Synthesis, spectral studies, pharmacological and insect antifeedant activities of some (E)-1-(2-(2-benzyloxy-3-methacrylate))-1-naphthyl enones

Totally twelve title compounds have been synthesized by Claisen-Schmidt condensation of (E)-methyl 2-(2-(((1-acetylnaphthalen-2-yl)oxy)methyl)phenyl)-3-methoxy acrylate and substituted benzaldehydes in presence of catalytic quantity of LiOH.H2O catalyst under stirring in room temperature. The yields of the compounds are more than 92%. The synthesized titled compounds were characterized by their physical constants, IR, NMR and Mass spectral data. The spectral data such as infrared ν COs-cis, s-trans, COester, NMR chemical shifts (δ, ppm) of Hα, Hβ, Cα, Cβ, CO of enone moiety, Hβʹ and CO of acrylate moieties have been correlated with Hammett substituent constants, F and R parameters. The antimicrobial, antioxidant and insect antifeedant activities of all synthesized compounds have been evaluated using corresponding bacterial and fungal strains, DPPH radical scavenging and Disc diffusion bio-assay of 4 th instar larvae Achoea Janata L with castor-leaf discs.


INTRODUCTION
Currently, chemists and organic synthetic researcher have paid much more attention for green solvent assited and ground chemistry synthesis [1][2][3][4][5][6]. These synthetic methodology have merits over than conventional methods such as easy work-up procedure, handling technique, nonhazardousness, environmental pollution free from atmosphere, shorter reaction time and better yields [7]. Aryl enones and methacrylates possess many biological activities such as antimicrobial [8,9], acute toxicity [10], haemo toxicity [11], in-vivo toxicity [12], genotoxicity [13], antioxidant [14], anticancer [15], antiviral [16], site-specific peroral delivery [17] antiinflammatory/analgesic [18], anti plasmodial [19], anti-tuberclosis [20] and insect antifeedant [21,22] activities due to presence of carbonyl and vinyl segments present in their structural moieties. Various catalysts were used for synthesis of enones by conventional heating methods [4,23,24,25]. Spectroscopic data have been utilized for prediction of ground state equilibration of organic molecules such as styrenes, E s-cis and s-trans styryl ketones, unsaturated acids and their derivatives, gauche-and anti-form of ω-halo acyl and its esters [26,27]. Infrared spectroscopy is one of the tool for studying structural elucidation, qualitative and quantitative analysis. NMR spectroscopy is useful for prediction of spatial arrangement of protons such as cisand transrefer with coupling constants and their interactions [28]. Spectroscopic data is used for studying structureactivity relationships of organic substrates through Hammett equation. Recently John Joseph et. al., have synthesized and studied the spectral correlation and antimicrobial activities of some methoxy substituted phenyl chalcones [29] . Thirunarayanan and his co-workers have studied the spectral correlation and pharmacological evaluation of chalcones, 1 H pyrazolines, N-acetyl-1 H-Pyrazolines, aryl acyl bromides and aryl ω-halo esters [27,30,31]. Sundararajan et al., have studied the solventfree synthesis, spectral QSAR study antimicrobial and insect antifeedant activities of poly halo

Infrared spectral study
In the present investigation, the authors have studied the effect of substituents on the infrared carbonyl stretches (cm -1 ) of keto-and ester-moiety of the synthesized (E)-2-benzyloxy-(3methoxyacrylate)-1-naphthyl enones. The CO s-cis and s-trans conformers are shown in Fig. 1. And the corresponding stretches of keto-and ester-moiety of the synthesized (E)-1-(2-(2-benzyloxy-(3methoxyacrylate))-1-naphthyl enones were presented in Table 2. These stretches were correlated with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis [2,6,14,19,[24][25][26][27][28][29][30][31][32]. In the infrared spectral correlation, the Hammett equation is employed as in the form of ν = ρσ + ν o (1) where ν is the frequency for the members of the series; ρ is the reaction constant; σ is the substituent constant and ν o is the frequency for the parent member of the series.   The results of statistical analysis are shown in Table 3. From the Table 3, The CO s-cis stretches of enones correlated satisfactorily with Hammett substituent constants, F and R parameters. The CO s-trans stretches of enones correlated satisfactorily with Hammett σ, σ + , σ I , constants and R parameters. The Hammett σ R constant and F parameter were fail in correlation. The CO ester stretches of enones correlated satisfactorily with Hammett substituent constants and F parameter. The R parameter was fail in correlation. All correlation gave positive ρ values. This implies that the normal substituent effect operates in all system. The degree of transmission of substituent effect on the νCO s-cis conformer is higher than that of νCO s-trans conformers. The failure in correlation was due to the inability of predicting the effect of substituent on the carbonyl group and associated with the resonance-conjugative structure as shown in Fig. 2. Volume 57 Table 3. Results of statistical analysis of infrared νCO s-cis , s-trans , CO ester , stretches (cm -1 ) of 1-(2benzyloxy-(3-methoxyacrylate))-1-naphthyl enones with Hammett σ, σ + , σ I , σ R, constants, F and R parameters.
r=correlation coefficient; I= intercept; ρ=slope; s=number of correlated derivatives The inability of some of the single parameter correlation to predict the substituent effects on the carbonyl stretches of the enones, they are worthful when seeking these in multi-correlation with σ I and σ R or F and R Swain-Lupton's [33] parameters. The generated multi-regression analysis equations are given in (2)(3)(4)(5)(6)(7).

H NMR spectral study
In nuclear magnetic resonance spectra, the chemical shifts (δ)(ppm) of 1 H or the 13 C nuclei depend on the electronic environment of the nuclei concerned. These chemical shifts have been correlated with reactivity parameters. Thus the Hammett equation was used in the form as shown in (8).
Where δ is the chemical shift of member of the series; ρ is the reaction constants; σ is the substituent constant and δ 0 is the chemical shift of the corresponding parent compound of the series. The assigned 1 H NMR chemical shifts (δ, ppm) of H α , H β of enone and H βʹ protons of enone and acrylate moieties of 2-benzyloxy-(3-methoxyacrylate)-1-naphthyl enones are presented in Table 2. These chemical shifts (ppm) were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analysis [2,6,14,19,[24][25][26][27][28][29][30][31][32]. The results of statistical analyses are given in Table 4. From the Table 4, the correlation of δH α chemical shifts (ppm) of the enones correlated satisfactorily with Hammett substituent constants, F and R parameters. The δH β and δH βʹ chemical shifts (ppm) correlated satisfactorily with Hammett σ, σ + , σ R constants and R parameters.
The Hammett σ I constant and F parameters were fail in the correlations for δH β and δH βʹ chemical shifts (ppm). The reflectance of substituent effect on the δH α (ppm) is sensitive than δH β and δH βʹ chemical shifts (ppm). All correlations gave positive ρ values. This shows that that normal substituent effect operates in all systems. The failure in correlation is due to the reason stated earlier and associated with the resonance-conjugative structure as shown in Fig. 2. Some of the single parameter correlations were fail for the δH β and δH βʹ proton chemical shifts (ppm) with Hammett substituent constants, F and R

13 C NMR spectral study
The assigned chemical shifts of δCO, C α , C β , CO ester , C αʹ , C βʹ 9ppm) of (E)-2-benzyloxy-(3methoxyacrylate)-1-naphthyl enones have been assigned and tabulated in Table 2. These chemical shifts were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analysis [2,6,14,19,[24][25][26][27][28][29][30][31][32]. The results of statistical analyses are presented in Table 5. From the Table 5, the chemical shifts of δCO, C α , C β of enone moieties are satisfactorily correlated with Hammett substituent constants, F and R parameters. The chemical shifts (ppm) of δCO ester is correlated satisfactorily with Hammett σ and σ + constants. The correlation of the chemical shifts (ppm) of δC αʹ is satisfactory with Hammett substituent constants, F and R parameters. The correlation of the chemical shifts (ppm) of δ C βʹ is satisfactory with Hammett σ, σ + , σ I constants and F parameters. The remaining Hammett sigma constants, F and R parameters were fail in correlation for the δCO ester and δ C βʹ chemical shifts (ppm). All correlations gave positive ρ values. This implies that the normal substituent effect operates in all systems. The failure in the correlation is due to the reasons stated earlier and associated with the resonance-conjugative structure as shown in Fig. 2.

Antimicrobial activities 3.3.1. Antibacterial sensitivity assay
Antibacterial activity assay of prepared 2-benzyloxy-(3-methoxyacrylate)-1-naphthyl enones were performed using Kirby-Bauer [34] disc diffusion technique. In every petri plate, about 0.5 mL of the test bacterial sample was spread over uniformly on the solidified Mueller Hinton agar using sterile glass spreader. Then the discs were made with 5mm of Whatmann No.1 filter paper, impregnated with the solution of the compounds placed on the medium using sterile forceps. Incubated the plates for 24 h at 37 o 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 measured antibacterial activities of all oxazine are presented in Table 6.
The antibacterial activity assay of all prepared enones were studied against two gram positive pathogenic strains Staphylococcus aureus, Enterococcus faecalis and four gram negative strains Escherichia coli, Klebsiella species, Psuedomonas and Proteus vulgaris. The disc diffusion technique was followed using the Kirby-Bauer[ ]method, at a concentration of 250 μg/mL with Ampicillin and Streptomycin were used as standard drugs. Compounds 4, 6 and 9 showed maximum zone of inhibition against B. substilis, with greater than 20 mm compared to the ketones 1-3, 5 and 10 are moderately active in 13-19 mm of zone of inhibition. Enone 9 was active with in 8-12 mm of zone of inhibition and the compounds 7 and 8 are inactive. The enones 1 and 6 were found to be effective against S. aureus within 20-24 mm of zone of inhibition.

Antifungal sensitivity assay
Antifungal sensitivity assay of synthesized enones were performed using Kirby-Bauer [34] disc diffusion technique. The PDA medium was prepared and sterilized as above. This is poured (ear bearing heating condition) to 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 15 mg of the oxazine in 1 mL 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 oxazine amines are presented in Table 7.
The study of antifungal activities of all 2-benzyloxy-(3-methoxyacrylate)-1-naphthyl enones has been done with Aspergillus niger, M.spp and T. virdi fungal stains and the dilution method was adopted. The drug dilution was kept as 50 μg/mL. Griseofulvin has been taken as the standard drug. The study of antifungal activities of all 2-benzyloxy-(3-methoxyacrylate)-1-naphthyl enones against A. niger showed that the two compounds 8 and 12 are effective with 20 mm as the zone of inhibition in 250 μg/L disc while ketones 4, 6, 7, 9 and 11 are active with 13-19 mm zone of inhibition and the compound 1 and 3 was the least active with 8-12 mm zone of inhibitions. Compounds 6, 10 and 12 are visible against M. spp. species within 20mm zone of inhibitions and the development of the fungal colony (2-3 colonies) are recorded for the compounds 2, 4 and 11. The inhibition of compounds 5, 8 and 11 against T. virdi were highly active and the enones 2-4, 6, 10 and 11 are active within 8-12 mm of zone of inhibition. Presence of halogens, methoxy, methyl and nitro substituents are responsible for antimicrobial activities of synthesized enones.

Antioxidant activity
The antioxidant activities of all synthesized enones have been evaluated by the DPPH radical scavenging effect [35]. The 0.1M acetate will be prepared by dissolving 1.64 g of sodium acetate in 15 mL of water and 150 μL of acetic acid. The final volume will be adjusted to 20 mL by adding water. The 0.2 mmol of DPPH solution will be 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 will be arranged with 1.0 mL of buffer solution mixed with 0.5 mL of DPPH solution. A series of various concentrations of synthesized enones and α-Tocofereol (1μg in 1 ml of ethanol) will be added to each tube and mixed well. After 30 minutes in room temperature the absorbance of each solution will be 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 will be expressed in terms of IC 50 (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,