Spiroacetals of Marine Origin

Abstract

The structures, origins and biological activities of marine-derived compounds incorporating a spiroacetal sub-structure are reviewed. Such compounds include okadaic acid, the ciguatoxins, the halichondrins, the spongistatins, the cephalostatins, the calyculins and the aplysiatoxins, the structures of which illustrate the highly varied and often complex molecular design produced by marine biota. Synthetic approaches to a number of these classes are discussed in detail, with particular attention given to the synthesis of calyculin A by the research groups of Evans, Masamune and Shioiri. These synthetic endeavours emphasise the undiminished influence of natural product chemistry on the nature and direction of organic chemistry. Furthermore, they demonstrate that despite the emergence of powerful methods for molecular structure determination, partial or complete stereocontrolled syntheses are still required to validate stereochemical detail in large, highly functionalised molecules. Finally, these discussions confirm the versatility of modern asymmetric synthetic methodology in tactical molecular construction.