Important classes of bioactive alkaloids from marine ascidians: structures, isolation and bioactivity.

An intensive research effort during the last 25 years has generated an impressive number of alkaloids isolated from marine ascidians, which remain unique among marine invertebrates in that they overwhelmingly produce this kind of metabolites. The present review is focused on some major groups of ascidians' bioactive alkaloids, useful as lead structures in the search and development of new drugs or as biological probes for physiological investigation. They include the lamellarins, the ecteinascidins, bis-steroidal pyrazines and pyridoacridines. Their often extraordinary structures and significant biological activities are illustrated, reported syntheses are outlined, and structure/activity relationships are discussed where sufficient data are available to draw such conclusions. Recent discoveries concerning the current state of potential and /or development of some of them as new drugs as well as the current knowledge regarding their modes of action are also summarized.