Author's personal copy 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