Bioactive Hydroanthraquinones and Anthraquinone Dimers from a Soft Coral-Derived <i>Alternaria</i> sp. Fungus

Five new hydroanthraquinone derivatives, tetrahydroaltersolanols C–F (<b>1</b>–<b>4</b>) and dihydroaltersolanol A (<b>5</b>), and five new alterporriol-type anthranoid dimers, alterporriols N–R (<b>12</b>–<b>16</b>), along with seven known analogues (<b>6</b>–<b>11</b> and <b>17</b>), were isolated from the culture broth and the mycelia of <i>Alternaria</i> sp. ZJ-2008003, a fungus obtained from a <i>Sarcophyton</i> sp. soft coral collected from the South China Sea. Their structures and the relative configurations were elucidated using comprehensive spectroscopic methods including 1D and 2D NOE spectra as well as single-crystal X-ray crystallography. Compound <b>13</b> represents the first isolated alterporriol dimer with a C-4–C-4′ linkage, and the absolute configuration of <b>4</b> was determined using the modified Mosher’s method. Compounds <b>1</b> and <b>15</b> exhibited antiviral activity against the porcine reproductive and respiratory syndrome virus (PRRSV), with IC₅₀ values of 65 and 39 μM, respectively. Compound <b>14</b> showed cytotoxic activity against PC-3 and HCT-116 cell lines, with IC₅₀ values of 6.4 and 8.6 μM, respectively