Novel Functional Tags: Design, Synthesis And Peptide Labeling

The development of novel kind of tags compatible with mass spectrometry (MS) analysisis crucial for further in-depth proteome research. Thus, in the present work, totally five novelimidazolium-based tags were designed and synthesized, and the effect of derivatization ofthese tags on the ionization of peptides was also investigated.Novel aromatic quaternary ammonium tags, including：1-(4-iodobutyl)-3-butylimidazoleiodide (IBBI),1-propanal-3-buthyl imidazole salt bromine (PPBI),1-[3-[(2-Iodo-1-oxoethyl)amino]propyl]-3-methylimidazolium bromide (IPMI),1-[3-[(2-Iodo-1-oxoethyl)amino]propyl]-3-butylimidazolium bromide (IPBI) and1-[3-[(2-Iodo-1-oxoethyl)amino]propyl]-3-hexylimidazolium bromide (IPHI) weresynthesized, and the structures of these tags were further verified via MS and NMR.The tag IPBI was firstly used for peptide labeling, a nearly100%derivatization yieldwas achieved with the developed tag. Furthermore, even thought the peptide derivatice wasstored at room temperature for one week, no noticeable change of the MALDI-TOF MSprofiling was observed, indicating its high stability. Moreover, both the ionization efficientand charge states of the derivatized peptides were obviously increased, outperforming thecommonly used tag IAA and IDA.The effect of derivatization of peptides via IPMI, IPBI, and IPHI were further exploitedfor cysteinyl-peptide analysis with superior labeling efficiency, high stability, improvedionization efficiency, and increased charge states. Interestingly, theN-hexyl-imidazolium-based tag, IPHI, designed with the strongest hydrophobicity, exhibitedthe most obvious ionization efficiency increment via MALDI-TOF MS analysis. However, itshould be noted that the introduction of hydrophobic moieties has no obvious influence on thecharge states of the peptides in ESI MS.