Flavin‐dependent halogenases are potentially useful biocatalysts for the regioselective halogenation of aromatic compounds. Haloaromatic compounds can be utilised in the synthesis and biosynthesis of pharmaceuticals and other valuable products. Here we report the first X‐ray crystal structure of a tryptophan 6‐halogenase (SttH), which enabled key residues that contribute to the regioselectivity in tryptophan halogenases to be identified. Structure‐guided mutagenesis resulted in a triple mutant (L460F/P461E/P462T) that exhibited a complete switch in regioselectivity; with the substrate 3‐indolepropionate 75 % 5‐chlorination was observed with the mutant in comparison to 90 % 6‐chlorination for the wild‐type SttH. This is the first clear example of how regiocomplementary halogenases can be created from a single parent enzyme. The biocatalytic repertoire of SttH was also expanded to include a range of indolic and non‐indolic substrates.
For enzyme‐catalysed biotransformations, continuous in situ detection methods minimise the need for sample manipulation, ultimately leading to more accurate real‐time kinetic determinations of substrate(s) and product(s). We have established for the first time an on‐line, real‐time quantitative approach to monitor simultaneously multiple biotransformations based on UV resonance Raman (UVRR) spectroscopy. To exemplify the generality and versatility of this approach, multiple substrates and enzyme systems were used involving nitrile hydratase (NHase) and xanthine oxidase (XO), both of which are of industrial and biological significance, and incorporate multistep enzymatic conversions. Multivariate data analysis of the UVRR spectra, involving multivariate curve resolution‐alternating least squares (MCR‐ALS), was employed to effect absolute quantification of substrate(s) and product(s); repeated benchmarking of UVRR combined with MCR‐ALS by HPLC confirmed excellent reproducibility.
Flow chemistry has been more frequently used in the development and manufacture of pharmaceuticals due to the progression of equipment and the availability of manufacturing facilities. This important tool for manufacture enables chemistries which were previously inefficient, hazardous, or not viable on scale in batch. Described herein is how continuous flow has been used to overcome issues with respect to the handling of hazardous materials in batch. The manufacturing step described is a Curtius reaction using diphenylphosphoryl azide (DPPA) as the azide precursor in the formation of a purinone at high temperatures with inline infrared monitoring.
Iridium-catalyzed C−H borylation reactions are a rapid and versatile entry into Suzuki coupling partners, but their inherent safety issues can limit their use in large-scale manufacture. The stoichiometric byproduct from this reaction, HBpin, can liberate hydrogen gas on contact with moisture in air, as well as acting as an effective borylating agent in the reaction, resulting in an additional pathway for the generation of hydrogen. Using a targeted, multidisciplinary approach, a C−H borylation process to generate a key intermediate in the synthesis of an API was redesigned in preparation for large-scale manufacture. Through careful evaluation of the existing process and the use of high-throughput experimentation, PAT techniques, NMR, process safety experimentation, and process engineering, the process was constructed so that inherent risks associated with this reaction were minimized and contained to a final controlled quench of the reactive byproducts of the reaction. The final process was transferred to a manufacturing facility, delivering >70 kg of the borylated product over two batches.
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