Synthesis and antibacterial activity of some new 1-heteroaryl-5-amino-4-phenyl-3-trifluoromethylpyrazoles

Treatment of 1,1,1-trifluoromethyl-3-cyano-3-phenylpropanone (1) with several heteroarylhydrazines (2a-e) in refluxing ethanol affords 1-heteroaryl-5-amino-4-phenyl-3-trifluoromethylpyrazoles (4) in a regioselective manner. The location of trifluoromethyl group at position-3 was established by a combined use of 13C and 19F NMR spectroscopy. The reaction proceeds through the intermediacy of the hydrazone which was isolated and characterized in one case (3e) by performing the reaction at room temperature. The compounds 3e and 4 were tested for their antibacterial property against six Gram-positive and three Gram-negative bacteria. Two compounds, namely 1-(benzothiazol-2'-yl)-5-amino-4-phenyl-3-trifluoromethylpyrazole (4a) and 1-(6'-methylbenzothiazol-2'-yl)-5-amino-4-phenyl-3-trifluoromethylpyrazole (4b) have displayed antibacterial activity comparable to the commercial antibiotics.