Cytotoxic acyl amides from the soil fungus Gymnascella dankaliensis

The soil fungus Gymnascella dankaliensis was collected in the vicinity of the Giza pyramids, Egypt. When grown on solid rice medium the fungus yielded four new compounds including 11'-carboxygymnastatin N (1), gymnastatin S (2), dankamide (3), and aranorosin-2-methylether (4), the latter having been reported previously only as a semisynthetic compound. In addition, six known metabolites (5-10) were isolated. Addition of NaCl or KBr to the rice medium resulted in the accumulation of chlorinated or brominated compounds as indicated by LC-MS analysis due to the characteristic isotope patterns observed. From the rice medium spiked with 3.5% NaCl the known chlorinated compounds gymnastatin A (11) and gymnastatin B (12) were obtained. All isolated compounds were unambiguously structurally elucidated on the basis of comprehensive spectral analysis (1D and 2D NMR, and mass spectrometry), as well as by comparison with the literature. Compounds 4, 7 and 11 showed potent cytotoxicity against the murine lymphoma cell line L5178Y (IC50 values 0.44, 0.58 and 0.64μM, respectively), whereas 12 exhibited moderate activity with an IC50 value of 5.80μM.