Acetoxycrenulide, a new bicyclic cyclopropane-containing diterpenoid from the brown seaweed Dictyota crenulata

The small brown seaweeds (Phaeophyta) of the family Dictyotaceae are conspicuous members of most highly competitive tropical and subtropical habitats. Chemical studies have shown that these algae produce a variety of unique secondary metabolites that perhaps function as defensive compounds in the natural habitat. In studies of this algal group from the Gulf of California, Mexico, the authors have encountered several Dictyota species that produce new diterpenoid ring systems. In this note the authors amplify earlier work by reporting, in full, the structure of a new diterpenoid, acetoxycrenulide, which is a major metabolite, along with pachydictyol A, of D. crenulata J. Agardh.