Nostosin G and Spiroidesin B from the Cyanobacterium Dolichospermum sp. NIES-1697.

Chemical investigation of the cyanobacterium Dolichospermum sp. NIES-1697 afforded nostosin G ( 1 ), a linear tripeptide, spiroidesin B ( 2 ), and two known compounds, anabaenopeptins I ( 3 ) and J ( 4 ). Planar structures and absolute configurations for 1 and 2 were determined by 2D NMR, HRMS, Marfey's methodology, chiral-phase HPLC, and enzymatic degradation. Nostosin G ( 1 ) is a unique example of a linear peptide containing three subunits, 4-hydroxyphenyllactic acid (Hpla), homotyrosine (Hty), and argininal, with potent trypsin inhibitory properties. The biosynthetic gene clusters for nostosin G ( 1 ) and spiroidesin B ( 2 ) were investigated based on the genome sequence of Dolichospermum sp. NIES-1697.