Discorhabdins and prianosins have been isolated from marine sponges such as New Zealand sponges of the genus Latrunculia, Okinawan sponge Prianos melanos, and Fijian sponge Zyzzya cf. Marsailis. Among the various discorhabdins (A ± R) isolated, discorhabdins A (1), [1a,b,d] B, [1b] D, [1c] Q, [1e] and R [1f] have a unique sulfur-containing fused-ring system incorporating an azacarbocyclic spirocyclohexadienone and a pyrroloiminoquinone system (Scheme 1), and show potent antitumor activity. [2] The discorhabdins have