Surugamides A–E, Cyclic Octapeptides with Four <scp>d</scp>-Amino Acid Residues, from a Marine Streptomyces sp.: LC–MS-Aided Inspection of Partial Hydrolysates for the Distinction of <scp>d</scp>- and <scp>l</scp>-Amino Acid Residues in the Sequence

Abstract

Surugamides A-E (1-5), cyclic octapeptides with four D-amino acid residues, were isolated from the broth of marine-derived Streptomyces sp. Their planar structures were determined by analyses of spectroscopic data, and the absolute configuration of constituent amino acid residues was determined by the Marfey's method. Differentiation of D-Ile and L-Ile in the sequence was established by chiral analysis of fragment peptides obtained from the partial hydrolysate, whose identification was conducted by LC-MS/MS.