The Chemistry and Pharmacology of the Alkaloid Barettin and Its Analogues from the Marine Sponge Geodia barretti: Progress and Perspectives

The cold-water siliceous sponge <i>Geodia barretti</i>, largely present in the North Atlantic Ocean, notably around Scandinavian costs, plays important roles in carbon and silicon cycling in the deep-sea. The demosponge provides a reservoir for numerous microorganisms. Bioactive natural products have been isolated from this sponge, in particular the indole alkaloid barettin discovered forty years ago. Barettin and analogues, notably 8,9-dihydrobarettin, 8,9-dihydro-8-hydroxybarrettin, bromobenzisoxalone barettin, and geobarrettins A-B, contribute to the maintenance of the sponge stability and security (anti-fouling) and the regulation of its microbial environment. The four indole alkaloids 6-bromo-8-hydroxyconicamin, 6-bromoconicamin, and geobarrettin C-D are also implicated in the defense of the sponge against physical and biochemical aggressions. Altogether, these ten natural products are essential to the sponge life. The present review presents a survey of the chemistry and biology associated with <i>Geodia barretti</i>. The pharmacological properties of (dihydro)barettin, notably their antioxidant and anti-inflammatory properties, are discussed, as well as the synthetic processes set up to produce these diketopiperazine derivatives. Their molecular targets and mechanism of action are also discussed. The review takes the sponge <i>G. barretti</i> from the depths of knowledge and brings barettin and analogues to the surface, with the hope of guiding future research in this field.