This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2017 New J. Chem., 2017, 41, 347--357 | 347 Cite this: New J. Chem., 2017, 41, 347 Identification and development of pyrazolo[4,3-c]- pyridine carboxamides as Mycobacterium tuberculosis pantothenate synthetase inhibitors† Suresh Amaroju, a Mahalakshmi Naidu Kalaga, a Singireddi Srinivasarao, a Agnieszka Napio ´ rkowska, b Ewa Augustynowicz-Kopec ´ , b Sankaranarayanan Murugesan, c Subhash Chander, c Rangan Krishnan a and Kondapalli Venkata Gowri Chandra Sekhar* a The purpose of this study was to prepare various 1-((1-(substituted)-1H-1,2,3-triazol-4-yl)methyl)-N,3- diphenyl-6,7-dihydro-1H-pyrazolo[4,3-c]pyridine-5(4H)-carboxamides using click chemistry. The synthesized compounds were characterized using various analytical techniques like NMR spectroscopy, mass spectrometry, and elemental analysis and screened for in vitro antitubercular activity against Mycobacterium tuberculosis (MTB) H37Rv strain and two ‘wild’ strains Spec. 210 and Spec. 192 using a classical test-tube method of successive dilution in Youmans’ modification of the Proskauer and Beck liquid medium and were evaluated for a MTB pantothenate synthetase (PS) inhibition study as well. The final analogues exhibited minimum inhibitory concentration ranging from 24.72 to 4200 mM. Among the compounds, 1-((1-(4- methoxyphenyl)-1H-1,2,3-triazol-4-yl)methyl)-N,3-diphenyl-6,7-dihydro-1H-pyrazolo[4,3-c]pyridine-5(4H)- carboxamide (7d) was found to be the most active compound with IC 50 1.01 Æ 0.32 mM against MTB PS; it inhibited MTB with MIC 24.72 mM and it was non-cytotoxic at 50 mM in the RAW 267 cell line. Further, 7d was docked into the crystal structure of MTB PS to investigate its binding interaction pattern. Introduction Tuberculosis (TB) is contagious and airborne. It has a major impact on society due to the emergence of multi-drug resistant strains of Mycobacterium tuberculosis (MTB). In addition, multidrug-resistant Mycobacterium tuberculosis (MDR-TB) and especially extensively drug resistant TB (XDR-TB) are now increasing in incidence in many areas around the world. 1 Around 9.6 million people fell ill with TB in 2014, including 1.2 million cases among people living with HIV. Globally in 2014, an estimated 0.48 million developed MDR-TB and there were an estimated 0.19 million deaths from MDR-TB. 1 There- fore, the development of new therapeutic drugs targeting MDR- TB and XDR-TB is important due to the lack of effective drug treatments. 2 The treatment of TB infections is generally carried out through the use of a combination of drugs including isoniazid (INH), rifampicin (RMP), pyrazinamide, ethambutol (ETB) and streptomycin. 3–6 In order to overcome the issue of resistance there is a challenging need to develop new drugs using novel targets of MTB. The biosynthetic pathway of pantothenate involves four steps catalyzed by panB, panC, panD, and panE genes. 7 The last step of pantothenate biosynthesis, viz., the ATP-dependent condensation of D-pantoate and b-alanine to form pantothenate, is catalyzed by PanC. Pantothenate is essential for several processes such as cell signaling, fatty acid metabolism, and synthesis of non-ribosomal peptides and polyketides. 8 The biosynthesis of pantothenate is essential for the growth of MTB. The pantothenate biosynthesis pathway is a latent drug target and hence is important for determining the growth and virulence of MTB, and PS is a very good target for developing new therapeutics to treat TB. 9,10 Till now many MTB PS inhibitors have been reported (Fig. 1), which include 5-tert-butyl-N-pyrazol-4-yl-4,5,6,7-tetra- hydrobenzo[ d]isoxazole-3-carboxamide derivatives (a), 8 3-phenyl- 4,5,6,7-tetrahydro-1H-pyrazolo[4,3- c]pyridine derivatives (b), 11 2,6- disubstituted 4,5,6,7-tetrahydrothieno[2,3- c]pyridine-3-carboxamide a Department of Chemistry, Birla Institute of Technology and Science-Pilani, Hyderabad Campus, Jawahar Nagar, Shameerpet Mandal, R. R. Dist. Hyderabad, 500078, Telangana, India. E-mail: kvgc@hyderabad.bits-pilani.ac.in, kvgcs@yahoo.com b Microbiology Department, National Tuberculosis and Lung Diseases Research Institute, 01-138 Warsaw, Poland c Medicinal Chemistry Research Laboratory, Department of Pharmacy, Birla Institute of Technology & Science, Pilani, 333031, India † Electronic supplementary information (ESI) available: Photophysical data, copies of NMR spectra for products and single crystal X-ray data. CCDC 1500428. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c6nj02671k Received (in Montpellier, France) 26th August 2016, Accepted 9th November 2016 DOI: 10.1039/c6nj02671k www.rsc.org/njc NJC PAPER Published on 10 November 2016. Downloaded on 11/01/2017 09:48:53. View Article Online View Journal | View Issue