Synthesis, antimycobacterial activity evaluation and mode of action of series of novel diketones

Background: The emergence and development of drug-resistant strains of bacteria are increasing threat to the society. More than 2 million people in the US alone become ill every year due to antibiotic-resistant infections and 23000 die from such infections. In EU, 25000 patients die annually as a result of infections caused by resistant bacteria. WHO estimates that 9 million people developed active tuberculosis in 2013 and 1.5 million people died from it. Multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis continue to spread worldwide with an estimated 480 000 new cases in 2013. Emergence of XDR-TB and TDR-TB has emphasized the necessity for development of new drugs that can effectively combat these newly evolved resistant strains of M. tuberculosis.
Material/methods: A series of 17 novel diketones were synthesised using substituted acetophenones and benzoyl chlorides by the Baker Venkataraman Reaction and were characterised using spectroscopic techniques IR, LC-MS, 1H and 13C-NMR. The minimum inhibtory concentration (MIC) of the synthesised compounds was evaluated against Mycobacterium smegmatis and Mycobacterium bovis BCG using broth micro-dilution assay according to CSLI guidelines. The in vitro cytotoxicity of the synthesised compounds was evaluated against murine macrophage J774 cell line by performing MTT assay. Scanning electron microscopy was performed to investigate the mode of action of the lead compound by treating the cells with 10 X MIC of the lead compound and Isoniazid.
Results: Two compounds 02 and 03 were found to have activity against Mycobacterium bovis BCG with MIC of 1 µg/ml and 2 µg/ml respectively. Compound 02 and compound 03 exhibited IC50 values of 23 µg /ml and 35 µg /ml respectively against J774 cells. The preliminary examination of Scanning Electron Microscopy (SEM) clearly shows the morphological changes in the cells that were treated with compounds 02 and 03, figure1. The whole genome sequencing will be performed to further confirm the mode of action.

Conclusions: The synthesised compounds are found to be active against Mycobacterium smegmatis and Mycobacterium bovis BCG. Further studies on mode of action and structure activity relationships will allow the development of more potent active compounds.