A facile synthesis of some novel thiazoles, arylazothiazoles, and pyrazole linked to thiazolyl coumarin as antibacterial agents

Abstract

5-bromosalicylaldehyde (1) was reacted with thiosemicarbazide to afford thiosemicarbazone derivative 2. The latter underwent cyclocondensation upon reaction with α-haloester, α-haloketone as well as hydrazonoyl halides affording 1,3-thiazoles and arylazothiazoles 3-6, respectively. On the other hand, pyrazolyl thiazolyl coumarin derivatives 9a–c and 11a–c was obtained via reaction of hydrazinylthiazole 8 with acetylacetone, trifloroacetylacetone, ethyl acetoacetate and/or arylazoacetylacetone 10a–c, respectively. Furthermore, thiazolotriazine derivative 12 was accomplished via reaction of 8 with ethyl 2-(2-phenylhydrazono)-2-chloroacetate. The structures of the newly prepared compounds were elucidated by spectral data. Eleven of the newly synthesized compounds were screened for their antibacterial activity. The results indicated that, compounds 5a, 5b, 9a, 9c, 11b and 12 were strong active toward Gram-positive bacteria Enterococcus faecalis. Compound 5a was strong active toward Gram-positive bacteria Staphylococcus aureus. Moreover, compounds 9b, 11b, and 12 were strong active toward Gram-negative bacteria Pseudomonas aeruginosa.