Phyllostoxin and phyllostin, bioactive metabolites produced by Phyllosticta cirsii, a potential mycoherbicide for Cirsium arvense biocontrol

Phyllosticta cirsii, a fungal pathogen isolated from diseased Cirsium arvense leaves and evaluated as a biocontrol agent of this noxious perennial weed, produces different phytotoxic metabolites with potential herbicidal activity when grown in liq. cultures. Phyllostictines A-D, four novel oxazatricycloalkenones, were recently isolated from this pathogen and chem. and biol. characterized. Further purifn. of the same org. ext. provided two other metabolites, named phyllostoxin and phyllostin, which were characterized by spectroscopic technique (essentially NMR and MS). Phyllostoxin and phyllostin proved to be a new pentasubstituted bicyclooctatrienylacetic acid ester and a new pentasubstituted hexahydrobenzodioxinecarboxylic acid Me ester, resp. When tested on punctured C. arvense leaves, phyllostoxin proved to be highly phytotoxic, causing rapid and large necrosis, whereas phyllostin had no phytotoxicity in this bioassay. This is not surprising, considering the noteworthy structural differences between the two compds., suggesting the presence of active functional groups in phyllostoxin not present in the other metabolite. These results further support the focused approach of finding novel metabolites with herbicidal properties by looking at the culture exts. of weed fungal pathogens.