title: IR action spectroscopy shows competitive oxazolone and diketopiperazine formation in peptides depends on peptide length and identity of terminal residue in the departing fragment.
abstract: The interplay between the entropically and enthalpically favored products of peptide fragmentation is probed using a combined experimental and theoretical approach. These b2 ion products can take either an oxazolone or diketopiperazine structure. Cleavage after the second amide bond is often a favorable process because the products are small ring structures that are particularly stable. These structures are structurally characterized by action IRMPD spectroscopy and semi-quantified using gas-phase hydrogen-deuterium exchange. The formation of the oxazolone and diketopiperazine has been thought to be largely governed by the identity of the first two residues at the N-terminus of the peptide. We show here that the length of the precursor peptide and identity of the third residue play a significant role in the formation of the diketopiperazine structure in peptides containing an N-terminal asparagine residue. This is additionally the first instance showing an N-terminal residue with an amide side chain can promote formation of the diketopiperazine b2 ion structure.
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, 484 W. 12th Ave, Columbus, OH 43210, USA. wysocki.11@osu.edu.
authors.forename: L J
authors.initials: LJ
authors.lastname: Morrison
authors.forename: J
authors.initials: J
authors.lastname: Chamot-Rooke
authors.forename: V H
authors.initials: VH
authors.lastname: Wysocki
mesh_terms: D054659:Diketopiperazines / Q000032:analysis*; D013058:Mass Spectrometry; D010080:Oxazoles / Q000032:analysis*; D010455:Peptides / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D054659:Diketopiperazines; D010080:Oxazoles; D010455:Peptides