ASYMMETRIC-SYNTHESIS OF CALYCULIN-C .1. SYNTHESIS OF THE C-1-C-25 FRAGMENT

We report our synthesis of the C-1-C-25 fragment of serine/threonine p hosphatase PP1 and PP2A inhibitor, calyculin C. Synthetic efforts were directed initially toward the synthesis of a spiroketal core fragment (7), which culminated in completion of the bottom half of the natural product. The synthesis of fragment 7 and subsequent elaboration relie d on an allylboration strategy for introduction of chirality. The C-1- C-8 fragment representing the potentially unstable tetraene moiety was introduced as a separate entity.