Chiral derivatising reagents

Fluorescence chiral derivatisation reagent for carboxylic acids. Light yellow needles (Me0H/Et20). Mp 255-257°. lotY -16.8° (c, 1 in MeOH). 

NMR can be a powerful tool for determination of enantiomeric excess or absolute configuration of the optically active compounds, however, these processes require the use of some auxiliaries, for example, chiral lanthanide shift reagents or chiral derivatising agent. In many cases, the starting point for determination of enantiopurity of amines, amino acids or diols is the formation of chiral imines. 

R and S diastereomers (AA5 = 10 ppm) and experience a large lanthanide induced shift with the CH3 resonating at +21 and +31 ppm respectively for (It)- and (5)-lactate respectively (c.f. +1.3 ppm in the free form). The large shifts exhibited by this unique chiral derivatising agent may be compared to the much smaller AA8 values reported for shift reagents which are generally of the order 1 ppm, and often <0.1 ppm. 

The types of derivatising reagents that may be used are shown in Figure 12.5. The products formed are called diastereomers. These compounds which possess two chiral centres have different physicochemical properties and are therefore separable by LC on conventional achiral LC columns. 

Three types of chiral auxiliary are widely used. Chiral derivatising agents (CDAs)[ l form diastereomers while chiral solvating agents (CSAs)t l and chiral lanthanide shift reagents (CLSRs)t l form diastereomeric complexes in situ with the substrate enantiomers. 

Derivatisation reagent for hplc separation of amine and amino acid enantiomers on chiral stationary phases. 

From these studies it has been shown that for a successful and efficient parallel kinetic resolution the following guidelines need to be adhered to a) derivatisation with two complementary chiral reagents have to occur without mutual interference [17] b) both reactions need to occur with similar but preferably equal rate and have complementary stereocontrol and c) afford distinct and easily separable products. 

Chiral separation by liquid chromatography can be divided into four approaches (i) derivatisation with a chiral reagent and separation of the resulting diastereomers on a non-chiral stationary phase (non-CSP) (ii) direct separation on a non-CSP by the use of a chiral mobile phase additive (iii) derivatisation with a non-chiral reagent and separation on a CSP and (iv) direct separation on a CSP. 

Buck RH, Krummen K. Resolution of amino add enantiomers by high-performance liquid chromatography using automated pre-column derivatisation with a chiral reagent. J Chromatogr 1984 315 279-85. 

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