Chemistry and synthesis of highly oxygenated alkaloids from Aaryllidaceae:: Lycoricidine, narciclasine, pancratistatin and analogs

Plants of the genus Amaryllidaceae produce a number of alkaloids and other non-basic related molecules, some of them showing antitumor activities. The low availability of these often-complex structures, coupled with their interesting biological properties, has stimulated a long-standing interest in the chemistry community. Total syntheses of challenging structures such as lycoricidine, narciclasine and pancratistatin, which are highly oxygenated tetracyclic systems comprising up to six contiguous chiral centers on ring C, have been accomplished. These well-known structures, more than thirty years for lycoricidine, continue to stimulate interest in synthetic work to provide enough synthetic material or analogs, and also are a model target to test or develop new synthetic methodologies. The synthetic studies around these complex phenanthridinones made use of the latest up-to-date synthetic methodologies and led to the development of novel methods of functionalization and carbon-carbon bond formation. The purpose of this review is to summarize recent total syntheses and synthetic approaches towards these three highly oxygenated members of this particular class of alkaloids over the last twenty years. The review is arranged according to the different strategies used for the construction of the benzophenanthridinone ring system.