Potent algicides based on the cyanobacterial alkaloid nostocarboline

Nostocarboline and seven derivatives were prepared and displayed minimal inhibitory concentration (MIC) values >= 100 nM against the growth of Microcystis aeruginosa PCC 7806, Synechococcus PCC 6911, and Kirchneriella contorta SAG 11.81, probably via the inhibition of photosynthesis. The natural product hybrid nostocarboline/ciprofloxacin displayed additional antibacterial activity against several Gram-negative bacteria (MICs >= 0.7 mu M). Nostocarboline can thus be considered a potent, selective, readily available, natural algicide.