An investigation of dipeptides containing polar and nonpolar side groups by curie-point pyrolysis tandem mass spectrometry

Abstract

Methionyl-leucine, leucyl-methionine, phenylalanyl-leucine, and leucyl-phenylalanine have been analyzed to determine dipeptide fragmentation mechanisms in Curie-point pyrolysis tandem mass spectrometry. Results show that fragmentations of dipeptides follow two general pathways, one involving direct cleavage of the dipeptide and the other involving cyclization of the dipeptide. Unique products and strong changes in relative mass spectral peak intensities arise, depending on constituent amino acid residues and their sequence. Also, the length and nature of the side groups strongly direct fragmentation. From these results, the major peaks in the spectra of eight other dipeptides could be readily explained; this suggests that a significant number of dipeptides follow the same general fragmentation mechanisms.

Insights into the Thermally Activated Cyclization Mechanism in a Linear Phenylalanine-Alanine Dipeptide

“…Since the first reports, 13 , 14 it has been generally recognized through mass spectrometry techniques that the sublimation of linear dipeptides may lead to the cyclization of the compound. This thermally induced cyclization has been confirmed by further reports, 15 − 17 and it is mentioned also in more recent studies. 18 , 19 However, a clear understanding of the process, combining measurements and computational studies, is still lacking, mainly due to the competition between thermal decomposition and cyclization reactions, 20 − 23 with the former often dominating.…”

Product compositions from pyrolysis of some aliphatic α-amino acids

“…5b). The main N-PACs were two-to three-ring carbonitriles, such as 13, 31-33, as well as acridine (14), carbazole (29), and norharman (30). Among the N-PACs, the yield of 29 was generally highest at all the temperatures, and passed through a maximum at 820 8C.…”

“…5. The major components of LTFT at 700 8C were the five-and six-member single-ring nitrogenous compounds, such as 6, 24 and 25, as well as NPACs such as 7, 13 and carbazole (29). As the temperature increased the yields of single-ring compounds decreased sharply.…”

“…Noguerola et al [29], and Hendricker and Voorhees [30] investigated the Curie-point pyrolysis-mass spectrometry of glycyl dipeptides. The results indicated the formation of diketopiperazines (DKP) by cyclization of the dipeptide.…”

Glycine homopeptides: the effect of the chain length on the crystal structure and solid state reactivity

“…Kinetics. Aside from standard synthetic methods, 93 the formation of DKPs was observed in the mass spectrometry experiments on dipeptides, [94][95][96] pyrolyzed oligopeptides 76 and thermally degraded proteins, 97 upon sublimation of dipeptides, 98,99 from thermally 100,101 or microwave [102][103][104] treated solutions and in few cases in the solid state. 105 In all cases the process involves cyclization through intramolecular aminolysis that can proceed in different pathways.…”