Three novel bromopyrrole alkaloids with a unique tetrahydrofuro[2,3-d]imidazolidin-2-one moiety, slagenins A similar to C (1 similar to 3), have been isolated from the Okinawan marine sponge Agelas nakamurai, and the structures were elucidated from spectroscopic data. (C) 1999 Elsevier Science Ltd. All rights reserved.