Cyclization reaction of peptide fragment ions during multistage collisionally activated decomposition: an inducement to lose internal amino-acid residues.

During characterization of some peptides (linear precursors of the cyclic peptides showing potential to be anticancer drugs) in an ion trap, it was noted that many internal amino acid residues could be lost from singly charged b ions. The phenomenon was not obvious at the first stage of collisionally activated decomposition (CAD), but was apparent at… CONTINUE READING