Bio-potent (5-chloro-2-thienyl)-3-(substituted phenyl) bicyclo[2.2.1]heptane-2-yl methanone derivatives

A series of (5-chloro-2-thienyl)(3-(substituted phenyl) bicyclo[2.2.1]hept-5-en-2-yl)methanones have been synthesized by fly-ash catalyzed [4+2] cycloaddition Diels-Alder reaction of cyclopentadiene and 5-chloro-2-thienyl chalcones under cooling conditions. The yields of the methanones are more than 60%. The synthesized (5-chloro-2-thienyl)(3-(substituted phenyl) bicyclo[2.2.1]hept-5-en-2-yl)methanones are characterized by their physical constants and spectral data. The antimicrobial, antioxidant and insect antifeedant activities of synthesized methanones have been studied using their respective bacterial, fungal strains, DPPH radical scavenging activity and Dethler’s leaf-discs bioassay method.

The mechanistic aspects of reactivity, selectivity, endo-exoand solvent effects of this Diels-Alder reaction has been reported [2][3][4][5][6]. Currently, solvent-free Diels-Alder reaction is plays an important role for the synthesis of organic substrates especially bicyclo compounds with stereo selectivity, specificity, due to easy handling work-up and technical procedure, non-hazardousness, shorter reaction time, non-polluted to the environment and good yields [1, 7,8].

1. General
In this present investigation, all chemicals utilized were procured from Sigma-Aldrich and E-Merck brands. Fly ash was collected from Thermal Power Plant-II, Neyveli Lignite Corporation (NLC), Neyveli, Tamil Nadu, India.
The NMR spectra of selective compounds were recorded in Bruker AV 400 spectrometer operating at 400 MHz for 1 H NMR spectra and 100 MHz for 13 C NMR spectra in CDCl 3 solvent using TMS as internal standard. Electron impact and chemical ionization mode FAB + mass spectra were recorded with a SHIMADZU spectrometer.
The completion of the reaction was monitored by thin layer chromatogram. Dichloromethane (10 mL) was added and extract was separated by filtration. The filtrate was washed with water, brine (10 mL), dried over on anhydrous Na 2 SO 4 and concentrated gave the solid product.
The chalcones containing electron donating substituents (OCH 3 ) gave higher yield than electron withdrawing (halogens and nitro) substituents. The effect of catalyst on this reaction was studied by varying the catalyst quantity from 0.1 to 0.5g. As the catalyst quantity increased from 0.1 to 0.4 g the percentage of product increased from 60-65%. Further increase the catalyst amount beyond 0.4 g, there is no increase in the percentage of product. The optimum quantity of catalyst loading was found to be 0.4 g. The effect of solvents on this reaction (entry 1) was studied with the same quantity of reactants with methanol,

1. Antimicrobial activities
The antimicrobial activities of synthesized (5-chloro-2-thienyl)(3-(substituted phenyl) bicyclo[2.2.1]hept-5-en-2-yl)methanones have been evaluated by measuring the mm of zone of inhibition of the compounds against the bacterial and fungal strains. In this present investigations, the author have chosen two gram positive pathogenic strains Staphylococcus aureus, Entrocccus faecalis while Escherichia coli, Klebsiella species, Psuedomonas and Proteus vulgaris were the gram negative strains. The disc diffusion technique was followed using the Kirby-Bauer [26] method, at a concentration of 250 μg/mL with Ampicillin and Streptomycin taken as the standard drugs. For the study of antifungal activities of all methanones using Candida albicans as the fungal strain and the disc diffusion technique was followed for the antifungal activity while the two other stains Penicillium species and Aspergillus niger, the dilution method will be used. The drugs dilution will be 50μg/mL. Grisseofulvin is taken as the standard drug.

1. 1. Antibacterial sensitivity assay
Antibacterial sensitivity assay of (5-chloro-2-thienyl)(3-substituted phenyl bicyclo [2.2.1]hept-5-en-2-yl)methanones were performed using Kirby-Bauer [26] disc diffusion technique. In each petri plate about 0.5 mL of the test bacterial sample was spread uniformly over the solidified Mueller Hinton agar using sterile glass spreader. Then the discs with 5mm diameter made up of Whatmann No.1 filter paper, impregnated with the solution of the compound were placed on the medium using sterile forceps. The plates were incubated for 24 h at 37 °C by keeping the plates upside down to prevent the collection of water droplets over the medium. After 24 h, the plates were visually examined and the diameter values of the zone of inhibition were measured. Triplicate results were recorded by repeating the same procedure.
The observed antibacterial activities of all (5-chloro-2-thienyl)(3-substituted phenyl bicyclo[2.2.1]hept-5-en-2-yl)methanones were presented in Table 1. Almost all compounds shows antibacterial activity. Methanones 2-5 and 9 were shown maximum zone of inhibition against Escherichia coli, with greater than 20 mm of zone of inhibition compared to the ketones 1 and 11 are active in 13-19 mm of zone of inhibition. ILCPA Volume 42

1. 2. Antifungal sensitivity assay
Antifungal activity of synthesized (5-chloro-2-thienyl)(3-substituted phenyl bicyclo [2.2.1] hept-5-en-2-yl)methanone were performed using Kirby-Bauer [26] disc diffusion technique. PDA medium was prepared and sterilized as above. It was poured (ear bearing heating condition) in the Petri-plate which was already filled with 1 mL of the fungal species. The plate was rotated clockwise and counter clock-wise for uniform spreading of the species. The discs were impregnated with the test solution. The test solution was prepared by dissolving 15mg of the methanone in 1mL of DMSO solvent. The medium was allowed to solidify and kept for 24 h. Then the plates were visually examined and the diameter values of zone of inhibition were measured. Triplicate results were recorded by repeating the same procedure.
The observed antifungal activities of all prepared methanones are presented in Table 1. The study of antifungal activities of all methanones against C. albicans, showed that the three The inhibition of ketones against A.niger was less in one compound 7, 8, 10 and 11 being highly active followed by 3, 6 and 9. The ketone 1, 2, 4 and 7 were moderately active with production of one fungal colony. Presence of a bromo, chloro, methoxy, methyl and nitro substituents are responsible for antimicrobial activities of methanones.
The final volume was adjusted to 20 mL by adding water. The 0.2 mmol of DPPH solution was prepared by dissolving 3.9 g of DPPH in 50 mL of ethanol. α-Tocofereol (1mg in 10 mL of ethanol) solution was prepared. A series of test tubes were arranged with 1.0 mL of buffer solution mixed with 0.5 mL of DPPH solution. A series of various concentrations of synthesized methanones and α-Tocofereol (1μg in 1 ml of ethanol) was added to each tube and mixed well. After 30 minutes in room temperature the absorbance of each solution was measured by UV spectrophotometer at 517 nm.
A mixture of buffer solution and ethanol used as the reference for the spectrophotometer. A graph was plotted with the weight of the compound Vs absorptions and IC50 values will be determined. The antioxidant activity was expressed in terms of IC50 (μg/mL, concentration required to inhibit DPPH radical formation by 50%). α-Tocofereol will be used as a positive control. The radical scavenging activity was calculated as, From the experimental statistical results, the observed antioxidant activities of methanones were presented in Table 1. From Table 1, the hydroxy and methoxy substituted methanones (6, 7 and 8) were shown significant antioxidant activity.
This test was performed with a 4 th instar larva Achoea Janata L against castor semilooper, were reared as described on the leaves of castor, Ricinus communis in the laboratory at the temperature range of 26 °C ±1 °C and a relative humidity of 75-85%. The leaf -disc bioassay method [20,21] was used against the 4 th instar larvae to measure the antifeedant activity. The 4 th instar larvae were selected for testing because the larvae at this stage feed very voraciously.
International Letters of Chemistry, Physics and Astronomy Vol. 42