Development of a novel imidazolium‐based aromatic quaternary ammonium tag: Synthesis and application to the efficient analysis of cysteinyl‐peptides by mass spectrometry

Abstract

Chemical derivatization is a very promising technique for improving analysis of peptides by mass spectrometry (MS). In this study, a novel kind of imidazolium-based aromatic quaternary ammonium tag, 1-[3-[(2-iodo-1-oxoethyl)amino]propyl]-3-butylimidazolium bromide (IPBI), designed with strong gas-phase basicity and a permanent positive charge, was firstly synthesized and further used for derivatization of cysteinyl-peptides with improved ionization efficiency and higher charge states. Both the model peptides and tryptic digests of proteins were used to evaluate the effect of IPBI derivatization on the MS performance of the derivatized peptides, and the results were further compared with the commonly used iodoacetamide (IAA) tag. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-MS and electrospray ionization (ESI)-MS were used to evaluate the ionization efficiency and charge states of the derivatized peptides. With model peptides as samples, a nearly 100% derivatization efficiency and superior stability were achieved via IPBI derivatization. By further analysis of both standard peptides and tryptic protein digests, the ionization efficiency and charge states of IPBI-derivatized peptides could be remarkably improved. For example, for protein bovine serum albumin, compared with the commercial available IAA tag, the identification efficiency of cysteinyl-peptides was increased about 67% by combining with IPBI derivatization. The results indicated that the novel tag is an effective derivatization reagent for cysteinyl-peptide identification. We hope it could be further used for high-efficiency cysteinyl-peptide identification in proteome research, especially those with low abundance and poor ionization efficiency.