Structural characterization of phytotoxic terpenoids from Cestrum parqui

Isolation, chemical characterization and phytotoxicity of nine polyhydroxylated terpenes (five C13nor-isoprenoids, two sesquiterpenes, a spirostane and a pseudosapogenin) from Cestrum parqui L'Herr are reported. In this work we completed the phytochemical investigation of the terpenic fraction of the plant and described the structural elucidation of polar isoprenoids using NMR methods. All the configurations of the compounds have been assigned by NOESY experiments. Four new structures have been identified as (3S,5R,6R,7E,9R)-5,6,9-trihydroxy-3-isopropyloxy-7-megastigmene, 5alpha-spirostan-3beta,12beta,15alpha-triol, and 26-O-(3'-isopentanoyl)-beta-d-glucopyranosyl-5alpha-furost-20(22)-ene-3beta,26-diol, and as an unusual tricyclic sesquiterpene. The compounds have been assayed for their phytotoxicity on lettuce at the concentrations ranging between 10(-4) and 10(-7)M. The activities of some compounds were similar to that of the herbicide pendimethalin.