Schizopeptin 791, a new anabeanopeptin-like cyclic peptide from the cyanobacterium Schizothrix sp.

Schizopeptin 791 (1), a new trypsin inhibitor, related in structure to the anabeanopeptins, was isolated from the hydrophilic extract of the cultured terrestrial cyanobacterium Schizothrix sp. Homo- and heteronuclear 2D NMR techniques as well as HRFABMS determined the gross structure of 1. The relative and absolute stereochemistry of 1 was deduced from a combination of spectral data and Marfey's method for HPLC. Prior to this finding, anabeanopeptins have been isolated only from water-bloom-forming strains of cyanobacteria.