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.