Strategies for the Identification of Cyclic Peptide Drugs and Their Impurities

spectra provided more regular c/z ion series and reduced spectral complexity, enabling straightforward analysis using commercial software. Applying optimized EThcD conditions and established fragmentation rules, impurities in atosiban and carbetocin were characterized, leading to the identification of three impurities in atosiban and two in carbetocin. This approach demonstrates the effectiveness of EThcD for structural elucidation and impurity profiling of cyclic peptide therapeutics.