Synthesis of marine toxins. A biomimetic approach to the novel spirobenzoquinonefuran stypoldione

Abstract

A synthesis of the spirobenzoquinonefuran unit, i.e.(10), present in stypoldione, a novel marine toxin found in the brown alga Stypopodium zonale which shows pronounced narcotic and hyperactive effects upon reef-dwelling fish, is described. The synthesis uses a strategy, viz(17)→(18)→(19)→(11)→(10), which has close similarities to the probable biogenesis of this portion of the natural product (scheme 1). The advanced precursors (30) and (36) for projected syntheses of deoxystypoldione (33) and stypodiol (3) respectively were also prepared, but neither substrate underwent polyene cyclization to the required pentacyclic molecules.