Ultrasound promoted green synthesis of spiro[pyrano[2,3-c]pyrazoles] as antioxidant agents

Ultrasound promoted, cerium ammonium nitrate catalyzed sustainable synthesis of spiro[indoline3,4'-pyrano[2,3-c]pyrazole] derivatives (4a-l) is reported herein. The synthesized compounds were screened for their antioxidant activities as free radical scavenging effect on diphenylpicryl hydrazine (DPPH center dot), 2,2'-azino-bis(3-ethylbenzthiazoline- 6-sulphonic acid) (ABTS(center dot+)) and nitric oxide (NO) radicals. The screened compounds showed potent scavenging activities against DPPH center dot, ABTS(center dot+) and NO radicals. In order to further extend on studies and to obtain a deep insight into structure activity relationship of this class of compounds, we designed N-substitution of indole moiety with the aim to study its antioxidant potential.