Discovery of 4-aryl-2-oxo-2H-chromenes as a new series of apoptosis
inducers using a cell- and caspase-based high-throughput screening assay
William Kemnitzer
a
, Songchun Jiang
a
, Hong Zhang
a
, Shailaja Kasibhatla
a
, Candace Crogan-Grundy
a
,
Charles Blais
b
, Giorgio Attardo
b
, Real Denis
b
, Serge Lamothe
b
, Henriette Gourdeau
b
, Ben Tseng
a
,
John Drewe
a
, Sui Xiong Cai
a,
*
a
Epicept Corporation, Inc. 6650 Nancy Ridge Drive, San Diego, CA 92121, USA
b
Shire Biochem Inc., 275 Armand-Frappier Blvd., Laval, Que., Canada H7V 4A7
article info
Article history:
Received 16 July 2008
Revised 26 August 2008
Accepted 2 September 2008
Available online 6 September 2008
Keywords:
Apoptosis inducers
Anticancer agents
abstract
As a continuation of our efforts to discover and develop the apoptosis inducing 4-aryl-4H-chromenes as
potential anticancer agents, we explored the removal of the chiral center at the 4-position and prepared a
series of 4-aryl-2-oxo-2H-chromenes. It was found that, in general, removal of the chiral center and
replacement of the 2-amino group with a 2-oxo group were tolerated and 4-aryl-2-oxo-2H-chromenes
exhibited SAR similar to 4-aryl-2-amino-4H-chromenes. The 4-aryl-2-oxo-2H-chromenes with a N-
methyl pyrrole fused at the 7,8-positions were highly active with compound 2a having an EC
50
value
of 13 nM in T47D cells. It was found that an OMe group was preferred at the 7-positon. 7-NMe
2
,7-
NH
2
, 7-Cl and 7,8 fused pyrido analogs all had low potency. These 4-aryl-2-oxo-2H-chromenes are a ser-
ies of potent apoptosis inducers with potential advantage over the 4-aryl-2-amino-4H-chromenes series
via elimination of the chiral center at the 4-position.
Ó 2008 Elsevier Ltd. All rights reserved.
Apoptosis, or programmed cell death, is the process for elimi-
nating excessive cells that may threaten tissue homeostasis and or-
gan morphogenesis. Unlike necrotic cell death, apoptosis involves a
series of precisely regulated events, including condensation of the
nucleoplasm and cytoplasm, chromosomal DNA fragmentation,
and the formation of apoptotic bodies, which are rapidly recog-
nized and eliminated by phagocytes.
1
The mechanism of apoptosis
has been intensively studied over the past decade and two path-
ways have been identified, both involving a cascade of initiator
and effector caspases.
2
Caspase-3 is the main executioner of apop-
tosis by cleaving multiple protein substrates in cells, leading to
irreversible cell death.
3
Defects in the apoptotic machinery is one
of the mainstays of cancers that leads to uncontrollable tumor cell
growth, as well as tumor resistance to chemotherapeutic treat-
ment.
4
Not surprisingly, many of the clinically useful cytotoxic
agents are known to induce apoptosis in cancer cells
5
and intense
efforts are ongoing to identify apoptosis inducers.
1,6
We have been
interested in the discovery and development of apoptosis inducers
as potential anticancer agents,
7
and have therefore developed a
cell-based high throughput-screening technology for apoptosis
inducers using our proprietary fluorescent caspase-3 substrate.
8
We have reported the discovery and structure–activity relation-
ships (SAR) of 4-aryl-4H-chromenes as a new series of potent
apoptosis inducers using our cell- and caspase-based Anti-cancer
Screening Apoptosis Program (ASAP) HTS assays. These compounds
were found to be tubulin inhibitors binding at or near the bind-
ing site of colchicine, with vascular disrupting activity and high
in-vivo activity in several anticancer animal models.
9,10
From
our screening hit 2-amino-3-cyano-7-dimethylamino-4-(3-meth-
oxy-4,5-methylenedioxy-phenyl)-4H-chromene (1a) (Chart 1), we
have identified 2-amino-4-(3-bromo-4,5-dimethoxyphenyl)-3-cy-
ano-7-dimethylamino-4H-chromene (1b) as a lead compound.
11
Additional SAR studies showed that cyclization of the 7,8-posi-
tions into a ring structure led to potent compounds, such as
2-amino-4-(3-bromo-4,5-dimethoxyphenyl)-3-cyano-4,7-dihydropyr-
rolo[2,3-h]chromene.
12
Introduction of a methyl group at the 7-po-
sition of the pyrrolo ring led to highly potent compounds such as
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.09.011
* Corresponding author. Tel.: +1 858 202 4006; fax: +1 858 202 4000.
E-mail address: scai@epicept.com (S.X. Cai).
Br
O
CN
NH
2
Me
2
N
OMe
MeO
1a
1b
OMe
O
CN
NH
2
Me
2
N
O
O
Br
O
CN
NH
2
OMe
MeO
1c
N
Chart 1.
Bioorganic & Medicinal Chemistry Letters 18 (2008) 5571–5575
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl