Oxalate Oxidase for In Situ H2 O2 -Generation in Unspecific Peroxygenase-Catalysed Drug Oxyfunctionalisations

Enhancing the expression of the unspecific peroxygenase in Komagataella phaffii through a combination strategy

The unspecific peroxygenase (UPO) from Cyclocybe aegerita (AaeUPO) can selectively oxidize C-H bonds using hydrogen peroxide as an oxygen donor without cofactors, which has drawn significant industrial attention. Many studies have made efforts to enhance the overall activity of AaeUPO expressed in Komagataella phaffii by employing strategies such as enzyme-directed evolution, utilizing appropriate promoters, and screening secretion peptides. Building upon these previous studies, the objective of this study was to further enhance the expression of a mutant of AaeUPO with improved activity (PaDa-I) by increasing the gene copy number, co-expressing chaperones, and optimizing culture conditions. Our results demonstrated that a strain carrying approximately three copies of expression cassettes and co-expressing the protein disulfide isomerase showed an approximately 10.7-fold increase in volumetric enzyme activity, using the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) as the substrate. After optimizing the culture conditions, the volumetric enzyme activity of this strain further increased by approximately 48.7%, reaching 117.3 U/mL. Additionally, the purified catalytic domain of PaDa-I displayed regioselective hydroxylation of R-2-phenoxypropionic acid. The results of this study may facilitate the industrial application of UPOs. KEY POINTS: • The secretion of the catalytic domain of PaDa-I can be significantly enhanced through increasing gene copy numbers and co-expressing of protein disulfide isomerase. • After optimizing the culture conditions, the volumetric enzyme activity can reach 117.3 U/mL, using the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) as the substrate. • The R-2-phenoxypropionic acid can undergo the specific hydroxylation reaction catalyzed by catalytic domain of PaDa-I, resulting in the formation of R-2-(4-hydroxyphenoxy)propionic acid.

Reaction engineering blocks ether cleavage for synthesizing chiral cyclic hemiacetals catalyzed by unspecific peroxygenase

Hemiacetal compounds are valuable building blocks in synthetic chemistry, but their enzymatic synthesis is limited and often hindered by the instability of hemiacetals in aqueous environments. Here, we show that this challenge can be addressed through reaction engineering by using immobilized peroxygenase from Agrocybe aegerita (AaeUPO) under neat reaction conditions, which allows for the selective C-H bond oxyfunctionalization of environmentally significant cyclic ethers to cyclic hemiacetals. A wide range of chiral cyclic hemiacetal products are prepared in >99% enantiomeric excess and 95170 turnover numbers of AaeUPO. Furthermore, by changing the reaction medium from pure organic solvent to alkaline aqueous conditions, cyclic hemiacetals are in situ transformed into lactones. Lactams are obtained under the applied conditions, albeit with low enzyme activity. These findings showcase the synthetic potential of AaeUPO and offer a practical enzymatic approach to produce chiral cyclic hemiacetals through C-H oxyfunctionalization under mild conditions.

A Simple Access to γ- and ε-Keto Arenes via Enzymatic Divergent C─H Bond Oxyfunctionalization

Performing divergent C─H bond functionalization on molecules with multiple reaction sites is a significant challenge in organic chemistry. Biocatalytic oxyfunctionalization reactions of these compounds to the corresponding ketones/aldehydes are typically hindered by selectivity issues. To address these challenges, the catalytic performance of oxidoreductases is explored. The results show that combining the peroxygenase-catalyzed propargylic C─H bond oxidation with the Old Yellow Enzyme-catalyzed reduction of conjugated C─C triple bonds in one-pot enables the regio- and chemoselective oxyfunctionalization of sp3 C─H bonds that are distant from benzylic sites. This enzymatic approach yielded a variety of γ-keto arenes with diverse structural and electronic properties in yields of up to 99% and regioselectivity of 100%, which are difficult to achieve using other chemocatalysis and enzymes. By adjusting the C─C triple bond, the carbonyl group's position can be further tuned to yield ε-keto arenes. This enzymatic approach can be combined with other biocatalysts to establish new synthetic pathways for accessing various challenging divergent C─H bond functionalization reactions.

Enantioselective High-Throughput Assay Showcased for the Identification of (R)- as well as (S)-Selective Unspecific Peroxygenases for C-H Oxidation

Identifying (bio)catalysts displaying high enantio-/stereoselectivity is a fundamental prerequisite for the advancement of asymmetric catalysis. Herein, a high-throughput, stereoselective screening assay is reported that gives information on enantioselectivity, stereopreference and activity as showcased for peroxygenase-catalyzed hydroxylation. The assay is based on spectrophotometric analysis of the simultaneous formation of NAD(P)H from the alcohol dehydrogenase catalyzed enantioselective oxidation of the sec-alcohol product formed in the peroxygenase reaction. The assay was applied to investigate a library comprising 44 unspecific peroxygenases (UPOs) containing 25 UPOs not reported yet. Thereby, previously non-described wild-type UPOs displaying (S)- as well as (R)-stereoselectivity for the hydroxylation of representative model substrates were identified, reaching up to 98 % ee for the (R)- and 94 % ee for the (S)-enantiomer. Homology models with concomitant docking studies indicated the structural reason for the observed complementary stereopreference.

Electrospinning of n-hemin/PAN Nanocomposite Membranes and Its Photo-Enhanced Enzyme-like Catalysis

Hemin possesses great potential in eliminating organic pollutants due to its mild reaction condition, light-harvesting efficiency, and environmental friendliness. However, it has drawbacks such as being easy to aggregate and hard to recycle, and poor stability should be improved in practical application. Herein, the subject developed an electrospinning approach to enable the hemin particulates to be immobilized onto polyacrylonitrile (PAN) nanofibers stably. Hydrogen peroxide (H₂O₂) was adopted as an oxidant in the system to simulate the enzymatic catalysis of hemin in an organism. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflection spectroscopy (DRS), and electron spin resonance spectroscopy (ESR) analysis was employed to discuss the morphology, structure, and mechanism of the prepared n-hemin/PAN nanocomposite membranes, and 0.02 mmol L^-1 of the rhodamine B (RhB) removal activity in different conditions was also verified with these membranes. The kinetic studies showed that n-hemin/PAN nanocomposite membranes maintained excellent properties both in adsorption and degradation. Around 42% RhB could be adsorbed in the dark, while 91% RhB decolorized under xenon lamp irradiation in 110 min, suggesting the catalytic performance of n-hemin/PAN was greatly driven by light irradiation. Differing from the axial coordinated hemin complexes, n-hemin/PAN would catalyze hydrogen peroxide into •OH radicals rather than •OOH and high-valent metal-oxo species. This work provides an effective way to support hemin as nanocomposite membranes, in which the molecular interaction between polymer and hemin made their light adsorption an obvious red shift.