Constituents of Xerolekia speciosissima (L.) Anderb. (Inuleae), and Anti-Inflammatory Activity of 7,10-Diisobutyryloxy-8,9-epoxythymyl Isobutyrate

Xerolekia speciosissima (L.) Anderb., a rare plant from the north of Italy, is a member of the Inuleae-Inulinae subtribe of the Asteraceae. Despite its close taxonomic relationship with many species possessing medicinal properties, the chemical composition of the plant has remained unknown until now. A hydroalcoholic extract from the aerial parts of X. speciosissima was analyzed by HPLC-DAD-MS(n), revealing the presence of caffeic acid derivatives and flavonoids. In all, 19 compounds, including commonly found chlorogenic acids and less frequently occurring butyryl and methylbutyryl conjugates of dicaffeoylquinic and tricaffeoylhexaric acids, plus two flavonoids, were tentatively identified. Chromatographic separation of a hydroalcoholic extract from the capitula of the plant led to the isolation of (+)-dehydrodiconiferyl alcohol 4-O-β-glucopyranoside, quercimeritrin, astragalin, isoquercitrin, 6-hydroxykaempferol-7-O-β-glucoside, quercetagitrin, methyl caffeate, caffeic acid, protocatechuic acid, chlorogenic acid and 1,5-dicaffeoylquinic acid. Composition of a nonpolar extract from the aerial parts of the plant was analyzed by chromatographic methods supported with (1)H-NMR spectroscopy. The analysis revealed the presence of loliolide, reynosin, samtamarine, 2,3-dihydroaromaticin, 2-deoxy-4-epi-pulchellin and thymol derivatives as terpenoid constituents of the plant. One of the latter compounds—7,10-diisobutyryloxy-8,9-epoxythymyl isobutyrate—at concentrations 0.5, 1.0 and 2.5 μM, significantly reduced IL-8, IL-1β and CCL2 excretion by LPS-stimulated human neutrophils.