The gas phase cyclization of deprotonated N-aryl-2-cyano-2-diazoacetamides

The document attached has been archived with permission from the publisher.1-Aryl-4-cyano-5-hydroxy-1,2,3-triazoles can be obtained in solution by base-catalysed cyclization of N-aryl-2-cyano-2-diazoacetamides. A similar reaction was shown to take place under conditions of negative ion chemical ionization in the ion source of a mass spectrometer. High resolution mass spectrometry, tandem mass spectrometry, charge reversal spectra, synthesis of the ions with known structures and quantum chemical calculations were used to prove the latter statement. The fact of the observed cyclization demonstrates once again the ability of mass spectrometry to study the gas phase chemical reactions that take place in solution.Vladislav V. Lobodin, Yuriy Yu. Morzherin, Tom Blumenthal, Daniel Bilusich, Vladimir V. Ovcharenko, John H. Bowie, and Albert T. Lebede

Identification of intermolecular disulfide linkages in underivatised peptides using negative ion electrospray mass spectrometry. A joint experimental and theoretical study

The definitive version may be found at www.wiley.comThe [M--H](-) ion of a symmetrical peptide containing one intermolecular disulfide linkage cleaves through the disulfide link to produce up to four fragment anions. Two of these characteristic fragments are formed by a cleavage initiated from the Cys enolate anion on the peptide backbone. The other fragment anions are formed by a cleavage directed from an anion site on the disulfide side chain. In the case of an unsymmetrical peptide containing one intermolecular disulfide, the [M--H](-) anion may cleave through the disulfide unit to give a maximum of eight cleavage anions. These fragmentations are low-energy processes as determined by theoretical calculations carried out at the HF/6-31G(d)//AM1 level of theory. Collision-induced mass spectra of the fragment anions may provide the sequence of the peptide.Daniel Bilusich, John H. Bowi

Determination of disulfide functionality in underivatised peptides using negative ion mass spectrometry: An aid to structure determination

© 2006 Bentham Science PublishersThis review outlines the mass spectrometric methods used to identify disulfide functionality in peptides, particularly cleavages from peptide (M-H)- parent anions. A brief introduction to characteristic negative ion fragmentations of peptides is given, including (i) the α and β cleavages which provide data analogous to that provided by Y+2 and B cleavages of MH+ ions, (ii) characteristic side chain cleavages, and (iii) γ backbone cleavages initiated from anion sites on the side chains of certain residues (e.g. Ser, Thr, Cys, Asp, Asn, Glu and Gln). The cystine disulfide functionality is difficult to identify from positive ion fragmentations of an MH+ parent cation of an underivatised peptide. However, the -S-S- group is readily identified by the diagnostic loss of the elements of H2S2 from the (M-H)- anion of the peptide. This process is anion directed (from that cystine backbone enolate anion closest to the Nterminal end of the peptide). The stepwise process is exothermic (by 4.6 kcal mol-1; calculations at the HF/6-31G(d)//AM1 level of theory) with a barrier of 9.1 kcal mol-1 to the highest energy transition state. If one of the cystine residues is Cterminal with a terminal CO2H moiety, the presence of a pronounced peak corresponding to the fragmentation sequence [(M-H)- - (H2S2 + CO2)]- identifies this functionality. The studied fragmentation processes are charge initiated; there is no evidence for the operation of any charge-remote processes.http://www.bentham.org/cac/contabs/cac2-4.htm#

Fragmentations of (M-H)(-) anions of underivatised peptides. PART 2: Characteristic cleavages of ser and cys and of disulfides and other post-translational modifications, together with some unusual internal processes

In a previous review (Bowie, Brinkworth, & Dua (2002); Mass Spectrom Rev 21:87-107) we described the characteristic backbone cleavages and side chain fragmentations which occur from (M-H)(-) parent anions of underivatized peptides. This work is briefly summarized in the present review. Cys was not described in the previous review: here we describe the Cys characteristic side chain loss of H(2)S, together with its gamma backbone cleavage. These processes are compared with those of the related Ser. All experimental observations are backed up with theoretical studies at the HF/6-31G(d)//AM1 level of theory, a level of theory which we have shown gives good geometries and acceptable relative energies. The negative ion cleavages of a number of post-translational modifications are described. Negative ion mass spectrometry is the method of choice for identification of disulfides in both peptides and proteins. Intramolecular disulfides are identified by the presence of the fragment anion [(M-H)(-)-H(2)S(2)], and CID MS2 of this fragment normally identifies the positions of the two Cys residues and often the full sequence of the peptide. An unsymmetrically substituted intermolecular disulfide can give up to eight characteristic fragment anions, and CID MS2 of some, or all of these often provides the full sequence of those peptides which form the initial intermolecular disulfide linkage. Negative ion cleavages of disulfides are the most energetically favored of all peptide negative cleavages studied to date. Negative ion mass spectrometry is also valuable for the identification of pyroglutamates, sulfates and phosphates. Finally, some unusual fragmentations are described which involve cyclization/elimination reactions which require the decomposing (M-H)(-) parent anions to adopt the same helical conformation that these peptides have in solution.Daniel Bilusich and John. H. Bowi