Fragment-Guided Genome\nMining of Octacyclic Cyclophane\nAlkaloids from Fungi

Nature uses compact but functionalized biosynthetic fragments\nas\nbuilding blocks to generate complex natural products. To leverage\nthis strategy for the discovery of natural products with new scaffolds,\nwe performed genome mining to identify biosynthetic gene clusters\n(BGCs) in fungi that embed genes that can synthesize targeted fragments.\nThe three-enzyme pathway that biosynthesizes the strained dityrosine\ncyclophane in the herquline A pathway was used to identify a large\nnumber of potential BGCs that may use the cyclophane as a fragment.\nCharacterization of a conserved BGC from fungal strains led to the\nisolation of octacyclin A, an octacyclic natural product with an unprecedented\nstructure, including two hetero-[3.3.1]bicycles and a combination\nof fused, bridged, and macrocyclic rings. Biosynthetic steps leading\nto octacyclin A were fully elucidated using pathway reconstitution\nand enzymatic assays, unveiling intriguing chemical logic and new\nenzymatic reactions in building the octacyclic core. Our work demonstrates\nthe potential utility of fragment-guided genome mining in expanding\nnatural product chemical space.