The Sapogenin Atroviolacegenin and Its Diglycoside Atroviolaceoside from Allium atroviolaceum

A phytochemical analysis of broadleaf wild leek, Allium atroviolaceum, has led to the isolation of a new sapogenin, named atroviolacegenin (1, Chart 1), and its diglycoside derivative, named atroviolaceoside (2), both possessing a hydroxyl group at C-27, a rare feature among sapogenins and saponins. On the basis of chemical and spectroscopic analyses, including 2D NMR spectroscopy and mass spectrometry, the structures of the new compounds were elucidated as (25R)-5alpha-spirostan-2alpha,3beta,6beta,27-tetrol (1) and (25R)-5alpha-spirostan-2alpha,3beta,6beta,27-tetrol 3-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-galactopyranoside (2). These compounds are accompanied by three known spirostanol and furostanol saponins. In addition, 4,4'-dihydroxy-3-methoxychalcone, p-coumaroyl-N-tyrosine, and p-feruloyl-N-tyrosine have been found in the flowers and bulbs. Atroviolacegenin and atroviolaceoside were assayed to evaluate their antispasmodic activity in the guinea-pig isolated ileum and the data compared to those previously found for tropeosides (3a/3b and 4a/4b) from Tropea red onion bulbs. The absence of activity for both atroviolacegenin and atroviolaceoside highlighted the key role of the furostanol-type aglycone moiety for antispasmodic activity.