Lipases in the preparation of β-blockers

Integrating Biocatalysis with Viscous Deep Eutectic Solvents in Lab-On-A-Chip Microreactors

The combination of deep eutectic solvents (DESs, ChCl/glycerol 1 : 2) with buffer (up to 15 % v/v) leads to solvent mixtures that exert viscosities below 25 mPa s^-1 at 45 °C while keeping their non-aqueous nature. This enables the setup of efficient enzymatic esterifications, which can also be applied in different continuous systems. Following those premises, the use of microreactors in biocatalytic reactions was explored using (low-viscous) DES-buffer media, showing that reactions could be performed efficiently. Under non-optimized conditions, the microreactor devices led to specific productivities considerably higher than those observed in the batch reactor (14 vs. 0.24 mg_product  min^-1  mg_biocat ^-1 ) at the same enzyme loadings and conversion of 6 % (to assure a fair comparison). Looking beyond, the combination of several microchannels (e. g., in scale-out fashion) with DES-water media may lead to powerful, sustainable, and efficient tools for industrial synthesis.

Shortening Synthetic Routes to Small Molecule Active Pharmaceutical Ingredients Employing Biocatalytic Methods

Biocatalysis, using enzymes for organic synthesis, has emerged as powerful tool for the synthesis of active pharmaceutical ingredients (APIs). The first industrial biocatalytic processes launched in the first half of the last century exploited whole-cell microorganisms where the specific enzyme at work was not known. In the meantime, novel molecular biology methods, such as efficient gene sequencing and synthesis, triggered breakthroughs in directed evolution for the rapid development of process-stable enzymes with broad substrate scope and good selectivities tailored for specific substrates. To date, enzymes are employed to enable shorter, more efficient, and more sustainable alternative routes toward (established) small molecule APIs, and are additionally used to perform standard reactions in API synthesis more efficiently. Herein, large-scale synthetic routes containing biocatalytic key steps toward >130 APIs of approved drugs and drug candidates are compared with the corresponding chemical protocols (if available) regarding the steps, reaction conditions, and scale. The review is structured according to the functional group formed in the reaction.

Immobilization of Pseudomonas stutzeri lipase through Cross-linking Aggregates (CLEA) for reactions in Deep Eutectic Solvents

The use of deep eutectic solvents (DES) with buffer as cosolvent (up to 10 % v/v) leads to low-viscous media in which lipases can perform synthetic reactions, instead of hydrolysis. This paper explores the immobilization of Pseudomonas stutzeri lipase (TL) in cross-linking aggregates (CLEA) to deliver robust derivatives that are active in media like choline chloride - glycerol DES with buffer as cosolvent. While the free TL enzyme was markedly inactive in these media, TL-CLEA derivatives perform esterifications and can be reused several times. Overall, results are consistent with previous experiments reported for other lipases in these DES-water media and confirm that CLEA immobilization turns out a very useful and straightforward alternative for generating active (bio)catalysts for DES-aqueous media systems. Immobilized systems open the possibility of performing continuous processes in low-viscous DES-buffer media.

Highly regio- and enantio-selective hydrolysis of two racemic epoxides by GmEH3, a novel epoxide hydrolase from Glycine max

A novel epoxide hydrolase from Glycine max, designated GmEH3, was excavated based on the computer-aided analysis. Then, gmeh3, a GmEH3-encoding gene, was cloned and successfully expressed in E. coli Rosetta(DE3). Among the ten investigated rac-epoxides, GmEH3 possessed the highest and best complementary regioselectivities (regioselectivity coefficients, αS = 93.7% and βR = 97.2%) in the asymmetric hydrolysis of rac-m-chlorostyrene oxide (5a), and the highest enantioselectivity (enantiomeric ratio, E = 55.6) towards rac-phenyl glycidyl ether (7a). The catalytic efficiency (kcatS/KmS = 2.50 mM-1 s-1) of purified GmEH3 for (S)-5a was slightly higher than that (kcatR/KmR = 1.52 mM-1 s-1) for (R)-5a, whereas the kcat/Km (5.16 mM-1 s-1) for (S)-7a was much higher than that (0.09 mM-1 s-1) for (R)-7a. Using 200 mg/mL wet cells of E. coli/gmeh3 as the biocatalyst, the scale-up enantioconvergent hydrolysis of 150 mM rac-5a at 25 °C for 1.5 h afforded (R)-5b with 90.2% eep and 95.4% yieldp, while the kinetic resolution of 500 mM rac-7a for 2.5 h retained (R)-7a with over 99% ees and 43.2% yields. Furthermore, the sources of high regiocomplementarity of GmEH3 for (S)- and (R)-5a as well as high enantioselectivity towards rac-7a were analyzed via molecular docking (MD) simulation.

From batch to fed-batch and to continuous packed-bed reactors: Lipase-catalyzed esterifications in low viscous deep-eutectic-solvents with buffer as cosolvent

This work explores for the first time the use of Deep Eutectic Solvents (DES) with phosphate buffer 100 mM pH 7 as cosolvent (10% v/v) in biocatalytic reactions in fed-batch and packed-bed bioreactors. The lipase-catalyzed esterification of glycerol and benzoic acid is studied, as it involves two substrates with different polarities (for which DES are needed). In the fed-batch bioreactor, the highest conversion (90%) was obtained at a substrate flow rate of 0.01 mL/min. The fed-batch operation increased the conversion by 59% compared to the batch mode. Regarding productivity, semi-continuous and continuous bioreactors showed analogous results. Upon recirculation of the reaction media in the continuous bioreactor, a conversion of 67% was achieved in 7 cycles of operation. The stability of the biocatalyst in the packed-bed bioreactor decreased only 2% in 10 days, demonstrating the attractiveness that low viscous DES-water mixtures with continuous processes may have.

Lipases in Green Chemistry: Deep Eutectic Solvents (DES) as New Green Solvents

Deep eutectic solvents (DES) may become important alternatives as versatile, biodegradable, and cost-effective solvents for biocatalysis. Especially for reactions where substrates and products of different polarities are combined, the design of a tailored solvent that may dissolve all compounds-while being enzyme-compatible at the same time-appears to be a strong ally in sustainable chemistry. Herein it is shown that the combination of DES with "water as cosolvent" (in a range from 5% to 20% water, v/v) leads to non-conventional solvents with significantly reduced viscosity. In these media, lipases and proteases can perform synthetic reactions efficiently, and hydrolytic side reactions remain suppressed (even at 20% water, v/v). The use of these less viscous non-conventional media could also provide options for hydrolase-catalyzed synthetic reactions even in continuous fashion.

Identification and characterization of epoxide hydrolase activity of polycyclic aromatic hydrocarbon-degrading bacteria for biocatalytic resolution of racemic styrene oxide and styrene oxide derivatives

A novel epoxide hydrolase (EHase) from polycyclic aromatic hydrocarbon (PAH)-degrading bacteria was identified and characterized. EHase activity was identified in four strains of PAH-degrading bacteria isolated from commercial gasoline and oil-contaminated sediment based on their growth on styrene oxide and its derivatives, such as 2,3- and 4-chlorostyrene oxides, as a sole carbon source. Gordonia sp. H37 exhibited high enantioselective hydrolysis activity for 4-chlorostyrene oxide with an enantiomeric ratio of 27. Gordonia sp. H37 preferentially hydrolyzed the (R)-enantiomer of styrene oxide derivatives resulting in the preparation of a (S)-enantiomer with enantiomeric excess greater than 99.9 %. The enantioselective EHase activity was identified and characterized in various PAH-degrading bacteria, and whole cell Gordonia sp. H37 was employed as a biocatalyst for preparing enantiopure (S)-styrene oxide derivatives.

Bioresolution of benzyl glycidyl ether using whole cells of Bacillus alcalophilus

The incubation of whole Bacillus alcalophilus cells grown on a mineral supplemented medium (MSM) containing 1% (w/v) sucrose as carbon source, 1.2% (w/v) tryptone as nitrogen source at pH 6.5 and temperature 30 °C in 24 h kinetically resolved benzyl glycidyl ether (1 mg/ml) to provide (S)-benzyl glycidyl ether with 30% ee and (R)-3-benzyloxypropane-1,2-diol with 40% ee.

Biocatalytic resolution of glycidyl phenyl ether using a novel epoxide hydrolase from a marine bacterium, Maritimibacter alkaliphilus KCCM 42376 [corrected]

As a continuous effort of developing highly enantioselective epoxide hydrolase from marine microorganisms, it was found that Maritimibacter alkaliphilus KCCM 42376 [corrected] was highly enantioselective toward racemic glycidyl phenyl ether (GPE). An open reading frame (ORF) encoding a putative epoxide hydrolase (EHase) was cloned from the genome of Maritimibacter alkaliphilus KCCM 42376 [corrected], followed by expression and purification in Escherichia coli. The purified EHase (REH) hydrolyzed (S)-GPE preferentially over (R)-GPE. Enantiopure (R)-GPE from kinetic resolution of 29.2 mM racemic GPE using the purified REH could be obtained with enantiopurity of more than 99.9% enantiomeric excess (ee) and 38.4% yield (theoretical, 50%) within 20 min (enantiomeric ratio (E-value): 38.4). The enantioselective activity of REH toward GPE was also confirmed by the analysis of the vicinal diol, 3-phenoxy-1,2-propanediol. To our knowledge, this study demonstrates the highest enantioselective resolution of racemic GPE using a purified biocatalyst among the known native EHases.

Efficient preparation of (R)-alpha-monobenzoyl glycerol by lipase catalyzed asymmetric esterification: optimization and operation in packed bed reactor

Optically active (R)-alpha-monobenzoyl glycerol (MBG) was synthesized by Candida antarctica lipase B (CHIRAZYME L-2) catalyzed asymmetric esterification of glycerol with benzoic anhydride in organic solvents. Various conditions, such as the type and composition of the organic solvent, water content of the system, reaction temperature, and concentrations of the substrates were systematically examined and optimized in screw-capped test tubes with respect to both the reaction rate and the enzyme selectivity. 1,4-Dioxane was found to be the best solvent and no additional water was needed for the system. The optimum temperature was around 30 degrees C, while the most suitable substrate concentrations were 100 mM each for glycerol and benzoic anhydride, respectively. However, when excessive anhydride (e.g., 200 mM) was used, the produced MBG could be further transformed into 1,3-dibenzoyl glycerol (DBG) by the same enzyme with a priority to (S)-MBG, resulting in a significant improvement of the product optical purity from ca. 50-70% e.e. Under optimal conditions (100 mM glycerol, 100-200 mM benzoic anhydride, dioxane, 25-30 degrees C), the enzymatic synthesis of (R)-MBG was successfully operated in a packed-bed reactor for about 1 week, with an average productivity of 0.79 g MBG/day/g biocatalyst in the case of continuous operation and 0.94 g MBG/day/g biocatalyst in the case of semicontinuous operation. After refinement and preferential crystallization of the crude product, (R)-MBG could be obtained in an almost optically pure form (>98% e.e.).

Enzymes involved in the glycidaldehyde (2,3-epoxy-propanal) oxidation step in the kinetic resolution of racemic glycidol (2,3-epoxy-1-propanol) by Acetobacter pasteurianus

It is already known that kinetic resolution of racemic glycidol (2,3-epoxy-1-propanol) takes place when Acetobacter pasteurianus oxidizes the compound to glycidic acid (2,3-epoxy-propionic acid) with glycidaldehyde (2,3-epoxy-propanal) proposed to be the transient seen in this conversion. Since inhibition affects the feasibility of a process based on this conversion in a negative sense, and the chemical reactivity of glycidaldehyde predicts that it could be the cause for the phenomena observed, it is important to know which enzyme(s) oxidise(s) this compound. To study this, rac.- as well as (R)-glycidaldehyde were prepared by chemical synthesis and analytical methods developed for their determination. It appears that purified quinohemoprotein alcohol dehydrogenase (QH-ADH type II), the enzyme responsible for the kinetic resolution of rac.-glycidol, also catalyses the oxidation of glycidaldehyde. In addition, a preparation exhibiting dye-linked aldehyde dehydrogenase activity for acetaldehyde, most probably originating from molybdohemoprotein aldehyde dehydrogenase (ALDH), which has been described for other Acetic acid bacteria, oxidised glycidaldehyde as well with a preference for the (R)-enantiomer, the selectivity quantified by an enantiomeric ratio (E) value of 7. From a comparison of the apparent kinetic parameter values of QH-ADH and ALDH, it is concluded that ALDH is mainly responsible for the removal of glycidaldehyde in conversions of glycidol catalysed by A. pasteurianus cells. It is shown that the transient observed in rac.-glycidol conversion by whole cells, is indeed (R)-glycidaldehyde. Since both QH-ADH and ALDH are responsible for vinegar production from ethanol by Acetobacters, growth and induction conditions optimal for this process seem also suited to yield cells with high catalytic performance with respect to kinetic resolution of glycidol and prevention of formation of inhibitory concentrations glycidaldehyde.

Solvent effect on lipase enantioselectivity. Evidence for the presence of two thermodynamic states

The enantioselectivity of lipase-catalyzed kinetic resolutions has been measured at various temperatures in binary mixtures of solvents. Varying the solvent composition and temperature had a profound effect on the enantiomeric ratio. The values for delta delta H(R-S)(#) and delta delta S(R-S)(#), calculated from the E values measured at various temperatures, were estimated as a function of the solvent composition. By plotting delta delta H(R-S)(#) versus delta delta S(R-S)(#) as a function of the solvent composition, an extreme was observed. The resulting "hairpin-type" enthalpy-entropy compensation plots can be described by assuming the presence of two thermodynamically distinct physical states, displaying different enantioselectivities, that are in equilibrium with one another. Changing the solvent composition results in a change in the equilibrium constant K(eq) for the two states. The intriguing bell-shaped curves of the enantioselectivity versus solvent composition observed for lipase-catalyzed kinetic resolutions can be described assuming a linear correlation for the logarithm of K(eq) and the solvent composition. Thus, a simulation of the two-state model adequately describes the solvent effects found for lipase-catalyzed kinetic resolutions in binary mixtures of solvents and possibly in series of homologous organic solvents.

A novel method for preparation of optically active alpha-monobenzoyl glycerol via lipase-catalyzed asymmetric transesterification of glycerol

One-step synthesis of optically active alpha-monobenzoyl glycerol is described by lipasecatalyzed transesterification of benzoate derivatives with glycerol in 1,4-dioxane.

Bioorganic reactions in microemulsions

Water-in-oil microemulsions, or reverse micelles, are being evaluated as a reaction medium for a variety of enzymatic reactions. These systems have many potential biotechnological applications. Important examples are the use of various lipase microemulsion systems for hydrolytic or synthetic reactions. This review illustrates the biotechnological applications of microemulsions as media for bioorganic reactions. The principal focus is on lipase catalyzed processes.

Synthesis of enantiopure epoxides through biocatalytic approaches

Enantiopure epoxides, as well as their corresponding vicinal diols, are valuable intermediates in fine organic synthesis, in particular for the preparation of biologically active compounds. The necessity of preparing such target molecules in an optically pure form has triggered much research, leading to the emergence of various new methods based on either conventional chemistry or enzymatically catalyzed reactions. In this review, we focus on the biocatalytic approaches, which include direct epoxidation of olefinic double bonds as well as indirect biocatalytic methods, and which allow for the synthesis of these important chiral building blocks in enantiomerically enriched or even enantiopure form.