Realizing the Continuous Chemoenzymatic Synthesis of Anilines Using an Immobilized Nitroreductase

Abstract

The use of biocatalysis for classically synthetic transformations has seen an increase in recent years, driven by the sustainability credentials bio-based approaches can offer the chemical industry. Despite this, the biocatalytic reduction of aromatic nitro compounds using nitroreductase biocatalysts has not received significant attention in the context of synthetic chemistry. Herein, a nitroreductase (NR-55) is demonstrated to complete aromatic nitro reduction in a continuous packed-bed reactor for the first time. Immobilization on an amino-functionalized resin with a glucose dehydrogenase (GDH-101) permits extended reuse of the immobilized system, all operating at room temperature and pressure in aqueous buffer. By transferring into flow, a continuous extraction module is incorporated, allowing the reaction and workup to be continuously undertaken in a single operation. This is extended to showcase a closed-loop aqueous phase, permitting reuse of the contained cofactors, with a productivity of >10 gproduct gNR‑55 –1 and milligram isolated yields >50% for the product anilines. This facile method removes the need for high-pressure hydrogen gas and precious-metal catalysts and proceeds with high chemoselectivity in the presence of hydrogenation-labile halides. Application of this continuous biocatalytic methodology to panels of aryl nitro compounds could offer a sustainable approach to its energy and resource-intensive precious-metal-catalyzed counterpart.

Application of Immobilized Enzymes in Flow Biocatalysis for Efficient Synthesis

“…In addition to the above examples, other immobilized oxidoreductases have been also utilized in flow processes. Dominguez’s group coimmobilized a nitroreductase (NR-55) and GDH-101 on an amino-functionalized resin, resulting in the reaction with a productivity of >10 g product g NR‑55 –1 and isolated yields of >50% for the product anilines . Mutti and co-workers developed a scalable reductive amination of benzaldehyde by an agarose hydrogel containing the coentrapped amine dehydrogenases (LE-AmDH-v1) and formate dehydrogenases (Cb-FDH), which afforded a 47% analytical yield and a STY of 7.4 g L –1 day –1 in continuous flow over 120 h …”

Harnessing a Biocatalyst to Bioremediate the Purification of Alkylglycosides

“…The immobilisation of AcCO6 has been demonstrated previously by us and others, [26,27] so we followed general procedures to immobilise AcCO6 onto a range of resins (see supporting information) including our own previously reported procedures for AcCO6 and other enzymes. [6,26] The resins examined included EziG and Lifetech ECR, with ECR8309F shown to be the most effective in this process. Both CFE and purified AcCO6 were immobilised seperately, with the purified form proving to be the most effective and immobilised at 1 wt%, with respect to the protein.…”

“…[3] As such, biocatalysis has transformed our capabilities and approach to synthetic chemistry, including for oxidation reactions. [4] Their mainstream use to date has been to effect key transformations for building molecules, [5][6][7][8] typically, via stepwise or combinatorial one-pot approaches. This delivers the desired transformation, and the enzyme is then removed/recycled.…”

Synthesis of Pharmaceutically Relevant Arylamines Enabled by a Nitroreductase from Bacillus tequilensis

“…[28] Furthermore, the efficiency of NRs has been boosted by immobilization and application in continuous flow reactors, where reaction and workup can be continuously undertaken in a single operation. [29] More recently, our group described a flavin-dependent NR from Bacillus amyloliquefaciens, BaNTR1, that exhibits nitroreductase activity towards a plethora of substituted nitroarenes and enables their selective conversion into the corresponding amino-, azoxy-, and azo-aromatics under photobiocatalytic conditions using chlorophyll as the photocatalyst. [30] Here, we describe the identification and characterization of a NR from Bacillus tequilensis, named BtNR, that can process bulky nitroarenes and promotes arylamine formation with high conversions and in good yields.…”