Efficient Production of Epoxy-Norbornane from Norbornene by an Engineered P450 Peroxygenase

Epoxy-norbornane (EPO-NBE) is a crucial building block for the synthesis of various biologically active heterocyclic systems. To develop an efficient protocol for producing EPO-NBE using norbornene (NBE) as a substrate, cytochrome P450 enzyme from Pseudomonas putida (CYP238A1) was examined and its crystal structure (PDB code: 7X53) was resolved. Molecular mechanism analysis showed a high energy barrier related to iron-alkoxy radical complex formation. Therefore, a protein engineering strategy was developed and an optimal CYP238A1^NPV variant containing a local hydrophobic "fence" at the active site was obtained, which increased the H₂ O₂ -dependent epoxidation activity by 7.5-fold compared with that of CYP238A1^WT . Among the "fence", Glu255 participates in an efficient proton transfer system. Whole-cell transformation using CYP238A1^NPV achieved an EPO-NBE yield of 77.6 g ⋅ L^-1 in a 30-L reactor with 66.3 % conversion. These results demonstrate the potential of this system for industrial production of EPO-NBE and provides a new biocatalytic platform for epoxidation chemistry.

Synthesis and crystal structures of two 1,3-di(alk-yloxy)-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borates

Two salts were prepared by methyl-ation of the respective imidazoline-2-thione at the sulfur atom, using Meerwein's salt (tri-methyl-oxonium tetra-fluorido-borate) in CH2Cl2. 1,3-Dimeth-oxy-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borate (1), C6H11N2O2S+·BF4 -, displays a syn conformation of its two meth-oxy groups relative to each other whereas the two benz-yloxy groups present in 1,3-dibenz-yloxy-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borate (2), C18H19N2O2S+·BF4 -, adopt an anti conformation. In the mol-ecules of 1 and 2, the methyl-sulfanyl group is rotated out of the plane of the respective heterocyclic ring. In both crystal structures, inter-molecular inter-actions are dominated by C-H⋯F-B contacts, leading to three-dimensional networks. The tetra-fluorido-borate counter-ion of 2 is disordered over three orientations (occupancy ratio 0.42:0.34:0.24), which are related by rotation about one of the B-F bonds.

2-(2-Azabicyclo[3.2.1]octa-3,6-dien-2-yl)-1,3-dimethoxyimidazolium hexafluoridophosphate

The title salt, C12H16N3O2+·PF6−, was obtained by the dipolar cycloaddition of norbornadiene to 2-azido-1,3-dimethoxyimidazolium hexafluoridophosphate. The methoxy groups attached to the imidazolium ring of the cation adopt ananticonformation [displacements of the C atoms from the ring plane = 1.386 (4) and −1.404 (3) Å]. In the crystal, weak inter-ionic C—H...F contacts are observed. The structure was refined as a two-component twin. Positional disorder of the fluorine atoms of the PF6anion was observed, the occupancy ratio being 0.562 (16):0.438 (16).