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

Interest in peptides incorporating boronic acid moieties is increasing due to their potential as therapeutics; diagnostics for a variety of diseases such as cancer. The utility ot peptide boronic acids may be expanded with access to vast libraries that can be deconvoluted rapidly and economically. Unfortunately, current detection protocols using mass spec-trometry are laborious and confounded by boronic acid trimerizjtion, which requires time-consuming analysis of dehydration products. These issues are exacerbated when the peptide sequence is unknown, as with de novo sequencing, and especially when multiple boronic acid moieties are present. Thus, a rapid, reliable, and simple method tor peptide identification is of utmost importance. Herein, we report the identification and sequencing of linear and branched peptide boronic acids containing up to five boronic acid groups by matrix-assisted laser desorption/ionization mass spectrometry (MALDl-MS). Protocols for preparation of pinacol boronic esters were adapted for efficient MALDl analysis of peptides. Additionally, a novel peptide boronic add detection strategy was developed in which 2,5-dihydroxybenzoic acid (DHB) served as both matrix and derivatizing agent in a convenient, in situ, on-plate esterification. Finally, we demonstrate that DHH-modified peptide boronic acids from a single bead can be analyzed by MALDI-MSMS analysis, validating our approach for the identification and sequencing of branched peptide boronic acid libraries. [ABSTRACT FROM AUTHOR]