Discovery and synthesis of novel benzofurazan derivatives as inhibitors of influenza A virus Ulrich Kessler a , Daniele Castagnolo b , Mafalda Pagano b , Davide Deodato b , Martina Bernardini b , Beatrice Pilger a , Charlene Ranadheera a , Maurizio Botta b,c,⇑ a PiKe Pharma GmbH, Zurich, Switzerland b Dipartimento Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, via A. Moro, 53100 Siena, Italy c Sbarro Institute for Cancer Research and Molecular Medicine, Center for Biotechnology, College of Science and Technology, Temple University, BioLife Science Bldg., Suite 333, 1900 N 12th Street, Philadelphia, PA 19122, USA article info Article history: Received 28 June 2013 Revised 8 August 2013 Accepted 9 August 2013 Available online 17 August 2013 Keywords: Antiviral agents Influenza virus Viral RNA polymerase Benzofurazan H1N1 abstract The identification of a novel hit compound inhibitor of the protein–protein interaction between the influ- enza RNA-polymerase PA and PB1 subunits has been accomplished by means of high-throughput screen- ing. A small family of structurally related molecules has been synthesized and biologically evaluated with most of the compounds showing micromolar potency of inhibition against viral replication. Ó 2013 Elsevier Ltd. All rights reserved. Human influenza viruses belong to the Orthomyxoviridae family, which consists of the genera influenza A, B, and C viruses. The Orthomyxoviridae are enveloped viruses containing a seg- mented, single-stranded, negative-sense RNA genome. While influenza A (FluA) viruses naturally infect a variety of animal as well as humans, influenza B (FluB) and C (FluC) viruses have been isolated predominantly from humans so far. 1 The recent emergence of the novel H1N1 influenza virus of swine origin 2–4 has directed the world’s attention towards influenza A viruses due to their ability to cause global pandemics, such as the 1918 ‘Spanish’ flu. Over the past century, mankind has relied mainly on vaccination in the fight against viral pathogens. As a conse- quence, very few antiviral drugs are available to date. However, in the absence of vaccines during the first wave of infections, antivirals are the only direct medical intervention for providing both protection against disease and therapeutic benefit to in- fected persons. Of the two classes of drugs approved for clinical use against influenza, the oldest and most affordable molecules are the M2 inhibitors, amantadine 1 and rimantadine 2. 5 How- ever, their use is actively discouraged due to huge viral resistance worldwide. The second class of anti-influenza drugs is repre- sented by the neuraminidase (NA) inhibitors, namely the oseltamivir (3, Tamiflu Ò ) and the zanamivir (4, Relenza Ò ) pos- sessing an improved safety profile when compared to M2 inhibi- tors (Fig. 1). Nevertheless, many influenza A strains, including the H1N1 strains circulating in Europe and in the US, are already resistant to oseltamivir, 6,7 suggesting a limited range of use for this type of drug. Moreover, the drug resistance is not restricted to FluA only, since the emergence of FluB viruses with reduced sensitivity to neuraminidase inhibitors has been recently demonstrated. 8,9 Hence, due to the continued emergence of new influenza variants, drug-resistant mutants and potential pandemic strains, our interest was directed toward the identification and develop- ment of new effective antiviral therapeutics. Over the last two decades, an increasing research effort has focused on the modu- lation of protein–protein interactions (PPIs) in order to develop novel therapeutic approaches and target-selective agents in drug discovery. The trimeric influenza RNA polymerase complex, consisting of the PB1, PB2 and PA subunits, is an attractive target for inhibition of viral replication due to the high level of conser- vation among different viruses and the low risk of resistance development. Since the N-terminal PA-interaction domain is highly conserved in different virus strains, molecules able to block the crucial PA–PB1 interaction can be expected to inhibit most, if not all, influenza viruses. Recently, Schwemmle et al. 10 reported the feasibility of targeting the protein–protein 0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bmcl.2013.08.048 ⇑ Corresponding author. Tel.: +39 0577 234306; fax: +39 0577234333. E-mail addresses: botta.maurizio@gmail.com, botta@unisi.it (M. Botta). Bioorganic & Medicinal Chemistry Letters 23 (2013) 5575–5577 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl