53. Bioinspired Synthesis of Pentacyclic Onocerane Triterpenoids
F. Bartels, Y. J. Hong, D. Ueda, M. Weber, T. Sato, D. J. Tantillo, M. Christmann
The first chemical synthesis of pentacyclic onocerane triterpenoids has been achieved. A putative biomimetic tricyclization cascade is employed to forge a fused decalin-/oxepane ring system. The synthetic route proceeds to (+)-cupacinoxepin in seven steps and to (+)-onoceranoxide in eight steps in the longest linear sequence, when starting from geranyl chloride and (+)-sclareolide. The bioinspired epoxypolyene cyclization is supported by computational and enzymatic studies.