Zamamistatin, a Significant Antibacterial Bromotyrosine Derivative from a Marine Sponge

Bacteria and diatoms are present soon after immersion in seawater, resulting in a biofilm that covers the surface. The establishment of this microfouling biofilm layer is soon followed by macrofouling by barnacles, mussels, and algae. To prevent such macrofouling, several metallic compounds, such as bis(tributyltin)oxide (TBTO), have been used in antifouling paints. However, since their use is restricted to prevent environmental pollution the development of environmentally acceptable antifouling agents has been expected. From marine algae, which are known to be one of the largest producers of biomass in the marine environment, several substances with potent an-tifouling activity have been isolated, such as fatty acids, lipopeptides, amides, alkaloids, terpenoids, lactones, pyrroles, and steroids [56].

We have especially searched for compounds to prevent microfouling, which would consequently prevent such macrofouling [57]. Antibacterial activity against the marine bacteria Rhodospirillum salexigens SCRC 113 strain with adhering properties was selected as a bioassay to identify such compounds. In our continuing search for such compounds, zamamistatin, a novel bromotyrosine derivative, was isolated from the Okinawan sponge Pseudocer-atina purpurea [58]. Zamamistatin exhibited significant antibacterial activity against R. salexigens (21 mm, 1.6 ^g/disk).

The molecular formula of zamamistatin was determined to be C18H18Br4 N2O6. Observation of only nine carbon signals by 13C NMR and its optical rotation value suggested that zamamistatin was an optically active dimer with a C2 symmetrical structure. On the basis of the analysis of 2D-NMR spectra, the structure of zamamistatin was elucidated to be 28, possess-

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