Synthesis and biological evaluation of 1,4-benzodiazepin-2-ones with antitrypanosomal activity John Spencer a,⇑ , Rajendra P. Rathnam a , Alan L. Harvey b , Carol J. Clements b , Rachel L. Clark b , Michael P. Barrett c , Pui Ee Wong c , Louise Male d , Simon J. Coles d , Simon P. Mackay b a School of Science, University of Greenwich at Medway, Chatham ME4 4TB, UK b Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK c Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation College of Medical, Veterinary and Life Sciences, Glasgow Biomedical Research Centre, University of Glasgow, 120 University Place, Glasgow G12 8TA, UK d UK National Crystallography Service, School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK article info Article history: Received 3 November 2010 Revised 23 December 2010 Accepted 5 January 2011 Available online 14 January 2011 Keywords: Parallel synthesis Microwaves Benzodiazepines Trypanosoma abstract A library of 1,4-benzodiazepines has been synthesized and evaluated against Trypanosoma brucei, a caus- ative parasite of Human African trypanosomiasis. Benzodiazepines possessing a P2- transporter motif were found to have MIC values as low as 0.78 lM. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Human African Trypanosomiasis (HAT or sleeping sickness) is caused by two subspecies of the parasite T. brucei, namely Trypan- osoma brucei rhodesiense (causing East African sleeping sickness) or Trypanosoma brucei gambiense (causing West African sleeping sick- ness). 1–5 Approximately 50,000 people are reported with this dis- ease annually although over 300,000 are infected but have not been diagnosed or treated. Current therapies for HAT have been in use for several decades (Fig. 1) 1–5 and, not surprisingly, have many shortcomings viz. high toxicity, prohibitive costs, undesirable routes of administration as well as poor efficacy. Melaminophenyl arsenicals, for example, melarsoprol, and diamidines, including pentamidine, possess ami- no-purine transporter (termed P2-) recognition motifs to facilitate access to the parasite; loss of this transporter accounts for added complications of drug resistance. 5 There is an urgent need for more effective treatments for HAT. We recently reported a series of 1,4-benzodiazepin-2,5-diones (Fig. 2) structurally related to the paullone nucleus, 6 which inter alia were tractable for parallel synthesis, drug discovery and lead generation with antileishmanial and antitrypanosomal activities. 7 Given the structural similarity of this series with 1,4-benzodiaze- pine-2-ones 8 (BZDs), we will describe the synthesis and biological evaluation of a library of the latter and their evaluation as antitry- panosomal agents. 2. Results and discussion C3 and C5 substituted BZDs 5–12 were synthesised from readily available 2-amino phenylketones 1–4 in a three step process, often without the need for purification. 8,9 The nitro analogue 14 was synthesised by treatment of 13 with KNO 3 in concentrated H 2 SO 4 (Scheme 1, Table 1). N1-Substituted BZD analogues 17–40 were synthesised by treating BZDs 5–16 with sodium hydride and alkyl- ation with the appropriate alkyl or benzyl halide. All of the synthesised compounds were screened for antitrypan- osomal activity against the bloodstream form of T. b. brucei strain S247 using the alamar blue assay technique. Minimum inhibitory concentrations (MIC) were determined by calculation of the per- centage of control values and confirmed by microscopic examina- tion. Preliminary biological evaluation of the parent N1 unsubstituted BZDs was performed and the following SAR was noted (Table 1): Substitution at the C3 position is important for biological activ- ity with the (S)-benzyl substituted compound 8 displaying an MIC value of 6.25 lM as opposed to 400 lM for the Valium-like 5 (entries 4 and 1, respectively). 0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2011.01.010 ⇑ Corresponding author. Tel.: +44 208 331 8215; fax +44 208 331 9805. E-mail address: j.spencer@gre.ac.uk (J. Spencer). Bioorganic & Medicinal Chemistry 19 (2011) 1802–1815 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry journal homepage: www.elsevier.com/locate/bmc