Essay: The Diels-Alder reaction

Totally twenty two aryl heptane [2.2.1] methanone derivatives including 2-hydroxy-1-naphthyl based heptene [2.2.1] methanones have been synthesized by aqueous phase fly-ash catalyzed [4+2] cycloaddition Diels-Alder reaction of cyclopentadiene and aryl chalcones. More than 60% of yields were observed in this cycloaddition. The synthesized aryl heptane[2.2.1] methanones are characterized by their physical constants and spectral data. The pharmacological evaluation such as antimicrobial, antioxidant and insect antifeedant activities of synthesized methanones have been studied using their respective bacterial, fungal strains, DPPH radical scavenging activeness and leaf-disc bioassay method. Halogen, methoxy and methyl substituted methanones showed good antibacterial activity. Bromo, methoxy, methyl and nitro substituted compounds shows good antifungal activity. The hydroxy and methoxy substituted ketones shows good antioxidant activity. The 4-chloro substituted compound showed significant insect antifeedant activity.
Key words: Green Diels-Alder reaction; 2-hydroxy-1-naphthyl chalcones; Cyclopentadiene; Antimicrobial activities, Antioxidant activity, Insect antifeedant activity.
1. Introduction
Among the stereo selective reactions, the Diels-Alder reaction is one of the most important for the synthesis of six-membered bicyclic compounds by [4+2] cycloaddition of a diene and dienophiles(Hayashi et al., 2008; Mubofu and Engberts, 2008). When this reaction is reversible in thermal condition then, it is called as retro-Diels-Alder reaction. The mechanistic aspects of reaction conditions, endo-exo- product selectivity and influence of solvents of this Diels-Alder reaction has been reported (Breslow et al., 1983; Reewlow and Marita, 1984; Otto et al., 1996; Otto and Engberts, 1999; Fringuelli et al., 2001). Currently, solvent-free Diels-Alder reaction plays an important role for the synthesis of organic substrates especially bicyclo compounds with product selectivity and ease handling work-up and technical procedure, non-hazardousness, shorter reaction time, non-polluted to the environment and good yields(Hayashi et al., 2008; Mubofu and Engberts, 2008; Boeersma et al., 2007; 2012). Rideout and Breslow (Rideout and Breslow 1980) have studied the aqueous phase reaction of cyclopentadiene and vinyl methyl ketones in water and they reported the solvent-free reaction rate is greater than 700 times faster than in non-aquesou media. Many kinds of catalysts including Lewis acids (Otto et al., 1996), Bronsted acids (Otto et al., 1996; Otto and Engberts, 1995), asymmetric catalyst with helical polymers (Megens and Roefes, 2011), Cu2+ ion-mediated nanotubes (Jin et al., 2011), DNA and Micellar based catalysts (Boersma et al., 2007; Roelfes, 2006; Kuo et al., 2011; Oltra and Roelfes, 2008; Otto et al., 1998) [have been used for this [4+2] cycloaddition Diels-Alder reaction of cyclopentadiene(diene) and E- chalcones(dienophiles). The unsaturated ketones, aza- vinyl ketones, substituted aryl bicyclo ketones possess important biological activities and antibodies (Boger et al., 1994). Recently, Thirunarayanan have reported more than 60% yields of 2-naphthyl based bicycle[2.2.1]heptane methanones using solvent assisted method(Thirunarayanan, 2014). The mono- or di- or tri- or poly -OH and ‘OCH3 substituted organic compounds possess significant antioxidant activities (Thirunarayanan et al., 2011; 2011a; 2013). Similarly, mono- or di- or tri- or poly halogenated enones possess insect antifeedant activities (Thirunarayanan et al., 2011a; 2013; Thirunarayanan, 2008; Thirunarayanan et al., 2010). From the thorough literature survey reveals that the synthesis and the study of pharmacological and insect antifeedant activities of 2-hydroxy-1-naphthyl based heptene [2.2.1] methanones were unavailable in the past. Hence, the author have taken efforts to synthesize some 2-hydroxy-1-naphthyl based heptene [2.2.1] methanones and evaluated their pharmacological activities such as antimicrobial, antioxidant and insect antifeedant activities using their respective bacterial and fungal strains, DPPH radical scavenging activeness and leaf disc bio-assay method.
2. Experimental
2.1. General
Chemicals used in this present work were procured from Sigma-Aldrich and E-Merck brands. The source of Fly ash is from the Thermal Power Plant-II, Neyveli Lignite Corporation (NLC), Neyveli, Tamil Nadu, India. The Mettler FP51 melting point apparatus was used for determining the melting points of all bicyclo[2.2.1]heptene-2-yl methanones in open glass capillaries and are uncorrected. Thermo scientific Nicolet iS5, US made Fourier transform spectrophotometer was used for recordingiInfrared spectra (KBr, 4000-400 cm-1) of methanones. The Bruker AV 400 NMR spectrometer was used for recording NMR spectra operating at 400 MHz for 1H NMR spectra and 100 MHz for 13C NMR spectra in CDCl3 solvent using TMS as internal standard. The mass spectra of methanones were recorded in SHIMADZU spectrometer using FAB+ Electron impact and chemical ionization mode.
From Himedia, Mumbai, India, the chemicals viz., nutrient broth, Mueller Hinton agar, potato dextrose agar, Tween-80 solution and other relevant materials required for the study in the present work have been procured. Microbial cultures were procured from Centre for Advanced studies-Marine Biology, Portonovo campus, Portonovo-608502, Annamalai University, India.
2.2. Synthesis of 2-hydroxy-1-naphthyl chalcones
The substituted styryl 2-hydroxy-1-naphthyl ketones were synthesised by literature method (Thirunarayanan et al., 2012).
2.2.General procedure for synthesis of 2-(2-hydroxy-1-naphthyl)-3-(substituted phenyl) bicyclo [2.2.1] hept-5-ene-2-yl-methanones
Appropriate equi-molar quantities of 2-hydroxy-1-naphthyl chalcones (2 mmol) in 15 mL of ethanol, cyclopentadiene (2 mmol), and 4g of fly-ash in 20 mL of water were stirred for 6 h in 0-4??C (Scheme1) and kept the reaction mixture for an overnight. The completion of the reaction was monitored by thin layer chromatogram. Dichloromethane (10 mL) was added and the extract was separated. The extract was washed with water, brine (10 mL), dried over on anhydrous Na2SO4 and concentrated gave the solid product. The crude product was further purified by recrystallization with ethanol.
3. Results and discussion
Attempt have been made for the synthesis of aryl 2-(2-hydroxy-1-naphthyl)-3-(substituted phenyl) bicyclo [2.2.1] hept-5-ene-2-yl-methanone derivatives by aqueous phase fly-ash catalysed Diels-Alder reaction with cyclopentadiene as diene and E-chalcones as dienophiles. Numerous chemical elements and their oxides such as (Thirunarayanan, 2010; Gopalakrishnan et al., 2007; El-Mogazi et al., 1988; Thirunarayanan and Sekar, 2013; Thirunarayanan et al., 2012) Si, Al, Fe, Ca, C, Mg, K, Na, S, Ti, P, Mn, organic mud and insoluble residues present in the fly-ash. The waste fly-ash was used as catalyst for organic synthesis. The fly-ash par??ticles are in the silt-sized range of 2-50 microns (El-Mogazi et al., 1988). Glass, mullite-quartz, and magnetic spinel are the three major mineralogical matrices identified in fly ash. The solubility of fly ash has been extensively investigated and it is largely dependent on factors specific to the extraction methods. The complete literature study reveals that, the long-term leaching studies predicts the fly ash will lose substantial amounts of waste soluble salts, but simulation models predict that the loss of trace elements from fly ash deposits through leaching will be very slow. Traces of radioisotopes are found to be the constituents of fly ash which do not appear to be hazardous. Hence, the author have synthesised aryl bicyclo [2.2.1] heptene-2-yl-methanones by aqueous phase Diels-Alder reaction of E-enones and cyclopentadiene under solvent-free cooling condition. During the process of cyclo addition reaction the chemical species present in the fly-ash was catalysed the [4+2] cycloaddition reaction. More than 60% of yield was observed in this reaction. The analytical physical constants and mass fragments are presented in Table 1. The reusability of catalyst in this cycloaddition reaction was studied with 2 mmol of 2-hydroxy-1-naphthyl chalcone and 2 mmol of cyclopentadiene (entry 11). The first run gave 65% of the product. The 2nd and 3rd runs gave 60 and 53%. The fourth and fifth runs yields are 40% only. The enone possess electron donating substituents (OCH3) gave higher yield than electron withdrawing (halogens and nitro) substituents. The catalytic effect of catalyst on this cyclo addition reaction was studied by varying the catalyst quantity from 0.1 to 6 g. As the quantity of catalyst increased from 0.1 to 0.4 g the percentage of yield increased from 60-65%. Further increase the catalyst quantity beyond 0.4 g, there is no increase in the percentage of yield. The effect of catalyst loading was illustrated in Fig.1. The optimum quantity of catalyst loading was in the cyclo addition reaction was found to be 0.4 g. The influence of solvents on this cyclo addition reaction (entry 11) was studied with the same quantity of reactants with solvents such as methanol, dichloromethane, dioxane and tetrahydrofuran and is presented in Table 2. The higher yield was obtained in ethanol with fly-ash in water medium. The infrared and NMR data of selective compounds are summarized below. The NMR spectra of selective compounds are presented in supplementary data(see supplementary data)
(2-Hydroxynaphthalen-1-yl)(3-phenylbicyclo[2.2.1]hept-5-en-2-yl)methanone 11: IR(KBr) 3424.34, 2992.35, 1673.57, 1543.26, 1437.68, 1028.58, 880.91 cm-1; 1H NMR (400MHz, CDCl3): ?? 2.653(dd, 1H, H1) J = 5.20 and 12.4Hz, 3.623(t, 1H, H2), 3.197(t, 1H, H3), 2.123(dd, 1H, H4) J=5.24 and 14.6Hz, 5.481(d, 1H, H5), 5.935(d, 1H, H6), 2.080(dd, 1H, H7) J=9.2 and 16.0Hz, 1.582(dd, 1H, H7′) J=6.8 and 12.4 Hz, 6.858-7.954(m, 11H, Ar-H); 13C NMR( 100MHz, CDCl3): ?? 190.53(CO), 40.33(C1), 54.47(C2), 46.03(C3), 50.29(C4), 135.47(C5,6),45.86(C7), 125.98-141.34(Ar-C).
(3-(3-Bromophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone 12: IR(KBr) 3428.18, 2982.56, 2812.63, 1673.28, 1548.82, 1465.37, 1128.79, 1083.79, 817.85 cm-1; 1H NMR(400MHz, CDCl3): ?? 3.073(dd, 1H, H1), J=7.34 and 9.24Hz, 3.786(t, 1H, H2), 3.601(t, 1H, H3), 2.643(dd, 1H, H4) J=7.36 and 10.45Hz, 6.619(d, 1H, H5), 6.612(d, 1H, H6), 2.037(dd, 1H, H7)J= 5.24 and 7.44 Hz, 1.784(dd, 1H, H7′) J=8.61 and 5.92Hz, 7.665-8.816(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 190.85(CO), 42.66(C1), 54.78(C2), 45.67(C3), 51.79(C4), 135.77(C5,6),46.23(C7), 123.52-156.89(Ar-C).
(3-(4-Bromophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone 13: IR(KBr) 3438.16, 2988.26, 2872.83, 1669.18, 1538.72, 1478.97, 1143.78, 1045.89, 837.78 cm-1; 1H NMR(400MHz, CDCl3): ?? 2.861(dd, 1H, H1) J = 9.6 and 10.6Hz, 3.762(t, 1H, H2), 3.581(t, 1H, H3), 2.819(dd, 1H, H4) J= 7.2 and 3.6Hz, 5.392(d, 1H, H5), 5.965(d, 1H, H6), 2.160(dd, 1H, H7)J=12.0 and 6.5 Hz, 1.611(dd, 1H, H7′) J= 9.6 and 12.8 Hz, 7.635-8.866(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 189.38(CO), 37.42(C1), 54.93(C2), 34.88(C3), 45.46(C4), 135.73(C5,6),44.54(C7), 126.78-142.96(Ar-C).
(3-(2-Chlorophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone 14: IR(KBr) 3432.34, 2996.49, 2889.89, 1683.49, 1595.19, 1461.02, 1234.87, 1088.76, 826.25 cm-1; 1H NMR(400MHz, CDCl3): ?? 3.034(dd, 1H, H1) J= 8.2 and 7.6Hz, 3.436(t, 1H, H2), 3.234(t, 1H, H3), 2.216(dd, 1H, H4) J= 6.2 and 8.2Hz, 6.223(d, 1H, H5), 6.325(d, 1H, H6), 2.034(dd, 1H, H7) J= 6.72 and 8.92Hz, 1.589(dd, 1H, H7′) J= 9.12 and 7.25Hz, 7.653-8.734(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 191.24(CO), 48.25(C1), 54.64(C2), 45.85(C3), 51.32(C4), 136.44(C5,6),46.51(C7), 124.36-152.47(Ar-C).
(3-(3-Chlorophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone 15: IR(KBr) 3422.13, 2946.09, 2837.09, 1673.59, 1515.89, 1481.02, 1165.28, 1058.27, 854.28 cm-1; 1H NMR(400MHz, CDCl3): ?? 2.738(dd, 1H, H1) J= 4.8 and 10.4Hz, 3.486(t, 1H, H2), 2.492(t, 1H, H3), 2.682(dd, 1H, H4) J= 14.8 and 9.2Hz, 5.493(d, 1H, H5), 6.965(d, 1H, H6), 2.412(dd, 1H, H7) J= 7.2 and 12.4 Hz, 1.445(dd, 1H, H7′) J= 9.2 and 8.4 Hz, 7.523-8.742(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 190.05(CO), 41.20(C1), 54.81(C2), 45.19(C3), 50.37(C4), 136.26(C5,6),46.22(C7), 125.69-148.80(Ar-C).
(3-(4-Chlorophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone 16: IR(KBr) 3422.58, 2982.56, 2882.33, 1673.78, 1562.27, 1478.07, 1138.59, 1089.99, 884.85 cm-1; 1H NMR(400MHz, CDCl3): ?? 3.087(dd, 1H, H1) J= 7.2 and 6.6Hz, 3.786(t, 1H, H2), 3.601(t, 1H, H3), 2.453(dd, 1H, H4) J= 9.6 and 10.6Hz, 6.017(d, 1H, H5), 6.102(d, 1H, H6), 2.037(dd, 1H, H7) J= 11.5 and 8.62Hz, 1.284(dd, 1H, H7′) J= 8.2 and 6.6Hz, 7.665-8.816(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 190.85(CO), 41.36(C1), 54.57(C2), 46.16(C3), 51.82(C4), 136.37(C5,6),46.73(C7), 126.57-153.69(Ar-C).
(3-(2-Hydroxyphenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl methanone: 17 IR(KBr) 3447.93, 2993.57, 2879.59, 1687.34, 1482.51, 1029.89, 881.78 cm-1; 1H NMR(400MHz, CDCl3): ?? 3.159(dd, 1H, H1) J= 7.82 and 6.72Hz, 3.566(t, 1H, H2), 3.792(t, 1H, H3), 2.613(dd, 1H, H4) J= 11.24 and 7.67Hz,6.417(d, 1H, H5),6.426(d, 1H, H6), 2.126(dd, 1H, H7) J= 5.23 and 7.86Hz, 1.056(dd, 1H, H7′) J= 10.22 and 8.76Hz, 7.156-8.560(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 189.92(CO), 42.92(C1), 54.63(C2), 46.67(C3), 51.79(C4), 136.23(C5,6), 47.04(C7), 125.12-139.92(Ar-C).
(3-(4-Hydroxyphenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl methanone: 18 IR(KBr) 3453.63, 2998.35, 2885.23, 1683.64, 1462.21, 1039.69, 875.28 cm-1; 1H NMR(400MHz, CDCl3): ?? 2.809(dd, 1H, H1) J=16.0 and 6.06Hz, 3.586(t, 1H, H2), 3.767(t, 1H, H3), 2.712(dd, 1H, H4) J=11.60 and 8.80Hz, 5.392(d, 1H, H5), 5.964(d, 1H, H6), 2.533(dd, 1H, H7) J= 12.0 and 8.0Hz, 1.588(dd, 1H, H7′) J=10.8 and 11.6Hz, 7.236-8.540(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 189.39(CO), 43.72(C1), 52.48(C2), 44.54(C3), 50.36(C4), 135.72(C5,6),47.57(C7), 125.35-153.29(Ar-C).
(3-(4-Methoxyphenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone: 19 IR(KBr) 3429.43, 3011.32, 2991.24, 1668.34, 1565.23, 1456.13, 1258.16, 1085.81, 824.98 cm-1; 1H NMR(400MHz, CDCl3): ?? 3.246(dd, 1H, H1) J= 6.8 and 18.4Hz, 3.821(t, 1H, H2), 3.186(t, 1H, H3), 2.756(dd, 1H, H4) J= 10.0 and 10.0Hz, 5.585(d, 1H, H5), 5.630(d, 1H, H6), 2.205(dd, 1H, H7) J= 12.8 and 7.6Hz, 1.441(dd, 1H, H7′) J= 10.8 and 11.6Hz, 3.693(s, 3H, OCH3), 7.662-8.365(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 190.05(CO), 42.72(C1), 46.17(C2), 54.37(C3), 51.32(C4), 136.34(C5,6), 45.86(C7), 62.78(OCH3), 125.79-158.82(Ar-C).
(3-(4-Methylphenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone: 20 IR(KBr) 3469.13, 3091.00, 2993.87, 1665.34, 1532.65, 1476.34, 1228.31, 1075.34, 873.96 cm-1; 1H NMR(400MHz, CDCl3): ?? 2.932(dd, 1H, H1) J= 10.2 and 6.63Hz, 3.698(t, 1H, H2), 3.1993(t, 1H, H3), 2.698(dd, 1H, H4) J= 9.84 and 7.66Hz, 6.436(d, 1H, H5), 6.498(d, 1H, H6), 2.045(dd, 1H, H7) J= 8.82 and 6.62Hz, 1.126(dd, 1H, H7′) J= 10.34 and 7.62Hz, 3.102(s, 3H, CH3), 7.322-8.304(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 189.05(CO), 42.02(C1), 54.20(C2), 46.64(C3), 51.83(C4), 136.32(C5,6), 45.56(C7), 25.87(CH3), 124.87-154.26(Ar-C).
(3-(3-Nitrophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone: 21 IR(KBr) 3459.86, 3097.15, 2889.31, 1691.36, 1578.32, 1465.37, 1342.36, 1105.35, 1023.34, 823.51cm-1; 1H NMR(400MHz, CDCl3): ?? 3.234(dd, 1H, H1) J= 10.28 and 8.63Hz, 3.668(t, 1H, H2), 3.551(t, 1H, H3), 2.679(dd, 1H, H4) J= 9.82 and 10.60Hz, 6.462(d, 1H, H5), 6.439(d, 1H, H6), 2.001(dd, 1H, H7) J= 6.82 and 6.68Hz, 1.742(dd, 1H, H7′) J= 8.84 and 6.62 Hz, 7.766-8.683(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 191.23(CO), 44.82(C1), 51.98(C2), 45.84(C3), 50.16(C4), 136.82(C5,6),47.37(C7), 124.95-154.95(Ar-C).
(3-(4-Nitrophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone: 22. IR(KBr) 3455.98, 3092.34, 1686.76, 1548.22, 1498.13, 1176.16, 998.83, 885.43 cm-1; 1H NMR(400 MHz, CDCl3): ?? 3.124(dd, 1H, H1) J= 17.2 and 6.1Hz, 3.743(t, 1H, H2), 3.527(t, 1H, H3), 2.756(dd, 1H, H4) J= 12.0 and 4.8Hz, 6.349(d, 1H, H5), 6.436(d, 1H, H6), 2.202(dd, 1H, H7) J= 12.8 and 4.8Hz, 1.4414(dd, 1H, H7’) J= 10.8 and 7.2Hz, 7.263-8.561(m, 10H, Ar-H); 13C NMR(100MHz, CDCl3): ?? 189.38(CO), 43.72(C1), 52.48(C2), 44.54(C3), 50.36(C4), 135.72(C5,6), 46.57(C7), 125.36-153.29(Ar-C).
3.1. Antimicrobial activities
Measuring the mm of zone of inhibition of the compounds against the bacterial and fungal strains method was adopted for the evaluation of antimicrobial activities of prepared 3-(substituted phenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanones (entries 11-22). 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 in the present investigations. At a concentarion of 250??g/mL, the disc diffusion technique was followed (Vanagamudi et al., 2013) with Ampicillin and Streptomycin taken as the standard drugs fro evaluation of mm of zone of inhibition. For the measurement of mm of zone of inhibition 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 was used. The drugs dilution concentration was 50??g/mL. Grisseofulvin was taken as the standard drug.
3.1.1. Antibacterial sensitivity assay
Antibacterial sensitivity assay of (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones (entries 11-22) were performed using (Vanagamudi et al., 2013) disc diffusion technique. On every petri plate about 0.5 mL of the test bacterial sample was spread uniformly over the solidified Mueller Hinton agar using sterile glass spreader. About 5mm diameter of the discs were made up of Whatmann No.1 filter paper and impregnated with the solution of the compound were placed on the medium using sterile forceps. The plates were incubated for 24 h at 37oC by keeping the plates upside down to prevent the collection of water droplets over the medium. After 24 h, each petri plates were visually examined and the diameter values of the zone of inhibition were measured. Repeating the same procedure, the triplicate results were recorded.
The disc diffusion technique was followed (Vanagamudi et al., 2013) at a concentration of 250 ??g/mL with Ampicillin and Streptomycin used as the standard drugs. The measured antibacterial activities in the terms of mm of zone of inhibition of all methanones were presented in Table 3. Compounds 13-16 were shown maximum zone of inhibition against Escherichia coli, with greater than 20 mm of zone of inhibition compared to the methanones 12, 19, and 22 are moderately active in 13-19 mm of zone of inhibition. Ketones 18 and 21 are active with in 8-12 mm of zone of inhibition. The methanone derivatives 14, 16 and 17 were found to be effective against S. aureus greater than 20-24 mm of zone of inhibition. Compounds 13, 19 and 20 were moderately active greater than 13-19 mm of zone of inhibition. The methanone 12 and 15 were active within 8-12 mm of zone of inhibition. The methanone derivatives 14 and 16 were more active against Pseudomonas showing greater than 20 mm zone of inhibition and the other derivatives 11, 13, 17, 18, 21 and 22 were showed the zone of inhibitions between 13-19 mm. Compounds 15, 19 and 20 have shown moderately active with the zone of inhibition of 8-12 mm. The ketones 12, 15, 16 and 22 are effective against Klebsiella with 20-24 mm zone of inhibition while the other ketones showed a moderate activity. The methanones 11, 14, 16 and 19 were active when it is screened against P. vulgaris and the other compounds were found to be less effective. The ketones 11, 13 and 15 showed activities against E-faecalis when they are screened with 20-24 mm zone of inhibition.
3.1.2. Antifungal sensitivity assay
The disc diffusion technique (Vanagamudi et al., 2013) was used for the measurement of antifungal sensitivity assay of synthesized (2-hydroxynaphthalen-1-yl)(3-substituted phenyl bicyclo[2.2.1]hept-5-en-2-yl)methanone (entries 11-22). The 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 strains. Rotated the plate with clockwise and counter clock-wise for uniform spreading of the species and impregnated the discs with test solution. Made the test solution by dissolving 15mg of the methanone in 1mL of DMSO solvent. Solidify the medium for 24 h. Visually examined the petri plates and the diameter values of zone of inhibition were measured. By repeating the same procedure. The t riplicate results were recorded
The observed antifungal activities of all prepared methanones (entries 11-22) are presented in Table 4. Evaluation of antifungal activities of all methanones against C. albicans, showed that the three compounds 19, 21 and 22 are effective with 20 mm as the zone of inhibition in 250 ??g/mL while methanones 13, 14, 16 and 17 are active with 13-19 mm zone of inhibition containing one fungal colony and the compounds 11 and 20 were least active with 8-12 mm zone of inhibition containing two or three fungal colonies. Methanones 12, 15 and 18 were inactive in antifungal activity and they contain heavy fungal colonies. Compounds 12, 19 and 20-22 are highly active against Penicillum species in 20mm of zone of inhibitions. Ketones 11, 17 and 18 are active and they show one fungal colony in 13-19 mm of zone of inhibition. Compounds 15 and 16 produced 2-3 fungal colonies and inactive in 8-12 mm of zone of inhibition against Penicillum species. Heavy fungal colonies were produced by the compounds 13 and 14 leads to inactive against Penicillum fungal strain species. The mm of zone inhibition of ketones against A.niger was higher for the compounds 14, 17, 21 and 22 at 20 mm of zone of inhibition. Compound 11, 12, 16, 19 and 20 being active in 13-19 mm of zone of inhibition with one fungal colony. The ketone 13 was least active with 2-3 fungal colonies against A. niger fungal strain in 8-12 mm of zone of inhibition. Compounds 15 and 18 are inactive against A. niger fungal strain and produced heavy fungal colonies. Presence of bromo, chloro, methoxy, methyl and nitro substituents are responsible for the enhancement of antimicrobial activities of methanones.
3.2. Antioxidant activity
Generally organic substrates possess hydroxy and methoxy substituents, they show antioxidant activities. Within this motive, the author wishes to testify the antioxidant activities of prepared methanones. The antioxidant activities of synthesized (2-hydroxynaphthalen-1-yl)(3-substituted phenyl bicyclo[2.2.1]hept-5-en-2-yl)methanones (entries 11-22) have been evaluated by the DPPH radical scavenging effect(Vanangamudi et al., 2013). Made the 0.1M acetate solution was prepared by dissolving 1.64 g of sodium acetate in 15 mL of water and 150 ??L of acetic acid. The final volume of the solution was adjusted to 20 mL by adding water. Made the e 0.2 mmol of DPPH solution was prepared by dissolving 3.9 g of DPPH in 50 mL of ethanol. ??-Tocofereol (1mg in 10 mL of ethanol) solution was prepared. The test tubes were arranged serially with 1.0 mL of buffer solution mixed with 0.5 mL of DPPH solution. A series of various concentrations of synthesized methanones and ??-Tocofereol (1??g in 1 ml of ethanol) were added to each tube and mixed well. After 30 minutes in room temperature the absorbance of each solution were 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 were determined. The antioxidant activity was expressed in terms of IC50 (??g/mL, concentration required to inhibit DPPH radical formation by 50%). ??-Tocofereol was 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 5. From Table 5, all compounds (11-22) are active and shows antioxidant activity referred with standard. The observed percentages of inhibition of DPPH radical scavenging activities are 31.18 ‘ 37.16 and the standard have 37. 34. Among all methanones, the hydroxy and methoxy substituted methanones (17 and 18) were shown most significant antioxidant activity.
3.3. Insect antifeedant activity
Presence of carbonyl, unsaturation and halogen substitutions in organic substrates, they possess insect antifeedant activity. Within the view, in the present study the author wishes to examine the insect antifeedant activity of these (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones (entries 11-22) and found to be active as insect antifeedants. This test was performed with a 4th 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 (Thirunarayanan et al., 2010) was used against the 4th instar larvae to measure the antifeedant activity. The 4th instar larvae were selected for testing because the larvae at this stage feed very voraciously.
3.3.1. Measurement of insect antifeedant activity of (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones
The 1.85 cm diameter castor leaf discs were punched and intact with the petioles. The synthesized (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones (entries 11-22) were dissolved in acetone at a concentration of 200 ppm dipped for 5 minutes. The air-dried leaf discs were kept in one litre beaker containing little water in order to facilitate translocation of water. The fresh leaf discs were used for the insect antifeedant activity measurement by spraying the compounds on the discs and feeding of 4th instar larvae of the test insect on the leaf disc for 24h. The total area of the leaf disc consumed by the insects were measured by bio-assay leaf disc method (Thirunarayanan et al., 2010).The observed antifeedant activity of (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones (entries 11-22) were presented in Table 6.
The results of the antifeedant activity of bicyclo[2.2.1]heptane-2-yl methanones are presented in Table 6 reveals that, the compound 16 (3-(4-chlorophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl)methanone was found to be reflect significant antifeedant activity. This test is performed with the insects which ate only two-leaf disc soaked under the solution of this compound. The total leaf-disc consumed for the compounds 12-15 are in the range of 3.5 to 5 and they showed enough antifeedant activity but lesser than 16. Compound 16 have the total leaf-disc consumed value is 3 and it have significant insect antifeedant activity. Further compound 16 was subjected to measure the antifeedant activity at different 50, 100, 150 ppm concentrations and the observation reveals that as the concentrations decreased, the activity also decreased. It is observed from the results in Table 7 and that the 16 (3-(4-chlorophenyl)bicyclo[2.2.1]hept-5-en-2-yl)(2-hydroxynaphthalen-1-yl) methanone showed an appreciable antifeedant activity at 150 ppm concentration. The methanone derivatives 11 and 17-22 were showed higher values of total leaf consumed in the range of 6- 9 and these are inactive for insect antifeedant activity.
4. Conclusions
Some aryl bicyclo [2.2.1] hept-5-en-2-yl-methanone derivatives including (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones have been synthesized by aqueous phase fly-ash catalyzed Diels-Alder [4+2] cycloaddition of cyclopentadiene and aryl E- chalcones. The yields of the methanones are more than 60%. The antimicrobial, antioxidant and insect antifeedant activities of (2-hydroxynaphthalen-1-yl)(3-substituted phenylbicyclo[2.2.1]hept-5-en-2-yl)methanones (entries 11-22) have been evaluated using disc diffusion method. Almost all halogen substituted compounds shows effective antibacterial activities against their bacterial strains. The parent, 4-nitro and methoxy substituted ketones shows good antibacterial activities against p.vulgaris, e. faecalis bacterial strains. Nitro substituted methanones shows significant antifungal activity against their fungal strains. The 3-Br and 2-OCH3 substituted ketones shows good antifungal activity against c. albicans and penicillium species stains. The 2-Cl and 2-OH substituted compounds shows significant antifungal activity against a. niger fungal strain. The DPPH radical scavenging activity method was adopted for measurement of antioxidant activities. All the compounds shows enough antioxidant activity against DPPH radical scavenging process. While the compounds have OH and OCH3 substituents shows significant antioxidant activity. The insect antifeedant activity of all ketones were measured using leaf-disc bioassay method. The halogen substituted compounds were shown enough insect antifeedant activity. Among the halogen substituted compounds, the 4-Cl substituted methanone shows good insect antifeedant activity.

Source: Essay UK - https://www.essay.uk.com/essays/science/essay-the-diels-alder-reaction/


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