3-Alkylpyridinium compounds as potential non-toxic antifouling agents

To date, around thirty bioactive 3-alkylpyridinium compounds, either in monomeric or oligomeric forms, have been identified in marine sponges belonging to the order Haplosclerida In this work, we have reviewed their biological activities, which include mainly cytotoxicity, ichthyotoxicity, inhibition of bacterial growth, and enzyme inhibition. Most of these activities increase with the increasing degree of oligomerization of the corresponding 3-alkylpyridinium compound. It was shown recently that 3-alkylpyridines also exhibit promising antifouling activities. Linear 3-octylpyridinium polymers (Poly-APS), isolated from the Mediterranean sponge Reniera sarai, showed a non-toxic reversible mechanism of settlement inhibition of Balanus amphitrite cypris larvae with an EC50 of 0.27 microg/mL. At the same time, their toxicity towards the organisms used in the toxicity bioassays (B. amphitrite nauplii, microalga Tetraselmis suecica and larvae of Mytilus galloprovincialis) was almost negligible in comparison to commercially available and currently used booster biocides based on copper and zinc complexes with pyrithione. Poly-APS and some other natural 3-alkylpyridines were also found to be very effective in preventing microbial biofilm formation. Preliminary tests have confirmed that some monomeric and oligomeric synthetic analogues of poly-APS also exert antifouling activity, which makes these compounds promising candidates as new environmentally-friendly ingredients in the new generation of antifouling coatings.