Studies on structure-activity relationship of sphaeropsidins A-F, phytotoxins produced by Sphaeropsis sapinea f. sp. cupressi

Six forms of sphaeropsidins (SA–SF), three- and tetra-cyclic unrearranged pimarane diterpenes produced by Sphaeropsis sapinea f. sp. cupressi, as well as eight derivatives obtained by chemical modification of SA–SC, were assayed for their bioactivity. The effect of each compound on plants which are host or non-host of the pathogen was investigated. Activity on some plant pathogenic fungi was also tested. Some structure–activity relationships have been identified for both phytotoxic and antifungal activity. It appears that the integrity of the tricyclic pimarane system, the preservation of the double bond C(8)–C(14), the tertiary hydroxyl group at C-9, the vinyl group at C-13, and the carboxylic group at C-10 as well as the integrity of the A-ring provide these molecules with non selective phytotoxic and antimycotic activity.