Synthesis and antioxidant activity of new 2-(2-oxoindoline-3-ylydene) substituted 5,6-dihydroimidazo[2,1-b]thiazolones and 6,7-dihydro-thiazolo[3,2-a]pyrimidinones

The paper presents the results of the study on the interaction of 5,6-dihydroimidazo[2,1-b]thiazoles and 6,7-dihydrothiazolo[3,2-a]pyrimidines with isatin derivatives. It was established that the condensation of the indicated reagents occurs selectively upon heating and without the use of a catalyst with the formation of addition products, 2-(2-oxoindolin-3-ylidene)-5,6-dihydroimidazo[2,1-b]thiazole-3(2H)-ones 6a–d and 2-(2-oxoindolin-3-ylidene)-6,7-dihydro-2H-thiazolo[3,2-a]pyrimidin-3(5H)-ones 7a–c, the structure of which was rigorously proven by 1H NMR (13C) spectroscopy and chromatography-mass spectrometry. All newly synthesized compounds were tested for antioxidant activity. According to the conducted bioscreening, the compounds 2-(5-nitro-2-oxoindolin-3-ylidene)-5,6-dihydroimidazo[2,1-b]thiazol-3(2H)-one 6d (I=84.5%) and 2-(5-nitro-2-oxoindolin-3-ylidene)-6,7-dihydro-2H-thiazolo[3,2-a]pyrimidin-3(5H)-one 7c (I=79.1%) exhibit the highest antioxidant action. This proves that electron-acceptor substituents in the 5-position of the 2,3-dihydro-1H-indoledione fragment contribute to a significant increase in antioxidant activity.