Discovery of 5-HT 6 receptor ligands based on virtual HTS Stefan Tasler, a, * Ju ¨ rgen Kraus, a Andreas Wuzik, a Oliver Mu ¨ ller, a Andrea Aschenbrenner, a Elena Cubero, b, * Rosalia Pascual, b Jordi-Ramon Quintana-Ruiz, b Alberto Dordal, b Ramon Merce ` b and Xavier Codony b a 4SC AG, Am Klopferspitz 19a, 82152 Planegg-Martinsried, Germany b ESTEVE, Av. Mare de De ´u de Montserrat 221, 08041 Barcelona, Spain Received 16 July 2007; revised 5 September 2007; accepted 5 September 2007 Available online 8 September 2007 Abstract—Based on a pharmacophore alignment on a 5-HT 6 ligand applying 4SCan Ò technology, a new lead series was identified and further structurally investigated. K i s down to 8 nM were achieved. Ó 2007 Elsevier Ltd. All rights reserved. The human 5-HT 6 receptor was first reported in 1996 and is now one of at least fourteen 5-HT receptors, which are grouped into seven families 5-HT 1 through 5-HT 7 . Except for 5-HT 3 , which is a ligand-gated ion channel, all subtypes represent GPCRs. The 5-HT 6 receptor is almost exclusively expressed in the CNS, it is positively coupled to adenylate cyclase and appears to regulate glutaminergic and cholinergic neuronal activity. For its pharmacological function, an involve- ment in schizophrenia, cognition, memory and learning, appetite control, convulsive disorder, affective state, and seizure is discussed. A few representatives of 5-HT 6 ligands have already entered clinical trials for the thera- peutic indications anxiety and cognitive impairment associated with schizophrenia and Alzheimer’s disease and displayed first encouraging results. 1 As crystal structure data was not available for this receptor, a usually preferable in silico docking approach could not be applied to the discovery of new structural types of 5-HT 6 ligands. Based on a highly potent agonist E-6837 (Fig. 1), which was generated at Esteve by focused syntheses of designed molecules, 2,3 a pharmaco- phore alignment on this compound was performed using 4SCan Ò4 with a virtual library of around 3.3 Mio commercially available compounds. A set of top 2000 compounds with the highest alignment score was further cross evaluated—likewise by alignment—against other known 5-HT 6 receptor ligands (e.g., SB-271046, SB- 357134, Ro 04-6790; K i s = 1.3, 3.2 and 50 nM, respec- tively), 5 to give additional criteria for a final selection of 235 compounds, which was submitted for biological testing in a binding assay on the 5-HT 6 receptor. 6 This initial screen directly led to the identification of three structurally closely related compounds 1–3 with K i values down to 61 nM (Fig. 1). Nitroarene 1 was identi- fied to be a partial agonist, 7 for which a receptor profile (72 targets) was screened at a compound concentration of 10 lM, including adrenoceptors, dopaminergic, 0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2007.09.016 Keywords: Serotonin receptor; 5-HT 6 ; GPCR; Molecular modeling; vHTS. * Corresponding authors. Fax: +49 89 70076329 (S.T.), +34 93 450 1611 (E.C.); e-mail addresses: stefan.tasler@4sc.com; ecubero@ esteve.es NO 2 H N N N O NO2 H N N N H O NO2 H N NH NH2 Ki = 61 nM Ki = 163 nM K i = 1490 nM 1 2 3 NH S NH N Cl O O E-6 837 Ki = 0.7 nM Figure 1. Template for a pharmacophore alignment and hit structures 1–3 from biological testing. Available online at www.sciencedirect.com Bioorganic & Medicinal Chemistry Letters 17 (2007) 6224–6229