Xanthones and oxepino[2, 3-b]chromones from three endophytic fungi

Karsten Krohn, Simeon F. Kouam, Guy M. Kuigoua, Hidayat Hussain, Stephan Cludius-Brandt, Ulrich Flörke, Tibor Kurtán, Gennaro Pescitelli, Lorenzo Di Bari, Siegfried Draeger, Barbara Schulz

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Abstract

Three new metabolites, microsphaeropsones A-C (1-3) with a unique oxepino[2,3-b]chromen-6-one (ring-enlarged xanthone) skeleton, were isolated from the endophytic fungus Microsphaeropsis species, co-occurring with their putative biogenetic anthraquinoide precursors citreorosein (4) and emodin (5). From another Microsphaeropsis species, large amounts of fusidienol A (8a), smaller amounts of emodin (5), the known aromatic xanthones 9a and 9b, the new 3,4-dihydrofusidienol A (8b), and the new aromatic xanthone 9c were isolated. The endophyte Seimatosporium species produced a new aromatic xanthone, seimatoxanthone A (10), and 3,4-dihydroglobosuxanthone A (12), closely related to a-diversolonic ester (13) from Microdiplodia sp. The structures were determined mainly by extensive 1D and 2D NMR experiments and supported by X-ray single-crystal analysis of 1 and the oxidation product 7. The absolute configurations of the microsphaeropsones A-C (1-3) were established by comparison of the electronic and vibrational circular dichroism (ECD and VCD) spectra of 1 with time-dependent DFT (TDDFT) and DFT calculations by using either the solid-state structures or DFT-optimized geometries as inputs. Preliminary studies indicated that 1, 2, and enone 7 showed antibacterial, fungicidal, and algicidal properties.

Original languageEnglish
Pages (from-to)12121-12132
Number of pages12
JournalChemistry - A European Journal
Volume15
Issue number44
DOIs
Publication statusPublished - Dec 1 2009

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Keywords

  • Anthraquinones
  • Biological activity
  • Circular dichroism
  • Density functional calculations
  • Xanthones

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

Cite this

Krohn, K., Kouam, S. F., Kuigoua, G. M., Hussain, H., Cludius-Brandt, S., Flörke, U., Kurtán, T., Pescitelli, G., Di Bari, L., Draeger, S., & Schulz, B. (2009). Xanthones and oxepino[2, 3-b]chromones from three endophytic fungi. Chemistry - A European Journal, 15(44), 12121-12132. https://doi.org/10.1002/chem.200900749