Discovery of pyrazolo[1,5-a]pyridines as p110a-selective PI3 kinase inhibitors Jackie D. Kendall a,b,⇑ , Patrick D. O’Connor a , Andrew J. Marshall a , Raphaël Frédérick a,  , Elaine S. Marshall a , Claire L. Lill c , Woo-Jeong Lee c , Sharada Kolekar c , Mindy Chao c , Alisha Malik c , Shuqiao Yu c , Claire Chaussade b,c,à , Christina Buchanan b,c , Gordon W. Rewcastle a,b , Bruce C. Baguley a,b , Jack U. Flanagan a,b , Stephen M.F. Jamieson a,b , William A. Denny a,b , Peter R. Shepherd b,c a Auckland Cancer Society Research Centre, School of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand b Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand c Department of Molecular Medicine and Pathology, School of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand article info Article history: Received 30 August 2011 Revised 9 November 2011 Accepted 16 November 2011 Available online 25 November 2011 Keywords: PI3 kinase PI3K PIK3CA p110a Pyrazolo[1,5-a]pyridine Sulfonohydrazide abstract We have made a novel series of pyrazolo[1,5-a]pyridines as PI3 kinase inhibitors, and demonstrated their selectivity for the p110a isoform over the other Class Ia PI3 kinases. We investigated the SAR around the pyrazolo[1,5-a]pyridine ring system, and found compound 5x to be a particularly potent example (p110a IC 50 0.9 nM). This compound inhibits cell proliferation and phosphorylation of Akt/PKB, a downstream marker of PI3 kinase activity, and showed in vivo activity in an HCT-116 human xenograft model. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Phosphoinositide-3-kinases (PI3 kinases) are lipid kinases which phosphorylate the 3 0 -hydroxyl group of phosphatidyl- inositol 4,5-diphosphate (PIP2) to phosphatidylinositol 3,4,5-tri- phosphate (PIP3). PIP3 then recruits PH domain containing proteins such as protein kinase B (PKB, also known as Akt) to the cell membrane. Once recruited, PKB is phosphorylated and acti- vated, leading to a cascade of cell signalling which control a range of cellular processes like cell proliferation, growth and survival. 1 Furthermore, lipid phosphatase PTEN which dephosphorylates PIP3, is often deleted or inactivated in many cancer types, leading to increased levels of PIP3 and increased tumour survival. 2 The PI3 kinases are split into three sub-families (class I, II and III), and class I is further split into class Ia and Ib based upon their mechanism of activation. The class Ia PI3 kinases are heterodimer- ic, consisting of a catalytic subunit (p110a, p110b or p110d) in complex with a regulatory subunit. 1 PIK3CA, the gene encoding for p110a, is often over-expressed and mutated in many cancer types. Two of the most common of these mutations (E545K and H1047R) have been confirmed as activating mutations and hence increase levels of PIP3. Mutations in p110b and p110d have not yet been reported. 3 Inhibitors of PI3 kinase, and in particular selective inhibitors of p110a, could prove to be an important new strategy in cancer treatment. A recent report indicates that inhibiting p110a alone can block tumour progression 4 however there are few reports of p110a selective PI3 kinase inhibitors in the literature. 4–8 Many groups are now trying to exploit PI3 kinase inhibitors as an approach to cancer therapy, as exemplified by the number of small 0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2011.11.029 Abbreviations: ATP, adenosine triphosphate; Boc, tert-butoxycarbonyl; CDI, 1,1 0 - carbonyldiimidazole; DMF, N,N-dimethylformamide; DMSO, dimethyl sulfoxide; DNPH, O-(2,4-dinitrophenyl)hydroxylamine; EDTA, ethylenediaminetetraacetic acid; ip, intraperitoneal; MEM, minimum essential medium; MSH, O-(mesitylsulfo- nyl)hydroxylamine; PDB, protein data bank; PEG-400, polyethylene glycol with molecular weight 380–420 g mol À1 ; PH domain, pleckstrin homology domain; PIK- 75, N 0 -((6-bromoimidazo[1,2-a]pyridin-3-yl)methylene)-N,2-dimethyl-5-nitro- benzenesulfonohydrazide; PIP2, phosphatidylinositol 4,5-diphosphate; PIP3, phos- phatidylinositol 3,4,5-triphosphate; PI3 kinase, phosphoinositide-3-kinase; PKB, protein kinase B; PTEN, phosphatase and tensin homologue; p-TsOH, p-toluene- sulfonic acid monohydrate; q.d., daily; SAR, structure–activity relationship; THF, tetrahydrofuran; TFA, trifluoroacetic acid; tlc, thin layer chromatography; Tris, tris(hydroxymethyl)aminomethane. ⇑ Corresponding author. E-mail address: j.kendall@auckland.ac.nz (J.D. Kendall).   Present address: Drug Design and Discovery Centre (D 3 C), University of Namur, FUNDP, 61 rue de Bruxelles, 5000 Namur, Belgium. à Present address: Centre for Cell Signalling, Barts Cancer Institute, Queen Mary University of London, John Vane Science Centre, Charterhouse Square, London EC1M 6BQ, UK. Bioorganic & Medicinal Chemistry 20 (2012) 69–85 Contents lists available at SciVerse ScienceDirect Bioorganic & Medicinal Chemistry journal homepage: www.elsevier.com/locate/bmc