Chemical constituents of Digitalis viridiflora

The genus Digitalis (Plantaginaceae) contains biennial or perennial species. It is represented by nine species in the flora of Turkey including D. viridiflora Lindley [1]. Phenylethanoid glycosides, cardiac glycosides, steroidal saponins and pregnane glycosides constitute the main group of secondary metabolites of the genus Digitalis [2, 3]. In continuation of our systematic survey on the chemical composition of Digitalis species growing in Turkey, we recently reported five phenylethanoid glycosides from D. viridiflora as the preliminary phytochemical research [4]. Further detailed chromatographic studies on the chemical constituents of the leaves of D. viridiflora led to the isolation of a new phenylethanoid glycoside named as digiviridifloroside (1) along with a known phenylethanoid glycoside (calceolarioside A), two flavonoids (scutellarein 7-O-β-D-glucopyranoside and hispidulin 7-O-β-D-glucopyranoside), two cleroindicins (cleroindicins B and F), a nucleoside (adenosine), as well as a mixture of β-D-glucopyranosyl-(1→6)-4-O-caffeoyl-α/β-glucopyranose and 3,4-dihydroxyphenylethanol which could be an artefact formed during isolation procedure. The structure of the new compound was established as 3,4-dihydroxy-β-phenylethoxy-6-O-(E)-feruloyl-β-D-glucopyranosyl-(1→6)-4-O-(E)-caffeoyl-β-D-glucopyranoside (1) based on extensive 1D- and 2D-NMR spectroscopy as well as MS. Digiviridifloroside (1) is the third example of rare phenylethanoid glycosides obtained from the genus Digitalis bearing two aromatic acyl units; the first two ones were reported from D. lanata [5].

References:

[1] Davis PH. 1978. Digitalis L. in “Flora of Turkey and the East Aegean Islands”, Vol. 6, Davis PH (ed). University Press: Edinburgh; 680 – 697.

[2] Kirmizibekmez H, et al., Phytother. Res. 2014; 28: 534 – 538.

[3] Calis I et al., Pharmazie 1999; 54: 926 – 930.

[4] Kirmizibekmez H Rec. Nat. Prod. 2015; 9: 369 – 373.

[5] Kirmizibekmez H, et al., Helv. Chim. Acta 2009; 92: 1845 – 1852.