Isolation, structure characterization and prediction of antioxidant activity of two new compounds from the leaves of Dodonaea viscosa native to the Sultanate of Oman

Traditionally, Dodonaea viscosa (D. viscosa) is used worldwide for the treatment of different chronic diseases. The current investigation involves the isolation, structure characterization and prediction of antioxidant compounds from the leaves of D. viscosa, which was collected from AL-Hamra, Sultanate of Oman. The leaves samples were used for the extraction of plant constituents with methanol by using hot extraction method. The methanol solvent was evaporated by usual method and the crude extract was dissolved in water and fractionation successively with different polarity solvents to give hexane, chloroform, ethyl acetate, butanol and water extracts, respectively. The antioxidant activity of different polarity crude extracts and isolated pure compounds was determined by modified 1,1-diphenyl-2-picryl-hydrazyl (DPPH) method. The highest antioxidant activity was found in hexane extract and the lowest antioxidant activity was found in butanol extract and followed by hexane > chloroform > ethyl acetate > methanol > water > butanol extract. The hexane and ethyl acetate crude extracts were used for the isolation and separation of antioxidant compounds by using different chromatographic techniques. The isolated pure compounds were characterized as 3,3′,4′,5,7-pentahydroxyflavane (1) and 4-methoxylstigmasterol (2) by MS, 1H NMR, 13C NMR, and 2D NMR. Both the compounds, 3,3′,4′,5,7-pentahydroxyflavane (1) and 4-methoxylstigmasterol (2) were isolated for the first time from the selected Omani plant species. The pure compounds obtained from hexane and ethyl acetate extracts of the selected plant species could be a good source of natural antioxidant.