First report on LC–ESI–MS/MS-Based phenolic profiling and bioactivity of <i>onosma serpentinica</i> extracts

Newly described endemic Onosma species adapted to serpentine habitats may represent promising sources of bioactive metabolites; however, the phytochemical and biological properties of Onosma serpentinica remain unknown. This study investigated the phytochemical composition and biological activities of O. serpentinica extracts obtained by ultrasound-assisted extraction using ethyl acetate, methanol, and water. Total phenolic and flavonoid contents were determined spectrophotometrically, while phenolic compounds were characterized using validated liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI–MS/MS) analysis. Antioxidant capacity was evaluated using multiple in vitro assays, and enzyme inhibitory activities were assessed against cholinesterases, tyrosinase, α-amylase, and α-glucosidase. The methanol extract exhibited the highest total phenolic (69.93 mg gallic acid equivalents/g extract) and flavonoid contents (38.32 mg rutin equivalents/g extract) and was particularly rich in rosmarinic acid (5840 µg/g extract), chlorogenic acid (1115 µg/g extract), and apigenin-7-glucoside (977 µg/g extract). It also showed the strongest antioxidant activity, with the lowest half maximal inhibitory concentration (IC50) values in 2,2-diphenyl-1-picrylhydrazyl (DPPH) (0.80 mg/mL) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) (0.58 mg/mL) assays and the highest relative antioxidant capacity index (RACI). The aqueous extract exhibited the strongest metal chelating activity (IC50: 1.14 mg/mL), whereas the ethyl acetate extract showed the highest α-amylase inhibition (IC50: 1.34 mg/mL). Overall, O. serpentinica represents a promising source of phenolic compounds with notable antioxidant and enzyme inhibitory properties. This study provides the first comprehensive report on the phenolic composition and bioactivity of O. serpentinica.