Synthesis and antioxidant assay of new nicotinonitrile analogues clubbed thiazole, pyrazole and/or pyridine ring systems

Abstract

AbstractA series of novel nicotinonitrile derivatives were synthesized by hybridization with thiazole, pyrazole, and pyridine ring systems using 4‐aminobenzohydrazide as link‐bridge. The synthetic strategy of nicotinonitrile‐thiazole analogues involves cyclization of the precursor N‐phenyl thiosemicarbazide derivative 4 with chloroacetic acid and phenacyl bromide. The reaction of hydrazide 3 with acetylacetone and/or ethyl acetoacetate was applied as a synthetic route for accessing 2‐((4‐(pyrazole‐1‐carbonyl)phenyl)amino)‐nicotinonitrile derivatives 9–10. The 2‐((4‐(4‐thiazolylidene‐pyrazole‐1‐carbonyl)‐phenyl)amino)nicotinonitriles 14–15 were obtained via a nucleophilic addition of pyrazolone 10 to phenyl isothiocyanate followed by cyclization with chloroacetone, phenacyl chloride, and/or ethyl bromoacetate. The 6‐amino‐4‐aryl‐3,5‐dicyano‐2‐oxo‐1‐(4‐substitutedbenzamido)‐pyridines 19 were synthesized by Knoevenagel condensation N′‐(2‐cyanoacetyl)‐benzohydrazide derivative 16 with substituted benzaldehydes followed by heating with malononitrile. All synthesized products were evaluated for their antioxidant potentialities using of 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) radical cation delcolorization assay. The nicotinonitrile‐thiazole hybrid 6b was found the most promising antioxidant agent with inhibition activity 86.27%.