Facile Analysis and Sequencing of Linear and Branched Peptide Boronic Acids by MALDI Mass Spectrometry

摘要

Interest in peptides incorporating boronic acidnmoieties is increasing due to their potential as therapeuticsdiagnostics for a variety of diseases such as cancer. The utilitynof peptide boronic acids may be expanded with access to vastnlibraries that can be deconvoluted rapidly and economically.nUnfortunately, current detection protocols using mass spectrometrynare laborious and confounded by boronic acidntrimerization, which requires time-consuming analysis of dehydration products. These issues are exacerbated when the peptidensequence is unknown, as with de novo sequencing, and especially when multiple boronic acid moieties are present. Thus, a rapid,nreliable, and simple method for peptide identification is of utmost importance. Herein, we report the identification and sequencingnof linear and branched peptide boronic acids containing up to five boronic acid groups by matrix-assisted laser desorption/ionizationnmass spectrometry (MALDI-MS). Protocols for preparation of pinacol boronic esters were adapted for efficient MALDI analysis ofnpeptides. Additionally, a novel peptide boronic acid detection strategy was developed in which 2,5-dihydroxybenzoic acid (DHB)nserved as both matrix and derivatizing agent in a convenient, in situ, on-plate esterification. Finally, we demonstrate that DHBmodifiednpeptide boronic acids from a single bead can be analyzed by MALDI-MSMS analysis, validating our approach for thenidentification and sequencing of branched peptide boronic acid libraries.