Depsipeptides from a Guamanian Marine Cyanobacterium, Lyngbya bouillonii, with Selective Inhibition of Serine Proteases.

Bouillomides A (1) and B (2) are two depsipeptide analogues of dolastatin 13. Isolated from a Guamanian sample of Lyngbya bouillonii, the planar structures were elucidated on the basis of HR-ESI-MS and NMR data, while the absolute configurations were determined by employing functional group conversions, modified Marfey's analysis, and detailed analyses of ROESY correlations. Compounds 1 and 2 selectively inhibited serine proteases elastase (IC(50) = 1.9 μM for both) and chymotrypsin (IC(50) = 0.17 and 9.3 μM, respectively) while showing no inhibition of trypsin (IC(50) > 100 μM).