Alternethanoxins A and B, polycyclic ethanones produced by Alternaria sonchi, potential mycoherbicides for Sonchus arvensis biocontrol

Alternaria sonchi is a fungal pathogen isolated from Sonchus arvensis and proposed as a biocontrol
agent of this noxious perennial weed. Different phytotoxic metabolites were isolated from solid
culture of the fungus. Two new polycyclic ethanones, named alternethanoxins A and B, were
characterized using essentially spectroscopic and chemical methods. Tested by leaf disk-puncture
assay on the fungal host plant and a number of nonhost plants, alternethanoxins A and B were
shown to be phytotoxic, whereas they did not possess antimicrobial activity tested at 100 ?g/disk.
Hence, alternethanoxins A and B have potential as nonselective natural herbicides. Some
structure-activity relationship observations were also made.