Biocatalysis conditions

General rules need to be adapted for different biotransformation processes because they are not based on the specific study of all systems. Biocatalysis conditions are optimized when carrying out experiments designed to increase knowledge of the process. 

In the enzyme design approach, as discussed in the first part of this chapter, one attempts to utilize the mechanistic understanding of chemical reactions and enzyme structure to create a new catalyst. This approach represents a largely academic research field aiming at fundamental understanding of biocatalysis. Indeed, the invention of functional artificial enzymes can be considered to be the ultimate test for any theory on enzyme mechanisms. Most artificial enzymes, to date, do not fulfill the conditions of catalytic efficiency and price per unit necessary for industrial applications. 

Hobbs, H.R. and Thomas, N.R., Biocatalysis in supercritical fluids, in fluorous solvents, and under solvent-free conditions. Chem. Rev., 2007, 107, 2786-2820. 

In this book, applied biocatalysis is defined as the application of a biocatalyst to achieve a desired conversion under controlled conditions in a bioreactor. This chapter focuses on the history of this field. 

Cephalosporins are -lactam antibiotics that block microbial cell wall synthesis. The original cephalosporin. Cephalosporin C, has only weak antibiotic activity. Therefore much more powerful second generation cephalosporins were developed by side-chain modification. Modifications at Cl are most effective but modifications at position 3 are also important so as to increase in vivo activity. Synthesis of the second generation cephalosporin cefuroxime requires the replacement of the C3 acetoxy side-chain of the precursor with a caibamate group. Chemical methods proceed via a hydroxylated intermediate which causes problems due to a tendency to lactonise at low pHs. Therefore development of a biocatalysis step was initiated in order to achieve selective reaction nnder mild conditions. 

In the context of this chapter biocatalysis is the use of enzymes or enzymes still associated with their parent cells, to carry out defined chemical reactions under controlled conditions, so as to efficiently convert raw materials into commercially more valuable products. Some of the commercial driving forces for the use of biocatalysts are listed in Table 13.1. 

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