On-Tissue Chemical Derivatization Reagents for MALDI-MSI

Introduction

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a fast growing technique and key tool for the analysis of biological tissues. It provides spatial distribution and quantitative information of the different type of analytes (such as proteins, peptides, small molecules, lipids, glycans, and drugs) within tissue sections. And thus, MALDI-MSI technique has been successfully applied in various fields. Despite the increasing improvements of this technique, the low detection sensitivity of some small molecules remains an important challenge to overcome. One of the most effective ways to solve this problem is on-tissue chemical derivatization (OTCD) by reagent. By reacting on-tissue chemical derivatization reagents with analytes in tissue sections can not only improve detection sensitivity of MALDI-MSI, but also can improve its specificity. In addition to their reactivity with a targeted chemical function, some on-tissue chemical derivatization reagents can also be used as a matrix, which simplifies the sample preparation procedure of MALDI-MSI. Today, on-tissue chemical derivatization reagents are increasingly employed in MALDI-MSI studies to improve the detection of small endogenous and exogenous molecules within tissues. Here, Alfa Chemistry presents an exhaustive summary of on-tissue chemical derivatization reagents used in MALDI-MSI studies ^[1-2].

Overview of On-Tissue Chemical Derivatization Reagents

We present a comprehensive summary of on-tissue chemical derivatization reagents recently used in various small molecules with different functional groups including amine, hydroxyl, carbonyl, carboxylic acid, thiol, and double bond in MALDI-MSI studies.

For Amine Functional Group: The derivatization reagents used for sensitive analysis of small molecules with amine functional group within tissues include p-N,N,N-trimethylammonioanilyl N'-hydroxysuccinimidyl carbamate iodide (TAHS), Trans-cinnamaldehyde, 4-hydroxy-3-methoxycinnamaldehyde (CA) derivatization, 2,4-diphenyl-pyranilium tetrafluoroborate (DPP-TFB), 4-(10-bromoanthracen-9-yl)-2-fluoro-1-methylpyridin-1-ium iodide (FMP-8), 4-(Anthracen-9-yl)-2-fluoro-1-ethylpyridin-1-ium iodide (FMP-9), 4-(Anthracen-9-yl)-2-fluoro-1-methylpyridin-1-ium iodide (FMP-10), 2-nitrobenzaldehyde (NBA), 4-sulphophenyl isothiocyanate (4-SPITC), sulfobenzoic acid succinimidyl ester (3-SBASE), N-succinimidyloxycarbonylmethyl tris(2,4,6-trimethoxyphenyl) phosphonium bromide (TMPP), etc.

Fig. 1. OTCD of amine functions in neurotransmitters by the DPP-TFB derivatization reagent.

For Phenolic Hydroxyl Functional Group: Fluoromethylpyridinium based reagents react not only with amines but also with hydroxyl groups in nucleophilic aromatic substitution. Thus, they are frequently used derivatization reagents for phenolic hydroxyl functional group. One of famous example is 2-fluoro-1- methylpyridinium p-toluene sulfonate (FMPTS) for derivatization of the phenolic hydroxyl group of cannabinoids in human hair. In addition, 4-(N-methyl)pyridinium boronic acid ((N-Me)Py+ B(OH)₂) is also applied for derivatization of molecules with phenolic hydroxyl functional group.

Fig. 2. FMPTS derivatization reagent reacts with targeting phenolic hydroxyl groups.

For Carbonyl Functional Group: Girard T (GirT) reagent, Girard P (GirP) reagent, 2,4-dinitrophenylhydrazine (DNPH) and 4-dimethylamino-6-(4-methoxy-1-naphthyl)-1,3,5-triazine-2-hydrazine (DMNTH) are frequently used for sensitive analysis of small molecules with carbonyl functional group within tissues. GirT and GirP reagent are used to detect ketones containing compound by a hydrazine-type condensation reaction, while DNPH and DMNTH are used to detect carbonyl containing compound.

Fig. 3. OTCD of ketone functions in steroids using the GirT derivatization reagent. Abbreviations: seminiferous tubule (ST), Leydig cells (LC).

For Carboxylic Acid Functional Group: Three derivatization reagents mainly used for sensitive analysis of small molecules with carboxylic acid functional group within tissues are 2-picolylamine, N,N-dimethylpiperazineiodide (DMPI) and N,N,N-trimethyl-2-(piperazin-1-yl)ethan-1-aminium iodide (TMPA).

Fig. 4. 2-Picolylamine (top) and DMPI (bottom) derivatization reagents react with targeting carboxylic acid groups.

For Thiol Functional Group: (E)-2-cyano-N-(2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)ethyl)-3-(4-hydroxyphenyl)-acrylamide (CHC-Mal) is frequently used derivatization reagents for thiol functional group. It is used to detect reduced proteins, such as α and β chains of reduced insulin, in porcine pancreatic tissues, and is also able to contribute to the detection of small thiol-containing metabolites such as glutathione, cysteine and cysteinyl glycine in porcine liver tissues.

Fig. 5. CHC-Mal derivatization reagents react with targeting thiol groups.

For Double Bond Functional Group: Benzaldehyde was used for distinguishing and imaging of lipid double bonds. In addition, ozone was used for sensitive analysis of unsaturated lipids under concentrated ozone atmosphere in a reaction chamber.

Alfa Chemistry is a global leading supplier of analytical chemistry reagents. We provide a wide range of high quality derivatization reagents for on-tissue chemical derivatization, and many other analytical chemistry products. If you cannot find the suitable products, Alfa Chemistry also offers you with custom synthesis service. If necessary, please don't hesitate to contact us.

References

Zhou Q., et al. Recent developments of novel matrices and on-tissue chemical derivatization reagents for MALDI-MSI[J]. Analytical and bioanalytical chemistry, 2021, 413: 2599-2617.
Merdas M., et al. On‐tissue chemical derivatization reagents for matrix‐assisted laser desorption/ionization mass spectrometry imaging[J]. Journal of Mass Spectrometry, 2021, 56(10): e4731.

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