2,5,6-Tribromo-1-methylgramine (TBG), isolated from the bryozoan Zoobotryon pellucidum was shown to be very efficient in preventing recruitment of larval settlement. In order to improve the compatibility of these compounds with other ingredients in antifouling paints, structural modification of TBG was focused most on halogen substitution and N-substitution. Four novel TBG analogues with higher lipophilic activity were synthesized. The structures of 6a～6d were established by 1H NMR, 13C NMR, IR spectra and elemental analysis. The bioassay results showed that all compounds (5～6) possessed good anti-algae activities, and the LC50 value against Nitzschia closterium showed that 6b and 6d exhibited higher activities (6b: LC50＝1.33 µg/mL, 6d: LC50＝1.06 µg/mL) than others. The primary quantitative structure activity relationship was discussed.

Key words: indole, synthesis, anti-algae activity, QSAR