Pyrroloquinoline derivatives from a Tongan specimen of the marine sponge Strongylodesma tongaensis

Pyrroloquinoline alkaloids are well known bioactive metabolites commonly found from latrunculiid sponges. Two new pyrroloquinoline alkaloids, 6-bromodamirone B (1) and makaluvamine W (2), were isolated from the Tongan sponge Strongylodesma tongaensis. Makaluvamine W (2) contains an oxazole moiety, which is rare in this large group of natural products, and is the first example of a pyrroloquinoline with nitrogen substitution at C-8. Both 1 and 2 lacked activity against a human promyelocytic leukemia cell line (HL-60), supporting the premise that an intact iminoquinone moiety plays a key role in the cytotoxicity of this compound class. The chemotaxonomic impact of these makaluvamine-type compounds is also discussed.