Metabolites from Microcystis aeruginosa Bloom Material Collected at a Water Reservoir near Kibbutz Hafetz Haim, Israel

An aqueous MeOH extract of Microcystis aeruginosa (IL-399) afforded three new protease inhibitors, micropeptin HH978 (1), mictopeptin, HH960 (2), and micropeptin HH992 (3), as well as the known aeruginosin GH553 and microguanidine AL772. The structures of the compounds were elucidated using 1D and 2D NMR techniques, as well as high-resolution mass spectrometry. The absolute configurations of 1-3 were determined using method for amino acid and chiral-phase, HPLC for hydroxy acids. The inhibitory activity of the compounds was determined for the serine proteases trypsin, thrombin, elastase, and chymotrypsin. The structure elucidation and biological activities of the new natural products are discussed.