Eight novel serine proteases inhibitors from a water bloom of the cyanobacterium Microcystis sp.

Eight new secondary metabolites, micropeptin MM836 (1), micropeptin MM850 (2), micropeptin MM916 (3), micropeptin MM932 (4), micropeptin MM978 (5), anabaenopeptin MM823 (6), anabaenopeptin MM850 (7), and anabaenopeptin MM913 (8), as well as the known anabaenopeptin B (9) were isolated from the hydrophilic extract of the cyanobacterium Microcystis sp. that was collected from a fishpond in Kibbutz Ma’agan Michael, Israel, in September 2006. The structure of the pure natural products was established by spectroscopic methods including 1D and 2D NMR, UV, and MS techniques. The absolute configuration of the chiral centers of the compounds was determined using Marfey’s method. The inhibitory activity of the compounds was determined against the serine proteases, trypsin, chymotrypsin, thrombin and elastase.