Synthesis of novel diaryl ethers and their evaluation as antimitotic agents

Article abstract of DOI:10.1016/j.bmcl.2006.12.048

A series of novel diaryl ethers possessing various functional groups were synthesized and evaluated for antiproliferative activity in human myeloid leukemia HL-60 cells. Among the compounds examined, compounds 10, 17, 20, 24, and 33 showed moderate to pot

Full text of DOI:10.1016/j.bmcl.2006.12.048

Bioorganic & Medicinal Chemistry Letters 17 (2007) 1799–1802
Synthesis of novel diaryl ethers and their evaluation
as antimitotic agents
Jin-Kyung In,a Mi-Sung Lee,a Jung-Eun Yang,a Jae-Hwan Kwak,a Heesoon Lee,a
Shanthaveerappa K. Boovanahalli,b Kyeong Lee,b,* Soo Jin Kim,c Seung Kee Moon,c
Sungsook Lee,c Nam Song Choi,c Soon Kil Ahnc and Jae-Kyung Junga,*
aCollege of Pharmacy, Chungbuk National University, Cheongju 361-763, Republic of Korea
bMolecular Cancer Research Center, KRIBB, Daejeon 305-333, Republic of Korea
cChong Kun Dang Research Institute 15-20, Cheonan 330-830, Republic of Korea
Received 21 September 2006; revised 6 November 2006; accepted 13 December 2006
Available online 21 December 2006
Abstract—A series of novel diaryl ethers possessing various functional groups were synthesized and evaluated for antiproliferative
activity in human myeloid leukemia HL-60 cells. Among the compounds examined, compounds 10, 17, 20, 24, and 33 showed mod-
erate to potent antiproliferative activity. These derivatives were further examined in terms of their abilities to inhibit tubulin poly-
merization; however, all of the tested compounds were relatively ineffective. The reference compound E7010 with an IC50 of 0.34 lM
exhibited potent antiproliferative activity and significantly inhibited tubulin polymerization in a dose-dependent manner.
Ó 2006 Elsevier Ltd. All rights reserved.
Antimitotic agents, which arrest cells in mitosis (the M
phase of the cell cycle), can be classified as tubulin inter-
active agents (TIAs).1 These tubulin-targeting agents are
generally divided into two major classes: microtubule-
stabilizing agents, like taxanes, epothilones, and disco-
dermolide, and microtubule-destabilizing agents, like
colchicine, vinca alkaloids, and cryptophycins.2,3
Although taxanes and vinca alkaloids are widely used
clinically to treat cancer, their structural complexities,
difficult formulations, lack of oral availability, and more
importantly, acquired and intrinsic resistance render
these drugs suboptimum for clinical treatment of can-
cer.4 Consequently, considerable interest is being shown
in the discovery and development of novel small mole-
cule inhibitors of tubulin polymerization that can cir-
cumvent the difficulties of natural products. In this
context, progress has recently been made on the devel-
opment of highly potent tubulin inhibitors and current-
ly, several compounds are undergoing clinical trials.5–10
Diaryl ethers represent an important class of synthetic
compounds recognized as potential anticancer drugs.
Experimental and pre-clinical models have demonstrat-
ed that a number of these compounds elicit outstanding
anticancer activity through the significant inhibition of
tubulin assembly accompanied by potent antiprolifera-
tive activity.11,12 Moreover, the diaryl ether scaffold is
found in a number of natural products and biologically
important molecules.13 In this context, several reports
have recently described various pharmacological evalua-
tions of compounds possessing diaryl ether motifs.14–16
As a result of our continuing studies aimed at the dis-
covery and development of potential antimitotic agents,
herein we report the synthesis, antiproliferative activi-
ties, and tubulin polymerization inhibitions of a series
of novel diaryl ethers.
A variety of substituted diaryl ethers, 3–25 and 28–33,
were prepared as outlined in Schemes 1–3. To facilitate
the efficient and diverse synthesis of the key diaryl ether
skeleton,17 the approach that emerged as being most
attractive was the Cu(OAc)2-mediated coupling reaction
developed by the Evans group,18 due to its mild reaction
conditions as compared with alternatives17 (room tem-
perature versus higher temperature, >80 °C). Thus,
treatment of 4- or 3,4-substituted arylboronic acids 1
and appropriate phenols 2 with Cu(OAc)2 in the
Keywords: Antimitotic agents; Tubulin polymerization; Diaryl ether;
Antiproliferative activity.
*
Corresponding authors. Tel.: +82 43 2612635; fax: +82 43 2682732
(J.-K. J); tel.: +82 42 8604382; fax: +82 42 8604595 (K. L); e-mail
addresses: kaylee@kribb.re.kr; orgjkjung@chungbuk.ac.kr
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.12.048

1800
J.-K. In et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1799–1802
Table 1. In vitro antiproliferative activities of diaryl ethers 3–21 and
E7010 in HL-60 cellsa
a
R1
A
R1
R
A
R
B
B
+
B(OH)2
HO
O
3-21
SO2NH
2a-d
1a-g
R1
R
MeO
HN
N
O
R
= 4-CN, 4-Cl, 4-NMe2, 3-F,4-OMe, 4-OMe, 3,4-di-OMe, 3,4-di-F.
R1 = 3-CO2Me, 4-COOEt, 3-OH-4-COOEt, 2,5-di-OMe.
E7010
3-21
Scheme 1. Reagents and condition: (a) Cu(OAc)2, Et3N, CH2Cl2, rt
42–84%.
OH
R1
IC50 (lM)
a
Compound
R
F
O
F
O
3
4-CN
4-N(Me)2
4-OMe
3-COOMe
3-COOMe
>20
>20
>20
>20
>20
>20
>20
3.5
MeO
MeO
MeO
4
OH
a
OEt
5
3-COOMe
3-COOMe
O
22
O
10
6
3-F,4-OMe
4-CN
7
4-COOEt
4-COOEt
8
4-N(Me)2
4-OMe
c
b
9
4-COOEt
4-COOEt
F
O
F
O
10
11
12
13
14
15
16
17
18
19
20
21
E7010
3-F,4-OMe
4-Cl
MeO
OMe
NHR
4-COOEt
4-COOEt
4-COOEt
>20
>20
>30
>30
>30
>30
1.5
N
Me
3,4-Di-OMe
3,4-Di-F
4-N(Me)2
4-OMe
O
O
25
Ph
23: R =
3-OH, 4-COOEt
3-OH, 4-COOEt
3-OH, 4-COOEt
3-OH, 4-COOEt
3-OH, 4-COOEt
2,6-Di-OMe
2,6-Di-OMe
2,6-Di-OMe
24: R =
3-F,4-OMe
3,4-Di-OMe
3,4-Di-F
4-CN
Scheme 2. Reagents: (a) LiOH, H2O–THF, 86%; (b) phenethylamine,
DCC, DMAP, THF, 53% for 23; cyclopropylamme, DCC, DMAP,
THF, 77% for 24; (c) Me(MeO)NH Æ HCl, i-PrMgCl, THF, 63%.
>30
>20
11.4
>20
0.34
4-N(Me)2
3-F,4-OMe
presence of Et3N and molecular sieve at room tempera-
ture afforded the desired diaryl ethers 3–2119 in modest
to high yields (Scheme 1).20
a All experiments were independently performed at least three times.
To identify the effect of ortho-substitution of the
B-ring on antiproliferative activity, ortho-substituted
diaryl ethers 28–33 were obtained by utilizing a se-
quence of reactions (Scheme 3). Ullmann coupling17
of the potassium salts of appropriate phenols 26 with
methyl 4-chloro-3-nitrobenzoate (27) gave the corre-
sponding diaryl ethers 28 and 29 possessing an
ortho-nitro group, which were subsequently reduced
to the related aniline derivatives 30 and 31. Diazotiza-
tion followed by iodination of these anilines, 30 and
31, gave the respective iodinated diaryl ethers 32 and
3319 in good yields.
As shown in Scheme 2, amide derivatives 23–2519 were
also prepared starting from ester 10, which appeared
to have promising antiproliferative activity (vide infra,
Table 1). To this end, ester 10 was subjected to alkaline
hydrolysis to give the corresponding acid 22. DCC-med-
iated coupling of the resulting 22 with appropriate
amines provided the amide analogues 23 and 24, in
53% and 77% yields, respectively. Reaction of ester 10
with N,O-dimethylhydroxylamine in the presence of iso-
propyl magnesium chloride21 provided the N-methoxy-
N-methylamide derivative 25.
O
O
O2N
O2N
a
OMe
OMe
R
+
R
Cl
OH
O
28: R = 4-OMe
29: R = 3,4-di-OMe
26a: R = 4-OMe
27
26b: R = 3,4-di-OMe
b
O
O
H2N
I
c
OMe
OMe
R
R
O
O
32: R = 4-OMe
33: R = 3,4-di-OMe
30: R = 4-OMe
31: R = 3,4-di-OMe
Scheme 3. Reagents and conditions: (a) aq KOH, reflux, 76–88%; (b) Pd/C, H2AcOH, rt; (c) (i) NaNO2, concd H2SO4, 0–5 °C; (ii) KI, H2O, rt-70 °C,
55–71% for two steps.

J.-K. In et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1799–1802
1801
Newly synthesized diaryl ethers 3–25 and 28–33 were
initially screened for their in vitro antiproliferative activ-
ity against human myeloid leukemia HL-60 cells. Re-
sults are tabulated as IC50 values in Tables 1–3.
of 1.5 lM. On the other hand, the other compounds
showed significantly poor inhibition. Interestingly, com-
pound 16, the 3-hydroxy derivative of 10, displayed poor
inhibitory activity. Analogue 20 with methoxy groups at
the 2 and 6 positions of ring B also exhibited considerable
activity with an IC50 of 14.1 lM. Based on the potent
inhibitory activities of diaryl ethers 10 and 17, we inves-
tigated the effects of replacing ester moieties with acid
and amide groups.
E7010, a novel sulfonamide antimitotic agent, was used
as a reference drug and as expected, this compound dis-
played potent antiproliferative activity with an IC50 of
0.34 lM.22,23 All assays were performed under standard
assay conditions by following a previously described
assay protocol.23 The in vitro inhibition data for com-
pounds 3–21 which were obtained using a straightfor-
ward single-step reaction are presented in Table 1.23
Initially, we explored the effects of various activating
groups on ring A whilst maintaining the ester moiety at
positions 3 or 4 on ring B; analogues 3–13. Of these, ana-
logue 10 with 3-fluoro-4-methoxy groups on A-ring
exhibited significant antiproliferative activity with an
IC50 of 3.5 lM, whereas all of the other derivatives dis-
played poor inhibitory activity. In view of the potent
activity of 10, we prepared more analogues 14–18 by
introducing a hydroxy group at position 3 of ring B. This
modification resulted in significant inhibition enhance-
ment, as represented by analogue 17, which had an IC50
As shown in Table 2, these derivatives showed markedly
reduced potency with the exception of amide 24 which
had an IC50 of 14.1 lM. This result suggested that the
size of the R (the ethoxy group of 10 and the cyclopro-
pylamide group of 24) would be important for potency.
To evaluate the significance of ortho-substitution on the
B-ring, we synthesized compounds 28–33. Of these com-
pounds, the iodo-derivative 33 exhibited considerable
potency with an IC50 of 5.62 lM, whereas, the nitro-
and amino-analogues showed significantly poor inhibi-
tion (Table 3). However, all of the active compounds
were less potent than the reference compound E7010.
Although much is not evident from these preliminary
structure–activity relationship studies, these findings of-
fer new possibilities for further improving potency.
To investigate whether these diaryl ethers affect microtu-
bule assembly, compounds 10, 17, 20, 24, and 33, which
exhibited moderate to potent antiproliferative activity in
HL-60 cells, were further tested with respect to tubulin
polymerization inhibition.24 E7010 was used as a posi-
tive control. Inhibitory activity of the tested compounds
was determined using HTS-Tubulin Polymerization As-
say Kits (Cytoskeleton, CDS01) and a previously
reported assay protocol.24 The results shown in Table
4 are presented as percentage inhibitions at the tested
concentrations. E7010 inhibited tubulin polymerization
in a dose-dependent manner, and complete inhibition
was observed at 10 lg/mL. On the other hand, com-
pounds 10, 17, 20, and 24 showed poor inhibitory pro-
files ranging from 13.3% to 8.7% inhibition, and
compound 33 was inactive at 10 lM.
Table 2. In vitro antiproliferative activity of diaryl ethers 22–25 in HL-
60 cellsa
F
O
MeO
R
O
22-25
a
Compound
R
IC50 (lM)
22
OH
>30
20.6
14.1
Ph
23
24
N
H
N
H
OMe
N
25
>30
Me
In summary, a series of novel diaryl ethers possessing
various functional groups were synthesized and initial
antiproliferative activity screening using human myeloid
leukemia HL-60 cells showed that some of these
a All experiments were independently performed at least three times.
Table 3. In vitro antiproliferative activity of diaryl ethers 28–33 in HL-
60 cellsa
Table 4. Inhibition of tubulin polymerization by diaryl ethers 10, 17,
20, 24, 33, and E7010a
O
R1
OMe
R
Compound
Concentration (lg/mL)
% of inhibitiona
O
28-33
Control
10
17
—
10
10
20
10
10
10
1
0%
12.5%
5.5%
R1
IC50 (lM)
a
Compound
R
13.3%
12.5%
8.7%
20
24
28
29
30
31
32
33
4-OMe
3,4-Di-OMe
4-OMe
NO2
NO2
NH2
NH2
I
>20
>20
>20
>20
>20
5.62
33
E7010
Inactive
40 %
3,4-Di-OMe
4-OMe
3,4-Di-OMe
3
10
74.6%
96.3%
I
a All experiments were independently performed at least two times.
a All experiments were independently performed at least three times.

1802
J.-K. In et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1799–1802
Beresis, R. T.; Castle, S. L.; Wu, J. H.; Jin, Q. J. Am.
Chem. Soc. 1998, 120, 8920; (c) Evans, D. A.; Dinsmore,
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analogues, that is, 10, 17, 20, 24, and 33, had potent to
moderate inhibitory activities. Based on these results,
further evaluations were conducted to investigate the
abilities of theses analogues to inhibit tubulin polymeri-
zation. However, all of the tested compounds exhibited
poor inhibition. Further study for mode of action of
these aryl ethers is under progress.
14. MacTough, S. C.; deSolms, S. J.; Shaw, A. W.; Abrams,
M. T.; Ciccarone, T. M.; Davide, J. P.; Hamilton, K. A.;
Hutchinson, J. H.; Koblan, K. S.; Kohl, N. E.; Lobell, R.
B.; Robinson, R. G.; Graham, S. L. Bioorg. Med. Chem.
Lett. 2001, 11, 1257.
15. Maria-Jesus, B.; Donald, C. M.; Garcia, D. M.; Nuria, D.;
Erwin, F. J.; Glen, H.W.; Edward Jr., M. J.; Howard, M.
C.; Concepcion, P.; James, Q. S.; Goodman, S. M.; Rae, S.
D.; Dean, S. R.; Kumiko, T.; Marie, T. E.; Nolan, W. C.;
WO-04/026305-A1, priority date, September 19, 2002;
publication date, April 1, 2004.
Taken together, our findings provide important infor-
mation of the structural features that influence the func-
tional activities of this class of compounds, and offer
new possibilities for further explorations to improve
potency.
16. Pulman, D. A.; Ying, B.-P.; Wu, S.-Y.; Gupta, S.;
Shimoharada, H.; Tsukamoto, M. USP-02/6,479,435,
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17. For recent reviews on diaryl ether formation, see: (a)
Sawyer, J. S. Tetrahedron 2000, 56, 5045; (b) Theil, F.
Angew. Chem., Int. Ed. Engl. 1999, 38, 2345.
18. (a) Evans, D. A.; Katz, J. L.; West, T. R. Tetrahedron
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Acknowledgments
This research was supported by the Regional Research
Centers Program of the Ministry of Education & Hu-
man Resources Development and by a grant of the
Korean Health 21 R&D Project, Ministry of Health &
Welfare, Republic of Korea (02-PJ2-PG6-DC02-0001).
19. All new synthetic compounds gave satisfactory analytical
and spectral data. Selected spectral data for compound 10:
1H NMR (300 MHz, CDCl3) d 7.94 (d, J = 8.9 Hz, 2H),
6.88 (d, J = 8.9 Hz, 3H), 6.71–6.92 (m, 3H), 4.29 (q,
J = 7.1 Hz, 2H), 3.83 (s, 3H), 1.31 (t, J = 7.1 Hz, 3H); 13C
NMR (125 MHz, CDCl3) d 166.0, 161.7, 153.6, 151.6,
148.7, 144.8, 131.6, 124.9, 116.7, 115.6, 114.2, 109.4, 60.8,
56.7, 14.3; IR (thin film, neat) 1715 cmÀ1; MS (FAB+) m/z
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