Chiral derivatization

Table 1. Analyte Functional Groups and Chiral Derivatizing Reagents...

This chapter will focus on topic 3, which is normally regarded to be chiral derivatization chromatography, but will also cover other topics that might be considered when applying derivatization techniques. The goal for the separation of the race-mates may be their analysis or their preparation. Both topics will be covered in this chapter. 

One of the most useful applications of chiral derivatization chromatography is the quantification of free amino acid enantiomers. Using this indirect method, it is possible to quantify very small amounts of enantiomeric amino acids in parallel and in highly complex natural matrices. While direct determination of free amino acids is in itself not trivial, direct methods often fail completely when the enantiomeric ratio of amino acid from protein hydrolysis must be monitored in complex matrices. 

Based on gasliquidchromatography (GLPC) amides, formed from various enantiomeric amines and the chiral-derivatizing reagent ( S)-(—)-JV-pentafluorobenzoylprolyl-l-imidazole, could be detected at nanogram levels [43],[44]... 

Fig. 7-1. General reaction scheme of chiral derivatization chromatography.

Yeste et al.7 have developed chiral derivatization protocols for determination of enantiopurity of chiral diols by the H and 19F NMR spectroscopy. Three-component method has required the treatment of diol with 2-formylphenylboronic acid and a-methyl-4-fluorobenzylamine [4],... 

In determination of the absolute configuration of a-chiral primary amines, BINOL derivatives were used as chiral derivatizing agent.10 In this procedure, the chiral substrate was derivatized with R and S enantiomers of the 2,-methoxy-l,l -binaphthalene-8-carbaldehyde and the XH spectra of both diastereomers were compared. Comparison of the chemical shift differences of the diastereomers has allowed determination of the absolute configuration of the chiral substrate [5]. 

Perez-Fuertes et al.6 8 have suggested the possibility of using the three-component chiral derivatizing approach for prediction of the absolute configuration of amines. Comparison of aH NMR spectra has shown significantly more deshielded signals of (S,S)-imino-boronate esters, derivative of a-amino esters than (S,R) diastereomers. 

Various chiral derivatizing agents have been reported for the determination of enantiomer compositions. One example is determining the enantiomeric purity of alcohols using 31P NMR.28 As shown in Scheme 1-8, reagent 20 can be readily prepared and conveniently stored in tetrahydrofuran (THF) for long periods. This compound shows excellent activity toward primary, secondary, and tertiary alcohols. To evaluate the utility of compound 20 for determining enantiomer composition, some racemic alcohols were chosen and allowed to react with 20. The diastereomeric pairs of derivative 21 exhibit clear differences in their 31P NMR spectra, and the enantiomer composition of a compound can then be easily measured (Scheme 1-8). 

Scheme 1-9. Chiral derivatizing agents used in 31P NMR analysis.

The use of diazaphospholidines as chiral derivatizing agents for the determination of the enantiomeric composition of choro- or bromohydrins has been reported. Thus, 31P NMR spectra of a range of diastereomeric derivatives have been described to show a systematic deshielding from 0.2 to 12.9 ppm of isomers 48 compared to isomers 49 <2000TA1273>. 

Butyl oleate, 10 492 y-Butyloxycarbonyl-L-leucine anhydride, chiral derivatizing reagent, 6 76t Butylparaben, antimicrobial used in cosmetics, 7 831t terl-Butyl peroxyacetate, 13 484 terl-Butyl peroxybenzoate, 13 486 2-sec-Butylphenol (OSBP), 2 221-222 health and safety data, 2 220t physical properties of, 2 205t o-sec-Butylphenol. See 2-sec-Butylphenol (OSBP)... 

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