Six novel alkaloids, segoline A (1), segoline B (2), isosegoline A (3), norsegoline (4), debromoshermilamine A (5), and eilatin (6), possessing the benzo-l,6-diazaphenanthroline ring system have been isolated from the Red Sea tunicate Eudistoma sp. Eilatin (6) is unusual in having a symmetrical heptacyclic structure. The structures of all compounds were elucidated on the basis of spectroscopic data and, in the cases of compounds 1 and 2, with chemical transformations. The relative configurations of the chiral compounds 1–3 is suggested on the basis of circular dichroism measurements. © 1989, American Chemical Society. All rights reserved.