Protease inhibitors from a water bloom of the cyanobacterium Microcystis aeruginosa

Five new protease inhibitors, micropeptins SD944 (1), SD979 (2), SD999 (3) and SD1002 (4) and microginin SD755 (5) were isolated along with two known inhibitors, micropeptin SF995 (6) and microcin SF608 (7), from the hydrophilic extract of Microcystis aeruginosa. The planar structure of compounds 1–5 was determined by homonuclear and inverse-heteronuclear 2D-NMR techniques as well as high-resolution mass spectrometry. The absolute configuration of the asymmetric centers was studied using Marfeyʹs method for HPLC. Compounds 1–4, 6 and 7 are serine-protease inhibitors while compound 5 was found to inhibit amino-proteases.