Substituted 5,7-Diphenyl-pyrrolo[2,3d ]pyrimidines: Potent Inhibitors of the Tyrosine Kinase c-Src Martin Missbach, a, * Eva Altmann, a Leo Widler, a Mira S Ï usÏ a, a Elisabeth Buchdunger, b Helmut Mett, b Thomas Meyer b and Jonathan Green a a Novartis Pharma AG, Therapeutic Areas Arthritis & Bone Metabolism, CH-4002 Basel, Switzerland b Novartis Pharma AG, Department of Oncology, CH-4002 Basel, Switzerland Received 2 February 1999; accepted 22 February 2000 AbstractÐ5,7-Diphenyl-pyrrolo[2,3d]pyrimidines represent a new class of highly potent inhibitors of the tyrosine kinase c-Src (IC 50 <50 nM) with speci®city against a panel of dierent tyrosine kinases. The substitution pattern on the two phenyl rings determines potency and speci®city and provides a means to modulate cellular activity. # 2000 Elsevier Science Ltd. All rights reserved. Introduction Compelling evidence indicates that the protein tyrosine kinase c-Src plays a unique and crucial role in osteo- clastic bone resorption. 1 4 Mutant mice with a dis- rupted Src gene have functionally inactive osteoclasts in the absence of any other overt pathological signs. c-Src may be responsible for the phosphorylation of cytoske- letal and/or docking proteins involved in the transloca- tion and exocytosis of vesicles during the resorptive process. Inhibitors of c-Src may be useful for the treat- ment of diseases characterized by excessive bone resorption such as osteoporosis and tumor-induced hypercalcemia. In addition, c-Src inhibitors could also be bene®cial in the treatment of c-Src overexpressing tumors, for example colon carcinoma. We started our investigation of substituted 5,7-diphenyl- pyrrolo[2,3d]pyrimidines as potential c-Src inhibitors based on the ®nding that the closely related pyrrazolo- pyrimidine CGP 191 inhibited c-Src phosphorylation with an IC 50 of 0.5 mM. The pyrrolopyrimidine analogue CGP 62464 proved to be ®ve times more potent (IC 50 =0.1 mM). 5 We therefore concentrated our eorts on optimising the 5,7-diphenyl-pyrrolo[2,3d]pyrimidine class with the aim to identify potent and speci®c com- pounds with good cellular activity. 6 Chemistry and methods The synthesis of a few 5,7-diphenyl-pyrrolo[2,3d]pyr- imidines had been described earlier, 7 but without any data on kinase inhibition. Our substituted 5,7-diphenyl- pyrrolo[2,3d]pyrimidines have been prepared as outlined by a generic example 8 in Scheme 1. The ®rst two steps to form the 2-amino-3-cyano-pyrrol usually gave yields between 50 and 80%. The sub- sequent 3-step cyclization to the pyrrolo[2,3d]pyr- imidine resulted in purer products than the alternative one pot reaction with formamide at high temperature and produced good yields of 65±85% over all three steps. 5,7-Diphenyl-pyrrolo[2,3d]pyrimidines with basic side chains were obtained by conversion of the hydroxy- methyl intermediate into the corresponding chloride, followed by treatment with various amines (neat or in a polar solvent). The proposed binding mode of CGP 62464 (compared to that of ATP) based on the pub- lished X-ray structure of human Src 9 is shown in Figure 2. According to this model, the 5,7-diphenyl-pyrrolo- [2,3d]pyrimidines bind at the ATP binding site in an orientation similar to that of ATP, making use of the same two hydrogen-bonds to and from the backbone of the enzyme (Met 341 and Glu 339). The 5-phenyl locks into a rather small pocket, which is not used by ATP itself. Similar interactions, as well as the existence of a hydrophobic pocket, have been proposed for the bind- ing mode of EGF-receptor inhibitors. 10 0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(00)00131-1 Bioorganic & Medicinal Chemistry Letters 10 (2000) 945±949 *Corresponding author. Fax: +41-61-6966071; e-mail: martin. missbach@pharma.novartis.com