Microwave-assisted synthesis, molecular docking and antitubercular activity of 1,2,3,4-tetrahydropyrimidine-5-carbonitrile derivatives Sahoo Biswa Mohan a,⇑ , B. V. V. Ravi Kumar a , S. C. Dinda b , D. Naik a , S. Prabu Seenivasan c , Vanaja Kumar c , Dharmarajsinh N. Rana d , Pathik S. Brahmkshatriya e a Department of Pharmaceutical Chemistry, Roland Institute of Pharmaceutical Sciences, Khodasinghi, Berhampur 760 010, India b School of Pharmaceutical Education and Research, Berhampur University, Odisha, India c Tuberculosis Research Centre, V.R. Ramanathan Road, Chennai 600 031, India d Department of Chemistry, Gujarat University, Ahmedabad, India e Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Systems, Flemingovo nám. 2, 166 10, Prague 6, Czech Republic article info Article history: Received 28 April 2012 Revised 24 September 2012 Accepted 5 October 2012 Available online 13 October 2012 Keywords: Antitubercular Binding interactions Luciferase reporter phage (LRP) assay Microwave-assisted Molecular docking abstract Based on bioisosteric similarities with isoniazid, a series of 1,2,3,4-tetrahydropyrimidine-5-carbonitrile derivatives has been designed. The target compounds have been synthesized by multicomponent reac- tion which involves one-pot organic reactions using ethylcyanoacetate, urea/thiourea and arylaldehydes in presence of ethanolic K 2 CO 3 . Two methodologies, conventional and microwave-assisted, have been adopted for the synthesis. The later strategy gave high yields in less than 10 min as compared to long hours using the former approach. Molecular docking of the target compounds into the enzyme Mycobac- terium tuberculosis enoyl reductase (InhA) revealed important structural information on the plausible binding interactions. Major binding interactions were found to be of dispersion type (residues Tyr158, Ile215, Met103 and Met199) and a hydrogen bond with Tyr158. Binding poses of the all the compounds were energetically favorable and showed good interactions with the active site residues. Few selected compounds were also evaluated for antitubercular activity in vitro against drug-sensitive M. tuberculosis H37Rv strain and clinically isolated S, H, R and E resistant M. tuberculosis by luciferase reporter phage (LRP) assay method. Some compounds displayed promising antimycobacterial activity comparable or less than the standard drugs isoniazid and rifampicin. Ó 2012 Elsevier Ltd. All rights reserved. Mycobacterium tuberculosis (MTB) is the underlying microor- ganism causing tuberculosis (TB) in humans. It is considered as the leading bacterial infectious agent. 1 Tuberculosis usually attacks the lungs but can also affect other parts of the body. It spreads through the air by patient’s cough, sneeze, or spit. 2 India accounts for nearly one-third of the global burden of tuberculosis and the disease is one of India’s most challenging public health problems. Approximately 2 million people acquire TB every year in India. 3 Furthermore, it is alarming to see the emergence of MTB strains resistant to all of the first line drugs (leading to the multi drug resistant TB, MDR–TB) and to isoniazid, rifampin, fluoroquinolone and at least one of three injectable second-line drugs (i.e., amika- cin, kanamycin, or capreomycin) (leading to the extensive drug- resistant TB, XDR–TB). 4 All the above facts reveal that there is an urgent need for the development of new potent drug molecules with unique divergent structure and novel mode of action which can be effective against resistant strains of mycobacteria. Isonicot- inic acid hydrazide (isoniazid, INH) belongs to the group of the first line antitubercular drugs being in clinical practice over 50 years. INH is believed to kill mycobacteria by inhibiting the biosynthesis of mycolic acids, critical component of the cell wall. 5 Thus, it was thought of interest to replace the pyridine ring of INH with its pyrimidine bioisostere (Scheme 1). This bioisosteric replacement followed molecular docking of the designed compounds into crys- tal structure of Mycobacterium tuberculosis enoyl reductase (InhA) (PDB Code 2H7I). 6 The present enzyme was chosen over a large number of other enoyl reductases as it has better resolution (1.62 Å) over many others (>2.0 Å). Compounds which were found promising in the docking study were evaluated for their antimycobacterial activity by luciferase reporter phage (LRP) assay method against M. tuberculosis H37Rv and clinically isolated S, H, R and E resistant M. tuberculosis at two concentrations (100 and 500 lg/ml). Multi-component reactions (MCRs) constitute a highly valuable synthetic tool for the construction of polyfunctionalized heterocy- clic compounds required for drug discovery programmes. 7,8 Thus, a series of 1,2,3,4-tetrahydropyrimidine-5-carbonitrile derivatives were synthesized based on multicomponent reaction (MCR) which involves one-pot organic reactions (Scheme 1). 9 This reaction 0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bmcl.2012.10.032 ⇑ Corresponding author. Tel.: +91 9040442719. E-mail address: biswamohan81@gmail.com (S.B. Mohan). Bioorganic & Medicinal Chemistry Letters 22 (2012) 7539–7542 Contents lists available at SciVerse ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl