Antiviral Alkaloids Produced by the Mangrove-Derived Fungus <i>Cladosporium</i> sp. PJX-41

Six new indole alkaloids including five new glyantrypine derivatives (<b>1</b>, <b>2a</b>, <b>2b</b>, <b>3</b>, <b>4</b>) and a new pyrazinoquinazoline derivative (<b>5</b>), together with eight known alkaloids (<b>6</b>–<b>13</b>), were isolated from the culture of the mangrove-derived fungus <i>Cladosporium</i> sp. PJX-41. Their structures were elucidated primarily by spectroscopic and physical data. The absolute configurations of compounds <b>1</b>–<b>9</b> were established on the basis of CD, NOESY data, and single-crystal X-ray diffraction analysis. Compounds <b>2b</b>, <b>5</b>, <b>7</b>–<b>9</b>, and <b>11</b> exhibited significant activities against influenza virus A (H1N1), with IC₅₀ values of 82–89 μM