Four novel metabolites from a water bloom of cyanobacteria

A sample of the cyanobacterium Microcystis sp. (IL-399) was collected from a water reservoir near Kibuttz Hafetz Haim, Israel, on the fall of 2008. The cyanobacterial cell mass was freeze-dried and extracted with a 7:3 MeOH/H₂O solution. The crude extract was separated using various chromatographic methods including flash-chromatography on an ODS column, gel-filtration on Sephadex LH-20 column and finally reversed-phase HPLC, to afford four new protease inhibitors: Micropeptin HH978, micropeptin HH960, micropeptin HH992 and aeruginosin HH553. The structures of the pure compounds were elucidated using 1D and 2D NMR techniques, as well as, high-resolution mass spectrometry. The stereochemistry of the new natural product was determined using Marfey's method for amino acid and chiral HPLC. The inhibitory activity of the natural products was determined for the serine proteases – trypsin and chymotrypsin. The structure elucidation and biological activity of the new natural products will be presented.