Synthesis, characterization of biologically potent novel chalcones bearing urea, thiourea and acetamide linkages

Three series of some novel chalcone based urea, thiourea and acetamide derivatives were designed, synthesized and screened for their antimicrobial and antifungal activities. All the synthesized compounds are first reported. The structures of the compounds were elucidated with the aid of elemental analysis and spectral methods including IR, 1 H-NMR spectral data. The prepared compounds were evaluated for antibacterial activity against two Gram-positive bacteria ( Staphylococcus aureus , Staphylococcus pyogenus ), two Gram-negative bacteria ( Pseudomonas aeruginosa , Escherichia coli ). The title compounds were also investigated for their antifungal activity using the broth micro dilution method. The bioassay results showed that compounds a few compounds showed good to superior in vitro antibacterial and antifungal activity.


INTRODUCTION
A higher occurrence of opportunistic microbial infections caused by various bacteria due to the fruition and broaden of multidrug-resistant microorganisms has become a widespread medical problem. Such infections most frequently cause severe morbidity and transience in incapacitated and resistant compromised patients. Such infections nearly all frequently affect resistant compromised individuals, patients with malignancies, and transplant recipients. Moreover, with an signal of around two million deaths each year. These facts further emphasize the imperative necessity to find new effectual and secure compounds to maintain and improve the management and prevention of opportunistic microbial and tubercular infections in an innovative era of exhaustive infectious disease control, elimination, and eradication. Chalcones comprise an important class of natural products belonging to the flavonoid family, which exhibit motivating biological activities together with anti-inflammatory [1], anti bacterial [2], anti oxidant [3], anti malarial [4] and anti cancer [5]. Due to their abundance in plants and ease of synthesis, this class of compounds has generated great interest for possible therapeutic uses. They are also effective in vivo as cell proliferating inhibitors, antitumor promoting and chemo preventing agents [6]. The above literature survey led us to consider the chalcone nucleus as a possible scaffold Chalcone based urea, thiourea and acetamide derivatives which are of substantial industrial importance, and are linked to a series of biological actions including herbicidal activity [7], inhibition of nitric oxide [8], antimicrobial [9], anti-HIV [10], anti-viral [11], HDL-elevating [12], and analgesic properties [13,14]. Some chalcone-urea derivatives exhibited anti-inflammatory [15] and anti-malarial activity [16].
In view of the need to discover potent novel antimicrobial agents, and our previous positive results on chalcones, we have synthesized novel chalcone thiourea, urea and acetamide derivatives and evaluated their antimicrobial and antifungal activity against different strains of bacteria and fungal using the broth micro dilution method and compared with some reference drugs.

1. Materials and Methods
All reagents were of analytical grade and use directly. All the melting points were determined in open glass capillary and are uncorrected. Progress of reaction was monitored by thin layer chromatography (TLC) using silica gel-G coated aluminium plates (0.5 mm thickness, Merck) and spots were visualized under UV radiation, purified by recrystalization and column chromatography. The IR spectra were recorded on BRUKER TENSOR Series using KBr pellets. 1 H NMR spectra were recorded on 300MHz BRUKER ULTRASHIELD using DMSO-d6 as a solvent and TMS as an internal reference and chemical shift values were expressed in δ ppm.
Ciprofloxacin and Chloramphenicol were used as reference antibacterial agents. Solution of the test compounds and reference drugs were dissolved in DMSO. The in vitro results of the antibacterial activity of the newly synthesized 30 compounds are presented in Table 1.
On the other hand investigation of antibacterial activity of the synthesized compounds against few Gram-positive strains related that S. pyogenus is more sensitive against most of the synthesized analogous as compared to S. aureus. It was found that present of 2-fluro (62.5 µg/ml) and 2-methyl group (100 µg/ml) on para position of 4b, 4e, 5b, 5e, 6b and 6e accelerate the antibacterial activity against S. pyosens. More over the Gram-negative bacteria S.aureus showed relative high sensitivity towards the analogs 4a, 4f, 5a, 5f, 6a and 6f at 100 µg/ml MIC level.

ANTIFUNGAL ACTIVITY
The minimum inhibitory concentration (MIC) of the synthesized compound was tested against fungi (Candida albicans MTCC 227, Aspergillus niger MTCC 282 and Aspergillus clavatus MTCC 1323) and assayed in vitro using broth micro dilution method standards with gradual dilution starting from (250, 200, 125,100, 50, 25, 12.5, 6.25, 3.125) µg/mL. Nystatin and Greseofulvin were used as reference antibacterial agents. Solution of the test compounds and reference drugs were dissolved in DMSO. The in vitro results of the antifungal activity of the newly synthesized 30 compounds are presented in Table 2.
Some of the compounds displayed moderate the good antibacterial activity. The in vitro antifungle activity of the synthesized analogues indicated that halogen and methyl group substituted analogs 4d, 4e, 4i, 5d, 5e, 5i, 6d, 6e and 6i have shown high efficacy against C. albicans & A. clavatus at 100 ug/ml MIC level. Greseofulvin 500 100 100

CONCLUSIONS
In conclusion, a new class of chalcone based urea, thiourea, acetamidd derivatives were synthesized and evaluated as antibacterial agents. The newly synthesized compounds exhibited promising antibacterial activities against two representative Gram-positive (Staphylococcus aureus and Staphylococcus pyogenus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa). These results makes novel chalcone and their urea, thiourea and acetamided derivatives interesting lead molecules for further synthetic and biological evaluation. It can be concluded that this class of compounds certainly holds great promise towards the pursuit to discover novel classes of antifungal agents. Further studies to acquire more information concerning structure -activity relationships are in progress.