Total Synthesis of the 7,10-Epimer of the Proposed Structure of Amphidinolide N, Part I: Synthesis of the C1-C13 Subunit.

Amphidinolide N, the structure of which has been recently revised, is a 26-membered macrolide featuring allyl epoxide and tetrahydropyran moieties with 13 chiral centers. Due to its challenging structure and extraordinary potent cytotoxicity, amphidinolide N is a highly attractive target of total synthesis. During our total synthesis studies of the 7,10-epimer of the proposed structure of amphidinolide N, we have synthesized the C1-C13 subunit enantio- and diastereoselectively. Key reactions include an l-proline catalyzed enantioselective intramolecular aldol reaction, Evans aldol reaction, Sharpless asymmetric epoxidation and Tamao-Fleming oxidation. To aid late-stage manipulations, we also developed the 4-(N-benzyloxycarbonyl-N-methylamino)butyryl group as a novel ester protective group for the C9 alcohol.

Total Synthesis of the 7,10-Epimer of the Proposed Structure of Amphidinolide N, Part II: Synthesis of C17-C29 Subunit and Completion of the Synthesis.

The total synthesis of 7,10-epimer of the proposed structure of amphidinolide N was accomplished. The requisite chiral C17-C29 subunit was assembled stereoselectively via Keck allylation, Shi epoxidation, diastereoselective 1,3-reduction, and a later oxidative synthesis of the THF framework. The C1-C13 and C17-C29 subunits were successfully coupled using a Enders RAMP "linchpin" as the C14-C16 three carbon unit, thereby controlling the chirality at C14 and C16. The labile allyl epoxy moiety was successfully constructed by Grieco-Nishizawa olefination at a final stage of the synthesis.