Synthesis and Free Radical Scavenging Activity of Pyranopyrazole-Based Tetrazole Compounds

Interest in the synthesis of heterocyclic compounds possessing potent biological activities has been on the increase of late. In this study, a novel series of tetrazole derivatives based on the pyranopyrazole skeleton was synthesized and studied for their antioxidant activities. Starting from a one-pot multicomponent reaction, the synthetic route included the synthesis of the pyranopyrazole skeletons first, followed by the introduction of the tetrazole ring through a [3+2] cycloaddition reaction. Reactions were effective and gave good yields for the target molecules. Confirmation of the structures of all synthesised compounds was performed using FTIR, ¹H NMR, ¹³C NMR, and mass spectrometric techniques, which collectively validated the formation of both the pyranopyrazole and tetrazole moieties.
Antioxidant activities of the synthesized derivatives were determined by standard in vitro tests, such as DPPH radical scavenging assays. The experimental results indicated that most of the title compounds possessed remarkable free-radical scavenging activity, and some of the analogues exhibited either comparable or higher activity than the standard antioxidant ascorbic acid. Further, this increased activity is seen to be driven by the synergy between the electron-rich pyranopyrazole ring system and the tetrazole group, which facilitates hydrogen atom donation and stabilization of reactive species. Structure–activity analysis further suggested that the presence of electron-donating substituents improved the antioxidant efficiency of the molecules.

Overall, the study demonstrates that pyranopyrazole-based tetrazoles represent a promising class of heterocyclic antioxidants with potential for further optimization and biological exploration. The findings provide a foundation for future studies aimed at developing these compounds as therapeutic agents for oxidative stress–related disorders.