Tanzawaic acid derivatives from freshwater sediment-derived fungus Penicillium sp.

Chemical investigation of a freshwater sediment-derived fungus, Penicillium sp. (S1a1), led to the isolation of three new tanzawaic acid derivatives, including penitanzchroman (1), tanzawaic acids Y (2) and Z (3), along with six known tanzawaic acid analogues (4-9), three known isochromans (10-12) and two known benzoquinones (13 and 14). The structures of the new compounds were established based on high-resolution mass spectrometry, and detailed analysis of one- and two-dimensional NMR spectroscopy. The relative configuration of the new compounds was assigned on the basis of NMR spectroscopic data including ROESY spectra. The absolute configuration was determined based on the specific optical rotation, in addition to biogenetic considerations in comparison with related co-isolated known metabolites. Penitanzchroman (1) constitutes a hitherto unprecedented skeleton, formed of tanzawaic acid A (5) and (3S)-6-hydroxy-8-methoxy-3,5-dimethylisochroman (10) linked by a C-C bond. Moreover, all compounds were evaluated for their antibacterial and cytotoxic activities.