Structure determination of violaceol-I and -II, new fungal metabolites from a strain of Emericella violacea.

A toxic metabolite, violaceol, which was isolated from the fungus, E. violacea, was found to be a mixture of two isomers. Violaceol-I (3) and -II (4) were isolated as tetraacetates through acetylation and preparative thin layer chromatography. The structures of violaceol-I and -II were determined as shown in Fig. 1 and 2, mainly by the analysis of the 1H- and 13C-nuclear magnetic resonance spectral data, especially the 13C-1H indirect spin coupling constants. Violaceols were lethal to mice and exhibited weak antimicrobial activity.