Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• enzymes (see below), this approach allows higher substrate loading (70–100 mM). Several enzymatic systems have been proposed in the literature, together with cofactor regeneration systems. As general rule, the oxidative and reductive steps are coupled with a related regeneration system. In this way, the

• most used enzymes for the cofactor regeneration are glucose dehydrogenase (glucose to glucuronic acid), lactate dehydrogenase (pyruvate to lactate), glutamate dehydrogenase (α-ketoglutarate to glutamate) and formate dehydrogenase (formate to CO2). In particular, the last enzyme is interesting because

• requirement of external systems for cofactor regeneration was circumvented and UDCA was obtained with a final yield of 75%. Interestingly, the addition of 2-hexanol led to an increase of NADH available for the reduction of 7-oxo-LCA and a final yield of 82% was observed. According to the authors, the presence

Engineering Pichia pastoris for improved NADH regeneration: A novel chassis strain for whole-cell catalysis

• Martina Geier,
• Christoph Brandner,
• Gernot A. Strohmeier,
• Mélanie Hall,
• Franz S. Hartner and
• Anton Glieder

Beilstein J. Org. Chem. 2015, 11, 1741–1748, doi:10.3762/bjoc.11.190

• reactions are catalyzed by cofactor-dependent enzymes. As cofactors represent a major cost factor, methods for efficient cofactor regeneration are required especially for large-scale synthetic applications. In order to generate a novel and efficient host chassis for bioreductions, we engineered the methanol

• . pastoris Δdas1 Δdas2 strain is capable of supplying the actual biocatalyst with the cofactor over a longer reaction period without the over-expression of an additional cofactor regeneration system. Thus, focusing the intrinsic carbon flux of this methylotrophic yeast on methanol oxidation to CO2 represents

• an efficient and easy-to-use strategy for NADH-dependent whole-cell conversions. At the same time methanol serves as co-solvent, inductor for catalyst and cofactor regeneration pathway expression and source of energy. Keywords: bioreduction; cofactor regeneration; dihydroxyacetone synthase; methanol

Biocatalytic hydroxylation of n-butane with in situ cofactor regeneration at low temperature and under normal pressure

• Svenja Staudt,
• Christina A. Müller,
• Jan Marienhagen,
• Christian Böing,
• Stefan Buchholz,
• Ulrich Schwaneberg and
• Harald Gröger

Beilstein J. Org. Chem. 2012, 8, 186–191, doi:10.3762/bjoc.8.20

• n-alkanes, which proceeds in the presence of a P450-monooxygenase advantageously at temperatures significantly below room temperature, is described. In addition, an enzymatic hydroxylation of the “liquid gas” n-butane with in situ cofactor regeneration, which does not require high-pressure

• conditions, was developed. The resulting 2-butanol was obtained as the only regioisomer, at a product concentration of 0.16 g/L. Keywords: biotransformations; cofactor regeneration; green chemistry; hydroxylation; P450-monooxygenase; Introduction The (regioselective) oxidative functionalization of

• ]. So far most hydroxylations of n-butane were performed without in situ cofactor regeneration, which is, however, a prerequisite for a synthetically useful process [10]. An exception is the recently reported process by Reetz et al. [9], which is based on the use of a glucose dehydrogenase and D-glucose

Coupled chemo(enzymatic) reactions in continuous flow

• Ruslan Yuryev,
• Simon Strompen and
• Andreas Liese

Beilstein J. Org. Chem. 2011, 7, 1449–1467, doi:10.3762/bjoc.7.169

• was used for cofactor regeneration, and immobilization of NADH on PEG prevented loss of the cofactor in the continuously operated reactor. Space-time yields of 700 g L−1 day−1 were achieved with the optimized reactor at 95% conversion. Deactivation of enzyme and PEG–NADH led to a decrease of

• continuous multistep enzymatic synthesis of fine chemicals, where cofactor regeneration is required. In such cases the whole-cell in vivo approach is advantageous over in vitro approaches, because it is not necessary to use immobilization or nanofiltration membranes for the retention of small cofactor

• stability. The multistep microbial biotransformations are also feasible for the continuous processes that do not require cofactor regeneration. Nöthe and coworkers developed a whole-cell membrane reactor operated in CSTR mode, with continuous product removal by ultrafiltration, for the microbial conversion