Synthesis and biological evaluation of bryostatin analogues: the role of the A-ring

The first biologically active member and a key intermediate of a new family of simplified bryostatin analogues are synthesized through an optimized esterification–macrotransacetalization strategy. This family incorporates both an ester linkage between C5 and C9 in addition to a C9 t-butyl substituent to mimic the bryostatin A-ring. Importantly, a free C7 alcohol is revealed late in the synthesis, allowing access to numerous C7 derivatized analogues.