Abstract
Enzymes, at the turn of the 21st century, are gaining a momentum. Especially in the field of synthetic organic chemistry, a broad variety of biocatalysts are being applied in an increasing number of processes running at up to industrial scale. In addition to the advantages of employing enzymes under environmentally friendly reaction conditions, synthetic chemists are recognizing the value of enzymes connected to the exquisite selectivity of these natural (or engineered) catalysts. The use of hydrolases in enantioselective protocols paved the way to the application of enzymes in asymmetric synthesis, in particular in the context of biocatalytic (dynamic) kinetic resolutions. After two decades of impressive development, the field is now mature to propose a panel of catalytically diverse enzymes for (i) stereoselective reactions with prochiral compounds, such as double bond reduction and bond forming reactions, (ii) formal enantioselective replacement of one of two enantiotopic groups of prochiral substrates, as well as (iii) atroposelective reactions with noncentrally chiral compounds. In this review, the major enzymatic strategies broadly applicable in the asymmetric synthesis of optically pure chiral compounds are presented, with a focus on the reactions developed within the past decade.
Highlights
Melanie Hall studied chemistry at the Ecole Nationale Superieure de Chimie de Rennes (ENSCR), France, and received her PhD in chemistry from the University ofGraz, Austria, under Prof
Systems based on heme-dependent unspecific peroxygenases (UPOs) that utilize hydrogen peroxide as oxidant are currently emerging.[188,189]
Stereocomplementary versions using 4-oxalocrotonate tautomerase (4-OT) displaying three mutations were obtained by changing the oxidant from t-BuOOH for attack on the Re-face, to hydrogen peroxide for attack on the Si-face of the alkene, and granted access to epoxides with ee values up to 98%; diastereoselectivity was in most cases good to very good (Scheme 21).[196]
Summary
Melanie Hall studied chemistry at the Ecole Nationale Superieure de Chimie de Rennes (ENSCR), France, and received her PhD in chemistry from the University of. Review the reaction proceeds through formation of the so-called Criegee intermediate The collapse of this intermediate leads to migration of one of the alkyl substituents of the substrate carbonyl to the oxygen atom derived from the oxidant, and eventually results in the formation of the ester or lactone product. – A prochiral compound can be transformed stereoselectively into a chiral product in enantiopure form Such reactions involve nucleophilic attack onto sp[2] hybridized carbon atoms embedded in a CQC-, CQO-, or CQN-double bond, and imply face recognition of the substrate molecular plane by the enzymes. The major strategies relying on enzymes for the key step of asymmetric synthesis are reviewed and classified in one of the following categories: (i) stereoselective reactions involving transformations of sp[2] hybridized carbon atoms, (ii) enantioselective reactions and (iii) atroposelective reactions. Special techniques leading to optically pure chiral compounds, such as desymmetrization, stereoinversion, cyclic deracemization and enantioconvergent processes[19,20,21,22,23,24,25,26] were intentionally not broadly covered
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