Chromatography of crude extracts of cultures of Pithomyces chartarum on silicic acid has been shown to separate the biologically active sporidesmins from a group of inactive metabolites. One of these inactive compounds has been purified and shown to be the dimethyl thioether analogue of sporidesmin, named spordesmin-D. Evidence is presented for the structure of another inactive metabolite, sporidesmin-F, which has not been obtained in crystalline form. Sporidesmin has been converted into sporidesmin-D by treatment with sodium borohydride and methyl iodide.