Diversity of Epoxide Hydrolase Biocatalysts

Abstract

Chiral epoxides and their derivatives are versatile intermediates for the synthesis of enantiopure organic chemicals. Chiral epoxides can be obtained through asymmetric epoxidation using either chemical catalysts or epoxidizing enzymes such as monooxygenases or chloroperoxidases. Alternatively hydrolytic kinetic resolution of racemic epoxides can yield a mixture containing, in an ideal situation, a single enantiomer of the remaining epoxide and a single enantiomer of the formed diol. Occasionally catalysts with complementary enantioselectivities and opposite regioselectivities can give through enantioconvergent hydrolysis one diol enantiomer in > 90% yield. Hydrolyses can also be performed with either metal catalysts or biological catalysts, mainly epoxide hydrolases. Epoxide hydrolases show great promise for the preparative scale hydrolysis of epoxides, because they are easy-to-use biocatalysts that accept a wide range of substrates, that do not require co-factors and that show improved activity when the substrate is present as a second water immiscible phase. X-ray structures for one fungal, one bacterial and two mammalian epoxide hydrolases are available as well as gene sequences for more than ninety five epoxide hydrolases. Expression systems in Escherichia coli and other hosts have also been developed and different assays suitable for high throughput screening have been developed and tested. The latter developments also made possible the first attempts at catalyst improvement through site directed mutagenesis and directed evolution. This review will give a comparative overview of the different types of epoxide hydrolases, which recently gave promising results for hydrolytic kinetic or enantioconvergent resolution of different types of epoxides and of results obtained with various recombinant epoxide hydrolases.

Evolution of tunnels in α/β-hydrolase fold proteins – what can we learn from studying epoxide hydrolases?

“…Several referential structural compartments were selected for further analysis (see Supplementary Table S2 ): the active site; buried and surface residues; main and cap domains; cap-loop; NC-loop; and α-helices, β-strands, and loops. The definitions of the cap-loop and NC-loop were taken from the works of Barth et al (40) and of Smit and Labuschagne(70). The NetSurfP service(44) was used to identify both buried and surface residues.…”

Gerry Brooks and epoxide hydrolases: four decades to a pharmaceutical

“…For microorganisms, EHs seem important in the catabolism of specific natural carbon sources as well as environmental contaminants 131, 132. However, microbial EHs are mainly studied for their potential uses in chiral chemistry (see Smit and Labuschagné133 for a recent review). Interestingly, in his seminal paper,3 Brooks reported that the hydration of asymmetrical epoxides is stereoselective, with mainly only one enantiomer hydrolyzed, paving the way for the use of EHs for enantiomeric biocatalysis.…”

An Unusual (R)‐Selective Epoxide Hydrolase with High Activity for Facile Preparation of Enantiopure Glycidyl Ethers

“…EHs are ubiquitously found in nature and have been identified in many organisms including mammals, plants, insects and various micro‐organisms 5. Some of them exhibit modest enantioseletivities toward phenyl glycidyl ether (PGE), e.g., Aspergillus niger EH4c and Agrobacterium radiobacter EH 6.…”