Multigram Scale Enzymatic Synthesis of (R)‐1‐(4′‐Hydroxyphenyl)ethanol Using Vanillyl Alcohol Oxidase

Abstract

The enantioselective oxyfunctionalisation of CÀH bonds is a highly interesting reaction, as it provides access to chiral alcohols that are important pharmaceutical building blocks. However, it is hard to achieve using traditional methods. One way in which it can be achieved is through the action of oxidative enzymes. Although many reports of the oxyfunctionalisation capabilities of enzymes at an analytical scale have been published, reports on the use of enzymes to achieve oxyfunctionalisation on a synthetically relevant scale are fewer. Here, we describe the scale-up of the conversion of 4-ethylphenol to (R)-1-(4'-hydroxyphenyl)ethanol using the flavin-dependent enzyme vanillyl alcohol oxidase. The process was optimised by testing different reaction media and substrate and enzyme concentrations and by performing it under an oxygen atmosphere. Under optimised reaction conditions, 4.10 g (R)-1-(4'-hydroxyphenyl)ethanol at 97% ee was obtained from 10 g 4-ethylphenol (isolated yield 36%). These results highlight some of the challenges that can be encountered during scale-up of an enzymatic oxyfunctionalisation process to a synthetically relevant scale and will be of use for the development of enzymatic processes for the synthesis of industrially relevant compounds.

Enzymatic Hydroxylations of sp3-Carbons

“…But simultaneously exchanging D170 decreases the turnover rate (D170E 5- to 100-fold less active than wild-type VAO, other variants are even 1000-fold less active) . VAO was used in a scale-up conversion of 4-ethylphenol ( 1 ) to ( R )-1-(4′-hydroxyphenyl)­ethanol ( 2 ) yielding 4.1 g hydroxylated product 2 (36%) with 97% ee …”

“…81 VAO was used in a scale-up conversion of 4-ethylphenol (1) to (R)-1-(4′hydroxyphenyl)ethanol (2) yielding 4.1 g hydroxylated product 2 (36%) with 97% ee. 84 p-Cresol methylhydroxylase (PCMH) is a flavocytochrome c enzyme found in several types of pseudomonad. It catalyzes the hydroxylation of p-cresol to p-hydroxybenzyl alcohol in aerobic and facultatively anaerobic bacteria, which is the first step in biological p-cresol degradation.…”

New frontiers in biocatalysis for sustainable synthesis

“…Biocatalytic oxidation attracts particular interest as a sustainable route to alcohols and aldehydes [41]. An excellent recent example concerns the synthesis of (R)-1-(4'-hydroxyphenyl)ethanol using vanillyl alcohol oxidase [42]. Indeed oxidases are of particular interest since they do not require additional cofactors.…”

Vanillyl alcohol oxidase

“…This manuscript will not focus on the potential biocatalytic applications of VAO. Readers interested in this aspect of the enzyme are referred to the following manuscripts [3][4][5][6][7][8][9].…”