Sulphopreussomerins: Sulfur-Containing Preussomerins Isolated from the Marine-Derived Fungus Pyrenochaetopsis indica

The organic extract of Pyrenochaetopsis indica CF-301929, a fungal strain collected from the Coral Sea in Australia, showed broad-spectrum activity against the fungal phytopathogens Zymoseptoria tritici, Colletotrichum acutatum, Fusarium proliferatum, and Magnaporthe grisea. After extensive purification, five compounds were isolated, including three new sulfur containing preussomerins 1-3 along with two previously described molecules, ascochytatin (4) and preussomerin G (5). The new compounds incorporate rare thioglycolic or 2-hydroxy-3-mercaptopropionic acid moieties in their structures, and they represent the first members of a new class of preussomerins that we have named sulphopreussomerins. Multiple spectroscopic analyses, including HRESIMS and 1D/2D NMR experiments were used to elucidate their structures while the proposed absolute configuration of compound 1 was assigned by comparison of the experimental and theoretical ECD spectra. When tested against a fungal phytopathogen panel, preussomerin G exhibited, as previously reported, strong antifungal activity and cytotoxicity, whereas sulphopreussomerin A and ascochytatin showed moderate antifungal activity against Z. tritici with no detectable cytotoxicity.