Sulfated Aeruginosins from Lake Kinneret: Microcystis Bloom, Isolation, Structure Elucidation, and Biological Activity

Aeruginosins are common metabolites of cyanobacteria. In the course of re-isolation of the known aeruginosins KT608A and KT608B for bioassay studies, we isolated three new sulfated aeruginosins, named aeruginosins KT688 (1), KT718 (2), and KT575 (3), from the extract of a Microcystis cell mass collected during the 2016 spring bloom event in Lake Kinneret, Israel. The structures of the new compounds were established on the basis of analyses of the 1D and 2D NMR, as well as HRESIMS data. Marfey’s method, coupled with HR ESI LCMS and chiral HPLC, was used to establish the absolute configuration of the amino acid and hydroxyphenyl lactic acid residues, respectively. Compounds 1–3 were tested for inhibition of the serine protease trypsin, and compounds 1 and 2 were found to exhibit IC₅₀ values of 2.38 and 1.43 µM, respectively.