Access to chiral α-substituted-β-hydroxy arylphosphonates enabled by biocatalytic dynamic reductive kinetic resolution

Taming Highly Enolizable Aldehydes via Enzyme Catalysis for Enantiocomplementary Construction of β-Hydroxyphosphonates

Taming highly enolizable aldehydes for catalytic asymmetric C-C coupling with nucleophiles remains an elusive challenge compared to widely explored simple alkyl or aryl aldehydes. Herein, we use ThDP-dependent enzymes to realize the direct C-C coupling of highly enolizable 2-phosphonate aldehydes with in situ-generated dynamically reversible nucleophiles (acyl anions). Unlike NHC-mediated reactions that yield complex mixtures of multiple adducts, our enzymatic process selectively produces biologically active β-hydroxy phosphonates with high yields (up to 95%) and excellent enantioselectivities (up to 99% ee). The products can be obtained on gram scales and exhibit rich reactivity for downstream transformations to afford diverse molecules. PfBAL (or its mutant A28G) and PaBAL enzymes serve as enantiocomplementary pairs, enabling the synthesis of both product configurations. Mechanistic studies proved that the entrance directions of the active cavities of these two enzyme pairs were distinct, leading to acyl anions formed from these two enzyme pairs attacking 2-phosphonate aldehydes from different orientations.

Biocatalytic dynamic reductive kinetic resolution of aryl α-chloro β-keto esters: divergent, stereocontrolled synthesis of diltiazem, clentiazem, and siratiazem

The first systematic study of ketoreductase (KRED)-catalyzed dynamic reductive kinetic resolution (DYRKR) on aryl α-chloro β-keto esters was performed, and 15 structurally diverse chiral anti-aryl α-chloro β-hydroxy esters were synthesized in 74-98% isolated yields, along with moderate-to-excellent diastereoselectivity (up to >99 : 1 dr) and good-to-excellent enantioselectivity (mostly >99% ee). LfSDR1-catalyzed complete reduction of 100 g L^-1 of substrate 6b at a ten-gram scale was achieved with a continuous fed-batch strategy, affording anti-(2S,3S)-1b, the key intermediate of diltiazem, in a record-breaking space-time yield of 96 g L^-1 d^-1. An eight-step synthesis of diltiazem, clentiazem, and siratiazem was accomplished in 32-45% overall yields, featuring this versatile biocatalytic reduction reaction as well as an efficient, green chlorination reaction in flow.

Ketoreductase Catalyzed (Dynamic) Kinetic Resolution for Biomanufacturing of Chiral Chemicals

Biocatalyzed asymmetric reduction of ketones is an environmentally friendly approach and one of the most cost-effective routes for producing chiral alcohols. In comparison with the well-studied reduction of prochiral ketones to generate chiral alcohols with one chiral center, resolution of racemates by ketoreductases (KREDs) to produce chiral compounds with at least two chiral centers is also an important strategy in asymmetric synthesis. The development of protein engineering and the combination with chemo-catalysts further enhanced the application of KREDs in the efficient production of chiral alcohols with high stereoselectivity. This review discusses the advances in the research area of KRED catalyzed asymmetric synthesis for biomanufacturing of chiral chemicals with at least two chiral centers through the kinetic resolution (KR) approach and the dynamic kinetic resolution (DKR) approach.

Application of Ketoreductase in Asymmetric Synthesis of Pharmaceuticals and Bioactive Molecules: An Update (2018-2020)

With the rapid development of genomic DNA sequencing, recombinant DNA expression, and protein engineering, biocatalysis has been increasingly and widely adopted in the synthesis of pharmaceuticals, bioactive molecules, fine chemicals, and agrochemicals. In this review, we have summarized the most recent advances achieved (2018-2020) in the research area of ketoreductase (KRED)-catalyzed asymmetric synthesis of chiral secondary alcohol intermediates to pharmaceuticals and bioactive molecules. In the first part, synthesis of chiral alcohols with one stereocenter through the bioreduction of four different ketone classes, namely acyclic aliphatic ketones, benzyl or phenylethyl ketones, cyclic aliphatic ketones, and aryl ketones, is discussed. In the second part, KRED-catalyzed dynamic reductive kinetic resolution and reductive desymmetrization are presented for the synthesis of chiral alcohols with two contiguous stereocenters.