Structural and stereochemical studies of hydroxyanthraquinone derivatives from the endophytic fungus Coniothyrium sp.

Four known hydroxyanthraquinones (1-4) together with four new derivatives having a tetralone moiety, namely coniothyrinones A-D (5-8), were isolated from the culture of Coniothyrium sp., an endophytic fungus isolated from Salsola oppostifolia from Gomera in the Canary Islands. The structures of the new compounds were elucidated by detailed spectroscopic analysis and comparison with reported data. The absolute configurations of coniothyrinones A (5), B (6), and D (8) were determined by TDDFT calculations of CD spectra, allowing the determination of the absolute configuration of coniothyrinone C (7) as well. Coniothyrinones A (5), B (6), and D (8) could be used as ECD reference compounds in the determination of absolute configuration for related tetralone derivatives. This is the first report of anthraquinones and derivatives from an isolate of the genus Coniothyrium sp. These compounds showed inhibitory effects against the fungus Microbotryum violaceum, the alga Chlorella fusca, and the bacteria Escherichia coli and Bacillus megaterium.