Biocatalytic Racemization Employing TeSADH: Substrate Scope and Organic Solvent Compatibility for Dynamic Kinetic Resolution

Abstract

Racemization in combination with a kinetic resolution is the base for a dynamic kinetic resolution (DKR). Biocatalytic racemization was successfully performed for a broad scope of sec‐alcohols by employing a single alcohol dehydrogenase (ADH) variant from Thermoanaerobacter pseudoethanolicus (formerly T. ethanolicus; TeSADH W110A I86A C295A). The catalyst employed as a lyophilized whole cell preparation or cell free extract, which tolerated various non‐water miscible organic solvents under micro‐aqueous or two‐phase conditions, whereby cyclohexane and n‐hexane suited best. Various concepts for combining the enzymatic racemization with an enzymatic kinetic resolution to achieve overall a bis‐enzymatic DKR were evaluated. A proof of concept showed a successful DKR with racemization in aqueous phase combined with acylation in the organic phase.

Enantiocomplementary C–H Bond Hydroxylation Combining Photo‐Catalysis and Whole‐Cell Biocatalysis in a One‐Pot Cascade Process

“…Firstly, the photocatalysts tend to denature the enzymes through disruption of the tertiary protein structure or inactivation of the cofactors. Furthermore, most KREDs are active in aqueous phase, only extremely few can tolerate organic media . Conversely, most reported photocatalysts were employed in anhydrous conditions.…”

Secondary Alcohol Dehydrogenases from Thermoanaerobacter pseudoethanolicus and Thermoanaerobacter brockii as Robust Catalysts

“… [73] This reaction was conducted in hexane and the two encapsulated enzyme systems were positioned such that the two did not touch each other, to avoid retardation of lipase‐catalyzed transesterification of the alcohol starting material (i. e., kinetic resolution). Subsequently, Kroutil and co‐workers accomplished this bi‐enzymatic DKR by compartmentalizing the Te SADH in TeaBag made of polyvinylidene difluoride membrane [74] . They used Ile86Ala/Trp110Ala/Cys295Ala Te SADH as the racemization catalyst.…”

“…Subsequently, Kroutil and co-workers accomplished this bi-enzymatic DKR by compartmentalizing the TeSADH in TeaBag made of polyvinylidene difluoride membrane. [74] They used Ile86Ala/Trp110Ala/Cys295Ala TeSADH as the racemization catalyst. These two examples show a proof of concept for bienzymatic DKR of alcohols, albeit with low efficiency.…”

Synthesis of enantiomerically pure alcohols and amines via biocatalytic deracemisation methods

“…Using a teabag-variation of the above-described bi-enzymatic DKR system ( Scheme 5 ), 53 Kroutil and coworkers also developed this approach by implementing a variant of Te SADH (i.e., containing the following mutations: W110A I86A C295A). 50 , 53 These two reports provided a proof-of-concept demonstration for a bi-enzymatic DKR of alcohols.…”

“…Using a teabag-variation of the above-described bi-enzymatic DKR system ( Scheme 5 ), 53 Kroutil and coworkers also developed this approach by implementing a variant of Te SADH (i.e., containing the following mutations: W110A I86A C295A). 50 , 53 These two reports provided a proof-of-concept demonstration for a bi-enzymatic DKR of alcohols. However, the productivity of this DKR was moderate because of diffusion limitation of the alcohol substrates, which was probably due to the complexity of the system requiring two liquid phases (organic and aqueous buffer) as well as tea-bag compartmentalisation of the lipase.…”