Topopyrone B is a naphthochromene that is 4H-naphtho[2,3-g]chromene-4,6,11-trione substituted by a chloro group at position 8, hydroxy groups at positions 5, 7 and 9 and a methyl group at position 2. It is isolated from a fungal strain Phoma sp.BAUA2861 and acts as an inhibitor of the enzyme topoisomerase I. It has a role as a metabolite, an EC 5.99.1.2 (DNA topoisomerase) inhibitor, an antiviral agent, an antineoplastic agent and an antimicrobial agent. It is an organochlorine compound, a naphthochromene, a member of phenols and a member of p-quinones.