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 μg/disk. Hence, alternethanoxins A and B have potential as nonselective natural herbicides. Some structure−activity relationship observations were also made.