Synthesis and antioxidant activity of 1,3,4-oxadiazole tagged thieno[2,3-d]pyrimidine derivatives

This study represents the synthesis of a new series of N-substituted phenyl-5-methyl-6-(5-(4-substituted phenyl)-1,3,4-oxadiazol-2-yl)thieno[2,3-d]pyrimidin-4-amine derivatives (4a-l) and substituted phenylamino-5-methylthieno[2,3-d]pyrimidine-6-carboxylic acid derivatives (3a-d). The newly synthesized compounds were characterized by (1)H NMR, (13)C NMR, LC-MS and IR analyses. All these novel compounds were screened for their in vitro antioxidant activity by employing DPPH, hydrogen peroxide, and nitric oxide radical scavenging assays. Compounds 4k, 4j, 4d, and 4e showed significant radical scavenging due to the presence of electron donating substituent on both sides of the thienopyrimidine ring enhances the activity and electron withdrawing groups like nitro decrease.