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Owing to its associated advantages such as the generation of two stereocenters in 100% maximum theoretical yield, mild reaction conditions and environmentally friendliness, ketoreductase (KRED)-catalyzed dynamic reductive kinetic resolution (DYRKR) is a versatile and appealing synthetic approach to access valuable chiral alcohols containing two or more stereocenters. Despite the considerable progress that has been made in this research field, previous studies mostly focused on ketone substrates with relatively simple structures. In the present study, ketoreductases YDR368w and YGL039w were identified through enzyme screening and applied to the KRED-catalyzed DYRKR of sterically hindered 2-aryl-1,5-benzothiazepin-3,4(2H,5H)-diones (1). Eleven structurally diverse chiral cis-(2S,3S)-2,3-dihydro-3-hydroxy-2-aryl-1,5-benzothiazepin-4(5H)-ones (cis-(2S,3S)-2), including the critical synthetic intermediates to the calcium channel blockers diltiazem and clentiazem, were prepared in 50–90% isolated yields with excellent stereoselectivities (all >20 : 1 dr and ≥99% ee). Finally, the successful execution of a gram scale synthesis and the demonstrated excellent recyclability of the immobilized ketoreductase (up to 20 cycles) both underscored the good application potential of the currently established DYRKR method. [ABSTRACT FROM AUTHOR]

Chemoenzymatic asymmetric synthesis of an anabolic-androgenic steroid (+)-boldenone (3) and its prodrug (+)-boldenone undecylenate (4) was accomplished starting from commercially available 4-androstene-3,17-dione (4-AD, 1) under both batch and continuous flow conditions. The key feature of the current synthesis is the construction of an enzymatic cascade process in a single Escherichia coli cell for straightforward synthesis of (+)-boldenone (3), enabled by the combined action of ReM2 (I51L/I350T), an engineered 3-ketosteroid-Δ1-dehydrogenase (Δ1-KstD) possessing 5-fold and 3-fold higher Δ1-dehydrogenation activity towards 4-AD and testosterone (2b) relative to the wild-type Δ1-KstD, respectively, and 17β-CR, a newly mined carbonyl reductase from Empedobacter stercoris showing strong C17-carbonyl reduction activity. With the optimal reaction conditions established for mutual tolerance between ReM2 and 17β-CR, complete conversion of 4-AD into (+)-boldenone was first realized in a conventional batch mode with a space-time yield (STY) of 1.09 g L−1 h−1. Furthermore, this single cell-catalyzed synthesis of (+)-boldenone was successfully implemented in continuous flow, achieving an order of magnitude higher STY (10.83 g L−1 h−1) than that for batch synthesis, which also represents the highest record for the biocatalytic synthesis of (+)-boldenone reported to date. Finally, (+)-boldenone undecylenate (4) was produced in a fully continuous flow mode with an overall yield of 75%, through telescoping the newly developed biocatalytic Δ1-dehydrogenation/17β-carbonyl reduction cascade with the follow-up esterification reaction. The present work not only provides a concise, efficient, and sustainable avenue for the asymmetric synthesis of (+)-boldenone and (+)-boldenone undecylenate, but also showcases the effectiveness and great potential of flow biocatalysis in the production of value-added compounds. [ABSTRACT FROM AUTHOR]

Abstract: Given their ability to reduce activated alkenes thereby generating up to two stereogenic centers, ene reductases from the old yellow enzyme (OYE) family have received much attention as effective biocatalysts. Through genome mining, a “classical” OYE, KYE2, was identified from Kluyveromyces marxianus CBS4857 and fully characterized in vitro. This NADPH‐dependent enzyme displayed a broad substrate spectrum for the bioreduction of activated alkenes. The highly stereoselective synthesis (>95 % ee) of various (R)‐profen methyl esters, including the synthesis of (R)‐flurbiprofen methyl ester on a semi‐preparative scale further demonstrates the potential of KYE2 to be developed as a general biocatalyst for chemical synthesis. [ABSTRACT FROM AUTHOR]

A systematic study on the enzymatic transglycosylation of 3′‐amino nucleosides has been reported. Using the commercially available 3′‐amino‐3′‐deoxythymidine as the sugar donor, 13 pyrimidine and purine nucleobases were shown as the viable sugar acceptors in the nucleoside phosphorylase EcPPNP‐ and/or nucleoside 2′‐deoxyribosyltransferase LlNDT‐catalyzed reactions, furnishing the corresponding 3′‐amino containing nucleosides in 23%–73% NMR yields at an analytical scale. The synthetic utility of this diversification approach was further showcased by the successful synthesis of 3′‐amino‐2′,3′‐dideoxy‐5‐bromouridine in 29% isolated yield at a preparative scale. The current work demonstrates the transglycosylation activity of EcPPNP for the first time, expands the substrate scope of LlNDT, and provides an efficient, direct access to various 3′‐amino nucleosides of high value. [ABSTRACT FROM AUTHOR]