Latonduines A and B, new alkaloids isolated from the marine sponge Stylissa carteri: structure elucidation, synthesis, and biogenetic implications.

[structure: see text] Latonduines A (6) and B (7), two new alkaloids with unprecedented heterocyclic skeletons, have been isolated from the Indonesian marine sponge Stylissa carteri. The structures of the latonduines were elucidated by analysis of spectroscopic data and confirmed by the total synthesis of latonduine A (6). It is proposed that ornithine is the biogenetic precursor to the aminopyrimidine fragment of the latonduines.