Tetrahydroanthraquinone Derivatives from the Endophytic Fungus Stemphylium globuliferm

Four new tetrahydroanthraquinone derivatives, namely, dihydroaltersolanol B (1), dihydroaltersolanol C (2), and the atropisomers acetylalterporriol D (3) and acetylalterporriol E (4), were obtained from the endophytic fungus Stemphylium globuliferum, which was isolated from Juncus acutus growing in Egypt. The structures of the new compounds were unambiguously elucidated on the basis of one- and two-dimensional NMR spectroscopy, as well as by high-resolution mass spectrometry and electronic circular dichroism (ECD) spectroscopy. In addition, seven known anthraquinone derivatives 5–11 were isolated and identified on the basis of their spectral characteristics and by comparison with literature data. Compounds 2, 4–7, 9, and 11 showed strong cytotoxicity against the murine lymphoma cell line L5178Y with IC50 values ranging from 1.25 to 10.4 μM. Compounds 1–4 were also tested for their antibacterial activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Only 2 exhibited moderate growth inhibition against S. aureus with a minimum inhibitory concentration (MIC) of 49.7 μM.