Biotransformation reactions overview

Overviews of QSAR studies for aquatic toxicity of chemicals which show narcosis are extensively discussed in several publications [93,94]. At first sight, it is quite remarkable that QSAR equations for all kinds of different species are so similar. On the other hand, the explanation is rather simple. It is generally accepted that the mechanism of narcosis is not a very specific process and each compoimd has the same intrinsic activity. In other words the external concentration of a compound at a fixed effect (e.g. narcosis or death) is only a fimction of the probability of a compound to reach its site of action. For many chemicals for which bioaccumulation is not influenced by biotransformation reactions, this probability is correlated to the octanol-water partition coefficient (K ) and this explains directly the correlation between and the external effect concentrations. 

Despite the diverse range of documented enzyme-catalyzed reactions, there are only certain types of transformations that have thus far emerged as synthetically useful. These reactions are the hydrolysis of esters, reduction/oxidation reactions, and the formation of carbon-carbon bonds. The first part of this chapter gives a brief overview by describing some examples of various biotransformations that can easily be handled and accessed by synthetic organic chemists. These processes are now attracting more and more attention from nonspecialists of enzymes. 

See also Biotransformations Microbial oxidations Microbial reductions applications of, 76 396-399 biocatalyst selection in, 76 404-409 biocatalysts in, 76 409-414 for drug metabolite production, 76 398-399 further advances in, 76 414 in hydrolysis, 76 400-401 multiphase reactions in, 777 412-414 scale-up of, 76 414 systematic studies of, 76 398 technique overview for, 76 403-414 timing of substrate additions in, 76 411-412 uses for, 777 400-403 Microbial waxes, 26 203 Microbiocides, triorganotins as, 24 817 Microbiological culture media, agar in, 73 68... 

Strategic importance of biocatalyzed synthetic transformations in terms of eco-compatibility and cheaper processes has been widely stressed previously. Among the developed biotransformations catalyzed by nitrilases or nitrile hydratases/ amidases systems, a special interest is focused toward stereoselective reactions able to give access to molecules otherwise impossible to obtain by classical chemical routes. Hereby, selected examples aim to offer an overview of research in this direction. Examples of industrial processes using nitrile hydrolyzing biocatalysts are also illustrated. 

Numerous authors have given overviews over biotransformations used in industry13-11. A very recent monograph summarizes almost 100 processes including many details on reaction conditions, screening of the biocatalyst or the product application 21. The use of biocatalysis from the viewpoint of a chemist in the laboratory is also summarized in several books. Recent ones are 12-14. ... 

Hydrolases — especially lipases — proved to be versatile biocatalysts for synthetic biotransformations [79, 80). The vast majority of the enzymatic stereoselective processes have been performed so far in batch mode [29, 30, 81]. Very recently, a review appeared on lipase-catalyzed reactions under continuous-flow conditions [82], and here we extend this overview with an analysis of the range of selectivities, effects of reaction conditions and the mode of enzyme immobilization on the lipase, and in general hydrolase-catalyzed continuous-flow biotransformations. 

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