Enantioselective total synthesis and absolute stereostructure of hippospongic acid A

A compound having the structure proposed for hippospongic acid A, a triterp ene that specifically inhibits gastrulation of starfish embryos, was synthe sized enantioselectively. The synthetic compound was not identical to the n atural product. Comparison of the NMR spectra of the natural and synthetic compounds led us to propose an alternative structure, which was confirmed b y enantioselective synthesis. The present synthesis established that the na tural product has the (R)-configuration. (C) 2001 Elsevier Science Ltd. All rights reserved.