A New Antioxidant Decalin Polyketide from Freshwater‐Sediment‐Derived Fungus Penicillium sp. Strain S1a1

Chromatographic workup for EtOAc (ethyl acetate) extract of an OSMAC (One Strain MAny Compounds)‐modified solid rice culture of the freshwater‐sediment‐derived fungus, Penicillium sp. (S1a1), afforded one new decalin polyketide derivative, tanzawaic acid Z1 (1). The chemical structure of the new derivative was unambiguously established based on extensive 1D (one‐) and 2D (two‐dimensional) NMR (Nuclear Magnetic Resonance) spectroscopic data along with ESI‐HRMS (ElectroSpray Ionization‐High Resolution Mass Spectrometry). Moreover, the relative configuration was determined based on NMR spectroscopic data including a ROESY (Rotational Overhauser Effect SpectroscopY) spectrum. The absolute configuration was suggested on the basis of the specific optical rotation, and biogenetic considerations in comparison with related previously isolated known metabolites from the same fungal strain. In addition, the antioxidant, antibacterial and cytotoxic activities of the new derivative were evaluated. Compound 1 proved to exert a promising antioxidant activity. A freshwater‐sediment‐derived fungus, Penicillium sp. (S1a1) has been herein subjected to an OSMAC (One Strain MAny Compounds) culturing approach using 3.5% salt as a stress factor. This afforded one new decalin polyketide metabolite, tanzawaic acid Z1 (1). Structure elucidation was unambiguously determined based on extensive state‐of‐the‐art analyses. The relative and absolute configurations of 1 are also determined in this study. Compound 1 revealed a promising antioxidant activity.