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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.
