Secondary Metabolites of Biological Significance from Echinoderms

Abstract

The extraordinary development of marine natural products chemistry during the last three decades has been prompted by the fact that marine organisms are sources of new natural products with unusual structural features that have no precedent among structures of terrestrial origin. The toxicological and pharmacological properties of many of these secondary metabolites as well as the growing interest in their biological role in the natural environment have led to the discovery of thousands of new molecules. Some of these have shown interesting biological activities and are actually candidates for the development of new drugs. Among marine organisms, echinoderms produce complex mixtures of secondary metabolites that may play an important role as defensive molecules. The phylum Echinodermata (Greek, echinos, spiny; derma, skin) comprises some of the most familiar seashore animals, widely distributed in all oceans and depths. The phylum is divided into five classes: Asteroidea (starfishes or sea stars), Holothuroidea (sea cucumbers or holothurians), Ophiuroidea (ophiuroids or brittle stars), Crinoidea (sea lilies and feather stars) and Echinoidea (sea urchins). The presence of polar saponins is constant in starfishes and sea cucumbers, while they have been found only occasionally in sponges, gorgonians, alcyonarians, green alga and in fishes of the genus Pardachirus. Ophiuroids contain sulfated polyhydroxylated steroids and only two sulfated steroidal monoglycosides have been reported in the ophiuroid Ophioderma longicaudum. On the contrary, there is no report of saponins in the classes Echinoidea and Crinoidea. Starfishes and sea cucumbers also are rich in glycosphingolipids (cerebrosides and gangliosides) and several bioactive novel structures have been isolated of both classes of echinoderms. The purpose of the present communication is to offer a general view of the structural characteristics and biological activities of the secondary metabolites of the classes Asteroidea, Holothuroidea and Ophiuroidea, focusing on recent examples, some of these from our laboratory.