Synthesis and evaluation of heteroaryl-ketone derivatives as a novel class of VEGFR-2 inhibitors Eugene L. Piatnitski Chekler a, * , Reeti Katoch-Rouse a , Alexander S. Kiselyov a , Dan Sherman a , Xiaohu Ouyang a , Ki Kim a , Ying Wang b , Yaron R. Hadari b , Jacqueline F. Doody b a Department of Chemistry, ImClone Systems Incorporated, New York, NY 10014, USA b Department of Protein Science, ImClone Systems Incorporated, New York, NY 10014, USA article info Article history: Received 8 May 2008 Revised 20 June 2008 Accepted 24 June 2008 Available online 28 June 2008 Keywords: Angiogenesis Kinase inhibitor Vascular endothelial growth factor abstract We have discovered novel inhibitors of VEGFR-2 kinase with low nanomolar potency in both enzymatic and cell-based assays. Active series are heteroaryl-ketone compounds containing a central aromatic ring with either an indazolyl or indolyl keto group in the ortho orientation to the benzylic amine group (Fig. 1). The best compounds were demonstrated to be inactive against a small select panel of tyrosine and serine/ threonine kinases with the exception of VEGFR-1 kinase, a close family member. In addition, the lead can- didate 8 displayed acceptable exposure levels when administered orally to mice. Ó 2008 Elsevier Ltd. All rights reserved. Angiogenesis, or formation of new blood vessels, is a highly complex process that involves proliferation, migration, and tissue infiltration by capillary endothelial cells from pre-existing blood vessels. It is an important physiological process involved in embry- onic development, 1,2 follicular growth, and wound healing as well as in pathological conditions such as tumor growth. 3–6 Vascular endothelial growth factor (VEGF), 7,8 an endothelial cell-specific mitogen, is the primary regulator of angiogenesis in vivo and it mediates its biological effect through high-affinity VEGF tyrosine kinase receptors, which are expressed on the surface of endothelial cells. 9 VEGF binds with high affinity to VEGFR-2 (also known as Ki- nase Domain Region (KDR) 7,10,11 to induce activation of the angio- genic signaling pathway. Murine gene knockouts of VEGFR-2 pr VEGF have led to embryonic lethality, a result of disorganized vas- cular endothelial cells, indicating the pivotal role of VEGF in angi- ogenesis. 12–14 Additionally, several antagonists and inhibitors currently in preclinical and clinical development have shown tu- mor regression concomitantly with inhibited angiogenesis. 15,16 Therefore, a direct inhibition of the kinase activity of VEGFR-2 should result in the reduction of angiogenesis and the subsequent suppression of tumor growth. During screening of the ImClone compound collection, we iden- tified a heteroaryl-ketone compound 4 that demonstrated promis- ing inhibition of VEGFR-2. We were encouraged to pursue the hit by the precedent set by Manley et al. in which anthranilamide- based inhibitors recapitulated the potency and binding mode of PTK787. 17 Promising biological data for compound 4 prompted us to proceed with the structure–activity analysis of the series, the results of which are presented in this letter. The heteroaryl-ke- tone series is a novel entry in this class of inhibitors which seek to exploit a similar mode of binding to the kinase domain of VEGFR-2. One of the key structural features of the heteroaryl-ketone series was the ortho substitution of the central aromatic ring with a ke- tone moiety and an anilinyl NH group (Fig. 1). We speculated that the resulting intramolecular hydrogen bond would consequently hold the shape of the molecule into a pseudo-bicyclic ring system. 0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2008.06.083 * Corresponding author. Tel.: +1 718 473 5557; fax: +1 484 865 9399. E-mail address: piatnits@gmail.com (E.L. Piatnitski Chekler). N X N Hydrophobic region O H Variable Tight binding pocket Region II Aromatic Ring (Rigid) Key hydrogen bond interaction to hold the shape of the molecule Region I Region III R 2 R 1 R 3 X = N or CH Figure 1. Pharmacophore hypothesis for the mode of binding of heteroaryl-ketones within the ATP-binding pocket of VEGFR-2. Bioorganic & Medicinal Chemistry Letters 18 (2008) 4344–4347 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl