STUDIES OF AUSTRALIAN ASCIDIANS .1. 6 NEW LAMELLARIN-CLASS ALKALOIDS FROM A COLONIAL ASCIDIAN, DIDEMNUM-SP

Six new polyaromatic alkaloids, lamellarin I (3), J (6), K (7), L (9), MR (11) and the triacetate (13) of lamellarin N, and four known alkal oids, lamellarin A (1), B (15), C (16) and the triacetate (14) of lame llarin D, have been isolated from the marine ascidian Didemnum sp. The structures were deduced by high-field n.mr.r. spectroscopy including C-13-H-1 shift-correlated two-dimensional (2D) n.mr.r. experiments and n.O.e. measurements. The triacetates (8) and (10) of two of the compo unds, lamellarin K (7) and lamellarin L (9), were dehydrogenated in hi gh yield by treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone i n ethanol heated under reflux. The products obtained were identical in all respects to the triacetates of lamellarin MR and N, respectively. The re-isolation of lamellarins A-D, which were previously obtained f rom the prosobranch mollusc Lamellaria sp., lends further support for the idea that these molluscs sequester the compounds from ascidians as food sources.