An Algicidal Agent against Harmful Algae Using Novel N¹-benzyl-N³, N³-diethylpropane-1,3-diamine Derivatives

Abstract

To develop a variety of algaecides for harmful algae control that cause water pollution, we synthesized a series of 79 derivatives based on the structure of N¹-benzyl-N³, N³-diethylpropane-1,3-diamine and analyzed their structure-activity relationships toward a harmful and a harmless algal species. Among the derivatives, the best algicidal activities with LC₅₀ values of 0.49 (compound 24) and 0.42 µM (compound 34) in Cyanobacteria, respectively were achieved when CH₃ and F groups were substituted at the R₂ position, with CH₃CH₃ group at the R₃ position, and amine chain length 3 at the R₄ position after fixing Cl substituent group at the R₁ position of the benzaldehyde group. The compounds 24 and 34 decreased the chlorophyll content of treated groups by approximately 75–80% as compared to the control. Algicidal activities for harmful algal species were as follows, in the order of greatest to the least: Microcystis sp. > Microcystis aeruginosa > Hererocapsa circularisquama > Chattonella marina > Heterosigma akashiwo. The acute toxicities of compounds 24 and 34 against Daphnia magna showed EC₅₀ values of 20.18 and 22.32 µM, respectively, which were approximately 46.4 and 44.69 times higher than the LC₅₀ value against Microcystis sp., showing low ecotoxicity. In the case of Danio rerio, they showed very low ecotoxicity with EC₅₀ values of 94.97 and 45.97 µM, respectively. These results indicate that compounds 24 and 34 could be potential agents for selectively controlling harmful algal blooms.