• Hymenosetin, a 3-decalinoyltetramic acid antibiotic from cultures of the ash dieback pathogen, Hymenoscyphus pseudoalbidus.

      Halecker, Sandra; Surup, Frank; Kuhnert, Eric; Mohr, Kathrin I; Brock, Nelson L; Dickschat, Jeroen S; Junker, Corina; Schulz, Barbara; Stadler, Marc; Helmholtz Centre for ifection research, Innhoffenstr. 7, D38124 Braunschweig, Germany. (2014-04)
      A 3-decalinoyltetramic acid, for which the trivial name hymenosetin is proposed, was isolated from crude extracts of a virulent strain of the ash dieback pathogen, Hymenoscyphus pseudoalbidus (="Chalara fraxinea"). This compound was produced only under certain culture conditions in submerged cultures of the fungus. Its planar structure was determined by NMR spectroscopy and by mass spectrometry. The absolute stereochemistry was assigned by CD spectroscopy and HETLOC data. Hymenosetin exhibited broad spectrum antibacterial and antifungal activities (including strong inhibition of MRSA), as well as moderate cytotoxic effects. So far, the metabolite proved inactive in assays for evaluation of phytotoxicity, whereas viridiol, another secondary metabolite known from H. pseudoalbidus, was regarded as phytotoxic principle of the pathogen against its host, Fraxinus excelsior. Further studies will show whether hymenosetin constitutes a defence metabolite that is produced by the pathogenic fungus to combat other microbes and fungi in the natural environment.
    • Monochlorinated calocerins A-D and 9-oxostrobilurin derivatives from the basidiomycete Favolaschia calocera.

      Chepkirui, Clara; Richter, Christian; Matasyoh, Josphat Clement; Stadler, Marc; Helmholtz Centre for infection research, Ihoffenstr. 7, 38124 Braunschweig, Germany. (2016-12)
      Eight previously undescribed compounds were isolated and characterised from the supernatant and mycelium of a culture of the basidiomycete Favolaschia calocera originating from Kakamega equatorial rainforest in Kenya. These were: 9- oxostrobilurins A, G, K and I and the four monochlorinated calocerins A, B, C and D. The calocerins extend our knowledge of halogenated compounds obtained from natural sources. Four further known compounds were also identified: strobilurin G, favolon, pterulinic acid and 2,3 -dihydro-1-benzoxepin derivative. The four oxostrobilurins exhibited prominent antifungal and cytotoxic activities while the four calocerins only showed cytotoxic activity.