Matrix-assisted laser desorption/ionization time-of-flight and nano-electrospray ionization ion trap mass spectrometric characterization of 1-cyano-2-substituted-benz[f]isoindole derivatives of peptides for fluorescence detection

A series of hexa- to decapeptides (molecular mass range 800-1200) were labe led with naphthalene-2,3-dicarboxaldehyde, which preferentially reacts with the primary amino groups of a peptide. A highly stable peptide conjugate i s formed, which allows selective analysis by fluorescence at excitation and emission wavelengths of 420 and 490 nm, respectively, After removal of unr eacted compounds, the peptide conjugates were characterized by matrix-assis ted laser desorption/ionization (MALDI) time-of-flight and nano-electrospra y ionization (ESI) ion trap mass spectrometry. They readily form both [M H](+) ions by MALDI and both [M + H](+) and [M + 2H](2+) ions by ESI, Furth ermore, the fragmentation behavior of the N-terminally tagged peptides, exh ibiting an uncharged N-terminus, was investigated applying post-source deca y fragmentation with a curved field reflector and collision-induced dissoci ation with a quadrupole ion trap. Fragmentation is dominated in both cases by series of a-, b- and y-type ions and [M + H - HCN](+) ions, Peptide bond s adjacent to the fluorescence label were less susceptible to cleavage than the bonds of the non-derivatized peptide ions, In general, the resulting f ragment ion patterns were less complex than those of the underivatized pept ides, Copyright (C) 1999 John Wiley & Sons, Ltd.