<i>Seco</i>[<scp>d</scp>-Asp³]microcystin-RR and [<scp>d</scp>-Asp³,<scp>d</scp>-Glu(OMe)⁶]microcystin-RR, Two New Microcystins from a Toxic Water Bloom of the Cyanobacterium <i>Planktothrix </i><i>r</i><i>ubescens</i>

Abstract

Two novel microcystins, seco[d-Asp(3)]microcystin-RR (1) and [d-Asp(3),d-Glu(OMe)(6)]-microcystin-RR (2), along with the known [d-Asp(3)]microcystin-RR (3), were isolated from a Planktothrix rubescens toxic bloom collected in Lake Bled, Slovenia. The structures were deduced using one- and two-dimensional NMR techniques, ESIMS/CID/MS analysis, and Marfey's method for determining the amino acids' absolute stereochemistry. Compounds 1 and 3 exhibit weak PP1 inhibitory activity. The NMR data of compound 3 are reported here for the first time.