Improvement of carbonyl reductase activity for the bioproduction of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate

Improving the catalytic performance of carbonyl reductase based on the functional loops engineering

Vibegron functions as a potent and selective β3-adrenergic receptor agonist, with its chiral precursor (2S,3R)-aminohydroxy ester (1b) being crucial to its synthesis. In this study, loop engineering was applied to the carbonyl reductase (EaSDR6) from Exiguobacterium algae to achieve an asymmetric reduction of the (rac)-aminoketone ester 1a. The variant M5 (A138L/A190V/S193A/Y201F/N204A) was obtained and demonstrated an 868-fold increase in catalytic efficiency (kcat/Km = 260.3 s-1 mM-1) and a desirable stereoselectivity (>99% enantiomeric excess, e.e.; >99% diastereomeric excess, d.e.) for the target product 1b in contrast to the wild-type EaSDR6 (WT). Structural alignment with WT indicated that loops 137-154 and 182-210 potentially play vital roles in facilitating catalysis and substrate binding. Moreover, molecular dynamics (MD) simulations of WT-1a and M5-1a complex illustrated that M5-1a exhibits a more effective nucleophilic attack distance and more readily adopts a pre-reaction state. The interaction analysis unveiled that M5 enhanced hydrophobic interactions with substrate 1a on cavities A and B while diminishing unfavorable hydrophilic interactions on cavity C. Computational analysis of binding free energies indicated that M5 displayed heightened affinity towards substrate 1a compared to the WT, aligning with its decreased Km value. Under organic-aqueous biphasic conditions, the M5 mutant showed >99% conversion within 12 h with 300 g/L substrate 1a (highest substrate loading as reported). This study enhanced the catalytic performance of carbonyl reductase through functional loops engineering and established a robust framework for the large-scale biosynthesis of the vibegron intermediate.

Structural-guided design to improve the catalytic performance of aldo-keto reductase KdAKR

Aldo-keto reductases (AKRs) are important biocatalysts that can be used to synthesize chiral pharmaceutical alcohols. In this study, the catalytic activity and stereoselectivity of a NADPH-dependent AKR from Kluyveromyces dobzhanskii (KdAKR) toward t-butyl 6-chloro (5S)-hydroxy-3-oxohexanoate ((5S)-CHOH) were improved by mutating its residues in the loop regions around the substrate-binding pocket. And the thermostability of KdAKR was improved by a consensus sequence method targeted on the flexible regions. The best mutant M6 (Y28A/L58I/I63L/G223P/Y296W/W297H) exhibited a 67-fold higher catalytic efficiency compared to the wild-type (WT) KdAKR, and improved R-selectivity toward (5S)-CHOH (dep value from 47.6% to >99.5%). Moreover, M6 exhibited a 6.3-fold increase in half-life (t1/2 ) at 40°C compared to WT. Under the optimal conditions, M6 completely converted 200 g/L (5S)-CHOH to diastereomeric pure t-butyl 6-chloro-(3R, 5S)-dihydroxyhexanoate ((3R, 5S)-CDHH) within 8.0 h, with a space-time yield of 300.7 g/L/day. Our results deepen the understandings of the structure-function relationship of AKRs, providing a certain guidance for the modification of other AKRs.

Semirational engineering of an aldo-keto reductase KmAKR for overcoming trade-offs between catalytic activity and thermostability

Enzyme engineering usually generates trade-offs between activity, stability, and selectivity. Herein, we report semirational engineering of an aldo-keto reductase (AKR) KmAKR for simultaneously enhancing its thermostability and catalytic activity. Previously, we constructed KmAKR_M9 (W297H/Y296W/K29H/Y28A/T63M/A30P/T302S/N109K/S196C), which showed outstanding activity towards t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate ((3R,5S)-CDHH), and t-butyl 6-cyano-(3R,5R)-dihydroxyhexanoate, the key chiral building blocks of rosuvastatin and atorvastatin. Under the guidance of computer-aided design including consensus residues analysis and molecular dynamics (MD) simulations, K164, S182, S232, and Q266 were dug out for their thermostability conferring roles, generating the "best" mutant KmAKR_M13 (W297H/Y296W/K29H/Y28A/T63M/A30P/T302S/N109K/S196C/K164E/S232A/S182H/Q266D). The T_m and T₅₀ ¹⁵ values of KmAKR_M13 were 10.4 and 6.1°C higher than that of KmAKR_M9 , respectively. Moreover, it displayed a significantly elevated organic solvent tolerance over KmAKR_M9 . Structural analysis indicated that stabilization of the α-helixes mainly contributed to thermostability enhancement. Under the optimized conditions, KmAKR_M13 completely asymmetrically reduced 400 g/l t-butyl 6-chloro-(5S)-hydroxy-3-oxohexanoate ((5S)-CHOH) in 8.0 h at a high substrate to catalyst ratio (S/C) of 106.7 g/g, giving diastereomerically pure (3R,5S)-CDHH (>99.5% d.e._P ) with a space-time yield (STY) of 449.2 g/l·d.

Biocatalytic Reduction Reactions from a Chemist's Perspective

Reductions play a key role in organic synthesis, producing chiral products with new functionalities. Enzymes can catalyse such reactions with exquisite stereo-, regio- and chemoselectivity, leading the way to alternative shorter classical synthetic routes towards not only high-added-value compounds but also bulk chemicals. In this review we describe the synthetic state-of-the-art and potential of enzymes that catalyse reductions, ranging from carbonyl, enone and aromatic reductions to reductive aminations.

Identification of a newly isolated Rhodotorula mucilaginosa NQ1 and its development for the synthesis of bulky carbonyl compounds by whole-cell bioreduction

A strain NQ1, which showed efficient asymmetric reduction of 3,5-bis(trifluoromethyl) acetophenone (BTAP) to enantiopure (S)-[3,5-bis(trifluoromethyl)phenyl]ethanol ((S)-BTPE), which is the key intermediate for the synthesis of a receptor antagonist and antidepressant, was isolated from a soil sample. Based on its morphological and internal transcribed spacer sequence, the strain NQ1 was identified to be Rhodotorula mucilaginosa NQ1. Some key reaction parameters involved in the bioreduction catalyzed by whole cells of R. mucilaginosa NQ1 were subsequently optimized, and the optimized conditions for the synthesis of (S)-BTPE were determined to be as follows: 5·0 ml phosphate buffer (200 mmol l^-1 , pH 7·0), 80 mmol l^-1 of BTAP, 250 g (wet weight) l^-1 of resting cell, 35 g l^-1 of glucose and a reaction for 18 h at 30°C and 180 rev min^-1 . The strain NQ1 exhibited a best yield of 99% and an excellent enantiomeric excess of 99% for the preparation of (S)-BTPE under the above optimal conditions, and could also asymmetrically reduce a variety of bulky prochiral carbonyl compounds to their corresponding optical hydroxyl compound with excellent enantioselectivity. These results indicated that R. mucilaginosa NQ1 had a good capacity to reduce BTAP to its corresponding (S)-BTPE, and might be a new potential biocatalyst for the production of valuable chiral hydroxyl compounds in industry.

High-Efficient Production of (S)-1-[3,5-Bis(trifluoromethyl)phenyl]ethanol via Whole-Cell Catalyst in Deep-Eutectic Solvent-Containing Micro-Aerobic Medium System

The ratio of substrate to catalyst (S/C) is a prime target for the application of asymmetric production of enantiomerically enriched intermediates by whole-cell biocatalyst. In the present study, an attractive increase in S/C was achieved in a natural deep-eutectic solvent (NADES) containing reaction system under microaerobic condition for high production of (S)-1-[3,5-bis(trifluoromethyl)phenyl]ethanol ((S)-3,5-BTPE) with Candida tropicalis 104. In PBS buffer (0.2 M, pH 8.0) at 200 rpm and 30 °C, 79.5 g (Dry Cell Weight, DCW)/L C. tropicalis 104 maintained the same yield of 73.7% for the bioreduction of 3,5-bis(trifluoromethyl)acetophenone (BTAP) under an oxygen-deficient environment compared with oxygen-sufficient conditions, while substrate load increased 4.0-fold (from 50 mM to 200 mM). Furthermore, when choline chloride:trehalose (ChCl:T, 1:1 molar ratio) was introduced into the reaction system for its versatility of increasing cell membrane permeability and declining BTAP cytotoxicity to biocatalyst, the yields were further increased to 86.2% under 200 mM BTAP, or 72.9% at 300 mM BTAP. After the optimization of various reaction parameters involved in the bioreduction, and the amount of biocatalyst and maltose co-substrate remained 79.5 g (DCW)/L and 50 g/L, the S/C for the reduction elevated 6.3 times (3.8 mM/g versus 0.6 mM/g). By altering the respiratory pattern of the whole-cell biocatalyst and exploiting the ChCl:T-containing reaction system, the developed strategy exhibits an attractive potential for enhancing catalytic efficiency of whole-cell-mediated reduction, and provides valuable insight for the development of whole-cell catalysis.

Asymmetric synthesis of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate using a self-sufficient biocatalyst based on carbonyl reductase and cofactor co-immobilization

tert-Butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate [(3R,5S)-CDHH] is the key chiral intermediate to synthesize the side chain of the lipid-lowering drug rosuvastatin. Carbonyl reductases showed excellent activity for the biosynthesis of (3R,5S)-CDHH. The requirement of cofactor NADH/NADPH leads to high cost for the industrial application of carbonyl reductases. In this study, a self-sufficient biocatalyst based on carbonyl reductase and NADP⁺ co-immobilization strategy was developed on an amino resin carrier LX-1000HAA (SCR-NADP⁺@LX-1000HAA). The self-sufficient biocatalyst achieved in situ cofactor regeneration and showed the activity recovery of 77.93% and the specific activity of 70.45 U/g. Asymmetric synthesis of (3R,5S)-CDHH using SCR-NADP⁺@LX-1000HAA showed high enantioselectivity (> 99% e.e.) and yield (98.54%). Batch reactions were performed for ten cycles without extra addition of NADP⁺, and the total yield of (3R,5S)-CDHH achieved at 10.56 g/g biocatalyst. The present work demonstrated the potential of the self-sufficient biocatalyst for the asymmetric biosynthesis of rosuvastatin intermediate.

Production of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate using carbonyl reductase coupled with glucose dehydrogenase with high space-time yield

tert-Butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate ((3R,5S)-CDHH) is an important chiral intermediate for the synthesis of rosuvastatin. The biotechnological production of (3R,5S)-CDHH is catalyzed from tert-butyl (S)-6-chloro-5-hydroxy-3-oxohexanoate ((S)-CHOH) by a carbonyl reductase, and this synthetic pathway is becoming a primary route for (3R,5S)-CDHH production due to its high enantioselectivity, mild reaction conditions, low cost, process safety, and environmental friendship. However, the requirement of the pyridine nucleotide cofactors, reduced nicotinamide adenine dinucleotide (NADH) or reduced nicotinamide adenine dinucleotide phosphate (NADPH) limits its economic flexibility. In the present study, a recombinant Escherichia coli strain harboring carbonyl reductase R9M and glucose dehydrogenase (GDH) was constructed with high carbonyl reduction activity and cofactor regeneration efficiency. The recombinant E. coli cells were applied for the efficient production of (3R,5S)-CDHH with a substrate conversion of 98.8%, a yield of 95.6% and an enantiomeric excess (e.e.) of >99.0% under 350 g/L of (S)-CHOH after 12 hr reaction. A substrate fed-batch strategy was further employed to increase the substrate concentration to 400 g/L resulting in an enhanced product yield to 98.5% after 12 hr reaction in a 1 L bioreactor. Meanwhile, the space-time yield was 1,182.3 g L^-1 day^-1 , which was the highest value ever reported by a coupled system of carbonyl reductase and glucose dehydrogenase.

Biocatalyzed Synthesis of Statins: A Sustainable Strategy for the Preparation of Valuable Drugs

Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are the largest selling class of drugs prescribed for the pharmacological treatment of hypercholesterolemia and dyslipidaemia. Statins also possess other therapeutic effects, called pleiotropic, because the blockade of the conversion of HMG-CoA to (R)-mevalonate produces a concomitant inhibition of the biosynthesis of numerous isoprenoid metabolites (e.g., geranylgeranyl pyrophosphate (GGPP) or farnesyl pyrophosphate (FPP)). Thus, the prenylation of several cell signalling proteins (small GTPase family members: Ras, Rac, and Rho) is hampered, so that these molecular switches, controlling multiple pathways and cell functions (maintenance of cell shape, motility, factor secretion, differentiation, and proliferation) are regulated, leading to beneficial effects in cardiovascular health, regulation of the immune system, anti-inflammatory and immunosuppressive properties, prevention and treatment of sepsis, treatment of autoimmune diseases, osteoporosis, kidney and neurological disorders, or even in cancer therapy. Thus, there is a growing interest in developing more sustainable protocols for preparation of statins, and the introduction of biocatalyzed steps into the synthetic pathways is highly advantageous—synthetic routes are conducted under mild reaction conditions, at ambient temperature, and can use water as a reaction medium in many cases. Furthermore, their high selectivity avoids the need for functional group activation and protection/deprotection steps usually required in traditional organic synthesis. Therefore, biocatalysis provides shorter processes, produces less waste, and reduces manufacturing costs and environmental impact. In this review, we will comment on the pleiotropic effects of statins and will illustrate some biotransformations nowadays implemented for statin synthesis.