Asymmetric synthesis enantiomer recognition

The existence of chirality in nature is of particular importance in numerous recognition processes, often illustrated by examples detectable by non-spectroscopic methods such as the different orange and lemon odors of R-(+)- and S-(-)-limonene, respectively (Fig. 3) [8]. As such, chiral discrimination is also of considerable consequence in the medical sciences, as often one enantiomer is pharmaceutically active whereas the other may show adverse side effects. A historic example is the anti-emetic activity of one of the enantiomers of thalidomide, while the other can cause fetal damage [9,10]. These considerations highlight the importance of chiral discrimination in the production of biologically active materials, whereas on the other hand, the design of routes to asymmetric synthesis presents an active challenge to synthetic chemists worldwide. 

The synthesis and study of chiral ionic liquids have been spurred by their potential in chiral recognition, enantiomer separation and in asymmetric synthesis [660, 661]. However, there have been relatively few single-crystal X-ray studies of single enantiomers of chiral ionic liquids. These are summarised in the following text, along with those of low-melting racemates and other relevant salts. 

In the course of chemical evolution, nature must have developed selective methods of amino acid synthesis and specific recognition. In this respect, what kind of chemical methods do we have presently to prepare amino acids in optically pure form and to selectively distinguish among enantiomers We will therefore examine in this section two approaches to asymmetric synthesis of amino acids using the concept of asymmetric induction and specific metal ion complexation. 

In 1980, K. B. Sharpless (then at the Massachusetts Institute of Technology, presently at The Scripps Research Institute) and co-workers reported a method that has since become one of the most valuable tools for ohiral synthesis. The Sharpless asymmetric epoxidation is a method for converting allylic alcohols (Section 11.1) to chiral epoxy alcohols with very high enantioselectivity (I. e., with preference for one enantiomer rather than formation of a racemic mixture). In recognition of this and other work in asymmetric oxidation methods (see Section 8.16A), Sharpless received half of the 2001 Nobel Prize in Chemistry (the other half was awarded to W. S. Knowles and R. Noyori see Section 7.14). The Sharpless asymmetric ep-... 

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