Exploiting racemases

Abstract

Chiral resolutions of racemic mixtures are limited to a theoretical yield of 50 %. This yield can be doubled by integration of a step-wise or continuous racemization of the non-desired enantiomer. Many of the different routes along which the racemization step can be conducted require harsh treatments and are therefore often incompatible with the highly functionalized state of many compounds relevant for the life science industries. Employing enzymatic catalysis for racemization can therefore be highly beneficial. Racemases allow racemization in one reaction step. Most representatives from this group are found in the domain of amino acid or amino acid derivative racemization, with few other examples, notably the racemization of mandelic acid. Corresponding to the importance of enantiospecific conversion of amino acid precursor racemates for the production of enantiopure amino acids, the most important biotechnological use for racemases is the racemization of such precursors. However, alternative uses, in particular for mandelate and amino acid racemases, are emerging. Here, we summarize the natural roles of racemases and their occurrence, the applications, and the biochemistry and engineering of this promising class of biocatalysts.

One‐step Synthesis of α‐Keto Acids from Racemic Amino Acids by A Versatile Immobilized Multienzyme Cell‐free System

“…[20a] Introducing this racemizations tep, the theoretical yield of 50 %c an be overcome and reach 100 %t hrough aD KR process. [18] (2) DAAO,aflavoenzyme that catalyzes [10a, 28] the stereospecific oxidatived eamination of the d-amino acid into the corresponding a-keto acid, ammonium ion, and H 2 O 2 ; [11] and (3) CATwas introduced in the system to removethe H 2 O 2 yielding innocuous water andO 2. CATisf undamentali nt his system because otherwise,H 2 O 2 could convert a-keto acids to onecarbon shorter carboxylic acids.…”

“…[16] Am ain disadvantage of KR is its limited yield of 50 %, and this step is usually economically inefficient. [18] Amino acid racemases (EC 5.1.1.X) are usually classified into two major categories, PLP-dependenta nd PLP-independent racemases, based on the use of pyridoxal-5-phosphate (PLP) as ac ofactor. In this way,t he addition of ar acemization step to the oxidative deamination of a dl-mixture by aD AAO could reach an ideal yield of 100 %o ft he desired product.…”

“…The enzymes that catalyze the conversion between amino acid enantiomersa re called amino acid racemases. [18] Amino acid racemases (EC 5.1.1.X) are usually classified into two major categories, PLP-dependenta nd PLP-independent racemases, based on the use of pyridoxal-5-phosphate (PLP) as ac ofactor. [19] Although these enzymesa re mainly monospecific (i.e.,r acemize one amino acid), the recently discovered PLP-dependentb road spectrum racemases (Bsrs) accept several amino acids as substrates, [20] thus having ag reat biotechnological potentialf or industrial applications.…”

Through the Looking Glass: Chiral Recognition of Substrates and Products at the Active Sites of Racemases and Epimerases

“…[43][44][45][46][47][48][49][50][51] In addition, the enzymes are useful for catalyzing enantiospecific biotransformation reactions. [52,53] The following sections survey the boundo rientations of substrates of PLP-dependent and PLP-independent racemases, as wella se pimerases and mutarotasesa cting on sugar substrates. At present, structures of both the substrate and product complexes of epimerases that utilize an S-adenosyl-l-methione-dependent radicale pimerization mechanism (e.g.,p roteusin epimerases [10,54] and carbpenem synthase [12] )a re not available so that comparisons of ligand binding orientations at the active sites of theseenzymes are not yet possible.…”

Assessment of process configurations to combine enantioselective chromatography with enzymatic racemization

“…Besides enhancing the reaction rate, enzymatic racemization allows the operation under mild process conditions. Despite their large potential, the amount of available racemases is still limited (Würges et al 2009;Radkov and Moe 2013;Femmer et al 2016). When immobilized on a resin and packed in a fixed bed reactor, enzymes can show high stability and no extra enzyme recovery step is needed (Wrzosek et al 2018).…”