Visible-Light Paternò–Büchi Reaction for Lipidomic Profiling at Detailed Structure Levels

Abstract

The Paternò–Büchi (PB) derivatization of carbon–carbon double bond (CC) has been increasingly employed with tandem mass spectrometry to analyze unsaturated lipids. It enables the discovery of altered or uncanonical lipid desaturation metabolism, which would be otherwise undetected by conventional methods. Although highly useful, the reported PB reactions only provide moderate yield (∼30%). Herein, we aim to determine the key factors that affect the PB reactions and develop a system with improved capabilities for lipidomic analysis. An Ir(III) photocatalyst is chosen as the triplet energy donor for the PB reagent under 405 nm light irradiation, while phenylglyoxalate and its charge-tagging version, pyridylglyoxalate, are developed as the most efficient PB reagents. The above visible-light PB reaction system provides higher PB conversions than all previously reported PB reactions. Around 90% conversion can be achieved at high concentrations (>0.5 mM) for different classes of lipids but drops as the lipid concentration decreases. The visible-light PB reaction has then been integrated with shotgun and liquid chromatography-based workflows. The limits of detection for locating CC in standard lipids of glycerophospholipids (GPLs) and triacylglycerides (TGs) are in the sub-nM to nM range. More than 600 distinct GPLs and TGs have been profiled at the CC location level or the sn-position level from the total lipid extract of bovine liver, demonstrating that the developed method is capable of large-scale lipidomic analysis.

Characterization of Oxidized Glycerophosphoethanolamines via Radical-Directed Dissociation Tandem Mass Spectrometry and the Paternò–Büchi Derivatization

“…PE 16:0/13-HODE was prepared via 15-LOX enzymatic oxidation and used as a model compound. Six PB reagents were evaluated, including benzoylformate (MB), , acetone, 2- and 3-acetylpyridines, 2,4,6-trifluoroacetophenone (triFAP), and 4-trifluoromethylacetophenone. Although triFAP and 2-aceytylpyridine were proved as efficient PB reagents for phospholipids and nonpolar lipids, they suffered from low reaction yield for oxidized PEs likely due to the presence of OH.…”

“…Although triFAP and 2-aceytylpyridine were proved as efficient PB reagents for phospholipids and nonpolar lipids, they suffered from low reaction yield for oxidized PEs likely due to the presence of OH. MB showed the best performance by providing relatively high PB conversion (43%) and abundant CC diagnostic ions in PB-MS 2 CID . Therefore, MB was used in all later PB-MS/MS experiments.…”

“…MB showed the best performance by providing relatively high PB conversion (43%) and abundant C�C diagnostic ions in PB-MS 2 CID. 22 Therefore, MB was used in all later PB-MS/MS experiments. Upon the PB reaction, the C�C is converted to an oxetane ring which facilitates the formation of C�C diagnostic ions, m F A/O , by MS 2 CID.…”

Lipid Isobaric Mass Tagging for Enhanced Relative Quantification of Unsaturated sn-Positional Isomers

“…Along with other method advancements for isomeric lipid characterization, − a few methodologies have been developed to target sn -positional isomer identification. These include charge inversion ion–ion reactions, anion/cation adduction of lipids, ,− radical-induced dissociation of bicarbonate-adducted lipids, CID fragmentation coupled with ozone-induced fragmentation, electron-induced dissociation of lipids, and coupling MS with ion mobility …”

Intramolecular Ring–Chain Equilibrium Elimination Strategy for Pinpointing C═C Positional and Geometric Isomers of N-Alkylpyridinium Unsaturated Fatty Acid Derivatives via Ion Mobility-Mass Spectrometry

“…In 2010, Gelb et al reported a new derivatization reagent N -(4-aminomethylphenyl)­pyridinium that can be coupled to eicosanoids via an amide linkage in quantitative yield, but the abundant carboxyl-containing metabolites in organisms will mask the signals of trace UFA . To further characterize UFA with information on CC location or geometry, several derivatization strategies combined with mass spectrometry (MS/MS) have been developed, such as ozone-induced dissociation, , epoxidation, and Paternò–Buchi reactions. − Recently, the Brenna group employed solvent-mediated covalent adduct chemical ionization tandem mass spectrometry (MS/MS) to enable rapid, unambiguous identification of UFA methyl esters at high sensitivity. − Wei et al presented a dual derivatization strategy based on a combination of acetone labeling of CC bonds and N , N -diethyl-1,2-ethanediamine labeling of carboxyl groups, which could enhance the mass spectrometry (MS) response of diagnostic ions . In 2022, our group developed a flexible and convenient N -tosylaziridination method to specifically pinpoint the numbers and locations of CC in MS/MS .…”