Phenolic Glycosides with antiproteasomal activity from Centaurea urvillei DC. subsp. urvillei

A new flavanone glycoside, naringenin-7-O-β-D-glucuronopyranoside, and a new flavonol glycoside, 6-hydroxykaempferol-7-O-β-D-glucuronopyranoside were isolated together with 12 known compounds, 5 flavone glycoside; hispidulin-7-O-β-D-glucuronopyranoside, apigenin-7-O-β-D-methylglucuronopyranoside, hispidulin-7-O-β-D-methylglucuronopyranoside, hispidulin-7-O-β-D-glucopyranoside, apigenin-7-O-β-D-glucopyranoside, a flavonol; kaempferol, two flavone; apigenin, and luteolin, a flavanone glycoside; eriodictyol-7-O-β-D-glucuronopyranoside, and three phenol glycoside; arbutin, salidroside, and 3,5-dihydroxyphenethyl alcohol-3-O-β-D-glucopyranoside from Centaurea urvillei subsp. urvillei. The structure elucidation of the new compounds was achieved by a combination of one- ((1)H and (13)C) and two-dimensional NMR techniques (G-COSY, G-HMQC, and G-HMBC) and LC-ESI-MS. The isolated compounds were tested for their antiproteasomal activity. The results indicated that kaempferol, a well known and widely distributed flavonoid in the plant kingdom, was the most active antiproteasomal agent, followed by apigenin, eriodictyol-7-O-β-D-glucuronopyranoside, 3,5-dihydroxyphenethyl alcohol-3-O-β-D-glucopyranoside, and salidroside, respectively.