Efforts toward the synthesis of maoecrystal V

Abstract

Maoecrystal V is a small, structurally complex member of a diverse class of bioactive natural products, the ent-kauranes. Its challenging structure and unusual highly selective cytotoxicity against HeLa cells have made this molecule an alluring target for the pursuit of total synthesis laboratories.

Reported here are two synthetic approaches that converge on a similar core skeleton from very different paths. The first involves an ambitious oxa-Michael/aldol/oxa-Michael carbonyl cascade from a substrate containing carefully designed electronic and structural reactivity. A rapid synthesis of this starting material was developed, allowing the possibility of a maoecrystal V core synthesis in fewer than ten steps. The innate reactivity of this substrate was also adapted to a proposed reductive aldol transformation.

The second approach, although treading similar chemical space to other published synthetic attempts via the Diels-Alder cycloaddition, was designed to avoid several primary weaknesses in those publications, with more flexibility and brevity in the process. Although advanced intermediates were obtained containing the carbon skeleton of maoecrystal V, a final key silicon oxidation step could not be overcome.