Antifouling Activity of Xylemin, Its Structural Analogs, and Related Polyamines

Biofouling, which is the accumulation of organisms on undersea structures, poses significant global, social, and economic issues. Although organotin compounds were effective antifoulants since the 1960s, they were banned in 2008 due to their toxicity to marine life. Although tin-free alternatives have been developed, they also raise environmental concerns. This underscores the need for effective, nontoxic antifouling agents. We previously synthesized N-(4-aminobutyl)propylamine (xylemin) and its structural analogs. In this study, we assayed the antifouling activity and toxicity of xylemin, its structural analogs, and related polyamines toward cypris larvae of the barnacle Amphibalanus amphitrite. Xylemin and its Boc-protected analog exhibited antifouling activities with 50% effective concentrations (EC₅₀) of 4.25 and 6.11 µg/mL, respectively. Four xylemin analogs did not show a settlement-inhibitory effect at a concentration of 50 µg/mL. Putrescine, spermidine, spermine, and thermospermine, which are xylemin-related polyamines, did not display antifoulant effects (EC₅₀ > 50 µg/mL). All evaluated compounds were nontoxic at a concentration of 50 µg/mL. These findings indicate that the size and structure of the N-alkyl group are essential for the antifouling activity of xylemin. Therefore, xylemin and its analogs hold promise as nontoxic, eco-friendly antifouling agents, offering a sustainable solution to biofouling in marine environments.