Assignment through chiroptical methods of the absolute configuration of fungal dihydropyranpyran-4-5-diones phytotoxins, potential herbicides for buffelgrass (cenchrus ciliaris) biocontrol

Radicinin and cochliotoxin (1 and 2) two phytotoxic pyranpyran-4,5-diones were isolated together with their close metabolites 3-epi-radicinin, radicinol, and its 3-epimer (3-5), from the culture filtrates of Cochliobolus australiensis, a fungus proposed as mycoherbcide for biocontrol of buffelgrass, a very noxious and dangerous weed. The absolute configuration of cochliotoxin was determined by chiroptical Optical Rotatory Dispersion (ORD), Electronic Circular Dichroism (ECD), and Vibrational Circular Dichroism (VCD)) and computational methods. The same methods were used to confirm that of radicinin, radicinol and their 3-epimers, previously determined with chemical, spectroscopic and ECD methods.