Kempopeptins A and B, serine protease inhibitors with different selectivity profiles from a marine cyanobacterium, Lyngbya sp.

Two cyclodepsipeptides named kempopeptins A (1) and B (2) were isolated from a collection of a Floridian marine cyanobacterium, Lyngbya sp., that had previously afforded the structurally related potent elastase inhibitors lyngbyastatin 7 and somamide B. The structures of 1 and 2 were elucidated mainly by 1D and 2D NMR spectroscopy, and the absolute configuration was established by chiral HPLC and Marfey's analysis of the degradation products. Kempopeptin A (1) exhibited an IC(50) against elastase of 0.32 mu M and against chymotrypsin of 2.6 mu M, while kempopeptin B (2) inhibited trypsin with an IC(50) of 8.4 mu M.