Insect antifeedant potent halogen substituted phenyl chalcones

Some 2′,3′,4′-trichlorophenyl chalcones [( E )-1-(2,3,4-trichlorophenyl)-3-(substituted phenyl)-2-propen-1-ones] have been synthesised using sulfated Titania catalyzed solvent-free aldol condensation between 2,3,4-trichloroacetophenone and substituted benzaldehydes. The purities of synthesised chalcones were checked by their analytical, physical and spectroscopic data reported in literature. The insect antifeedant activities of these chalcones have been studied using 4 th instar larvae Achoea Janata L by castor leaf disc bio-assay method. The chloro substituted chalcones shows significant insect antifeedant activity.

These chalcones also used as corrosion inhibitors in iron and steel utensil and equipment manufacturing industries [23].
These chalcones are also precursor key intermediate for synthesis of important biologically active higher organic heterocycles such as flavones, flavonoids, chromones, aurones and azole related compounds [24,25].
In agricultural field they play with much more important role as insect antifeedants. Dasharathi et al., have studied the solvent assisted synthesis and insect antifeedant activities of some multi-substituted naphthyl styryl ketones [26]. Vibhut et al., have studied the insect antifeedant activities of some chalcones by invitro bio-asssay method [27].
Therefore, the authors taken efforts for studying the insect antifeedant activities of the above chalcones by solvent-free synthesis and checked the purities by reported analytical, physical constants and spectral data [37][38][39][40][41].

1. General
All chemicals used were procured from Sigma-Aldrich and Merck chemical companies. Mettler FP51 melting point apparatus was used for determining the melting point of all synthesized chalcones in open glass capillaries and are uncorrected.
The absorption maxima (λmax, nm), of all chalcones were determined by recording the ultraviolet spectra on ELICO BL 222 ultraviolet spectrophotometer using spectral grade methanol. The AVATAR-300 Fourier transform spectrophotometer was used for recording infrared spectra (KBr, 4000-400 cm -1 ) of all chalcones in KBr disc.
The Bruker AV400 series type NMR spectrometer was utilized for recording NMR spectra of all chalcones, operating at 400MHz for 1 H and 100 MHz for 13 C spectra in CDCl 3 solvent using TMS as internal standard. Mass spectra of all synthesised chalcones were recorded on SHIMADZU mass spectrometer using chemical ionization technique.
The solution was concentrated and purified by re-crystallization. The synthesized chalcones were characterized by their physical constants, UV, IR, 1 H and 13 C NMR and Mass spectral data. Analytical and Mass spectral data are presented in Table 1. ILCPA Volume 20 Scheme 1. Synthesis of 2′,3′,4′-trichlorophenyl chalcones.

3. Measurement of insect antifeedant activities of 2′,3′,4′-trichlorophenyl chalcones
The castor Leaf discs of a diameter of 1.85 cm were punched with the petioles intact. All chalcones were dissolved in acetone at a concentration of 200 ppm dipped for 5 minutes. The air-dried leaf discs were placed in 1 L beaker containing little water in order to facilitate translocation of water. Therefore the leaf discs remains fresh throughout the duration of the rest, 4 th instar larvae of the test insect, which had been preserved on the leaf discs of all synthesised 2′,3′,4′-trichlorophenyl chalcones and allowed to feed on them for 24 h. The area of the leaf disc consumes were measured by Dethlers [36] method. The observed antifeedant activity of 2′,3′,4′-trichlorophenyl chalcones are presented in Table 2 and Table 3.

RESULTS AND DISCUSSION
The multipronged activities present in different 2′,3′,4′-trichlorophenyl chalcones are intended to examine their insect antifeedant activities against castor semilooper. The larvae of Achoea janata L were reared as described on the leaves of castor Riclmus cammunls in the laboratory at the temperature range of 26° C ±1 °C and a relative humidity of 75-85 %. The leaf -disc bioassay method 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.
The results of the antifeedant activity of substituted styryl 2′,3′,4′-trichlorophenyl ketones were presented in Table 2 and it reveals that the compounds 2-5 were found to reflect remarkable antifeedant among all other naphthones. This test is performed with the insects which are only two-leaf disc soaked under the solution of this compound. Compounds 2-5 also show enough antifeedant activity but lesser than 5. Further compound 5 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 3 and that the 4-chlorostyryl 2′,3′,4′-trichlorophenyl ketone 5 showed an appreciable antifeedant activity at 150 ppm concentration.