Biocatalysis chemists

The aspects of medium engineering summarized so far were a hot topic in biocatalysis research during the 1980s and 1990s [5]. Nowadays, all of them constitute a well-established methodology that is successfully employed by chemists in synthetic applications, both in academia and industry. In turn, the main research interests of medium engineering have moved toward the use of ionic liquids as reaction media and the employment of additives. 

In the last decade, biocatalysis in nonaqueous media, using hydrolases, has been widely used for organic chemists. The possibilities that these biocatalysts offer for the preparation of different types of organic compounds, depending upon the nucleophile... 

Leresche JE, Meyer HP (2006) Chemocatalysis and biocatalysis (biotransformation) some thoughts of a chemist and of a biotechnologist. Org Process Res Dev 10 572-580... 

For a while, in the early 1990s, the interest in the use of enzymes in organic synthesis increased at an almost exponential rate and two-volume works were needed even to summarize developments in the field151. Now, at the turn of the century, it is abundantly clear that the science of biotransformations has a significant role to play in the area of preparative chemistry however, it is, by no stretch of the imagination, a panacea for the synthetic organic chemist. Nevertheless, biocatalysis is the method of choice for the preparation of some classes of optically active materials. In other cases the employment of man-made catalysts is preferred. In this review, a comparison will be made of the different methods available for the preparation of various classes of chiral compounds161. 

So, in the final analysis, biocatalysis should not be considered in a separate sector available only to the specialist bioorganic chemist. It is one method, in the portfolio of catalytic techniques, that is available to all chemists for the solution of present and future problems in organic synthesis. To erect a Chinese wall between the natural and non-natural catalysts is totally illogical and prevents some creative thinking, particularly in the area of coupled natural/ non-natural catalysts11611 and biomimetic systems11621. 

Perhaps less clear to a newcomer to a particular area of chemistry is when to use biocatalysis as a key step in a synthesis, and when it is better to use one of the alternative non-natural catalysts that may be available. Therefore we set out to extend the objective of Preparative Biotransformations, so as to cover the whole panoply of catalytic methods available to the synthetic chemist, incorporating biocatalytic procedures where appropriate. 

Another environmental issue is the use of organic solvents. The use of chlorinated hydrocarbons, for example, has been severely curtailed. In fact, so many of the solvents favored by organic chemists are now on the black list that the whole question of solvents requires rethinking. The best solvent is no solvent, and if a solvent (diluent) is needed, then water has a lot to recommend it. This provides a golden opportunity for biocatalysis, since the replacement of classic chemical methods in organic solvents by enzymatic procedures in water at ambient temperature and pressure can provide substantial environmental and economic benefits. Similarly, there is a marked trend toward the application of organometal-lic catalysis in aqueous biphasic systems and other nonconventional media, such as fluorous biphasic, supercritical carbon dioxide and ionic liquids. ... 

Thus far only three reports regarding the directed evolution of enantioselective EHs have appeared 95,96,143), notwithstanding the fact that these enzymes, even as wild types, constitute important catalysts in synthetic organic chemistry 7-12,144,145). Indeed, since two EHs became commercially available recently, this type of biocatalysis offers exciting prospects for the practicing organic chemist. 

A major reason why synthetic chemists have become interested in biological methods as mentioned above, is that biocatalysis shows selectivity and specificity in catalysis. This interest in turn is mainly due to the need to synthesise enantiopure compounds as chiral building blocks for dmgs and agrochemicals. 

An early success story, which has been pivotal for the advancement of enantioselective biocatalysis among organic synthetic chemists, touches on the work of... 

The application of biocatalysis, that is the use of enzymes as catalysts in synthetic organic chemistry, has a number of attractions for the chemist wishing to design greener manufacturing processes ... 

Thus the use and practice of biocatalysis at full scale has waxed and waned over the years. In the past, one factor limiting the use of biocatalysis has been the availability of a variety of enzymes and the time taken to refine/evolve enzymes for specific industrial apphcations. Hydrolytic enzymes such as lipases and proteases designed for other industrial uses such as detergents and food processing have always been available in bulk, and indeed used by process chemists. 

It is clear from the examples in this book that the use of biocatalysis can produce some very cost-effective and environmentally acceptable processes, and the authors anticipate that the use of this technology will increase as synthetic organic chemists realize its value and begin to look for strategic disconnections in the synthetic sequence of new target molecules where a biocatalytic step can be applied to utmost benefit. Thus, biocatalysis should be seen as a routine part of the synthetic toolbox and, in some cases, the reagent of choice for transformations such as the reduction of ketones to chiral alcohols, and not as a technology of last resort when all else has failed. 

From different disciplines, biotechnology and biocatalysis are seen from very dif ferent angles and perspectives (Figure 1.1). Chemistry and chemists emphasize a molecularly-oriented perspective dominated by compounds and transformations, whereas chemical engineering and thus chemical engineers favor a process-oriented perspective of reactions and processes lastly, biology and its practitioners contribute a systems-oriented perspective of description at the organism level as well as in their view of evolution. 

The production of single enantiomers of drug intermediates is increasingly important in the pharmaceutical industry. Biocatalysis provides organic chemists an alternate opportunity to prepare pharmaceutically important chiral compounds. The advantages of biocatalysis over chemical catalysis are that enzyme-catalyzed reactions are stereoselective and regioselective, and can be carried out at ambient temperature and atmospheric pressure providing an environmentally friendly system. The selective examples presented in this... 

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