Original article 1,4eDiarylpiperazines and analogs as anti-tubercular agents: Synthesis and biological evaluation D. Forge a, 1 , D. Cappoen b,1 , J. Laurent a , D. Stanicki a , A. Mayence c , T.L. Huang c , L. Verschaeve d , K. Huygen b, * , J.J. Vanden Eynde a, ** a University of Mons-UMONS, Laboratory of Organic Chemistry, 20 place du Parc, B-7000 Mons, Belgium b Scientific Institute of Public Health WIV-ISP, Service Immunology, Engelandstraat 642, B-1180 Ukkel, Belgium c Division of Basic Pharmaceutical Sciences, College of Pharmacy, Xavier University of Louisiana, 1 Drexel Drive, New Orleans, LA 70125, USA d Scientific Institute of Public Health WIV-ISP, Operational Directorate of Public Health and Surveillance, J. Wytsmanstraat 14, B-1050 Brussels, Belgium article info Article history: Received 22 November 2011 Received in revised form 19 December 2011 Accepted 22 December 2011 Available online 21 January 2012 Keywords: Mycobacterium tuberculosis 1,4-Diarylpiperazines Anti-mycobacterial activity Cytotoxicity abstract Despite progress in modern chemotherapy to combat tuberculosis, the causative pathogen Mycobacte- rium tuberculosis (M.tb.) is far from eradicated. Bacillary resistance to anti-mycobacterial agents, bacillary persistence and human immunodeficiency virus (HIV) co-infection hamper current drug treatment to completely cure the infection, generating a constant demand for novel drug candidates to tackle these problems. A small library of novel heterocyclic compounds was screened in a rapid luminometric in vitro assay against the laboratory M.tb. strain H37Rv. A group of amidines was found to have the highest potency and was further evaluated for acute toxicity against C3A hepatocytes. Next, the most promising compounds were evaluated for activity against a multi-drug resistant clinical isolate. The group of amidines was also tested for their ability to kill intracellular M.tb. residing in mouse J774A.1 macrophages. Finally, we report on a correlation between the structural differences of the compounds and their anti-mycobacterial activity. Ó 2012 Elsevier Masson SAS. All rights reserved. 1. Introduction Since the introduction of streptomycin in the early 20th century, modern chemotherapy has played a significant role in mankind’s fight against tuberculosis (TB) [1,2]. The actual standard first line treatment regimen is comprised of a combination of four drugs, i.e. isoniazid, rifampicin, ethambutol and pyrazinamide. Despite its efficacy to kill actively replicating Mycobacterium tuberculosis (M.tb.), the pathogen has not been eradicated [3]. Although some interesting new drug candidates are under devel- opment, the current drug regimen is more than 40 years old. Development of novel drug candidates is a slow process and M.tb. is a fearsome opponent [1,3,4]. With the unique structure of its thick, lipid-rich cell wall, it is hardly permeable for chemothera- peutic compounds [5]. The emergence of multi-drug resistant (MDR) M.tb., predominantly caused by non-compliance to the current drug regimen, has rendered the actual treatment ineffec- tive in many cases [5,6]. This is well documented through the data presented by the World Health Organization (WHO) [7]. Drug regimens with various second-line agents are needed for the treatment of MDR M.tb. On the flip side, expansion of the various drug regimens has resulted in a heavier burden for patients because of the increased toxicity of the treatment. At the same time, healthcare organizations have faced an increase in adminis- tration and production costs. Additional resistance to fluo- roquinolones (FQ) and (second-line) injectable drugs has led to emergence of extensively-drug resistant (XDR) M.tb., which caused new outbreaks of the disease at the start of the 21st century [5e7]. Another trait of M.tb. that makes it a difficult target for chemotherapy is that the bacillus is capable to become metaboli- cally inactive and to reside in a dormant stage within the host phagocytic cells. These ‘persister’ bacteria are estimated to survive in one third of the world population as a latent infection, but so far no active drugs against these dormant bacilli are available for therapy [8e10]. Moreover, the AIDS pandemic has exacerbated the situation, as persons co-infected with HIV present with an annual 10% risk to reactivate a latent TB infection, as compared to non-HIV * Corresponding author. Tel.: þ3223733370; fax: þ3223733367. ** Corresponding author. Tel.: þ3265373337. E-mail addresses: kris.huygen@wiv-isp.be (K. Huygen), Jean-Jacques.Vandeneynde@ umons.ac.be (J.J. Vanden Eynde). 1 Both authors contributed equally to this work. Contents lists available at SciVerse ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech 0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmech.2011.12.035 European Journal of Medicinal Chemistry 49 (2012) 95e101