Activity controlled isolation of secondary metabolites in Origanum rotundifolium Boiss, investigation of structures and investigation of antioxidance activities

Natural products play an importand role in drug discovery and development process. They have been used in traditional medicine from ancient times. In this work, aerial parts of Origanum rotundifolium Boiss were extracted with hexane, ethyl acetate, methanol sequentially. After removal of the solvent, the solid part was boiled in water then partitioned with ethyl acetate to yield the water/EtOAc extract. The antioxidant activities of all these extracts were carried out using different antioxidant assays, including 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH•) scavenging, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, reducing power. Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and trolox were used as standards. Total phenolic contents of extracts were also determined. Water/EtOAc extract exhibited the most antioxidant effect and included the most phenolic compounds among the extracts. Hence, water/EtOAc extract was subjected to chromatography to isolate the active compounds. The structures of isolated compounds were elucidated by 1D, 2D NMR and LC-TOF/MS. Apigenin (1), ferulic acid (2), vitexin (3), caprolactam (4), rosmarinic acid (5), and globoidnan A (6) were isolated and identified. Globoidnan A (6), vitexin (3), and rosmarinic acid (5) revealed the excellent DPPH• scavenging effect with the IC50 values of 22.4, 31.4, 47.2 μM respectively. Vitexin (3) (IC50 3.6), globoidnan A (6) (IC50 4.6), apigenin (1) (IC50 8.9), and ferulic acid (2) exhibited more ABTS•+ activity than standard trolox (IC50 13.8 μg/mL). The Origanum rotundifolium could be a promising natural antioxidant for food and pharmaceutical industries.