Syntheses and evaluation of antioxidant activity of sydnonyl substituted thiazolidinone and thiazoline derivatives Original Research Article

3-Aryl-4-formylsydnone 4′-phenylthiosemicarbazones (3a–d) and 3-aryl-4-formylsydnone thiosemicarbazones (3e–h), which are precursors of 3-aryl-4-heterocyclic sydnones, are prepared by the condensation of 3-aryl-4-formylsydnones (1a–d) with 4′-phenylthiosemicarbazide (2a) and thiosemicarbazide (2b), respectively. The thiosemicarbazones 3 reacted with cyclic reagents such as ethyl chloroacetate (4a), ethyl 2-chloroacetoacetate (4b) and 2-bromoacetophenone (4c) to produce heterocyclic substituted sydnone derivatives 5–7 that possess 4-oxo-thiazolidine and thiazoline groups. The antioxidant activity of synthesized compounds 5a–7h was evaluated. Among these compounds, 4-methyl-2-[(3-arylsydnon-4-yl-methylene)hydrazono]-2,3-dihydro-thiazole-5-carboxylic acid ethyl ester (6e–h) and 4-phenyl-2-[(3-arylsydnon-4-yl-methylene)hydrazono]-2,3-dihydro-thiazoles (7e–h) exhibit the potent DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity, comparable to that of vitamin E.