Bioactive polysubstituted alkyl sulfates from Mediterranean ascidians

The sulphate group is a common feature of echinoderm metabolites, like sulphated saponins with triterpenoid or steroidal aglycones and has also been encountered in sponges’ metabolites, in the form of sulphated sterols and phenol sulphates. Only a few examples of sulfated alkanes/alkenes have been reported from marine sources and, recently, they have been shown to be commonly present in remarkably amounts in Mediterranean tunicates.1 Most of these compounds, often having quite simple structures, are cytotoxic or antimicrobial. More complex polysubstituted alkyl sulfates have also been isolated from ascidians; a remarkable example is turbinamide, a bioactive metabolite isolated few years ago in our laboratory from Sidnyum turbinatum.2 This molecule demonstrated a strong and selective cytotoxic effect against neuronal rather than immune system cells.3 An extensive investigation we have carried out on several species of Mediterranean ascidians evidenced that complex sulphated polyketides are quite widespread in these organisms. We have indeed isolated two new polysubstituted alkyl sulphates from two different Mediterranean ascidians (Sidnyum elegans and Ciona edwardsii) whose structures are referable to that of turbinammide. The new compounds also exhibited a strong cytotoxic activity against C6 glioma cells; their structural analogy with turbinamide allowed also evaluating the influence of slight structural modifications on the activity.