Biocatalytic production of (S)-4-bromo-3-hydroxybutyrate and structurally related chemicals and their applications

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.

The total synthesis of calcium atorvastatin

A practical and convergent asymmetric route to calcium atorvastatin (1) is reported.

Biocatalytic deracemisation of aliphatic β-hydroxy esters: Improving the enantioselectivity by optimisation of reaction parameters

Optically pure aliphatic β-hydroxy esters were prepared from their racemates by deracemisation using the biocatalyst Candida parapsilosis ATCC 7330. High optical purity (up to >99 %) and good yields (up to 71 %) of the product secondary alcohols were obtained. This study highlights the importance of optimization of reaction conditions using ethyl-3-hydroxybutanoate as the model substrate to improve the enantioselectivity (enantiomeric excess from 9 to 98 %). The present study emphasises the broad substrate scope of the biocatalyst towards deracemisation. This is the first report of Candida parapsilosis ATCC 7330-mediated deracemisation of various alkyl-3-hydroxybutanoates to produce either the (R)-enantiomers (methyl, ethyl, propyl, butyl, t-butyl, allyl-3-hydroxybutanoates) or (S)-enantiomers (pentyl, iso-amyl and iso-propyl-3-hydroxybutanoates).

Discovery of a reductase-producing strain recombinant E. coli CCZU-A13 using colorimetric screening and its whole cell-catalyzed biosynthesis of ethyl (R)-4-chloro-3-hydroxybutanoate

An NADH-dependent reductase (SsCR) was discovered by genome data mining. After SsCR was overexpressed in E. coli BL21, recombinant E. coli CCZU-A13 with high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (R)-4-chloro-3-hydroxybutanoate ((R)-CHBE) was screened using one high-throughput colorimetric screening strategy. After the reaction optimization, a highly stereoselective bioreduction of COBE into (R)-CHBE (>99% ee) with the resting cells of E. coli CCZU-A13 was successfully demonstrated in n-butyl acetate-water (10:90, v/v) biphasic system. Biotransformation of 600mM COBE for 8h in the biphasic system, (R)-CHBE (>99% ee) could be obtained in the high yield of 100%. Moreover, the broad substrate specificity in the reduction of aliphatic and aromatic carbonyl compounds was also found. Significantly, E. coli CCZU-A13 shows high potential in the industrial production of (R)-CHBE (>99% ee) and its derivatives.

Biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by NADH-dependent reductase from E. coli CCZU-Y10 discovered by genome data mining using mannitol as cosubstrate

The reductase (PgCR) from recombinant Escherichia coli CCZU-Y10 displayed high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE). To efficiently synthesize (S)-CHBE (>99 % enantiomeric excess (ee)), the highly stereoselective bioreduction of COBE into (S)-CHBE with the whole cells of E. coli CCZU-Y10 was successfully demonstrated in a dibutyl phthalate-water biphasic system. The appropriate ratio of the organic phase to water phase was 1:1 (v/v). The optimum reaction temperature, reaction pH, cosubstrate, NAD(+), and cell dosage of the biotransformation of 100 mM COBE in this biphasic system were 30 °C, 7.0, mannitol (2.5 mmol/mmol COBE), 0.1 μmol/(mmol COBE), and 0.1 g (wet weight)/mL, respectively. Moreover, COBE at a high concentration of (1,000 mM) could be asymmetrically reduced to (S)-CHBE in a high yield (99.0 %) and high enantiometric excess value (>99 % ee). Significantly, E. coli CCZU-Y10 shows high potential in the industrial production of (S)-CHBE (>99 % ee).

Effect of ribose, xylose, aspartic acid, glutamine and nicotinic acid on ethyl (S)-4-chloro-3-hydroxybutanoate synthesis by recombinant Escherichia coli

Most reductases which belong to the short chain dehydrogenase/reductase (SDR) superfamily require NAD (P) H for activity. Addition of this cofactor was still necessary for the production of ethyl (S)-4-chloro-3-hydroxybutanoate by Escherichia coli even when a cofactor regeneration system was constructed by co-expressing carbonyl reductase from Pichia stipitis (PsCRI) and glucose dehydrogenase from Bacillus megaterium (BmGDH). In an attempt to reduce dependence on the expensive cofactor, compounds directly or indirectly involved in NADP synthesis were added to the medium. Only glutamine and xylose enhanced the content of intracellular NADP (H) and the concentration of product. The concentration and yield of (S)-CHBE reached 730 mM and 48.7%, with 30 g/L of glutamine and 40 g/L of xylose, a 2.6-fold increase over the control without the addition of the two compounds.

New opportunities for biocatalysis: driving the synthesis of chiral chemicals

Various biocatalytic methods have been developed for the synthesis of chiral chemicals, which have made their synthesis more environmentally friendly and product-specific. New opportunities for biocatalysis, including new scientific developments in genomics and protein engineering technologies, novel process developments and the increased availability of useful enzymes, offer many possibilities for the manufacture of new chiral compounds and deliver greener and economically competitive processes. In this review, new opportunities for biocatalysis in the preparation of chiral molecules are outlined and highlighted.

Highly efficient synthesis of chiral alcohols with a novel NADH-dependent reductase from Streptomyces coelicolor

An NADH-dependent reductase (ScCR) from Streptomyces coelicolor was discovered by genome mining for carbonyl reductases. ScCR was overexpressed in Escherichia coli BL21, purified to homogeneity and its catalytic properties were studied. This enzyme catalyzed the asymmetric reduction of a broad range of prochiral ketones including aryl ketones, α- and β-ketoesters, with high activity and excellent enantioselectivity (>99% ee) towards β-ketoesters. Among them, ethyl 4-chloro-3-oxobutanoate (COBE) was efficiently converted to ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), an important pharmaceutical intermediate, in water/toluene biphasic system. As much as 600 g/L (3.6M) of COBE was asymmetrically reduced within 22 h using 2-propanol as a co-substrate for NADH regeneration, resulting in a yield of 93%, an enantioselectivity of >99% ee, and a total turnover number (TTN) of 12,100. These results indicate the potential of ScCR for the industrial production of valuable chiral alcohols.

Biochemical characterisation of a NADPH-dependent carbonyl reductase from Neurospora crassa reducing α- and β-keto esters

A gene encoding an NADPH-dependent carbonyl reductase from Neurospora crassa (nccr) was cloned and heterologously expressed in Escherichia coli. The enzyme (NcCR) was purified and biochemically characterised. NcCR exhibited a restricted substrate spectrum towards various ketones, and the highest activity (468U/mg) was observed with dihydroxyacetone. However, NcCR proved to be very selective in the reduction of different α- and β-keto esters. Several compounds were converted to the corresponding hydroxy ester in high enantiomeric excess (ee) at high conversion rates. The enantioselectivity of NcCR for the reduction of ethyl 4-chloro-3-oxobutanoate showed a strong dependence on temperature. This effect was studied in detail, revealing that the ee could be substantially increased by decreasing the temperature from 40 °C (78.8%) to -3 °C (98.0%). When the experimental conditions were optimised to improve the optical purity of the product, (S)-4-chloro-3-hydroxybutanoate (ee 98.0%) was successfully produced on a 300 mg (1.8 mmol) scale using NcCR at -3 °C.

Purification and characterization of a novel NADH-dependent carbonyl reductase from Pichia stipitis involved in biosynthesis of optically pure ethyl (S)-4-chloro-3-hydroxybutanoate

A novel NADH-dependent dehydrogenases/reductases (SDRs) superfamily reductase (PsCRII) was isolated from Pichia stipitis. It produced ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] in greater than 99% enantiomeric excess. This enzyme was purified to homogeneity by ammonium sulfate precipitation followed by Q-Sepharose chromatography. Compared to similar known reductases producing (S)-CHBE, PsCR II was more suitable for production since the purified PsCRII preferred the inexpensive cofactor NADH to NADPH as the electron donor. Furthermore, the Km of PsCRII for ethyl 4-chloro-3-oxobutanoate (COBE) was 3.3 mM, and the corresponding Vmax was 224 μmol/mg protein/min. The catalytic efficiency is the highest value ever reported for NADH-dependent reductases from yeasts that produce CHBE with high enantioselectivity. In addition, this enzyme exhibited broad substrate specificity for several β-keto esters using NADH as the coenzyme. The properties of PsCRII with those of other carbonyl reductases from yeasts were also compared in this study.

Biosynthesis of (S)-4-chloro-3-hydroxybutanoate ethyl using Escherichia coli co-expressing a novel NADH-dependent carbonyl reductase and a glucose dehydrogenase

A novel NADH-dependent carbonyl reductase (PsCR II) gene with an open reading frame of 855bp encoding 285 amino acids was cloned from Pichia stipitis. Analysis of the amino acid sequence of PsCR II revealed less than 55% identity to known reductases that produce (S)-4-chloro-3-hydroxybutanoates ethyl [(S)-CHBE]. When NADH was provided as an electron donor, Escherichia coli with pET-22b-PsCRII exhibited an activity of 15U/mg protein using 4-chloro-3-oxobutanoate ethyl (COBE) as a substrate. This activity was the highest ever reported for reductases, with the exception of PsCR I, which in our previous analysis required NADPH for catalysis. Biocatalysis of COBE to (S)-CHBE was investigated using E. coli with a polycistronic plasmid pET-BP II co-expressing PsCR II and a glucose dehydrogenase in a water/butyl acetate system for 24h. The transformants gave a molar yield of 91%, and an optical purity of the (S)-isomer of higher than 99% enantiomeric excess.

Construction and co-expression of a polycistronic plasmid encoding carbonyl reductase and glucose dehydrogenase for production of ethyl (S)-4-chloro-3-hydroxybutanoate

Biocatalysis of ethyl 4-chloro-3-oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] was carried out using Escherichia coli co-expressing a carbonyl reductase gene from Pichia stipitis and a glucose dehydrogenase gene from Bacillus megaterium. An efficient polycistronic plasmid with a high-level of enzyme co-expression was constructed by changing the order of the genes, altering the Shine-Dalgarno (SD) regions, and aligned spacing (AS) between the SD sequence and the translation initiation codon. The optimal SD sequence was 5-TAAGGAGG-3, and the optimal AS distance was eight nucleotides. Asymmetric reduction of COBE to (S)-CHBE with more than 99% enantiomeric excess was demonstrated by transformants, using a water/ethyl caprylate system. The recombinant cells produced 1260 mM product in the organic phase, and the total turnover number, defined as moles (S)-CHBE formed per mole NADP(+), was 12,600, which was more than 10-fold higher than in aqueous systems.