Preparation and phytotoxicity study of lappalone from dehydrocostuslactone

Abstract

Lappalone, a sesquiterpene lactone isolated from the roots of Saussurea lappa, was successfully synthesized for the first time from dehydrocostuslactone following a four-step synthetic route, in which the first step was a photoaddition of acetaldehyde, with a global yield of 14%. The starting material, dehydrocostuslactone, was isolated in gram scale from Saussurea lappa root extracts. The phytotoxicity profiles of the product, the starting material and the intermediates were obtained in two different bioassays: on etiolated wheat coleoptiles and on seeds of Standard Target Species (STS). Low IC50 values were found for lappalone vs. dehydrocostuslactone (161 μM and 839 μM in cress roots, respectively), reaching 60–80% inhibition percentages at the highest concentrations. These bioassays indicated the higher potential allelopathic activity of the sesquiterpene lappalone (C17) when compared with dehydrocostuslactone (C15) and the intermediates in the synthetic route.