Metabolic Blockade-Based\nGenome Mining of Saccharopolyspora erythraea SCSIO 07745: Discovery\nand Biosynthetic Pathway of Aminoquinolinone Alkaloids Bearing 6/6/5\nTricyclic and 6/6/6/5 Tetracyclic Scaffolds

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