Sphaeropsidin F, a new pimarane diterpene produced in vitro by the cypress pathogen Sphaeropsis sapinea f. sp. cupressi

A new pimarane diterpene was isolated from liquid cultures of Sphaeropsis sapinea f. sp. cupressi, a plant pathogenic fungus causing a form of canker disease of Italian cypress (Cupressus sempervirens L.). The metabolite, characterized by spectroscopic methods, was named sphaeropsidin F. When assayed on test plants sphaeropsidin F caused less severe symptoms that those of sphaeropsidin A, which is the main toxin produced by this fungus. A solution of sphaeropsidin F (0.1 mg mL–1) tested on severed cypress twigs caused yellowing of the apical leaves of C. sempervirens twigs, whereas C. macrocarpa and C. arizonica were not affected. This shows that the three cypress species had a different grade of sensitivity to the action of the toxin. As already demonstrated for rings B and C, the modification of the A ring strongly reduced the biological activity of the molecule.