Pyrylium Salts as Reactive Matrices for MALDI-MS Imaging of Biologically Active Primary Amines

Abstract

Abstract. Many neuroactive substances, including endogenous biomolecules, environmental compounds, and pharmaceuticals possess primary amine functional groups. Among these are catecholamine neurotransmitters (e.g., dopamine), many substituted phenethylamines (e.g., amphetamine), as well as amino acids and neuropeptides. In most cases, mass spectrometric (ESI and MALDI) analyses of trace amounts of such compounds are challenging because of their poor ionization properties. We present a method for chemical derivatization of primary amines by reaction with pyrylium salts that facilitates their detection by MALDI-MS and enables the imaging of primary amines in brain tissue sections. A screen of pyrylium salts revealed that the 2,4-diphenyl-pyranylium ion efficiently derivatizes primary amines and can be used as a reactive MALDI-MS matrix that induces both derivatization and desorption. MALDI-MS imaging with such matrix was used to map the localization of dopamine and amphetamine in brain tissue sections and to quantitatively map the distribution of the neurotoxin β-N-methylamino-L-alanine.

Imaging mass spectrometry in drug development and toxicology

“…However, detection of these small molecules is hampered by interference of matrix cluster ions. This limitation can be overcome by matrix-free laser desorption/ionization (LDI) approaches as well as other strategies including e.g., use of a stable isotope modified matrix, derivatization or MS/MS methodologies (Nilsson et al 2010; Northen et al 2007; Prentice et al 2016; Shariatgorji et al 2012b, 2015). The first experiment designed to study drug distribution using MALDI IMS in a whole-body mouse section was published in 2005 by Rohner et al (2005).…”

“…For example, quantitative brain imaging of the environmental neurotoxin β- N -methylamino- l -alanine (BMAA)—suggested to be involved in neurodegenerative disorders (Cox et al 2016; Spencer et al 1987)—was performed after derivatization with 2,4-diphenyl-pyranylium (DPP) by relating the signals for BMAA in dosed rats a calibration curve constructed by spotting known concentrations of BMAA on a control tissue section (Shariatgorji et al 2015). Moreover, it has been demonstrated that IMS can be used for quantification of the organochloride pesticide chlorodecone in the mouse liver (Lagarrigue et al 2014).…”

Development of an Imaging Mass Spectrometry Technique for Visualizing Localized Cellular Signaling Mediators in Tissues

“…By expanding this concept, not only the exogenous drug but also the endogenous metabolites, including steroid hormones 54) (Fig. 4B), minor amino acids, 27) and monoamine neurotransmitters along with their precursor/decomposed metabolites 55,56) (Fig. 4C), were successfully visualized.…”

“…is is presumably because these aromatic amino acids possess the ability to absorb ultraviolet light, which might cause them to exert "matrix" e ects, suggesting that TAHS functions as a type of "reactive matrix." 56) In other words, the TAHS derivatization method provided an opportunity to analyze minor amino acids by improving their ionization e ciency, especially for aromatic amino acids.…”

Chemoselective reactions and their applications in metabolite isolation and analysis.

“…For example, other cationic aromatic aromatic molecules such as pyrylium salts are frequently used to enhance ionization of amine metabolites for easy MS detection [201]. Hence, we hypothesize these molecules would be detected in positive ion MS with far greater sensitivity and thus serve to profile the CA fraction of a mixture.…”