Anthranilamides: new antimicroalgal active substances from a marine Streptomyces sp.

2-[Methyl-(3-phenylpropionyl)amino]-benzoic acid (1e) was isolated from a culture of marine Streptomyces sp. strain B7747. Analogous compounds have potential importance as phytotoxic substances, hence compound 1e and the analogues 1a approximately 1d and 1f approximately 3a were synthesised. Antimicroalgal activity of the anthranilamide analogues showed that esters 1b, 1f and 2b were more active than the free acids. The minimum inhibitory concentration (MIC) against Chlorella vulgaris, Chlorella sorokiniana, Chlorella salina and Scenedesmus subspicatus ranged from 20 to 107 micrograms/ml. All anthranilamides were inactive against Staphylococcus aureus, Escherichia coli, and Mucor miehei.