Discovery of 1,4-Disubstituted 3-Cyano-2-pyridones: A New Class of Positive Allosteric Modulators of the Metabotropic Glutamate 2 Receptor Jose María Cid,* ,† Guillaume Duvey, ⊥ Gary Tresadern, † Vanthea Nhem, ⊥ Rocco Furnari, ⊥ Philippe Cluzeau, ⊥ Juan Antonio Vega, † Ana Isabel de Lucas, † Encarnació n Matesanz, † Jose ́ Manuel Alonso, † María Lourdes Linares, † Jose ́ Ignacio Andre ́ s, † Sonia M. Poli, ⊥ Robert Lutjens, ⊥ Hassan Himogai, ⊥ Jean-Philippe Rocher, ⊥ Gregor J. Macdonald, ‡ Daniel Oehlrich, ‡ Hilde Lavreysen, § Abdelah Ahnaou, § Wilhelmus Drinkenburg, § Claire Mackie, ∥ and Andre ́ s A. Trabanco † † Neuroscience Medicinal Chemistry, Janssen Research & Development, Janssen-Cilag S.A., Jarama 75, 45007-Toledo, Spain ‡ Neuroscience Medicinal Chemistry, § Neuroscience Biology, and ∥ Discovery ADME/Tox, Janssen Research & Development, Janssen Pharmaceutica NV, Turnhoutseweg 30, B-2340, Beerse, Belgium ⊥ Addex Pharmaceuticals, 12 Chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland * S Supporting Information ABSTRACT: The discovery and characterization of compound 48, a selective and in vivo active mGlu2 receptor positive allosteric modulator (PAM), are described. A key to the discovery was the rational exploration of the initial HTS hit 13 guided by an overlay model built with reported mGlu2 receptor PAM chemotypes. The initial weak in vitro activity of the hit 13 was quickly improved, although compounds still had suboptimal druglike properties. Subsequent modulation of the physicochemical properties resulted in compounds having a more balanced profile, combining good potency and in vivo pharmacokinetic properties. Final refinement by addressing cardiovascular safety liabilities led to the discovery of compound 48. Besides good potency, selectivity, and ADME properties, compound 48 displayed robust in vivo activity in a sleep−wake electroencephalogram (sw-EEG) assay consistent with mGlu2 receptor activation, in accordance with previous work from our laboratories. ■ INTRODUCTION Glutamate is the major excitatory neurotransmitter in the central nervous system (CNS) of vertebrates and modulates the synaptic response via activation of either ionotropic (iGlu) or metabotropic glutamate (mGlu) receptors. 1−3 Eight G-protein- coupled mGlu receptor subtypes are known and have been classified into three groups based on homology, pharmacology, and signaling pathways: group I, mGlu1 and mGlu5 receptors; group II, mGlu2 and mGlu3 receptors; group III, mGlu4, -6, -7, and -8 receptors. 4,5 Group I receptors are primarily expressed postsynaptically, whereas both groups II and III are mainly presynaptic where they reduce glutamate release. 6,7 The group II mGlu2 receptor is widely distributed in the brain, and high levels are found in forebrain and limbic areas such as prefrontal cortex, hippocampus, and amygdala where excessive glutamate neurotransmission may be implicated in the pathophysiology of anxiety and schizophrenia. 8−11 It is therefore expected that activation of mGlu2 receptors may provide anxiolytic and/or antipsychotic effects. 12−15 This was confirmed in a phase II trial with LY2140023, a prodrug of the mixed mGlu2/3 receptor agonist LY404039, which showed improvements in positive and negative symptoms in schizophrenic patients. 16 In addition, anxiolytic efficacy of the agonist LY354740 was demonstrated in a CO 2 inhalation study by reduction in number and severity of panic symptoms in patients with DMS-IV panic disorder. 17 Multiple preclinical studies have shown the efficacy of mGlu2 receptor activation in animal models of disorders such as anxiety/stress and depression. 18,19 Constrained glutamate agonists such as LY404039 and LY354740 bind at the orthosteric site, and behavioral studies in knockout mice suggest that their activity is mGlu2 receptor mediated. 20,21 Receptor activation with positive allosteric modulators (PAMs) which act via alternative allosteric site(s) offers several advantages. First, allosteric molecules are likely to be less polar and have improved CNS penetration, as they do not require amino acid functional groups necessary at the orthosteric site. The allosteric site(s) can be less conserved and therefore allow improved mGlu receptor subtype selectivity. They only act in the presence of endogenous glutamate and so may be less prone to cause receptor desensitization, 22,23 and they respond to physiological glutamate fluctuations. Given these potential advantages, the number of reported mGlu2 receptor PAM chemical series has increased over the past years Received: December 14, 2011 Published: February 24, 2012 Article pubs.acs.org/jmc © 2012 American Chemical Society 2388 dx.doi.org/10.1021/jm2016864 | J. Med. Chem. 2012, 55, 2388−2405