A Chimeric Styrene Monooxygenase with Increased Efficiency in Asymmetric Biocatalytic Epoxidation

The styrene monooxygenase (SMO) system from Pseudomonas sp. consists of two enzymes (StyA and StyB). StyB catalyses the reduction of FAD at the expense of NADH. After the transfer of FADH₂ from StyB to StyA, reaction with O₂ generates FAD‐OOH, which is the epoxidising agent. The wastage of redox equivalents due to partial diffusive transfer of FADH₂, the insolubility of recombinant StyB and the impossibility of expressing StyA and StyB in a 1:1 molar ratio reduce the catalytic efficiency of the natural system. Herein we present a chimeric SMO (Fus‐SMO) that was obtained by genetic fusion of StyA and StyB through a flexible linker. Thanks to a combination of: 1) balanced and improved expression levels of reductase and epoxidase units, and 2) intrinsically higher specific epoxidation activity of Fus‐SMO in some cases, Escherichia coli cells expressing Fus‐SMO possess about 50 % higher activity for the epoxidation of styrene derivatives than E. coli cells coexpressing StyA and StyB as discrete enzymes. The epoxidation activity of purified Fus‐SMO was up to three times higher than that of the two‐component StyA/StyB (1:1, molar ratio) system and up to 110 times higher than that of the natural fused SMO. Determination of coupling efficiency and study of the influence of O₂ pressure were also performed. Finally, Fus‐SMO and formate dehydrogenase were coexpressed in E. coli and applied as a self‐sufficient biocatalytic system for epoxidation on greater than 500 mg scale.     

Bioproduction of Chiral Epoxyalkanes using Styrene Monooxygenase from Rhodococcus sp. ST‐10 (RhSMO)

We describe the enantioselective epoxidation of straight‐chain aliphatic alkenes using a biocatalytic system containing styrene monooxygenase from Rhodococcus sp. ST‐10 and alcohol dehydrogenase from Leifsonia sp. S749. The biocatalyzed enantiomeric epoxidation of 1‐hexene to (S)‐1,2‐epoxyhexane (>44.6 mM) using 2‐propanol as the hydrogen donor was achieved under optimized conditions. The biocatalyst had broad substrate specificity for various aliphatic alkenes, including terminal, internal, unfunctionalized, and di‐ and tri‐substituted alkenes. Here, we demonstrate that this biocatalytic system is suitable for the efficient production of enantioenriched (S)‐epoxyalkanes.

     

Asymmetric Epoxidation of Allylic Alcohols Catalyzed by (≡SiO) x Ta(OEt)3-x (Dialkyl Tartrate Diolate): Influence of the Reaction Conditions

Silica-supported chiral tantalum alkoxides are active catalysts for the asymmetric epoxidation of propenol and trans hex-2-en-1ol. The influence of different parameters on their catalytic performance was followed: the impregnation duration by a tartrate (step in their preparation); the nature of the solvent (CH₂Cl₂, pentane, toluene) and of the oxidant (TBHP, CHP, H₂O₂); poisoning effects by water or t-butanol; the reaction temperature and the substrate concentration.     

Cover Feature: Exploring the Flexibility of the Glycopeptide Antibiotic Crosslinking Cascade for Extended Peptide Backbones (ChemBioChem 6/2023)

The glycopeptide antibiotics (GPAs) are a clinically approved class of antimicrobial agents that classically function through the inhibition of bacterial cell-wall biosynthesis by sequestration of the precursor lipid II. The oxidative crosslinking of the core peptide by cytochrome P450 (Oxy) enzymes during GPA biosynthesis is both essential to their function and the source of their synthetic challenge. Thus, understanding the activity and selectivity of these Oxy enzymes is of key importance for the future engineering of this important compound class. Recent reports of GPAs that display an alternative mode of action and a wider range of core peptide structures compared to classic lipid II-binding GPAs raises the question of the tolerance of Oxy enzymes for larger changes in their peptide substrates. In this work, we explore the ability of Oxy enzymes from the biosynthesis pathways of lipid II-binding GPAs to accept altered peptide substrates based on a vancomycin template. Our results show that Oxy enzymes are more tolerant of changes at the N terminus of their substrates, whilst C-terminal extension of the peptide substrates is deleterious to the activity of all Oxy enzymes. Thus, future studies should prioritise the study of Oxy enzymes from atypical GPA biosynthesis pathways bearing C-terminal peptide extension to increase the substrate scope of these important cyclisation enzymes.     

Towards a Greener Epoxidation Method: Use of Water‐Surfactant Media and Catalyst Recycling in the Platinum‐Catalyzed Asymmetric Epoxidation of Terminal Alkenes with Hydrogen Peroxide

Remarkable improvements in enantioselectivity as well as recycle were observed in the catalytic asymmetric epoxidation of terminal alkenes with a chiral, electron‐poor platinum(II ) catalyst with hydrogen peroxide as terminal oxidant in water‐surfactant media.