In the title compound, C11H9NO3, the phenyl and isoxazole rings form a dihedral angle of 56.64 (8)°. The carb­oxy group is almost in the same plane as the isoxazole ring with a C—C—C—O torsion angle of −3.3 (2)°. In the crystal, pairs of O—H⋯O hydrogen bonds link the mol­ecules into head-to-head dimers. C—H⋯N hydrogen bonds and π–π stacking inter­actions between phenyl rings [centroid–centroid distance = 3.9614 (17)Å] link the dimers into a three-dimensional network.

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The asymmetric unit of the title compound, C16H11FN2OS, comprises two independent mol­ecules in which the benzothia­zole rings are essentially planar, with maximum deviations of 0.038 (2) and 0.045 (3) Å. The central benzothia­zole ring makes dihedral angles of 4.87 (13) and 0.64 (12)° and 4.04 (12) and 3.67 (12)° with the two terminal phenyl rings in the two independent mol­ecules. In the crystal, mol­ecules are connected via weak inter­molecular C—H⋯O hydrogen bonds forming supra­molecular chains along the c axis.

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The importance of heterocyclic chemistry in biological systems is well established. Compounds possessing isoxazole and isoxazoline ring system show a variety of biological activities (insecticidal, antibacterial, antibiotic, antitumour, antifungal, etc.) 1,2 and they also serve as prodrugs for an antiarthritic agent. 3 Isoxazolines also serve as important building blocks for the synthesis of biologically active molecules. 2 This has prompted us to synthesise new heterocycles and to study their biological activities.1,3-Dipolar cycloaddition reactions are useful tools for constructing biologically potent five membered heterocycles 2,4 and nitrile oxides serve as excellent 1,3-dipoles. Apart from the usual synthesis of nitrile oxides, 5 Rai et al. have developed new methods for generating nitrile oxides involving oxidative dehydrogenation of aldoximes using oxidants such as chloramine-T (CAT) 6 and mercuric acetate. 7 Since nitrile oxides dimerise readily, they are usually generated in situ and trapped by dipolarophiles.The classical method employed for the synthesis of isoxazoles involves 1,3-dipolar cycloaddition reactions of nitrile oxides to alkynes. For instance, the reaction of nitrile oxides with diethyl acetylenedicarboxylate affords diethyl 3-arylisoxazole-4,5-dicarboxylates. In continuation of our work on 1,3-dipoar cycloaddition reactions of nitrile oxides with various dipolarophiles, 8 here we have adopted our own method 7 for converting aldoximes into nitrile oxides and used ethyl α-cyanocinnamates as the alkene part of the dipolarophile with a hope to get more biologically potent heterocycles. The precursor cyanocinnamates were prepared by the reaction of aldehydes with ethyl cyanoacetate. 9 This paper also describes the synthesis and results of the biological testing of ethyl 3,5-diarylisoxazole-4-carboxylates 4 for their antifungal and antibacterial activities against the Gram negative bacterium Escherichia coli, Gram positive bacterium Bacillus cirroflagellosus, and the fungi Aspergillus niger and Fusarium poa. E. coli, B. cirroflagellosus and A. niger cells were found to be resistant to the compounds at the 20µg and 100µg concentrations, while F. poa cells were found to be resistant to 100µg concentrations. All compounds showed noticeable antimicrobial activity, which was indicated by the clearing zones present around the discs in comparision with the positive control. The results of the antibacterial and antifungal activity of the synthesised compounds were given in Tables 1 and 2.In a typical reaction of nitrile oxide with ethyl α-cyanocinnamate, an equimolar mixture of 3,4-dimethoxybenzaldehyde oxime 1, the α,β-unsaturated compound 2 and chloramine-T trihydrate in ethanol was refluxed on a water bath for 3 hours. The reaction was followed by TLC and continued until the disappearance of starting materials was observed. After the usual work up, the product 4a was obtained in 68% yield. The ethyl 3,5-diarylisoxazole-4-carboxylate (4) may be formed by elimination of HCN from the cycloadduct 3. Al...