Three Novel Protease Inhibitors from a Natural Bloom of the Cyanobacterium <i>Microcystis </i><i>a</i><i>eruginosa</i>

Abstract

Two new trypsin inhibitors, micropeptins EI992 (1) and EI964 (2), and a modified linear peptide aeruginosin EI461 (3) were isolated from the hydrophilic extract of two samples of Microcystis aeruginosa, collected from the Einan Reservoir in Israel. Homonuclear and heteronuclear 2D-NMR techniques as well as HRFABMS determined the gross structures of 1-3. The relative and absolute stereochemistry of 1-3 was deduced by a combination of spectral data and Marfey's method for HPLC. Aeruginosin EI461 (3) differs from the 14 known aeruginosins in the relative and absolute stereochemistry of the Choi-6-hydroxyl substituent.