Total Synthesis of the Callipeltoside Aglycon

Abstract

Following macrolactonization, a Sonogashira coupling leads efficiently from 1 and 2 to the aglycon of the structurally unique cytotoxic macrolide callipeltoside A, isolated in tiny quantities from the lithistid sponge Callipelta sp. Key steps in the preparation of macrolide precursor 1 include a boron-mediated anti-aldol coupling (A) in tandem with Yamamoto's vinylogous aldol reaction (B). TES=triethylsilyl.