Benzosceptrins A and B with a Unique Benzocyclobutane Skeleton and Nagelamide S and T from Pacific Sponges

Four new dimeric pyrrole-2-aminoimidazole alkaloids have been isolated from the Pacific marine sponges Agelas cf. mauritiana and Phakellia sp. They include the unusual C2 symmetrical benzosceptrins A (4) and B (5), which each possess a unique benzocyclobutane skeleton and nagelamides S (6) and T (7). Their structures and relative configuration were elucidated from spectroscopic data. Plausible biogenetic paths for these compounds are also proposed in this paper.