Phytotoxic steroidal saponins from Agave offoyana leaves

Abstract

A bioassay-guided fractionation of Agave offoyana leaves led to the isolation of five steroidal saponins (1–5) along with six known saponins (6–11). The compounds were identified as (25R)-spirost-5-en-2α,3β-diol-12-one 3-O-{α-L-rhamnopyranosyl-(1→3)-O-β-D-glucopyranosyl-(1→2)-O-[β-D-xylopyranosyl-(1→3)]-O-β-D-glucopyranosyl-(1→4)-O-β-D-galactopyranoside} (1), (25R)-spirost-5-en-3β-ol-12-one 3-O-{α-L-rhamnopyranosyl-(1→3)-O-β-D-glucopyranosyl-(1→2)-O-[β-D-xylopyranosyl-(1→3)]-O-β-D-glu copyranosyl-(1→4)-O-β-D-galactopyranoside} (2), (25R)-spirost-5-en-3β-ol-12-one 3-O-{β-D-xylopyrano syl-(1→3)-O-β-D-glucopyranosyl-(1→2)-O-[β-D-xylopyranosyl-(1→3)]-O-β-D-glucopyranosyl-(1→4)-O-β -D-galactopyranoside} (3), (25R)-26-O-β-D-glucopyranosylfurost-5-en-3β,22α,26-triol-12-one 3-O- {α-L-rhamnopyranosyl-(1→3)-O-β-D-glucopyranosyl-(1→2)-O-[β-D-xylopyranosyl-(1→3)]-O-β-D-glucopyrano syl-(1→4)-O-β-D-galactopyranoside} (4) and (25R)-26-O-β-D-glucopyranosylfurost-5-en-3β,22α,26-triol- 12-one 3-O-{β-D-xylopyranosyl-(1→3)-O-β-D-glucopyranosyl-(1→2)-O-[β-D-xylopyranosyl-(1→3)]-O-β- D-glucopyranosyl-(1→4)-O-β-D-galactopyranoside} (5) by comprehensive spectroscopic analysis, including one- and two-dimensional NMR techniques, mass spectrometry and chemical methods. The phytotoxicity of the isolated compounds on the standard target species Lactuca sativa was evaluated.