Amphidinolides F and C2: An Odyssey in Total Synthesis.

Amphidinolides F, C, C2, and C3 are marine natural products isolated from dinoflagellates species. They share the same macrolactone core, with the difference between them residing at the side chain level. A predominant feature of these amphidinolides is the presence of two -THF rings inside the macrolactone core, which is thought to be built by C-glycosylation with titanium enolate of -acetyl oxazolinethiones. Thus, the original strategy for their total synthesis was based on the assembly of three main fragments corresponding to C-C, C-C, and C-C or C-C disconnections. Whereas synthesis of all fragments was successful, the C-glycosylation reaction between C and C turned out to be an issue. Therefore, a second route was designed. The new disconnection between C and C was based on a sulfone addition and a desulfonylation sequence. Our convergent strategy allowed the total synthesis of amphidinolide F and enabled a new unifying route toward the synthesis of amphidinolides C, C2, and C3 using a late-stage divergent approach. Although there were unsatisfying yields at some critical steps, our work culminated into the first total synthesis of amphidinolide C2.