Convenient synthesis and evaluation of antioxidant property of functionalized spiro indolinone-dihydroquinazolinones

In the present study an efficient synthetic pathway has been developed for the library synthesis of diversely functionalized spiro indolinone-dihydroquinazolinones from easily available isatins and 2-aminobenzamides by acid catalyzed condensation at 70 °C in ethanol. The outcome of the ROS scavenging analysis over the synthesized spiro compounds displays significant variation in their respective antioxidant properties with the change of substituent at different positions. Noteworthy, the spiro compounds substituted with phenyl ring at nitrogen atom either in indolinone or dihydroquinazolinone moiety show a promising defensive capability towards OH (≈ 83% at 80 µM against control) and O₂^- (≈ 78% at 20 µM against epinephrine auto-oxidation). Almost every single spiro compound exhibits substantial reducing power, especially compounds containing dihydroquinazolinone moiety substituted with aromatic ring at amide nitrogen (N-3) exhibit remarkable reducing property. IC₅₀ and TEAC (Trolox Equivalent Antioxidant Capacity) values reveal that the spiro compound substituted with phenyl ring to indolic nitrogen (N-1) possesses significant antioxidant potency (IC₅₀ ≈ 22.67 µM) and substantial OH scavenging ability (TEAC ≈ 0.82) comparable to highly potent antioxidant Trolox.