Anti-Barnacle Activities of Isothiocyanates Derived from β-Citronellol and Their Structure-Activity Relationships

Antifouling agents with low toxicity are in high demand for sustaining marine industries and the environment. This study aimed to synthesize 15 isothiocyanates derived from beta-citronellol and evaluate their antifouling activities and toxicities against cypris larvae of the barnacle Amphibalanus amphitrite. The synthesized isothiocyanates exhibited effective antifouling activities (EC50=0.10-3.33 mu g mL(-1)) with high therapeutic ratios (LC50/EC50 > 30). Four isothiocyanates with an amide or isocyano group showed great potential as effective antifouling agents (EC50=0.10-0.32 mu g mL(-1), LC50/EC50=104-833). The enantiomers of the isothiocyanates only slightly differed in their antifouling activities. These results may serve as a basis for further research and development of beta-citronellol-derived isothiocyanates as effective low-toxic antifouling agents. To the best of our knowledge, this study is the first to report the antifouling activities of isothiocyanates derived from accessible natural products.