Practical methods for biocatalysis and biotransformations 2

A new field in green chemistry refers to the increasing use of enzymes as biocatalysts, useful for enantio- or stereoselective reactions and this is exactly what the book under consideration here is about. The authors focus on the application of enzymes in industry, allowing cleaner and safer processes, by replacing catalysts that rely on the use of highly toxic chemicals and large amounts of solvents and energy. The book gives several suitable examples to describe the biocatalytic functions. Nowadays, large developments have been seen in this field, to avoid the environmental impact on current processing.

Chapter 1 gives a brief overview about different types of enzymes with their industrial applications for the preparation of active pharmaceutical ingredients (APIs) in a descriptive way. Chapter 2 describes the reductive amination process for the preparation of chiral amines, by using a transaminase as a biocatalyst and for the preparative scale synthesis, engineered biocatalysts. This chapter details the complete preparative and analytical procedure for the synthesis of chiral amines and also manifests the enzymatic mechanism for the formation of the product. Chapter 3 mainly focuses on the reduction of electron deficient alkenes in an asymmetric manner, using enoate reductase as the biocatalyst. It mentions the application of the newly found enzymatic process, which overcomes some traditional metal catalyzed processes and produces products with a higher selectivity. Chapter 4 describes the reduction of the carbonyl groups for the production of chiral alcohols, using immobilization of enzymes on a support and explains how engineered enzymes can be used for the preparation of APIs in large scales. Chapter 5 is basically dedicated to the enzymes that convert unactivated C–H to a C–OH group in a regioselective and stereoselective manner. This also describes how mutagenesis can be applied in finding the enzyme mutants that have inverted stereospecificity, along with applications of biotransformations, to increase the yield of the product, using some descriptive examples.

Chapter 6 specifically describes the enzymes that selectively oxidize alcohols to ketones or aldehydes and not to the over-oxidized product like acids or any other side product. It also discusses some techniques by which the cofactor of the enzyme can be reused, the desymmetrization technique for the preparation of single atropisomers with higher enantiomeric excess. Some other ways for enantioselective and chemoselective oxidations are also discussed. Chapter 7 focuses on the oxidation of organic compounds other than alcohols. It provides a smart solution for how to overcome the problem of product inhibition, using an in situ substrate feed protocol. Isotope labeling was applied to understand the biotransformation pathway in this process. Chapter 8 describes the application of hydrolases and related enzymes, which have industrial applications for the preparation of pharmaceutical products on a large scale. Immobilization of these enzymes on a support, which enhances the stability of the enzyme, is detailed. The biotransformation approach, the desymmetrization technique, and continuous reaction using immobilized enzyme processes, are outlined. Chapter 9 talks about the industrial application of transferases for alkylation, glycosylation and phosphorylation processes. It describes several advantages of the biocatalytic pathway in the glycosylation process. The applications of cross-linked enzyme aggregates, which can be reused several times, and biotransformations, are also discussed in detail. Chapter 10 is devoted to C–C bond forming reactions and decarboxylation reactions, using some immobilization techniques, along with the cost analysis for the process. Compounds related to Pictet-Spengler synthesis can be prepared in an environmentally friendly way. The increase in decarboxylation activity by using structure-guided directed evolution is also mentioned. Chapter 11 focuses on the halogenation, dehalogenation and heteroatomic oxidation reactions. Haloalkane dehalogenases can be useful in the synthesis of haloalkanes, haloalcohols, etc. The advantages of the bioresolution process are also described in this chapter. Chapter 12 describes the multi-enzymatic, tandem, cascade reaction approaches for the synthesis of industrial, useful drugs in a one pot synthesis, using several examples. It also describes the co-factor recycling technique and how to shift the reaction equilibrium to a favorable one.

This book is truly written for experts in the field of biocatalysis and provides even more insight and comprehensive views. It may be somewhat more difficult to read for the beginner and there are certainly other books around which serve that purpose. Yet, if the beginner aims to get a true insight, then this is still a very good choice. Each chapter of the book is written in a comprehensive manner, to provide broad information about different processes. The book is useful both for industry as well as academia, as it gives insightful explanations about the synthetic procedures of different products, and at the end of every chapter, the analytical data provides a wealth of information about the product. Yet especially seen through industrial glasses, it would have been even more beneficial if more focus had been placed on the cost analysis of the processes, from an industrial perspective. Each chapter outlines a mechanism of an enzymatic reaction, which is helpful in understanding the basic concepts concerning the product formation. There are several examples of drugs that are synthesized on a pilot scale plant, which is relevant for industry, as it gives detailed information ranging from the preparation of an enzyme catalyst to product analysis using different techniques. The numerous references given at the end of each topic will add more knowledge about the techniques described in this book.