A practical chemoenzymatic process to access (R)-quinuclidin-3-ol on scale

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.

Magnetic Combined Cross-Linked Enzyme Aggregates of Ketoreductase and Alcohol Dehydrogenase: An Efficient and Stable Biocatalyst for Asymmetric Synthesis of (R)-3-Quinuclidinol with Regeneration of Coenzymes In Situ

Enzymes are biocatalysts. In this study, a novel biocatalyst consisting of magnetic combined cross-linked enzyme aggregates (combi-CLEAs) of 3-quinuclidinone reductase (QNR) and glucose dehydrogenase (GDH) for enantioselective synthesis of (R)-3-quinuclidinolwith regeneration of cofactors in situ was developed. The magnetic combi-CLEAs were fabricated with the use of ammonium sulfate as a precipitant and glutaraldehyde as a cross-linker for direct immobilization of QNR and GDH from E. coli BL(21) cell lysates onto amino-functionalized Fe3O4 nanoparticles. The physicochemical properties of the magnetic combi-CLEAs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and magnetic measurements. Field emission scanning electron microscope (FE-SEM) images revealed a spherical structure with numerous pores which facilitate the movement of the substrates and coenzymes. Moreover, the magnetic combi-CLEAs exhibited improved operational and thermal stability, enhanced catalytic performance for transformation of 3-quinuclidinone (33 g/L) into (R)-3-quinuclidinol in 100% conversion yield and 100% enantiomeric excess (ee) after 3 h of reaction. The activity of the biocatalysts was preserved about 80% after 70 days storage and retained more than 40% of its initial activity after ten cycles. These results demonstrated that the magnetic combi-CLEAs, as cost-effective and environmentally friendly biocatalysts, were suitable for application in synthesis of (R)-3-quinuclidinol essential for the production of solifenacin and aclidinium with better performance than those currently available.

Structural analysis of enzymes used for bioindustry and bioremediation

Microbial enzymes have been widely applied in the large-scale, bioindustrial manufacture of food products and pharmaceuticals due to their high substrate specificity and stereoselectivity, and their effectiveness under mild conditions with low environmental burden. At the same time, bioremedial techniques using microbial enzymes have been developed to solve the problem of industrial waste, particularly with respect to persistent chemicals and toxic substances. And finally, structural studies of these enzymes have revealed the mechanistic basis of enzymatic reactions, including the stereoselectivity and binding specificity of substrates and cofactors. The obtained structural insights are useful not only to deepen our understanding of enzymes with potential bioindustrial and/or bioremedial application, but also for the functional improvement of enzymes through rational protein engineering. This review shows the structural bases for various types of enzymatic reactions, including the substrate specificity accompanying cofactor-controlled and kinetic mechanisms.

RANEY® cobalt--an underutilised reagent for the selective cleavage of C-X and N-O bonds

RANEY® cobalt, which was first prepared in the 1930s, is known to function effectively as a catalyst for certain chemoselective reductions. However, its utility in chemical synthesis does not seem to have been fully appreciated. This first comprehensive survey of the literature on chemical transformations involving RANEY® cobalt attempts to redress matters by, among other things, highlighting the differences between the performance of this system and its much more well-known but usually less selective congener RANEY® nickel. A reliable method for preparing consistently effective RANEY® cobalt is presented together with a protocol that avoids the need to use it with high pressures of dihydrogen. As such, it is hoped more attention will now be accorded to the title reagent that offers considerable promise as a powerful tool for chemical synthesis, particularly in the assembly of polycyclic frameworks through tandem reductive cyclisation processes.

Structural basis of stereospecific reduction by quinuclidinone reductase

Chiral molecule (R)-3-quinuclidinol, a valuable compound for the production of various pharmaceuticals, is efficiently synthesized from 3-quinuclidinone by using NADPH-dependent 3-quinuclidinone reductase (RrQR) from Rhodotorula rubra. Here, we report the crystal structure of RrQR and the structure-based mutational analysis. The enzyme forms a tetramer, in which the core of each protomer exhibits the α/β Rossmann fold and contains one molecule of NADPH, whereas the characteristic substructures of a small lobe and a variable loop are localized around the substrate-binding site. Modeling and mutation analyses of the catalytic site indicated that the hydrophobicity of two residues, I167 and F212, determines the substrate-binding orientation as well as the substrate-binding affinity. Our results revealed that the characteristic substrate-binding pocket composed of hydrophobic amino acid residues ensures substrate docking for the stereospecific reaction of RrQR in spite of its loose interaction with the substrate.

Gene cloning and characterization of two NADH-dependent 3-quinuclidinone reductases from Microbacterium luteolum JCM 9174

We used the resting-cell reaction to screen approximately 200 microorganisms for biocatalysts which reduce 3-quinuclidinone to optically pure (R)-(-)-3-quinuclidinol. Microbacterium luteolum JCM 9174 was selected as the most suitable organism. The genes encoding the protein products that reduced 3-quinuclidinone were isolated from M. luteolum JCM 9174. The bacC gene, which consists of 768 nucleotides corresponding to 255 amino acid residues and is a constituent of the bacilysin synthetic gene cluster, was amplified by PCR based on homology to known genes. The qnr gene consisted of 759 nucleotides corresponding to 252 amino acid residues. Both enzymes belong to the short-chain alcohol dehydrogenase/reductase (SDR) family. The genes were expressed in Escherichia coli as proteins which were His tagged at the N terminus, and the recombinant enzymes were purified and characterized. Both enzymes showed narrow substrate specificity and high stereoselectivity for the reduction of 3-quinuclidinone to (R)-(-)-3-quinuclidinol.

Production of (R)-3-quinuclidinol by E. coli biocatalysts possessing NADH-dependent 3-quinuclidinone reductase (QNR or bacC) from Microbacterium luteolum and Leifsonia alcohol dehydrogenase (LSADH)

We found two NADH-dependent reductases (QNR and bacC) in Microbacterium luteolum JCM 9174 (M. luteolum JCM 9174) that can reduce 3-quinuclidinone to optically pure (R)-(−)-3-quinuclidinol. Alcohol dehydrogenase from Leifsonia sp. (LSADH) was combined with these reductases to regenerate NAD⁺ to NADH in situ in the presence of 2-propanol as a hydrogen donor. The reductase and LSADH genes were efficiently expressed in E. coli cells. A number of constructed E. coli biocatalysts (intact or immobilized) were applied to the resting cell reaction and optimized. Under the optimized conditions, (R)-(−)-3-quinuclidinol was synthesized from 3-quinuclidinone (15% w/v, 939 mM) giving a conversion yield of 100% for immobilized QNR. The optical purity of the (R)-(−)-3-quinuclidinol produced by the enzymatic reactions was >99.9%. Thus, E. coli biocatalysis should be useful for the practical production of the pharmaceutically important intermediate, (R)-(−)-3-quinuclidinol.