Stigonemapeptin, an Ahp-Containing Depsipeptide with Elastase Inhibitory Activity from the Bloom-Forming Freshwater Cyanobacterium <i>Stigonema</i> sp.

Abstract

Stigonemapeptin (<b>1</b>), a depsipeptide containing an Ahp (3-amino-6-hydroxy-2-piperidone) residue, was isolated from a bloom sample of the freshwater cyanobacterium <i>Stigonema</i> sp. collected from North Nokomis Lake in the Highland Lake District of northern Wisconsin. The planar structure was determined by 1D and 2D NMR experiments as well as HRESIMS analysis. The absolute configurations of the amino acids were determined using the advanced Marfey’s method after acid hydrolysis. Stigonemapeptin (<b>1</b>), characterized by the presence of the Ahp residue, also contained the modified amino acids Abu (2-amino-2-butenoic acid) and <i>N</i>-formylated Pro. Stigonemapeptin (<b>1</b>) showed <i>in vitro</i> elastase and chymotrypsin inhibitory activity, with IC₅₀ values of 0.26 and 2.93 μM, respectively