Two new natural 10-membered macrolides (1, 2) and one chromene-4,5-dione derivative (3), named stagonolides J and K and stagochromene A, respectively, were isolated from the phytopathogenic fungus Stagonospora cirsii S-47, together with two known compounds, stagonolide A (4) and herbarumin I (5). Stagonolides J and K and stagochromene A were characterized as (5E,7R*,8S*,9R*)-7,8-dihydroxy-9-propyl-5-nonen-9-olide, (5E,7R,9S)-7-hydroxy-9-propyl-5-nonen-9-olide, and (2R*,3R*)-3-hydroxy-2-propyltetrahydro-2H-chromene-4,5(3H,4aH)-dione, respectively, by spectroscopic (mostly by NMR and ESIMS) data. Compounds 1-5 showed different rates of phytotoxic activity on punctured leaf discs of Sonchus arvensis. The antimicrobial, cytotoxic, and antiprotozoal activity of isolated compounds was also evaluated. Based on our data, stagonolide K and herbarumin I can be proposed as a potential scaffold for the development of a new natural herbicide and estimated as possible selection/quality markers of a bioherbicide based on S. cirsii, while stagonolide A can be considered as a mycotoxin.
Keywords: bioherbicide; macrolides; mycotoxin; stagochromene; stagonolide.