Antifungal Activities of Ketoazomethines of Phenyl Glyoxal and p-Substituted Anilines

A new series of ketoazomethines were synthesized by condensation of phenyl glyoxal (prepared by partial oxidation of acetophenone) with various p-substituted anilines viz. p-Cl, p-Br, p-NO2, p-(C2H5)2N and p-CH3. These compounds were characterized by elemental analysis, IR and H NMR. The synthesized ketoazomethines were screened for their antifungal activity against hazardous fungi namely Fusarium oxysporum, Alternaria brassicola, Sclerotium and Pythium.


Experimental
All the chemicals used were either E-Merck or Qualigens.Melting points of all the compounds determined in open glass capillaries were uncorrected.Elemental analysis of samples was carried out on Euro EA elemental analyzer.Infrared spectra were recorded in KBr medium on Thermo Nicollet Nexus FT-IR spectrophotometer and 300MHz NMR spectra were recorded in dimethylsulphoxide medium on Varian C-13 NMR spectrometer using TMS as internal standard.Column chromatography was carried out using silica gel (finer than 200#).Characterization data is presented in Table 1 and spectral data in Table 2

Preparation of phenyl glyoxal
Phenyl glyoxal was prepared by the partial oxidation of acetophenone with selenium dioxide.Reaction mixture containing acetophenone (0.1 mol,1) and selenium dioxide (0.1 mol) in round bottom flask containing 95% ethyl alcohol was refluxed for 4-6 h.Orange yellow reaction mixture was decanted and concentrated over water bath and dissolved in ether to remove selenium from the product.

Preparation of ketoazomethines(4a-f) (Scheme 1)
Phenyl glyoxal (2, 0.2 mol) and aniline (3A-F, 0.2 mol) were taken in a round bottom flask containing 100 mL of ethanol and refluxed on water bath for 8 h.Excess of ethanol was removed from reaction mixture and cooled at room temperature.Then it was poured in ice cold water and filtered.Solid obtained were collected and recrystallized with ethanol.

Preparation of medium and sample solutions
For the preparation of PDA (Potato Dextrose Agar) medium 250 g potato pieces boiled in water were filtered and filtrate was made up to 1 liter.To this solution 20 g dextrose powder was added followed by heating to a syrupy viscous consistency.Standard solutions of all the samples of 50 ppm concentration were prepared by dissolving known quantity of compounds in known volume of DMSO (dimethylsulphoxide).
Antifungal activities were performed by paper disc method 18 .First of all PDA medium was sterilized in Autoclave and then poured into autoclaved Petri dishes near the gas flame, to avoid contamination and these plates were placed in Laminar Air Flow for an hour.There after filter paper discs dipped in sample solution were placed on medium in Petri dish and kept in Laminar Air Flow for half an hour.Fungus bit of 1mm diameter was put at a distance of 1 cm from paper disk wet in sample solution and Petri dishes were sealed with paraffin film in incubator at 25-30 0 C for 72-96 h for growth of fungus.Fungal growth was measured as the mean of distances from inoculation point of fungus to its maximum growth in three directions.Three replicates were used for each fungus.
The synthesized compounds were subjected to antifungal screening and compared against a standard fungicide Diethane M-45 and DMSO as control with no inhibition; results are given in Table 3.

Table 1 .
. Physical characteristics and elemental analysis of ketoazomethines

Table 2 .
Spectral data of ketoazomethines