Linking Phenolic Composition with Biological Activities in Three Endemic Marrubium Taxa

This study investigates the relationship between phenolic composition and biological activities of three endemic Marrubium taxa, namely Marrubium parviflorum subsp. oligodon (Boiss.) Seybold, Marrubium cephalanthum Boiss. & Noë, and Marrubium globosum Montbret & Aucher ex Benth. Ethanolic extracts prepared from the aerial parts were analyzed by HPLC-UV and twelve phenolic compounds were quantitatively identified. Among the investigated taxa, M. cephalanthum exhibited the highest phenolic content with verbascoside, rutin, and hyperoside as the predominant constituents. This taxon also showed the strongest antioxidant activity in DPPH (IC₅₀ = 26.28 μg/mL) and CUPRAC (A₀.₅ = 29.82 μg/mL) assays. In contrast, M. globosum demonstrated the highest activity in the ABTS assay (IC₅₀ = 3.58 μg/mL) and showed relatively higher cholinesterase inhibitory activity (AChE: A₀.₅ = 65.14 μg/mL; BChE: A₀.₅ = 132.73 μg/mL). Regarding lipoxygenase inhibition, M. parviflorum subsp. oligodon exhibited the strongest effect (IC₅₀ = 106.55 μg/mL), followed by M. cephalanthum and M. globosum. No considerable inhibitory activity was observed against α-glucosidase or α-amylase under the tested conditions. Overall, the findings indicate that variations in phenolic composition may be associated with differences in biological activities among the investigated taxa. These results contribute to the understanding of the phytochemical–bioactivity relationship in Marrubium species and provide a basis for further bioactivity-guided studies.