Stagonolides B-F, Nonenolides Produced by Stagonospora cirsii, a Potential Mycoherbicide of Cirsium arvense”

S. cirsii, a fungal pathogen isolated from C. arvense and proposed as a potential mycoherbicide of this perennial noxious weed, produces phytotoxic metabolites in liq. and solid cultures. Recently, the main metabolite, stagonolide (I), with interesting phytotoxic properties, was isolated from a liq. culture and characterized as a new nonenolide. In the present work this same fungus, grown in solid culture, exhibited an increased capacity to produce nonenolides. Five new nonenolides, named stagonolides B-F, were isolated and characterized using spectroscopic methods. When tested by a leaf disk puncture assay at a concn. of 1 mg/mL, these compds. showed no toxicity to C. arvense and Sonchus arvensis, whereas I was highly toxic. I and stagonolide C (II) were weakly toxic to Colpoda steinii, a protozoan, when tested at 0.05 mg/mL, with the other stagonolides nontoxic. A no. of structure-activity relationship observations were made.