Moreover, recent studies suggest
that the interactions between RAGE and Ab peptides may be the culprit behind Alzheimer’s disease (AD).
Inhibitors of the RAGE–Ab interactions would not only prevent the accumulation of toxic Ab in the brain,
and but also block the progress of AD, therefore, have the potential to provide a ‘disease-modifying ther-
apy’. In this study, we have developed a series of 6-phenoxy-2-phenylbenzoxazole analogs as novel inhi-
bitors of RAGE. Among these derivatives, we found several effective inhibitors that block the RAGE–Ab
interactions without causing significant cellular toxicity. Further testing showed that compound 48 sup-
pressed Ab induced toxicity in mouse hippocampal neuronal cells and reduced Ab levels in the brains of a
transgenic mouse model of AD after oral administration.
Received 6 April 2015
Revised 12 May 2015
Accepted 13 May 2015
Available online xxxx
Keywords:
Receptor for advanced glycation end
products, RAGE
Alzheimer’s disease
Amyloid b
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Ab across the BBB, thus causes the accumulation of Ab in the
brain.7,8
Alzheimer’s disease (AD) is the most common cause of demen-
tia, accounting for 50–75 percent of the cases worldwide.1
Although the cause and progression of AD are still not completely
understood, amyloid b (Ab) plaques are considered to be one of the
most important hall mark changes in the brains of AD patients.2 Ab
plaques, known to cause neuronal damage and chronic inflamma-
tion, are derived from Ab peptides accumulated inside the brain. Ab
peptides are mainly produced from proteolytic cleavage of amyloid
precursor proteins (APPs), and the influx and clearance of Ab pep-
tides inside the brain are regulated by the blood–brain barrier
(BBB).3,4 According to the vascular hypothesis in AD pathogenesis,
damaged brain vasculature leads to abnormal BBB permeation,
which in turn accelerates the accumulation of Ab peptides in the
brain.5 The elevated levels of Ab peptides promote a cascade of
events that eventually lead to neuronal damage and dementia.6
The mechanisms underlying toxic Ab accumulation and AD patho-
genesis remain unclear, however, Zlokovic and colleagues demon-
strated that the receptor for advanced glycation end products
(RAGE) plays a crucial role in the transportation of plasma-derived
RAGE is a transmembrane receptor expressed on the surface of
diverse cells including monocytes, neurons, and vascular endothe-
lial cells.9,10 RAGE is known as a pattern recognition receptor,
which binds to multiple ligands.11 There are several endogenous
ligands including AGE (advanced glycation end products),9 S100
proteins,12 HMGB1 (high-mobility group box1; amphoterin),13
and Ab peptides.7,8 Interestingly, most of these ligands are linked
to several chronic diseases such as cancer,14 diabetic nephropa-
thy,15 atherosclerosis16 and AD.17 It is hypothesized that RAGE acti-
vates the nuclear factor kappa B (NF-jB) upon binding to these
ligands and triggers inflammatory responses.18 Furthermore, pro-
longed exposure to high concentrations of the ligands results in a
positive feedback cycle, which, in turn, leads to chronic
inflammation.19
In addition to the significant role of RAGE in chronic inflamma-
tion, direct involvement of RAGE in AD has drawn much attention
in hopes to find novel therapeutics. RAGE is overexpressed in AD
induced animals and human AD patients, and it acts as major
transporters of Ab peptides into the brain.7,8 Furthermore, the
interactions between Ab peptides and RAGE induce oxidative stress
and chronic inflammation in the brain, and accelerate neuronal
damage and cognitive decline.18,20–22 It has been reported that
anti-RAGE antibodies suppress detrimental effects of Ab peptides
⇑
Corresponding author. Tel.: +82 2 880 7846; fax: +82 2 888 0649.
E-mail address: jeewoo@snu.ac.kr (J. Lee).
http://dx.doi.org/10.1016/j.bmc.2015.05.022
0968-0896/Ó 2015 Elsevier Ltd. All rights reserved.
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2
K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
in transgenic mice models of AD, suggesting that RAGE is a promis-
ing therapeutic target for AD.23–25 Taken together, inhibitors of
RAGE–Ab interactions would block the accumulation of toxic Ab
in the brain, protect neurons from oxidative damage, and interfere
with the progress of AD. Therefore, these inhibitors have the poten-
tial to provide a ‘disease-modifying therapy’, whereas most AD
therapies developed to date are symptomatic treatments that can
improve cognitive functions and memory.
Initial efforts to develop therapies based on RAGE–Ab interac-
tions were mostly focused on anti-RAGE antibodies and soluble
RAGE proteins. However, recently, Zlokovic and colleagues
reported a small molecule RAGE-specific inhibitor that reduced
brain Ab level and Ab-induced cellular stress in an animal model
of AD.26 In addition, a RAGE-specific inhibitor developed by
TransTech Pharma, TTP-488, has reached phase 3 trial in patients
with mild to moderate AD. Inspired by these approaches, we per-
formed a pharmacophoric analysis based on the small molecule
ligands that were reported previously.27–31 We established a hypo-
thetical pharmacophore model, and identified the principal phar-
Compounds 12 and 18 were produced by amide reduction of com-
pounds 17 and 23 respectively.
Syntheses of 6-phenoxy-2-phenylbenzoxazole derivatives con-
taining a flexible aminoalkyl chain (26–75) were carried out by fol-
lowing the pathway described in Scheme 3. The phenoxy group of
6a–e were alkylated with 1-bromo-2-chloroethane (n = 1) or 1-
bromo-3-chloropropane (n = 2) to generate compounds 24 and
25 respectively. Compounds 26–30 were prepared from compound
24a by addition of the corresponding amines, and compounds
31–75 were prepared from compounds 25a–e. More specifically,
compounds 31–34, 37–61, and 64–75 were obtained via a simple
substitution reaction with the corresponding amines. Compounds
35, 36, 62, and 63 were generated by deprotecting the Boc group
from compounds 33, 34, 60, and 61 respectively.
2.2. Inhibition of the RAGE–Ab interaction
To evaluate whether the synthesized inhibitors can effectively
block the interactions between RAGE and Ab, we tested all com-
pounds using fluorescence resonance energy transfer (FRET) assay
along with MTT assay for cytotoxicity as presented in Table 1–3.
For the FRET assay, we first incubated biotinylated human RAGE
proteins and streptavidin–Cy3 conjugates, and then added Ab–
FITC conjugates and each compound. Based on the FRET signals
between RAGE–Cy3 and Ab–FITC in the presence of a vehicle con-
trol, the reduction of the FRET signals induced by each inhibitor
was recorded and calculated as percent inhibition. Additionally,
we assessed cytotoxicity of each compound by performing MTT
assays using HT22 cells (mouse hippocampal neuronal cell line).
Among the 4-chlorophenoxy benzoxazole derivatives, com-
pounds with a longer and flexible spacer (compounds 26–52,
Table 2) are likely to have higher activity compared to derivatives
with a shorter and constrained spacer (compounds 7–23, Table 1).
However, when we compared the compounds with the same N-
alkyl groups, for example, compounds 27 to 37, 28 to 40, 29 to
48, no clear tendency was observed. Among the derivatives with
various N-alkyl groups, compounds with morpholine (28 and 40)
and piperazine groups (41–52) were more likely to be active than
the rest of the analogues. Although, compounds with diethyl amine
(26, 31, and 53) and Boc-protected pyrrolidine groups (33 and 34)
appeared to inhibit FRET signals to some extent, all of these com-
pounds demonstrated noticeable cytotoxicity. Within the group
of compounds containing piperazine moiety, compounds with
the N-alkylcarbamate group (44–48) mostly showed good inhibi-
tory effects. On the other hand, the analogues containing an aro-
matic substituent on the N-alkyl group (14–16, 20–22, 30, 39,
49–52) were generally insoluble in water, therefore we were
unable to measure any FRET signals from these compounds.
When we replaced the 4-Cl group on the phenyl ring with var-
ious substituents (compounds 53–75, Table 3), we noticed that the
4-F and 4-CF3 containing derivatives appeared to show better sol-
ubility and higher activity compared to the 4-t-Bu substituted ana-
logues, suggesting that these substituents may be the key
pharmacophore for binding. Overall, we identified several highly
active compounds showing inhibition values greater than 40%.
On the basis of these measurements, we decided to exclude any
compounds showing cytotoxicity greater than 20% for further
testing, and selected 20 compounds (17, 19, 28–29, 36, 41, 46–48,
60–61, 65–68, 70–73, 75) exhibiting significant percent inhibition
values (>20%) with low cytotoxicity (<20%) at the indicated
concentrations.
macophores including an aryloxy group,
a dialkylaminoalkyl
group, and lipophilic substituents. On the basis of these findings,
we designed a series of small molecule inhibitors of RAGE–Ab
interactions as depicted in Figure 1. In this study, we synthesized
a novel series of 6-phenoxy-2-phenylbenzoxazole analogues and
evaluated their ability to block RAGE–Ab interactions in vitro and
in vivo.
2-Phenylbenzoxazole core
N
R1
O
R2
O
O
6-Phenoxy region
Aminoalkyloxy region
Figure 1. Design of 6-phenoxy-2-phenylbenzoxazole analogues as RAGE inhibitors.
2. Results and discussion
2.1. Chemistry
Syntheses of 6-phenoxy-2-(4-oxyphenyl)benzoxazole interme-
diates 6a–e were carried out by following the synthetic pathway
described in Scheme 1. First, the biaryl ether fragments, 2a–e, were
synthesized by alkylating various substituted phenols with 2-ben-
zyloxy-4-fluoro-1-nitro-benzene 1. Debenzylation at the ortho-po-
sition was achieved in good yields (74–99%) by using
trifluoroacetic acid. Subsequent reduction of nitro group with tin
chloride and hydrochloric acid afforded compounds 4a–e.
Condensation of compounds 4a–e with 4-formylphenyl acetate,
followed by oxidation using DDQ successfully constructed the
key benzoxazole fragments 5a–e in moderate to good yields
(43–78%). Deacetylation of 5a–e with sodium hydroxide generated
6-phenoxy-2-(4-oxyphenyl)benzoxazole intermediates 6a–e.
Syntheses
of
6-(4-chlorophenoxy)-2-phenylbenzoxazole
derivatives containing a piperidine (7–23) were performed by fol-
lowing the pathway described in Scheme 2. Mitsunobu reaction of
6a with Boc-protected piperidinyl alcohols afforded compound 7
and 8. After the Boc group was removed by using trifluoroacetic
acid, the free amine nitrogen was substituted by using a base
and alkyl halide or acyl halide to afford compounds 13, 15–17,
19, and 21–23. Compounds 14 and 20 were obtained via palla-
dium-catalyzed cross coupling reactions with bromobenzene.
2.3. Inhibition of the Ab induced cytotoxicity
It has been reported that the RAGE–Ab interactions induce var-
ious inflammatory responses,32 and amplify Ab induced toxicity in
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
3
a
b
R=4-Cl
NO2
c
NH2
OH
NO2
OBn
a
R=4-t-Bu
R
R
c R=4-F
R=4-CF3
R=3-CF3
d
e
O
OR
O
F
4
6
2
R = Bn
1
b
3 R = H
N
O
N
d
e
R
OH
R
OAc
O
O
O
5
Scheme 1. Synthesis of 6-phenoxy-2-(4-oxyphenyl)benzoxazole intermediates. Reagents and conditions: (a) K2CO3, DMF, 140 °C, overnight; (b) CF3CO2H, CH2Cl2, rt, 5 h; (c)
SnCl2–2H2O, concd HCl, 2-propanol, reflux, 2 h; (d) (i) 4-formylphenyl acetate, MeOH, 45 °C, 2 h, (ii) DDQ, CH2Cl2, rt, 30 min; (e) 2 N NaOH solution, MeOH, rt, 6 h.
Cl
Cl
Cl
N
O
N
O
a
b
O
OH
N
Boc
O
O
O
n
7 n=0
n=1
6a
8
Cl
N
O
N
O
c
O
O
N R
NH
O
n
n
11-23
9
10
n=0
n=1
Scheme 2. Synthesis of compounds 7–23. Reagents and conditions: (a) Boc-4-hydroxypiperidine or N-Boc-4-piperidine–methanol, DIAD, PPh3, THF, rt, 48 h; (b) TFA, DCM, rt,
5 h; (c) see Section 4 for detailed procedures.
N
O
N
O
b
a
R1
O
6
R1
O
O
O
n
n
Cl
R2
24
n=1
26-75
25 n=2
Scheme 3. Synthesis of compounds 26–75. Reagents and conditions: (a) 1-bromo-3-chloropropane or 1-bromo-2-chloroethane, K2CO3, CH3CN, 60 °C, overnight; (b) amines,
Na2CO3, KI, n-BuOH, 105 °C, 36 h.
neurons,33 therefore, we believe that RAGE inhibitors may have
protective effects against Ab induced cytotoxicity. To investigate
the protective effects of the selected compounds, we determined
effect in HT22 cells, therefore, we chose compound 48 for further
testing in vivo.
cell viability via MTT assay after incubating HT22 cells with 2
lM
2.4. Studies of the Ab-lowering effect in vivo
of aggregated Ab, and 10 M of each compound for 18 h. Based
l
on the cellular viability of Ab treated cells in the presence of a vehi-
cle, we calculated percent inhibition values for each compound.
Among the tested compounds, compounds 29, 47, 48, 67, and 75
significantly inhibited Ab induced cytotoxicity (>50%) compared
to the vehicle control as described in Table 4. Notably, all five com-
pounds contain a (4-alkoxycarbonylpiperazin-1-yl)alkyloxy side
chain, indicating that this functional group is crucial for inhibiting
the RAGE–Ab interactions in cells. These compounds also share a
flexible chain between the phenylbenzoxazole core and the ami-
noalkyl moiety, which coincides with the same preference
observed in the FRET assay. In addition, three out of these five com-
pounds have a 4-Cl substituent on R1 position, suggesting a poten-
tially favorable interaction around this region. Among these five
analogues, compound 48 appeared to inhibit the RAGE–Ab interac-
tions significantly in vitro, and also showed the greatest protective
To examine whether the selected compound 48 can block the
transport of Ab in vivo, we tested this compound in a transgenic
animal model of AD, APPsw/PS1 mice. There are two major species
of Ab peptides in plasma, namely, Ab1–40, and Ab1–42. Generally,
Ab1–40 is much more abundant in cells and tissues, which
accounts for ꢀ90% of the secreted Ab peptides, however, Ab1–42
is thought to be more neurotoxic and prone to aggregation.34
Therefore, we decided to measure the levels of these two forms
of Ab peptides in addition to the amount of amyloid plaques in
tested mice. First, we administered compound 48 orally at
50 mg/kg every two days for 4 weeks, and determined the accumu-
lation of Ab1–40, and Ab1–42 from the post-mortem brain homo-
genates by enzyme-linked immunosorbent assay (ELISA). As
demonstrated in Figure 2a, compound 48 effectively reduced the
brain levels of Ab1–40 without any noticeable side effects,
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
Table 1
In vitro activity of compounds 7–23*
Cl
N
O
O
O
R
Compound
R
Inhibition of FRET signals (%)
NA
Cytotoxicity (%)
NT
N
O
7
O
9
20.6
19.5
15.3
20.6
74.3
38.2
NH
N
11
12
N
13
14
12.7
ND
86.5
ND
N
N
N
15
16
17
N
ND
ND
ND
NT
N
ND
N
N
20.0
O
N
O
8
NA
NT
O
NH
N
10
18
NA
2.1
29.0
4.1
19
20
N
N
26.2
ND
NT
ND
N
21
ND
ND
N
N
N
22
23
5.1
NA
82.4
32.7
O
N
Abbreviations. NA: not active, NT: not toxic, ND: not determined.
*
All measurements were performed in triplicate. FRET signals were collected in the presence of 40 nM of Ab42 and 4
RAGE–Cy3.
l
M of each compound after incubating for 1 h with
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
5
Table 2
In vitro activity of compounds 26–52*
Cl
N
O
O
O
R
Compound
R
Inhibition of FRET signals (%)
33.5
Cytotoxicity (%)
85.2
N
N
N
N
26
27
28
18.5
25.7
21.4
NT
O
N
29
30
O
N
24.6
ND
NT
O
N
N
N
ND
31
32
4.9
NA
32.1
NT
N
N
O
33
34
90.2
16.6
63.2
58.2
N
N
N
H
O
O
O
N
H
35
36
37
19.6
29.9
2.2
NT
N
N
NH2
NH2
NT
32.4
N
N
38
39
16.6
NA
32.2
NT
N
N
N
N
O
40
41
42
NA
NT
NH
N
42.7
24.3
18.5
69.3
OH
N
43
44
3.3
NA
3.3
NT
N
N
N
O
N
N
O
O
O
45
6.6
NT
(continued on next page)
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Table 2 (continued)
Compound
R
Inhibition of FRET signals (%)
Cytotoxicity (%)
NT
O
O
O
46
47
48
41.2
25.9
40.0
N
N
N
O
O
O
N
N
N
NT
NT
49
50
NA
NT
N
N
N
N
N
N
N
25.1
25.1
N
N
N
F
51
52
ND
ND
ND
N
N
N
Cl
ND
N
Abbreviations. NA: not active, NT: not toxic, ND: not determined.
*
All measurements were performed in triplicate. FRET signals were collected in the presence of 40 nM of Ab42 and 4
RAGE–Cy3.
l
M of each compound after incubating for 1 h with
Table 3
In vitro activity of compounds 53-75*
N
O
R1
O
R2
O
Compound
R1
R2
Inhibition of FRET signals (%)
NA
Cytotoxicity (%)
74.1
53
4-t-Bu
N
N
N
54
55
4-t-Bu
4-t-Bu
NA
NA
49.4
NT
O
N
56
57
4-t-Bu
4-t-Bu
ND
ND
ND
ND
N
N
O
N
N
O
N
N
58
59
4-t-Bu
4-t-Bu
ND
NA
ND
NT
N
N
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
7
Table 3 (continued)
Compound
R1
R2
Inhibition of FRET signals (%)
Cytotoxicity (%)
NT
O
O
60
61
4-t-Bu
26.8
61.6
N
N
N
H
O
O
4-t-Bu
8.2
N
H
62
63
64
65
66
4-t-Bu
4-t-Bu
4-F
NA
12.8
60.3
NT
N
N
NH2
NH2
54.7
5.4
N
N
4-F
30.3
56.7
NT
O
4-F
NT
N
O
67
4-F
21.0
15.2
N
O
N
68
69
70
4-CF3
4-CF3
4-CF3
34.9
44.3
32.1
NT
N
93.4
NT
N
N
O
O
71
4-CF3
27.8
7.9
N
O
N
N
N
72
73
74
3-CF3
3-CF3
3-CF3
24.1
42.7
NA
NT
4.4
NT
O
N
O
75
3-CF3
22.8
NT
N
O
N
Abbreviations. NA: not active, NT: not toxic, ND: not determined.
*
All measurements were performed in triplicate. FRET signals were collected in the presence of 40 nM of Ab42 and 4 lM of each compound after incubating for 1 h with
RAGE–Cy3.
suggesting that this compound blocked the transportation of
plasma Ab1–40 into the brain. Compound 48 also appeared to
reduce levels of Ab1–42, however, observed differences were
within the error range (Fig. 2b). Additionally, we quantified the
amount of amyloid plaque in the brains of transgenic mice by
staining with Congo red. As shown in Figure 2c, compound 48
appeared to reduce amyloid deposits compared to a vehicle con-
trol, however, the average number of plaques was within the error
range. We speculated that although compound 48 adequately
blocked the transport of peripheral Ab1–40, which consist of a
large fraction of circulating Ab peptides, it did not seem to affect
the RAGE–Ab interactions inside the brain significantly.
Table 4
Inhibition of Ab induced cytotoxicity*
Compound
Inhibition of Ab induced cytotoxicity (%)
29
47
48
67
75
50.6
54.4
65
62.3
56.2
*
All measurements were performed in triplicate. The cell viability was measured
after incubating HT22 cells with 2
pound for 18 h.
lM of aggregated Ab and 10 lM of each com-
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
(a)
(b)
(c)
**
Figure 2. The brain levels of (a) human Ab1–40, (b) Ab1–42, and (c) amyloid plaques in APPsw/PS1 mice. The concentrations of Ab and the number of amyloid plaques per
section are expressed as the means standard deviation. (Vehicle, n = 4; compound 48, n = 5 at 50 mg/kg).
4.1.1.2. 2-(Benzyloxy)-4-(4-tert-butylphenoxy)-1-nitrobenzene
(2b). Compound 2b was synthesized with 4-tert-phenol by follow-
ing the Section 4.1.1. Yield 58%; 1H NMR (300 MHz, CDCl3) d 7.95
(d, 1H, J = 9.2 Hz), 7.34–7.42 (m, 7H), 6.94 (d, 2H, J = 8.8 Hz), 6.65
(d, 2H, J = 2.4 Hz), 6.52–6.48 (m, 1H), 5.16 (s, 2H), 1.36 (s, 9H).
3. Conclusion
In this work, we have developed a series of 6-phenoxy-2-
phenylbenzoxazole derivatives as a potential AD therapeutics.
We evaluated their ability to inhibit the RAGE–Ab interactions
in vitro, and assessed their protective effects against Ab induced
cytotoxicity. Structure–activity relationship analysis revealed that
4.1.1.3. 2-Benzyloxy-4-(4-fluorophenoxy)-1-nitro-benzene (2c).
Compound 2c was synthesized with 4-fluorophenol by following
the Section 4.1.1. Yield 94%; 1H NMR (300 MHz, CDCl3) d 7.95 (d,
1H, J = 9.0 Hz), 7.41–7.32 (m, 5H), 7.12–7.05 (m, 2H), 7.02–6.96
(m, 2H), 6.60 (d, 1H, J = 2.4 Hz), 6.48 (dd, 1H, J = 9.0, 2.7 Hz), 5.16
(s, 2H).
compounds with
a (4-(alkoxycarbonyl)piperazin-1-yl)alkyloxy
side chain inhibited the RAGE–Ab interactions significantly, and
retained cellular viability against Ab induced toxicity. Based on
these findings, we selected compound 48 as a promising candidate,
and tested its efficacy in a transgenic mice model of AD. The results
from in vivo study suggested that compound 48 appeared to block
Ab transport across the BBB, resulting in the reduced levels of Ab1–
40 in the brain. Further structural optimization of the benzoxazole
series is currently underway, and we believe that this study can
provide valuable insights into RAGE as a promising target for dis-
ease-modifying AD therapy.
4.1.1.4. 2-Benzyloxy-4-(4-trifluoromethylphenoxy)-1-nitro-benzene
(2d). Compound 2d was synthesized with4-(trifluoromethyl)phenol
by following the Section 4.1.1. Yield 55%; 1H NMR (300 MHz, CDCl3) d
7.97 (d, 1H, J = 9.0 Hz), 7.64 (d, 2H, J = 8.7 Hz), 7.39–7.33 (m, 5H), 6.68
(d, 1H, J = 2.4 Hz), 6.59 (dd, 1H, J = 9.0, 2.4 Hz), 5.18 (s, 2H).
4.1.1.5. 2-Benzyloxy-4-(3-trifluoromethylphenoxy)-1-nitro-
benzene (2e). Compound 2e was synthesized with 3-(trifluo-
romethyl)phenol by following the Section 4.1.1. Yield 81%; 1H
NMR (300 MHz, CDCl3) d 7.97 (d, 1H, J = 9.0 Hz), 7.55–7.51 (m,
2H), 7.42–7.31 (m, 6H), 7.21–7.18 (m, 1H), 6.68 (d, 1H,
J = 2.4 Hz), 6.54 (dd, 1H, J = 9.0, 2.4 Hz), 5.18 (s, 2H).
4. Experimental section
4.1. Chemistry
All chemical reagents were commercially available. Flash col-
umn chromatography was performed using silica gel 60 (230–
400 mesh, Merck) with the indicated solvents. 1H NMR spectra
were recorded on JEOL JNM-LA 300 and Bruker Avance 400 MHz
FT-NMR spectrometers. Chemical shifts are reported in ppm units
with Me4Si as a reference standard. Mass spectra were recorded on
a VG Trio-2 GC–MS and a 6460 Triple Quad LC/MS.
4.1.2. General procedure for preparation of compounds 3a–3e
To a solution of compound 2 (1.0 equiv) in DCM was added tri-
fluoroacetic acid (excess), and then the mixture was stirred for 5 h
at room temperature. The reaction mixture was evaporated under
reduced pressure. The residue dissolved in EtOAc was washed with
water and brine. The organic layer was dried over MgSO4, filtered
and concentrated in vacuo. The resulting crude residue was puri-
fied by recrystallization with DCM/isopropyl alcohol system.
4.1.1. General procedure for preparation of compounds 2a–2e
A mixture of 2-benzyloxy-4-fluoro-1-nitro-benzene (1.0 equiv),
alcohol (1.1 equiv) and potassium carbonate (1.5 equiv) in DMF
was stirred for 14 h at 140 °C. The reaction mixture was evaporated
under reduced pressure. The residue was dissolved in EtOAc, and
washed with water and brine. The organic layer was dried over
MgSO4, filtered and concentrated in vacuo. The resulting crude
residue was purified by recrystallization in DCM/isopropyl alcohol
system to yield the corresponding biaryl ether fragments 2a–2e.
4.1.2.1. 5-(4-Chlorophenoxy)-2-nitro-phenol (3a). Yield 78%;
1H NMR (300 MHz, CDCl3) d 10.88 (s, 1H), 8.09 (d, 2H, J = 9.6 Hz),
7.41 (d, 2H, J = 8.7 Hz), 7.05 (d, 1H, J = 9.0 Hz), 6.59 (dd, 1H,
J = 9.3, 2.4 Hz), 6.51 (d, 1H, J = 2.4 Hz).
4.1.2.2. 5-(4-Fluorophenoxy)-2-nitro-phenol (3c). Yield 86%; 1H
NMR (300 MHz, CDCl3) d 10.90 (s, 1H), 8.09 (d, 1H, J = 9.6 Hz), 7.16–
7.05 (m, 4H), 7.58 (dd, 1H, J = 9.6, 2.7 Hz), 6.48 (d, 1H, J = 2.7 Hz).
4.1.1.1. 2-Benzyloxy-4-(4-chlorophenoxy)-1-nitro-benzene (2a).
Compound 2a was synthesized with 4-chlorophenol by following
Section 4.1.1. Yield 85%; 1H NMR (300 MHz, CDCl3) d 7.95 (d, 1H,
J = 9.3 Hz), 7.41–7.31 (m, 7H), 6.95 (m, 2H), 6.62 (d, 1H,
J = 2.7 Hz), 6.51 (dd, 1H, J = 9.0, 2.4 Hz), 5.16 (s, 2H).
4.1.2.3. 5-(4-Trifluoromethyl-phenoxy)-2-nitro-phenol (3d).
Yield 74%; 1H NMR (300 MHz, CDCl3) d 10.88 (s, 1H), 8.13 (d, 1H,
Please cite this article in press as: Choi, K.; et al. Bioorg. Med. Chem. (2015), http://dx.doi.org/10.1016/j.bmc.2015.05.022

K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
9
J = 9.0 Hz), 7.71 (d, 2H, J = 8.7 Hz), 7.21 (d, 2H, J = 8.7 Hz), 6.65–6.58
7.27–7.19 (m, 3H), 7.09–7.06 (m, 1H), 7.99 (d, 2H, J = 8.6 Hz),
(m, 2H).
2.35 (s, 3H), 1.34 (s, 9H).
4.1.2.4. 5-(3-Trifluoromethyl-phenoxy)-2-nitro-phenol (3e).
Yield 99%; 1H NMR (300 MHz, CDCl3) d 7.38–7.27 (m, 2H), 7.16
(s, 1H), 7.05 (d, 1H, J = 7.9 Hz), 6.73 (d, 1H, J = 8.1 Hz), 6.40–6.35
(m, 2H); MS (FAB) m/z 299 [M+H]+.
4.1.4.3. Acetic acid 4-[6-(4-fluorophenoxy)-benzoxazol-2-yl]-
phenyl ester (5c). Yield 71%; 1H NMR (300 MHz, CDCl3) d 8.23
(d, 2H, J = 9.0 Hz), 7.69 (d, 1H, J = 8.7 Hz), 7.26 (d, 2H, J = 8.7 Hz),
7.16 (d, 1H, J = 2.1 Hz), 7.07–7.03 (m, 5H), 2.34 (s, 3H).
4.1.3. General procedure for preparation of compounds 4a–4e
To a stirred solution of compound 3 in 2-propanol (1.0 equiv)
was added tin(II)chloride (3.0 equiv) and concd HCl (cat.) at room
temperature. The mixture was refluxed for 2 h, and then concen-
trated under reduced pressure. The residue was diluted with
EtOAc and washed with saturated aqueous sodium bicarbonate
solution, and brine. The organic layer was dried over MgSO4, fil-
tered and concentrated in vacuo. The residue was purified by silica
gel chromatography (EtOAc/n-Hex) to afford the corresponding
compounds.
4.1.4.4. Acetic acid 4-[6-(4-trifluoromethyl-phenoxy)-benzoxa-
zol-2-yl]-phenyl ester (5d). Yield 75%; 1H NMR (300 MHz, CDCl3)
d 8.25 (d, 2H, J = 9.0 Hz), 7.75 (d, 1H, J = 8.7 Hz), 7.61 (d, 2H,
J = 8.4 Hz), 7.28 (m, 3H), 7.12–7.08 (m, 2H), 2.35 (s, 3H).
4.1.4.5. Acetic acid 4-[6-(3-trifluoromethyl-phenoxy)-benzoxa-
zol-2-yl]-phenyl ester (5e). Yield 43%; 1H NMR (300 MHz, CDCl3)
d 8.22 (d, 2H, J = 8.6 Hz), 7.72 (d, 1H, J = 8.6 Hz), 7.48–7.35 (m, 2H),
7.29–7.18 (m, 5H), 7.07 (dd, 1H, J = 8.6, 2.2 Hz), 2.33 (s, 3H).
4.1.5. General procedure for preparation of compounds 6a–6e
To a stirred solution of compound 5 (1.0 equiv) in MeOH was
added 2 N NaOH (excess) at room temperature. After the mixture
was stirred for 6 h, MeOH was removed under reduced pressure.
The mixture was acidified with 1 N HCl and extracted with
EtOAc. The organic layer was washed with brine, and dried over
MgSO4. The final filtrate was concentrated in vacuo. The resulting
residue was purified by silica gel chromatography (EtOAc/n-Hex)
to afford the corresponding products.
4.1.3.1. 2-Amino-5-(4-chlorophenoxy)-phenol (4a). Yield 53%;
1H NMR (300 MHz, CDCl3) d 7.23 (d, 2H, J = 9.0 Hz), 6.87 (d, 2H,
J = 9.0 Hz), 6.76 (m, 1H), 6.46 (m, 2H).
4.1.3.2. 2-Amino-5-(4-tert-butylphenoxy)phenol (4b). To a stir-
red solution of compound 2b (1.0 g, 2.6 mmol) in DCM/THF (3:1)
was added palladium on carbon (55% in H2O) at room temperature.
The reaction mixture was stirred under H2 gas for 15 h. The reaction
mixture was filtered through a pad of celite. The filtrate was evap-
orated under reduced pressure, and the resulting crude residue was
purified by silica gel chromatography to afford the product. Yield
75%; 1H NMR (300 MHz, CDCl3) d 7.28 (d, 2H, J = 8.7 Hz), 6.86 (d,
2H, J = 8.7 Hz), 6.74 (d, 2H, J = 8.1 Hz), 1.28 (s, 9H).
4.1.5.1. 4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phenol (6a).
Yield 99%; 1H NMR (300 MHz, CDCl3) d 8.10 (d, 2H, J = 8.7 Hz),
7.67 (d, 1H, J = 8.7 Hz), 7.32 (m, 2H), 7.20 (d, 1H, J = 2.1 Hz),
7.06–6.96 (m, 3H), 6.20 (br s, 1H).
4.1.3.3. 2-Amino-5-(4-fluorophenoxy)-phenol (4c).
Yield
4.1.5.2. 4-(6-(4-tert-Butylphenoxy)benzo[d]oxazol-2-yl)phenol
59%; 1H NMR (300 MHz, CDCl3) d 7.02–6.88 (m, 4H), 6.74 (d, 1H,
J = 8.4 Hz), 6.47–6.38 (m, 2H).
(6b). Yield 88%; 1H NMR (300 MHz, CDCl3)
d 8.10 (d, 2H,
J = 8.8 Hz), 7.65 (d, 1H, J = 8.4 Hz), 7.37 (d, 2H, J = 8.8 Hz), 7.20 (d,
1H, J = 2.2 Hz), 7.07–7.03 (m, 1H), 7.00–6.94 (m, 4H), 5.56 (s, 1H),
1.33 (s, 9H).
4.1.3.4. 2-Amino-5-(4-trifluoromethyl-phenoxy)-phenol (4d).
Yield 44%; 1H NMR (300 MHz, CDCl3) d 7.53 (d, 2H, J = 8.4 Hz),
6.98 (d, 2H, J = 8.4 Hz), 6.78 (d, 1H, J = 9.0 Hz), 6.50 (m, 2H).
4.1.5.3. 4-[6-(4-Fluorophenoxy)-benzoxazol-2-yl]-phenol (6c).
Yield 99%; 1H NMR (300 MHz, DMSO) d 10.35 (br s, 1H), 8.00 (d,
2H, J = 8.7 Hz), 7.42 (d, 1H, J = 2.1 Hz), 7.24 (d, 2H, J = 8.7 Hz),
7.13–7.03 (m, 3H), 7.97 (d, 2H, J = 8.7 Hz).
4.1.3.5. 2-Amino-5-(3-trifluoromethyl-phenoxy)-phenol (4e).
Yield 99%; 1H NMR (300 MHz, CDCl3) d 7.36–7.24 (m, 2H), 7.14
(s, 1H), 7.04 (d, 1H, J = 7.9 Hz), 6.69 (d, 1H, J = 8.1 Hz), 6.42–6.39
(m, 2H), 4.97 (br s, NH2).
4.1.5.4.
4-[6-(4-Trifluoromethyl-phenoxy)-benzoxazol-2-yl]-
phenol (6d). Yield 95%; 1H NMR (300 MHz, DMSO) d 10.37 (s,
1H), 8.02 (d, 2H, J = 8.7 Hz), 7.76 (d, 2H, J = 8.7 Hz), 7.64 (d, 1H,
J = 2.1 Hz), 7.17 (m, 3H), 6.98–6.91 (m, 3H).
4.1.4. General procedure for preparation of compounds 5a–5e
A mixture of compound 4 (1.0 equiv) and 4-formylphenyl acet-
ate (1.0 equiv) in methanol was heated to 45 °C for 2 h. The mix-
ture was evaporated under reduced pressure. The residue was
dissolved in methylene chloride and then 2,3-dichloro-5,6-di-
cyano-1,4-benzoquinone (DDQ, 1.1 equiv) was added at room tem-
perature. After 30 min, the mixture was diluted with
methylenechloride, washed with saturated NaHCO3 solution, and
brine. The organic layer was dried over MgSO4, filtered and concen-
trated in vacuo. The residue was purified by silica gel chromatog-
raphy (EtOAc/n-Hex) to afford the corresponding products.
4.1.5.5.
4-[6-(3-Trifluoromethyl-phenoxy)-benzoxazol-2-yl]-
phenol (6e). Yield 97%; 1H NMR (300 MHz, CD3OD) d 8.22–7.98
(m, 2H), 7.62 (d, 1H, J = 8.6 Hz), 7.55–7.49 (m, 1H), 7.39 (d, 1H,
J = 7.7 Hz), 7.28–7.21 (m, 3H), 7.04 (dd, 1H, J = 8.6, 2.2 Hz), 6.95–
6.91 (m, 2H).
4.1.6. General procedure for preparation of compounds 7 and 8
To a stirred solution of compound 6a, Boc-4-hydroxypiperidine
(or N-Boc-4-piperidine–methanol or other alcohol) (1.5 equiv) and
triphenylphosphine (1.5 equiv) in THF was added DIAD (1.5 equiv)
at 0 °C. After the mixture was stirred for 1 h at 0 °C and another
48 h at room temperature, the reaction mixture was diluted with
water. The resulting mixture was extracted with EtOAc, and
washed with water and brine. The organic layer was dried over
sodium sulfate, filtered and concentrated in vacuo. The crude resi-
due was purified by silica gel chromatography to afford the corre-
sponding compounds.
4.1.4.1. Acetic acid 4-[6-(4-chlorophenoxy)-benzoxazol-2-yl]-
phenyl ester (5a). Yield 59%; 1H NMR (300 MHz, CDCl3) d 8.23
(d, 2H, J = 9.0 Hz), 7.71 (d, 1H, J = 8.7 Hz), 7.35–7.24 (m, 4H), 7.21
(d, 1H, J = 2.4 Hz), 7.08–6.96 (m, 3H), 2.35 (s, 3H).
4.1.4.2. 4-(6-(4-tert-Butylphenoxy)benzo[d]oxazol-2-yl)phenyl
acetate (5b). Yield 78%; 1H NMR (300 MHz, CDCl3) d 8.28 (d,
2H, J = 8.6 Hz), 7.68 (d, 1H, J = 8.6 Hz), 7.38 (d, 2H, J = 8.8 Hz),
Please cite this article in press as: Choi, K.; et al. Bioorg. Med. Chem. (2015), http://dx.doi.org/10.1016/j.bmc.2015.05.022

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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
4.1.6.1. 2-(4-(1-Methylpiperidin-4-yloxy)phenyl)-6-(4-chloro-
phenoxy)-benzo[d]oxazole (7). Compound 7 was synthesized
with Boc-4-hydroxypiperidine by following the Section 4.1.6.
Yield 78%; 1H NMR (300 MHz, CDCl3) d 8.13 (d, 2H, J = 8.7 Hz),
7.67 (d, 1H, J = 8.7 Hz), 7.31 (d, 2H, J = 8.7 Hz), 7.19 (d, 1H,
J = 2.4 Hz), 7.05–6.96 (m, 5H), 4.59 (m, 1H), 3.70 (m, 2H), 3.38
(m, 5H), 1.95 (m, 2H), 1.82 (m, 2H), 1.47 (s, 9H); MS (FAB) m/z
521 [M+H]+; mp 140 °C.
4.1.10. 2-(4-(1-Isopropylpiperidin-4-yloxy)phenyl)-6-(4-chloro-
phenoxy)benzo[d]oxazole (13)
A mixture of compound 9 (0.040 g, 0.095 mmol), 2-iodo-propane
(0.010 mL, 0.095 mmol) and potassium carbonate (0.026 g,
0.190 mmol) in DMF was stirred overnight at room temperature.
The reaction mixture was evaporated under reduced pressure. The
residue dissolved in DCM was washed with water, and brine. The
organic layer was dried over MgSO4 sulfate and concentrated in
vacuo. The resulting crude residue was chromatographed on a silica
gel to give the product. Yield 34%; 1H NMR (300 MHz, CDCl3) d 8.13
(d, 2H, J = 8.7 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (d, 2H, J = 9.0 Hz), 7.19
(d, 1H, J = 2.4 Hz), 7.05–6.94 (m, 5H), 4.47 (m, 1H), 2.84 (m, 3H), 2.53
(m, 2H), 2.14 (m, 2H), 1.92 (m, 2H), 1.12 (d, 6H, J = 6.6 Hz); MS (FAB)
m/z 463 [M+H]+; mp 104 °C.
4.1.6.2. 4-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phenoxy-
methyl}-piperidine-1-carboxylic acid tert-butyl ester (8).
Compound 8 was synthesized with N-Boc-4-piperidine methanol
by following the Section 4.1.6. Yield 40%; 1H NMR (300 MHz,
CDCl3) d 8.19 (d, 2H, J = 9.0 Hz), 7.66 (d, 1H, J = 8.6 Hz), 7.64 (d,
2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.2 Hz), 7.05–6.95 (m, 5H), 4.16
(br, 2H), 3.88 (d, 2H, J = 6.4 Hz), 2.76 (t, 2H, J = 13.1 Hz), 2.00 (br,
1H), 1.84 (d, 2H, J = 13.1 Hz), 1.47 (s, 9H), 1.35–1.27 (m, 2H); MS
(FAB) m/z 535 [M+H]+; mp 210 °C.
4.1.11. 2-(4-(1-Phenylpiperidin-4-yloxy)phenyl)-6-(4-chlorophe-
noxy)benzo[d]oxazole (14)
To a solution of compound 9 (0.050 g, 0.12 mmol), bromobenzene
(0.015 mL, 0.14 mmol), 2-(di-t-butylphosphino)biphenyl (0.007 g,
0.024 mmol) and Pd2(dba)3 (0.003 g, 0.012 mmol) in toluene was
added sodium tert-butoxide (0.014 g, 0.14 mmol). After the mixture
was stirred at 80 °C for 8 h, the mixture was filtered and concen-
trated. The resulting residue was diluted in EtOAc and washed with
NaHCO3 solution and brine. The organic layer was dried and concen-
trated. The crude residue was chromatographed on a silica gel to give
the product. Yield 47%; 1H NMR (300 MHz, CDCl3) d 8.15 (d, 2H,
J = 8.7 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.33–7.25 (m, 4H), 7.19 (d, 1H,
J = 2.1 Hz), 7.06–6.96 (m, 5H), 6.87 (t, 1H, J = 7.2 Hz), 4.59 (m, 1H),
3.53 (m, 2H), 3.15 (m, 2H), 2.15 (m, 2H), 2.00 (m, 2H); MS (FAB)
m/z 497 [M+H]+; mp 147 °C.
4.1.7. General procedure for preparation of compounds 9 and 10
To a stirred solution of compounds 7 or 8 in DCM was added tri-
fluoroacetic acid (20 equiv) at room temperature. After the mixture
was stirred for 5 h, the reaction mixture was evaporated under
reduced pressure. The residue dissolved in DCM was washed with
NaHCO3 and brine. The organic layer was dried over MgSO4 and
concentrated in vacuo. The resulting crude residue was purified
by recrystallization in DCM/hexane system.
4.1.7.1. 6-(4-Chlorophenoxy)-2-(4-(piperidin-4-yloxy)phenyl)-
benzo[d]oxazole (9). Yield 79%; 1H NMR (400 MHz, CDCl3) d
8.11 (d, 2H, J = 8.8 Hz), 7.64 (d, 1H, J = 8.4 Hz), 7.29 (d, 2H,
J = 8.4 Hz), 7.17 (d, 1H, J = 2.0 Hz), 7.02–6.94 (m, 5H), 4.48 (m,
1H), 3.15 (m, 2H), 2.77 (m, 5H), 2.04 (m, 2H), 1.72 (m, 2H); MS
(FAB) m/z 421 [M+H]+; mp 117 °C.
4.1.12. 2-(4-(1-(Pyrimidin-2-yl)piperidin-4-yloxy)phenyl)-6-(4-
chlorophenoxy)benzo[d]oxazole (15)
To a suspension of compound 9 (0.050 g, 0.12 mmol) and potas-
sium carbonate (0.033 g, 0.24 mmol) in DMF was added 2-
chloropyrimidine (0.016 g, 0.14 mmol). The mixture was refluxed
overnight. The reaction mixture was evaporated under reduced
pressure. The residue was dissolved in EtOAc, and then washed
with water, and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. The residue was purified by silica gel
chromatography to afford the product. Yield 45%; 1H NMR
(300 MHz, CDCl3) d 8.32 (d, 2H, J = 4.8 Hz), 8.15 (d, 2H, J = 9.0 Hz),
7.67 (d, 1H, J = 9.4 Hz), 7.31 (d, 2H, J = 3.0 Hz), 7.20 (d, 1H,
J = 2.1 Hz), 7.07–6.96 (m, 5H), 6.49 (t, 1H, J = 4.8 Hz), 4.69 (m,
1H), 3.18 (m, 2H), 3.75 (m, 2H), 2.05 (m, 2H), 1.90 (m, 2H); MS
(FAB) m/z 499 [M+H]+; mp 175 °C.
4.1.7.2. 6-(4-Chlorophenoxy)-2-[4-(piperidin-4-ylmethoxy)-
phenyl]-benzoxazole (10). Yield 91%; 1H NMR (300 MHz, CDCl3)
d 8.13 (d, 2H, J = 9.1 Hz), 7.66 (d, 1H, J = 8.6 Hz), 7.30 (d, 2H,
J = 9.0 Hz), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.94 (m, 5H), 3.88 (d, 2H,
J = 6.2 Hz), 3.49 (s, 1H), 3.21–3.17 (br, 2H), 2.73–2.65 (m, 2H),
1.98–1.76 (m, 3H), 1.43–1.34 (m, 2H); MS (FAB) m/z 435 [M+H]+;
mp 198 °C.
4.1.8. 2-(4-(1-Methylpiperidin-4-yloxy)phenyl)-6-(4-chlorophe-
noxy)-benzo[d]oxazole (11)
This compound was prepared with 4-hydroxy-1-methylpiperi-
dine by following the general procedure described for compounds
7 and 8. Yield 25%; 1H NMR (300 MHz, CDCl3) d 8.13 (d, 2H,
J = 9.0 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (d, 2H, J = 9.0 Hz), 7.19 (d,
1H, J = 2.1 Hz), 7.05–6.94 (m, 5H), 4.45 (m, 1H), 2.73 (m, 2H),
2.34 (m, 5H), 2.07 (m, 2H), 1.91 (m, 2H); MS (FAB) m/z 435
[M+H]+; mp 115 °C.
4.1.13. 2-(4-(1-Benzylpiperidin-4-yloxy)phenyl)-6-(4-chlorophe-
noxy)benzo[d]oxazole (16)
To a suspension of compound 9 (0.035 g, 0.083 mmol), potas-
sium carbonate (0.023 g, 0.17 mmol) in acetonitrile was added
benzylbromide (0.011 mL, 0.091 mmol). The mixture was refluxed
overnight. The reaction mixture was evaporated under reduced
pressure. The residue was dissolved in EtOAc and then washed
with water, and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. The residue was purified by silica gel
chromatography to afford the product. Yield 59%; 1H NMR
(300 MHz, CDCl3) d 8.12 (d, 2H, J = 9.0 Hz), 7.66 (d, 1H, J = 8.7 Hz),
7.34–7.27 (m, 6H), 7.19 (d, 1H, J = 2.1 Hz), 7.05–6.95 (m, 6H),
4.43 (m, 1H), 3.55 (s, 2H), 2.76 (m, 2H), 2.35 (m, 2H), 2.02 (m,
2H), 1.87 (m, 2H); MS (FAB) m/z 511 [M+H]+; mp 140 °C.
4.1.9. 2-(4-(1-Ethylpiperidin-4-yloxy)phenyl)-6-(4-chlorophe-
noxy)-benzo[d]oxazole (12)
To a stirred solution of compound 17 (0.037 g, 0.080 mmol) in
THF (20 mL) was added LAH (1 M sol. in THF) (0.16 mL, 0.16 mmol)
at 0 °C. The reaction mixture was stirred for 2 h at room tempera-
ture, and then quenched with water and saturated NaHCO3 solu-
tion. The resulting mixture was dried over sodium sulfate,
filtered and concentrated in vacuo. The residue was purified by sil-
ica gel chromatography to afford the product. Yield 14%; 1H NMR
(300 MHz, CDCl3) d 8.13 (d, 2H, J = 9.0 Hz), 7.67 (d, 1H, J = 8.7 Hz),
7.31 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.95 (m, 5H),
4.48 (m, 1H), 2.80 (m, 2H), 2.50 (m, 4H), 2.11 (m, 2H), 1.94 (m,
2H), 1.15 (d, 3H, J = 7.2 Hz); MS (FAB) m/z 449 [M+H]+; mp 100 °C.
4.1.14. 1-(4-(4-(6-(4-Chlorophenoxy)benzo[d]oxazol-2-yl)phe-
noxy)piperidin-1-yl)ethanone (17)
To a stirred mixture of compound 9 (0.050 g, 0.12 mmol) and
acetyl chloride (0.010 mL, 0.14 mmol) in DCM was added TEA
Please cite this article in press as: Choi, K.; et al. Bioorg. Med. Chem. (2015), http://dx.doi.org/10.1016/j.bmc.2015.05.022

K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
11
(0.020 mL, 0.14 mmol) at room temperature for 2 h. The reaction
mixture was evaporated under reduced pressure. The residue dis-
solved in EtOAc was washed with water, and brine. The organic
layer was dried over MgSO4 and concentrated in vacuo. The result-
ing residue was chromatographed on a silica gel to give the prod-
uct. Yield 81%; 1H NMR (300 MHz, CDCl3) d 8.15 (d, 2H, J = 9.0 Hz),
7.67 (d, 1H, J = 8.4 Hz), 7.31 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H,
J = 2.4 Hz), 7.06–6.96 (m, 5H), 4.67 (m, 1H), 3.78–3.67 (m, 3H),
3.46 (m, 1H), 2.14 (s, 3H), 1.99–1.86 (m, 4H); MS (FAB) m/z 463
[M+H]+; mp 156 °C.
with water and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. The crude residue was purified by silica
gel chromatography to afford the product. Yield 48%; 1H NMR
(300 MHz, CDCl3) d 8.31 (d, 2H, J = 4.7 Hz), 8.14 (d, 2H, J = 8.8 Hz),
7.66 (d, 1H, J = 8.6 Hz), 7.30 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H,
J = 2.2 Hz), 7.05–6.95 (m, 5H), 6.46 (t, 1H, J = 4.8 Hz), 4.84 (d, 2H,
J = 13.2 Hz), 3.91 (d, 2H, J = 6.4 Hz), 2.98–2.89 (m, 2H), 2.17–1.94
(m, 3H), 1.43–1.35 (m, 2H); MS (FAB) m/z 513 [M+H]+; mp 176 °C.
4.1.19. 2-[4-(1-Benzyl-piperidin-4-ylmethoxy)-phenyl]-6-(4-
chlorophenoxy)-benzoxazole (22)
4.1.15. 6-(4-Chlorophenoxy)-2-[4-(1-ethyl-piperidin-4-ylmethoxy)-
phenyl]-benzoxazole (18)
To suspension of compound 10 (0.025 g, 0.057 mmol), potas-
sium carbonate (0.016 g, 0.11 mmol) in acetonitrile was added
benzylbromide (0.010 mL, 0.063 mmol). The mixture was refluxed
overnight. The reaction mixture was evaporated under reduced
pressure. The residue was dissolved in EtOAc and then washed
with water and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. The crude residue was purified by silica
gel chromatography to afford the product. Yield 76%; 1H NMR
(300 MHz, CDCl3) d 8.13 (d, 2H, J = 8.8 Hz), 7.66 (d, 1H, J = 8.6 Hz),
7.51–7.40 (m, 5H), 7.31 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.6 Hz),
7.05–6.94 (m, 5H), 5.43 (s, 2H), 4.95 (s, 2H), 4.09–4.03 (m, 4H),
3.25–3.17 (m, 2H), 2.37–2.04 (m, 3H MS (FAB) m/z 525 [M+H]+;
mp 103 °C.
To a stirred solution of LAH (0.004 g, 0.092 mmol) in THF was
added compound 23 (0.020 g, 0.046 mmol) at 0 °C. The reaction
mixture was stirred for 2 h at room temperature, and then
quenched with water and saturated NaHCO3 solution. The result-
ing mixture was dried over sodium sulfate, filtered and concen-
trated in vacuo. The residue was purified by silica gel
chromatography to afford the product. Yield 37%; 1H NMR
(300 MHz, CDCl3) d 8.12 (d, 2H, J = 9.0 Hz), 7.64 (d, 1H, J = 8.4 Hz),
7.28 (d, 2H, J = 9.0 Hz), 7.17 (d, 1H, J = 1.8 Hz), 7.03–6.93 (m, 5H),
4.68 (m, 1H), 3.93–3.85 (m, 2H), 3.13–3.04 (m, 1H), 2.63–2.55
(m, 1H), 2.09 (s, 3H), 2.02–1.83 (m, 2H), 1.35–1.23 (m, 6H); MS
(FAB) m/z 463 [M+H]+; mp 142 °C.
4.1.20. 1-(4-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phenoxy-
methyl}-piperidin-1-yl)-ethanone (23)
4.1.16. 6-(4-Chlorophenoxy)-2-[4-(1-isopropyl-piperidin-4-yl-
methoxy)-phenyl]-benzoxazole (19)
To a stirred mixture of compound 10 (0.050 g, 0.11 mmol) and
acetyl chloride (0.010 mL, 0.14 mmol) in DCM was added TEA
(0.02 mL, 0.14 mmol) at room temperature for 1 h. The reaction mix-
ture was evaporated under reduced pressure. The residue dissolved
in EtOAc was washed with water, and brine. The organic layer was
dried over MgSO4 and concentrated in vacuo. The resulting crude
residue was chromatographed on a silica gel to give the product.
Yield 72%; 1H NMR (300 MHz, CDCl3) d 8.12 (d, 2H, J = 9.0 Hz), 7.64
(d, 1H, J = 8.4 Hz), 7.28 (d, 2H, J = 9.0 Hz), 7.17 (d, 1H, J = 1.8 Hz),
7.03–6.93 (m, 5H), 4.68 (d, 1H, J = 13.2 Hz), 3.93–3.85 (m, 2H),
3.13–3.04 (m, 1H), 2.63–2.55 (m, 1H), 2.09 (s, 3H), 2.02–1.83 (m,
2H), 1.35–1.23 (m, 4H); MS (FAB) m/z 477 [M+H]+; mp 160 °C.
A mixture of compound 10 (0.025 g, 0.057 mmol), 2-iodo-pro-
pane (0.010 mL, 0.097 mmol) and potassium carbonate (0.0080 g,
0.057 mmol) in DMF was stirred for 14 h at room temperature.
The reaction mixture was evaporated under reduced pressure.
The residue dissolved in DCM was washed with water, and brine.
The organic layer was dried over MgSO4 and concentrated in vacuo.
The resulting residue was chromatographed on a silica gel to give
the product. Yield 40%; 1H NMR (300 MHz, CDCl3) d 8.13 (d, 2H,
J = 9.0 Hz), 7.66 (d, 1H, J = 8.6 Hz), 7.30 (d, 2H, J = 8.7 Hz), 7.19 (d,
1H, J = 2.4 Hz), 7.05–6.95 (m, 5H), 3.92 (br, 3H), 3.21 (br, 3H),
2.50 (br, 2H), d 2.02–1.25 (m, 9H), 0.88–0.85 (m, 1H); MS (FAB)
m/z 477 [M+H]+; mp 179 °C.
4.1.21. General procedure for preparation of compounds 24 and
25
4.1.17. 6-(4-Chlorophenoxy)-2-[4-(1-phenyl-piperidin-4-ylmet-
hoxy)-phenyl]-benzoxazole (20)
To a stirred solution of compound 6 (1.0 equiv) in acetonitrile
was added 1-bromo-2-chloroethane (or 1-bromo-3-chloro-pro-
pane) (2.0 equiv) and potassium carbonate (2.0 equiv) at room
temperature. After the mixture was stirred overnight at 60 °C,
the reaction mixture was evaporated under reduced pressure.
The residue was dissolved in EtOAc, and then washed with water,
and brine. The organic layer was dried over sodium sulfate and
concentrated in vacuo. The crude residue was purified by silica
gel chromatography to afford the corresponding products.
To a solution of compound 10 (0.025 g, 0.057 mmol), bro-
mobenzene
(0.010 mL,
0.068 mmol),
2-(di-t-butylphos-
phino)biphenyl (0.0030 g, 0.011 mmol) and Pd2(dba)3 (0.0060 g,
0.0057 mmol), in toluene was added sodium tert-butoxide
(0.0060 g, 0.069 mmol) and the mixture was stirred at 80 °C for
2 h. The reaction mixture was filtered and concentrated. The
resulting residue was diluted in EtOAc and washed with NaHCO3
solution and brine. The organic layer was dried and concentrated.
The resulting crude residue was chromatographed on a silica gel
to give the product. Yield 34%; 1H NMR (300 MHz, CDCl3) d 8.14
(d, 2H, J = 8.8 Hz), 7.66 (d, 1H, J = 8.6 Hz), 7.32–7.24 (m, 3H), 7.19
(d, 1H, J = 2.2 Hz), 7.05–6.95 (m, 5H), 6.85 (t, 1H, J = 7.3 Hz), 3.94
(d, 2H, J = 6.1 Hz), 3.75 (d, 2H, J = 12.4 Hz), 2.81–2.74 (m, 2H),
2.00–1.97 (m, 3H), 1.58–1.54 (m, 2H); MS (FAB) m/z 511 [M+H]+;
mp 165 °C.
4.1.21.1. 2-[4-(2-Chloroethoxy)-phenyl]-6-(4-chloro-phenoxy)-
benzoxazole (24a).
Yield 85%; 1H NMR (300 MHz, CDCl3) d
8.14 (d, 2H, J = 9.0 Hz), 7.68 (d, 1H, J = 8.7 Hz), 7.31 (d, 2H,
J = 9.0), 7.20 (d, 1H, J = 2.1), 7.06–6.96 (m, 5H), 4.32 (t, 2H,
J = 5.7 Hz), 3.86 (t, 2H, J = 5.7 Hz).
4.1.21.2. 6-(4-Chlorophenoxy)-2-[4-(3-chloro-propoxy)-phenyl]-
4.1.18. 6-(4-Chlorophenoxy)-2-[4-(1-pyrimidin-2-yl-piperidin-
4-ylmethoxy)-phenyl]benzoxazole (21)
benzoxazole (25a).
Yield 81%; 1H NMR (300 MHz, CDCl3) d
8.10–8.17 (m, 2H), 7.66 (d, 1H, J = 8.6 Hz), 7.28–7.33 (m, 2H), 7.20
(d, 1H, J = 2.2 Hz), 6.95–7.05 (m, 5H), 4.21 (t, 2H, J = 5.8 Hz), 3.77
(t, 2H, J = 6.2 Hz), 2.24–2.32 (m, 2H).
To a suspension of compound 10 (0.025 g, 0.057 mmol) and
potassium carbonate (0.016 g, 0.11 mmol) in DMF was added 2-
chloropyrimidine (0.008 g, 0.069 mmol). The mixture was refluxed
overnight. The reaction mixture was evaporated under reduced
pressure. The residue was dissolved in EtOAc, and then washed
4.1.21.3. 6-(4-tert-Butylphenoxy)-2-(4-(3-chloropropoxy)phenyl)-
benzo[d]oxazole (25b). Yield 69%; 1H NMR (300 MHz, CDCl3) d
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
8.14 (d, 2H, J = 9.0 Hz), 7.65 (d, 1H, J = 8.6 Hz), 7.37 (d, 1H,
J = 8.8 Hz), 7.18 (d, 1H, J = 2.0 Hz), 7.04–6.96 (m, 5H), 4.21 (t, 2H,
J = 5.9 Hz), 3.78 (t, 2H, J = 6.2 Hz), 2.35–2.22 (m, 2H), 1.33 (s, 9H).
was prepared with 1-(2-pyrimidyl)-piperazine by following the
Section 4.1.22. Yield 83%; 1H NMR (300 MHz, CDCl3) d 8.31 (d,
2H, J = 4.77 Hz), 8.14 (d, 2H, J = 8.61 Hz), 7.67 (d, 1H, J = 8.58 Hz),
7.31 (d, 2H, J = 8.25 Hz), 7.2 (d, 1H, J = 2.19 Hz), 7.05 (d, 2H,
J = 8.79 Hz), 6.97 (d, 2H, J = 8.4 Hz), 6.51 (t, 1H, J = 4.77 Hz), 4.24
(t, 2H, J = 5.31 Hz), 3.87 (t, 2H, J = 4.77 Hz), 2.91 (s, 2H), 2.68 (s,
4H); MS (FAB) m/z 528 [M+H]+; mp 164 °C.
4.1.21.4. 6-(4-Fluorophenoxy)-2-[4-(3-chloropropoxy)-phenyl]-
benzoxazole (25c). Yield 73%; 1H NMR (300 MHz, CDCl3) d 8.14
(d, 2H, J = 8.7 Hz), 7.66 (d, 1H, J = 8.7 Hz), 7.15 (d, 2H, J = 2.4 Hz),
7.06–7.00 (m, 7H), 4.21 (t, 2H, J = 6.3 Hz), 3.78 (t, 2H, J = 6.0 Hz),
2.28 (m, 2H).
4.1.22.6. (3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phenoxy}-
propyl)-diethyl-amine (31). Compound 31 was prepared with
diethylamine by following the Section 4.1.22. Yield 32%; 1H NMR
(300 MHz, CDCl3) d 8.13–8.17 (m, 2H), 7.66 (d, 1H, J = 8.6 Hz),
7.29–7.32 (m, 3H), 7.19 (d, 1H, J = 2.4 Hz), 6.96–7.05 (m, 4H),
4.14 (t, 2H, J = 5.8 Hz), 2.86 (m, 6H), 2.20 (m, 2H), 1.27 (m, 6H).
MS (FAB) m/z 450 [M+H]+; mp 155 °C.
4.1.21.5. 6-(4-Trifluoromethyl-phenoxy)-2-[4-(3-chloropropoxy)-
phenyl]-benzoxazole (25d). Yield 75%; 1H NMR (300 MHz, CDCl3)
d 8.17 (d, 2H, J = 9.0 Hz), 7.72 (d, 1H, J = 8.7 Hz), 7.60 (d, 2H,
J = 8.7 Hz), 7.26 (m, 1H), 7.09–7.00 (m, 2H).
4.1.21.6. 6-(3-Trifluoromethyl-phenoxy)-2-[4-(3-chloropropoxy)-
phenyl]-benzoxazole (25e). Yield 80%; 1H NMR (300 MHz, CDCl3)
d 8.16 (d, 2H, J = 9.0 Hz), 7.71 (d, 1H, J = 8.6 Hz), 7.48–7.43 (m, 1H),
7.36 (d, 1H, J = 7.9 Hz), 7.27–7.18 (m, 3H), 7.08–7.02 (m, 3H), 4.21
(t, 2H, J = 5.9 Hz), 3.78 (t, 2H, J = 6.2 Hz), 2.32–2.24 (m, 2H).
4.1.22.7. 6-(4-Chlorophenoxy)-2-[4-(3-pyrrolidin-1-yl-propoxy)-
phenyl]-benzoxazole (32). Compound 32 was prepared with
1-(2-pyrimidyl)-piperazine by following the Section 4.1.22. Yield
59%; 1H NMR (300 MHz, CDCl3) d 8.13 (m, 2H), 7.67 (d, 1H,
J = 8.7 Hz), 7.31 (m, 2H), 7.19 (d, 1H, J = 2.1 Hz), 7.05–6.95 (m,
5H), 4.13 (t, 2H, J = 6.3 Hz), 2.71 (m, 6H), 2.11 (m, 2H), 1.85 (m,
4H). MS (FAB) m/z 448 [M+H]+; mp 98 °C.
4.1.22. General procedure for preparation of compounds 26–75
A mixture of compounds 24a (for compounds 26–30; 1.0 equiv)
or 25a–25e (for compounds 31–75; 1.0 equiv), secondary amine
(1.5 equiv), KI (2.0 equiv), and Na2CO3 (6.0 equiv) in n-BuOH was
heated to 105 °C for 24 h. The mixtures was cooled to room tem-
perature and evaporated under reduced pressure. The residue
was dissolved in EtOAc and then washed with water, and brine.
The organic layer was dried over sodium sulfate and concentrated
in vacuum. The resulting residue was purified by silica gel chro-
matography to afford the corresponding products (18–99%).
4.1.22.8. (R)-[1-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-
phenoxy}-propyl)-pyrrolidin-3-yl]-carbamic acid tert-butyl ester
(33). Compound 33 was prepared with (R)-3-(Boc-amino)pyrrolidine
by following the Section 4.1.22. Yield 66%; 1H NMR(300 MHz, CDCl3) d
8.14 (d, 2H, J = 8.7 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (d, 2H, J = 8.7 Hz),
7.19 (d, 1H, J = 2.4 Hz), 7.05–6.96 (m, 5H), 4.86 (br s, 1H), 4.13 (m, 3H),
2.87 (br s, 1H), 2.65 (m, 4H), 2.32 (m, 2H), 2.03 (m, 2H), 1.63 (br s, 1H),
1.46 (s, 9H). MS (FAB) m/z 564 [M+H]+; mp 124 °C.
4.1.22.1. (3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phenoxy}-
ethyl)-diethylamine (26). Compound 26 was prepared with
diethylamine by following the Section 4.1.22. Yield 49%; 1H NMR
(300 MHz, CDCl3) d 8.14 (d, 2H, J = 9.0 Hz), 7.67 (d, 1H, J = 8.7 Hz),
7.31 (m, 2H), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.96 (m, 5H), 4.15 (t,
2H, J = 6.0 Hz), 2.94 (t, 2H, J = 6.2 Hz), 2.68 (d, 4H, J = 7.2 Hz), 1.10
(t, 3H, J = 7.2 Hz). MS (FAB) m/z 437 [M+H]+; mp 98 °C.
4.1.22.9.
phenoxy}-propyl)-pyrrolidin-3-yl]-carbamic acid tert-butyl
ester (34). Compound 34 was prepared with (S)-3-(Boc-
(S)-[1-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-
amino)pyrrolidine by following the Section 4.1.22. Yield 63%; 1H
NMR (300 MHz, CDCl3) d 8.14 (d, 2H, J = 9.0 Hz), 7.67 (d, 1H,
J = 8.7 Hz), 7.32 (d, 2H, J = 9.9 Hz), 7.19 (d, 1H, J = 2.1 Hz), 7.05–
6.95 (m, 5H), 4.85 (br s, 1H), 4.13 (m, 3H), 2.88 (br s, 1H), 2.65
(m, 4H), 2.29 (m, 2H), 2.03 (m, 2H), 1.65 (br s, 1H), 1.45 (s, 9H).
MS (FAB) m/z 564 [M+H]+; mp 125 °C.
4.1.22.2. 6-(4-Chlorophenoxy)-2-[4-(2-piperidin-1-yl-ethoxy)-
phenyl]-benzoxazole (27). Compound 27 was prepared with
piperidine by following the Section 4.1.22. Yield 58%; 1H NMR
(300 MHz, CDCl3) d 8.14 (m, 2H), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (m,
2H), 7.19 (d, 1H, J = 2.1 Hz), 7.05–6.96 (m, 5H), 4.24 (t, 2H,
J = 5.9 Hz), 2.87 (t, 2H, J = 5.9 Hz), 2.60 (br s, 4H), 1.66 (m, 4H),
1.49 (m, 2H). MS (FAB) m/z 449 [M+H]+; mp 130 °C.
4.1.22.10.
(R)-1-(3-{4-[6-(4-Chloro-phenoxy)-benzooxazol-2-
yl]-phenoxy}-propyl)-pyrrolidin-3-ylamine (35). To a stirred
solution of compound 33 (0.060 g, 0.13 mmol) in DCM (1.0 mL)
was added trifluoroacetic acid (0.16 mL, 2.1 mmol) at room tem-
perature. After stirred for 5 h, the reaction mixture was evaporated
under reduced pressure. The residue dissolved in DCM was washed
with 2 N NaOH and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. The resulting crude was purified
recrystallization with DCM/hexane system. Yield 51%; 1H NMR
(300 MHz, CDCl3) d 8.13 (d, 2H, J = 9.7 Hz), 7.67 (d, 1H, J = 8.7 Hz),
7.31 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.96 (m, 5H),
4.12 (t, 2H, J = 6.0 Hz), 3.66 (m, 1H), 3.01–2.61 (m, 6H), 2.26–2.08
(m, 3H), 1.67 (m, 1H). MS (FAB) m/z 464(M+H); mp 110 °C.
4.1.22.3. 6-(4-Chlorophenoxy)-2-[4-(3-morpholin-4-yl-ethoxy)-
phenyl]-benzoxazole (28). Compound 28 was prepared with
morpholine by following the Section 4.1.22. Yield 47%; 1H NMR
(300 MHz, CDCl3) d 8.14 (m, 2H), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (m,
2H), 7.19 (d, 1H, J = 2.1 Hz), 7.05–6.96 (m, 5H), 4.20 (t, 2H,
J = 5.7 Hz), 3.75 (t, 4H, J = 4.7 Hz), 2.84 (m, 2H), 2.60 (t, 4H,
J = 4.7 Hz). MS (FAB) m/z 451 [M+H]+; mp 139 °C.
4.1.22.4. 4-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phenoxy}-
ethyl)-piperazine-1-carboxylic acid tert-butyl ester (29).
Compound 29 was prepared with N-Boc piperidine by following
the Section 4.1.22. Yield 42%; 1H NMR (300 MHz, CDCl3) d 8.14 (m,
2H), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (m, 2H), 7.19 (d, 1H, J = 2.4 Hz),
7.05–6.95 (m, 5H), 4.19 (t, 2H, J = 5.6 Hz), 3.47 (m, 4H), 2.86 (m,
4H), 2.54 (m, 4H), 1.48 (s, 9H). MS (FAB) m/z 550 [M+H]+; mp 100 °C.
4.1.22.11. (S)-1-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-
phenoxy}-propyl)-pyrrolidin-3-ylamine (36). This compound
was prepared from compound 34 by following the procedure
described for compound 35. Yield 43%; 1H NMR (300 MHz,
CDCl3) d 8.13 (d, 2H, J = 8.7 Hz), 7.67 (d, 1H, J = 8.4 Hz), 7.31 (d,
2H, J = 8.7 Hz), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.96 (m, 5H), 4.12 (t,
2H, J = 6.0 Hz), 3.52 (m, 1H), 2.78–2.56 (m, 4H), 2.49 (m, 1H),
2.35 (m, 1H), 2.22 (m, 1H), 2.02 (m, 2H), 1.49 (m, 1H). MS (FAB)
m/z 464 [M+H]+; mp 106 °C.
4.1.22.5. 6-(4-Chlorophenoxy)-2-{4-[2-(4-pyrimidin-2-yl-piper-
azin-1-yl)-ethoxy]-phenyl}-benzoxazole (30). Compound 30
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
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4.1.22.12. 6-(4-Chlorophenoxy)-2-[4-(3-piperidin-1-yl-propoxy)-
phenyl]-benzoxazole (37). This compound was prepared with
piperidine by following the Section 4.1.22. Yield 69%; 1H NMR
(300 MHz, CDCl3) d 8.13 (d, 2H, J = 9.0 Hz), 7.66 (d, 1H, J = 8.6 Hz),
7.30 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.2 Hz), 6.94–7.05 (m, 5H),
4.14 (t, 2H, J = 5.9 Hz), 2.85–2.90 (m, 6H), 2.29 (m, 2H), 1.89 (m,
2H), 1.61 (m, 2H), 0.82–0.94 (m, 2H). MS (FAB) m/z 462 [M+H]+;
mp 200 °C.
2H, J = 5.4 Hz), 2.56 (m, 12), 2.01 (m, 2H); MS (FAB) m/z 508
[M+H]+; mp 112 °C.
4.1.22.19. 4-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-piperazine-1-carboxylic acid methyl ester
(44).
This compound was prepared with piperazine-1-car-
boxylic acid methyl ester by following the Section 4.1.22. Yield
63%; 1H NMR (300 MHz, CDCl3) d 8.14 (d, 2H, J = 8.7 Hz), 7.67 (d,
1H, J = 8.7 Hz), 7.31 (m, 2H), 7.20 (d, 1H, J = 2.1 Hz), 7.05–6.96
(m, 5H), 4.11 (t, 2H, J = 6.3 Hz), 3.70 (s, 3H), 3.50 (br s, 4H), 2.56
(t, 2H, J = 7.1 Hz), 2.43 (br s, 4H), 2.01 (m, 2H). MS (FAB) m/z 522
[M+H]+; mp 144 °C.
4.1.22.13. 2-{4-[3-(4-tert-Butyl-piperidin-1-yl)-propoxy]-phenyl}-
6-(4-chlorophenoxy)-benzoxazole (38). This compound was
prepared with 4-tert-butyl-piperidin HCl salt by following the
Section 4.1.22. Yield 62%; 1H NMR (300 MHz, CDCl3) d 8.14 (m,
2H), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (m, 2H), 7.19 (d, 1H, J = 2.1 Hz),
7.05–6.95 (m, 5H), 4.10 (t, 2H, J = 6.6 Hz), 3.06 (d, 1H, J = 1.1 Hz),
2.54 (t, 2H, J = 7.5 Hz), 2.10–1.89 (m, 4H), 1.68 (d, 2H,
J = 13.2 Hz), 1.39 (m, 2H), 1.01 (m, 1H), 0.86 (s, 9H). MS (FAB)
m/z 519 [M+H]+; mp 128 °C.
4.1.22.20. 4-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-piperazine-1-carboxylic
acid
ethyl
ester
(45). This compound was prepared with piperazine-1-car-
boxylic acid ethyl ester by following the Section 4.1.22. Yield
62%; 1H NMR (300 MHz, CDCl3) d 8.14 (d, 2H, J = 8.7 Hz), 7.67 (d,
1H, J = 8.7 Hz), 7.31 (m, 2H), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.96
(m, 5H), 4.18–4.09 (m, 4H), 3.50 (t, 4H, J = 5.0 Hz), 2.56 (t, 2H,
J = 7.2 Hz), 2.44 (t, 4H, J = 5.0 Hz), 2.01 (m, 2H), 1.27 (t, 3H,
J = 7.1 Hz). MS (FAB) m/z 536 [M+H]+; mp 123 °C.
4.1.22.14. 6-(4-Chlorophenoxy)-2-{4-[3-(4-phenyl-piperidin-1-
yl)-propoxy]-phenyl}-benzoxazole (39). This compound was
prepared
with
4-phenyl-piperidin
by
following
the
Section 4.1.22. Yield 26%; 1H NMR (300 MHz, CDCl3) d 8.14 (d,
2H, J = 8.7 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.34–7.19 (m, 8H), 7.05–
6.96 (m, 5H), 4.14 (t, 2H, J = 6.3 Hz), 3.13 (d, 2H, J = 11.4 Hz),
2.64–2.50 (m, 3H), 2.10 (m, 4H), 1.87 (m, 4H). MS (FAB) m/z 539
[M+H]+; mp 120 °C.
4.1.22.21. 4-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-piperazine-1-carboxylic acid isobutyl ester
(46). This compound was prepared with piperazine-1-carboxylic
acid isobutyl ester by following the Section 4.1.22. Yield 60%; 1H
NMR (300 MHz, CDCl3) d 8.14 (d, 2H, J = 9.0 Hz), 7.67 (d, 2H,
J = 8.7 Hz), 7.31 (m, 2H), 7.19 (d, 1H, J = 2.4 Hz), 7.05–6.96 (m,
5H), 4.11 (t, 2H, J = 6.3 Hz), 3.87 (d, 2H, J = 6.6 Hz), 3.51 (t, 4H,
J = 5.1 Hz), 2.56 (t, 2H, J = 7.2 Hz), 2.44 (t, 4H, J = 4.8 Hz), 2.04–
1.89 (d, 3H), 0.94 (d, 6H, J = 6.6 Hz). MS (FAB) m/z 564 [M+H]+;
mp 107 °C.
4.1.22.15. 6-(4-Chlorophenoxy)-2-[4-(3-morpholin-4-yl-propoxy)-
phenyl]-benzoxazole (40). This compound was prepared with
morpholine by following the Section 4.1.22. Yield 45%; 1H NMR
(300 MHz, CDCl3) d 8.14 (d, 2H, J = 9.0 Hz), 7.67 (d, 1H, J = 8.6 Hz),
7.30 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.2 Hz), 6.94–7.05 (m, 5H),
4.11 (t, 2H, J = 6.2 Hz), 3.71–3.74 (m, 4H), 2.46–2.57 (m, 6H),
1.96–2.05 (m, 2H). MS (FAB) m/z 464 [M+H]+; mp 130 °C.
4.1.22.22. 4-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-piperazine-1-carboxylic acid isopropyl ester
(47). This compound was prepared with piperazine-1-carboxylic
acid isopropyl ester by following the Section 4.1.22. Yield 58%;
1H NMR (300 MHz, CDCl3) d 8.14 (d, 2H, J = 8.7 Hz), 7.67 (d, 1H,
J = 8.7 Hz), 7.31 (m, 2H), 7.19 (d, 1H, J = 2.1 Hz), 7.05–6.96 (m,
5H), 4.92 (m, 1H), 4.11 (t, 2H, J = 6.3 Hz), 3.49 (t, 4H, J = 5.0 Hz),
2.55 (t, 2H, J = 7.2 Hz), 2.43 (t, 4H, J = 4.8 Hz), 2.01 (m, 2H), 1.24
(d, 6H, J = 6.3 Hz). MS (FAB) m/z 550 [M+H]+; mp 108 °C.
4.1.22.16. 6-(4-Chlorophenoxy)-2-[4-(3-piperazin-1-yl-propoxy)-
phenyl]-benzoxazole (41). This compound was prepared from
compound 48 by following the Section 4.1.7. Yield 54%; 1H NMR
(300 MHz, CDCl3) d 7.77 (d, 2H, J = 8.7 Hz), 7.45 (d, 1H, J = 8.7 Hz),
7.34–7.25 (m, 2H), 7.18 (m, 1H), 7.01–6.90 (m, 5H), 6.83 (s, 1H),
4.08 (t, 2H, J = 6.3 Hz), 2.92 (t, 4H, J = 4.9 Hz), 2.50 (m, 6H), 2.00
(m, 2H). MS (FAB) m/z 463 [M+H]+; mp 120 °C.
4.1.22.17. 6-(4-Chlorophenoxy)-2-{4-[3-(4-methyl-piperazin-1-
yl)-propoxy]-phenyl}-benzoxazole (42). This compound was
4.1.22.23. 4-(3-{4-[6-(4-Chlorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-piperazine-1-carboxylic acid tert-butyl ester
(48). This compound was prepared with N-Boc-piperzaine by fol-
lowing the Section 4.1.22. Yield 36%; 1H NMR (300 MHz, CDCl3) d
8.13 (d, 2H, J = 9.0 Hz), 7.66 (d, 1H, J = 8.6 Hz), 7.30 (d, 2H,
J = 9.0 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.95–7.05 (m, 5H), 4.11 (t, 2H,
J = 6.2 Hz), 3.42–3.46 (m, 4H), 2.55 (t, 2H, J = 7.0 Hz), 2.40–2.43
(m, 4H), 1.98–2.03 (m, 2H), 1.46 (s, 9H). MS (FAB) m/z 564
[M+H]+; mp 147 °C.
prepared
with
4-methyl-piperazine
by
following
the
Section 4.1.22. Yield 86%; 1H NMR (300 MHz, CDCl3) d 8.14 (d,
2H, J = 8.7 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.31 (d, 2H, J = 9.0 Hz),
7.19 (d, 1H, J = 2.1 Hz), 7.05–6.96 (m, 5H), 4.11 (t, 2H, J = 6.3 Hz),
2.57 (m, 10H), 2.33 (s, 3H), 2.02 (m, 2H). MS (FAB) m/z 478
[M+H]+; mp 110 °C.
4.1.22.18. 2-(4-(3-(4-(6-(4-chlorophenoxy)benzo[d]oxazol-2-yl)-
phenoxy)-propyl)-piperazin-1-yl)ethanol (43).
A
mixture of
4.1.22.24. 6-(4-Chlorophenoxy)-2-{4-[3-(4-phenyl-piperazin-1-
yl)-propoxy]-phenyl}-benzoxazole (49). This compound was
prepared with N-phenyl piperazine by following the
Section 4.1.22. Yield 61%; 1H NMR (300 MHz, CDCl3) d 8.14 (d,
2H, J = 8.7 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.33–7.25 (m, 4H), 7.20 (d,
1H, J = 2.4 Hz), 7.05–6.84 (m, 8H), 4.14 (t, 2H, J = 6.3 Hz), 3.23 (t,
4H, J = 4.8 Hz), 2.64 (m, 6H), 2.06 (m, 2H). MS (FAB) m/z 540
[M+H]+; mp 162 °C.
compound 24 (0.040 g, 0.086 mmol), 2-bromoethanol and K2CO3
(0.024 g, 0.17 mmol) in DMF was heated to 100 °C for 18 h. The
mixtures was cooled to room temperature and evaporated under
reduced pressure. The residue was dissolved in EtOAc and then
washed with water, and brine. The organic layer was dried over
sodium sulfate, filtered and concentrated in vacuum. The resulting
residue was purified by silica gel chromatography to afford the
product. Yield 34%; 1H NMR (300 MHz, CDCl3) d 8.13 (d, 2H,
J = 9.0 Hz), 7.67 (d, 1H, J = 8.7 Hz), 7.30 (d, 2H, J = 8.4 Hz), 7.19 (d,
1H, J = 2.1 Hz), 7.05–6.96 (m, 5H), 4.10 (t, 2H, J = 6.3 Hz), 3.62 (t,
4.1.22.25. 2-(4-(3-(4-(Pyrimidin-2-yl)piperazin-1-yl)propoxy)-
phenyl)-6-(4-chlorophenoxy)-benzo[d]oxazole
(50). This
Please cite this article in press as: Choi, K.; et al. Bioorg. Med. Chem. (2015), http://dx.doi.org/10.1016/j.bmc.2015.05.022

14
K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
compound was prepared with 2-(piperazin-1-yl)pyrimidine by fol-
lowing the Section 4.1.22. Yield 34%; 1H NMR (300 MHz, CDCl3) d
8.31 (d, 2H, J = 4.8 Hz), 8.14 (d, 2H, J = 8.7 Hz), 7.67 (d, 1H,
J = 8.7 Hz), 7.30 (d, 2H, J = 8.4 Hz), 7.19 (d, 1H, J = 2.1 Hz), 7.04–
6.96 (m, 5H), 6.49 (t, 1H, J = 4.8 Hz), 4.16 (t, 2H, J = 6.3 Hz), 3.85
(t, 2H, J = 5.1 Hz), 2.61–2.53 (m, 6), 2.01 (m, 2H); MS (FAB) m/z
542 [M+H]+; mp 114 °C.
compound was prepared with tert-butyl piperazine-1-carboxylate
by following the Section 4.1.22. Yield 68%; 1H NMR (300 MHz,
CDCl3) d 8.13 (d, 2H, J = 9.0 Hz), 7.64 (d, 1H, J = 8.8 Hz), 7.37 (d, 2H,
J = 8.8 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.95–7.06 (m, 5H), 4.11 (t, 2H,
J = 6.4 Hz),3.44 (t, 4H, J = 4.9 Hz), 2.54 (t, 2H, J = 7.0 Hz), 2.42 (t, 4H,
J = 5.0 Hz), 1.96–2.05 (m, 2H), 1.46 (s, 9H), 1.33 (s, 9H); MS(FAB)
m/z 586 [M+H]+; mp 146 °C.
4.1.22.26. 6-(4-Chlorophenoxy)-2-(4-{3-[4-(5-fluoro-pyrimidin-
2-yl)-piperazin-1-yl]-propoxy}-phenyl)-benzoxazole (51). This
compound was prepared with 5-fluoro-2-piperazin-1-yl-pyrim-
idine by following the Section 4.1.22. Yield 35%; 1H NMR
(300 MHz, CDCl3) d 8.19 (s, 2H), 8.14 (d, 2H, J = 8.6 Hz), 7.66 (d,
1H, J = 8.6 Hz), 7.31 (d, 2H, J = 8.6 Hz), 7.19 (d, 1H, J = 2.2 Hz),
7.05–6.95 (m, 5H), 4.14 (t, 2H, J = 6.2 Hz), 3.79 (t, 4H, J = 4.7 Hz),
2.61–2.52 (m, 6H), 2.05 (t, 2H, J = 7.5 Hz); MS (FAB) m/z 542
[M+H]+; mp 114 °C.
4.1.22.33. 6-(4-tert-Butylphenoxy)-2-(4-(3-(4-(pyrimidin-2-yl)-
piperazin-1-yl)propoxy)phenyl)benzo[d]oxazole (58). This com-
pound was prepared with 2-(piperazin-1-yl)pyrimidine by follow-
ing the Section 4.1.22. Yield 53%; 1H NMR (300 MHz, CDCl3)d 8.31
(d, 2H, J = 4.8 Hz), 8.13 (d, 2H, J = 9.0 Hz), 7.64 (d, 1H, J = 8.6 Hz),
7.36 (d, 2H, J = 8.8 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.95–7.06 (m, 5H),
6.48 (t, 1H, J = 4.8 Hz), 4.13 (t, 2H, J = 6.2 Hz), 3.85 (t, 4H,
J = 5.0 Hz), 2.52–2.61 (m, 6H), 2.00–2.10 (m, 2H), 1.33 (s, 9H);
MS(FAB) m/z 564 [M+H]+; mp 129 °C.
4.1.22.27. 6-(4-Chlorophenoxy)-2-(4-{3-[4-(5-chloro-pyrimidin-
2-yl)-piperazin-1-yl]-propoxy}-phenyl)-benzoxazole (52). This
compound was prepared 5-chloro-2-piperazin-1-yl-pyrimidine
by following the Section 4.1.22. Yield 19%; 1H NMR (300 MHz,
CDCl3) d 8.22 (s, 2H), 8.14 (d, 2H, J = 8.8 Hz), 7.66 (d, 1H,
J = 8.6 Hz), 7.31 (d, 2H, J = 9.0 Hz), 7.19 (d, 1H, J = 2.2 Hz), 7.05–
6.96 (m, 5H), 4.14 (t, 2H, J = 6.2 Hz), 3.82 (t, 4H, J = 4.9 Hz), 2.62–
2.52 (m, 6H), 2.08–2.03 (m, 2H); MS (FAB) m/z 576 [M+H]+; mp
160 °C.
4.1.22.34. 6-(4-tert-Butylphenoxy)-2-(4-(3-(pyrrolidin-1-yl)pro-
poxy)phenyl)benzo[d]oxazole (59). This compound was pre-
pared with pyrrolidine by following the Section 4.1.22. Yield
94%; 1H NMR (300 MHz, CDCl3) d 8.13 (d, 2H, J = 8.8 Hz), 7.64 (d,
1H, J = 8.6 Hz), 7.37 (d, 2H, J = 9.0 Hz), 7.18 (d, 1H, J = 2.0 Hz),
6.94–7.06 (m, 5H), 4.13 (t, 2H, J = 6.2 Hz), 2.73–2.89 (m, 6H),
2.13–2.23 (m, 2H), 1.90–1.95 (m, 4H), 1.33 (s, 9H); MS(FAB) m/z
471 [M+H]+; mp 155 °C.
4.1.22.35. (R)-tert-Butyl 1-(3-(4-(6-(4-tert-butylphenoxy)benzo-[d]-
oxazol-2-yl)phenoxy)propyl)pyrrolidin-3-ylcarbamate (60). This
compound was prepared with (R)-(+)-3-tert-butyl pyrrolidin-3-yl-
carbamate by following the Section 4.1.22. Yield 91%; 1H NMR
(300 MHz, CDCl3) d 8.13 (d, 2H, J = 9.0 Hz), 7.65 (d, 1H, J = 8.6 Hz),
7.37 (d, 2H, J = 8.8 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.95–7.07 (m, 5H),
4.97 (br s, 1H), 4.21 (br s, 1H), 4.11(t, 2H, J = 6.2 Hz), 2.93 (m,
1H), 2.65–2.70 (m, 4H), 2.27–2.38 (m, 2H), 2.02–2.06 (m, 3H),
1.48–1.65 (m, 1H), 1.44 (s, 9H), 1.33 (s, 9H);MS(FAB) m/z 586
[M+H]+; mp 126 °C.
4.1.22.28. 3-(4-(6-(4-tert-Butylphenoxy)benzo[d]oxazol-2-yl)-
phenoxy)-N,N-diethylpropan-1-amine (53).
This compound
was prepared with diethylamine by following the Section 4.1.22.
Yield 79%; 1H NMR (300 MHz, CDCl3) d 8.13 (d, 2H, J = 9.0 Hz),
7.64 (d, 1H, J = 8.6 Hz), 7.36 (d, 2H, J = 8.8 Hz), 7.18 (d, 1H,
J = 2.2 Hz), 6.95–7.06 (m, 5H), 4.12 (t, 2H, J = 6.2 Hz), 2.70–2.83
(m, 6H), 2.02–2.14(m, 2H), 1.33 (s, 9H), 1.16 (t, 6H, J = 7.1 Hz);
MS (FAB) m/z 473 [M+H]+; mp 84 °C.
4.1.22.29. 6-(4-tert-Butylphenoxy)-2-(4-(3-(piperidin-1-yl)-
propoxy)phenyl)benzo[d]oxazole (54). This compound was pre-
pared with piperidine by following the Section 4.1.22. Yield 99%;
1H NMR (300 MHz, CDCl3) d 8.12 (d, 2H, J = 8.6 Hz), 7.64 (d, 1H,
J = 8.6 Hz), 7.36 (d, 2H, J = 7.0 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.95–
7.06 (m, 5H), 4.09 (t, 2H, J = 6.2 Hz), 2.49–2.61 (m, 6H), 2.03–2.13
(m, 2H), 1.63–1.70 (m, 4H), 1.43–1.54 (m, 2H), 1.33 (s, 9H);
MS(FAB) m/z 485 [M+H]+; mp 122 °C.
4.1.22.36. (S)-tert-Butyl 1-(3-(4-(6-(4-tert-butylphenoxy)benzo[d]-
oxazol-2-yl)phenoxy)propyl)pyrrolidin-3-ylcarbamate (61). This
compound was prepared with (S)-(+)-3-tert-butyl pyrrolidin-3-ylcar-
bamate by following the Section 4.1.22. Yield 90%; 1H NMR
(300 MHz, CDCl3) d 8.12 (d, 2H, J = 8.6 Hz), 7.65 (d, 1H, J = 8.4 Hz),
7.37 (d, 2H, J = 8.6 Hz), 7.18 (d, 1H, J = 2.4 Hz), 6.96–7.07 (m, 5H),
4.11 (t, 2H, J = 6.2 Hz), 2.80–2.91 (m, 1H), 2.60–2.63 (m, 3H), 2.20–
2.35 (m, 1H), 1.96–2.07 (m, 2H), 1.58 (br s, 5H), 1.44 (s, 9H), 1.33
(s, 9H); MS(FAB) m/z 586 [M+H]+; mp 106 °C.
4.1.22.30. 6-(4-tert-Butylphenoxy)-2-(4-(3-morpholinopropoxy)-
phenyl)benzo[d]oxazole (55). This compound was prepared with
morpholine by following the Section 4.1.22. Yield 89%; 1H
NMR(300 MHz, CDCl3) d 8.13 (d, 2H, J = 8.8 Hz), 7.64 (d, 1H,
J = 8.6 Hz), 7.37 (d, 2H, J = 8.8 Hz), 7.18 (d, 1H, J = 2.4 Hz), 6.95–7.06
(m, 5H), 4.11 (t, 2H, J = 6.2 Hz), 3.73 (t, 4H, J = 4.6 Hz), 2.46–2.56
(m, 6H), 1.95–2.05 (m, 2H), 1.33 (s, 9H); MS(FAB) m/z 487 [M+H]+;
mp 127 °C.
4.1.22.37. (R)-1-(3-(4-(6-(4-tert-Butylphenoxy)benzo[d]oxazol-
2-yl)phenoxy)propyl)pyrrolidin-3-amine (62). This compound
was prepared from compound 60 by following the procedure
described for compound 35. Yield 25%; 1H NMR (300 MHz,
CDCl3) d 8.12 (d, 2H, J = 8.8 Hz), 7.64 (d, 1H, J = 8.6 Hz), 7.37 (d,
2H, J = 8.6 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.96–7.06 (m, 5H), 4.11 (t,
2H, J = 6.4 Hz), 3.70–3.76 (m, 1H), 2.89–3.13 (m, 6H), 2.75–2.79
(m, 2H), 2.23–2.30 (m, 1H), 2.09–2.14 (m, 2H), 1.70–1.80 (m, 1H),
1.33 (s, 9H); MS(FAB) m/z 486 [M+H]+; mp 142 °C.
4.1.22.31. 6-(4-tert-Butylphenoxy)-2-(4-(3-(4-tert-butylpiper-
azin-1-yl)propoxy)phenyl)benzo[d]-oxazole (56). This com-
pound was prepared with tert-butyl piperazine by following the
Section 4.1.22. Yield 96%; 1H NMR (300 MHz, CDCl3) d 8.12 (d,
2H, J = 9.0 Hz), 7.64 (d, 1H, J = 8.6 Hz), 7.37 (d, 2H, J = 8.8 Hz),
7.18 (d, 1H, J = 2.2 Hz), 6.95–7.06 (m, 5H), 4.09 (t, 2H, J = 6.4 Hz),
2.55–2.75 (m, 10H), 1.96–2.06 (m, 2H), 1.33 (s, 9H), 1.17 (s, 9H);
MS(FAB) m/z 542 [M+H]+; mp 158 °C.
4.1.22.38. (S)-1-(3-(4-(6-(4-tert-Butylphenoxy)benzo[d]oxazol-
2-yl)phenoxy)propyl)pyrrolidin-3-amine (63). This compound
was prepared from compound 61 by following the procedure
described for compound 35. Yield 42%; 1H NMR (300 MHz,
CDCl3) d 8.12 (d, 2H, J = 8.8 Hz), 7.64 (d, 1H, J = 8.6 Hz), 7.37 (d,
2H, J = 8.8 Hz), 7.18 (d, 1H, J = 2.2 Hz), 6.96–7.06 (m, 5H), 4.11 (t,
2H, J = 6.4 Hz), 3.63–3.72 (m, 1H), 2.91–3.07 (m, 4H), 2.87 (t, 2H,
J = 7.5 Hz),2.66–2.80 (m, 2H), 2.22–2.29 (m, 1H), 2.09–2.14 (m,
4.1.22.32. tert-Butyl 4-(3-(4-(6-(4-tert-butylphenoxy)benzo[d]-
oxazol-2-yl)phenoxy)propyl)piperazine-1-carboxylate (57). This
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K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
15
2H), 1.64–1.72 (m, 1H), 1.33 (s, 9H); MS(FAB) m/z 486 [M+H]+; mp
119 °C.
(300 MHz, CDCl3) d 8.15 (d, 2H, J = 8.7 Hz), 7.71 (d, 1H, J = 8.7 Hz),
7.60 (d, 2H, J = 8.4 Hz), 7.27 (d, 1H, J = 3.0 Hz), 7.09–7.01 (m, 5H),
4.12 (d, 2H, J = 6.3 Hz), 3.46 (br s, 4H), 2.56 (m, 2H), 2.43 (m, 4H),
2.02 (m, 2H), 1.47 (s, 9H). MS (FAB) m/z 598 [M+H]+; mp 149 °C.
4.1.22.39.
(3-{4-[6-(4-Fluorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-diethylamine (64). This compound was prepared
with diethylamine by following the Section 4.1.22. Yield 20%; 1H
NMR (300 MHz, CDCl3) d 8.13 (d, 2H, J = 9.0 Hz), 7.65 (d, 1H,
J = 8.4 Hz),), 7.15 (d, 1H, J = 2.1 Hz),), 7.06–6.99 (m, 7H),), 4.12 (t,
2H, J = 6.0 Hz),), 2.72 (m, 6H)), 2.07 (m, 2H),), 1.13 (t, 6H,
J = 7.1 Hz). MS (FAB) m/z 435 [M+H]+; mp 99 °C.
4.1.22.47. (3-{4-[6-(3-Trifluoromethyl-phenoxy)-benzooxazol-
2-yl]-phenoxy}-propyl)-diethylamine (72). This compound
was prepared with diethylamine by following the Section 4.1.22.
Yield 19%; 1H NMR (300 MHz, CDCl3) d 8.19–8.16 (m, 2H), 7.71
(d, 1H, J = 8.6 Hz), 7.49–7.36 (m, 2H), 7.25–7.18 (m, 3H), 7.09–
6.99 (m, 3H), 4.21 (t, 2H, J = 5.5 Hz), 3.34–3.22 (m, 6H), 2.49 (m,
2H), 1.51 (t, 6H, J = 7.1 Hz). MS (FAB) m/z 485 [M+H]+; mp 95 °C.
4.1.22.40. 6-(4-Fluorophenoxy)-2-[4-(3-piperidin-1-yl-propoxy)-
phenyl]-benzoxazole (65). This compound was prepared with
piperidine by following the Section 4.1.22. Yield 67%; 1H NMR
(300 MHz, CDCl3) d 8.13 (m, 2H), 7.65 (d, 1H, J = 8.4 Hz), 7.15 (d,
1H, J = 2.4 Hz), 7.06–7.00 (m, 7H), 4.11 (t, 2H, J = 6.3 Hz), 2.58–
2.51 (m, 6H), 2.09 (m, 2H), 1.67 (m, 4H), 1.48 (br s, 2H). MS
(FAB) m/z 446 [M+H]+; mp 123 °C.
4.1.22.48. 6-(4-Trifluoromethyl-phenoxy)-2-[4-(3-piperidin-1-
yl-propoxy)-phenyl]-benzoxazole (73). This compound was
prepared with piperidine by following the Section 4.1.22. Yield
18%; 1H NMR (300 MHz, CDCl3) d 8.18–8.15 (m, 2H), 7.71 (d, 1H,
J = 8.6 Hz), 7.49–7.36 (m, 2H), 7.25–7.19 (m, 3H), 7.09–6.98 (m,
3H), 4.17 (t, 2H, J = 5.7 Hz), 3.19–3.14 (m, 6H), 2.54–2.51 (m, 2H),
2.17–2.04 (m, 4H), 1.73 (m, 2H). MS (FAB) m/z 497 [M+H]+; mp
76 °C.
4.1.22.41. 6-(4-Fluorophenoxy)-2-[4-(3-morpholin-4-yl-propoxy)-
phenyl]-benzoxazole (66). This compound was prepared with
morpholine by following the Section 4.1.22. Yield 79%; 1H NMR
(300 MHz, CDCl3) d 8.13 (m, 2H), 7.65 (d, 1H, J = 8.4 Hz), 7.15 (d,
1H, J = 2.4 Hz), 7.06–7.00 (m, 7H), 4.12 (t, 2H, J = 6.3 Hz), 3.74 (t,
4H, J = 4.7 Hz), 2.60–2.48 (m, 6H), 2.02 (m, 2H). MS (FAB) m/z
448 [M+H]+; mp 130 °C.
4.1.22.49. 6-(3-Trifluoromethyl-phenoxy)-2-[4-(3-morpholin-4-
yl-propoxy)-phenyl]-benzoxazole (74). This compound was
prepared with morpholine by following the Section 4.1.22. Yield
73%; 1H NMR (300 MHz, CDCl3) d 8.15 (d, 2H, J = 8.8 Hz), 7.70 (d,
1H, J = 8.6 Hz), 7.48–7.43 (m, 1H), 7.36 (d, 1H, J = 7.7 Hz), 7.27–
7.18 (m, 3H), 7.08–7.00 (m, 3H), 4.12 (t, 2H, J = 6.2 Hz), 3.73 (t,
4H, J = 4.6 Hz), 2.57–2.48 (m, 6H), 2.06–1.97 (m, 2H). MS (FAB)
m/z 499 [M+H]+; mp 108 °C.
4.1.22.42. 4-(3-{4-[6-(4-Fluorophenoxy)-benzoxazol-2-yl]-phe-
noxy}-propyl)-piperazine-1-carboxylic acid tert-butyl ester
(67). This compound was prepared with N-Boc-piperazine by fol-
lowing the Section 4.1.22. Yield 65%; 1H NMR (300 MHz, CDCl3) d
8.13 (m, 2H), 7.65 (d, 1H, J = 8.7 Hz), 7.15 (d, 1H, J = 2.1 Hz),
7.06–7.00 (d, 7H), 4.11 (t, 2H, J = 6.3 Hz), 3.45 (t, 4H, J = 5.0 Hz),
2.55 (t, 2H, J = 7.2 Hz), 2.42 (m, 4H), 2.01 (m, 2H), 1.48 (s, 9H).
MS (FAB) m/z 548 [M+H]+; mp 155 °C.
4.1.22.50. 4-(3-{4-[6-(3-Trifluoromethyl-phenoxy)-benzoxazol-
2-yl]-phenoxy}-propyl)-piperazine-1-carboxylic acid tert-butyl
ester (75). This compound was prepared with N-Boc-piperazine
by following the Section 4.1.22. Yield 91%; 1H NMR (300 MHz,
CDCl3) d 8.15 (d, 2H, J = 8.8 Hz), 7.70 (d, 1H, J = 8.6 Hz), 7.48–7.43
(m, 1H), 7.36 (d, 1H, J = 7.7 Hz), 7.27–7.18 (m, 3H), 7.08–7.01 (m,
3H), 4.12 (t, 2H, J = 6.2 Hz), 3.45 (t, 4H, J = 4.8 Hz), 2.55 (t, 2H,
J = 7.1 Hz), 2.42 (t, 4H, J = 4.8 Hz), 2.06–1.97 (m, 2H), 1.47 (s, 9H).
MS (FAB) m/z 598 [M+H]+; mp 110 °C.
4.1.22.43. (3-{4-[6-(4-Trifluoromethyl-phenoxy)-benzoxazol-2-
yl]-phenoxy}-propyl)-diethyl-amine (68). This compound was
prepared with diethylamine by following the Section 4.1.22.
Yield 58%; 1H NMR (300 MHz, CDCl3) d 8.15 (m, 2H), 7.71 (d, 1H,
J = 8.7 Hz), 7.60 (d, 2H, J = 9.0 Hz), 7.27 (d, 1H, J = 2.4 Hz), 7.09–
7.01 (m, 5H), 4.12 (t, 2H, J = 6.2 Hz), 2.73–2.65 (m, 6H), 2.05 (m,
2H), 1.11 (t, 6H, J = 7.2 Hz). MS (FAB) m/z 485 [M+H]+; mp 93 °C.
4.2. Biological study
4.2.1. Preparation of biotinylated-human-RAGE and human
Ab1–42
4.1.22.44. 6-(4-Trifluoromethyl-phenoxy)-2-[4-(3-piperidin-1-
yl-propoxy)-phenyl]-benzoxazole (69). This compound was
prepared with diethylamine by following the Section 4.1.22.
Yield 62%; 1H NMR (300 MHz, CDCl3) d 8.15 (d, 2H, J = 8.4 Hz),
7.71 (d, 1H, J = 8.4 Hz), 7.60 (d, 2H, J = 9.0 Hz), 7.27 (d, 1H,
J = 2.4 Hz), 7.09–7.01 (m, 5H), 4.11 (t, 2H, J = 6.3 Hz), 2.58–2.51
(m, 6H), 2.09 (m, 2H), 1.67 (m, 4H), 1.48 (br s, 2H). MS (FAB) m/z
497 [M+H]+; mp 121 °C.
Biotinylated-human-RAGE proteins and Ab peptides were pre-
pared as previously described.35 Briefly, the bacterially expressed
RAGE proteins were purified by immobilized metal affinity chro-
matography. Dried Ab42-FITC (M2585, BACHEM) and Ab peptides
(American peptide Inc. USA) were completely dissolved in hexaflu-
oroisopropanol at rt for 1–3 days and lyophilized. The resulting Ab
film was stored at ꢁ80 °C Before each use, the Ab film was dis-
solved in dimethylsulfoxide (DMSO). For Ab induced cytotoxicity
4.1.22.45. 6-(4-Trifluoromethyl-phenoxy)-2-[4-(3-morpholin-4-
yl-propoxy)-phenyl]-benzoxazole (70). This compound was
prepared with morpholine by following the Section 4.1.22. Yield
78%; 1H NMR (300 MHz, CDCl3) d 8.15 (d, 2H, J = 9.0 Hz), 7.71 (d,
1H, J = 8.4 Hz), 7.60 (d, 2H, J = 8.7 Hz), 7.27 (d, 1H, J = 3.0 Hz),
7.09–7.02 (m, 5H), 4.12 (d, 2H, J = 6.3 Hz), 3.74 (d, 4H, J = 4.7 Hz),
2.58–2.50 (m, 6H), 2.03 (m, 2H). MS (FAB) m/z 499 [M+H]+; mp
110 °C.
test, 200 lM of Ab peptides solution in PBS was incubated for
24 h at 4 °C to generate toxic aggregates.
4.2.2. FRET assay
FRET assays were performed using a F200 reader (TECAN). In
this format, 2.5
Cy3-streptavidin (016-160-084, Jackson ImmunoResearch) were
mixed in 100 L of PBS and incubated at rt for 30 min. And, then
50 L of 40 nM Ab42-FITC (M2585, BACHEM) and 50 L of 4
of each compound were added to the mixture. Assays were per-
formed at a final volume of 200 L and a final DMSO concentration
lg of biotinylated-human-RAGE and 200 ng of
l
l
l
lM
4.1.22.46. 4-(3-{4-[6-(4-Trifluoromethyl-phenoxy)-benzoxazol-
2-yl]-phenoxy}-propyl)-piperazine-1-carboxylic acid tert-butyl
l
ester (71).
This compound was prepared with N-Boc-piper-
of 0.1% v/v in untreated 96 well clear bottom black plate (Corning).
All measurements were carried out in triplicate. Plates were read at
azine by following the Section 4.1.22. Yield 57%; 1H NMR
Please cite this article in press as: Choi, K.; et al. Bioorg. Med. Chem. (2015), http://dx.doi.org/10.1016/j.bmc.2015.05.022

16
K. Choi et al. / Bioorg. Med. Chem. xxx (2015) xxx–xxx
1 h after mixing the components. FEs were calculated using the fol-
lowing formula:
stored at 4 °C overnight in neutral buffered 10% formalin solution
then immersed in a solution of 30% sucrose in PBS. Serial 30- m-
l
thick coronal tissue sections were cut on a cryostat (Leica) and
stored in cryoprotectant (25% ethylene glycol and 25% glycerol in
0.05 M PB) at ꢁ20 °C. Areas of amyloid deposition in mice brain
were determined by staining with 0.2% Congo-Red (Sigma) solu-
tion as described in the manufacturer’s protocol. For quantification,
digital images were captured at 10ꢂ magnification on an Olympus
IX81 Imaging System. Image J software (NIH Image, Bethesda, MD)
was used to quantify positive pixels and total area.
Fda þ inhibitor
FE ¼ 1 ꢁ
Fd þ vehicle
where da is the donor emission in the presence of the acceptor and
d is the donor emission in the absence of the acceptor and vehicle is
0.1% DMSO. Percentage inhibition was determined using the calcu-
lated FEs.
4.2.3. Cytotoxicity test
4.2.6. Statistical analysis
Mouse hippocampal HT22 cells were received from Dr. Inhee
Mook-Jung at Seoul National University (Seoul, Korea). The cells
were cultured in DMEM (Dulbecco’s Modified Eagle’s Medium,
Gibco-BRL) supplemented with 10% fetal bovine serum, 100 U/mL
penicillin, and 100 mg/mL streptomycin at 37 °C in a humidified
atmosphere containing 5% CO2 and 95% air. The cells were plated
into 96 well culture plates at a density of 5000 cells per well in
All data are shown as mean SEM. Statistical differences
between groups were defined by t-test using GraphPad Prism 4
software (Version 4.03, GraphPad software, Inc.). A p-value <0.05
was considered statistically significant.
Acknowledgments
100
10
tion of cell viability, 15
2-yl]-2,5-diphenyltetrazolium bromide (MTT) was added to each
well and incubated for 3 h. The formazan formed was dissolved
in acidic 2-propanol, and optical density was measured at
570 nm using a microplate reader (Sunrise, TECAN). MTT reduction
measured at 570 nm was converted to percentage cell growth by
using the following formula.
l
l
L DMEM. The following day the cells were treated with
M of each compound and incubated for 18 h. For determina-
L of 5 mg/mL of 3-[4,5-dimethylthiazol-
This work was supported by the Korea Science and Engineering
Foundation (KOSEF) Grant (NRF-2009-0081669) funded by the
Korea Government (MOST).
l
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