Akiva Gross

Potentially commercial enzymatic processes for the fine and specialty chemical industries

Abstract The use of enzymatic transformations instead of traditional chemical methods has many potential advantages in the fine and specialty chemical industries. Some systems are now close to commercialization and will have applications in the resolution of chiral compounds, lipolytic modifications of fats and oils, biosynthesis of peptides and enzymatic polymerization.

Chapter 31. Enzyme Assisted Transformations in Organic Media

Publisher Summary This chapter discusses the enzymatic and whole cell biocatalysis in which a significant portion of thereaction medium contains an organic component. The major solvent systems that have been described in the chapter are all-organic, incorporating small amounts of dissolved water; aqueous/organic two-phase mixtures; and aqueous/miscible organic co-solvent systems. Various reviews have described the enzyme classes used in all aqueous systems to prepare amino acids, hydroxy acids, chiral alcohols, and natural products. Reaction rates in organic media are strongly affected by solvent type and are sometimes slower than in water. Enzyme stability can be enhanced, even at high temperatures, because of the low water content of the reaction system. For whole cell biocatalysis, potent nonpolar solvents lower toxicity and minimize the disruption of cell membranes. Solvent polarity and properties affect cell viability. The extent of medium solvation has even been shown to reverse enzyme-substrate preference. Also, the use of a second phase or co-solvent can alter the enantioselectivity of enzyme. In two-phase systems, the organic phase serves as a reservoir for poorly water soluble substrates, minimizing the reaction volume. For more polar substrates, the second phase serves to regulate the aqueous phase concentrations of reactants and products. If either substrate or product is an inhibitor to the enzyme, removal by partitioning into the organic phase lessens its effect. Biocatalyst immobilization for two-phase and co-solvent media use is treated as for all-aqueous solvents. All-organic reaction solvents offer the significant advantage of ease, because enzyme/cells can be entrapped within, dried onto, or precipitated on insoluble particles.