Accurate Mass MS/MS/MS Analysis of Siderophores Ferrioxamine B and E1 by Collision-Induced Dissociation Electrospray Mass Spectrometry

Siderophores are bacterially secreted, small molecule iron chelators that facilitate the binding of insoluble iron (III) for reuptake and use in various biological processes. These compounds are classified by their iron (III) binding geometry, as dictated by subunit composition and include groups such as the trihydroxamates (hexadentate ligand) and catecholates (bidentate). Small modifications to the core structure such as acetylation, lipid tail addition, or cyclization, make facile characterization of new siderophores difficult by molecular ion detection alone (MS¹). We have expanded upon previous fragmentation-directed studies using electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS/MS) and identified diagnostic MS³ features from the trihydroxamate siderophore class for ferrioxamine B and E1 by accurate mass. Diagnostic features for MS³ include C-C, C-N, amide, and oxime cleavage events with proposed losses of water and -CO from the iron (III) coordination sites. These insights will facilitate the discovery of novel trihydroxamate siderophores from complex sample matrices. [Figure not available: see fulltext.]