Phomentrioloxin, a Fungal Phytotoxin with Potential Herbicidal Activity, and its Derivatives: A Structure–Activity Relationship Study

Phomentrioloxin is a phytotoxic geranylcyclohexenetriol produced in liquid culture by Phomopsis sp. (teleomorph: Diaporthe gulyae), a potential mycoherbicide proposed for the control of the annual weed Carthamus lanatus. In this study, seven derivatives obtained by chemical modifications of the toxin were assayed for phytotoxic, antimicrobial, and zootoxic activities, and the structure-activity relationships were examined. Each compound was tested on nonhost weedy and agrarian plants, fungi, Gram+ and Gram- bacteria, and on brine shrimp larvae. The results provide insights into an investigation of the structural requirements for activity. The hydroxy groups at C-2 and C-4 appeared to be important features for the phytotoxicity, as well as an unchanged cyclohexentriol ring. A role seemed also to be played by the unsaturations of the geranyl side chain. These findings could be useful for understanding the mechanisms of action of new natural products, for identifying the active sites, and possibly in devising new herbicides of natural origin.