Triterpenoid saponins from the aerial parts of Solidago virgaurea alpestris with inhibiting activity of Candida albicans yeast-hyphal conversion

Abstract As part of research for treatments to combat oral dryness, our evaluation of the activity of an aqueous extract of Solidago virgaurea (L.) ssp. alpestris (Asteraceae) revealed activity against Candida albicans hyphae, the pathogenic form of this yeast. Systematic bioassay-guided fractionation of this extract gave an active saponin-containing fraction from which six oleanane-type triterpenoid saponins were isolated. Three of these were isolated for the first time, as 3- O -( β - d -glucopyranosyl-(1 → 3)- β - d -glucopyranosyl)-28- O -( β - d -fucopyranosyl-(1 → 2)- α - l -rhamnopyranosyl-(1 → 3)- β - d -xylopyranosyl-(1 → 4)- α - l -rhamnopyranosyl-(1 → 2)- β - d -xylopyranosyl)-polygalacic acid (virgaureasaponin 4), 3- O -( β - d -glucopyranosyl)-28- O -( β - d -fucopyranosyl-(1 → 2)- α - l -rhamnopyranosyl-(1 → 3)- β - d -xylopyranosyl-(1 → 4)- α - l -rhamnopyranosyl-(1 → 2)- β - d -xylopyranosyl)-polygalacic acid (virgaureasaponin 5) and 3- O -( β - d -glucopyranosyl)-28- O -( α - l -rhamnopyranosyl-(1 → 3)- β - d -xylopyranosyl-(1 → 4)- α - l -rhamnopyranosyl-(1 → 2)-[5- O -acetylapiofuranosyl-(1 → 3)-[4- O -(3-(3-hydroxy-1-oxobutoxy)-1-oxobutyl)]- β - d -fucopyranosyl]-polygalacic acid (virgaureasaponin 6). Their structures were established by carrying out 1D and 2D NMR experiments along with HRMS analyses. All of the six saponins were evaluated to ascertain their inhibition of C. albicans yeast-hyphal conversion, and four of them showed significant inhibition.