Chiral derivatisation agents

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. 

Chiral platinum (and palladium) ethene complexes derived from Diop [2,2-dimethyl-4,5-bis-(diphenylphosphinomethyl)-l,3-dioxolane] act as chiral derivatising agents for the 31P-based NMR assay of the enantiomeric purity of certain chiral alkenes and allenes80. 

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. 

For a number of reasons it is usually preferable to use a chiral stationary phase (CSP) rather than a chiral derivatising agent. A CSP will normally be preferred to a chiral mobile phase additive, partly because the use of a chiral selector as a mobile phase additive will lead to much... 

The method chosen was that of Johnson and coworkers (ref. 66) which involves the use of a chiral oxazaphospholidine-2-thione as a chiral derivatising agent for Ip NMR analysis of... 

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. 

Parker D, Taylor RJ. Scope and limitations of organometallic chiral derivatising agents for the P NMR determination of the enantiomeric purity of chiral t donors. Tetrahedron 1988 44 2241-2248. 

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