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Über dieses Buch

The use of natural catalysts -enzymes -for the transformation of non-natural man-made organic compounds is not at all new: they have been used for more than one hundred years, employed either as whole cells, cell organelles or isolated enzymes [1, 2]. Certainly, the object of most of the early research was totally different from that of the present day. Thus the elucidation of biochemical pathways and enzyme mechanisms was the main reason for research some decades ago. It was mainly during the 1980s that the enormous potential of applying natural catalysts to transform non-natural organic compounds was recognized. What started as a trend in the late 1970s could almost be called a fashion in synthetic organic chemistry in the 1990s. Although the early euphoria during the 'gold rush' in this field seems to have eased somewhat, there is still no limit to be seen for the future development of such methods. As a result of this extensive, recent research, there have been an estimated 12000 papers published on the subject. To collate these data as a kind of 'super-review' would clearly be an impossible task and, furthermore, such a hypothetical book would be unpalatable for the non-expert [3-6].

Inhaltsverzeichnis

Frontmatter

1. Introduction and Background Information

Abstract
Any exponents of classical organic chemistry will probably hesitate to consider a biochemical solution for one of their synthetic problems. This would be due, very often, to the fact, that biological systems would have to be handled. When growth and maintainance of whole microorganisms is concerned, such hesitation is probably justified. In order to save endless frustrations a close collaboration with a biochemist is highly recommended to set up and use fermentation systems [1,2]. On the other hand isolated enzymes (which may be obtained increasingly easily from commercial sources either in a crude or partially purified form) can be handled like any other chemical catalyst [3]. Due to the enormous complexity of biochemical reactions compared to the repertoire of classical organic reactions, it follows that most of the methods described will have a strong empirical aspect. This ‘black box’ approach may not entirely satisfy the scientific purists, but as organic chemists are rather prone to be pragmatists, they may accept that the understanding of a biochemical reaction mechanism is not a conditio sine qua non for the success of a biotransformation. In other words, a lack of understanding of biochemical reactions should never deter us from using them if their usefulness has been established. Notwithstanding, it is undoubtedly an advantage to have an acquaintance with basic biochemistry, and with enzymology, in particular.
Kurt Faber

2. Biocatalytic Applications

Abstract
Of all the types of enzyme-catalyzed reactions, hydrolytic transformations involving amide- and ester-bonds are the easiest to perform using proteases, esterases or lipases. A lack of sensitive cofactors which would have to be recycled, and a large number of readily available enzymes possessing relaxed substrate specificities to choose from, are the main features which have made hydrolases the favourite class of enzyme for organic chemists during the past decade. About two thirds of the total research in the field of biotransformations has been performed using hydrolytic enzymes of this type [1]. The reversal of the reaction, giving rise to ester- or amide-synthesis, has been particularly well investigated using enzymes in solvent systems of low water activity. The special methodologies involved in this latter type of reaction are described in Section 3.1.
Kurt Faber

3. Special Techniques

Abstract
Most biocatalysts can be used in a straightforward manner by regarding them as chiral catalysts and by applying standard methodology but, in addition, some special techniques have been developed in order to broaden their range of applications. In particular, using biocatalysts in non-aqueous media rather than in water can lead to the gain of some significant advantages as long as some specific guidelines are followed. Furthermore, ‘fixation’ of the enzyme by immobilization may be necessary, and the use of membrane technology may be advantageous as well. For both of the latter topics only the most simple techniques which can be adopted in an average organic chemistry laboratory are discussed (Section 3.2).
Kurt Faber

4. State of the Art and Outlook

Abstract
The biotransformations described in this book show that the area is in an active state of development and that enzymes have captured an important place in contemporary organic synthesis [1, 2]. This is reflected by the fact that in 1991 8% of all papers published in the area of synthetic organic chemistry contained elements of biotransformations [3]. The frequency of use of a particular biocatalyst is not evenly distributed among the various types of transformations but follows a pattern shown in Figure 4.1 [4]. In this book, attention has been focused on those methods which are most useful for and accessible to synthetic chemists — the rating of methods according to their general applicability and reliability is intended!
Kurt Faber

5. Appendix

Without Abstract
Kurt Faber

Backmatter

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