Steroidal Saponins from Furcraea hexapetala Leaves and Their Phytotoxic Activity

Four new steroidal saponins (1–4) along with 13 known saponins were isolated from the leaves of Furcraea hexapetala. The new compounds were identified as (20R,22R,25R)-3β-hydroxy-5α-spirostan-12-one 3-O-{α-l-rhamnopyranosyl-(1→4)-O-β-d-glucopyranosyl-(1→3)-O-[β-d-glucopyranosyl-(1→3)-O-β-d-glucopyranosyl-(1→2)]-O-β-d-glucopyranosyl-(1→4)-O-β-d-galactopyranoside} (1), (25R)-3β-hydroxy-5α-spirost-20­(21)-en-12-one 3-O-{α-l-rhamnopyranosyl-(1→4)-O-β-d-glucopyranosyl-(1→3)-O-[β-d-glucopyranosyl-(1→3)-O-β-d-glucopyranosyl-(1→2)]-O-β-d-glucopyranosyl-(1→4)-O-β-d-galactopyranoside} (2), (25R)-5α-spirostan-3β-ol 3-O-{β-d-glucopyranosyl-(1→2)-O-β-d-glucopyranosyl-(1→2)-O-β-d-glucopyranosyl-(1→4)-O-β-d-galactopyranoside} (3), and (25R)-5β-spirostan-3β-ol 3-O-{β-d-glucopyranosyl-(1→6)-O-β-d-galactopyranoside} (4) by spectroscopic analysis, including one- and two-dimensional NMR techniques, mass spectrometry, and chemical methods. The phytotoxicity of the isolated compounds against the standard target species Lactuca sativa was evaluated. Structure–activity relationships for these compounds with respect to phytotoxic effects are discussed.