Ultrasound-assisted extraction of endemic <i>Stachys antalyensis</i> : LC–ESI–MS/MS phenolic profiling and <i>in vitro</i> antioxidant, enzyme-inhibitory, and cytotoxicity evaluation

<i>Stachys antalyensis</i>, an Anatolian endemic species, was investigated for its phenolic composition and in vitro bioactivities. Methanolic and aqueous extracts were prepared by ultrasound-assisted extraction and analyzed using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The methanolic extract exhibited higher total phenolic content (TPC; 58.29 mg gallic acid equivalents (GAE)/g) and total flavonoid content (TFC; 19.30 mg rutin equivalents (RE)/g) than the aqueous extract (28.72 mg GAE/g and 5.26 mg RE/g, respectively). Verbascoside (7961 µg/g) and chlorogenic acid (5358 µg/g) were the major constituents. In antioxidant assays, the methanolic extract showed stronger activity, with EC₅₀ or IC₅₀ values of 1.31 mg/mL in the phosphomolybdenum assay, 0.86 mg/mL in the cupric ion reducing antioxidant capacity assay (CUPRAC), 0.67 mg/mL in the ferric reducing antioxidant power assay (FRAP), and 4.19 mg/mL in the 2,2-diphenyl-1-picrylhydrazyl assay (DPPH), while the aqueous extract was more effective in ferrous ion chelation (IC₅₀: 1.14 mg/mL). The methanolic extract inhibited α-glucosidase (IC₅₀: 1.28 mg/mL), tyrosinase (IC₅₀: 1.06 mg/mL), and acetylcholinesterase (IC₅₀: 1.61 mg/mL). Cytotoxicity assays on human lung carcinoma (A549) and mouse fibroblast (L929) cell lines showed low toxicity between 250-2000 µg/mL, with cell viability ≥80% for A549 and ≥69% for L929 at 2000 µg/mL after 48 h. Overall, <i>S. antalyensis</i> is a phenolic-rich natural source with antioxidant and enzyme inhibitory potential.