Diterpenoid Synthesis in Brown Seaweeds of the Family Dictyotaceae

Abstract

Brown seaweeds (Phaeophyta), taxonomically placed within the family Dictyotaceae, are common inhabitants of the shallow water and intertidal community, particularly in subtropical and tropical ecosystems. No less than thirteen genera have been assigned to this distinct family (Figure 1), all of which are characterized by their flattened thalli, which emanate from single apical cell division. Despite extreme herbivore activity in most subtropical and tropical areas, seaweeds of the Dictyotaceae are observed in abundance and are apparently avoided by many fishes and Crustacea. Bioassay experiments with extracts from various species in this family have shown that substances toxic to fish1, bacteria2–4, and viruses5 are produced by these algae. Subsequent studies of the natural products chemistry of a few species, particularly those of the genus Dictyopteris, have shown the production of a diverse group of substances including sesquiterpenes6, C11 hydrocarbons and sulphur-containing compounds7, and C21 hydroquinones of mixed biogenesis8. C21 chromanols, also of mixed biogenetic origin, have been reported from the closely related alga Taonia 9 (Figure 2). Presumably these unique substances are involved in providing selective advantage against predation.