Short communicationSynthesis, structural activity relationship and anti-tubercular activity of novel pyrazoline derivatives
Graphical abstract
In the present investigation, a series of 5-(-4-(substituted) phenyl)-3-(4-hydroxy-3-methylphenyl)-4,5-dihydro-1H-1-pyrazolyl-2-toluidino methane thione and 5-(substituted) phenyl-3-(4-hydroxy-3-methylphenyl)-4,5-dihydro-1H-1-pyrazolyl-2-methoxyanilino methane thione were synthesized by the reaction between hydrazine hydrate and chalcones (3a–k) followed by condensation with appropriate aryl isothiocyanate which yielded N-substituted pyrazoline derivatives. Newly synthesized compounds were tested for their in vitro anti-tubercular activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system. Among the synthesized compounds, compound anilino-3-(4-hydroxy-3-methylphenyl)-5-(2,6-dichlorophenyl)-4,5-dihydro-1H-1-pyrazolylmethanethione (6i) was found to be more active agent against M. tuberculosis H37Rv with minimum inhibitory concentration of 0.0034 μM.
Introduction
Tuberculosis, an infectious disease caused by Mycobacterium tuberculosis, is the primary cause of mortality in the world. Mycobacteria are ubiquitous organisms that are becoming increasingly important intracellular pathogens that establish an infection in oxygen-rich macrophage of the lung [1]. The emergence of AIDS, decline of socioeconomic standards and a reduced emphasis on tuberculosis control programs contribute to the disease's resurgence in industrialized countries [2]. Resistance of M. tuberculosis strains to anti-mycobacterial agents is an increasing problem worldwide [3], [4], [5]. However, powerful new anti-TB drugs with new mechanism of action have not been developed in the last 40 years. In spite of severe toxicity on repeated dosing of isoniazid (INH), it is still considered to be a first line drug for chemotherapy of tuberculosis [6]. Literature survey reveals that pyrazoline derivatives are active against many mycobacteria [7], [8], [9], [10]. The current work describes the synthesis of novel pyrazoline moiety with encouraging anti-mycobacterial activity against M. tuberculosis H37Rv.
Section snippets
Chemistry
5-(-4-(Substituted) phenyl)-3-(4-hydroxy-3-methylphenyl)-4,5-dihydro-1H-1-pyrazolyl-2-toluidino methane thione and 5-(substituted) phenyl-3-(4-hydroxy-3-methylphenyl)-4,5-dihydro-1H-1-pyrazolyl-2-methoxyanilino methane thione (5a–k) and (6a–k) described in this study are shown in Table 1, Table 2, Table 3, and a reaction sequence for the preparation is outlined in Scheme 1. The chalcones were prepared by reacting 3-methyl-4-hydroxy acetophenone with appropriate aldehyde in the presence of a
Experimental
The entire chemicals were supplied by E. Merck (Germany) and SD Fine Chemicals (India). Melting points were determined by open tube capillary method and are uncorrected. Purity of the compounds was checked on thin layer chromatography (TLC) plates (silica gel G) in the solvent system toluene–ethyl formate–formic acid (5:4:1) and benzene–methanol (8:2), the spots were located under iodine vapors or UV light. IR spectra were obtained on a Perkin–Elmer 1720 FT-IR spectrometer (KBr pellets). 1H NMR
4-[5-(Substituted) phenyl-4,5-dihydro-1H-3-pyrazolyl]-2-methylphenol (4a–k)
To a solution of chalcone (3a–k) in ethanol, hydrazine hydrate (99%) was added drop wise. The reaction mixture was heated under reflux for 7 h and then cooled and poured onto crushed ice. The solid pyrazoline product was filtered and recrystallized from ethanol (4a–k).
3-(4-Hydroxy-3-methylphenyl)-5-(substituted) phenyl-4,5-dihydro-1H-1-pyrazolyl-2-toluidino methane thione (5a–k)
To a solution of pyrazoline (4a–k) (0.01 mol) in ethanol (20 ml) was added 2-methyl aryl isothiocyanate (1.501 ml, 0.01 mol) and the reaction mixture was refluxed for 4 h. The reaction mixture was cooled and then poured onto crushed ice. The obtained solid was filtered, washed with water and purified from ethanol to give compounds (5a–k).
3-(4-Hydroxy-3-methylphenyl)-5-(substituted) phenyl-4,5-dihydro-1H-1-pyrazolyl-2-methoxyanilino methane thione (6a–k)
To a solution of pyrazolines (0.01 mol) (4a–k) in ethanol (20 ml) was added 2-methoxy aryl isothiocyanate (1.661 ml, 0.01 mol) and the reaction mixture was refluxed for 4 h. The reaction mixture was cooled and then poured onto crushed ice. The obtained solid was filtered, washed with water and purified from ethanol to give compounds (6a–k).
Biology
The primary screening was conducted at concentration of 6.25 μg/ml (or molar equivalent of highest molecular weight compound in a series of congeners) against M. tuberculosis H37Rv (ATCC27294) in BACTEC 12B medium using the BACTEC 460 radiometric system [11], [12]. Compounds demonstrating at least 90% inhibition in the primary screen were re-examined at lower concentration (MIC) in broth micro-dilution assay with Almar Blue. The MIC was defined as the lowest concentration inhibiting 99% of the
Acknowledgements
The author (M. Shahar Yar) wishes to express his thanks to the University Grant Commission, New Delhi, India for the research award. We thank the Tuberculosis Antimicrobial Acquisition and Coordinating Facility (TAACF), National Institute of Allergy and Infectious Diseases Southern Research Institute/GW Long Hansen's Disease Center, Colorado State University Birmingham, Alabama, USA, for the in vitro anti-mycobacterial screening and Dr. Kiran Smith, National Cancer Institute, USA, for valuable
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