The enantioselective total synthesis of (+)-Symbioimine

(+)-Symbioimine is a marine-derived alkaloid isolated by Uemura in 2004 from a culture of Symbiodinium sp., a dinoflagellate that is a symbiont of the acoel flatworm Amphiscolops sp. This natural product has been found to inhibit osteoclastogenesis in the murine monocytic cell line RAW264 (EC₅₀ = 44 micrograms/mL), suggesting that either it or its analogues may offer a new opening to the development of preventative treatments for osteoporosis. In addition, it has been found to exhibit inhibition of Cycloxygenase (COX-2), suggesting possible use as an antiinflammatory. From a structural perspective, the bicyclic cyclohexenyl imine moiety is a unique feature endemic to several marine natural products. While it is postulated that these natural products undergo some version of the Diels-Alder reaction in their biosyntheses, there has yet to be an investigation that has yielded a general method for its incorporation. Herein I describe our investigation into and completion of the convergent, biomimetic, enantioselective total synthesis of (+)- Symbioimine, featuring an intramolecular, iminium- activiated Diels-Alder reaction that constructs the 6,6,6- tricyclic iminium framework as a single. Additionally, I will also report on our discoveries into the reactivity of various 2,3-dihydropyridine intermediates, the results of which may assist in the synthesis of the several other structurally similar natural products