Meroterpenes are widely distributed among marine organisms; they are particularly abundant within brown algae, but other important sources include microorganisms and invertebrates. In the present review the structures and bioactivities of meroterpenes from marine invertebrates, mainly sponges and tunicates, are summarized. More than 300 molecules, often complex and with unique skeletons originating from intra- and inter-molecular cyclizations, and/or rearrangements, are illustrated. The reported syntheses are mentioned. The issue of a potential microbial link to their biosynthesis is also shortly outlined.

No abstract

The marine environment contains a number of plants, animals and micro organisms, which, due to the unique adaptations to their habitat, elaborate a wide diversity of natural products with specific bioactivities. These products provide a rich source of chemical diversity that can be used to design and develop new potentially useful therapeutic agents. The huge variety of the structures present in marine organisms has been illustrated through the case study of the sponge Plakortis simplex, whose chemical analysis, started in our laboratories about ten years ago, revealed an incredible variety and abundance of secondary metabolites. The obtained results have been presented with the intention of drawing some conclusions of general relevance. Particularly, the problem of the limited availability of natural compounds for both structural and preliminary pharmacological studies has been discussed, this issue becoming a serious obstacle when the pharmacological research reaches a more advanced stage. Furthermore, the origin of the chemodiversity in Plakortis simplex and, in general, in marine invertebrates has been discussed; in this respect, the possible cooperative role of symbiotic micro-organisms in the biosynthesis of the varied metabolic content typical of these organisms has been considered.

In the present study, 13 bromopyrrole alkaloids, including the oroidin analogs hymenidin (2), dispacamide B (3) and dispacamide D (4), stevensine (5) and spongiacidin B (6), their derivatives lacking the imidazole ring bromoaldisin (7), longamide B (8) and longamide A (9), the dimeric oroidin derivatives sceptrin (10) and dibromopalau’amine (11), and the non-oroidin bromopyrrolohomoarginin (12), manzacidin A (13), and agelongine (14), obtained from marine sponges belonging to Axinella and Agelas genera have been screened in vitro against four parasitic protozoa, i.e., two Trypanosoma species (T. brucei rhodesiense and T. cruzi), Leishmania donovani and Plasmodium falciparum (K1 strain, a chloroquine resistant strain), responsible of human diseases with high morbidity and, in the case of malaria, high mortality. Our results indicate longamide B (8) and dibromopalau’amine (11) to be promising trypanocidal and antileishmanial agents, while dispacamide B (3) and spongiacidin B (6) emerge as antimalarial lead compounds. In addition, evaluation of the activity of the test alkaloids (2–14) against three different enzymes (PfFabI, PfFabG, PfFabZ) involved in the de novo fatty acid biosynthesis pathway of P. falciparum (PfFAS-II) identified bromopyrrolohomoarginin (12) as a potent inhibitor of PfFabZ. The structural similarity within the series of tested molecules allowed us to draw some preliminary structure-activity relationships. Tests against the mammalian L6 cells revealed important clues on therapeutic index of the metabolites. This is the first detailed study on the antiprotozoal potential of marine bromopyrrole alkaloids.

A tutorial review aimed to introduce natural product chemists to the predictions of natural product configurations by ECD and OR calculations.