Antitumor agents 278. 4-Amino-2H-benzo[h]chromen-2-one (ABO) analogs as potent in vitro anti-cancer agents

Article abstract of DOI:10.1016/j.bmcl.2010.05.079

4-Amino-2H-benzo[h]chromen-2-one (ABO) analogs were designed, synthesized, and evaluated for cytotoxic activity. Among all 4-substituted ABO analogs, cyclohexyl (12), N-methoxy-N-methylacetamide (14), and various aromatic derivatives (15-25 and 27) exhibited promising cell growth inhibitory activity with ED₅₀ values of 0.01-5.8 μM against all tested tumor cell lines. The 4′-methoxyphenyl derivative (18) and 3′-methylphenyl derivative (24) showed the most potent antitumor activity against a broad range of cancer cell lines with ED₅₀ values of 0.01-76 μM. Preliminary SAR results indicated that substitutions on nitrogen are critical to the antitumor potency.

Full text of DOI:10.1016/j.bmcl.2010.05.079

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4085–4087
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Antitumor agents 278. 4-Amino-2H-benzo[h]chromen-2-one (ABO) analogs
as potent in vitro anti-cancer agents
Yizhou Dong a, Kyoko Nakagawa-Goto a, Chin-Yu Lai a, Susan L. Morris-Natschke a, Kenneth F. Bastow b,
Kuo-Hsiung Lee a,
*
a Natural Products Research Laboratories, Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599-7568, United States
b Division of Medicinal Chemistry and Natural Products, Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599-7568, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
4-Amino-2H-benzo[h]chromen-2-one (ABO) analogs were designed, synthesized, and evaluated for cyto-
toxic activity. Among all 4-substituted ABO analogs, cyclohexyl (12), N-methoxy-N-methylacetamide
(14), and various aromatic derivatives (15–25 and 27) exhibited promising cell growth inhibitory activity
Received 5 April 2010
Revised 17 May 2010
Accepted 19 May 2010
Available online 24 May 2010
with ED50 values of 0.01–5.8
l
M against all tested tumor cell lines. The 40-methoxyphenyl derivative (18)
and 30-methylphenyl derivative (24) showed the most potent antitumor activity against a broad range of
cancer cell lines with ED50 values of 0.01–76
nitrogen are critical to the antitumor potency.
l
M. Preliminary SAR results indicated that substitutions on
Keywords:
4-Amino-2H-benzo[h]chromen-2-one
analogs (ABO)
Ó 2010 Elsevier Ltd. All rights reserved.
Cytotoxic activity
Structure–activity relationships
Natural products have been one of the most significant sources
for drugs and drug leads.1–3 In 2004, our group isolated a new com-
pound, neo-tanshinlactone (1, Fig. 1),4,5 that showed potent anti-
breast cancer activity. Our recent results proved that 4-ethyl
neo-tanshinlactone (2) is a selective and potent in vivo anti-breast
cancer agent in three different mouse models.6 In order to study
the contribution of the individual rings of 1 and improve its phar-
macological properties, we designed five different scaffolds, which
led to the discovery and development of three series of novel anti-
cancer agents: 2-(furan-2-yl)naphthalen-1-ol (FNO), 6-aryl-4H-
furo [3,2-c]pyran-4-one (AFPO), and tetrahydronaphthalene-1-ol
(TNO) derivatives.7–9 The promising results and useful information
we obtained from these studies encouraged us to design and devel-
op additional novel anti-cancer agents based on 1.
Structural simplification and bio-isosteric replacement are
powerful and highly productive tools for analog design and drug
development.10 In our continuing studies, we combined these
two strategies to further explore the structure of 1 and develop
more potent analogs. Previously, we designed a simplified scaffold
3 by breaking the furan ring-D (Fig. 1);7 however, this compound
series did not show significant anti-cancer activity. We then de-
signed scaffold 4 (ABO), by replacing the oxygen in 3 with nitrogen.
Braccio et al. reported numerous pyran derivatives, including four
compounds with this scaffold, which showed activity against
Ehrlich ascites tumor cells.11 These positive results supported our
design and investigation of this scaffold. We introduced different
substituent groups around the skeleton of 4 to establish prelimin-
ary SAR and develop more potent analogs. Because our prior study
showed that 2-analogs with an ethyl group at the C-4 position pos-
sessed much higher potency than 1-analogs with a hydrogen at the
same position (Fig. 1), we also evaluated the effect of an ethyl
group (R1 = Et) in the corresponding position (C-7) in 4. This Letter
reports the synthesis of novel ABO analogs, discovery of new ana-
logs with potent antitumor activity, and identification of prelimin-
ary SAR.
All target compounds 9–31 were synthesized from 4-hydrox-
ybenzochromenones 5 and 6 (Scheme 1).4 Treatment of 5 and 6
with POCl3 afforded the related chlorides 7 and 8, respectively.11
Differently substituted amino groups were then incorporated to
study the effect of position, hydrogen bond donor or acceptor,
and group size. Compounds, 9–10, 13–14, and 16–31 were newly
O
O
O
C
O
O
O
B
D
4
O
NR2R3
OR2
A
7
R1
4
R
R1
3
4
R = Me: Neo-tanshinlactone (1)
R = Et: 4-Ethyl neo-tanshinlactone (2)
* Corresponding author. Tel.: +1 919 962 0066; fax: +1 919 966 3893.
E-mail address: khlee@unc.edu (K.-H. Lee).
Figure 1. Structures of neo-tanshinlactone (1), 4-ethyl neo-tanshinlactone (2),
previously reported scaffold 3, and newly designed scaffold 4.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.05.079

4086
Y. Dong et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4085–4087
O
O
O
O
O
O
b for 9-13
and 28-30
,
NR2R3
OH
Cl
a
c for 14 and 31
d for 15-27
R1
R1
5, R1= H
6, R1= Et
R1
7, R1= H
8, R1= Et
9-31
O
N
R1= R2= H
R3=
O
Me
O
O
11
17
9
10
12
14
13
1'
4'
F
Br
Me
Et
OMe
18
20
19
16
15
Me
MeO
Br
Me
OMe
Br
24
26
27
23
25
22
21
O
O
O
O
O
O
N
O
O
O
N
H
N
N
N
O
O
Et
31
29
30
28
Scheme 1. Reagents and conditions: (a) POCl3, Et3N, reflux, 1 h; (b) aliphatic amines, EtOH, reflux, 2 h; (c) 2-amino-N-methoxy-N-methylacetamide hydrobromide, Et3N,
EtOH, 55 °C; (d) aromatic amines, ethylene glycol, 160 °C, 1 h.
prepared by substitution reaction of the chloride in 6 or 7 with var-
ious amines according to reported procedures.11,12 Compounds 11,
12, and 15 were previously synthesized by Braccio’s group.11
All synthesized analogs 9–31 were tested for in vitro cytotoxic
activity against a panel of human tumor cell lines according to pre-
viously published methods (Table 1).7 Cell lines included A549
(non small cell lung cancer), DU145 (prostate cancer cell line), KB
(nasopharyngeal carcinoma), and KB-vin (vincristine-resistant
MDR KB subline), MDA-MB-231 (estrogen receptor negative breast
cancer), SK-BR-3 (estrogen receptor negative, HER2 over-express-
ing breast cancer), ZR-75-1 (estrogen receptor positive breast can-
cer). While the parent compound, 1, displayed selective activity
against SK-BR-3 and ZR-7-51 breast cancer cell lines, ABO analogs
showed a broad activity spectrum against all seven cancer cell lines
tested.
Concerning analogs with aliphatic R2/R3 amino substituents, 12
with a cyclohexyl group showed much higher activity than the
methyl, propyl, and cyclopropyl derivatives 9–11, which suggested
a bulky amino group is favored. The tertiary amines 28–30 were
essentially inactive; thus, the secondary amine could play a critical
role in the antitumor activity. The NH might act as a hydrogen
bond donor, which can be important to ligand–receptor interac-
tion. Compounds 14 with an N-methoxy-N-methylacetamide
group and 13 methyl acetate group were between 3- and 60-fold
more potent depending on the cell lines tested, respectively, than
10 with a propyl group. These results suggested that a hydrogen
bond acceptor may be favored in this side chain.
Table 1
Cytotoxicity of 9–31 against human tumor cell line panela,b
Compd KB
KB-vin A549 DU145 SKBR-3 ZR-75-1 MDA-MB-231
1
9
>30 >30
>30 >30
>30 10.60
>30
>30
>30
29.8
0.72
4.7
>30
>30
>30
9.6
0.97
4.1
0.95
>30
>30
20.8
1.3
3.8
4.5
1.6
0.38
0.30
0.13
1.1
0.50
1.6
0.95
>30
>30
19.5
5.8
>30
>30
19.8
10.0
4.1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
7.8
9.9
0.61 0.43
4.6
2.2
3.1
3.0
6.7
4.2
5.8
3.1
3.2
0.48
0.91
13.0
0.79
0.01
3.2
0.44 0.50
0.22 0.17
0.28 0.18
0.11 0.13
0.98
0.25
0.20
0.17
0.81
0.72
1.3
0.82
0.37
0.30
0.11
0.78
0.52
1.3
0.27
15.3
1.4
0.02
>30
6.8
8.3
7.3
2.6
0.76
1.3
>30
0.47
30
30
>30
>30
Concerning aromatic R2/R3 substituents, most aromatic deriva-
tives, regardless of the position and type of functional group on the
phenyl ring, showed significant cytotoxicity with ED50 values of
1.2
0.41 0.47
2.1 0.84
0.51
3.1
4.3
0.01–2.1 lM. The only exception was the 3’-Br analog, 26, which
dramatically lost inhibitory activity and suggested that halogen
may not be favored at this position. Among all aromatic deriva-
tives, 15–27, 40-MeO analog 18 and 30-Me analog 24 were the most
potent against all tested tumor cell lines (ED50 values of 0.01–
0.50 0.47
0.16 0.15
0.14 0.14
0.22 0.17
>30 >30
0.27 0.20
>30 20.8
>30 10.9
>30 >30
21.5 19.7
0.60
0.19
0.15
0.29
>30
0.25
>30
>30
>30
17.6
0.76
0.23
0.14
0.27
>30
0.30
>30
>30
>30
16.2
0.64
0.26
0.15
0.30
>30
0.32
>30
>30
>30
17.4
4.7
0.38
0.08
0.50
>30
0.53
>30
>30
3.9
0.76
lM). Naphthyl analog 27 also displayed potent activity
(ED50 = 0.27–0.53
lM). These results may indicate that an aromatic
group is suitable to fit into the binding pocket of the target protein,
resulting in potent activity.
We also investigated the difference between hydrogen and
ethyl as the R1 substituent by comparison of 14 and 31, respec-
tively. Compound 14 was 5- to 38-fold more potent than the
18.2
a
Mean ED50
(lM), from three or more independent tests.
b
Standard deviations are provided in Supplementary data.

Y. Dong et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4085–4087
4087
related R1-ethyl analog, 31. Thus, hydrogen is favored over ethyl in
Supplementary data
ring-A, which contrasts with the SAR of 1-analogs. Moreover, 14
displayed broader antitumor activity compared with 1, which
could suggest a different mechanism of action. Interestingly, ana-
log 30 showed unique selective activity against the ZR-75-1 cell
Supplementary data (spectroscopic data for 9–31 and statistical
analysis (standard deviations) for cytotoxicity data) associated
with this article can be found, in the online version, at
doi:10.1016/j.bmcl.2010.05.079.
line (ED50 = 3.9
>30 M).
lM) compared with other tested cell lines (ED50
l
In conclusion, we designed 4-amino-2H-benzo[h]chromen-2-
one (ABO) analogs by structural simplification and bio-isosteric
replacement of neo-tanshinlactone (1), and investigated in vitro
antitumor activity. The results indicated that ring-D of 1 is critical
to both potency and tumor-tissue selectivity. Based on this study, a
novel class of anti-cancer agents, ABO derivatives, was discovered
and preliminary SAR around this scaffold was established as fol-
lows: (1) secondary amine (R2 or R3 = H) is preferred over tertiary
amine (R2 and R3 – H); (2) bulky groups are favored at R2/R3 posi-
tion; (3) 30-bromo phenyl group can cause dramatic loss of po-
tency, and (4) at R1 position, a hydrogen is better than an ethyl
group. Compounds 18 and 24 were the most potent analogs
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This work was supported by NIH Grant CA-17625 from the Na-
tional Cancer Institute, awarded to K.-H.L.