Six new polyaromatic alkaloids, lamellarin I (3), J (€9, K (7), L (9), M (11) and the triacetate (13) of lamellarin N, and four known alkaloids, lamellarin A (I), B (15), C (16) and the triacetate (14) of lamellarin D, have been isolated from the marine ascidian Didemnum sp. The structures were deduced by high-field n.m.r. spectroscopy including l 3 c -'~ shift-correlated two-dimensional ( 2~) n.m.r. experiments and n.0.e. measurements. The triacetates (8) and (10) of two of the compounds, lamellarin K (7) and lamellarin L (9), were dehydrogenated in high yield by treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in ethanol heated under reflux. The products obtained were identical in all respects to the triacetates of lamellarin M and N, respectively. The re-isolation of lamellarins A-D, which were previously obtained from the prosobranch mollusc Lamellaria sp., lends further support for the idea that these molluscs sequester the compounds from ascidians as food sources.Marine ascidians have proven to be rich sources of structurally diverse alkaloids, many of which exhibit a broad spectrum of biological activity.l Members from the family Didemnidae are generally highly coloured, encrusting organisms, colonial by habit, and characteristically contain chemical constituents which are derived from amino acids.2 The polyaromatic lamellarin alkaloids, for example, are probably derived from three tyrosine residues. It has also been suggested that the lamellarins may be distantly related to the tunichromes, reducing blood pigments isolated from the ascidian Ascidia nigra.l The lamellarin skeleton was first identified in an isolate from a prosobranch mollusc, Lamellaria sp., from pa la^,^ but has more recently been found in the didemnid ascidian Didemnum chartaceum from the Seychelles? Of the eight lamellarin-based alkaloids isolated to date, the structures of lamellarins A (1) and E (2) were elucidated by X-ray methods, while the Faulkner, D.
