New aeruginazoles, a group of thiazole-containing cyclic peptides from Microcystis aeruginosa blooms

Three related cyclic peptides, aeruginazole DA1497 (1), aeruginazole DA1304 (2), and aeruginazole DA1274 (3), were isolated from the freshwater cyanobacteria, Microcystis aeruginosa, bloom material collected on October 2007 from the Dalton water-reservoir in Northern Israel. Aeruginazoles DA1304 (2), DA1338 (4), and DA1372 (5) were isolated as an inseparable mixture from a bloom material of M. aeruginosa collected from the same water-reservoir on August 2000. Their structures were elucidated using a combination of various spectroscopic techniques, mainly NMR and MS, while the absolute stereochemistry of the chiral centers were determined by Marfey’s method. Aeruginazoles 1–3 were tested in various bioassays (antibacterial, cytotoxicity, and protease inhibition). Aeruginazole DA1497 (1) showed a mild antimicrobial activity against Staphylococcus aureus, but was inactive like the rest of the compounds in all other bioassays.