Molecular design, synthesis and docking study of benz[ b]oxepines and 12-oxobenzo[ c]phenanthridinones as topoisomerase 1 inhibitors

Benz[ b]oxepines 4a– g and 12-oxobenzo[ c]phenanthridines 5a– d were designed and synthesized as constrained forms of 3-arylisoquinolines through an intramolecular radical cyclization reaction. Radical cyclization of O-vinyl compounds preferentially led to the 7- endo-trig cyclization pathway to the benz[ b]oxepines and 12-oxobenzo[ c]phenanthridines through 6- exo-trig path as minor products. Among the synthesized compounds, benz[ b]oxepine derivative 4e exhibited potent in vitro cytotoxicity against three different tumor cell lines, as well as topoisomerase 1 inhibitory activity. A Surflex–Dock docking study was performed to clarify the topoisomerase 1 activity of 4e.