4-Amino-6-arylamino-pyrimidine-5-carbaldehyde hydrazones as potent ErbB-2/EGFR dual kinase inhibitors Guozhang Xu * , Marta C. Abad, Peter J. Connolly, Michael P. Neeper, Geoffrey T. Struble, Barry A. Springer, Stuart L. Emanuel, Niranjan Pandey, Robert H. Gruninger, Mary Adams, Sandra Moreno-Mazza, Angel R. Fuentes-Pesquera, Steven A. Middleton Johnson & Johnson Pharmaceutical Research and Development, Medicinal Chemistry, 8 Clarke Drive, Cranbury, NJ 08512, USA article info Article history: Received 24 April 2008 Revised 7 July 2008 Accepted 8 July 2008 Available online 10 July 2008 Keywords: Receptor tyrosine kinase ErbB-2 EGFR Hydrazones Quinazoline Bioisostere abstract Members of a novel class of 4-amino-6-arylamino-pyrimidine-5-carbaldehyde hydrazones were identi- fied as potent dual ErbB-2/EGFR kinase inhibitors using concept-guided design approach. These com- pounds inhibited the growth of ErbB-2 over-expressing human tumor cell lines (BT474, N87, and SK- BR-3) in vitro. Compound 15 emerged as a key lead and showed significant ability to inhibit growth fac- tor-induced receptor phosphorylation in SK-BR-3 cells (IC 50 = 54 nM) and cellular proliferation in vitro (IC 50 = 14, 58, and 58 nM for BT474, N87, and SK-BR-3 respectively). The X-ray co-crystal structure of EGFR with a close analog (17) was determined and validated our design rationale. Ó 2008 Elsevier Ltd. All rights reserved. The type I receptor tyrosine kinases (RTK) are involved in vari- ous aspects of cell growth, survival, and differentiation. 1 Among the known RTKs, the epidermal growth factor receptor (EGFR) and ErbB-2 (HER-2) are two widely studied proteins that are pro- totypic members of the ErbB family that also includes ErbB-3 (Her-3) and ErbB-4 (HER-4). 2 Over-expression of ErbB-2 and EGFR has been associated with aggressive disease and poor patient prog- nosis in a range of human tumor types (e.g. breast, lung, ovarian, prostate, and squamous carcinoma of head and neck). 3 Disruption of signal transduction of these kinases has been shown to have an antiproliferative and therapeutic effect. 4 Various approaches have been developed to target the ErbB signaling pathways including monoclonal antibodies (trastuzumab/Herceptin Ò and cetuximab/ Erbitux Ò ) directed against the receptor and synthetic tyrosine ki- nase inhibitors (gefitinib/Iressa Ò , 2, and erlotinib/Tarceva Ò , 4). 5 Since many tumors over-express ErbB receptors and/or ligands, simultaneous targeting of multiple erbB receptors therefore be- comes a promising approach to cancer treatment. Lapatinib (Tyk- erb Ò , 3), a potent dual EGFR/ErbB-2 inhibitor, was recently approved for the treatment of ErbB-2 positive breast cancer. 6 Among various scaffolds employed as ErbB-2/EGFR kinase inhibitors (Fig. 1), 5c,6,7 the 4-anilinoquinazoline scaffold (2, 3, and 4) is the most commonly utilized template for inhibition of the ErbB family. The quinazoline moiety fits into the ATP-binding pocket in the kinase domain, while the aniline ring fills an adjacent lipophilic pocket. In an effort to develop non-anilinoquinazoline small molecular ATP-competitive ErbB-2/EGFR inhibitors as cancer therapeutics, we recently reported a novel series of 4-aminopyrimidine-5-carb- aldehyde oximes (6) 8 that are potent dual inhibitors of EGFR and ErbB-2 tyrosine kinases (Fig. 2). This scaffold effectively mimics the well-known quinazoline kinase template by forming a pseu- do-bicyclic structure with the help of an intramolecular hydrogen bond between the 4-amino group and the oxime nitrogen atom. Further bioisosteric replacement of the oxime moiety with hydra- zone leads to aminopyrimidine hydrazone (7), in which the intra- molecular NH...N@C hydrogen bond is maintained and would function as mimics of the phenyl ring of the quinazoline (Fig. 2). Although the hydrazone side chain is expected to orient toward the solvent front (vide infra), a cyclic N,N-disubstituted hydrazone might gain additional kinase potency due to the restricted bond rotation of the side chain. We report here the synthesis and struc- ture–activity relationships (SAR) of this series as dual ErbB-2/EGFR kinase inhibitors and the X-ray crystal structure of representative compound 17 in complex with EGFR. 4-Amino-6-arylaminopyrimidine-5-carbaldehyde hydrazones were synthesized according to the two-step sequence outlined in Scheme 1. Treatment of 4-amino-6-chloro-pyrimidine-5-carbalde- hyde (8) 9 with the appropriate aniline in DMSO at 100 °C for 3 h 0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2008.07.020 * Corresponding author. Tel.: +1 609 655 6915; fax: +1 609 655 6930. E-mail address: gxu4@prdus.jnj.com (G. Xu). Bioorganic & Medicinal Chemistry Letters 18 (2008) 4615–4619 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl