Derivatization strategies

Derivatization of a racemic compound with an achiral group may play an important role in the analysis of a chiral compound (Fig. 7-15). In the case of substances with low or no UV-activity, the compounds can be rendered detectable by introducing an UV-absorbing or fluorescent group. If the racemate itself shows selectivity on a chiral stationary phase (CSP), this method can be applied to reduce the limit of detection. Examples have been reported in the literature, especially for the derivatization of amino acids which are difficult to detect using UV detection. Different derivatization strategies can be applied (Fig. 7-16). 

The castor plant is widely considered to be a nuisance plant, because it proliferates rapidly in poor, depleted soils that cannot sustain other more important commercial crops. It spreads quickly as a weed, and in some places has been listed as an intrusive species to be eliminated [51, 52]. Nevertheless, in recent years the industrial volume of castor oil has increased dramatically, driven primarily by the global interest in renewable resources for fuel and feedstocks as an alternative to petrochemicals. The majority of the volume growth has come from the Asian continent, primarily from India, where the castor plant is harvested commercially [53]. In addition to its direct use in pol3mrethane products, the oil and its components have been the focus of innovative new derivatization strategies to improve their properties for use in plastics, while retaining high levels of renewable content in the final products. These developments will be described in Section 4.5. 

Enantiomer separation by hydrogen-bonding stationary phases generally requires substrate derivatization. Hence versatile derivatization strategies have been devised124. In some cases, enantiomer separation on Chirasil-Val may be carried out without prior derivatization, e.g., for alcohols and bifunctional carbonyl compounds145. A survey on compound classes which have been separated into enantiomers is available128. 

From Hclmchen s and Pirkle s10-17 work it has become evident, however, that to obtain a pronounced diastereoselectivity on polar adsorbents (e.g., silica gel), it seems mandatory to follow a derivatization strategy for generating amides, carbamates and/or ureas, but not esters, of chiral analytes such as amines, acids, alcohols, or thiols using the appropriate CDAs. For better illustration, see Figure 1. 

In this chapter we have exemplified this type of derivatization strategy on a number of cases, all of which were reported in the literature with a well-documented experimental protocol. We expect that a growing number of examples will be published in the coming years, both in the patent literature (because of the industrial focus of the field) and in scientific journals. The added value of parallel and combinatorial chemistry will be further substantiated by these examples. 

Rice, K.G. (2000) Derivatization strategies for preparing N-glycan probes. Anal. Biochem., 283, 10-16. 

Husek, P. and P. Simek. 2006. Alkyl chloroformates in sample derivatization strategies for GC analysis. Review on a decade use of the reagents as esterifying agents. Cum Pharmaceut. Anal. 2 23-43. 

Fig. 5 Examples which demonstrates the versatility of an alkyne-functionalized [(tpm)Mn (CO)3]+ complex for both derivatization strategies, as well as the regio-flexibility with this chemistry...

While PEG-based supports are widely used for liquid-phase combinatorial chemistry, other non-PEG-based soluble polymers have also been reported for combinatorial applications. A recent review (276) contains an exhaustive list of homo- and copolym-eric soluble supports used in peptide, oligonucleotide, and oligosaccharide synthesis, including combinatorial chemistry. Two of these supports have also been used for small organic molecule synthesis. Homopolymeric polyvinyl alcohol was used in conjunction with PEG for a protection/derivatization strategy in solution (284), and the copolymer between isopropylacrylamide and acrylic acid was used in the catalytic hydrogenation of a Cbz group (285). 

The fluorescence detector is a specific and concentration-sensitive detector. It is based on the emission of photons by electronically excited molecules. Fluorescence is especially observed for analytes with large conjugated ring systems, e.g., polynuclear aromatic hydrocarbons and their derivatives. In order to extend its applicability range, pre-column or post-column derivatization strategies have been developed [9]. 

H. Steen, M. Maim, A new derivatization strategy for the analysis ofphosphopeptides by precursor ion scanning in positive ion mode, J. Am. Soc. Mass Spectrom., 13 (2002) 996. 

The ESI-MS characteristics of ohgosaccharides are strongly determined by the identity. The ESI-MS of oligosaccharides is complicated by their hydrophihcity, which limits their surface activity in the ESI droplets. Derivatization strategies to reduce their hydrophihcity, e.g., permethylation or introducing chromophores or fluorophores (Ch. 20.3.5), generally result in an improved response. Permethylated oligosaccharides can be analysed as protonated molecules or as sodium adducts in positive-ion ESI-MS. 

Various other derivatization strategies have been reported, e.g., V-(2-diethylamino)ethyl-4-aminobenzamide [7], 2-aminonaphthalene trisulfone (ANTS) [60], 2-amino-5-bromopyridine [61]. With the latter label, isotope tagging of the oligosaccharides is achieved, enabhng easy access to sequence information through the diagnostic twin peaks. 

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). 

Derivatization may be performed before the sample is injected into the liquid chromatograph (pre-column), as in the derivatization reactions used with gas chromatography. In liquid chromatography the derivatization may, as an alternative, be performed post-column, i.e., the reagent is added to the effluent from the column. The advantages and disadvantages of these two derivatization strategies are discussed in section 4.3.3. 

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... 

A similar derivatization strategy also exists for the selective detection of phosphoserine- and phosphothreonine-containing peptides in the positive-ion... 

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. 

Hernandez-Cassou, S., Saurina, J. (2011). Derivatization strategies for the determination of biogenic amines in wines by chromatographic and electrophoretic techniques. Journal of Chromatography B, 879, 1270-1281. http //dx.doi.Org/10.1016/j.jchromb.2010.ll.020. 

Figure 2 Derivatization strategies for permanently coating the capillary surface. Si-O bonds are formed through silanization (A). Si-C bonds are formed using a Grignard reaction (B).

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