Dibenzo-α-pyrones from the endophytic fungus <i>Alternaria</i> sp. Samif01: isolation, structure elucidation, and their antibacterial and antioxidant activities
<p>The EtOAc extract of the liquid fermentation of <i>Alternaria</i> sp. Samif01, an endophytic fungus obtained from <i>Salvia miltiorrhiza</i> Bunge, showed antibacterial activity against several tested bacterial pathogens. Fractionation of this extract led to the isolation of seven dibenzo-α-pyrones (<b>1</b>–<b>7</b>), including one new compound, 2-acetoxy-2-<i>epi</i>-altenuene (<b>1</b>) and one new natural product, 3-<i>epi</i>-dihydroaltenuene A (<b>2</b>). The structures of the new metabolites were elucidated by comprehensive analysis of the spectroscopic data including (1D, 2D) NMR and HRESIMS, while the absolute configuration of <b>1</b> was determined by TDDFT–ECD computation. Altenuisol (<b>5</b>), 4-hydroxyalternariol-9-methyl ether (<b>6</b>), and alternariol (<b>7</b>) showed inhibitory activities against the tested bacteria with minimum inhibitory concentration values in the range of 86.7–364.7 μM. A preliminary structure–antibacterial activity relationship was discussed. In addition, compounds <b>2</b>, <b>5</b> and <b>6</b> displayed promising antioxidant effects using DPPH and hydroxyl radical assays. The cytotoxicity of the isolated compounds was evaluated as well.</p> <p>The endophytic fungus <i>Alternaria</i> sp. Samif01 isolated from <i>Salvia miltiorrhiza</i> Bunge produced seven bioactive dibenzo-α-pyrones, including one new compound (<b>1</b>), whose absolute configuration was determined by ECD calculation.</p
