Synthesis, characterisation and biological screening of s - triazine based chalcones and its derivatization into phenyl pyrazolines, isoxazoles

Heterocyclic derivatives such as phenyl pyrazolines and isoxaxoles were prepared from s - triazine based chalcones. Chalcones (A 1 - A 5 ) are synthesised by the reaction of compound (V) with various aromatic aldehydes. Moreover, further reaction of chalcones with phenyl hydrazine hydrochloride and hydroxylamine hydrochloride in the presence of alkali gives phenyl pyrazolines (A 6 - A 10 ) and isoxazoles (A 11 - A 15 ) derivatives respectively. The structures of the newly synthesised compounds were confiremed by spectroscopic (IR, 1 H NMR, 13 C NMR) and elemental analysis. All the newly synthesised compounds have been screened for their antimicrobial activity against selected Gram - positive (S. aureus and S. pyogenus), Gram - negative (E. coli and P. aeruginosa) bacterial and fungal strains (C. albicans, A. niger and A. clavatus).


INTRODUCTION
The main fears for human beings are a variety of diseases. Scientists and doctors are still struggling to find solutions with various forms of medications. Today's new medicines are results of inexorable effort made by human civilization time to time. The most common compounds of chalconoid group are the chalcones, which provide new class of medicines due to the pharmacologically active moiety and various biological activities. The chalcones are 1, 3 -diarylprop -2 -en -1 -one, form a broad class of compounds containing two aromatic rings bound with vinyl ketone fragment. Chalcones are useful intermediates for obtaining the variety of heterocycles [1][2][3][4][5]. Various chalcone derivatives are remarkable materials for their second harmonic generation [6]. They are naturally occurring plant metabolites possess a broad spectrum of biological activities such as cancer cell lines [7][8], antimitotic [9], antiinflammatory [10], hepatoprotective [11], molluscicidal properties [12], heme oxygenase-1 [13], antimicrobial [14] etc... . So, this broad spectrum of applications encouraged us to search for another addition to the existed molecule.
Pyrazoline derivatives with a phenyl group at 5 -position show good film-forming properties, excellent features of blue photoluminescence and electroluminescence [15]. Pyrazoline derivatives have a long history of application in agrochemicals and pharmaceutical industry as herbicides and active pharmaceuticals. Now days, a major portion of research in heterocyclic chemistry has been devoted to 2-pyrazolines containing diverse aryl groups as substituents. Pyrazoline derivatives are well known for their different biological activities such as antifeedant [16], anti-inflammatory [17], antiviral [18], antidepressant [19], antibacterial [20], antifungal [21] etc... . Many class of chemotherapeutic agents containing pyrazoline nucleus are in clinical use such as orisul (antibacterial), antipyrine (antipyretic), butazolidine (anti-inflammatory). So based on the above biological activities exhibited by the pyrazoline compounds, we reported here, the synthesis and biological screening of some novel phenyl pyrazoline derivatives.
Among heterocycles, the isoxazole unit constitutes an easily accessible nucleus that is present in a number of natural and pharmacological compounds [22], display a wide range of organic reactivities and used as an effective means of preparing new molecular scaffolds [23]. Isoxazoles have been repeatedly shown as useful synthons in organic synthesis [24]. Isoxazoles shows a broad spectrum of biological properties like fungicidal [25], antimicrobial [26], antitubercular [27], antiviral [28] etc... . So in this regard, we have synthesised some novel isoxazole derivatives and screened this compounds to antimicrobial activitiy.

Material
All the chemicals and solvents which used for reaction were purified after getting from commercial suppliers. Melting points were taken in open capillaries using paraffin bath and were uncorrected. IR spectra were recorded on Shimadzu IR Affinity -1 FTIR spectrometer (V max -1), 1 H NMR were recorded on Bruker Avance -DPX 400 MHz NMR spectrometer using CDCl 3 as a solvent and TMS as internal reference and 13 C NMR spectra were recorded on the same instrument at 100 MHz operating frequency using DMSO as a solvent and TMS as internal reference. The chemical shifts are expressed in parts per million (ppm) downfield from the internal standard and signals are quoted as s (singlet), d (doublet) and m (multiplate). The coupling constants (J) are given in Hertz (Hz). All the compounds were analyzed for carbon, hydrogen and nitrogen by the Perkin-Elmer 240 C H N elemental analyzer and the results were within ±0.4% of theoretical values. The purity of synthesised compounds were checked by thin layer chromatography conducted on Silica Gel 60 F-254 (Merck) plates of 0.25 mm thickness and the spots were located using toluene : methanol (12 : 6 v/v) eluents and visualized with UV (254 nm) light or keeping the plates in iodine chamber.

Antimicrobial evaluation
All the newly synthesised compounds were screened for antibacterial and antifungal activity by Broth dilution method [30] against a panel of selected Gram -positive (S. aureus MTCC 96 and Streptococcus pyogenes MTCC 442) and Gram -negative bacteria (E. coli MTCC 443 and P. aeruginosa MTCC 441) and selected fungal strains (C. albicans MTCC 227, A. niger MTCC 282 and A calavatus MTCC 1323). DMSO was used as a solvent. Ampicillin and Chloramphenicol was used as a standard drug for antibacterial activity while Greseofulvin and Nystatin was used as a standard drug for antifungal activity. The results are showed in Table -2.

CONCLUSION
In outline, we have synthesised some bioactive chalcones and convert them into pyrazoline and isoxazole moiety by using conventional method. The method adopted for the synthesis of pharmacologically important molecules in this investigation is simple, efficient, and inexpensive. The IR, 1 H NMR, 13 C NMR spectral analysis and elemental analysis of all International Letters of Chemistry, Physics and Astronomy Vol. 47 the newly synthesised compounds confirmed that purity of the entire synthesised compound is good.
All the synthesised compounds were screened for antimicrobial activity. Majority of the synthesised compounds were found to potentially active against both selected Gram positive, Gram negative organisms and selected fungal organisms. From the results of antibacterial and antifungal activity, it can be concluded that compounds A 2, A 7 and A 12 were found more active then the remaining compounds due to the present of chlorine atom. So overall it was revealed that the no substitution on phenyl ring showed no inhibition of the tested bacteria while the compounds that showed some inhibition was due to the presence of substitution of methoxy, chloro, phenoxy and nitro group on some position of the phenyl ring. These finding conclued that the titled compounds have the properties to kill the microbes in some extent when compared with standared drug. These result suggest that chalcone and their derivatives have an opportunity to behave as broad spectrum antimicrobial agents and have exellent scope for further development as commercial antimicrobial agents .