Pyrrospirone Z and related decahydrofluorene alkaloids produced by the new coprophilous species Schizothecium keniense (Schizotheciaceae, Sordariales)

A decahydrofluorene-class alkaloid, pyrrospirone Z (1 a), along with pyrrospirone F (2), pyrrospirone M (3), GKK 1032 A 2 (4), daldinol (5), orthosporin (6), and 3, 4 - dihydro- 3, 4, 8 - trihydroxy- 1 (2 H) - naphthalenone (7), was purified from the new coprophilous species Schizothecium keniense, isolated from dung in Kenya. Structural elucidation was achieved using comprehensive 1 D and 2 D NMR spectroscopy, and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), with relative configurations assigned based on NOESY correlations.

Among the compounds, pyrrospirone F (2) and GKK 1032 A 2 (4) displayed significant antibacterial activity against the Gram-positive bacteria Bacillus subtilis (MIC = 4.2 μg / mL and 8.3 μg / mL, respectively) and Staphylococcus aureus (MIC = 8.3 μg / mL for both). Additionally, compounds 2 and 4 showed mild antifungal activity against the filamentous fungi Mucor hiemalis at 33.3 μg / mL. Cytotoxicity assays revealed that GKK 1032 A 2 (4) was the most potent compound, with IC 50 values ranging from 2.0 µM to 8.1 µM across the tested human cancer cell lines.

This work represents the first investigation of the chemical constituents of the genus Schizothecium and underscores the potential of coprophilous fungi as valuable sources of biologically active metabolites.