Cytotoxic Steroidal Saponins from the Flowers of Allium leucanthum

Allium leucanthum C. Koch is an endemic Caucasian species that grows in Georgia. The flowers are used in traditional medicine. Phytochemical investigation allowed the isolation of seven spirostanol type saponins from the flowers. Their structures were elucidated on the base of NMR and HRESIMS spectrometry data. A new compound, which we have named leucospiroside A (5), has been identified as (25R)-5 alpha-spirostane-2 alpha,3 beta,6 beta-triol 3-O-beta-glucopyranosyl-(1 -> 3)-beta-glucopyranosyl-(1 -> 2)-[beta-glucopyranosyl-(1 -> 3)]-beta-glucopyranosyl-(1 -> 4)-beta-galactopyranoside. The six others were known substances, but are described in this plant for the first time. The crude extract, spirostanol and furostanol fractions, as well as isolated compounds, were evaluated for their in vitro cytotoxic activity. Compounds 1-3 and 5 were found to be the most active, with relatively similar IC50 values ranging from 3.7 to 5.8 mu M for a lung cancer cell line (A549) and 5.6 to 8.2 mu M for a colon cancer cell line (DLD-1).