Bioactive Phenolic Acid Derivatives and Undescribed Esculetin Glycosides from Pseudopodospermum szowitzii (DC.) Kuth

Pseudopodospermum szowitzii (DC.) Kuth. a member of the Asteraceae family, grows naturally in the Irano-Turanian phytogeographical area, including Anatolia. In Anatolia, P. szowitsii, known as "goftigoda," has edible young leaves and roots and is used in folk medicine for antidiabetic and analgesic properties. Nine compounds, including chlorogenic acid and derivatives from the ethyl acetate layer as well as 2,4,6-trimethoxyphenyl-1-O-β-glucopyranoside, 2,4,6-trimethoxyphenyl-1-O-β-apiofuranosyl-(1→6)-β-glucopyranoside, esculetin 6-O-β-glucopyranoside, and esculetin 6-O-β-apiofuranosyl-(1→6)-β-glucopyranoside from the water part of the methanolic extract, were isolated as known compounds. Notably, all esculetin derivatives have been isolated from the Pseudopodospermum for the first time, and among them, three compounds, esculetin 6-O-β-xylosyl-(1→6)-β-glucopyranoside, esculetin 6-O-β-glucopyranosyl-(1→3)-β-glucopyranoside, and esculetin 6-O-β-glucopyranosyl-(1→6)-β-glucopyranoside, were isolated as new esculetin heterosides that have not yet been isolated from any natural sources. The antioxidant activities of the total extract, phases, fractions, and compounds of P. szowitsii were also tested by evaluating their radical-scavenging capacities against DPPH and ABTS radicals. The ethyl acetate phase and the isolated compounds displayed significant antioxidant activity. The most active compound was caffeic acid, with IC₅₀ values of 2.7 µg/mL and 3.4 µg/mL against DPPH and ABTS radicals, respectively, followed by dicaffeoylquinic acid derivatives and their methyl esters. On the other hand, none of the coumarin derivatives exhibited significant radical-scavenging activity.