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Separation of Enantiomers

  • Erscheinungsdatum: 06.05.2014
  • Verlag: Wiley-VCH
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Separation of Enantiomers

In one handy volume this handbook summarizes the most common synthetic methods for the separation of racemic mixtures, allowing an easy comparison of the different strategies described in the literature. Alongside classical methods, the authors also consider kinetic resolutions, dynamic kinetic resolutions, divergent reactions of a racemic mixture, and a number of 'neglected' cases not covered elsewhere, such as the use of circularly polarized light, polymerizations, 'ripening' processes, dynamic combinatorial chemistry, and several thermodynamic processes. The result is a thorough introduction to the field plus a long-needed, up-to-date overview of the chemical, biological, and physical methods and their applications. Newcomers to the field, students as well as experienced synthetic chemists will benefit from the highly didactic presentation: Every method is presented in detail, from relatively simple separation problems to advanced complex resolution methods. A senior lecturer at the University of Sydney's School of Chemistry, Matthew Todd gained his BA and PhD from Cambridge University, UK, where he later became a fellow in chemistry. Prior to taking up his current position in 2006, he was a postdoctoral fellow at the University of California, Berkeley, USA, from 1999 to 2000, and then became a lecturer in organic chemistry at the Department of Chemistry, Queen Mary, University of London from 2001 to 2005. Dr. Todd has received several grants as well as the Accelerating Science Award Program in recognition of his open source malaria project. He has participated in 8 conferences, and has 45 journal articles and a book chapter to his name. Alongside open source drug discovery, his research group is investigating synthetic methodology, responsive metal complexes, and asymmetric catalysis.

Produktinformationen

    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 400
    Erscheinungsdatum: 06.05.2014
    Sprache: Englisch
    ISBN: 9783527650903
    Verlag: Wiley-VCH
    Größe: 15758 kBytes
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Separation of Enantiomers

1
Introduction: A Survey of How and Why to Separate Enantiomers

Matthew Todd

This book is about the separation of enantiomers by synthetic methods, which is to say methods involving some chemical transformation as part of the separation process. We do not in this book cover chromatographic methods for the separation of enantiomers [1]. Nor do we focus on methods based on crystallizations as these have been amply reviewed elsewhere (see below). We are concerned mainly therefore with resolutions that involve a synthetic component, so mostly with the various flavours of kinetic resolutions through to more modern methods such as divergent reactions of a racemic mixture (DRRM). This introduction briefly clarifies the scope of the book.

The reasons such methods are of continued importance are threefold:

Society: the need for enantiopure compounds . New molecules as single enantiomers are important to our continued well-being because they are the feedstocks of new medicines, agrochemicals, fragrances and other features of modern society in a chiral world. Of the 205 new molecular entities approved as drugs between 2001 and 2010, 63% were single enantiomers [2]. Nature provides an abundance of enantiopure compounds, but we seek, and need, to exceed this by obtaining useful unnatural molecules as single enantiomers, and we may reasonably want to access both enantiomers of some compounds.
Academia: the basic science involved in the behaviour of chiral compounds . If we seek the state of the art in our discipline, we cannot help but think that rapid and selective chemical distinction between enantiomers, which results in their facile separation, is something beautiful in itself. There have been many successful methods developed for the synthetic separation of enantiomers, as we shall see, and these are both de facto interesting and instructive to consider for the design of future examples of such processes. The relationship between kinetic resolution and asymmetric catalysis is strong, and one can inform the design of the other. It is hoped that the diverse examples described in this book stimulate thoughts in the reader of what is possible next.
Industry: the need for new methods . There remain many classes of compounds that still cannot be resolved, or where efficiencies are too low for widespread adoption. It is still the case that classical resolution techniques are overwhelmingly used over other more complex methods. Of the 128 drug candidate molecules assessed in a recent industry survey, half were being developed as single enantiomers, and the sources of the stereocentres were mainly the chiral pool (55%) with resolution (28%) and asymmetric synthesis (10%) responsible for fewer examples [3]. This is, predictably, a feature of economics as much as science and one must not be too quick to judge new fields like asymmetric catalysis versus older ones like classical resolution. Pasteur added something enantiopure to a racemate in 1853 [4], whereas the catalytic prowess of a metal centre surrounded by chiral ligands was first demonstrated only in 1968 [5]. In addition, many chiral acids and bases have proven to be useful in classical resolutions, while Nature does not seem to be so generous in its supply of molecules that can effect catalytic, asymmetric transformations. The great progress made in synthetic chemistry has not (yet) brought us to the position that allows us to make any enantiopure substance in quantity given that resources are always limited. That leaves us with the synthesis of a racemate from which we pick one enantiomer out. Such a process can be remarkably efficient and cost-effective, if such tools are available, but the great successes described in this book should not hide the fact that we require better separation methods with wide applicability if we are to avoid an overreliance on jus

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