Phytotoxins produced by Phoma chenopodiicola, a fungal pathogen of Chenopodium album

Two phytotoxins were isolated from the liquid culture of Phoma chenopodiicola, a fungal pathogen proposed for the biological control of Chenopodium album, a common worldwide weed of arable crops. The two phytotoxins appeared to be a new tetrasubstituted furopyran and a new ent-pimaradiene. From the same culture a new tetrasubstituted isocoumarin was also isolated. These compounds were characterized by using spectroscopic (essentially 1D and 2D NMR and HR ESI MS) and chemical methods as 3-(3-methoxy-2,6-dimethyl-7aH-furo[2,3-b]pyran-4-yl)-but-2-en-1-ol, (1S,2S,3S,4S,5S,9R,10S,12S,13S)-1,3,12-triacetoxy-2,hydroxy-6-oxo-ent-pimara-7(8),15-dien-18-oic acid 2,18-lactone, 4,5,7-trihydroxy-3-methyl-isochroman-1-one, and consequently named chenopodolan D, chenopodolin B and chenisocoumarin. The absolute configuration to chenisocoumarin was assigned applying an advanced Mosher’s method through the derivatization of it secondary hydroxylated carbon C-4, while that of chenopodolan D by application of quantum mechanical calculations of chiroptical (ECD and ORD) properties. Assayed by leaf puncture to non-host weeds Chenopodolan D and chenopodolin B showed phytotoxicity while chenisocoumarin and the 9-O-acetyl derivative of chenopodolan D were inactive. These results confirm that the nature of the side chain at C-4 in chenopodolans and in particular its hydroxylation are important features to impart activity. The activity of chenopodolin B could also be explained by its possible hydrolization into chenopodolin.