Synthesis of ()-Dibromoagelaspongin

Significance

Dibromoagelaspongin is an oroidin-derived guanidine alkaloid isolated from an Agelas sp. sponge and probably occurs in nature as a racemate. The structurally related phakellins have cytostatic activity. In this first total synthesis, the tetracyclic core is assembled by two consecutive Pummerer-type additions to a sulfur-substituted imidazole.