Synthesis and antimicrobial activity of 3-(2-thienyl)-4-arylazo-5-hydroxy-5-trifluoromethyl-Δ2-isoxazolines and 3-(2-thienyl)-4-arylazo-5-trifluoromethylisoxazoles

1-(2-Thienyl)-2-arylazo-4,4,4-trifluorobutane-1,3-diones 4, obtained by the condensation of aryldiazonium salts 2 with 1-(2-thienyl)-4,4,4-trifluoromethyl-1,3-butanedione 3, on treatment with hydroxylamine hydrochloride yielded 3-(2-thienyl)-4-arylazo-5-hydroxy-5-trifluoromethyl-Δ2-isoxazolines 5. Subsequently, dehydration of 5-hydroxy-5-trifluoromethyl-Δ2-isoxazolines 5 to corresponding 3-(2-thienyl)-4-arylazo-5-trifluoromethylisoxazoles 6 was achieved by treating them with acetic anhydride or EtOH–H2SO4. The structure of the compounds was established on the basis of IR, NMR (1H, 13C and 19F), mass spectral studies and elemental analyses. All the compounds were screened for their in vitro antibacterial activity against four pathogenic bacterial strains such as Bacillus subtilis, Staphylococcus aureus (Gram-positive), Pseudomonas fluorescens, Escherichia coli (Gram-negative) and in vitro antifungal activity against two pathogenic fungal strains namely, Candida strain, Saccharomyces cerevisiae. Most of the compounds showed moderate to significant antibacterial activity selectively against Gram-positive bacteria and antifungal activity against S. cerevisiae.

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► Convenient synthesis of 5-hydroxy-5-trifluoromethyl-Δ2-isoxazolines.
► Acidic dehydration to corresponding 5-trifluoromethylisoxazoles.
► Characterisation through multinuclear NMR spectral data.
► Moderate to significant antibacterial and antifungal activities.