Phenolic Compounds from the Leaf Extract of Artichoke (<i>Cynara scolymus</i> L.) and Their Antimicrobial Activities

TLDR

Eight phenolic compounds were isolated from the n‑butanol fraction of artichoke leaf extracts and identified by HPLC/ESI‑MS/MS and NMR as four caffeoylquinic acids and four flavonoids. The n‑butanol extract and all eight isolated phenolics displayed antimicrobial activity against seven bacteria, four yeasts, and four molds, with chlorogenic acid, cynarin, luteolin‑7‑rutinoside, and cynaroside showing the strongest effects (MIC 50–200 µg/mL) and being more potent against fungi than bacteria. Keywords: artichoke, Cynara scolymus L., antimicrobial activity, phenolic compounds, caffeoylquinic acid derivatives, flavonoids.

Abstract

A preliminary antimicrobial disk assay of chloroform, ethyl acetate, and n-butanol extracts of artichoke (Cynara scolymus L.) leaf extracts showed that the n-butanol fraction exhibited the most significant antimicrobial activities against seven bacteria species, four yeasts, and four molds. Eight phenolic compounds were isolated from the n-butanol soluble fraction of artichoke leaf extracts. On the basis of high-performance liquid chromatography/electrospray ionization mass spectrometry, tandem mass spectrometry, and nuclear magnetic resonance techniques, the structures of the isolated compounds were determined as the four caffeoylquinic acid derivatives, chlorogenic acid (1), cynarin (2), 3,5-di-O-caffeoylquinic acid (3), and 4,5-di-O-caffeoylquinic acid (4), and the four flavonoids, luteolin-7-rutinoside (5), cynaroside (6), apigenin-7-rutinoside (7), and apigenin-7-O-β-D-glucopyranoside (8), respectively. The isolated compounds were examined for their antimicrobial activities on the above microorganisms, indicating that all eight phenolic compounds showed activity against most of the tested organisms. Among them, chlorogenic acid, cynarin, luteolin-7-rutinoside, and cynaroside exhibited a relatively higher activity than other compounds; in addition, they were more effective against fungi than bacteria. The minimum inhibitory concentrations of these compounds were between 50 and 200 μg/mL. Keywords: Artichoke; Cynara scolymus L.; antimicrobial activity; phenolic compounds; caffeoylquinic acid derivatives; flavonoids