Onosma gracilis (Trautv.) and O. oreodoxa (Boiss. & Heldr.): Phytochemistry, in silico docking, antioxidant and enzyme inhibitory activities.

• Chemical composition and biological activity of two Onosma species were studied. • Rosmarinic acid, hesperidin and hyperoside were found as the major compounds. • The samples exhibited remarkable antioxidant and enzyme inhibitory activity. • Hyperoside was a potent inhibitor on the ezymes. In this study, it was aimed to determine the in vitro antioxidant and enzyme inhibitory activities of methanol (MeOH) extracts isolated from Onosma gracilis (Trautv.) and O. oreodoxa (Boiss. & Heldr.). O. oreodoxa was found to be richer in both phenolics and flavonoids than O. gracilis. The amounts of total phenolics and flavonoids in O. oreodoxa were 53.76 mg GAEs/g and 25.29 mg QEs/g, respectively. In addition to spectrophometric analysis, in chromatographic analyzes, twenty-four and twenty-six compounds were identified in O. gracilis and O. oreodoxa , respectively. High amounts of hesperidin (6647.2 and 5260.75 µg/g extract, respectively), hyperoside (7153.26 and 10216.74 µg/g extract, respectively) and rosmarinic acid (21824.33 and 87493.19 µg/g extract, respectively) were found in O. gracilis and O. oreodoxa. While O. oreodoxa showed higher activity in cupric reducing antioxidant power (CUPRAC), ferric reducing antioxidant power (FRAP), phosphomolybdenum, 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging, and ferrous ion chelating assays (324.22, 175.41, 719.50, 125.60 mg TEs/g extract and 25.11 mg EDTAEs/g extract, respectively), ABTS radical scavenging activity of O. gracilis (164.55 mg TEs/g extract) was higher than that of O. oreodoxa. O. gracilis also exhibited higher inhibitory activity on acetylcholinesterase (AChE), butyrylcholinesterase (BChE) (2.57 mg GALAEs/g extract) and α-glucosidase (1674.24 mg ACEs/g extract). On the other hand, the sample showing the most effective inhibition on α-amylase and tyrosinase was O. oreodoxa (417.34 mg ACEs/g extract and 136.18 mg KAEs/g extract, respectively). As a result of the molecular docking analysis performed to determine the contribution of hesperidin, hyperoside and rosmarinic acid to the enzyme inhibitory activity, the binding affinity and inhibition constant of hyperoside to all enzymes were quite high and therefore it was concluded that it may be the compound that contribute to the activity. [ABSTRACT FROM AUTHOR]