Flavonoids from Piper crocatum Ruiz & Pav.: Isolation, structural characterization, antioxidant properties, and density functional theory insights

Flavonoid constituents were isolated from the leaves of Piper crocatum Ruiz & Pav. by chromatographic separation. Two flavonoids, kumatakenin ( 1 ) and pachypodol ( 2 ), were identified through detailed spectroscopic analyses, including 1 H and 13 C NMR and high-resolution mass spectrometry. Notably, kumatakenin is reported here for the first time as a constituent of P. crocatum , thereby expanding the phytochemical profile of this species. The antioxidant activity of the isolated compounds was evaluated using in vitro chemical assays, with compounds 1 and 2 exhibiting IC₅₀ values of 42.3 and 7.1 μ g/mL , respectively, in superoxide anion scavenging assay, while IC₅₀ values of 204.8 and 58.3 μ g/mL , respectively, were obtained in the DPPH radical scavenging assay. To support the experimental observations, DFT calculations were performed, revealing differences in frontier molecular orbital energies (ΔE HOMO–LUMO = −0.15098 eV for 1 and − 0.15087 eV for 2 ) and thermodynamic descriptors relevant to radical-scavenging mechanisms. Energetic analysis indicated that the hydrogen atom transfer (HAT) pathway is thermodynamically favored for both compounds, consistent with the experimentally observed activity trend ( Q > 2 > 1 ). Comparative analysis further suggested that methoxy substitution influences the electronic structure and associated thermodynamic parameters, which is consistent with the observed differences in antioxidant behavior. Overall, this study contributes to the chemical characterization of P. crocatum flavonoids and provides a structure–property interpretation of their antioxidant activity based on combined experimental and computational approaches. • Kumatakenin ( 1 ) was first reported from Piper crocatum. • Kumatakenin ( 1 ) and pachypodol ( 2 ) exhibited notable antioxidant properties as DPPH free-radical and superoxide anion scavengers, with compound 2 exhibiting greater activity than compound 1 . • Density Functional Theory (DFT) studies showed that Hydrogen Atom Transfer (HAT) mechanism is preferred by these compounds, where hydroxyl group at C4’ position is more reactive to transfer hydrogen and form a stable radical.