Synthesis of rac-hippospongic acid A and revision of the structure

rac-Hippospongic acid A of the reported structure 1 and the revised structure 2 were synthesized. The synthetic strategy of these compounds consists of homologation of (2E,6E,10E)-geranylgeraniol and (2E,6E)-farnesol, respectively, Wadsworth–Emmons reaction, and cyclization to form the tetrahydropyran ring bearing an α-methylene group on the carboxylic moiety. Spectral comparisons of the synthetic compounds 1, 2 and the natural product suggested that hippospongic acid A bears the structure of 2.