Isolation and Characterization of Secondary Metabolites from Endemic and Edible <i>Polygonum sivasicum</i> with In Vitro Antioxidant and Cytotoxic Activities

<i>Polygonum sivasicum</i> Kit Tan and Yildiz, one of the eight endemic <i>Polygonum</i> species in Türkiye, belongs to the Polygonaceae family. Preliminary phytochemical investigation of methanol and hexane extracts of <i>P. sivasicum</i> resulted in four compounds, namely, annphenone (<b>1</b>), hyperoside (<b>2</b>), daucosterol (<b>3</b>), and β-sitosterol (<b>4</b>). Their structures were elucidated by 1D-, 2D-NMR, and HRESIMS analyses. This study signifies the first isolation of annphenone from the <i>Polygonum</i> genus. Antioxidant capabilities of different extracts of <i>P. sivasicum</i> were carried out using DPPH^·, ABTS^·+, CUPRAC, metal chelating, and β-carotene linoleic acid bleaching assays, and their effectiveness was quantified through IC₅₀ values. Furthermore, 27 phenolic compounds were identified using LC-HRESIMS from methanol extract, which has the highest antioxidant activity among the <i>P. sivasicum</i> extracts. The major phenolic constituents identified were hyperoside (4535.0 μg/g extract), rutin (4387.4 μg/g extract), and chlorogenic acid (3306.6 μg/g extract). GC-MS analysis determined palmitic acid, α-linolenic acid, and 8,11-octadecadieonic acid as major fatty acids in the hexane extract. The cell viability profile of <i>P. sivasicum</i> methanol extract and its isolates hyperoside, annphenone, and daucosterol was evaluated on fibroblast (CCD-1079Sk), breast carcinoma (MCF-7) and lung carcinoma (A549) cell lines. Annphenone exhibited IC₅₀ values of 0.25 ± 0.01 mg/mL against the A549 cell line and 0.36 ± 0.02 mg/mL against the MCF-7 cell line. The selective cytotoxicity observed for daucosterol against the A549 cell line, with a high selectivity index of 1.44, underscores its potential as a promising candidate for drug development. The study establishes a framework integrating phytochemical profiling with biological assays to identify therapeutic agents from endemic plants.