Structure Revision of the Fungal Phytotoxin Cavoxin and of Its Corresponding Chroman-4-one Cavoxone by X‑ray Crystallography

Cavoxin
(1) was isolated as the main phytotoxin produced
by Phoma cava Schulzer, a toxigenic fungus isolated
from Castanea spp. Its structure was determined by
1D NMR and MS in 1985 along with that of the corresponding chroman-4-one
cavoxone (2), an artifact formed by acid treatment of 1. Since that time cavoxin was shown to be phytotoxic, antifungal,
antifeedant, herbicidal, and antirust with potential application in
agriculture and medicine. During a study aimed at improving cavoxin’s
production by P. cava, single crystals for X-ray
diffractometric analysis were obtained. The X-ray crystallography
characterization confirmed only in part the structure proposed for
cavoxin (1), revealing a different substitution pattern
on the aromatic ring, as depicted in the revised structure 3.