Chemical derivatization strategies

Metabolites are small molecules that participate as substrates or products in metabolic reactions essential for the normal function of a cell. This molecular class comprises a wide range of compounds, from amino acids to lipids, organic acids, and nucleotides (11). The wide range of concentration and different chemical properties make the analysis of these compounds a challenging task. Usually, high-resolution mass spectrometers and chemical derivatization strategies are necessary to resolve isobaric interferences, increase ionization efficiency, and overcome chemical background effects from the matrix-assisted laser desorption/ionization (MALDI) matrix or the tissue matrix itself (12). 

Chemical Derivatization Strategies to Direct the Fragmentation Reactions of Protonated Peptides... 

Numerous chemical derivatization strategies have been developed also to direct the fragmentation reactions of protonated peptides toward the selective formation of single characteristic sequence-type product ions [85-87]. For example, Sununerfield and coworkers have demonstrated that N-terminal derivatization, with phenyliso-thiocyanate to form the corresponding phenylthiocarbamoyl (PTC) derivative, results in exclusive fragmentation of the amide bond between the first two amino... 

Chemical derivatization methods provide a useful additional tool for protein structural analysis, particularly when conpled with the multistage tandem mass spectrometric capabilities of modern ion trap mass spectrometers. The objective of this chapter was to provide a brief overview of the chemical derivatization strategies that are employed currently to address the challenges associated with protein identification, characterization, and quantitative analysis as well as for the characterization of protein-protein interactions. 

In Chapter 4 is discussed the bottom-up or shotgun tand mass spectrometric approach to protein identification and characterization, which is the complementary method to top-down proteomics that is discussed in Chapter 3. In order to overcome the limitations of bottom-up proteomics, chemical derivatization strategies are... 

S Chemical Derivatization Strategies Derivatization techniques combined with LC-MS/MS have proven to be very useful for the characterization of novel and unusual metabolites (Prakash and Cui, 1997 Miao et ak, 2005 Prakash et ak, 2007c). Derivatization is useful when (1) a metabolite is unstable, (2) a metabolite is very polar, (3) a metabolite is volatile, (4) to characterize the functional group, (5) to prove MS fragmentation, and (6) to improve sensitivity when metabolite is present in trace amounts. 

Lam and Ramanathan, 2002 Ohashi et al., 1998). Recently, Liu and Hop (2005) thoroughly reviewed the chemical derivatization strategies for the characterization of drug metabolites by LC—MS, and the reader is directed to the review for more information. In this part, we will focus on the online H/D exchange techniques, particularly those that utilize LC—MS as the mode of metabolite analysis. 

Many of the chemical derivatization methods employed in these strategies involve the use of an activation step that produces a reactive intermediary. The activated species then can be used to couple a molecule containing a nucleophile, such as a primary amine or a thiol group. The following sections describe the chemical modification methods suitable for derivatizing individual nucleic acids as well as oligonucleotide polymers. 

Isolation of the feeding factor for M. sexta was a far more difficult task. Whereas 2-tridecanone is a simple, stable molecule soluble in organic solvents, the feeding factor is water soluble, occurs at trace levels in plant tissue, and is easily hydrolyzed under mild alkaline or acidic conditions with subsequent loss of biological activity. The isolation of such a compound was a formidable obstacle requiring a departure from the more classical approach of hydrolysis or chemical derivatization followed by isolation of the lipophilic product. The necessity that pure substance be isolated with retention of biological activity required some basic research in modem separation techniques to develop a suitably mild isolation strategy. 

In 2002, for the first time, CPMV was regarded as an addressable nanobuilding block [79]. First, experiments were conducted in order to test selective chemical derivatization of wild-type virions later, several mutant particles were made, such as cysteine mutants [80] and histidine mutants [81]. Different bioconjugation strategies were applied and a set of biological and organic and inorganic chemical molecules have been attached to CPMV. 

Other strategies, such as on-line H/D exchange LC/-MS/MS and chemical derivatization, were well-established approaches for characterization of small... 

D. Q. Liu and C. E. C. A. Hop, Strategies for characterization of drug metabolites using liquid chromatography-tandem mass spectrometry in conjunction with chemical derivatization and on-line H/D exchange approaches,/. Pharm. Biomed. Anal. 37 (2005), 1-18. 

Figure 1. The bioorthogonal chemical reporter strategy. First, unnatural monosaccharides are metabolically incorporated into glycoconjugates. Next, the unnatural functionality (black square) is covalently tagged using appropriately derivatized reagents (white square).

It has been demonstrated also that the iTRAQ tandem mass spectrometric quantitative analysis strategy can be used in conjunction with the quadrupole ion trap by performing multiple stages of mass analysis (that is, MS ) [125], For example, chemical derivatization with the iTRAQ reagent not only labels the N-terminus of a peptide, but the lysine side chain also. Thus, tryptic peptides with a modified lysine residue present at the C-terminus will produce a yj product ion at m/z 291 following ClD-tandem mass spectrometry. To generate the low m/z iTRAQ reporter ions required for quantitation, the yj product ion is isolated and subjected to data-dependent CID-MS. Using this approach, peptide identification is achieved in the MS/MS scan, while quantitation is achieved via MS. ... 

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