Secondary Metabolites from the Leaves of Digitalis viridiflora

Abstract

A new phenylethanoid glycoside, named digiviridifloroside (1), was isolated from the leaves of Digitalis viridiflora Lindley along with a known phenylethanoid glycoside calceolarioside A (2), two flavonoid glycosides, scutellarein 7-O-β-D-glucopyranoside (3) and hispidulin 7-O-β-D-glucopyranoside (4), two cleroindicins, cleroindicins B (5) and F (6), a nucleoside, adenosine (7), as well as a mixture of β-glucopyranosyl-(1→6)-4-O-caffeoyl-α/β -glucopyranose and 3,4-dihydroxyphenylethanol. The structure of the new compound was established as 3,4-dihydroxy-β-phenylethoxy-6-O-(E)-feruloyl-glucopyranosyl-(1→6)-4-O-(E)-caffeoyl-β-glucopyranoside (1) based on extensive 1D- and 2D-NMR spectroscopy, as well as HR-ESI-MS. Digiviridifloroside represents a rare type of phenylethanoid glycoside which bears two aromatic acyl units in its structure. In addition to phytochemical studies, the isolates were evaluated for their in vitro antimicrobial activities against three pathogenic bacteria and three yeast strains using a microdilution method. Among the tested compounds, 5 exhibited moderate antibacterial activity against Bacillus cereus NRRLB 3711 with a MIC value of 25 μg/mL, whereas compounds 5 and 6 showed relatively high anticandidal activity against Candida strains with MIC values down to 12.5 μg/mL, in comparison to the standard antimicrobial compounds.