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The document attached has been archived with permission from the publisher.1-Aryl-4-cyano-5-hydroxy-1,2,3-triazoles can be obtained in solution by base-catalysed cyclization of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

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#