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19
Chemoenzymatic Multistep One-Pot Processes

Harald Gr¨ oger and Werner Hummel

19.1
Introduction: Why Chemoenzymatic Cascades and Why One-Pot Processes?

In recent decades, biocatalysis has developed toward a key technology for the
technical-scale production of chiral building blocks in the fine chemicals and
pharmaceutical industry [1, 2]. Spectacular selectivities, together with often high
catalytic activities and favorable economic data of such processes, have tremen-
dously contributed to this development. In spite of these achievements, however,
biotransformation steps have often been considered as a different type of process
technology compared to ‘‘classic chemical’’ or chemocatalytic reactions. Conse-
quently, integration of biotransformation into multistep organic synthesis is still
rare, in particular in the field of multistep one-pot processes [3–7]. Such an inte-
gration of biotransformations, however, would be very desirable in terms of both
economy and ecology since the combination of reactions toward one-pot processes
shortens the number of overall required work-up steps. By saving such time- and
capacity-consuming and waste-producing (!) work-up steps, solvent usage can be
dramatically reduced and also space-time yields can be significantly improved.
However, in spite of all these advantages, there are also some challenges
ahead when developing chemoenzymatic one-pot processes. A major challenge
is to achieve compatibility between the different types of ‘‘classic’’ chemical and
chemocatalytic processes on one hand (which are often preferentially carried out
in organic media) and enzyme catalysis (for which water is typically the reaction
medium of choice) on the other. Furthermore, high conversions and yields of the
individual steps are crucial as well in order to reduce the complexity of the finally
resulting reaction mixture.

19.2
Concepts of Chemoenzymatic Processes
Two different concepts of chemoenzymatic one-pot processes in terms of the
reaction types involved have been mainly studied so far (Scheme 19.1). The first

Cascade Biocatalysis: Integrating Stereoselective and Environmentally Friendly Reactions, First Edition.
Edited by Sergio Riva and Wolf-Dieter Fessner.
c 2014 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2014 by Wiley-VCH Verlag GmbH & Co. KGaA.