Syntheses of aromatic substituted hydrazino-thiazole derivatives to clarify structural characterization and antioxidant activity between 3-arylsydnonyl and aryl substituted hydrazino-thiazoles

This work clarifies the structural characterization and antioxidant activity between aromatic and 3-arylsydnonyl substituted hydrazino-thiazoles by further synthesizing a series of aromatic ring-substituted hydrazino-thiazole derivatives 8a-h and 9a-h. Hydrazino-thiazole derivatives 8a-h and 9a-h were obtained by reacting aromatic or heterocyclic aromatic aldehyde thiosemicarbazones 7a-h with cyclization reagents ethyl 2-chloroacetoacetate (2a) and 2-bromoacetophenone (2b), respectively. The ORTEP drawings of compounds 8g, 8h and 9f provide strong evidence of the structure of aromatic thiazole derivatives 8a-h and 9a-h. Undoubtedly, the structure of compounds 3e-h and 4e-h synthesized by the reaction of 3-aryl-4-formylsydnone thiosemicarbazones 1e-h with cyclization reagents 2a and 2b in the previous work should have the thiazole moiety, and not the thiazoline moiety. Both the new thiazole derivatives 8a-h and 9a-h and the 3-arylsydnonyl-substituted derivatives 3e-h and 4e-h were investigated to determine their antioxidant activity by two tests that have been highly documented-the direct scavenging effect on a stable free 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and the inhibition of the 2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical. Results of this study demonstrate that not only the thiazole ring and the aryl ring has the contribution to the antioxidant activities, the sydnone ring of 3-arylsydnonyl moiety also has its considerable contribution.