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.