Catalysis biocatalytic

Comparison of the two strategies for PCA synthesis from DHS depends upon the ultimate goal of die process. If synthesis of PCA as a final product is the goal, the two-step conversion that relies on thermal dehydration of DHS is superior. However, if PCA is needed only as an intermediate which will undergo further catalysis, biocatalytic synthesis using DHS dehydratase is superior, since the need for separate, sequential biocatalytic processes can be avoided. 

It is apparent that the use of enzymatic catalysis continues to grow Greater availabiUty of enzymes, development of new methodologies for thek utilization, investigation of enzymatic behavior in nonconventional environments, and the design and synthesis of new biocatalysts with altered selectivity and increased stabiUty are essential for the successhil development of this field. As more is learned about selectivity of enzymes toward unnatural substrates, the choice of an enzyme for a particular transformation will become easier to predict. It should simplify a search for an appropriate catalyst and help to estabhsh biocatalytic procedures as a usehil supplement to classical organic synthesis. 

Schmid, A., Hofstetter, K., Feiten, H.J., Holhnann, R, Witholt, B. (2001) Integrated Biocatalytic Synthesis on Gram Scale The Highly Enantio Selective Preparation of Chiral Oxiranes with Styrene Monooxygenase. Advanced Synthesis Catalysis, 343(6-7), I il-l il. 

Homogenous (Homo) Heterogeneous (Het) Biocatalytic (Bio) Phase Transfer Catalysis (PTC). 

Kroutil, W., Mang, H., Edegger, K. and Faber, K. (2004) Biocatalytic oxidation of primary and secondary alcohols. Advanced Synthesis Catalysis, 346, 125-142. 

Tang, Y.-F., Xu, J.-H., Ye, Q. and Schulze, B. (2001) Biocatalytic preparation of (S)-phenyl glycidyl ether using newly isolated Bacillus megaterium ECU1001. Journal of Molecular Catalysis B Enzymatic, 13, 61-68. 

Poessl, T.M., Kosjek, B., Ellmer, U. et al. (2005) Non-racemic halohydrins via biocatalytic hydrogen-transfer reduction of halo-ketones and one-pot cascade reaction to enantiopure epoxides. Advanced Synthesis and Catalysis, 347 (14), 1827-1834. 

Stampfer, W., Edegger, K., Kosjek, B. et al. (2004) Simple biocatalytic access to enantiopure (.Sj-1 -hetero-arylethanols employing a microbial hydrogen transfer reaction. Advanced Synthesis and Catalysis, 346 (1), 57-62. 

Van den Heuvel, R.H.H., Laane, C. and van Berkel, W.J.H. (2001) Exploring the biocatalytic potential of vanillyl-alcohol oxidase by site-directed mutagenesis. Advanced Synthesis and Catalysis, 343 (6-7), 515-520. 

Poechlauer, P., Skranc, W. and Wubbolts, M. (2004) The large-scale biocatalytic synthesis of enantiopure cyanohydrins, in Asymmetric Catalysis on Industrial Scale (eds H.-U. Blaser and E. Schmidt), Wiley-VCH Verlag GmbH, pp. 151-164. 

Full exploitation of cascade conversions by the true integration of biocatalytic and chemocatalytic procedures requires merging human s chemistry with nature s reaction conditions the latter impose a much stricter constraint with respect to reaction temperature, pressure and medium (Fig. 13.16). Consequently, a renaissance in the field of synthetic organic chemistry and catalysis is necessary to develop novel conversion processes that meet biocatalytic conditions. 

The expected contribution of catalysis in this area will derive both from the availability, at low processing costs, of new monomers obtained from biomasses and from the development of an optimized combination of biotechnology processes with classical and new biocatalytic processes. Research priorities for catalysis in the area of polymers from renewable materials for packaging, furniture, domestic water purification and recycling include the need to develop novel catalysts, e.g., for functionalization of polymeric and dendrimeric materials, with side-chain photoactive molecular switches (to be used as smart materials), or the development of multifunctional materials, combining, for example, nanofiltration with catalytic reactivity. 

Fechter, M.H., Gruber, K., Avi, M., Skranc, W., Schuster, C., Pbchlauer, P., Klepp, K.O. and Griengl, H., Stereoselective biocatalytic synthesis of (S)-2-hydroxy-2-methylbutyric acid via substrate engineering by using thio-disguised precursors and oxynitrilase catalysis. Chem. Eur. J., 2007,13, 3369. 

It has often been found that enzymes retain their activity when suspended in ionic liquids of low hydrogen bond basicity, but they are inactive in those with high hydrogen bond basicity (e.g., Cl , NOi", and acetate-containing ionic liquids) 274). Some recent biocatalytic reactions are discussed below, with an emphasis on the function of the ionic liquids in enzyme catalysis. 

On the basis of encouraging work in the development of L-proline-DMSO and L-proline-ionic liquid systems for practical asymmetric aldol reactions, an aldolase antibody 38C2 was evaluated in the ionic liquid [BMIM]PF6 as a reusable aldolase-ionic liquid catalytic system for the aldol synthesis of oc-chloro- 3-hydroxy compounds (288). The biocatalytic process was followed by chemical catalysis using Et3N in the ionic liquid [BMIM]TfO at room temperature, which transformed the oc-chloro-(3-hydroxy compounds to the optically active (70% ee) oc, (3-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was also shown to be reusable for Michael additions and the reaction of fluoromethylated imines. 

Often, it appears that the possible role of heterogeneous catalysis in this scenario is not receiving sufficient attention in comparison with that of the biocatalytic methods. Therefore, in the present chapter we will highlight some of the existing possibilities for converting bio-resources, primary... 

Enzyme catalysis of reactions (biocatalysis) is a branch of biotechnology (Hauer 1999 Crameri 1999). The superiority of biocatalytic methods of synthesis, particularly if carried out in a continuum (Orsat 1999), is often manifestly clear, only limited by the cost of replacing the old chemical plants (Pachlatko 1999 Schmid 2001). Illustrative examples of biocatalytic plants are illustrated in Chart 14.2. 

The enormous research activity devoted to metalloporphyrins, and in special, to the noble metal porphyrins is governed by the idea of biomimesis, i.e. the desire of chemists to understand and imitate nature with its ingenious biocatalytic pathways. In this respect, two important neighbouring disciplines to synthetic chemistry will be touched on in this article electrochemistry (Sect. 5.1) and catalysis (Sect. 5.2). However, in order to keep the article within certain limits, only some notes will be given on these fields, which sometimes are linked by the term electrocatalysis and bear some relevance to material science. Further... 

The chemoenzymatic synthesis of chiral alcohols is a field of major interest within biocatalytic asymmetric conversions. A convenient access to secondary highly enan-tiomerically enriched alcohols is the usage of alcohol dehydrogenases (ADHs) (ketoreductases) for the stereoselective reduction of prochiral ketones. Here, as in many other cases in asymmetric catalysis, enzymes are not always only an alternative to chemical possibilities, but are rather complementary. Albeit biocatalysts might sometimes seem to be more environmentally friendly, asymmetric ketone reduction... 

The majority of biocatalytic processes fall into the category of coordination catalysis, although there are a few that involve organometallic catalysis e.g., reactions mediated by nickel-dependent (see earlier discussion and Chapter 9) and vitamin-B-12-dependent enzymes (see Chapter 13). 

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