The selective oxidation of thioanisole to sulfoxide using a highly efficient electroenzymatic cascade system.

Sulfoxides are remarkably useful in asymmetric synthesis and drug development. Herein, we propose a new electroenzymatic cascade route to selectively synthesize methyl phenyl sulfoxide rather than methyl phenyl sulfone by the oxidation of thioanisole. Chloroperoxidase (CPO) functionalized with 1-ethyl-3-methylimidazolium bromide (ILEMB) is encapsulated into dendritic N-doped mesoporous carbon nanospheres (NMCNs) modified with polyethyleneimine (NMCNs-PEI) to form a biohybrid (CPO-ILEMB@NMCNs-PEI). The in situ generation of hydrogen peroxide (H2O2) species by the two-electron oxygen reduction reaction (2e−ORR) on NMCNs-PEI initiates the subsequent selective oxidation of thioanisole by CPO-ILEMB. NMCNs-PEI shows not only high electroactivity for the 2e−ORR but also good biocompatibility for CPO-ILEMB immobilization. The mesopores in NMCNs-PEI can provide a protective space for the encapsulated enzyme, ensuring the operational stability of the enzyme and avoiding the escape of H2O2, which result in high catalytic activity. The experimental results suggest that the catalytic efficiency of the electroenzymatic cascade system with the CPO-ILEMB@NMCNs-PEI biohybrid is up to 4.5 times higher than that of the free CPO-ILEMB catalytic system with H2O2 generated by NMCNs-PEI for the oxidation of thioanisole to produce methyl phenyl sulfoxide. [ABSTRACT FROM AUTHOR]