Nonsymmetrical B-carboline dimers from an ascidian, Didemnum sp.

In addition to the previously reported symmetrical B-carboline dimer 1, an ascidian Didemnum sp. yielded trace amounts of B-carboline and the nonsymmetrical B-carboline dimers 2, 3, and 5. The structures of the nonsymmetrical dimers were confirmed by nonselective synthesis of 2 and 3 from B-carboline, which also yielded additional dimers 4 and 6.