Novel s -Triazinyl Schiff Base/Chalcone Congeners: Rational, Synthesis, Antimicrobial and Anti-TB Evaluation

The occurrence of Multi Drug Resistant (MDR) infectious microbial strains has been increased upto alarming level which affects the public health worldwide. To cure this problem, a library of s - triazinyl derivatives comprising schiff base or chalcone motif have been rationalized, synthesized and screened for their in vitro antibacterial activity against five bacterial strains ( Staphylococcus aureus MTCC 96, Bacillus subtilis MTCC 441, Escherichia coli MTCC 739 , Pseudomonas aeruginosa MTCC 741 and Klebsiella pneumoniae MTCC 109) and four fungal strains ( Aspergillus niger MTCC 282 , Aspergillus fumigates MTCC 343 , Aspergillus clavatus MTCC 1323 , Candida albicans MTCC 183) using broth dilution technique. All the newly synthesized scaffolds were further evaluated for their in vitro anti-TB efficacy against the tubercular strain ( Mycobacterium tuberculosis H37Rv) using Lowenstein-Jensen MIC method. All the derivatives were well characterized by IR, 1 H NMR, 13 C NMR, elemental analysis as well as mass spectroscopy.


INTRODUCTION
Multidrug resistant strength of a variety of infectious microbial flora towards existing standard drugs has been increased in recent decade which is serious health problem worldwide. Antimicrobial resistant (AMR) is a phenomenon of infectious microbial flora to resist antimicrobial agents to which it was previously sensitive [1]. Various multidrug resistant microbes including bacteria, fungi, viruses, parasites etc. exhibit such type of resistant profile against traditional standard drugs including antibiotics, antifungals, antivirals, antimalarials etc. which results in failure or ineffectiveness of the standard treatment, so that the rate of spread of infectious disease also increases. The appearance of methicillin-resistant Staphylococcus aureus (MRSA), a multidrug resistant gram-positive bacterial strain, poses infectious disease.  In the current period, some tubercular strains of Mycobacterium tuberculosis cause MDR-Tuberculosis (TB) and extensively drug-resistant XDR-TB which generally affects the lungs [2]. The current figures of World Health Organization (WHO) for the year 2012 showed 8.6 million people suffered with TB and 1.3 million died from TB. An estimated 530 000 children became ill with TB and 74 000 HIV-negative children died of TB [3]. In context of the above discussion, the cost of these troubles highlights the urgent need to develop new medicinal agents which have relatively higher efficiency to sustain a pool of new bioactive scaffolds.
In context of the above discussion, the cost of these troubles indicate the urgent need to develop new medicinal agents having relatively higher potency with reference to traditional drugs to sustain a pool of novel antimicrobial agents. Hence, rational and synthesis of novel bioactive agents likely to be unaffected by existing resistance mechanisms is an area of vast implication for medicinal chemists showed the urgent need to combat such impasse. The rationalization of novel bioactive agents with more selectivity and little toxicity persist an area of intensive research in synthetic medicinal chemistry. s-Triazine derivatives represents an imperative group of drugs possessing miscellaneous medical applications by means of their widespread medicinal attribute such as antibacterial [4], antifungal [5], anti-TB [6], anticancer [7,8], antimalarial [9], anti-HIV [10] etc. Some triazine based drugs e.g. Altretamine, Triethylenemelamine and Atrazine ( Fig. 1) have also been used for therapeutic purpose in clinic. Many chemists have synthesized effective antimicrobial agents containing s-triazine as a core moiety [11,12]. Schiff base possessing molecule having good inhibitory profile also been synthesized by many workers [13,14]. Triazine derivatives endowed with chalcone residue were also found to exhibit 58 ILCPA Volume 38 superior medicinal applications [15]. In this study, we have designed and developed a variety of s-triazine derivatives endowed with schiff base or chalcone residue [16][17][18][19][20].

1. Material and methods
All the chemicals and solvents used for the synthesis work acquired from commercial sources were of analytical grade, and were used without further purification. Melting points were determined by using open capillary tubes and are uncorrected. TLC was checked on E-Merck pre-coated 60 F254 plates and the spots were rendered visible by exposing to UV light or iodine. IR spectrums were recorded on SHIMADZU HYPER IR. NMR spectra were recorded by 400 MHz BRUKER AVANCE instrument using TMS as internal standard (Chemical Shift in δ, ppm) and DMSO-d6 as a solvent. Spectra were taken with a resonant frequency of 400 MHz for 1 H and 100 MHz for 13 C NMR. The splitting patterns are designated as follows; s, singlet; d, doublet; dd, doublet of doublets; and m, multiplet. Elemental analysis was done on "Haraeus Rapid Analyser". The mass spectra were recorded on JOEL SX-102 (EI) model with 60 eV ionizing energy.

Synthesis of 4-((4-chloro-6-(cyclopropylamino)-1,3,5-triazin-2-yl)amino)benzonitrile (3)
To a stirred solution of 2 (5 g, 0.0188 mol) in dry DMF (20 mL), slowly added a solution of cyclopropyl amine (1.07 g, 0.0188 mol) in DMF (30 mL) and K 2 CO 3 (2.6 g, 0.0188 mol) at room temperature. The reaction mixture was stirred at room temperature for 9 hrs. After the completion of reaction, the reaction mass was dumped into crushed ice, solid was filtered, washed with water, dried to give crude product. The crude product was purified by column chromatography to get the pure product (

General procedure for the synthesis of compounds 5a-j
A mixture of 4 (5 g, 0.0134 mol), appropriate amine (0.0134 mol) and glacial acetic acid (0.5 mL) in ethanol (50 mL) was refluxed for 12 hrs. After the completion of reaction, the reaction mass was cooled to room temperature, dumped into crushed ice, solid was filtered, washed with water and then dried to give the desired crude product. The crude was then purified by column chromatography to get pure title compound.          162.75, 162.23, 161.12, 150.30, 143.54, 134.40, 133.13, 130.30, 121.52, 120.90, 119.

General procedure for the synthesis of compounds 6a-j
A mixture of 4 (5 g, 0.0134 mol), appropriate acetophenone (0.0134 mol) and sodium hydroxide (0.51 g, 0.0147 mol) in methanol (50 mL) was refluxed for 15 hrs. After the completion of reaction, the reaction mass was cooled to room temperature, dumped into crushed ice, solid was filtered, washed with water and then dried to give the desired crude product. The crude was then purified by column chromatography to get pure title compound.

BIOLOGICAL EVALUATION
All newly synthesized s-triazinyl schiff bases and chalcone derivatives were accessed for their in vitro antimicrobial evaluation against five bacterial strains (