A novel on-tissue cycloaddition reagent for mass spectrometry imaging of lipid C=C position isomers in biological tissues

Application of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to investigate the spatiotemporal alterations of lipids in biological tissues has brought many significant results. However, the presence of structural isomers varying in C=C double bond (DB) locations makes isomer-resolved MSI an urgent need. Herein, we introduce a new type of light-driven on-tissue [2+2] cycloaddition reaction coupled with MALDI-MS/MS imaging to identify lipid DB position isomers and their spatial signatures in biological tissues. 3-Benzoylpyridine was introduced as a novel derivatization reagent, and it exhibited great reactivity toward lipid C=C bond to form oxetanes under both ultraviolet light and visible light irradiation. With this approach, DB position isomers of lipids were imaged with highly differential levels in distinct regions of rat brain, providing an accurate and spatially resolved approach to study tissue lipidomics. An isomer-resolved lipid imaging method was developed by coupling light-driven derivatization with MALDI-MS imaging technique. By introducing 3-benzoylpyridine as a novel derivatization reagent and conducting on-tissue MALDI-MS/MS imaging analysis, we successfully map the spatial distributions of lipid C=C position isomers in biological tissues.