Metabolic Blockade-Based Genome Mining of <i>Saccharopolyspora erythraea</i> SCSIO 07745: Discovery and Biosynthetic Pathway of Aminoquinolinone Alkaloids Bearing 6/6/5 Tricyclic and 6/6/6/5 Tetracyclic Scaffolds

Metabolic blockade-based genome mining of the marine sediment-derived <i>Saccharopolyspora erythraea</i> SCSIO 07745 led to the discovery of 11 novel aminoquinolinone alkaloids, oxazoquinolinones A-J (<b>1</b>-<b>10</b>), characterized by an oxazolidone[3,2-α]quinoline-5,8-dione scaffold, and oxazoquinolinone K (<b>11</b>), featuring an unprecedented fused 6/6/6/5 tetracyclic core ring system. Additionally, 5 new biosynthetic intermediates or shunt products (<b>12</b>-<b>16</b>) and a known metabolite sannanine (<b>17</b>) were identified. Their structures were elucidated by extensive spectroscopic analyses and a comparison of electronic circular dichroism and single-crystal X-ray diffraction. On the basis of the functional gene analyses and structures of the intermediates or shunt products, plausible biosynthetic pathways for compounds <b>1</b>-<b>17</b> were proposed. Additionally, oxazoquinolinone K (<b>11</b>) obviously inhibited cell invasion of human glioma cell line LN229 cells at 10 μM.