Polycitone B and prepolycitrin A: two novel alkaloids from the marine ascidian Polycitor africanus

Two novel compounds, polycitone B (4) and prepolycitrin A (3), were isolated from the marine ascidian Polycitor africanus. The structures of these new dibromotyrosine metabolites were established mainly on the basis of NMR spectroscopic data. Isolation of compound 3 supports the earlier suggestion that it is the bioprecursor of polycitrin A (2).