Protease inhibitors from three fishpond water blooms of Microcystis spp.

Four new natural products, micropeptin GH979 (1), microginin GH787 (2), micropeptin HM978 (3), and micropeptin HA983 (4), as well as 10 known protease inhibitors and hepatotoxins, were isolated from the hydrophilic extract of three samples of cyanobacteria (Microcystis spp.) that were collected from fishponds in Kibbutz Giva’at Haim, Kibbutz Hama’apil, and Kibbutz Gan Shmuel. The structures of the pure natural products were elucidated using spectroscopic methods, including UV, 1D and 2D NMR, 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 for the serine proteases: trypsin, chymotrypsin, thrombin and elastase, and the metalloprotease, aminopeptidase N.