Microfluidic enzymatic transformations

Table 10.3 Enzymatic transformations in microfluidic reactors in solution phase.

In order to increase the efficiency of biocatalytic transformations conducted under continuous flow conditions, Honda et al. (2006, 2007) reported an integrated microfluidic system, consisting of an immobilized enzymatic microreactor and an in-line liquid-liquid extraction device, capable of achieving the optical resolution of racemic amino acids under continuous flow whilst enabling efficient recycle of the enzyme. As Scheme 42 illustrates, the first step of the optical resolution was an enzyme-catalyzed enantioselective hydrolysis of a racemic mixture of acetyl-D,L-phenylalanine to afford L-phenylalanine 157 (99.2-99.9% ee) and unreacted acetyl-D-phenylalanine 158. Acidification of the reaction products, prior to the addition of EtOAc, enabled efficient continuous extraction of L-phenylalanine 157 into the aqueous stream, whilst acetyl-D-phenylalanine 158 remained in the organic fraction (84—92% efficiency). Employing the optimal reaction conditions of 0.5 gl min 1 for the enzymatic reaction and 2.0 gl min-1 for the liquid-liquid extraction, the authors were able to resolve 240 nmol h-1 of the racemate. 

In some cases, substrates and enzymes are not soluble in the same solvent. To achieve efficient substrate conversion, a large interface between the immiscible fluids has to be established, by the formation of microemulsions or multiple-phase flow that can be conveniently obtained in microfluidic devices. Until now only a couple of examples are published in which a two-phase flow is used for biocatalysis. Goto and coworkers [431] were first to study an enzymatic reaction in a two-phase flow in a microfluidic device, in which the oxidation ofp-chlorophenol by the enzyme laccase (lignin peroxidase) was analyzed (Scheme 4.106). The surface-active enzyme was solubilized in a succinic acid aqueous buffer and the substrate (p-chlorophenol) was dissolved in isooctane. The transformation ofp-chlorophenol occurred mainly at... 

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