Exploring a Symmetry Based Logic for Palau'amine Synthesis
Palau'amine is a natural product originally isolated in 1993 from the marine sponge Stylotella aurantium. It is reported to posess impressive biological activities, including: antifungal, antibacterial, and antineoplastic characters. Moreover, it is a strong immunosuppressant (IC50<18ng/mL, allogenic lymphocyte reaction). The molecule has a complex polycyclic structure having a contiguous array of eight stereogenic centers. It is unusually rich in heteroatoms. A recent revision of its relating stereochemistry has brought further attention to this fascinating molecule. The current strategy of our group features a chlorination initiated cascade process on a symmetric precursor that assembles the skeleton of palau'amine with in a single operation. A symmetric bisalkylidene precursor for this process was synthesized. During the process, two new methodologies were developed: a titanocene dichloride mediated regioselective and stereoselective dimerization of heterocyclic dineolates; and a chemoselective Rh(I) carbene complexes catalyzed conjugation hydrosilylation of enamides. Our core idea was subsequently validated by the formation of the spirocyclopentane motif in palau'amine by an electrophilic halogen induced desymmetrization.