Structure–activity relationship studies of the phytotoxic properties of the diterpenicmoiety of breviones

Abstract

Brevianes are a family of bioactivemeroterpenoids originally described in fungi of the family Penicillium. These compounds have attracted a great deal of interest not only because of their unusual skeleton, suggesting a mixed mevalonate and polyketide biogenetic pathway, and their unusual oxa-spiro ring fused to an 𝜶-pyrone, but also because of the bioactivities shown bymanymembers of this family.

During the course of a project aimed at the total synthesis of natural breviones A to E, the authors were able to synthesise the diterpenic moiety of brevianes and abeo-brevianes. As a result, a collection of 25 compounds were synthesised and tested for bioactivity by two different bioassays. The bioassays used were etiolated wheat coleoptiles (Triticum aestivum) and seedlings in petri dishes. The plant species tested in the seedling bioassaywere the commercial dicots lettuce and cress and themonocot weeds Echinochloa crus-galli and Lolium rigidum.

The results clearly show that expanded phenanthrene-like compounds corresponding to the diterpenicmoiety of abeo-brevianes are more selective towards E. crus-galli in comparison with L. rigidum. Such selectivity can reach up to one order ofmagnitude (200-fold) andmakes someof the compoundsgood candidates as leads for the development of more specific herbicides.