Phytochemical profiling and antioxidant activity of Ononis angustissima

Ononis L. is a large genus of perennial herbs and shrubs of the Fabaceae family [1] known to be very rich in phenolic derivatives [2]. Some Ononis species are favorite foods for sheeps, goats, donkeys and other animals; the young shoots are succulent and sweet and in some Saharian countries are consumed as culinary vegetables [1,3]. Recently some herbal teas containing Ononis species as major component are sold in the market. Several plants of the genus are used as folk medicine remedies for the treatment of jaundice, urinary tract inflammations and kidney stones; besides, some species have been used for wounds healing, eczema and rheumatic complaints, against skin cancer and lesions and topically used as antiseptic and antimicrobial agents [4]. The ethnopharmacology importance and the richness in flavonoids of this genus prompted us to carry out further studies [5,6] on O. angustissima Lam, a plant widely present in Sahara regions. An antioxidant-oriented approach was carried out on aerial part extracts and exudate, leading to the isolation and structural characterization of three new natural flavonoids, 5',7-dihydroxy-2'-methoxy-isoflavone 4'-O-β-D-glucopyranoside (1), (3S)-7-hydroxy-4'-methoxy-isoflavane 3'-β-D-glucopyranoside (2), and kaempferol 3-O-β-D-glucopyranoside-7-O-(2'''-acetyl)-β-D-galactopyranoside (3) (Fig. 1), together with fifteen known phenolic derivatives. In order to deepen and full characterize the phytochemical profile of O. angustissima, a LC-HRESIMS and LC-HRESIMS/MS analyses of its extracts were also performed. The antioxidant activity of extracts, fractions and pure compounds was tested by three different assays. Multiple reaction mechanisms are usually involved in the antioxidant capacity evaluation of the natural compounds, therefore the Relative Antioxidant Capacity Index (RACI) was applied as an integrated approach to compare the results obtained by different methods.