Backbone fragmentations of [M–H] anions from peptides. Reinvestigation of the mechanism of the beta prime cleavage

Authors


J. H. Bowie, Department of Chemistry, The University of Adelaide, South Australia, 5005.

E-mail: John.Bowie@adelaide.edu.au

Abstract

RATIONALE

An experimental study has shown that the structure of a β' ion proposed earlier is incorrect. Backbone cleavage β' anions have structures R(NH) from systems [[RNHCH(X)CONHCH(Y)CO2H (or C-terminal CONH2) – H] (where R is the rest of the peptide molecule and X and Y represent the α side chains of the individual amino acid residues).

METHODS

Ab initio calculations were carried out at the CAM-B3LYP/6-311++g(d,p) level of theory.

CONCLUSIONS

The calculations suggest that RNH ions are formed by SNi cyclisation processes involving either (i) the C-terminal CO2 or C-terminal [CONH] as appropriate, or (ii) an enolate ion [-NHC(Y)-] cyclising at the backbone CH of the -CH(X)- group. Concomitant C–N bond cleavage then liberates an RNH ion, processes which can occur along the peptide backbone. Copyright © 2012 John Wiley & Sons, Ltd.

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