Novel pyridinium-based tags: synthesis and characterization for highly efficient analysis of thiol-containing peptides by mass spectrometry.

In this study, a novel type of pyridinium-based tags, 1-[3-[(2-iodo-1-oxoethyl)amino]propyl]-4-methylpyridinium bromide (IMP) and 1-[3-[(2-iodo-1-oxoethyl)amino]propyl]-4-propylpyridinium bromide (IPP), were designed, synthesized, and applied to the derivatization of thiol-containing peptides. With model peptides as the sample, the labeling efficiency and the stability of the peptide derivatives were investigated. The results indicate that nearly 100% derivatization yield was achieved with the developed tags and the peptide derivatives were stable at room temperature for at least one week. Furthermore, improved ionization efficiency and increased charge states were achieved via both matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MS) and electrospray ionization (ESI) MS, of which IPP exhibited the more obvious improvement of ionization efficiency. Further analysis of tryptic digests of bovine serum albumin (BSA) and α-transferrin, showed that increased identification efficiency of the thiol-containing peptides was achieved by combination with IMP or IPP derivatization. For example, the identification efficiency of the thiol-containing peptides of α-transferrin increased more than 42% upon combination with the IMP or IPP derivatives. We anticipate the novel tags are promising for highly efficient thiol-containing peptide identification in proteome research, especially for low concentrations.