Physicochemical and biological properties of luteolin-7-O-β-D-glucoside (cynaroside) isolated from Anthriscus sylvestris (L.) Hoffm.

A simple method for isolation of luteolin-7-O-beta-d-glucoside (cynaroside) from a short-lived perennial plant Anthriscus sylvestris (L.) Hoffm. is described. Cynaroside was isolated in high purity as documented by high-performance liquid chromatography (HPLC), thermal, and nuclear magnetic resonance (NMR) analyses. Isolated cynaroside shows biological activity especially against Gram-negative bacteria, exhibits antimutagenic activity, suppresses biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus, and increases frequency of mutations leading to ciprofloxacin resistance in Salmonella typhimurium. Additionally, electron paramagnetic resonance (EPR) spectroscopy and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assay confirmed its antioxidant and radical scavenging activity. In situ EPR and ultraviolet-visible (UV-Vis) spectroelectrochemical experiments were performed to follow the oxidation reactions of cynaroside in dimethyl sulfoxide solutions. The primary oxidation step takes place on the 1,2-dihydroxybenzene subunit leading to an unstable semiquinone anion radical as proved by EPR spectroscopy and quantum chemical calculations. Spectroelectrochemical and antioxidant studies indicate an important role of the deprotonated form of cynaroside in its redox and antioxidant behavior.