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204 9 Stereoselective Hydrolase-Catalyzed Processes in Continuous-Flow Mode

sequences and posttranslational modifications by multienzymatic reactions in a
continuous flow system using immobilized enzymes (trypsin, chymotrypsin, or
alkaline phosphatase) in microreactors was reported [58]. A recent review focused
on the proteolysis step by using reactors with immobilized protease to provide for
rapid analysis of protein sequences [59].

9.1.2
Nonstereoselective Enzymatic Processes
Biocatalytic steps are already being used to manufacture a wide range of products,
including drugs, agrochemicals, organic fine chemicals, and polymers on a large
scale [60, 61]. Several lipase-catalyzed reactions were studied in continuous sys-
tems for food and related applications. For example, esterification of glycerol with
acetic acid derivatives [62], (poly)unsaturated fatty acids [63], interesterification of
butterfat [64], production of structured lipids by acidolysis [65, 66], alcoholysis for
the production of biodiesel [67–69] or lubricants [70], glycerolysis for monoglyc-
eride production [71], and hydrolysis of the oil content of waste water [72] were
investigated in continuous systems.

9.2
Enzyme-Catalyzed Stereoselective Reactions in Continuous-Flow Systems

Although the technological knowledge on fermentation and bioprocesses has been
available for thousands of years [73], exploitation of the potential of biocatalysts
in the laboratory started only about 200 years ago. This section focuses on the
recent developments of the utilization of this versatile class of catalysts under
continuous-flow conditions.

9.2.1
Stereoselective Processes Catalyzed by Nonhydrolytic Enzymes

While the application of hydrolases predominates in this field, interesting
continuous-flow applications with members of other types of enzymes have been
also developed (Figure 9.2 and Table 9.3).
For example, horse liver alcohol dehydrogenase (HLADH) was noncovalently
immobilized on a membrane and packed into a PBR [74] operated in a recirculated
loop mode for the reduction of racemic 2-phenyl-tetrahydropyran-4-one 1 in
the presence of NADH. The HLADH-reactor coupled with an enzymic cofactor
regeneration system in the mobile phase could convert the substrate to the
enantiopure (S,S)- and (R,S)-2. The immobilized HLADH reactor was stable over 6
◦
months when stored at 5 C.
An agitated tube reactor (ATR) system was investigated for the KR of d,l-alanine
3 by d-amino acid oxidase [75]. The improved mass transfer under flow conditions